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Annex A. Land resources

Summary
A.1. Factors affecting soil formation
A.2. Characteristics of the vegetation
A.3. Land capability classes
A.4. Environmental management of land resources
A.5. Land capability in selected watersheds

Summary

Leslie R. Holdridge's analytic method of establishing life zones was used to define five complete and two transition life zones. The criteria are location, climatic conditions, topography and natural vegetation. The life zones defined are tropical dry forest, tropical dry forest transition to tropical very dry forest, tropical moist forest, subtropical moist forest, subtropical wet forest, subtropical wet forest, transition to subtropical rain forest and subtropical rain forest. In Saint Lucia, the zones are located in nearly concentric rings as a consequence of the topography and the rainfall pattern.

Eight land capability classes were defined based on soil fertility, stoniness, soil drainage, depth, slope, erosion hazard and rainfall. The land capability classes in 31 watersheds are summarized in Tables A-7 and A-8. Class I soils comprise 2.65 percent of the total land area; they are suitable for cultivation and irrigation, and have flat topography and no limiting factors. Class II soils comprise 0.94 percent of the total land area; they are also suitable for cultivation and irrigation, having flat to rolling topography; limiting factors can be compensated by good management. Class III soils, 1.20 percent of the total area, are suitable for cultivation or irrigation; they have flat to rolling topography and limiting factors such as medium-fertility soil due to stoniness or shallowness. They require intensive management. Class IV soils, 0.78 percent of the total area, have limited cultivation or irrigation possibilities and may be prone to erosion due to hilly topography. They require limited management when used for permanent tree crops; if clean cultivation is attempted, the danger of erosion increases, requiring soil conservation measures. Class V soils, 3.82 of the total area, are unsuitable for cultivation but are suitable for intensive pasture. There are severe limitations, especially drainage considerations, and intensive management is required. Class VI soils, 16.90 percent of the total area, are unsuitable for cultivation but appropriate for permanent crops; soil cover is shallow and stony soils impose severe limiting conditions, requiring strict conservation measures. Class VII soils, 67.01 percent of the total area, are usually natural forest and unsuitable for cultivation; in selected areas they can support timber production or permanent crops. There are extremely severe limitations associated with this class and requirements for strict conservation measures. Class VIII soils, 6.70 percent of the total area, are unsuitable for any cultivation and are appropriate only for national parks and wildlife zones; they should be left in their natural state and protected. The distribution of land capability classes has been mapped and will appear in the Saint Lucia Development Atlas, a collection of maps of the country in preparation by the OAS.

Encroachment on natural forest and the clearing of land on the steep mountainous interior for the cultivation of bananas has caused serious erosion. This has reduced the infiltration capacity of critical watersheds, reducing water flow in rivers during dry seasons and causing excessive run-off during wet seasons. Erosion adversely affects coastal ecosystems through sedimentation, and damages irrigation systems by silting their channels, rendering valuable land unusuable because of the high cost of clearing these channels. Slumping, sliding, gullying and sheet erosion are common on improperly cleared soils. Solutions to these problems require comprehensive changes in cultivation practices (such as diversification), investment in infrastructure, adoption of soil-conserving cultivation practices, mixed cropping and the protection of existing forests. Analyses of major river basins are presented summarizing soil, life zones, rainfall, land capability and management recommendations.

A.1. Factors affecting soil formation

A.1.1. Geology and lithology
A.1.2. Climate
A.1.3. Relief
A.1.4. Soil characteristics

Of the five major factors influencing the formation of soils (parent material, climate, topography, vegetation and time) the narrow range of parent materials from which the soils have developed and the wide variation in rainfall patterns (see A.2.2) caused by the steep topography of the island are the ones that best explain the great variety of soils in Saint Lucia.1 A brief review of these basic characteristics is of help in understanding the origin of the soils existing in the country.

1 Stark, J., et al., Soil and Land-Use Surveys N°20, Saint Lucia, The Regional Research Centre, Imperial College of Tropical Agriculture, University of the West Indies, Trinidad and Tobago, October 1966.

A.1.1. Geology and lithology

Saint Lucia is almost entirely of volcanic origin, presenting andesite, dacite and basalt rock formations probably of Tertiary or Quaternary age. Sedimentary beds occur but are of small extent. Beds of mixed sedimentary and volcanic origin are more common; they have good bedding and stratification such as tuffs, agglomerate tuffs and conglomerates.2

2 Newman, W.R., A Report on General and Economic Geological Studies, St. Lucia, West Indies, United Nations, Programme of Technical Assistance, St. Lucia, November 1965 (mimeo).

The north, east and central sections of the island are geologically older than the midwestern section. The youngest areas of Saint Lucia are the fan-shaped glacis slopes in the south. Uplift has certainly affected the island, since coral limestone has been found in small quantities between 100 feet and 150 feet above sea level. This coral limestone is believed to belong to the Pleistocene age.3 "A shower or series of showers of dacitic-type ash, containing abundant bipyramidal quartz crystals, have fallen at a relatively recent date over most of Saint Lucia especially the south and central parts, probably at the time of the last eruption in the Soufriere area. Of varying depth when deposited and of even greater variation in depth after early movement and transport by rain and water, the effects of this layer of ash over different underlying materials can be seen in many soil profiles. A large number of Saint Lucia's soils are developed from a combination of different lithological parent materials."4

3 Stark, J., et al., op. cit.

4 Ibid.

A.1.2. Climate

Saint Lucia's location (between 13° 43' 00" and 14° 07' 00" latitude north and 60° 53' 00" and 61° 05' 00" longitude west of Greenwich) defines its tropical climate tempered by the influence of the ocean and the northeasterly trade winds. Table A-1 shows the average monthly temperatures at three stations, all at less than 100 feet above sea level. The average temperature during winter (December-May) is approximately 2.5°C lower than in summer (June-November). Considering the topographic configuration and on-site temperature measurements, it is estimated that temperatures decrease by 1°C for each 100 meters of altitude change (3.5°F over 1 000 feet).

TABLE A-1. SAINT LUCIA AVERAGE MONTHLY TEMPERATURES (°C)

Station

Period

Jan

Feb

Mar

Apr

May

Jun

Jul

Aug

Sep

Oct

Nov

Dec

Average

Hewanorra

73/80

25.6

25.8

25.8

26.5

27.6

27.7

27.8

27.7

27.7

27.4

26.9

26.0

26

Roseau

69/78

24.7

24.7

25.1

25.7

26.7

27.2

23.1

26.9

26.8

26.4

26.0

24.8

26

Union

75/80

25.7

26.2

26.2

26.0

26.8

27.6

27.7

27.6

27.5

27.7

27.4

26.8

27

Source: Ministry of Agriculture, Land and Water Use Unit.

In Saint Lucia, 50 percent of the yearly evaporation occurs during the dry season from December to May (see Table A-2). However, the relative humidity shows little variation, on average, as indicated by Table A-3 (Roseau Station). Rainfall patterns in Saint Lucia are highly dependent on elevation. High levels of rainfall (over 150 inches) occur in the mountainous interior, whereas the lowlands in the south and north receive less than 60 inches per year (see Annex B, section B.2).

TABLE A-2. AVERAGE MONTHLY EVAPORATION (Pan A)

Roseau Station 78/80


Jan

Feb

Mar

Apr

May

Jun

Jul

Aug

Sep

Oct

Nov

Dec

TOTAL

(mm)

112

118

146

180

153

146

143

138

130

105

105

105

1 632

(inches)

4.41

4.64

5.75

6.14

7.09

6.02

5.75

5.63

5.43

5.12

4.13

4.13

64.64

Union Station Union Station

(mm)

134

132

181

168

173

145

146

134

130

118

99

102

1 662

(inches)

5.27

5.22

7.13

6.60

6.82

5.70

5.74

5.27

5.10

4.65

3.90

4.03

65.43

TABLE A-3. RELATIVE HUMIDITY (%)

Roseau Station 68/70 and 72/79

Jan

Feb

Mar

Apr

May

Jun

Jul

Aug

Sep

Oct

Nov

Dec

Average

75.1

72.8

71.9

69.7

72.6

74.1

74.4

76.5

76.0

77.1

75.8

75.4

74.3

Source: Ministry of Agriculture, Land and Water Use Unit.

A.1.3. Relief

The island has a steep, mountainous topography except in the south and extreme north. Saint Lucia is crossed by a central mountain ridge running axially south-southwest to north-northeast, which causes a radial drainage pattern with rivers running to the coasts on either side of the island (see Annex B, section B.1).

Three main physiographic areas can be distinguished. The first comprises the central, eastern and northern parts of the island, which have mature relief and alluvial valleys (Roseau, Cul de Sac, Fond D'Or and Marquis); peaks range from 200 feet in the north to 1 800 feet in the center. The second area is the midwestern section, starting south of the Roseau Valley and extending 5 miles inland up to the Pitons; the area includes the highest and most precipitous mountains (Mount Gimie 3 117 feet, Piton Canarie 3 012 feet, Paix Bouche 2 445 feet) and youthful land forms. It contains the only active soufriere (hot water sulphur spring) on the island. The third region, located in the southwestern section of Saint Lucia, is characterized by a fan-shaped glacis sloping gently seaward, deeply cut by narrow gorges.

A.1.4. Soil characteristics

Although the range of parent rocks is narrow (andesites, dacites and occasional basalts), there are a variety of forms (from fine ash to coarse agglomerates and dikes) with different compactness and porosity; when combined with the climate they are significant in soil formation.5 While the island temperature is relatively uniform, it has a widely varying rainfall pattern. Thus the parent materials are subject to different amounts of leaching.

5 Ibid.

The complicated and steep topography of the island and dacitic ash showers contribute to the further differentiation of soil types. "In comparatively stable areas with heavy rainfall and little or no dry season, latosols or latosolic soils have developed. The clay of these soils is usually kaolinitic, but it is thought that allophane and illite may also occur under special conditions. In dry areas with several months dry season, expanding lattice clays of the montmorillonitic type are found, sometimes associated with pan formation resulting from cementation by siliceous products released by weathering."6

6 Ibid.

A.2. Characteristics of the vegetation

A.2.1. Ecological classification
A.2.2. Methodology used in the classification
A.2.3. Description of life zones

A.2.1. Ecological classification

Although there are numerous methodologies of environmental classification, the one used here is the classification of Natural Life Zones or World Plant Formations, devised by Leslie R. Holdridge.7 This system has been used in the environmental mapping of a number of Latin American countries; it permits cartographic identification and depiction of the relationships between climatic factors.

7 Holdridge, Leslie R., Life Zone Ecology, 1967.

The system uses the relationships between mean annual biotemperature, average annual precipitation and the potential evapotranspiration derived from these two measurements, to divide altitudinal and latitudinal belts into life zones. These major climatic units are closely correlated with characteristic plant associations, defined by the physiognomy of the natural vegetation. From climatic data, the classification can be used to predict the natural vegetation of an area or suggest crop species. Conversely, observation of the natural vegetation can be used to predict environmental conditions where such data are not available.

When using the life zone classification, three limitations must be borne in mind. First, ecological change is usually gradual rather than abrupt. Second, other factors such as soil type, wind and salt spray may have a significant effect. For instance, thin soils will dry out rapidly in the dry season and therefore support a drier type of vegetation than valley bottoms that have the same climate but deeper soils fed by rivers from wetter areas. Third, the historical effect of man on observed vegetation must not be forgotten. Clearing dry areas for cultivation promotes soil erosion which cannot support regrowth. Where there is cutting for charcoal and for banana crops, a return to the original climax vegetation is indefinitely delayed.

When mapping, each life zone is assigned a different symbol and colour. The symbol consists of the name of the base region or altitudinal belt, in capital letters, followed by the name of the formation or life zone in small letters. For example, S-wf represents the Subtropical wet forest formation. Transitional formations also carry geometric figures which indicate temperature and/or precipitation variation. For example, S-df > S-vdf indicates the life zone Subtropical dry forest transition to Subtropical very dry forest.

A.2.2. Methodology used in the classification

The information contained on the topographic map was studied as basis for the actual mapping of the class boundaries through field observations using Holdridge's system.

i. Cartographic compilation

The life zones were sketched on a 1:50 000 scale topographic map after field verification of life zone boundaries on the ecologic map.

ii. Preparation of the ecologic map

The investigatory work included an analysis of precipitation and temperature data. The identification of life zones from knowledge of vegetation is based on physiognomic differentiation observable in natural secondary vegetation. Life zone identification was facilitated by observing cultivation indicators such as typical crops, the organization of agricultural activities and land use in the densely populated areas.

Elevation levels were verified by altimeter to determine the altitudinal belts. At points within a life zone where a change was observed in vegetation or cultivation practices, or the presence was noted of indicator species that did not correspond to the life zone identified, the elevation was calculated to determine the corresponding altitudinal belt. These indicators provided the basis for the projection of a line on the topographic maps. In projecting the lines, orographic position, wind direction and atmospheric factors were considered.

iii. Life Zones of Saint Lucia

The ecology of Saint Lucia is extremely diverse; vegetation ranging from cacti to giant evergreen forest trees is found within a few miles. Five life zones and two transitional life zones were identified. Their arrangement is almost that of concentric rings, as a result of rainfall increases towards the mountainous centre of the island. The major life zones are:

- Tropical dry forest
- Tropical dry forest transition to Tropical very dry forest
- Tropical moist forest
- Subtropical moist forest
- Subtropical wet forest
- Subtropical wet forest transition to Subtropical rain forest
- Subtropical rain forest

A.2.3. Description of life zones

i. Tropical dry forest (T-df)

a. Location

The areas belonging to this life zone form a continual coastal belt around Saint Lucia except for the area around Soufriere, which is Tropical moist forest (T-mf), and the extreme south and north of the island, which are transitions to Tropical very dry forest (T-vdf). The belt is wider in the north, east and south than in the west: in the west it extends inland a maximum of one mile, while in the east it reaches up to 3.5 miles inland. The lower valleys of all the rivers in the country belong to the Tropical dry forest. Most of the main agricultural lands of the Marquis, Fond D'Or, Dennery, Troumasse, Canelles and Vieux Fort rivers belong to this life zone. However, deep soils in these valleys and the rivers flowing through them produce growing conditions closer to those of Tropical moist forest.

b. Climatic conditions

Generally, the Tropical dry forest formation has temperatures above 24°C (Hewanorra International Airport). Precipitation in the life zone is recorded by a number of rain gauges. Its annual rainfall varies from 61.26 in (1 556 mm) at La Fargue to 85.16 in (2 163 mm) at Corinth. Its average potential evapotranspiration may be 60 percent higher than the total annual precipitation.

c. Topography and vegetation

The coastal belt of Tropical dry forest has been cleared in the past. Some areas have been largely abandoned, while in others natural vegetation has been replaced by permanent agriculture. Rainfall seasonal crops can be productive, but intensive agriculture requires irrigation infrastructure. The secondary woodlands have variable growth and lack of cultivated structure. Most of the growth is shrubby. The composition of these secondary woodlands is chiefly Goyavier, Myrtaceae spp.; Grand Feville, Cocolobis pubescens L.; Adegond, Maytemus elliptica (Lamb) Urb.; Commier maudit, Bursera simaruba.

The shrub species include Faramea occidentalis v.a., Myrcia citrifolia a., Ixora ferrea f., Melastomaceae spp. O., Aiphenes minima r., Fagard trifoliata, Ardisia guadalupensis and Tabernaemontana citrifolia. Most of the dry woodlands do not contain large trees. Instead they consist of a low, dense thicket of saplings. The most severely degraded areas often become covered with croton thicket, principally Croton populifolius, C. choristolephis and C. wuellschlaegilianus with mats of Pitcairnia albucidifolia on rocks. Whether these areas, if left alone, would eventually support their previous climax vegetation is a matter for debate.

d. Considerations for appropriate land use

Natural vegetation in flat areas of the Tropical dry forest has completely disappeared, and the land is now used for agriculture. The land in these flat areas consists of alluvial soils that constitute the more valuable soils of the country because of their high capability (classes I to V). These are irrigable soils and, except for class V, can be used for intensive cultivation of many annual crops.

In appropriate soil conditions, and with supplementary irrigation, the climate characteristics of this life zone allow production of a wide variety of crops such as avocados, pineapples, watermelons, sugar cane, cotton, sesame, bananas, rice, peanuts, beans, yams, cassava, corn, tobacco, cacao, tomatoes and grapes. Wood from these climatic conditions is in high demand all over the world, including Tectona grandis, Swietenia macrophylla, Tabebura spp., and Credrella spp.

ii. Tropical dry forest transition to tropical very dry forest (T-df > T-vdf)

The areas identified are in the extreme north and south, near Cap and Vieux Fort respectively, which are Saint Lucia's driest areas. The dry scrub woodlands merge into thorn scrub and poor grazing similar to thorn savannah.

Rainfall is 51.80 inches (1 313 mm) in the extreme north; the soils are predominantly shallow and stony, which prevents their use for agriculture. In certain areas of alluvial and colluvial soils the land is suitable for agriculture with irrigation.

iii. Tropical moist forest (T-mf)

a. Location

Areas belonging to this formation extend over the important agricultural valleys in-country. The widest areas of the Tropical moist forest are in the eastern part of the island, occupying a large portion of the Cul de Sac and Roseau valleys. The Marquis and Fond D'Or river valleys and the Soufriere area also have characteristics of Tropical moist forest zone.

b. Climatic conditions

The Tropical moist forest zone has as climatic limits average temperatures above 24°C and an average annual rainfall between 2 000 and 4 000 mm. In Saint Lucia, it is possible to find these conditions from sea level (Soufriere) to approximately 150 m above sea level.

Rainfall occurs all year, and the annual average precipitation varies from 2 199 mm in Roseau to 2 786 mm in Vanard. The wet season is from June to December; June and October are the months of most precipitation. During this period, run-off is extensive and adequate drainage is essential for both agriculture and roads. Generally, there is a water shortage from January to May, the worst months being February and March.

c. Topography and vegetation

The topography is flat to undulating in the greater part of this life zone; elevations vary from sea level to 150 m. Trees used to make up the natural vegetation, but the forests have been cleared for agriculture with only a few remnants left.

d. Considerations for appropriate land use

The determining factors for land use in this life zone are soil type, gradient and proper selection of species. The cost of agricultural production is higher than in drier zones - first, because of the need for more intensive control of pests and diseases, which are more common and numerous owing to the greater humidity, and, second, because of the periodic need for cultural practices owing to the rapidity with which most of the cultivated soils lose their fertility.

Agriculture in this life zone requires careful management. The farmer who continously works the same land finds that rainfall leaches out plant nutrients, exhausting the soil and rendering the land unproductive.

Proper selection of crops is very important. An example of a species improperly selected would be pineapple. It is unable to compete with the faster growing weeds, and the fruit will be of inferior quality because it requires a long dry season for concentration of the sugar in the fruit. The only lands suitable for intensive agriculture are those of very fertile alluvial soils; even here only high-yield crops can be profitable. Lands with shallow soils and moderate gradient are the best suited for perennials such as cacao, certain tropical fruits and coffee, on a smaller scale. Due to the variable deficit of water in the areas of this life zone between January to May, usually occurring in February and March, the establishment of irrigation can be advantageous.

iv. Subtropical moist forest (S-mf)

a. Location

This life zone is of limited extent and is isolated between areas of Tropical dry forest. These lands are located at higher altitudes than the Tropical dry forest, between 400 to 1 000 feet above sea level.

b. Climatic conditions

This formation has as climatic limits a mean annual temperature between 18 and 24°C and an average annual rainfall between 1 000 and 2 000 mm.

There are two rain gauges located in this life zone, one in Patience and another in Girand (see Table A-4). The amount of rainfall is the same as in the Tropical dry forest, but, because of the lower temperature, the evapotranspiration is also lower and consequently more water is available.

The soils, however, are shallow, stony and low in fertility.

c. Topography and vegetation

The relief varies from very undulating to broken. Because of edaphic conditions in this life zone, the vegetation consists of species characteristic of drier ecosystems.

TABLE A-4. SUBTROPICAL MOIST FOREST (S-mf)

River Basin or Area

Rain Gauge Name

Continuity years

Average annual rainfall

mm

in

Black Bay

Giraud

1933-47

2,490

98

Fond

Patience

1951-80

2,000

79

Source: Oelsner, J., "Water Resources," OAS Technical Report, Castries, June 1981.

d. Considerations for appropriate land use

There are two areas with characteristics of Subtropical moist forest, one around Mount Gomier, in the southwestern part of the country, and the other around Mt. Victoria in the eastern part. In both cases the edaphic conditions prevent agricultural use for seasonal crops. These two areas, along with others belonging to the Tropical dry forest, are considered marginal land for agricultural use except for certain species like cashew, or trees for charcoal or methanol production.

v. Subtropical wet forest (S-wf)

a. Location

The lands in this life zone are located primarily between the slopes of the mountains that form a south-southwest to north-northeast axial ridge and the belt consisting of Tropical dry forest and Subtropical moist forest. The Subtropical wet forest is the largest life zone of the country.

b. Climatic conditions

Climatic conditions in this life zone vary under the influence of the anticyclones and the trade winds that traverse the country. The rainfall pattern is similar to that of the Tropical moist forest and Subtropical moist forest except that the orographic rain is heavier. Because the rain is longer in duration, it exerts a major influence on the composition and physiognomy of the vegetation.

This formation has climatic limits between 18 and 24°C and an annual rainfall between 2 000 and 4 000 mm.

Within this life zone, average annual rainfall ranges from 2 117 in Londonderry to 2 970 in Barre de L'Isle, which has recorded the highest precipitation (see Table A-5). The temperature in this life zone varies according to location and is estimated at 24°C near the coast, but falls to as low as 18°C on the slopes at 2 950 feet (900 m) above sea level.

TABLE A-5. SUBTROPICAL WET FOREST (S-wf)

Rain Gauge Name

Continuity (years)

Average Annual Rainfall

mm

in

Woodlands

1933-54

2 904

114.33

Londonderry

1933-60

2 117

83.36

Park

1933-68

2 297

90.45

Beausejour

1933-48

2 606

102.61

La Perle

1933-50

2 283

89.91

Barre de L'Isle

1941-80

2 970

116.92

Note: This formation has climatic limits between 18 and 24° C.
Source: Oelsner, J., op. cit.

The average potential evapotranspiration may be estimated at 60 percent less than the total average annual precipitation. In this life zone, three-fifths of the rain water escapes as run-off, so that the rivers carry water throughout the year.

c. Topography and vegetation

The topography is predominantly mountainous in this life zone. The elevation ranges from 500 feet (152 m) to 1 000 feet (304 m). The natural vegetation consists of tree species of variable commercial value. Most of the primary forest has been cut down, with the remaining natural forest on the steepest slopes.

The boundary between the Tropical moist forest and the Subtropical wet forest was identified by the existence of tree ferns (the natural vegetation of this life zone) after crossing the Ravine Creviche in the Castries-Dennery border zone, near Barre de L'Isle Ridge.

d. Considerations for appropriate land use

The main determining factors for land use in this life zone are soil type, gradient and species. The cost of seasonal agricultural production is higher than in drier zones, for two reasons. There is a need for adequate drainage infrastructure and for control of pests and diseases, which because of greater humidity are more common and numerous. Second, there is a need for land rotation because of the rapidity with which most of the cultivated soils lose their fertility.

The lands suitable for intensive agriculture are those containing very fertile alluvial soils. Lands with shallow soils and moderate gradient are best suited for perennials such as cacao, rubber, subtropical fruits and coffee and tea on a smaller scale.

The steeply sloping lands not suitable for agriculture should be kept forested. With efficient management, these forests can supply wood and serve as protection for the catchment basins. Failure to do so will result in accelerated erosion of the best soils, located in the lower part of the river basin, as has happened in some areas of the Fond D'Or valley (Dennery Estate), where the irrigation channels are completely filled with silt from the erosion of the upper part of the valley. This situation prevents the use of the land under irrigation.

In the deforested areas, commercially valuable species such as pine in the Barre de L'Isle area and eucalyptus in the Millet area have been established with good results. Another species used in some countries with similar life zones, besides Pinus occidentalis, is Didynopanax morototoni.

The guava (Psidium spp.) grows in second growth areas dispersed throughout the country as in the Chopin Ridge. The fruit of this tree can provide the basis for the development of a large scale industry, as can other subtropical fruits. The experiments on fruit processing carried out by the Union Agricultural Station will be useful in establishing such an industry. Cultivation of bananas is recommended only on the mild slopes and alluvial soils.

vi. Subtropical wet forest transition to Subtropical rain forest (S-wf S-rf)

The areas identified are at higher altitude and have more rainfall than the Subtropical wet forest. These rains preclude the use of the land for agricultural purposes and it is recommended that the area remain forested for the protection of the catchment basin.

An exception is Belle Plaine, where even with an average annual rainfall of 4 259 mm agriculture is possible because of the high quality of soil (Table A-6). Improvement of the drainage system is required.

TABLE A-6. SUBTROPICAL WET FOREST TRANSITION TO SUBTROPICAL RAIN FOREST (S-wf S-rf)

Area or River Basin

Rain Gauge Name

Continuity years

Average Annual Rainfall

mm

in

Troumasse

Quilesse

1935-78

3 743

147.35

Canelles

Edmund Forest

1980



Choiseul

Bath Nursery

1950-80

2 623

103.30

Choiseul

Belle Plaine

1933-48

4 259

167.69

Soufriere

La Dauphine

1933-40



Source: Oelsner, J., op. cit.

vii. Subtropical rain forest (S-rf)

a. Location

The Subtropical rain forest area is centered in the wet forest zone. The rain forest areas are located at the headwaters of the Troumasse and Roseau (Canelles) rivers, between Mt. Gimie and Piton St. Esprit, and in the northeastern part of this area.

b. Climatic conditions

No meteorological data have been recorded for this life zone in Saint Lucia. However, the plant species and physiognomy endow it with distinct characteristics that differentiate it from the wet forest zone. This zone receives the highest rainfall in Saint Lucia, in the form of orographic rains. The average annual rainfall is probably about 4 000 mm. The temperature varies around 19°C. The average potential evapotranspiration may be estimated at 75 percent less than mean annual rainfall. In this life zone, more than three-fourths of the rain reaches the rivers, which therefore carry water throughout the year.

c. Topography and vegetation

Relief is broken over the greater part of this zone. The elevation ranges from 1 000 to 2 000 feet (300-600 m). The natural vegetation consist of trees, characteristically covered with parasitic and epiphytic plants. The species native to this life zone grow more rapidly than those of the wet forest zone and exibit great natural regeneration.

d. Considerations for appropriate land use

Because of the excessive humidity, the lands of the Subtropical rain forest life zone are valueless for direct agriculture. It is essential that the natural plant cover of these lands be preserved as a means of controlling run-off and soil erosion.

A.3. Land capability classes

A.3.1. Definition of land capabilities
A.3.2. Characteristics of the land classes
A.3.3. Land availability by capability classes

A.3.1. Definition of land capabilities

Land capability classes were defined using information available on the characteristics of the 49 different soils that exist in Saint Lucia,8 mapped at a scale of 1:25 000. Data on slopes were taken from the 1:25 000 scale map of Saint Lucia (DOS Edition 3, 1974); this information in conjunction with the climatic information was used to define land capability.

8 Stark, J. et. al., op. cit., pp. 28-46, and Soil Map of Saint Lucia scale 1:25 000.

The following criteria were used to characterize the soils:

- fertility: subdivided into high, medium or low;
- stoniness: subdivided into high, moderate and low;
- drainage: subdivided into good, moderate and poor;
- depth: either shallow or deep; and
- erosion hazard: either high, moderate or low.

These variations in soil characteristics were defined using the detailed information supplied by the soil survey in relation to soil location, parent material, topographic conditions where they occur, propensity to erosion, vegetation, physiography, drainage, stoniness, permeability, horizontal profile, chemical characteristics, etc.

Slopes were subdivided into groups: 0 to 5 percent, 5-10 percent, 10-15 percent, 15-20 percent, 20-25 percent, 25-30 percent and 30 percent and over. The available rainfall information was analyzed and the different areas of the country were divided into areas of low, moderate and high rainfall.

Using these criteria, the different soils of Saint Lucia were classified in eight land capability classes.9 Given the multiple combinations possible, the classification of each soil poses a specific problem. A slight variation in slope or rainfall pattern may determine a change in capability class of a basically homogeneous soil type in a fairly small area. It is not possible to document each of the classifications made; in the following sections, the broad characteristics of each land capability class will be indicated and examples of soils in each class will convey the criteria used in the classification.

9 Klingebiel, A., and P. Montgomery, "Land Capability Classification," Agriculture Handbook, No. 210, 1966.

The eight classes of lands were mapped on a 1:25 000 scale map and measured with a planimeter in order to estimate the availability of land resources in each of the 31 watersheds identified. Table A-7 shows average of land capability classes for the various river basins and basin areas. The river basins listed in Table A-7 are shown on Map A-1. Table A-8 contains information illustrative of specific characteristics of land capability classes in selected river basins and areas.

A.3.2. Characteristics of the land classes

a. Land capability class I

Included in land capability class I are all lands suitable for cultivation and irrigation with flat topography and no major limiting factors. With good management, these lands are highly productive and do not present special conservation problems (see Table A-8).

b. Land capability class II

These lands are also suitable for irrigation and cultivation. They have flat to gently undulating topography. Limiting factors are not severe and can be compensated for with good management practices. High productivity can be attained with good management and by implementing moderate conservation measures, generally drainage or contour planting in undulating areas (see Table A-8).

TABLE A-7 LAND CAPABILITY CLASSES BY RIVER BASINS

Source: Pretell, O. and S. Polius, "Land Capability Classification and Crop Allocation in Saint Lucia," OAS/Ministry of Agriculture Technical Report, Saint Lucia: October, 1981.

Oelsner, J., "Natural Resources and Agricultural Development: Mater Resources", OAS Technical Report, op. cit.

Map A-1. Saint Lucia. River Basins and Areas

Source: Pretell, O. and J. Polius, 'Land Capability Classification and Allocation in Saint Lucia,' O.A.S./Ministry of Agriculture Technical Report, Saint Lucia, October, 1981

c. Land capability class III

Class III contains lands suitable for cultivation and irrigation with flat to undulating topography but with limiting factors (generally medium fertility soils, or moderate stoniness or shallowness). Medium to high productivity can be attained under intensive management and conservation, particularly from sheet erosion (see Table A-8).

d. Land capability class IV

This group of lands hat limited cultivation or irrigation possibilities. Flat to very undulating topography may make these lands prone to erosion. When used for permanent tree crops, limited soil conservation measures are required; with other crops requiring clean cultivation, the danger of erosion increases, demanding soil conservation as part of the technological management package. Medium productivity can be attained with good management (see Table A-8).

e. Land capability class V

These are lands which are unsuitable for cultivation but suitable for intensive pasture. Severe limiting factors exist, particularly drainage considerations. When intensive management is applied, high productivity is possible with pasture and crops adapted to water-logged conditions. Soil conservation is necessary for long-term preservation of these lands (see Table A-8).

f. Land capability class VI

These lands are unsuitable for cultivation but appropriate for permanent crops (tree crops, fruit trees) and natural pasture. Under certain conditions of soil and climate, some intercropping is possible with annuals which require no tilling. Topography, shallow soils and stoniness are very severe limiting conditions. Use of these lands requires strict observance of soil conservation measures (see Table A-8).

g. Land capability class VII

Land in Class VII is normally natural forest unsuitable for cultivation. In selected areas, timber production is possible; in areas where soils, topography and climatic conditions are better, coffee and cacao can be grown. Extremely severe limitations are associated with this class of lands and strict conservation measures should be observed in their use (see Table A-8).

TABLE A-8. RIVER BASINS: AREAS ILLUSTRATIVE OF SPECIFIC CHARACTERISTICS OF LAND CAPABILITY CLASSES

Source: Pretell, O., and J. Polius, "Land Capability Classification and Crop Allocation in Saint Lucia," OAS/Ministry of Agriculture Technical Report, Saint Lucia: October 1981.

Olsner, J., "Natural Resources and Agricultural Development: Water Resources", OAS Technical Report, op. cit.

h. Land capability class VIII

Land totally unsuited to cultivation, suitable only for national parks and wildlife zones. These lands should be left in their natural state and protected (see Table A-8).

A.3.3. Land availability by capability classes

Table A-9 is based on the information contained in Table A-7 and shows the skewed distribution of land capability classes. The predominance of class VII and the lack of land in the desirable classes I-IV is evident.

TABLE A-9. LAND CAPABILITY CLASSES: TOTAL AREA AND CULTIVATION POSSIBILITIES

Class

Land area (acres)

% of total area

Cultivation possibility

I

3 989.70

2.65

Cultivable

II

1 422.03

0.94

Cultivable

III

1 809.57

1.20

Cultivable

IV

1 178.08

0.78

Limited cultivation

V

5 757.58

3.82

Pasture

VI

25 477.51

16.90

Permanent crops

VII

101 050.70

67.01

Timber, natural forest

VIII

10 103.90

6.70

National park


150 789.07 or 235.6 sq mi

100.00


Source: Table A-7.

The factors that render areas unsuitable for agriculture are steep slopes, shallow soil, stoniness, low fertility and aridity. Despite these factors, population pressure results in attempted intensive cultivation of these lands and their degradation. A study should be done and the findings serve as a basis for the provision of alternative technological packages that would allow continued productive use of the lands, both in low and high population density areas.

Lands suitable for intensive agriculture, Classes I-IV, cover about 8 400 acres, or about 5.5 percent of the total land of the country. Intensive agriculture will continue to be established in these areas. Efforts must be made to maintain these high-potential lands in agricultural production and restrict their use for urban and industrial activities.

It is evident that land of a particular class is not continuous in its distribution. For example, Class I soils are found scattered over twenty river basins, and range in size from under 10 acres, in the Savannes Bay-Vieux Fort area, to over 700 acres in Cul de Sac. Such a pattern makes it difficult to plan for the optimum utilization of any one or more parcels of land in a particular class (Table A-7).

A.4. Environmental management of land resources

A.4.1. Environmental considerations for management of agricultural natural resources
A.4.2. Characteristics of soil erosion
A.4.3. Principles of land resource management
A.4.4. Recommendations for land resource management

A.4.1. Environmental considerations for management of agricultural natural resources

Water unifies and links all ecosystems; indeed, rainfall patterns play a major role in explaining soil formation in Saint Lucia (Annex B, section B-2). Further, another water-related process, erosion, is at the root of the gradual degradation of land resources on the island.

Erosion can be the result of natural factors (heavy rainfall over very steep slopes) or be catalyzed by man's activities (deforestation of areas with steep slopes and shallow soils). These two problems differ in terms of the capacity that society has to cope with them. Whereas the effects of natural erosion can be modified by man's action (reforestation, contour drainage construction, etc.), man-generated erosion can normally be avoided or at least reduced to manageable proportions.

Although man's activities have been the cause of some soil erosion for many years (sugar cane cultivation, shallow soils, timber exploitation in unsuitable areas, etc.) the recent practice of cultivating bananas in the steep mountainous interior of the island has caused serious erosion to take place; encroachment into natural forest to expand banana cultivation is daily aggravating the problem. Population pressure on a limited amount of good agricultural lands, together with a highly concentrated land ownership pattern, creates the need to cultivate unsuitable lands and this in turn fosters soil erosion.

Heavy erosion adversely affects coastal ecosystems through sedimentation on seabed vegetation, an initial component of the animal food chain. Mangrove forests, which often reduce all the effects of heavy erosion, are being destroyed to accommodate tourism development.

Clearing of forest lands for agriculture has seriously reduced the infiltration capacity of many of the most critical watersheds on the island, reducing water flow in streams and rivers during dry spells. Excessive water run-off is at the origin of the heavy soil loss being experienced in many areas of the country.

Encroachment into protected areas is increasing soil damage. This is the case at the Castries Waterworks Reserve (created in 1916), which covers the slopes of Piton Flore and La Sorciere. It contains mainly primary forest with some advance second growth. It is connected by a narrow strip along the Barre de L'Isle or central watershed to the southern and more extensive block of forested public land. This was not a defined forest reserve until recently and has not been well protected, so that, while there is a large central core of inaccessible primary forest, shifting cultivators have been very active at the periphery.

The present Central Forest Reserve covers approximately 16 561 acres, or about 11 percent of the total area of the country. There has been a variable degree of intervention. For photointerpretation and fieldwork, accessible areas were defined. Three kinds of use or degrees of intervention can be defined: 1) natural forest, 2) secondary forest, plantations of maho, mahogany and pine or a combination of clandestine agroforestry activities, and 3) areas cleared for agriculture.

The part of the Central Forest Reserve with the greatest degree of intervention is the Castries Waterworks Reserve area in the north, where almost one-third of the area has been cleared and is under secondary forest. In the strip along the Barre de L'Isle more than 75 percent is under secondary forest, plantation of pines and agroforestry activities, with some areas dedicated to agriculture. These two areas of the Central Forest Reserve (Castries Waterworks Reserve and Barre de L'Isle) are the headwaters of the Fond D'Or river basin, and intervention affects profoundly the lands at the bottom of the valley, which are of high capability, classes I to IV, and have one of the best irrigation systems in the island. This intervention is causing accelerated soil erosion that damages the irrigated lands by silting the channels of the irrigation system, making the land unsuitable for irrigation because of the high cost of maintenance of the channel. The damage has been so great that areas of valuable land have been declared marginal for agriculture use.

In the southern part of the Central Forest Reserve the intervention occurs mainly in the south portion, affecting directly the Troumasse, Canelles, Vieux Fort and Doree river basins.

A.4.2. Characteristics of soil erosion

Many of the soils that are found in Saint Lucia are very susceptible to erosion. Slumping and sliding are common on recently cleared soils in the steep interior where tree roots are no longer present to retain the soil. Gully erosion is commonly found in Saint Lucia under various slope and rainfall conditions. When no drains are built, gullies often start near roads and footpaths where water flow concentrates, increasing its erosive power. All sloping cultivated lands in Saint Lucia are affected by sheet erosion of the surface soil. This soil is rich in organic matter and has important physical and chemical properties. Adverse effects of sheet erosion are more rapidly and severely felt on shallow soils resting upon hard substratum.

Once soil has been lost very little can be done to remedy the problem; over the years decreasing yields and abandoned lands are the result of heavy erosion. The pattern of shifting cultivation practiced by small farmers and squatters in the interior hills is a consequence of the process of permanent exhaustion of the land base; after a few years of cultivating a patch of cleared forest, yields decrease so much that the land is abandoned and new forest is cleared. Heavy erosion and water loss are the ill effects of such practices.

A.4.3. Principles of land resource management

The adverse impact of man's activities is the result of economic, social and environmental factors. Avoidance of these adverse effects requires change in all the interacting factors. Although soil erosion is an important negative consequence arising from current agricultural practices in Saint Lucia, the solution to these problems is not just technical (in terms of soil conservation practices and investment in the required infrastructure). Only when agricultural output generates a sufficient surplus can capital investment in soil conservation be profitable. New husbandry practices and crop combinations may be required to reverse the exhaustion of fertility.10

10 Pool, D., "Natural Resource Management," OAS Technical Report, Castries, October 1981 (mimeo).

A solution of the soil erosion problem now facing Saint Lucia involves the introduction of important changes into structural factors of the country's agricultural development process. Diversification of production (introduction of tree crops in areas not suitable for clean cultivation), increases in productivity and in value added locally to agricultural production (so as to generate capital for investing in soil conservation), and redistribution of underutilized lands to reduce pressures on lands unsuitable for cultivation are structural changes that are necessary to foster a sound pattern of natural resource utilization in the agricultural sector and to reduce the risks of soil erosion.

A.4.4. Recommendations for land resource management

Sound utilization of land resources involves consideration of an environmental management dimension prior to decisions regarding what constitutes the best land uses. Land capability, as discussed in the preceding section, is one aspect of this issue. Soil conservation is the other aspect that defines the limitations affecting the use of the resources.

Parent material, slope cover and rainfall determine a soil's risk of erosion. Given the topography of Saint Lucia and the variety of rainfall patterns that exists, it is not possible to make specific soil conservation recommendations applicable to all circumstances. Nevertheless, as a general framework, the following guidelines are applicable to soil conservation and the slope of lands.

i. Lands with slopes of over 30 percent should not be used for agriculture; the permanent vegetative cover must be protected.

ii. Lands with slopes of 20-30 percent can be used for tree crops and forestry with conservation measures to avoid gully erosion and landslides in areas of high rainfall.

iii. Lands with slopes of 10-20 percent can be farmed using soil conservation measures as appropriate (terracing, benches, etc.).

iv. Lands with slopes of less than 10 percent can be intensively farmed depending on other aspects of land capability; in areas of heavy rainfall, the steeper lands may require soil conservation measures (contour planting, terracing, etc.) and others may require drainage.

Less than 20 percent of the lands in Saint Lucia can be farmed without important soil conservation investment; this is indeed a restrictive situation, particularly when returns from agriculture are not very high.11

11 Stark, J., et al., op. cit., p.27.

Among the soil conservation measures, those involving low capital investment (contour drains, planting patterns perpendicular to slope, permanent tree cover to provide protection to the soil) are to be encouraged for small hillside farming communities. Capital intensive conservation practices such as bench terracing and orchard benches should be undertaken on a small scale when land use changes are attempted to move toward high productivity crops. In the absence of specific soil conservation measures, mixed cropping of bananas and ground provisions as currently practiced in many small hillside farming communities is to be encouraged for the soil conservation benefits and for helping the farmer to spread the risks of natural disasters.

Protection of existing forests is important not only to preserve the water catchment areas of important watersheds but also to avoid excessive water run-off that may damage agricultural lands downstream. Protection of coastal ecosystems (mangrove forests, for instance) is necessary to preserve fishing grounds and scenic beauties in the country. Coastal waters are also being threatened by shipping activity.

Specific environmental management recommendations were prepared for each of the watersheds analysed in the study, taking into consideration the general criteria spelled out above and the particular characteristics of each watershed (rainfall patterns, soils, slopes, etc.).12

12 Pretell, O., and J. Polius, op. cit.

A.5. Land capability in selected watersheds

A.5.1. Marquis River basin
A.5.2. Roseau River basin
A.5.3. Vieux Fort River basin
A.5.4. Canelles River basin
A.5.5. Troumasse River basin
A.5.6. Fond d'Or River basin
A.5.7. Cul de Sac River basin

To illustrate the main characteristics of the detailed land capability analyses made, profiles of land capabilities for the important watersheds are summarized in this section. The main environmental management recommendations for these watersheds are also given. The watersheds of the Marquis, Roseau, Vieux Fort, Canelles, Troumasse, Fond D'Or and Cul de Sac Rivers have been selected because they include the important water resources (Annex B) and most of the good agricultural lands in the country. Detailed information concerning other watersheds included in Table A-7 can be found in the original analysis of land capability classes.13

13 Ibid.

A.5.1. Marquis River basin

i. General characteristics

Located in the northeast of the island, it has 7 659 acres. In the upper parts of the river basin the parent rock is comprised of hornblende andesite, andesite ash and altered andesite. The middle and lower portions of the river basin are on basalt with some andesite. Along the river there are detectable concentrations of manganese. The average annual temperature is above 24°C and the average annual rainfall is about 88 inches (2 240 mm). Tropical dry forest characterizes the lower part of the valley; the upper part is Tropical moist forest. The watershed divide near the coast is characterized by Subtropical moist forest; the interior is Subtropical wet forest. The rainfall near the coast is 70 inches (1 778 mm); it is more than 100 inches (2 540 mm) in the upper river basin (see Table A-10).

ii. Soil conditions

Along the central part of the valley alluvial soils of medium to high fertility occur with almost no requirement for special management. Near the coast the alluvial soils have limiting problems of drainage and salinity. A great portion of the soil bordering the alluvials has slopes from 5° to 20°, where the major limitations are drainage and erosion, and is thus classified as Class VI, suitable for tree crops. The soils with slopes primarily of 20° have been classified as class VII with limitations of erosion. Soils with slopes between 20° and 30°, near the coastal area, have been classified as Class VII with the limitation of aridity; these are marginal for agricultural use except for production of trees to be used for charcoal and methanol, and permanent fruit trees like cashew.

iii. Crop allocation

Marquis is the most fertile river basin in the northeast because it receives the most water. Nevertheless some irrigation is necessary in the lower valley area during dry spells.

iv. Environmental management

The upper watershed requires total protection since it serves as a water source for Castries. Any human intervention within the water catchment area will increase erosion, producing sediment that will result in deterioration of the water supply and quality. Alluvial soils along the Marquis River can be intensively cultivated with good management and conservation practices.

Class VI soils can be used for permanent tree crops or managed for forestry production as appropriate. Experience with bench terraces cropped with bananas, coconuts and fruit trees has been positive.

A.5.2. Roseau River basin

i. General characteristics

This is the largest river basin in the country, covering 11 989 acres. The development of land is constrained by an obvious water deficit. The parent material consists of some recent alluvial material in the lower river basin. The middle and upper river basin lies on andesite porphyry, andesite ash and altered andesite. The estimated average annual temperature is 26°C and the average annual rainfall ranges from 70 inches (1 778 mm) to 150 inches (3 810 mm). The life zones that characterize the area are Subtropical rain forest in the upper river basin, Tropical moist forest in the middle and Tropical dry forest in the lower basin (see Table A-11).

TABLE A-10. MARQUIS RIVER BASIN LAND CAPABILITY

Land capability class

Acres

Percentage of total basin area

Crop allocation

Limitation

I

265.30

3.5

Vegetables, bananas, limited food crops, sugar cane

None

II

49.41

0.6

Vegetables, bananas, limited food crops, sugar cane

Drainage (alight)

III

72.57

0.9

Vegetables, bananas, limited food crops, sugar cane

Drainage (slight)

IV

-

-

-

-

V

24.70

0.3

Permanent tree crops, limited food crops

Slope, erosion, drainage

VI

2 178.58

28.4

Permanent tree crops, limited food crops

Slope, erosion, drainage

VII

4 784.46

62.5

Timber and charcoal

Erosion

VIII

284.10

3.7

-

-

Total

7 659.12

100.0



Source: Pretell, O., and J. Polius, "Land Capability Classification and Crop Allocation in Saint Lucia," OAS/Ministry of Agriculture Technical Report, Saint Lucia: October, 1981. Oelsner, J., "Natural Resources and Agricultural Development: Water Resources", OAS Technical Report, op. cit.

ii. Soil conditions

Approximately 1 310 acres of land have been identified as being of high quality, located between the delta of the Roseau River and its junction with the Millet River. Another 1 440 acres on gently sloping land with erosion hazard can be used for tree crop establishment.

iii. Environmental management

Management of the upper watershed in the Forest Reserve requires absolute protection to prevent degradation and adverse effects on downstream areas, and also to maintain stable water supplies for domestic agricultural and industrial use. Proper forestry management should allow exploitation only in selected areas (plantation and natural forest management).

Limitations of classes VI and VII land allow only agroforestry production systems that provide fruit tree crops as well as charcoal and limited timber production. Some conservation measures such as contour drains and grass barriers should be implemented on a watershed basis. Terrace construction is not recommended because of high rainfall and unstable soil conditions.

Land classified I, II and III can be used for banana cultivation or more intensive crops as market and economic conditions dictate. Control of erosion and proper management are required to maintain these soils in continuous production. Irrigation may be required in the dry season.

Further salt water intrusion should be prevented at the mouth of the Roseau River. Control of industrial contaminants is necessary to maintain fisheries habitat along the coast.

A.5.3. Vieux Fort River basin

i. General characteristics

The basin covers about 7 205 acres and originates from an undisturbed forest area which receives over 150 inches (3 810 mm) of rainfall annually. The parent materials of the lower part are dacite (Belfond pumice flows) and tuffs, in the middle part they are andesite porphyry and in the upper part andesite ash and aphyric basalt. The average annual temperatures are 26.4°C in the coastal area and less than 24°C in the upper parts of the basin. The life zones that characterize the river basin are Tropical dry forest in the coastal area, Tropical moist forest in the middle valley area and Subtropical wet forest and Subtropical rain forest in the upper part (See Table A-12).

TABLE A-11. ROSEAU RIVER BASIN LAND CAPABILITY

Land capability class

Acres

Percentage of total basin area

Crop allocation

Limitation

I

753.47

6.3

Food crops, bananas

None

II

404.53

3.4

Food crops, bananas

Drainage (slight)

III

121.99

1.0

Food crops, bananas

Drainage (slight)

IV

27.79

0.2

Limited food crops, pasture, bananas

Drainage

V

3.09

-

Limited food crops, pasture, bananas

Drainage

VI

1 440.55

12.0

Cocoa, citrus, avocado, mango, other tree crops

Erosion, slope

VII

7 923.81

66.1

Permanent tree crops, tree crops: timber and charcoal species

Slope, erosion

VIII

1 313.94

11.0

-

-

Total

11 989.17

100.0



Source: Pretell, O., and J. Polius, "Land Capability Classification and Crop Allocation in Saint Lucia," OAS/Ministry of Agriculture Technical Report, Saint Lucia: October 1981. Oelsner, J., "Natural Resources and Agricultural Development: Water Resources", OAS Technical Report, op. cit.

ii. Soil conditions

This long river basin is composed of an intricate pattern and distribution of soils. The flat alluvials are not continuous and are broken by soils having steep slopes. There are about 1 042 acres of flat land suitable for irrigation. The upper and middle basin are formed by highly erodable soils that are subject to slipping.

iii. Environmental management

The upper watershed requires protection. Because of high precipitation and steep topography, agricultural practices must include strict conservation measures in order to prevent soil loss. Permanent tree crops mixed with banana production will help to reduce soil loss.

The flat coastal plain is relatively fertile but requires irrigation to sustain intensive agriculture of either crops or pasture.

A.5.4. Canelles River basin

i. General characteristics

The Canelles River has its origin in the area with the highest recorded rainfall. The forest cover of the headwaters area should be protected. It is a long, narrow basin, covering 4 188 acres. The parent rock in the lower part consists of dacite (Belfond pumice flows) and tuffs, the center part of andesite prophyry and in the upper part of andesite ash and altered andesite. Aphyric basalt occurs in the head water area. The average annual temperature is 26°C in the coastal area; it it less than 24°C in the headwaters. The average annual rainfall is 60 inches (1 523 mm) in the coastal area and more than 150 inches (3 810 mm) in the headwaters. The lower part of the river basin is characterized by Tropical dry forest, the middle part by Subtropical wet forest and the upper part by Subtropical rain forest (see Table A-13).

ii. Soil conditions

Along the river are about 240 acres of alluvial soil (Class I) suitable for irrigation and intensive agriculture. The hills on both sides of the river in the coastal area have shallow soils and, combined with existing arid conditions, have marginal value for agricultural use. The soils of the hills in the center part of the river basin are steeper (5° to 20°); their main limitations are erosion and, in some places, poor drainage and low fertility. In the upper part of the basin the soils are highly erodable and subject to slipping.

TABLE A-12. VIEUX FORT RIVER BASIN LAND CAPABILITY

Land capability class

Acres

Percentage of total basin area

Crop allocation

Limitation

I

208.44

2.9

Food crops, bananas, sugar cane

None

II

-

-

-

-

III

-

-

-

-

IV

29.34

0.4

Food crops, bananas, sugar cane

-

V

805.97

11.2

Limited food crops, pasture

Drainage

VI

1 347.91

18.7

Cocoa, citrus, mango, other tree crops

Erosion, slope

VII

4 781.77

66.4

Permanent tree crops (coconuts, timber and charcoal species)

Erosion, slope, land slippage

VIII

32.42

0.4

-

-

Total

7 205.85

100.0



Source: Pretell, O., and J. Polius, "Land Capability Classification and Crop Allocation in Saint Lucia," OAS/Ministry of Agriculture Technical Report, Saint Lucia: October 1981. Oelsner, J., "Natural Resources and Agricultural Development: Water Resources", OAS Technical Report, op. cit.

TABLE A-13. CANELLES RIVER BASIN LAND CAPABILITY

Land capability class

Acres

Percentage of total basin area

Crop allocation

Limitation

I

240.86

5.7

Food crops, bananas

None

II

-

-

-

-

III

-

-

-

-

IV

-

-

-

-

V

15.44

0.4

Limited food crops, pasture

Drainage

VI

631.50

15.1

Citrus, cacao, avocado, mango

Erosion, slope

VII

3 301.07

78.8

Permanent tree crops, timber and charcoal species

Erosion, shallow soils

VIII

-

-

-

-

Total

4 188.07

100.0



Source: Pretell, O., and J. Polius, "Land Capability Classification and Crop Allocation in Saint Lucia," OAS/Ministry of Agriculture Technical Report, Saint Lucia: October 1981. Oelsner, J., "Natural Resources and Agricultural Development: Water Resources", OAS Technical Report, op. cit.

iii. Environmental management

The upper watershed lying within the Forest Reserve requires protection because if vegetation is removed the combined effects of heavy rainfall and steep topography will cause erosion. The Mount Gimie and Quilesse areas produce heavy stream flow in highly erodable soils. Production forestry should be carried out only in selected areas. The upper watershed is a parrot habitat also requiring protection from intensive human intervention.

Owing to high precipitation and heavily dissected topography, the practice of growing bananas on steep soils must be subject to strict conservation measures to prevent soil loss. Mixing permanent tree crops with banana trees (currently practiced in some areas) will help to reduce soil loss.

Marginal dry coastal lands can be used for charcoal production or extensive livestock raising but will not support intensive agriculture because of water shortage and low soil fertility.

Alluvial soils found in the lower portion of the Canelles River can be used for intensive banana production if good soil conservation practices are followed.

A.5.5. Troumasse River basin

i. General characteristics

The basin is located in the southeast and has 9 599 acres. It originates from an undisturbed forest area which has the highest recorded rainfall on the island, over 150 inches (3 810 mm) annually. The river basin has variable temperatures, from about 26°C in the coastal area to about 17°C at the top of Mount Gimie. Parent material is andesite or prophyry in the lower basin and andesite ash altered andesite in the upper part. The life zones that characterize this river basin are Tropical dry forest in the coastal area, Tropical moist forest in the middle valley, and Subtropical wet forest and Subtropical rain forest at higher altitudes (see Table A-14).

ii. Soil conditions

The principal soil-forming factors here are rainfall and topography. In the coastal area there are marginal lands; limiting factors are aridity, shallowness and steepness. The soils peripheral to the central valley have high erosion hazards and are subject to slumping. In the center of the valley are 643 acres of good land suitable for irrigation.

iii. Environmental management

In the management of the watershed the same guidelines should be followed as in the Canelles River basin.

TABLE A-14. TROUMASSE RIVER BASIN LAND CAPABILITY

Land capability class

Acres

Percentage of total basin area

Crop allocation

Limitation

I

273.29

2.8

Food crops, bananas, sugar cane

None

II

-

-

-

-

III

46.32

0.5

Food crops, bananas, sugar cane

Slope (gentle)

IV

81.83

0.9

Limited food crops, pasture, fruit trees

Drainage, slope

V

242.41

2.5

Limited food crops, pasture, fruit trees

Drainage, slope

VI

2 768.39

28.8

Citrus, avocado, cacao, mango

Slope, erosion

VII

5 584.65

58.2

Permanent tree crops, timber and charcoal species

Slope, erosion

VIII

602.16

6.3

Leave in natural state

-

Total

9 599.05

100.0



Source: Pretell, O., and J. Polius, "Land Capability Classification and Crop Allocation in Saint Lucia," OAS/Ministry of Agriculture Technical Report, Saint Lucia: October 1981. Oelsner, J., "Natural Resources and Agricultural Development: Water Resources", OAS Technical Report, op. cit.

A.5.6. Fond d'Or River basin

i. General characteristics

Located in the eastern part of the island (near Roseau and Cul de Sac) this basin contains the largest expanse of irrigable agricultural land. The parent material consists of agglomerate tuffs, andesite agglomerate and mud flow flanking the lower basin, while andesite agglomerate, andesite ash and altered andesite occur in the upper part. The average annual temperature is 26°C. The average annual rainfall is about 79 inches (2 007 mm) at La Caye in the lower river basin. The lower part of the basin is characterized by Tropical dry forest; further inland Tropical moist forest gives way to Subtropical wet forest with changing altitude. The basin's total area is 9 992.76 acres (see Table A-15).

ii. Soil conditions

The most valuable land in the basin is the flat alluvium, having land capability varying between classes I and IV. However, land clearing of the upper parts of the basin has created a high erosion hazard, causing silting of the drainage system in the valleys. The soils in the hills close to the coast are very shallow and rest on a cemented parent material, which creates conditions typical of drier areas; hence they are marginal for agricultural use. The hilly soils in the center of the river basin, especially around Mabouya, have high erosion hazards and are subject to slumping. The steeper soils of the upper river basin have erosion problems.

iii. Environmental management

The upper limits of the watershed lie within the Forest Reserve; these lands should be maintained as natural forest and not cultivated.

Areas that are gently sloping and receive sufficient rainfall (Dernier Riviere, Fond Petit, Morne Panache) are suitable for the establishment of permanent crops. Erosion control is necessary where landslips and soil movement are a problem. Terracing may be tested in appropriate areas.

Only a small area is available for intensive cultivation of vegetables or annual crops. Under present economic conditions bananas are the most appropriate crop in classes I, II and III soils. Proper soil conservation and management are required for good yields.

Marginal dry coastal lands can be managed as natural forests supplying charcoal on a sustained basis. Reforestation should only be considered in denuded areas. Clearing natural forest to plant fast growing species is not an economically or ecologically wise policy.

TABLE A-15. FOND D'OR RIVER BASIN LAND CAPABILITY

Land capability class

Acres

Percentage of total basin area

Crop allocation

Limitation

I

646.94

6.5

Food crops, bananas, sugar cane

None

II

231.6

2.3

Food crops, bananas, sugar cane

Drainage (slight)

III

245.5

2.5

Food crops, bananas, sugar cane

Drainage (moderate)

IV

78.74

0.8

-

-

V

81.83

0.8

Limited food crops, pasture, fruit trees

Drainage (severe)

VI

2 336.07

23.4

Citrus, avocado, cacao papaya, other permanent tree crops and limited semipermanent tree crops

Erosion, slope, land slipping

VII

6 069.46

60.7

Some permanent tree crops, timber and charcoal species

Land slipping, erosion

VIII

3 02.62

3.0

Leave in natural state


Total

9 992.76

100.0



Source: Pretell, O., and J. Polius, "Land Capability Classification and Crop Allocation in Saint Lucia," OAS/Ministry of Agriculture Technical Report, Saint Lucia: October 1981. Oelsner, J., "Natural Resources and Agricultural Development: Water Resources", OAS Technical Report, op. cit.

TABLE A-16. CUL DE SAC RIVER BASIN LAND CAPABILITY

Land capability class

Acres

Percentage of total basin area

Crop allocation

Limitation

I

776.63

6.9

Food crops, bananas, sugar cane

None

II

594.44

5.3

Food crops, bananas, sugar cane

Drainage (slight)

III

-

-

-

-

IV

98.82

0.9

Limited food crops, bananas, pasture

Erosion, drainage (severe)

V

75.66

0.7

Limited food crops, bananas, pasture

Erosion, drainage (severe)

VI

1 232.11

11.0

Mango, citrus, avocado, other tree crops

Erosion, slopes

VII

8 376.66

74.8

Permanent tree crops

Erosion, slopes

VIII

46.32

0.4

-

-

Total

11 200.64

100.0



Source: Pretell, O., and J. Polius, "Land Capability Classification and Crop Allocation in Saint Lucia," OAS/Ministry of Agriculture Technical Report, Saint Lucia: October 1981. Oelsner, J., "Natural Resources and Agricultural Development: Water Resources", OAS Technical Report, op. cit.

A.5.7. Cul de Sac River basin

i. General characteristics

The basin is situated in the central western part of the island and covers 11 200 acres. It is the third largest river basin on the island, but has the largest extent of land suitable for irrigation. The river has its origin in the area with the highest rainfall. The greater portion of the basin lies in andesite ash and altered andesite. The average annual temperature is 26°C and the average annual rainfall varies from 80 inches (2 030 mm) to 150 inches (3 810 mm) in the headwaters. The basin is characterized by Tropical moist forest except for the upper part near the headwaters, which is Subtropical wet forest and Subtropical rain forest (see Table A-16).

ii. Soil conditions

There are about 1 545 acres of land suitable for irrigation, of which 469 acres are suitable for intensive cultivation. The soil in the upper part of the river basin has erosion hazards. The slopes bordering the river basin are subject to erosion and sliding.

iii. Environmental management

The area of the Forest Reserve should be extended to include steeply sloping lands near the Barre de L'Isle to prevent cultivation, which would cause soil loss, and to provide a larger water catchment area under protection. These soils are highly erodable and should not be cultivated. Natural forests should be maintained for protective cover and wildlife habitat. Production forestry should be carefully managed in selected areas.

Erosion control is critical in areas which are otherwise suitable for tree crops and agroforestry. Charcoal production and management of the natural forest may provide some forestry products in appropriate areas. Natural vegetation should be kept on river banks to prevent slumping and soil loss.

Bananas and/or fruit tree crops can be successfully grown in alluvial soils. Irrigation may be necessary during the dry months. Before any intensive vegetable production is undertaken in the lower Cul de Sac valley, the problem of flooding and drainage must be resolved. Successful drainage operations in the lower valley are dependent on the adoption of compatible drainage systems by the oil transshipment terminal.

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