Biological Conservation 43 (1988) 115-135
Forest Ecosystems and Nature Conservation in Sri Lanka
Zoologisches Institut der Universit~it, Seidlstr. 25, D-8000 Miinchen 2, Federal Republic of Germany
(Received 1 February 1987; revised version received 22 June 1987; accepted 3 July 1987)
A BSTRA CT
Problems related to the conservation of natural forests and the associated faunal communities in Sri Lanka are discussed. Particular reference is made to endemic plant and animal species. The present status of natural forests in Sri Lanka is outlined and the major factors contributing to their decline are described. The most important impacts on the forests are direct or indirect consequences of growth of the human population and associated measures to extend and/or improve land use. The most extinction-prone animal species in Sri Lanka are the larger carnivores such as leopards and eagles, large herbivores (elephant and deer), and habitat specialists, which include most of the endemic vertebrates. Better management and extension of the existing reserves through reafforestation could lower extinction rates of the indigenous and/or endemic plant and animal species.
Ideas of preserving nature in Sri Lanka date back to the advent of Buddhism, about 2500 years BP. Sanctuaries were already established in the 12th century (cf. Crusz, 1973; DeAlwis, 1969), most probably even earlier. Although these ideas are still alive today the basic background of present- day conservationists, as well as of society itself, has changed considerably.
Conservation can be defined as 'the management of human use of the biosphere so that it may yield the greatest sustainable benefit to present generations while maintaining its potential to meet the needs and aspirations of future generations' (IUCN, 1980).
This paper describes the present status and future trends that might 115
Biol. Ctmserl,. 0006-3207/88/$03-50 ~'~ Elsevier Applied Science Publishers Ltd. England. 1988. Printed in Great Britain
116 W. Erdelen
influence the further existence of the forest ecosystems in Sri Lanka. The so- called 'values' of moist tropical forest ecosystems and environmental consequences of their removal have been discussed by Balakrishnan & Easa (1982) and Poore (1979). This paper (1) gives an outline of the present distribution of the 'natural' forests, more or less uninfluenced by man, and the associated vertebrate communities; (2) shows trends affecting Sri Lanka's flora and fauna now or in the near future; and (3) outlines the major factors contributing to the extinction of plant and animal species or populations in Sri Lanka. Finally, a number of suggestions are given to improve conservation measures and to maximise long-term existence of the natural plant and animal communities.
The ideas presented here are the result of almost 4 years of field experience in Sri Lanka in the course of studies on ecology, systematics, and biogeography of lizards (Erdelen, 1984).
THE ENVIRONMENTAL BACKGROUND
Size, relief, climate, and types of natural vegetation in Sri Lanka
Sri Lanka is situated between longitudes E 79 39' and 81 5Y, and latitudes N 5 54' and 9 52'. The island is pear-shaped and has an area of 65 610 km". It is connected to India by a continental shelf and separated from it by the shallow Palk Strait (maximum depth about 15 m, minimum width about 35 km) and the Gulf of Mannar.
The relief of Sri Lanka may be subdivided into three peneplains (Adams, 1929) with average altitudes of 30m, 500m, and 1500-1800m (Domr6s, 1976). The second and third peneplain form the Central Highlands in the southern half of the island, and comprise the Knuckles Mountains in the north-east, the Central Massif with the island's highest mountain, the Pidurutalagala (2524 m), and the Sabaragamuwa ridges in the south-west (Fig. 1).
Temperature, relative humidity and day length show only slight seasonal variations. Mean annual temperatures are between 27C at sea level and 15C at about 1900 m altitude. Humidity is generally high throughout the year (annual averages between 80-85%).
Sri Lanka is commonly subdivided into two climatic subregions, referred to as Dry Zone and Wet Zone (see Fig. 1).
The classification of the vegetation of Sri Lanka is mainly based on the publications of Koelmeyer (1957, 1958), Gaussen et al. (1965, 1968), Fernando (1968) and Mueller-Dombois (1968). Based on Dittus (1977), Crusz & Nugaliyadde (1978) and Crusz (1984, 1986), Sri Lanka can be
Forest ecosystems and nature conservation in Sri Lanka 117
6 4 aU Km
80 81 i i i
Fig. I. Relief and major vegetation types in Sri Lanka, based on Crusz (1984, 1986), Crusz & Nugaliyadde (1978), and Dittus, 1977). A1, A2 = monsoon scrub jungle ('arid zone forest' sensu Dittus (1977); A3 = semi-evergreen forest; A4 = intermediate forest; B = rain forest and grassland below 3000 ft (c. 900 m); C (hatched) = rain forest and grassland between 3000 and 5000 ft (c. 900-1500 m); D (black) = rain forest and grassland above 5000 ft (c. 1500 m). 150 = 150 m isohypse. KN = Knuckles Mountains. Border line between B and A4 more or
less coinciding with border of the Wet Zone (SW) and Dry Zone of Sri Lanka.
subdivided into 7 zones (Fig. 1). For more detailed subdivisions, floristic composit ions and nomenclatures see Gaussen et aL (1968), Peeris (1975), Perera (1975), Grel ler & Ba lasubramaniam (1980), Werner (1984) and Ba lasubramaniam (1985). A discussion o f the origin o f the grasslands o f Sri Lanka is given in Pemadasa (1984).
Distribution of flora and fauna
The flora o f Sri Lanka has 3365 species o f angiosperms (Gunati l leke & Gunati l leke, 1983) and comprises endemics, species which also occur on the
118 IV. Erdelen
TABLE 1 Endemism in the Vertebrates and the Angiosperms in Sri Lanka (Data from Crusz (1986) and Gunatilleke &
Taxon Species Endemic Endemic number species species
Fishes 59 16 27 Amphibians 37 19 51 Reptiles 139 70 50 Birds ~ 237 20 8 Mammals 85 12 14 Total 557 137 25 Angiosperms 3305 830 25
a Only freshwater fishes. Only resident birds.
Indian peninsula, and species which are not found in India but in the Malesian or African region (Abeywickrama, 1959).
Data on non-angiosperms are scanty, an exception possibly being the ferns (e.g. Sledge, 1982), and hardly anything is known about their distribution patterns. Accordingly, they are not treated further here. Similarly, our present knowledge on distribution of most of the invertebrate groups in Sri Lanka is rather poor, and only the vertebrates are treated in detail.
Species numbers and data on endemism for the vertebrates and the angiosperms are given in Table 1. The overall percentage of endemic species is the same for both groups (25%). Within the vertebrate taxa, however, there is considerable variation in the degree of endemism. The more mobile taxa, i.e. the birds and mammals, have fewer endemics than the other three groups. The highest numbers of endemics are found in the amphibians and reptiles. The angiosperms have 27 (Abeywickrama, 1956), fishes 3, amphibians 1, reptiles 9, birds 0 and mammals 4 endemic genera (Crusz, 1986 and pers. comm.; Crusz & Daundasekara, in press).
The geographic distribution of the endemics shows a clear pattern (Fig. 2). The smallest number are found in the relatively dry areas of Sri Lanka (A) and the highest numbers in the lowlands of the Wet Zone (B), followed by zones C (montane forest zone) and D (cloud forest zone). In the angiosperms the pattern is similar and the differences between the Dry and Wet Zones seem to be even more pronounced (Fig. 2). As there were no separate data available for zones C and D these had to be taken as one unit.
A quantitative analysis of the densities of endemic species per vegetational
Forest ecosystems and nature conservation in Sri Lanka 119
~LU Zo m ku ~0.
0' A B C+D
A B C D
Fig. 2. Absolute numbers (black) and percentages (open bars) ofendemic species per taxon in the different vegetation zones A (comprising A1, A2, A3 and A4), B, C and D (for definitions see Fig. 1). Top: Data for the angiosperms (raw data from Gunatilleke & Gunatilleke, 1983). For zones C and D no separate data were available. Bottom: 1 = fishes,
2 = amphibians, 3 = reptiles, 4 = birds, 5 = mammals.
zone would be desirable within the context of conservation. This was carried out by Senanayake (1977) and Senanayake et al. (1977) for the amphibians, lizards, and birds. As pointed out by Crusz (1986 and pets. comm.), one possible source of error in these studies is the use of 'surveyors' areas instead of absolute surface area. This is probably of particular importance in mountainous country.
FACTORS AFFECT ING CONSERVATION MEASURES
Human settlements and land use
The first time large areas were cleared for cultivation (mainly of rice) was during the advent of the Sinhalese, approx. 2500 Be. As can be seen from the
120 W. Erdelen
Fig. 3. Forest cover and major crops in Sri Lanka. Combined after Geiser & Sommer (1982) and the Sri Lanka Map of Vegetative Cover (Survey Department, Sri Lanka). Black = dense natural forest, dots = land under rice cultivation, hatching = rubber, vertical lines = tea, horizontal lines = coconut. Locations for orientations: C = Colombo, J = Jaffna, T = Trincomalee. K = Kanneliya Forest. PR = Pidurutalagala Ridge. PW = Peak Wilder- ness. S = Sinharaja Forest. For information on relief and delimitation of Dry Zone and Wet
Zone see Fig. 1.
Forest ecosystems and nature conservation in Sri Lanka 121
distribution of the so-called 'tanks' (water reservoirs for irrigation purposes (Fig~ 4 in Abeywickrama, 1956)) the natural vegetation in the Dry Zone must have been severely affected. Hence it is assumed by some authors that there are no primary forests left in the Dry Zone (e.g. Holmes, 1951, 1958). This matter is discussed in more detail in DeRosayro (1960).
During the time of the old Sinhalese kingdoms (2250 BP to the beginning of the 16th century) there were only few settlements in the Wet Zone (DeRosayro, 1960). According to Abeywickrama (1956), large-scale plantation in the Wet Zone was introduced in the last 200 years, under the influence of the British. The introduction of coffee in the early 19th century, and later the planting of tea and rubber, caused the most significant impact on the forests in the wet mountainous regions. For construction work and for use as firewood on a large scale exotic trees such as Eucalyptus, Cupressus, and Acacia were planted in the hills. Furthermore, as a consequence of the growing tea industry, the number of settlements in the hills has increased considerably during the last 100 years (for an overview see Werner, 1984).
Since Sri Lanka became independent (1948) these trends have continued. As a result, much of Sri Lanka's area is under cultivation now (Fig. 3, and below).
Present status of natural vegetation and protected areas
Remote sensing under the Sri Lanka/Swiss Satellite Image Interpretation Project, carried out in 1981, gave a figure of 24.9% for the 'natural' forest cover, which amounts to approx. 16 300 km 2 (Fig. 3; for details see Geiser & Sommer, 1982). With more than 50% forest cover in the 1950s Sri Lanka was well above the world average and above the average for the Asian nations (Anon., 1978a). The highest percentage of forest cover today is found in the lowlands of the Dry Zone (Fig. 3, approx. 30%), followed by the Central Hills and the lowland Wet Zone. Large continuous patches of forest are left in the north-western, north-eastern and south-eastern parts only. These forests represent the semi-evergreen type of monsoon forest. The only two larger areas in the Wet Zone, of which only 9% are still under natural forest cover (Gunatilleke & Gunatilleke, 1983), are the Sinharaja Man and Biosphere Reserve (90 km 2) and the Kanneliya Forest (Fig. 3), the latter still being harvested for timber by the Plywoods Corporation. The only large continuous areas of more or less natural forest in the Central Hills are the Peak Wilderness Sanctuary (224 km 2) and the Pidurutalagala Ridge (Fig. 3). There is heavy encroachment at the border of the Peak Wilderness; settlements and shifting cultivation are extending into the sanctuary (Werner, 1985). The present status of the montane and cloud forests along
122 IV. Erdelen
1900 1950 2000
Fig. 4. Trends in human population growth (POP) and forest cover (FC) in Sri Lanka. Population in millions and forest cover in per cent of total land area of Sri Lanka. Data on population growth are from th~Department of Census and Statistics, data on forest cover are from Nanayakkara (1982). Fitting of data points by an exponential regression model:
Yl = c~ ec2t, where y~ = population or forest cover in the year t, c~, c 2 = constants.
. . . .
10 8 6 t. 2 0 0 2 t. 6 8 10
Fig. 5. Age pyramid for Sri Lanka, based on 1981 census (courtesy, Department of Census and Statistics, Colombo) Abscissa: human population in hundred thousands. Ordinate: age
classes. Total census in 1981: 14 847 000.
Forest ecosystems and nature conservation in Sri Lanka 123
the Pidurutalagala Ridge has to be considered critical (Werner, 1984). To sum up, the units with the highest degrees of endemism, viz. the Wet Zone lowlands and the Central Hills (see Fig. 2), nowadays have only very little natural forest cover.
The potentially maximum extent of protected areas in Sri Lanka, including forest reserves, proposed reserves and wildlife reserves, is about 15 693 km 2 (Department of Census and Statistics, 1985, Table 50). This is, however, a rather optimistic estimate as in the greater part of these areas there is already more or less heavy encroachment on the forests, even in forest reserves.
The human population in Sri Lanka is growing rapidly (Fig. 4). Predictions based on an exponential regression model would give an estimate of about 20.8 millions for the year 2000. This is equivalent to a population density of 318 individuals per km 2.
Most problems related to conservation measures are direct or indirect consequences of growth of the human population. From 1900 to 1982 (last census available) the population in Sri Lanka increased from 3.6 to 15-2 millions, which is more than 400%. The age pyramid for Sri Lanka (Fig. 5) is typical for a developing country, the broad base indicating a high percentage of children, as generally found in the fast-growing populations of the Third World. Even strict birth control measures can scarcely prevent further growth due to the lower age classes reaching sexual maturity.
As would be expected, the trend in natural forest cover runs opposite to the population (Fig. 4). According to predictions based on extrapolations of the present trend we should...