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Landscape Ecology 13: 135–148, 1998. c 1998 Kluwer Academic Publishers. Printed in the Netherlands.
The impact of shifting cultivation on a rainforest landscape in West Kalimantan: spatial and temporal dynamics Deborah Lawrence1 , David R. Peart2 and Mark Leighton3 1
Department of Botany, Duke University, Durham NC 27708-0339, U.S.A. (current address) and Department of Anthropology, Harvard University, Cambridge MA 02138, U.S.A.; 2 Department of Biology, Dartmouth College, Hanover NH 03755, U.S.A.; 3 Department of Anthropology, Harvard University, Cambridge MA 02138, U.S.A.; corresponding author Received 7 September 1996; Revised 22 March 1997; Accepted 10 July 1997
Keywords: shifting cultivation, land-use change, deforestation, rainforest landscape, West Kalimantan, Indonesia
Abstract To assess the role of shifting cultivation in the loss of rainforests in Indonesia, we examined the spatial and temporal dynamics of traditional land-use north of Gunung Palung National Park in West Kalimantan. We analyzed the abundance, size, frequency, and stature (by tree size) of discrete management units (patches) as a function of landuse category and distance from the village. Data were gathered from point samples along six 1.5-km transects through the landscape surrounding the Dayak village of Kembera. Most land was managed for rice, with 5% in current production, 12% in wet-rice fallows (regenerating swamp forest), and 62% in dry-rice fallows (regenerating upland forest). The proportion of land in dry-rice increased with distance from the village; rubber gardens (17% of the total area), dominated close to the village. The size of rubber trees declined with distance, reflecting the recent establishment of rubber gardens far from the village. Fruit gardens accounted for only 4% of the area. From interviews in Kembera and three other villages, we estimated rates of primary forest clearing and documented changes in land-use. Most rice fields were cleared from secondary forest fallows. However, 17% of dry-rice fields and 9% of wet-rice fields were cleared from primary forest in 1990, resulting in the loss of approximately 12 ha of primary forest per village. Almost all dry-rice fields cleared from primary forest were immediately converted to rubber gardens, as were 39% of all dry-rice fields cleared from fallows. The rate of primary forest conversion increased dramatically from 1990 to 1995, due not to soil degradation or population growth but rather to changes in the socio-economic and political environment faced by shifting cultivators. Although the loss of primary forest is appreciable under shifting cultivation, the impact is less than that of the major alternative land-uses in the region: timber extraction and oil palm plantations. Introduction Shifting cultivation is frequently identified as the primary cause of deforestation in the tropics (Myers 1993; Riswan and Hartanti 1996) despite controversy about the ultimate causes of forest conversion. Because shifting cultivation is practiced by people living in or near the forest, it will have a continuing impact on rainforests. To evaluate this impact, we have assessed the rate of primary forest clearing associated with shifting cultivation, explored the causes of this deforestation, and determined the ultimate fate of
cleared lands. Within this framework, we can properly assess the role of shifting cultivation, both as a factor in the degradation and loss of tropical rainforests, and as a system of management for their conservation or rehabilitation. In Indonesia, 1.2 million hectares (m ha) of tropical rainforest is deforested every year (FAO 1993). Selective logging disturbs an additional 1.2 m ha of primary forest per year, but this disturbance is not considered deforestation, or permanent alienation from forest use (Grainger 1984; FAO 1993). Deforestation following logging is often blamed on shifting cultiva-
136 tors, who are assumed to use logging roads to expand into previously uncultivated areas. In the Philippines, however, Kummer (1992) demonstrated that failed economic development and extensive timber extraction encouraged the expansion of non-shifting, smallscale agriculture. In Malaysia (Repetto 1988) and Thailand (Feeny 1984), large-scale industrial agriculture replaced logged forest. Perhaps in Indonesia, as in the Philippines, much of the deforestation has been wrongly attributed to shifting cultivation by the original, non-migrant hill farmers (see Collins et al. 1991; Riswan and Hartanti 1996). Throughout the tropics, people who engage in shifting cultivation often exploit standing primary forest for game, timber and other products, as well as clearing it for agriculture (Denslow and Padoch 1988; Poffenberger 1990; Anderson 1990). We distinguish shifting cultivation from other systems of “slash-andburn� encompassing a wide range of land-uses that rely on fire simply to clear rainforest for cultivation or further development. Under shifting cultivation, farmers return to clear and cultivate a patch after a given time interval, whereas under some types of slash-andburn they may never revisit the same patch. In Indonesia, shifting cultivators create and manage several types of secondary forest, in addition to growing upland rice (e.g., Michon 1991; Padoch and Peters 1993; Salafsky 1994; Lawrence et al. 1995). Few households can establish all their land holdings near the village. Because household labor is limited, travel time decreases productive work time. Thus distant land is managed less intensively, even though the effort necessary to avoid vertebrate pest damage increases with distance. We hypothesize that the tradeoff between productive work and travel influences decisions about the purpose, size, and location of different forest types. These are the land-use decisions that have traditionally structured human-dominated rainforest landscapes. By necessity, traditional patterns of land-use are changing in response to a changing economic, sociopolitical and ecological environment. These changes may have profound implications for landscape scale patterns of land-use, including the distribution of primary forest, and they present major challenges to conservation and development policy (Kartawinata et al. 1984; Dove 1985a; Abell 1988). A study of landscape dynamics, both spatial and temporal, can elucidate the rationale behind landuse decisions by shifting cultivators. Furthermore, it should allow us to predict both the effects of those
decisions on the landscape and the constraints on future land-use decisions. While studies on a regional or global scale yield estimates of forest conversion for a wide area (e.g., Skole and Tucker 1993; Houghton 1994), detailed local analyses can be effective in clarifying the context and mechanisms of conversion, which are important for a thorough understanding of the dynamics of land-use and for effective policy implementation (Dirzo and Garcia 1992; Ojima et al. 1994). Ultimately, regional satellite-image based analyses should be integrated with ground based studies of well chosen focal areas (Moran et al. 1994). We restricted ourselves to a ground based case study because our primary purpose was to understand the context, causes, and effects of deforestation rather than to monitor it on a large scale. We determined the rate of deforestation associated with shifting cultivation in an intensive study area. We examined the effect of local management systems on secondary forest structure, analyzing both the individual land-use unit (see also Lawrence et al. 1995) and the villagebased landscape. We addressed the following questions: 1) How much primary forest is cleared every year by shifting cultivators and for what purpose? 2) What are the characteristics of the major land-use types found in the landscape under shifting cultivation (size, frequency, stage of development)? 3) How does the distribution of land-use types change with distance from the village? and 4) What is the future of the landscape under shifting cultivation? Our simple and inexpensive methods (interviews and long transects) could be widely applied for rapid assessment of landscape dynamics at a small scale, e.g., around national parks or timber concessions.
Methods Study site We conducted this study in the landscape surrounding the Dayak village of Kembera in the Simpang Hulu district of the Ketapang regency in West Kalimantan, Indonesia (Figure 1a; note correction of the location stated in Lawrence et al. 1995). The area was chosen for its location and history. Kembera is about 25 km north of Gunung Palung National Park (GPNP, 90,000 ha), between the Gunung Juring Forest Reserve (GJFR, 10,000 ha) and an active timber concession (60,000 ha). Markets are accessible in the wet season by boat (2–3 days roundtrip). Permanent
137 village-based, long-fallow shifting cultivation and tree crop production have been continuous in this region for over 200 years in a system similar to that found elsewhere in Kalimantan (Dove 1985b; Padoch 1985; Mackie et al. 1987; Inoue and Lahjie 1990). Commercial logging has occurred within 1–5 km of Kembera and nearby villages over the last 5 years. Over this same time period, the GJFR boundaries have been redrawn to include lands formerly claimed by the villagers. Kembera and its neighbors thus fall within the realm of a potential buffer zone for conservation forest (GPNP or GJFR) and production forest (the timber concession). From April 1991–April 1992, we conducted surveys in Kembera and the neighboring villages of Banjur, Keranji-Baya, and Jelutung (all Dayak villages, except Jelutung which was Melayu; Figure 1a). The village of Kembera, inhabited by 475 people in 96 households, was the largest of these. Lawrence et al. (1995) provide a detailed description of Kembera. With ca. 3500 ha of managed forest and agricultural lands, the population density of Kembera was ca. 14 persons/km2 of cultivated land. The size of the other villages ranged from 37–66 households, but the cultivated areas were not quantified. Except for Jelutung, which was established 20–25 years ago, the villages were established from 60–100’s of years ago. Land-use/forest conversion surveys To define major categories of land-use and to estimate transition rates among them, we conducted interviews in all four villages in 1991–2, and we returned to Kembera for follow-up surveys in 1993 and 1995. We interviewed 20–50% of the households (randomly sampled) in Banjur, Keranji-Baya, and Jelutung. In 1991, we sampled 29% of all households in Kembera (22 randomly selected households plus an additional six of eight trader households); 71% were sampled in 1993 and 42% in 1995 (these were opportunistic samples depending on the availability of residents at the time of the survey). Respondents were asked what type of forest they had cleared to plant the previous year’s rice field, the disposition of the field after the rice harvest, and other questions on local land-use classification and practices, forest use, marketing activities, and household demographics. These discussions led to the designation of seven major land-use types, which were confirmed through observations in the field (Table 1).
Sampling the landscape Managed land surrounding the village of Kembera was sampled along six 1.5-km long transects arrayed in a stratified, random design. Managed land was defined as that which had been previously cleared and planted and was currently in use or lying fallow. It included rice fallows (jamih in the Kemberan language or bawas in Indonesian), dry and wet rice fields (mu, payak/ladang, ladang payak), fruit gardens (kampung buah/tembawang), and rubber gardens (kebun geta/kebun karet). The only land-use type that was not systematically sampled, nor encountered on the transects, was the homegarden (pekarangan) although almost every house had one. Like fruit gardens, but generally much smaller in extent (< 500 m2 ) and stature (< 20 m), the homegardens contain food, ornamental and medicinal plants, and are restricted to the area around houses. Transects were placed perpendicular to the central axis of the village which was clearly defined by a foot path running east-west from the edge of primary forest in the mountains to the border of village lands downriver (Figure 1b). Sampling was centered on the 2 km of this path that ran through the center of the village; 2 km were added at either end of this central segment. The transects were stratified such that one transect originated within each km of the central axis, running alternately north and south from this line. Within these spatially defined strata, transects were randomly placed. The 1800 ha area defined by the transect layout (6 km 3 km) represents about half of the total area managed by the village. At sample points every 25 m along the transects, we classified land within a radius of 12.5 m as one of the seven land-use types in Table 1. We also estimated the diameter at breast height (dbh) for the largest trees within this radius. Because stands of trees in managed land are dominated by an even-aged cohort that becomes established after the most recent clearing, the tree community within a land-use unit tends to be quite uniform in stem size. This characteristic was useful for defining patch boundaries. Successive points along the transect that were classified as the same land-use type and had like-sized tree communities were considered as part of one patch or unit (i.e., originally cleared at the same time). We further assumed that the mean size of patches was proportional to the mean length of the transect traversing the patches. Transect-length was calculated as the number of sequential points comprising one land-use unit (patch) multiplied by the dis-
138
Figure 1. a) Map of Kalimantan with inset (to scale) showing location of the study area north of Gunung Palung National Park. b) Map of the study area, Kembera, showing the location of transects (n = 6), each 1.5 km long.
139 Table 1. Characteristics of the seven major land-use types in Kembera. Forest type
Patch size range, mean (ha)
Tree density 10 cm dbh (trees ha,1 )
Characteristic vegetation
Basal area of trees 10 cm dbh (m2 ha,1 )
Dry rice fielda
0.6–1.5, 1.1
0
0
Dry rice fallowb
as above
523
23
Wet rice fielda Wet rice fallowc Fruit gardenb
0.1–1.0, 0.5 as above ca. 0.1–0.7, 0.5
0 ca. 20 406
0
Rubber gardenb
ca. 0.5–2.0, 1.2
337
20
Primary forestd
10,000 ha
ca. 584
42
several varieties of upland rice with annual vegetables such as eggplant, cucumbers, corn, relishes, various greens; often cassava or rubber seedlings; no standing trees tree community ranging from homogeneous to diverse (3–42 spp/0.10 ha); often simple vertical structure with monolayer of tree crowns several varieties of wet rice; no standing trees few woody shrub species sparsely distributed, mostly sedges diverse tree community (14–32 spp/0.10 ha); tree crowns in multiple layers primarily rubber trees, often intercropped with fruit trees (3–15 spp/0.10 ha); simple vertical structure unless natural recruitment by rubber is advanced species rich tree community with complex vertical structure 23– 35 spp/0.075 ha);
1
58
a The
sizes of dry- and wet-rice fields were determined by mapping currently planted fields (n = 11 for dry-rice, n = 8 for wet-rice). Mean size of rubber gardens was estimated by dividing the number of trees per garden (from interviews, n = 25 gardens, range = 60–300 trees) by the mean density per garden (217/ha[Lawrence 1996]). The size of fruit gardens (n = 30)was estimated by walking through gardens or along their perimeters. b For dry-rice fallows (18–30 yrs old, n = 11), fruit gardens ( 50–150 years old, n = 10) and rubber gardens (12–30 yrs old, n = 11), density, basal area, and species richness of trees 10 cm dbh were determined from plot data (Lawrence et al 1995). c Young wet rice fallows (ca. 3–10 yrs) were preferred for cultivation. Older wet rice fallows were not sampled; while abundant, these were seldom returned to cultivation. Density and basal area of woody vegetation in young wet rice fallows were estimated from visual tallies at each transect sample point. d Data for primary forest are from 4 plots (each 0.075 ha) in Gunung Juring Forest Reserve, near Kembera. The area of primary forest accessible to people in Kembera was estimated as the protected area within 15 km of the village (not including logged forest).
>
>
tance between points (25 m). By examining patterns in the sizes of the largest cohort of trees in these patches, we assessed landscape-wide variation in the stature of different land-use types. In analyzing the percentage of the managed landscape in each land-use type, we excluded the samples (11%) that fell in primary forest (see eastern-most transect, Figure 1b). To analyze the effects of distance on the proportion of different land-use types, we performed a series of permutation tests. The null hypothesis was that the distribution of land-use types does not vary with distance from the central axis (our “neutral model” of landscape structure sensu Gardner et al. 1987). According to this null hypothesis, the observed sequence of patches along a transect is as likely as any other, random ordering. Constraining the data to keep the points that fell within a single patch together and to keep the patches within their original transect, we randomly ordered the patches of each transect 1000
times. For each such ordering, we calculated the mean distance from the central axis for patches of each type and then calculated a mean for each type over all six transects. With these 1000 mean distances, we created a reference distribution of possible means. We compared the mean distance observed in the field against this distribution to evaluate the probability that a given type was generally observed closer or farther away than expected. We computed P-values by counting the number of averages that were more extreme than the observed average and dividing by 1000. We analyzed changes in patch size and tree size by linear regression against distance to the central axis.
140
Figure 2. Allocation of managed land to different uses within 1.5 km of the central axis of Kembera. n = 366 point samples along 6 transects, each 1.5 km long. Primary forest (encountered on only one transect) accounted for 11% of total transect samples and was excluded from the data shown.
Results Spatial patterns resulting from shifting cultivation in Kembera In 1992, 79% of the managed land (i.e., excluding primary forest) was in current rice fields or secondary forest fallows, 17% in rubber gardens, and 4% in fruit gardens (Figure 2). Dry-rice production accounted for 65% of the sample; 4.6% of this dry-rice land (or 3% of the sampled area) was in current production. Nonirrigated wet-rice occupied 14% of the land of which 14.3% was in current production. For 94 patches encountered along transects in Kembera, land-use types were non-randomly distributed with respect to distance from the central axis of the village. Dry-rice was found farther away from the village than expected under the null hypothesis of no distance-dependence (p = 0.012). Wet-rice and rubber were found closer than expected (p = 0.042 and p < 0.001 respectively). Only six fruit gardens were recorded, with no significant trend in their abundance with distance. The proportion of land in dryrice production increased from 47% within 0.5 km to 75% more than 1.0 km away (Figure 3). In contrast, land in rubber production decreased from 38% within 0.5 km to 3% beyond 1.0 km. Wet-rice in Kembera (current fields and fallows) was limited to the area within 1.0 km.
Figure 3. Change in land allocation with distance for Kembera in 1992. Values are percentages of transect point samples within each distance range that fell within each land-use category. Values for dry- and wet-rice include both active rice fields and fallows. Primary forest in the sample was excluded.
The size of individual rubber gardens decreased with distance (p = 0.020), while that of dry-rice fields and fallows increased (p = 0.040). Neither the size of wet-rice fields and fruit gardens nor the size of trees in rice fallows and fruit gardens showed any trend with distance. The size of rubber trees decreased significantly with distance (p = 0.035). Variation in forest stature across the landscape Overall, managed forests in Kembera were composed of small to medium-sized trees, with the largest cohort of trees in a given patch rarely exceeding 50 cm dbh. When all types of forest (i.e., excluding current wet- and dry-rice fields) were considered together, the largest cohorts of trees were < 30 cm dbh in 75% of all patches (Figure 4e). Very large trees were found only in fruit gardens (60–109 cm dbh, Figure 4d). In 52% of the rubber gardens, trees in the largest cohort were < 20 cm dbh (not yet productive); 40% of the gardens had trees 20–29 cm dbh (productive), leaving 8% with trees up to 49 cm dbh (senescent, Figure 4c). For dry-rice fallows, which dominated the managed landscape, the modal tree size class was 10–19 cm dbh (32% of all point samples, Figure 4a). Only 20% of the dry-rice fallows had a community dominated by trees < 10 cm dbh; an additional 42% contained trees between 20 and 39 cm dbh, and 6% had trees between 40 and 59 cm dbh. In contrast, 47% of the wet-rice fallows had trees < 10 cm dbh. Analysis of size structure confirmed field observations of two distinct types of
141 Forest clearing and conversion: patch dynamics under shifting cultivation
Figure 4. Size structure of trees in managed forest land. Values are percentages of land in each land-use type whose largest cohort of trees is within the size range indicated.
wet-rice fallow in Kembera. Forty-nine percent of the fallows encountered were dominated by sedges with a few woody stems; 51% were dominated by mediumsized trees and looked much like natural swamp forest.
Most households in the region farmed two rice fields each year, one wet and one dry. These fields were cleared either from primary forest (in the timber concession or in GJFR) or secondary forest fallows. In 1990, over all four villages, an average of 17% of dry-rice fields and 9% of wet-rice fields were cleared directly from primary forest (Table 2). The proportion of dry-rice fields converted from primary forest was highest in Keranji-Baya (32%), and lowest in Jelutung (8%), where the proportion of wet-rice cleared directly from primary forest was highest (17%). In 1990, between 3 and 15 ha of primary forest were cleared per village, or an average of 0.18 ha per household in 1990. The remaining fields, i.e., 68–92% of dry-rice patches and 83–100% of wet-rice patches (depending on the village), were established by clearing secondary forest. The average fallow length in the area for fields converted from secondary forest was 12.9 years for dry-rice and 2.7 years for wet-rice (20.5 and 3.5 years respectively, in Kembera). The second major transition between land-use types, besides the conversion from forest to rice, is the creation of rubber gardens. Rubber gardens always originate in dry-rice fields. In 1990–1991, half of all dry-rice fields in the region were planted to rubber (Table 3). However, the conversion of rice fields cleared from primary forest was much greater than that of fields cleared from fallows. Across the four villages surveyed, 97% (87–100%) of fields originally cleared from primary forest were converted to rubber, vs. only 39% (13–50%) of rice fields originally cleared from fallows. In the focal village of Kembera, the rate of primary forest conversion changed dramatically from 1990 to 1995. In 1990–1991, only 11–15% of all dry-rice fields were cleared from primary forest (Figure 5a). Since 1992, the proportion of fields that were converted from primary forest increased, reaching 64% in 1995. As a result, the amount of primary forest cleared by the village as a whole increased to ca. 58 ha per year, or 0.61 ha per household per year. The length of the fallow for fields converted from secondary forest showed no significant trend over the period 1990– 1995, varying from 13–27 years, and averaging 19 years for the 6-year period (Figure 5b). The rate of establishment of rubber gardens also increased in Kembera from 1990 to 1995. Kembera had the lowest rate of conversion from fallows to rice
142 Table 2. Origin of dry- and wet-rice fields north of Gunung Palung National Park in 1990: conversion from primary forest and secondary forest fallows. Village
Number of fields sampled
From primary foresta
From fallowa
Primary forest converted village total (ha)b
Primary forest converted /household (ha)c
Mean fallow length
0.15 0.32 0.08 0.16 0.18
12.9 (n = 14) 12.5 (n = 12) 5.6 (n = 7) 20.5 (n = 6) 12.9
0.00 0.05 0.06 0.02 0.03
– 3.7 (n = 6) 1.0 (n = 5) 3.5 (n = 8) 2.7
Dry-rice Banjur Keranji-Baya Jelutung Kembera Average
21 19 12 26 –
3 (14%) 6 (32%) 1 ( 8%) 4 (15%) 17%
18 (86%) 13 (68%) 11 (92%) 22 (85%) 83%
9.6 12.2 3.1 15.0 10.0
Wet-rice Banjur Keranji-Baya Jelutung Kembera Average
3 7 6 23 –
0 1 (14%) 1 (17%) 1 ( 4%) 9%
3 (100%) 6 (86%) 5 (83%) 22 (96%) 91%
0.0 2.0 2.3 1.6 1.5
a Number,
percent of fields converted. Village total from dry rice = (Pr )(Ht )(Hd )(Ad ) where Pr = percent of fields converted from primary forest to rice (in table), Ht = total number of households in the village, Hd = percent of households farming dry rice, and Ad = average size of a dry rice field. For Kembera, Ht = 96; Hd was estimated, conservatively, at 0.9, because sample data were lacking. Ad = 1.13 ha. Village total from wet rice = (Pr )(Ht )(Hw )(Aw ) as above, substituting Hw = percent of households farming wet rice for Hd (percent farming dry rice). In Kembera, Ht = 96; in Banjur, Ht = 66; in Keranji-Baya, Ht = 38; in Jelutung, Ht = 37. For all villages, Hw and Aw were estimated based on data from Kembera: Hw = .82 and Aw = 0.46 ha. c Conversion per household = village total/H . t b
Table 3. Number and percent of dry-rice fields converted to rubber in 1990–1991, classified by original forest type. Village
Banjur Keranji-Baya Jelutung Kembera Averagea
a Average
Cleared from fallows fields Converted sampled to rubber # # (%)
Cleared from primary forest fields Converted sampled to rubber # # (%)
Overall fields sampled #
Converted to rubber # (%)
16 12 10 24 –
3 6 1 4 –
19 18 11 28 –
11 (58%) 10 (56%) 6 (55%) 7 (25%) 49%
8 (50%) 5 (41%) 5 (50%) 3 (13%) 39%
3 (100%) 5 (87%) 1 (100%) 4 (100%) 97%
of percents, treating each village as an independent sample.
to rubber in 1990–1, but reached or exceeded the rate of conversion in other villages by 1992–3 (Figure 5c compared with Table 3). The proportion of rubber gardens that were created in rice fields cleared from primary forest was similar to that in other villages,
and very high (> 80%) for the entire period. Because the number of fields converted from primary forest increased, the total amount of land converted from primary forest to rice to rubber increased as well (Figure 5d).
143 Discussion Deforestation: shifting cultivation vs. industrial land-use
Figure 5. Changes in land-use dynamics in Kembera from 1990– 1995. a) percent of dry-rice fields converted from primary forest; b) mean fallow length of dry-rice fields converted from secondary forest fallows; c) percent of fields converted to rubber gardens; d) estimated amount of land converted to rubber (number of dryrice fields percent of dry-rice fields from primary forest field size percent of fields converted to rubber). For c) and d) - - originally cleared from fallows; — originally cleared from primary forest.
In Kembera, over 50 ha of primary forest have been cut annually for several years, and much of this land has been converted to rubber gardens (Figure 5). Kembera, Jelutung, and Keranji-Baya lie within a 60,000-ha timber concession between GPNP and GJFR, along with three other small villages. We estimate primary forest clearing in all six villages is around 200 ha per year. The area disturbed annually by industrial logging in this same area is probably 2–3.5 times that disturbed by shifting cultivation. In a 60,000-ha concession, selective logging by the Indonesian TPTI system allows the exploitation of 10–17 blocks of 100 ha (depending on the density of harvested species; after Curran and Kusneti 1992). Sixty percent of the forest is accessible to mechanized logging, and 70% of the logged area is moderately to heavily disturbed (Cannon et al. 1994), resulting in substantial disturbance of 400 to 700 ha of lowland rainforest per year. Across Kalimantan, an increasing proportion of selectively logged forest is converted to monospecific plantations, as concessionaires turn to plantation forestry in lieu of waiting for a second cut under the selective logging system. As in Malaysia and Thailand, disturbance due to logging may ultimately represent a permanent loss of mature forest whether or not shifting cultivators are near by. An industrial oil-palm plantation on the eastern border of GPNP had planned to clear-cut and burn 3000 ha per year from 1993 to 1997 (V. Suma, exmayor of Kembera, pers. comm.). If this deforestation were evenly distributed over the entire lifetime of the oil-palm trees (ca. 25 years), it would result in the loss of 600 ha per year. This rate of deforestation is three times that of shifting cultivation and affects an area four times as large. In contrast to plantation forestry or industrial agriculture, disturbance by shifting cultivation shares several important characteristics with natural disturbances due to tree falls, wind throws and small-scale forest fires and landslides. With shifting cultivation, relatively small patches of disturbed forest are produced at a low rate, dispersed non-uniformly in the landscape, and distributed consistently through time. The disturbance associated with plantation establishment is not distributed evenly in time or space. Mean gap size under shifting cultivation (ca. 1 ha) is signif-
144 icantly larger than that found in primary forest (10– 120 m2 ) and naturally regenerating secondary forests (80 m2 ; Yavitt et al. 1995 and references therein). Consequently, the grain of the landscape is quite different, and yet, percent open area is similar. In primary forest, 1–7.5% of the landscape is in the gap-phase (see Yavitt et al. 1995); primary rain forest in Indonesia is likely to fall into the lower end of this range (Poore 1968). In 80-yr old, neotropical secondary forest, Yavitt et al. (1995) found 4.3% of the area in gaps; in this study of shifting cultivation, we found 5% cleared at any one time (Figure 2). Despite recent increases in primary forest clearing, shifting cultivation, as practiced in the Kembera region represents a land-use alternative that minimizes the extent of primary forest loss compared to industrial timber extraction or plantation forestry. Will shifting cultivation continue to have a relatively low impact on primary forests? The answer depends on what factors drive primary forest clearing and whether their effects are changing over time. Causes of deforestation by shifting cultivators The expansion of cultivated land into primary rainforest near Kembera has been caused by the desire for economic development and political security. The people of Kembera want the goods and services procured with cash, especially secondary education for their children, health care and quality housing. They rely on rubber cultivation to meet their cash needs. Poor families can borrow land for rice cultivation. By traditional law, however, they may not convert this borrowed land to rubber; they must claim and cut primary forest for rubber cultivation. The total area of productive rubber gardens (those with trees > 20 cm dbh) should increase by 40% from 1992 to 2002, assuming a conservative diameter growth rate of 1 cm per year (Lawrence, unpublished data). This increase far out-paces population growth of approximately 2% per year (P. Kleinman, pers. comm.). Over the next five years, conversion to rubber could decline considerably, at least temporarily, as labor becomes limiting. High rates of primary forest conversion to rubber may persist, however, if the political environment does not change. The most recent expansion of rice cultivation into primary forest, followed immediately by rubber cultivation, was the result of an organized effort to gain tenure over lands traditionally owned by the village but presently exploited by timber concessionaires. It
was a direct response to the threatened replacement of selective logging (natural forest management) by industrial plantation forestry. The villagers believed that monospecific plantations could not provide them with the benefits of primary forest or selectively logged forest (e.g., locally useful and marketable timber, habitat for wild game, and clean water). Rather than forfeit current and future use of the land, the villagers decided to claim the land by planting rubber. By Indonesian law, unmanaged fallows are not in use, and thus may be expropriated. In contrast, planted trees signify an “improvement” and indicate that the land is in use. Furthermore, rubber, like oil-palm or wood pulp, is a significant source of foreign exchange and revenue for the national government. Thus, rubber gardens may be tolerated as an alternative to industrial plantations, but this remains to be seen. Deforestation in Kembera is not a direct consequence of soil degradation caused by unsustainable cultivation practices (Kleinman et al. 1996), nor simply a response to population growth. If land availability had decreased due to population growth, we would expect some farmers to respond by clearing primary forest to maintain adequate rice production. Others, however, are likely to have shortened the fallow period of land already in cultivation because clearing primary forest requires more labor than clearing secondary forest (Freeman 1955). Where primary forest still exists, both responses to land scarcity should occur together. However, the increase in primary forest clearing in Kembera was not correlated with a decrease in fallow length (Figure 5a, b), supporting our assertion that deforestation is currently driven by political and economic factors and not primarily by ecological constraints on rice production. Considering the relationship between fallow length and primary forest conversion over a broad geographic range reinforces this point. We combined data on eight villages in East Kalimantan (Inoue and Lahjie 1990) with our data from West Kalimantan before land tenure became a major issue (1990–1). In general, less primary forest was cleared when the fallow period was long (Figure 6). Despite variation in settlement history, population density, and proximity to major urban centers none of the villages exceeded an apparent limit to this relationship between fallow length and primary forest conversion. The striking exception to this pattern was Kembera in 1994–5.
145 labor demand. During these periods, they can prevent incursions from vertebrate pests such as monkeys, deer, and birds. Further, the effects of any crop losses are mitigated by the increased size of rice fields at greater distances, as in other parts of Kalimantan (Jessup 1981; Dove 1985b; Mackie et al. 1987). Implications of the expansion of rubber (1993â&#x20AC;&#x201C;present)
Figure 6. The relationship between primary forest clearing and fallow length for eight sites in East Kalimantan (EK, Inoue and Lahjie 1990) and four sites in West Kalimantan (WK, this study). Dashed line drawn by eye to indicate the apparent limit in the relationship between fallow length and the percent of fields converted from primary forest in a given village. indicates villages close to major urban areas.
Integrating rubber and rice in the landscape (ca. 1950â&#x20AC;&#x201C;1992) Although most rubber has been planted in fields cleared from primary forest over the past five years, rubber has also replaced secondary forest fallows at a lower rate, since ca. 1950. The spatial pattern resulting from this replacement may reflect the hypothesized trade off between travel and productive work. In 1992, rubber dominated close to the village (Figure 3) because efficient exploitation requires regular, but short ( 1/2 day) visits over many months. Only recently did villagers begin planting rubber more than a kilometer from the village, as evidenced by the lower frequency of rubber gardens and the smaller size of rubber trees further from the village. Rubber garden size also decreased with distance. Once villagers decided to plant rubber farther away, they may have chosen to reduce future labor requirements of the productive garden by limiting its size. Alternativley, they may have reduced the time invested in vigilance during the establishment phase when deer browsing is severe, especially at the edges of gardens far from the village. Managing a distant rubber garden often entails relocating the household for several years (an option which has been pursued in Kembera). In contrast, rice can be cultivated further from the village (Figure 3) because households can move to the fields for days or weeks if necessary during seasonal periods of high
Adding long-lived tree crops to subsistence farming systems inevitably results in an adjustment of the balance among food crops, fallows, and forest. Because putting land into rubber means keeping it out of rice, the decision may ultimately affect both the rate at which primary forest is converted and the length of the fallow. Changes in either parameter would affect both the composition of the landscape and its ability to supply resources to the village. Because both primary and secondary forest are being converted to rubber (Table 3), the land base for dry-rice cultivation diminishes every year. To meet future rice needs, either more land must be brought into cultivation or land-use must be intensified. Clearing primary forest in the reserve is already prohibited, and the villagers have agreed to respect the boundaries in exchange for input into defining them. Similar constraints exist for land in the timber concession. Access to this land will be more restricted if it is converted to a plantation. Villagers could look for additional land within their managed forest area, but they are unlikely to clear fruit or rubber gardens. Land-intensive alternatives are clearly needed. The people of Kembera could shift from cultivating both dry-rice and wet-rice to cultivating wet-rice only, a trend already evident in other areas of West Kalimantan (Padoch 1985). Other options would be to shorten the fallow or to extend the cultivation period. Shortening the fallow may not be a viable option if soil fertility declines and fertilizer inputs are not available (Nye and Greenland 1960; Kleinman et al. 1996). Extending the cultivation period beyond one or two years would require intensive weeding or the use of herbicides. Even if fertilizers and herbicides were available, currently they are not affordable. Alternatively, villagers could grow rubber in fallows, maintaining the traditional (non-rubber) fallow rotation of 15â&#x20AC;&#x201C;25 years. However, rubber production would be curtailed after only 5â&#x20AC;&#x201C;15 years. The clearing of existing, productive rubber to plant rice seems unlikely. A fundamental shift to a more cash-based
146 economy (in which rice could be purchased with rubber revenue) would reduce the amount of land needed for local rice production and allow a longer fallow period for the managed rubber-fallow. A major cost is that local food self-sufficiency would be sacrificed. Our assessment of the dynamics of rubber and rice in Kalimantan differs significantly from that of Dove (1993), who sees rubber as entirely complementary to dry-rice cultivation. While we agree that these crops are compatible in the household economy, as cash from rubber can effectively substitute for lost rice production, the ecological differences between dry-rice and rubber have major implications for landscape dynamics. Because the fallow length for dryrice (8–20 years across Kalimantan) is much shorter than the lifetime of a rubber garden (30–40 years), the two land-uses can not substitute for one another in the landscape. Elsewhere in the tropics, the expansion of tree crops has resulted in adjustments to the distribution and turnover of other land-use types in the agroecosystem. In Nigeria, increasing the total area under cultivation was the initial response to a rapid expansion of tree crops grown for cash. Eventually, the fallow period was reduced along with the area devoted to food crops (Osunade 1991). Within 30 years, local food production was inadequate to meet demand. Similarly, in Sumatra, Indonesia, the expansion of rubber came partly at the expense of remaining primary forests, but it also reduced the extent of upland dryrice (Mary and Michon 1987). In contrast, in tropical China, rather than reducing the land allocated to rice production, rubber displaced other agroforestry systems (Saint Pierre 1991). Landscape patterns associated with slash-and-burn world-wide Although the causes of deforestation and trajectories of regrowth differ among tropical regions, comparing their landscape dynamics is informative. We compared our data with contemporaneous data from satellite-image based studies of slash-and-burn systems in Africa and Amazonia (Skole et al. 1994; Moran et al. 1994; Chatelain et al. 1996). We focused on land that had been cleared from primary forest and was currently under food crops (or bare), tree crops, pasture, or secondary forest. These categories corresponded to current rice fields, rubber or fruit gardens, (nothing comparable to pasture) and fallows in our study, which we defined collectively as managed land.
A broad pattern of temporal change in land-use allocation was evident since the beginning of deforestation. A higher proportion of land was in food crops, or bare, in areas more recently opened up to human settlement (Figure 7). The proportion of managed land in secondary forest seemed to increase over time, approaching within 25 years the proportion found in a rainforest landscape dominated by humans for over 200 years (this study). Although the proportion of secondary forest was similar between landscapes with 25 and 200 years of deforestation, secondary forest in Northeast Brazil was dominated by younger vegetation (> 80% of secondary forest consisted of trees < 10 years old; Moran et al. 1994). In Kembera, assuming diameter growth rates of 1–2 cm per year, only 20–52% of the area in secondary forest was < 10 years old (Figure 4a). The difference in forest age-structure may be due to a longer fallow rotation in West Kalimantan or to the sporadic course of land development in Northeast Brazil where periods of rapid clearing have been followed by periods of abandonment.
Conclusion In the area near GPNP, shifting cultivation results in less deforestation than industrial land-use such as timber extraction and oil-palm plantations, especially when we consider that logged forest is often converted to other uses. Though rubber cultivation appears to be the proximate cause of deforestation, political and economic insecurity are the ultimate causes. Rubber has profoundly affected the spatial pattern of the landscape, initially reflecting trade-offs between work and travel time. The increasing predominance of rubber will ultimately determine the dynamics of dry-rice cultivation, once the exclusive factor defining the landscape. Contrary to what happens in areas where forest is cleared for permanent agriculture or pasture development, land-use intensification and the development of a cash-dependent economy should result in a forested landscape in parts of West Kalimantan currently dominated by shifting cultivation. The managedrubber fallow would be longer, resulting in bigger trees across the landscape. Despite potential increases in forest stature, the diversity of these forests would decline if rubber replaces dry-rice fallows (Lawrence 1996; Lawrence and Mogea 1996). Thus, while rubber would not change the grain of the landscape
147
Figure 7. The proportion of deforested land in use or in succession in three regions of the moist tropics. Categories for the three satellite image-based studies (Southwest Ivory Coast [SIC], North Brazil [NB], and West Brazil [WB]) were similar, including a category for open or cropped land and one to many categories for secondary forest. In addition, tree crops were distinguished in SIC, and heavily degraded primary forest was included in the secondary forest number presented here. Pastures were identified in NB but not in WB, thus part of the WB landscape in crop/bare may actually be in pasture.
under shifting cultivation, at the patch level, complexity would be lost. These changes in the structure and dynamics of the landscape may affect the persistence of primary forest species whose original habitat is increasingly threatened. Further research is necessary on how processes of forest regeneration are constrained by changes in the managed landscape.
debt to the people of Kembera for their hospitality and assistance. D. Higdon and A. Ruetters provided statistical assistance. We also thank C. Cannon, L. Curran and C. Webb for support in the field and discussion. Comments by P. Kleinman, W. Schlesinger, J. Clark, and two reviewers improved the manuscript.
References Acknowledgments Funding for this research was provided by a grant from the Conservation, Food, and Health Foundation, Incorporated (DCL). Grants from the United States Agency for International Development PSTC Program (DRP and ML), The Duke University Chapter of the Sigma Xi, The Center for International Studies at Duke University, The Nature Conservancy, and The Garden Club of America/World Wildlife Fund (DCL) provided additional support for the final stages of the project. The research would not have been possible without the sponsorship of the Center for Research and Development in Biology of the Indonesian Institute of Sciences (LIPI) in Indonesia and The Peabody Museum at Harvard University in the United States. We owe a great
Abell, T.M. 1988. The application of land systems mapping to the management of Indonesian forests. The Journal of World Forest Resource Management 3: 111–128. Anderson, A.B. 1990. Alternatives to deforestation: steps toward sustainable use of the Amazon rain forest. Columbia University Press, New York. Cannon, C.H., Jr., D.R. Peart, M. Leighton, and K. Kartawinata. 1994. The structure of lowland rainforest after selective logging in West Kalimantan, Indonesia. Forest Ecology and Management 67: 49–68. Chatelain, C., L. Gautier, and R. Spichiger. 1996. A recent history of forest fragmentation in Southwestern Ivory Coast. Biodiversity and Conservation 5: 37–54. Collins, M., J. Sayer, and T.C. Whitmore. 1991. The conservation atlas of tropical forests: Asia and the Pacific. Simon and Schuster, New York. Curran, L.M., and M. Kusneti. 1992. Applied research recommendations for production forest management based on a preliminary economic and ecological review of the Indonesian selective cut-
148 ting and harvesting system (TPTI). USAID/Associates in Rural Development, Jakarta. Denslow, J.S., and C. Padoch. 1988. People of the tropical rainforest. University of California Press, Berkeley. Dirzo, R., and M. Garcia. 1992. Rates of deforestation in Los Tuxtlas, a neotropical area in Southeast Mexico. Conservation Biology 6: 84–100. Dove, M.R. 1985a. Plantation development in West Kalimantan I: extant population/land balances. Borneo Research Bulletin 17: 95–105. Dove, M.R. 1985b. Swidden Agriculture in Indonesia. Mouton, Berlin. Dove, M.R. 1993. Smallholder rubber and swidden agriculture in Borneo: a sustainable adaptation to the ecology and economy of the tropical forest. Economic Botany 47: 136–147. FAO. 1993. Forest resources assessment 1990: Tropical countries. Food and Agriculture Organization, Rome. Feeny, D. 1984. Agricultural expansion and forest depletion in Thailand 1900–1975. Yale University, New Haven, Connecticut. Freeman, D.J. 1955. Report on the Iban of Sarawak. Government of Sarawak, Kuching (republished in 1992 by S. Abdul Majeed & Co. as “The Iban of Borneo.”) Gardner, R.H., B.T. Milne, M.G. Turner, and R.V. O’Neill. 1987. Neutral models for the analysis of broad-scale landscape pattern. Landscape Ecology 1: 19–28. Grainger, A. 1984. Quantifying changes in forest cover in the humid tropics: overcoming current limitations. The Journal of World Forest Resource Management 1: 3–64. Houghton, R.A. 1994. The worldwide extent of land-use change. BioScience 44: 305–313. Inoue, M., and A.M. Lahjie. 1990. Dynamics of swidden agriculture in East Kalimantan. Agroforestry Systems 12: 269–284. Jessup, T. 1981. Why do Apo Kayan shifting cultivators move? Borneo Research Bulletin 13: 16–32. Kartawinata, K., H. Soedjito, T. Jessup, A.P. Vayda, and C.J.P. Colfer. 1984. The impact of development on interactions between people and forests in East Kalimantan: a comparison of two areas of Kenyah Dayak settlement. The Environmentalist 4: 87–95. Kleinman, P.J.A., R.B. Bryant, and D. Pimentel. 1996. Assessing ecological sustainability of slash-and-burn agriculture through soil fertility indicators. Agronomy Journal 88 (2): 122–127. Kummer, D.M. 1992. Upland agriculture, the land frontier and forest decline in the Philippines. Agroforestry Systems 18: 31–46. Lawrence, D.C. 1996. Trade-offs between rubber production and maintenance of diversity: the structure of rubber gardens in West Kalimantan, Indonesia. Agroforestry Systems 34 (1): 83–100. Lawrence, D.C., M. Leighton, and D.R. Peart. 1995. Availability and extraction of forest products in managed and primary forest around a Dayak village in West Kalimantan, Indonesia. Conservation Biology 9: 76–88. Lawrence, D.C. and J. Mogea. 1996. A preliminary analysis of tree diversity under shifting cultivation north of Gunung Palung National Park. Tropical Biodiversity 3 (3): 297–319. Mackie, C., T.C. Jessup, A.P. Vayda, and K. Kartawinata. 1987. Shifting cultivation and patch dynamics in an upland forest in East Kalimantan, Indonesia. In proceedings of a conference on
“The impact of man’s activities on tropical upland forest ecosystems.” pp. 465–518. Faculty of Forestry, Universiti Pertanian Malaysia, Selangor, Malaysia. Mary, F., and G. Michon. 1987. When agroforests drive back natural forests: a socio-economic analysis of a rice-agroforest system in Sumatra. Agroforestry Systems 5: 27–55. Michon, G. 1991. The damar gardens: existing buffer zones at Pesisir area of Sumatra Selatan National Park, Lampung. Symposium on rain forest protection and national park buffer zones. Ministry of Forestry, Government of Indonesia, Manggala Wanabakti, Jakarta, Indonesia. Moran, E.F., E. Brondizio, P. Mausel, Y. Wu. 1994. Integrating Amazonian vegetation, land-use, and satellite data. BioScience 44: 329–338. Myers, N. 1993. Tropical forests: the main deforestation fronts. Environmental Conservation 20: 9–16. Nye, P.H., and D.J. Greenland. 1960. The soil under shifting cultivation. Commonwealth Bureau of Soil Science, Farnham Royal, England. Ojima, D.S., K.A. Galvin, and B.L. Turner, II. 1994. The global impact of land-use change. BioScience 44: 300–304. Osunade, M.A.A. 1991. Agricultural change by supplanting process in a traditional farm system. International Journal of Ecology and Environmental Sciences 17: 201–210. Padoch, C. 1985. Labor efficiency and intensity of land use in rice production: an example from Kalimantan. Human Ecology 13: 271–289. Padoch, C., and C.M. Peters. 1993. Managed forest gardens in West Kalimantan, Indonesia. In Potter, C.S., J.J. Cohen, and D. Janczewski (eds.) Perspectives on biodiversity: case studies of genetic resource conservation and development. pp. 167–176. American Association for the Advancement of Science Press, Washington, D.C. Poffenberger, M. 1990. Keepers of the Forest. Kumarian Press, West Hartford, Connecticut. Poore, M.E.D. 1968. Studies in Malaysian rainforest I: The forest on Triassic sediments in Jengka Forest Reserve. Journal of Ecology 56: 143–196. Repetto, R. 1988. The forest for the trees? Government policies and the misuse of forest resources. World Resources International, Washington, D.C. Riswan, R., and L. Hartanti. 1995. Human impacts on tropical forest dynamics. Vegetatio 121: 41–52. Saint-Pierre, C. 1991. Evolution of agroforestry in the Xishuangbanna region of tropical China. Agroforestry Systems 133: 159–176. Salafsky, N. 1994. Forest gardens in the Gunung Palung region of West Kalimantan, Indonesia. Agroforestry Systems 28: 237–268. Skole, D.L., and C.J. Tucker. 1993. Tropical deforestation and habitat fragmentation in the Amazon: satellite data from 1978 to 1988. Science 260: 1905–1910. Skole, D.L., W.H. Chomentowski, W.A. Salas, and A.D. Nobre. 1994. Physical and human dimensions of deforestation in Amazonia. BioScience 44: 314–322. Yavitt, J.B., J.J. Battles, G.E. Lang, and D.H. Knight. 1995. The canopy gap regime in a secondary neotropical forest in Panama. Journal of Tropical Ecology 11: 391–402.