An Assessment of Trends in the Extent of Swidden in Southeast Asia

Swidden systems consisting of temporarily cultivated land and associated fallows often do not appear on land use maps or in statistical records. This is partly due to the fact that swidden is a diverse and dynamic land use system that is difficult to map and partly because of the practice of grouping land covers associated with swidden systems into land use or land cover categories that are not self-evidently linked to swiddening. Additionally, in many parts of Southeast Asia swidden systems have changed or are in the process of changing into other land use systems. This paper assesses the extent of swidden on the basis of regional and national sources for nine countries, and determines the pattern of changes of swidden on the basis of 151 cases culled from 67 articles. Findings include (1) a majority of the cases document swidden being replaced by other forms of agriculture or by other livelihood systems; (2) in cases where swiddening is still practiced, fallow lengths are usually, but not always, shorter; and (3) shortened fallow length does not necessarily indicate a trend away from swidden since it is observed that short fallow swidden is sometimes maintained along with other more intensive farming practices and not completely abandoned. The paper concludes that there is a surprising lack of conclusive data on the extent of swidden in Southeast Asia. In order to remedy this, methods are reviewed that may lead to more precise future assessments.     

Environmental Consequences of the Demise in Swidden Cultivation in Southeast Asia: Carbon Storage and Soil Quality

The effects of swidden cultivation on carbon storage and soil quality are outlined and compared to the effects of the intensified production systems that swidden systems of Southeast Asia transform into. Time-averaged aboveground carbon stocks decline by about 90% if the long fallow periods of traditional swidden cultivation are reduced to 4 years and by about 60% if swidden cultivation is converted to oil palm plantations. Stocks of soil organic carbon (SOC) in tree plantations are 0–40% lower than stocks in swidden cultivation, with the largest losses found in mechanically established oil palm plantations. Impacts of tree plantations on soil quality are to a large extent determined by management. Conversion of swiddening to continuous annual cropping systems brings about substantial losses of time-averaged aboveground carbon stocks, reductions of SOC stocks and generally leads to declining soil quality. Knowledge of carbon storage in belowground biomass of tree based systems of the tropics is sparse but failure to include this pool in carbon inventories may significantly underestimate the total biomass of the systems. Moreover, studies that consider the ecological reasons behind farmers’ land use decisions as well as spatial variability in biogeophysical and edaphological parameters are needed to evaluate the effects of the ongoing land use transitions in Southeast Asia.     

Ecosystem Services and Biodiversity in a Rapidly Transforming Landscape in Northern Borneo

Because industrial agriculture keeps expanding in Southeast Asia at the expense of natural forests and traditional swidden systems, comparing biodiversity and ecosystem services in the traditional forest–swidden agriculture system vs. monocultures is needed to guide decision making on land-use planning. Focusing on tree diversity, soil erosion control, and climate change mitigation through carbon storage, we surveyed vegetation and monitored soil loss in various land-use areas in a northern Bornean agricultural landscape shaped by swidden agriculture, rubber tapping, and logging, where various levels and types of disturbance have created a fine mosaic of vegetation from food crop fields to natural forest. Tree species diversity and ecosystem service production were highest in natural forests. Logged-over forests produced services similar to those of natural forests. Land uses related to the swidden agriculture system largely outperformed oil palm or rubber monocultures in terms of tree species diversity and service production. Natural and logged-over forests should be maintained or managed as integral parts of the swidden system, and landscape multifunctionality should be sustained. Because natural forests host a unique diversity of trees and produce high levels of ecosystem services, targeting carbon stock protection, e.g. through financial mechanisms such as Reducing Emissions from Deforestation and Forest Degradation (REDD+), will synergistically provide benefits for biodiversity and a wide range of other services. However, the way such mechanisms could benefit communities must be carefully evaluated to counter the high opportunity cost of conversion to monocultures that might generate greater income, but would be detrimental to the production of multiple ecosystem services.     

Policies,Political-Economy,and Swidden in Southeast Asia

For centuries swidden was an important farming practice found across the girth of Southeast Asia. Today, however, these systems are changing and sometimes disappearing at a pace never before experienced. In order to explain the demise or transitioning of swidden we need to understand the rapid and massive changes that have and are occurring in the political and economic environment in which these farmers operate. Swidden farming has always been characterized by change, but since the onset of modern independent nation states, governments and markets in Southeast Asia have transformed the terms of swiddeners’ everyday lives to a degree that is significantly different from that ever experienced before. In this paper we identified six factors that have contributed to the demise or transformation of swidden systems, and support these arguments with examples from China (Xishuangbanna), Laos, Thailand, Malaysia, and Indonesia. These trends include classifying swiddeners as ethnic minorities within nation-states, dividing the landscape into forest and permanent agriculture, expansion of forest departments and the rise of conservation, resettlement, privatization and commoditization of land and land-based production, and expansion of market infrastructure and the promotion of industrial agriculture. In addition we note a growing trend toward a transition from rural to urban livelihoods and expanding urban-labor markets.

Carbon outcomes of major land‐cover transitions in SE Asia: great uncertainties and REDD+ policy implications

Policy makers across the tropics propose that carbon finance could provide incentives for forest frontier communities to transition away from swidden agriculture (slash‐and‐burn or shifting cultivation) to other systems that potentially reduce emissions and/or increase carbon sequestration. However, there is little certainty regarding the carbon outcomes of many key land‐use transitions at the center of current policy debates. Our meta‐analysis of over 250 studies reporting above‐ and below‐ground carbon estimates for different land‐use types indicates great uncertainty in the net total ecosystem carbon changes that can be expected from many transitions, including the replacement of various types of swidden agriculture with oil palm, rubber, or some other types of agroforestry systems. These transitions are underway throughout Southeast Asia, and are at the heart of REDD+ debates. Exceptions of unambiguous carbon outcomes are the abandonment of any type of agriculture to allow forest regeneration (a certain positive carbon outcome) and expansion of agriculture into mature forest (a certain negative carbon outcome). With respect to swiddening, our meta‐analysis supports a reassessment of policies that encourage land‐cover conversion away from these [especially long‐fallow] systems to other more cash‐crop‐oriented systems producing ambiguous carbon stock changes – including oil palm and rubber. In some instances, lengthening fallow periods of an existing swidden system may produce substantial carbon benefits, as would conversion from intensely cultivated lands to high‐biomass plantations and some other types of agroforestry. More field studies are needed to provide better data of above‐ and below‐ground carbon stocks before informed recommendations or policy decisions can be made regarding which land‐use regimes optimize or increase carbon sequestration. As some transitions may negatively impact other ecosystem services, food security, and local livelihoods, the entire carbon and noncarbon benefit stream should also be taken into account before prescribing transitions with ambiguous carbon benefits.     

Saving Slash-and-Burn to Save Biodiversity

Several prominent articles have recently revived the debate on how to advance and reconcile two pressing global issues: conservation of biodiversity, and food production for an increasing human population. These discussions contrast a ‘land-sparing/intensive agriculture’ strategy with a ‘biodiversity-friendly’ agriculture approach. We propose that swidden or shifting cultivation should be an important component of the latter approach in the tropics because many swidden systems maintain very high levels of biodiversity while providing livelihood for populations in tropical forest areas worldwide. We suggest further that when many swidden systems are viewed without prejudice and in broader spatial and longer temporal perspectives, the conservationist aspects of the systems become evident.     

Farmers’ Perspectives on Vital Soil-related Ecosystem Services in Intensive Swidden Farming Systems in the Peruvian Amazon

A growing dilemma is how to conserve Amazonian forest while allowing local people to secure their livelihoods. Small-scale swidden farming in Amazonia is entirely dependent on the continued provision of ecosystem services (ES) that generate the conditions for agriculture. This study identified soil-related ES needed for, and enhanced by, productive swidden systems from the farmer’s perspective. Workshops in six farming communities in northeastern Peru discussed various land uses, swidden systems that continue to be productive, and swidden systems on degraded land. The participating farmers noted changes in their production systems and described the ES (or lack thereof) in terms of soil quality, crop production quantity and quality, burning practices, forest regeneration, and farming skill. The central elements described in farmers’ own strategies for managing soil-related ES were fallow management for biomass production and crop diversity, factors identified as central to future ES management work in established agricultural areas in Amazonia.     

Aquatic Ecosystem Impacts of Land Sharing Versus Sparing: Nutrient Loading to Southeast Asian Rivers

As world food demand continues to increase, two broad strategies for agricultural production have been widely discussed: land sparing and land sharing. Reflecting tradeoffs between the extent and intensity of agricultural use, land sparing maximizes the ratio of conserved to agricultural land, whereas land sharing allows more extensive, nature-friendly transformation of the agroecological matrix. Freshwater ecosystems are rarely considered in weighing these strategies, despite being strongly affected by land-use change. Here we analyze how shifting from extensive to intensive agricultural practices is altering dry season riverine nutrient availability and algal growth in upland Southeast Asia, which is experiencing rapid conversion from swidden—or shifting—cultivation to fertilized row crops. In situ algal growth assays and nutrient concentration data from eleven catchments representing a spectrum of land use and population densities show that intensive agriculture is associated with significantly elevated nitrate concentrations but no shift in phosphorus. As a result, nitrogen to phosphorus ratios increases dramatically, shifting algal growth toward colimitation by nitrogen and phosphorus. Geochemical analysis of suspended solids suggested comparable geological inputs across basins, but dissolved rare earth elements reveal that inorganic fertilizers are changing water chemistry in parallel with land use. Taken together, our analyses suggest that the transition from low-input land-sharing management (swidden) to high-input land-sparing practices (intensive row-crop agriculture) underway in Southeast Asia has profound consequences for river ecosystems. Such nutrient loading can affect river productivity and food webs, suggesting that land-use conservation strategies for Southeast Asia need to account for impacts on freshwater ecosystems.     

Change in Phylogenetic Community Structure during Succession of Traditionally Managed Tropical Rainforest in Southwest China

Tropical rainforests in Southeast Asia are facing increasing and ever more intense human disturbance that often negatively affects biodiversity. The aim of this study was to determine how tree species phylogenetic diversity is affected by traditional forest management types and to understand the change in community phylogenetic structure during succession. Four types of forests with different management histories were selected for this purpose: old growth forests, understorey planted old growth forests, old secondary forests (∼200-years after slash and burn), and young secondary forests (15–50-years after slash and burn). We found that tree phylogenetic community structure changed from clustering to over-dispersion from early to late successional forests and finally became random in old-growth forest. We also found that the phylogenetic structure of the tree overstorey and understorey responded differentially to change in environmental conditions during succession. In addition, we show that slash and burn agriculture (swidden cultivation) can increase landscape level plant community evolutionary information content.     

Who Counts? Demography of Swidden Cultivators in Southeast Asia

Swidden cultivators are often found as a distinct category of farmers in the literature, but rarely appear in population censuses or other national and regional classifications. This has led to a worldwide confusion on how many people are dependent on this form of agriculture. The most often cited number of 200–300 million dates back to the early 1970s, but the source is obscure. We assess available, published data from nine countries in Southeast Asia and conclude that on this basis it is not possible to provide a firm estimate of the number of swidden cultivators in the region. A conservative range of 14–34 million people engaged in swidden cultivation in the region is suggested, however. We argue that along with improved knowledge of swidden livelihoods, there is an urgent need to develop techniques that will allow for better estimates of swidden populations in order to secure appropriate rural development and poverty reduction in swidden areas.     

乡村景观生物多样性研究进展

乡村景观是一种人文和自然共生的复合生态系统, 为生物多样性的维持提供了支持。目前, 中国传统乡村地区生物多样性的维持正面临着农业集约化、人工林树种单一化、非农业用地急剧扩张及生态传承机制解体等复杂多样的威胁, 亟待展开深入研究。本文在总结乡村景观生物多样性相关概念及特征的基础上, 通过文献分析概括了国际乡村景观生物多样性的热点研究方向, 包括农业集约化下的生物多样性管理、区域尺度乡村景观与生物多样性的协同关系、局地尺度不同乡村景观类型的物种多样性及乡村景观中的生物文化多样性, 进一步梳理了国内在相关研究方向上的主要进展并指出研究不足。在此基础上提出未来研究展望, 包括突出生物文化多样性特征、加强多时空尺度分析、深化动态维持机制研究、推进生物多样性研究在乡村生态景观规划中的全过程应用等建议。     

Predicting Plant Diversity Patterns in Madagascar: Understanding the Effects of Climate and Land Cover Change in a Biodiversity Hotspot

Climate and land cover change are driving a major reorganization of terrestrial biotic communities in tropical ecosystems. In an effort to understand how biodiversity patterns in the tropics will respond to individual and combined effects of these two drivers of environmental change, we use species distribution models (SDMs) calibrated for recent climate and land cover variables and projected to future scenarios to predict changes in diversity patterns in Madagascar. We collected occurrence records for 828 plant genera and 2186 plant species. We developed three scenarios, (i.e., climate only, land cover only and combined climate-land cover) based on recent and future climate and land cover variables. We used this modelling framework to investigate how the impacts of changes to climate and land cover influenced biodiversity across ecoregions and elevation bands. There were large-scale climate- and land cover-driven changes in plant biodiversity across Madagascar, including both losses and gains in diversity. The sharpest declines in biodiversity were projected for the eastern escarpment and high elevation ecosystems. Sharp declines in diversity were driven by the combined climate-land cover scenarios; however, there were subtle, region-specific differences in model outputs for each scenario, where certain regions experienced relatively higher species loss under climate or land cover only models. We strongly caution that predicted future gains in plant diversity will depend on the development and maintenance of dispersal pathways that connect current and future suitable habitats. The forecast for Madagascar’s plant diversity in the face of future environmental change is worrying: regional diversity will continue to decrease in response to the combined effects of climate and land cover change, with habitats such as ericoid thickets and eastern lowland and sub-humid forests particularly vulnerable into the future.     

Biodiversity conservation in cocoa production landscapes: an overview

Cocoa agroforests that retain a floristically diverse and structurally complex shade canopy have the potential to harbour significant levels of biodiversity, yet few studies have documented the plant and animal species occurring within these systems or within landscapes dominated by cocoa production. In this special issue, we bring together nine studies from Latin America, Africa and Asia that document the contribution of cocoa agroforestry systems to biodiversity conservation, and explore how the design, management and location of these systems within the broader landscape influence their value as habitats, resources and biological corridors. Tree diversity within the cocoa production systems is variable, depending on management, cultural differences, location and farm history, among other factors. Animal diversity is typically highest in those cocoa agroforests that have high plant diversity, structurally complex canopies, and abundant surrounding forest cover. In general, both plant and animal diversity within cocoa agroforests is greater than those of other agricultural land uses, but lower than in the original forest habitat. There are several emerging threats to biodiversity conservation within cocoa production landscapes, including the loss of remaining forest cover, the simplification of cocoa shade canopies and the conversion of cocoa agroforestry systems to other agricultural land uses with lower biodiversity value. To counter these threats and conserve biodiversity over the long-term, land management should focus on conserving native forest habitat within cocoa production landscapes, maintaining or restoring floristically diverse and structurally complex shade canopies within cocoa agroforests, and retaining other types of on-farm tree cover to enhance landscape connectivity and habitat availability.     

Agriculture erases climate constraints on soil nematode communities across large spatial scales

Anthropogenic conversion of natural to agricultural land reduces aboveground biodiversity. Yet, the overall consequences of land‐use changes on belowground biodiversity at large scales remain insufficiently explored. Furthermore, the effects of conversion on different organism groups are usually determined at the taxonomic level, while an integrated investigation that includes functional and phylogenetic levels is rare and absent for belowground organisms. Here, we studied the Earth's most abundant metazoa—nematodes—to examine the effects of conversion from natural to agricultural habitats on soil biodiversity across a large spatial scale. To this aim, we investigated the diversity and composition of nematode communities at the taxonomic, functional, and phylogenetic level in 16 assemblage pairs (32 sites in total with 16 in each habitat type) in mainland China. While the overall alpha and beta diversity did not differ between natural and agricultural systems, all three alpha diversity facets decreased with latitude in natural habitats. Both alpha and beta diversity levels were driven by climatic differences in natural habitats, while none of the diversity levels changed in agricultural systems. This indicates that land conversion affects soil biodiversity in a geographically dependent manner and that agriculture could erase climatic constraints on soil biodiversity at such a scale. Additionally, the functional composition of nematode communities was more dissimilar in agricultural than in natural habitats, while the phylogenetic composition was more similar, indicating that changes among different biodiversity facets are asynchronous. Our study deepens the understanding of land‐use effects on soil nematode diversity across large spatial scales. Moreover, the detected asynchrony of taxonomic, functional, and phylogenetic diversity highlights the necessity to monitor multiple facets of soil biodiversity in ecological studies such as those investigating environmental changes.     

Intensive agriculture erodes β-diversity at large scales

Biodiversity is declining from unprecedented land conversions that replace diverse, low-intensity agriculture with vast expanses under homogeneous, intensive production. Despite documented losses of species richness, consequences for β-diversity, changes in community composition between sites, are largely unknown, especially in the tropics. Using a 10-year data set on Costa Rican birds, we find that low-intensity agriculture sustained β-diversity across large scales on a par with forest. In high-intensity agriculture, low local (α) diversity inflated β-diversity as a statistical artefact. Therefore, at small spatial scales, intensive agriculture appeared to retain β-diversity. Unlike in forest or low-intensity systems, however, high-intensity agriculture also homogenised vegetation structure over large distances, thereby decoupling the fundamental ecological pattern of bird communities changing with geographical distance. This ~40% decline in species turnover indicates a significant decline in β-diversity at large spatial scales. These findings point the way towards multi-functional agricultural systems that maintain agricultural productivity while simultaneously conserving biodiversity.     

Landscape heterogeneity metrics as indicators of bird diversity: Determining the optimal spatial scales in different landscapes

Species distribution models are often used to study the biodiversity of ecosystems. The modelling process uses a number of parameters to predict others, such as the occurrence of determinate species, population size, habitat suitability or biodiversity. It is well known that the heterogeneity of landscapes can lead to changes in species’ abundance and biodiversity. However, landscape metrics depend on maps and spatial scales when it comes to undertaking a GIS analysis.We explored the goodness of fit of several models using the metrics of landscape heterogeneity and altitude as predictors of bird diversity in different landscapes and spatial scales. Two variables were used to describe biodiversity: bird richness and trophic level diversity, both of which were obtained from a breeding bird survey by means of point counts. The relationships between biodiversity and landscape metrics were compared using multiple linear regressions. All of the analyses were repeated for 14 different spatial scales and for cultivated, forest and grassland environments to determine the optimal spatial scale for each landscape typology.Our results revealed that the relationships between species’ richness and landscape heterogeneity using 1:10,000 land cover maps were strongest when working on a spatial scale up to a radius of 125–250 m around the sampled point (circa 4.9–19.6 ha). Furthermore, the correlation between measures of landscape heterogeneity and bird diversity was greater in grasslands than in cultivated or forested areas. The multi-spatial scale approach is useful for (a) assessing the accuracy of surrogates of bird diversity in different landscapes and (b) optimizing spatial model procedures for biodiversity mapping, mainly over extensive areas.     

Relocating plants from swidden fallows to gardens in Southwestern China

As upland farmers in Southeast Asia change from shifting cultivation to permanent agriculture and lose access to swidden-fallow forests and their resources, they are introducing economically important forest and fallow plants into their house gardens. We describe this process in Daka, a village of Hani ethnicity in Yunnan Province, China. Daka smallholders collect both seeds and seedlings from fallow forests and transfer the plants to house gardens, initiating the transformation of wild species to a cultivated or semi-domesticated one. Two kinds of species are commonly transferred from swidden fallows to house gardens. Some are particularly rare, others are plants in great demand. Between 1998 and 2000 Daka households earned an average of US$68.20 annually from the products of fallow forests. We also found that villagers harvest and use 76 plant species from fallow forests and 126 species from house gardens. Twenty-two species found in house gardens that had been transferred from fallow forests. Households vary widely in the frequency with which they engage in this pattern. We believe that local knowledge of these practices is a potentially important resource in the development of other areas of smallholder farming.     

Land use change in Asia and the ecological consequences

Viewed within a historical context, Asia has experienced dramatic land transformations, and currently more than 50% of Asian land area is under agriculture. The consequences of this transformation are manifold. Southeast Asia has the highest deforestation rate of any major tropical region. Many of the world’s large rivers and lakes in Asia have been heavily degraded. About 11 of 19 world megacities with more than 10 million inhabitants are in Asia. These land use activities have resulted in substantial negative ecological consequences, including increased anthropogenic CO₂ emissions, deteriorated air and water quality, alteration of regional climate, an increase of disease and a loss of biodiversity. Although land use occurs at the local level, it has the potential to cause ecological impact across local, regional and global scales. Reducing the negative environmental impacts of land use change while maintaining economic viability and social acceptability is an major challenge for most developing countries in Asia.     

Low-Intensity Agricultural Landscapes in Transylvania Support High Butterfly Diversity: Implications for Conservation

European farmland biodiversity is declining due to land use changes towards agricultural intensification or abandonment. Some Eastern European farming systems have sustained traditional forms of use, resulting in high levels of biodiversity. However, global markets and international policies now imply rapid and major changes to these systems. To effectively protect farmland biodiversity, understanding landscape features which underpin species diversity is crucial. Focusing on butterflies, we addressed this question for a cultural-historic landscape in Southern Transylvania, Romania. Following a natural experiment, we randomly selected 120 survey sites in farmland, 60 each in grassland and arable land. We surveyed butterfly species richness and abundance by walking transects with four repeats in summer 2012. We analysed species composition using Detrended Correspondence Analysis. We modelled species richness, richness of functional groups, and abundance of selected species in response to topography, woody vegetation cover and heterogeneity at three spatial scales, using generalised linear mixed effects models. Species composition widely overlapped in grassland and arable land. Composition changed along gradients of heterogeneity at local and context scales, and of woody vegetation cover at context and landscape scales. The effect of local heterogeneity on species richness was positive in arable land, but negative in grassland. Plant species richness, and structural and topographic conditions at multiple scales explained species richness, richness of functional groups and species abundances. Our study revealed high conservation value of both grassland and arable land in low-intensity Eastern European farmland. Besides grassland, also heterogeneous arable land provides important habitat for butterflies. While butterfly diversity in arable land benefits from heterogeneity by small-scale structures, grasslands should be protected from fragmentation to provide sufficiently large areas for butterflies. These findings have important implications for EU agricultural and conservation policy. Most importantly, conservation management needs to consider entire landscapes, and implement appropriate measures at multiple spatial scales.