Search

Shifting cultivation, an age-old agricultural practice, is a major factor in forest cover change across Southeast Asia, where repeated cycles of vegetation disturbance and regrowth lead to far-reaching environmental and socio-economic impacts. The present study aims to assess the spatio-temporal patterns of vegetation disturbance and regrowth caused by shifting cultivation in Tripura state of India, over the past three decades, utilizing temporal segmentation of time-series Landsat data. The study analyzed vegetation disturbance and regrowth patterns in a shifting cultivation landscape from 1991 to 2020 using normalized burn ratio trends through LandTrendr, validated by the TimeSync tool. Six land use and land cover classes, viz., forests and trees outside forests, rubber plantation, shifting cultivation, water bodies, agriculture, and settlements, were mapped with an accuracy of 83.08% using a random forest classifier. This classification enabled the identification of the effective study area, which included forest areas with shifting cultivation patches. The analysis revealed that 2533.96 km 2 of the study area remained undisturbed, 568.43 km 2 experienced low-magnitude disturbance, 1501.11 km 2 were moderately disturbed, and 184.82 km 2 were highly disturbed. The shifting cultivation cycles in the study area show considerable variation. Low-magnitude disturbance indicates a single slash-and-burn event in the past three decades, moderate-magnitude disturbance involves fallow periods of over 10 years, and high-magnitude disturbance occurs with fallow periods of less than 8 years. The study revealed a shift from traditional shifting cultivation to more permanent agricultural practices in parts of Tripura. In response to incentives for commercial crops, cultivators are increasingly adopting long-term cultivation, including the growing of pineapple, areca nut, and rubber, as well as intercropping with papaya, banana, lemon, tapioca, pepper, and ginger. These plots are, however, abandoned if the yields become economically unviable. The expansion of monoculture cultivation significantly reduces the available area for shifting cultivation, thereby compelling jhum cultivators to revisit their jhum patches more frequently. This study is a first-of-its-kind attempt in the Indian context and sheds light on changing patterns in an age-old agricultural practice., Competing Interests: Declarations Competing interests The authors declare no competing interests., (© 2024. The Author(s).)

For millennia, Maya farmers (i.e., milperos) throughout Mesoamerica have managed milpa: sequential agroforests initiated by slashing and burning patches of secondary forest and then cultivating a diverse polyculture of trees and annual crops. To reduce greenhouse gas emissions associated with deforestation, the Mexican government and non-governmental organizations have urged milperos to cease burning. We collaborated with Maya milperos in several communities in the Montes Azules Biosphere Reserve region in Chiapas, Mexico to determine carbon retained as char in traditional milpas, carbon loss associated with burning, and effects of burning on soil quality. We found the carbon retention of char in Maya milpas (24 ± 6.5% of C in vegetation) is 4-1400% higher than other slash-and-burn agroecosystems reported in the literature. Burning resulted in significant carbon loss of 12.6 (±3.6) t C ha -1 yr -1 , but this was partially mitigated by char production (3.0 [±0.6] t C ha -1 yr -1 ) and incomplete combustion of woody biomass. The effects of burning on soil were minimal, with the only significant changes observed being increases in pH, potassium availability, and cation exchange capacity (2, 100, and 7%, respectively). The mean residence times of charred materials were at least double that of uncharred biomass. While there is a risk that shortening fallow periods would undermine the sustainability of Maya swidden agroecology, proper management and secure land tenure can help maintain intensive production without enduring environmental degradation. The char produced in these swiddens and successional management could allow this agroforestry system to be a long-term carbon sink., Competing Interests: Declaration of competing interest The authors declare the following financial interests/personal relationships which may be considered as potential competing interests: Tomasz B Falkowski reports financial support was provided by Cornell Atkinson Center for Sustainability. Ronald Nigh reports a relationship with Dana A.C. that includes: non-financial support., (Copyright © 2023 Elsevier Ltd. All rights reserved.)

Elucidating dynamics of soil microbial communities after disturbance is crucial for understanding ecosystem restoration and sustainability. However, despite the widespread practice of swidden agriculture in tropical forests, knowledge about microbial community succession in this system is limited. Here, amplicon sequencing was used to investigate effects of soil ages (spanning at least 60 years) after disturbance, geographic distance (from 0.1 to 10 km) and edaphic property gradients (soil pH, conductivity, C, N, P, Ca, Mg, and K), on soil bacterial and fungal communities along a chronosequence of sites representing the spontaneous succession following swidden agriculture in lowland forests in Papua New Guinea. During succession, bacterial communities (OTU level) as well as its abundant (OTU with relative abundance > 0.5%) and rare (<0.05%) subcommunities, showed less variation but more stage-dependent patterns than those of fungi. Fungal community dynamics were significantly associated only with geographic distance, whereas bacterial community dynamics were significantly associated with edaphic factors and geographic distance. During succession, more OTUs were consistently abundant ( n = 12) or rare ( n = 653) for bacteria than fungi (abundant = 6, rare = 5), indicating bacteria were more tolerant than fungi to environmental gradients. Rare taxa showed higher successional dynamics than abundant taxa, and rare bacteria (mainly from Actinobacteria, Proteobacteria, Acidobacteria, and Verrucomicrobia) largely accounted for bacterial community development and niche differentiation during succession., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2021 Lin, Baldrian, Li, Novotny, Heděnec, Kukla, Umari, Meszárošová and Frouz.)

In an attempt to maximize yields of food crops, smallholder farmers have, over the years, increasingly employed agricultural practices such as slash-and-burn and slash-and-mulch on Chromolaena odorata dominated fallow farmlands. However, owing to recently introduced "Horizontal Natural Product Transfer" concept, concerns have been raised over how these common agricultural practices could potentially lead to toxic pyrrolizidine alkaloids (PAs), from decaying or burnt C. odorata residues, taken up by food crops and subsequently accumulate in the food chain. A field experiment was therefore conducted to analyze the PA contents in the tissues of maize (Zea mays L.) plants grown on slash-and-burn and slash-and-mulch plots, previously dominated with Chromolaena odorata, using liquid chromatography mass spectroscopy (LC-ESI-MS/MS). The results revealed, in general, trace amounts of PAs in the maize tissues (i.e. roots, leaves and grains) at maturity while significantly higher levels were detected in the surface soils sampled before sowing (for both plots), 45 days after sowing (slash-and-burn plot) and 90 days after sowing (slash-and-mulch plot). These findings demonstrate, for the first time, the leaching out of PAs from C. odorata residues (e.g. mulch and ash particles) and taken up by maize tissues. In spite of its air polluting and farmland degrading effects, slash-and-burn agricultural practices could lead, in the long term, to relatively lower accumulation of PAs in maize cultivated on PA-plant dominated fallow farmlands, hence smallholder farmers are encouraged to frequently employ this farming system., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2020 Elsevier Ltd. All rights reserved.)

Shifting cultivation is a globally important form of agriculture covering over 280 million hectares in the tropics, but it has often been blamed for deforestation and forest degradation. In North East India (NEI) it has been practiced for millennia and it is an important element of the cultural identity of indigenous communities. It is often practiced on slopping lands with fragile soils (mostly Acrisols), which are prone to rapid degradation with cultivation. The shortened fallow cycle as practised currently is ecologically unsustainable and economically not viable. This study aimed to quantify (i) changes in soil bulk density, aggregate stability and compaction in relation to chronosequence and soil depth, (ii) changes in the proportion of macro, meso, and micro aggregates and associated soil organic carbon (SOC) content in relation to soil depth and fallow chronosequence, and (iii) determine the minimum fallow length that achieves SOC stocks comparable with adjacent intact forest land. The proportion of soil macro-aggregates and meso-aggregates significantly varied with land-use and soil depth as well as their interactive effects. Across all soil depths, forest land had the highest proportion of macro-aggregates (75.6%), while the currently cultivated land had the least proportion (51.1%). The SOC contents in macro-aggregates increased with fallow age and decreased with soil depth; the highest (1.95%) being in the top 10 cm soil of 20 years old fallows and the lowest (0.39%) in 21-30 cm depth of 5 years old fallows. Multivariate analysis identified bulk density and porosity as the most important variables to discriminate between land use practices. The analysis provided evidence for significant changes in soil compaction, aggregate stability and SOC content with the transition from undisturbed forest to slash-and-burn cultivation and fallow phases. It is concluded that a minimum of 20 years of fallow period is required to achieve SOC content and C stocks comparable with intact forest land., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2020 Elsevier B.V. All rights reserved.)

This account describes the context, history and outcomes of a series of studies into the ecology of slash-and-burn (S-B) agriculture in the world's humid tropics. These studies, which began in the mid-1980s, identified promising lines of research and continued to field trials, in Central America, of candidate agricultural systems as possible sustainable alternatives to the practice. The only system to emerge from 7 years' comparative trial with any promise of sustainability, in this context, was the agroforestry technique known as alley-cropping; but only with trees of the genus Inga . Inga alley-cropping then underwent field trials with subsistence farming families in northern Honduras. The system was aimed at the twin objectives of achieving food security in basic grains, on minimal inputs, and of providing the means of eliminating further S-B in the region. Since then, Inga alley-cropping has become the heart of a sustainable and integrated rural livelihood model (the Guama Model) which is being implemented successfully in northern Honduras with some 300 families. These families had been attempting to subsist on a few hectares of land degraded by decades or centuries of S-B. The development of Inga alley-cropping, supplemented by rock phosphate and other mineral supplements, as a sustainable subsistence and cash crop alternative means that land previously being held in reserve for subsequent S-B operations can now be planted to permanent forms of agroforestry. Entire landscapes can be re-greened by productive agroforest vegetation. Achieving this at scale will require the investment of huge extension effort and funds. However, the environmental, social and economic returns are also huge; and they are sustainable. In this programme,we are seeing the vitality and goodwill of hundreds of families focussed on the raising, planting and management of trees in ways that feed the living organisms of the soil and, hence, feed themselves. In so cheerfully planting out their own futures, they plant and reshape the future of their own country. Replicating this at scale, as Rattan Lal outlines below, could reshape the future of this planet. In the mid-1980s, progress on sustainable alternatives to S-B, especially in rain forests, was frustrated by a lack of conclusiveness in the literature as to why soil fertility fails so rapidly post-burn; but also by a degree of contradiction on the impacts of the burn on certain plant nutrients. Hands (Hands 1988 The ecology of shifting cultivation. MSc thesis, University of Cambridge) concentrated on the role of soil phosphorus and attempted to resolve these contradictions. The Cambridge Alley-cropping Projects (1988-2002) continued this theme and threw light on the question of sustainable food production in rain forest environments., (© 2021 The Authors.)

Traditional tropical agriculture often entails a form of slash-and-burn land management that may adversely affect ecosystem services such as pollination, which are required for successful crop yields. The Yucatán Peninsula of Mexico has a >4000 year history of traditional slash-and-burn agriculture, termed 'milpa'. Hot 'Habanero' chilli is a major pollinator-dependent crop that nowadays is often grown in monoculture within the milpa system.We studied 37 local farmers' chilli fields (sites) to evaluate the effects of landscape composition on bee communities. At 11 of these sites, we undertook experimental pollination treatments to quantify the pollination of chilli. We further explored the relationships between landscape composition, bee communities and pollination service provision to chilli.Bee species richness, particularly species of the family Apidae, was positively related to the amount of forest cover. Species diversity decreased with increasing proportion of crop land surrounding each sampling site. Sweat bees of the genus Lasioglossum were the most abundant bee taxon in chilli fields and, in contrast to other bee species, increased in abundance with the proportion of fallow land, gardens and pastures which are an integral part of the milpa system.There was an average pollination shortfall of 21% for chilli across all sites; yet the shortfall was unrelated to the proportion of land covered by crops. Rather, chilli pollination was positively related to the abundance of Lasioglossum bees, probably an important pollinator of chilli, as well indirectly to the proportion of fallow land, gardens and pastures that promote Lasioglossum abundance. Synthesis and applications . Current, low-intensity traditional slash-and-burn ( milpa ) agriculture provides Lasioglossum spp. pollinators for successful chilli production; fallow land, gardens and pasture therefore need to be valued as important habitats for these and related ground-nesting bee species. However, the negative impact of agriculture on total bee species diversity highlights how agricultural intensification is likely to reduce pollination services to crops, including chilli. Indeed, natural forest cover is vital in tropical Yucatán to maintain a rich assemblage of bee species and the provision of pollination services for diverse crops and wild flowers.

Sugarcane (Saccharum spp.) is grown on over 8 million ha in Brazil and is used to produce ethanol and sugar. Some sugarcane fields are burned to facilitate harvesting, which can affect the soil microbial community. However, whether sugarcane pre-harvest burning affects the community of arbuscular mycorrhizal fungi (AMF) and symbioses development is not known. In this study, we investigated the early impacts of harvest management on AMF spore communities and root colonization in three sugarcane varieties, under two harvest management systems (no-burning and pre-harvest burning). Soil and root samples were collected in the field after the first harvest of sugarcane varieties SP813250, SP801842, and RB72454, and AMF species were identified based on spore morphology. Diversity indices were determined based on spore populations and root colonization determined as an indicator of symbioses development. Based on the diversity indices, spore number and species occurrence in soil, no significant differences were observed among the AMF communities, regardless of harvest management type, sugarcane variety or interactions between harvest management type and sugarcane variety. However, mycorrhiza development was stimulated in sugarcane under the no-burning management system. Our data suggest that the sugarcane harvest management system may cause early changes in arbuscular mycorrhiza development.

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., (© 2012 Blackwell Publishing Ltd.)

Deforestation in the Brazilian Amazon has resulted in the conversion of >230,000 km 2 of tropical forest, yet little is known on the quantities of biomass consumed or the losses of nutrients from the ecosystem. We quantified the above-ground biomass, nutrient pools and the effects of biomass burning in four slashed primary tropical moist forests in the Brazilian Amazon. Total above-ground biomass (TAGB) ranged from 292 Mg ha -1 to 436 Mg ha -1 . Coarse wood debris (>20.5 cm diameter) was the dominant fuel component. However, structure of the four sites were variable. Coarse wood debris comprised from 44% to 69% of the TAGB, while the forest floor (litter and rootmat) comprised from 3.7 to 8.0% of the TAGB. Total biomass consumption ranged from 42% to 57%. Fires resulted in the consumption of >99% of the litter and rootmat, yet <50% of the coarse wood debirs. Dramatic losses in C, N, and S were quantified. Lesser quantities of P, K, and Ca were lost by combustion processes. Carbon losses from the ecosystem were 58-112 Mg ha -1 . Nitrogen losses ranged from 817 to 1605 kg ha -1 and S losses ranged from 92 to 122 kg ha -1 . This represents losses that are as high as 56%, 68%, and 49% of the total above-ground pools of these nutrients, respectively. Losses of P were as high as 20 kg ha -1 or 32% of the above-ground pool. Losses to the atmosphere arising from primary slash fires were variable among sites due to site differences in concentration, fuel biomass, and fuel structure, climatic fluctuations, and anthropogenic influences. Compared to fires in other forest ecosystems, fires in slashed primary tropical evergreen forests result in among the highest total losses of nutrients ever measured. In addition, the proportion of the total nutrient pool lost from slash fires is higher in this ecosystem compared to other ecosystems due to a higher percentage of nutrients stored in above-ground biomass.