Biomass carbon (C) stocks and species richness and diversity are interlinked, and they co-vary along an elevational gradient. To test these hypotheses of inter-connectiveness and covariation in the Western Ghats (peninsular India) context, we enumerated 16 moist forest plots as well as 18 rubber (Hevea brasiliensis) and coconut (Cocos nucifera) plantations each. Our main objectives were to assess the aboveground biomass C (AGB-C) stocks and the association between plant diversity and forest AGB-C stocks along an elevation gradient. Species-specific allometric equations and Ordinary Kriging interpolation were used to predict and map AGB-C and species diversity. AGB-C stocks varied significantly among forest (381.69 ± 25.87 Mg ha–1), rubber (73.92 ± 7.76 Mg ha–1), and coconut (21.19 ± 1.23 Mg ha–1) stands. Forest AGB-C stocks also decreased linearly with increasing elevation. Although rubber and coconut AGB-C declined with elevation, the differences were not significant. The richness and diversity of arboreal species were higher in mid-elevation forests compared to low/high-elevation sites (unimodal pattern). With Simpson’s diversity index ranging from 0.695 to 0.865, Shannon index of 1.445–2.231, and Equitability of 0.883–0.994, our study sites exhibited moderate to high species diversity and encompassed 26 IUCN Red-listed species. Diversity and AGB-C were significantly correlated, indicating that the results support the hypothesis on inter-connectiveness. Overall, the forests at low and mid-elevations showed greater potential for C sequestration and biodiversity conservation, implying the need for adaptive management (designing actions) of these forests to mitigate the impending global climate change and conserve biodiversity.

Agroforestry systems (AFS) represent combinations of trees, arable crops, and/or pastures. Being assemblages of diverse life-forms, they exhibit complex biophysical interactions. For instance, the multistrata canopies shade the understory crops by intercepting a significant amount of the incoming solar radiation. Optimizing understory productivity, thus, requires understanding the elements that affect the canopy transmittance of photosynthetically active radiation (PAR) and its spatiotemporal dynamics. We systematically reviewed the peer-reviewed literature involving 145 tropical and subtropical tree + crop combinations. The theoretical underpinnings of interspecific interactions in developing agroforestry stands were elucidated using a conceptual model. Additionally, the linkage between subcanopy PAR levels and yield was established for 11 arable crops. PAR reaching the understory and the subcanopy yield levels were tremendously variable across AFS. Relative yields ranged from 6 to 188% of the sole crops. Stage of stand development, canopy architecture, and management factors are cardinal determinants of canopy light extinction, understory PAR availability, and yield. The yield of shade-tolerant crops either increased (“over-yielding”) or remained the same as PAR levels decreased within certain limits, albeit with intraspecific variations. The tree-crop interaction effects on yield were positive, negative, or neutral. In total, 19 cases showed positive responses, 29 were neutral, and 113 were negative, with a few overlapping responses depending on the tree, crop, and management. This implies that the key to ecological intensification is component selection and management. Agroforestry, while containing the loss of, maintaining, or even increasing understory yields, thus maximizes overall (tree + crop) outputs and land equivalent ratio.

IntroductionHomegardens are one of the oldest agroforestry systems reported around the world. These agroforestry systems are often reported as harbingers of plant biodiversity conservation. However, a comprehensive understanding of these systems from the perspective of species level agrobiodiversity conservation is often missing.MethodologyThis study first visualizes the comprehensive role of homegardens in species level agrobiodiversity conservation and then assesses any variation in agrobiodiversity along diverse Socio-ecological Zones (SEZs) in the study site. The prominent SEZs identified in the study site were Protected Area (PA), Riverine (RI), Rural Market (RM), and Tea Estate (TE). Eight ethnic/linguistic groups were also identified at the study site. Agrobiodiversity inventorying of 192 homegardens from 16 villages was done.ResultsThe results of the study highlight that homegardens in the study site have high species level agrobiodiversity concentration (101 total tree species reported, 39.58% of homegardens (HGs) had more than 10 varieties of vegetables, 68% had atleast one variety of bamboo, 76% had atleast one banana variety, 20.83% had pond). A total of 64% of HGs had livestock and around 85% had poultry. Moreover, this agrobiodiversity distribution also varied along different SEZs. The livestock diversity indices ranged from 0.49 (TE) to 1.04 (PA). The average plant diversity among homegarden was found to be in the range of 1.09 (PA) to 1.48 (TE) for Shannon, 0.45 (PA) to 0.66 (TE) for Simpson, 0.31 (PA) to 0.71 (TE) for Pileou evenness and 2.39 (PA) to 2.76 (RM) for Margalef. The plant composition reflected the dominance of the food species i.e. an average of 37% in each SEZ. Sorenson similarity index among different SEZs for plant and livestock was found to be highest between the HGs of the PA and RM (0.82). Among the ethnic/linguistic groups, the highest mean number of plant species (51) was found among the Mishing tribe. Also, high similarity index (0.78) was found in plant and livestock composition among the Mishing and the Bodo tribes.DiscussionThe findings imply that HGs exemplify diversified and integrated systems, showcasing their potential to play a crucial role in the development of sustainable food systems.

Homegarden (HG) agroforestry combines biological carbon (C) sequestration with biodiversity conservation outcomes. Although C stocks and species richness of HGs vary along elevational gradients and as a function of holding sizes, there is no consensus on the nature and magnitude of such variations. Field studies were conducted in the Western Ghats region of central Kerala, India (180 homesteads in 20 selected panchayats), to evaluate the effects of elevation (near sea level to 1938 m) and garden size (162–10,117 m 2 ) on aboveground C stocks and floristic diversity. The C stocks (per unit area) of HGs (arborescent species) were highly variable (0.63–93.65 Mg ha –1 ), as garden management was highly individualistic and it exhibited a weak negative relationship with elevation. Likewise, there was a weak negative relationship between C stocks and garden size. Tree stocking levels (stems/garden) and species richness (species/garden) positively impacted total C stocks per garden. Floristic diversity was high in the study area (753 species) and included many rare and endangered species (43 IUCN Red-Listed species) making homegardens circa situm reservoirs of biodiversity. Elevation and holding size exerted a weak negative linear relationship on Simpson’s floristic diversity index, which ranged from 0.26 to 0.93 for the arboreal species. Homegardens, regardless of elevation or size, contribute to C sequestration and agrobiodiversity conservation and help achieve the UN Sustainable Development Goals (SDGs), particularly Climate Action (SDG-13) and conserving agrobiodiversity (SDG-15, Life on Land).

The linkage between biological carbon (C) sequestration and plant diversity, as well as how these parameters change along an elevational gradient in natural and managed ecosystems, has sparked interest in discussions about climate change mitigation and biodiversity conservation. Biomass C stocks and species richness and diversity are interlinked and they co-vary along an elevational gradient. To address this hypothesis, we examined the aboveground biomass C (AGB-C) data from 16 forest plots of 600 m2 each and 18 rubber (Hevea brasiliensis) and coconut (Cocos nucifera) plantations of 300 m2 each, situated along an elevational gradient from coastal lowlands to around 2000 m altitude in the southern Western Ghats (WG) of peninsular India. Ordinary Kriging interpolation was attempted to predict and map the forest AGB-C stocks and species diversity patterns. The mean AGB-C stocks varied significantly (p<0.05) among the forest (381.69 ± 25.87 Mg ha–1), rubber (73.92 ± 7.76 Mg ha–1), and coconut (21.19 ± 1.23 Mg ha–1) stands. AGB-C stocks in forests decreased linearly with elevation (p<0.05). Rubber and coconut plantations, although showed a modest decline in AGB-C stocks along the elevational gradient, the differences were not significant, owing to the interplay of a range of site factors and managerial interventions. The richness and diversity of arboreal species were higher at mid-elevation forests than at the low and high-elevation sites. Simpson’s diversity index (D) for the mid-elevation (932–1012 m) Vallakkadavu-Arunippalam site was 0.812 and Shannon (H’) index, 2.001, followed by a decrease at higher elevations (Munnar, 1855–1958 m; D=0.695, H’=1.445), signifying a unimodal pattern for floristic diversity variations. With mean Simpson’s diversity index in the range of 0.695 to 0.865, Shannon (H’) values of 1.445 to 2.231, and Equitability of 0.883 to 0.994, our study sites in the WG had moderate to high species diversity. The correlation between AGB-C stocks and plant diversity indexes such as Simpson’s index (r = 0.321; p<0.05), Shannon index (r = 0.228; p<0.05), and Equitability (r = 0.334; p<0.05) was significant (p < 0.05). The geostatistical model was not able to predict the AGB-C stocks and species diversity precisely due to the high spatial variability observed. Generally, the low and mid-elevation forests have a higher potential for biological C sequestration and biodiversity conservation respectively. However, they may be subjected to greater anthropogenic influences than the forests at the high-elevation sites. Adaptive management of low and mid-elevation WG forests could, therefore, benefit in mitigating the impending global climate change and conserving biodiversity.

Stabilizing greenhouse gas (GHG) emissions from croplands as agricultural demand grows is a critical climate change mitigation strategy. Depending on management, the Agriculture, Forestry, and Other Land Use (AFOLU) sector can be both a source as well as a net sink for carbon. Currently, it contributes 25% of the global anthropogenic carbon emissions. Although India’s emissions from this sector are around 8% of the total national GHG emissions, it can contribute significantly to the country’s aspirations of reaching net-zero emissions by 2070. In this review, we explain the carbon footprints of the AFOLU sector in India, focusing on enteric fermentation, fertilizer and manure management, rice paddies, burning of crop residues, forest fires, shifting cultivation, and food wastage. Furthermore, using the standard autoregressive integrated moving average method, we project India’s AFOLU sector emission routes for 2070 under four scenarios: business as usual (BAU) and three emission reduction levels, viz., 10%, 20%, and 40% below BAU. The article focuses on how the AFOLU sector can be leveraged proactively to reach the net-zero emission goals. Increasing forest cover, agroforestry, and other tree-based land-use systems; improving soil health through soil management, better crop residue, and livestock feed management; emission avoidance from rice ecosystems; and reducing food waste are all important strategies for lowering India’s AFOLU sector carbon footprints.

Agricultural intensification in the past has led to many land-use-related issues around the world, and nature-based solutions (NbS) in farming seek to offset those negative consequences. NbS, in addition to promoting sustainable production of goods and resources and preserving ecosystem integrity, provides a range of ecosystem services. Mixed-species systems such as agroforestry, including the coconut-based farming systems (CBFS), are excellent examples of NbS. The CBFS, which involves many sciophytic agricultural crops, not only ensures economic benefits, but also improves crop productivity. They produce a variety of food items (fruits, nuts, tubers, and so on), earning the moniker "coconut-based food forests," and have the potential to enrich agrobiodiversity. Biological carbon sequestration is another important attribute of CBFS. Crop combinations that include a variety of species, particularly tree crops, have the potential to increase carbon sequestration while also delivering diverse provisioning and cultural services. Kerala, the "Land of Coconut Trees," witnessed a "coconut boom" from 1955 to 2000, although production and area have been fluctuating since then. The functional dynamics of CBFS and the natural resource challenges they address, as well as the ecosystem services CBFS provides and the biodiversity outcomes, are reviewed in this article, with a focus on Kerala.

Homegarden, a type of agroforestry system, is one of the earliest thriving traditional food systems reported. Studying the contribution of homegardens in the context of Sustainable Development Goals (SDGs) is crucial when the COVID-19 pandemic has hindered the achievement of many of the crucial SDGs. In this review, we focused on 94 peer-reviewed papers on homegardens from 2010 to 2021 to interrelate them with the corresponding targets and indicators of each SDG. The SDGs were classified into five categories, each focusing on a specific aspect: Category 1 (SDGs 1–5, poverty dimension), Category 2 (SDGs 6–9, development infrastructures), Category 3 (SDGs 10–12, sustainable production and consumption), Category 4 (SDGs 13–15, green infrastructures), and Category 5 (SDGs 16–17, green institutions). The distribution of the 94 papers analyzed was 92%, 23%, 33%, 51%, and 50% in each of the SDG categories, respectively. Category 1 and SDG 2 were found to be most realized in the homegarden literature. Important observations were found that highlight homegardens’ probable use in providing food security, nutritional needs, health and wellness, preservation of agrobiodiversity, and enduring sustainability. Homegardens appear to be an important strategy for attaining the SDGs and can be accomplished with proper planning, in addition to taking into consideration how the traditional societies have sustained it for long.

Rice, the staple food for the people of Kerala, is cultivated since time immemorial in the state. The 15th century Malayalam book of verse titled Krishi Gita describes the cultivation systems and locally adapted varieties of rice for various ecological and geographic regions of medieval Kerala. Although rice constitutes the principal crop of the state, its area has been declining since the mid-1970s: i.e., from 8.82 lakh hectares in 1974-75, the area has dropped to 2.02 lakh hectares in 2018-19 (77.1% reduction). The production has also declined from 13.76 lakh tonnes in 1972-73 to 5.78 lakh tonnes in 2018-19. While low per capita land availability (0.13 ha) has led to increasing land use intensification in Kerala, abandoned farmlands are also increasing, which is paradoxical. Conversion of paddy fields to cash crops is widespread. The net result is a major decline in area and production of rice in Kerala, which has made serious inroads into the state's food production capacity. In addition, it affected the diverse kinds of ecosystem services provided by the crop. Rice ecology in the state is varied and is strongly conditioned by local climate and land forms. It rangesfrom below sea-level cultivation (e.g., Kuttanad, Pokkali and Kole lands) to rice paddies in the High Ranges of Idukki and Wayanad (800-1500 m above sea-level). Rice cultivation also has profound environmental implications including climate change impacts. This paper reviews the literature on ecological and historical aspects of rice production in Kerala.

The COVID-19 pandemic and the associated lockdown – often regarded as a “Global Human Confinement Experiment” – has created an unprecedented situation around the globe. While the reduced human presence and mobility, causing declines in visitation rates of protected areas, may generally favour biodiversity conservation in natural ecosystems, the pandemic has caused major disruptions of the food supply chain. Furthermore, the “reverse migration” of labour has led to scarcity of workforce in many localities hitting agricultural operations. The cumulative effect is food insecurity for millions of people in both the developed and developing countries. It is therefore crucial to encourage local food production systems at the household and community levels. Tropical homegardens, which are resilient and sustainable production systems, are important in this respect. Homegardening is a unique farming system, which combines divergent production and service functions around the homesteads and contribute to the supply of fresh food at the household level. Being a decentralized production system, such practices may reduce food wastage along the supply chain. A prominent structural attribute of homegardens is the great diversity of species ranging from creeping herbs to tall trees and livestock, implying their potential for biodiversity conservation. Although land-use systems are challenged as never before in the wake of the pandemic, homegardening may provide a way forward to overcome the looming food insecurity at the household level in the rural areas of many countries.

Black pepper is a very important spice and medicinal crop of India. The country produces about 62,000 metric tonnes of black pepper annually, of which 10–12% is exported. Kerala with an area of 82,761 ha under the crop is a leading producer of the spice in India. It is grown under varied agro-ecologies in the state ranging from sea-level to High Ranges. The crop, a climber, is cultivated either as a monocrop trailed on different multipurpose support trees (called “standards”, e.g. Ailanthus triphysa, Erythrina indica, Garuga pinnata, Gliricidia sepium etc.) or in the homesteads along with assorted trees like Areca catechu, Cocos nucifera, Artocarpus heterophyllus, Mangifera indica and the like. Trailing a sciophytic (shade-loving) climber on woody perennial support trees makes it a unique agronomic system and an excellent example of agroforestry. Attractive prices, albeit fluctuations, long shelf-life of the produce, and the ability to provide a range of ecosystem services including supporting and regulatory services (e.g. carbon sequestration and soil fertility enrichment), make black pepper production an attractive land use option in Kerala. This paper reviews the literature on agroecology of the crop with particular reference to Kerala.

Fine roots play a major role in water and mineral uptake and nutrient cycling in woody perennial-based ecosystems. Just as other biomass components, stand density manipulation and tree pruning may influence fine root production (FRP) and its decomposition dynamics. However, quantitative information on FRP and its turnover under different density and pruning regimes are meagre for most tropical trees. A field study was conducted to characterize FRP and associated nutrient release under varying stand density and pruning regimes in a 12-year-old Acacia mangium stand in Kerala, India. Soil ingrowth core method was employed for quantifying FRP and sequential core method for estimating standing fine root biomass. Annual FRP estimates were 5.78, 5.39, 3.74, and 3.38 Mg ha–1 for the 5000, 2500, 1250 and 625 trees ha−1 treatments, respectively. Allometric models based on tree diameter and basal area gave a good fit for annual FRP. Fine root turnover rates ranged from 2.81 to 3.16 yr−1, which however, was not influenced by stand density. Carbon stocks ranged from 1.36 to 2.39 Mg ha−1 with highest FRP during rainy season and lowest during the dry period. The litterbag study using nylon mesh bags indicated that annual fine root mass loss ranged from 76.2 (5000 trees ha−1) to 96.8% (625 trees ha−1). Tree pruning had only modest effects on tree growth, FRP, and carbon and nutrient release patterns. The study highlights the importance of stand density manipulation in altering A. mangium FRP, soil carbon and mineral nutrient dynamics.