Modeling Experiments for Evaluating the Effects of Trees, Increasing Temperature, and Soil Texture on Carbon Stocks in Agroforestry Systems in Kerala, India

Abstract

Research Highlights: Agroforestry systems in the humid tropics have the potential for high rates of production and large accumulations of carbon in plant biomass and soils and, thus, may play an important role in the global C cycle. Multiple factors can influence C sequestration, making it difficult to discern the effect of a single factor. We used a modeling approach to evaluate the relative effects of individual factors on C stocks in three agricultural systems in Kerala, India. Background and Objectives: Factors such as plant growth form, management, climate warming, and soil texture can drive differences in C storage among cropping systems, but the relationships among these factors and their effects are complex. Our objective was to use CENTURY, a process-based model of plant–soil nutrient cycling, in an experimental mode to evaluate the effects of individual factors on C stocks in soil and biomass in monocultures (annuals or trees) and agroforestry systems. Materials and Methods: We parameterized the model for this region, then conducted simulations to investigate the effects on C stocks of four experimental scenarios: (1) change in growth form; (2) change in tree species; (3) increase in temperature above 20-year means; and (4) differences in soil texture. We compared the models with measured changes in soil C after eight years. Results: Simulated soil C stocks were influenced by all factors: growth form; lignin in tree tissues; increasing temperature; and soil texture. However, increasing temperature and soil sand content had relatively small effects on biomass C. Conclusions: Inclusion of trees with traits that promoted C sequestration such as lignin content, along with the use of best management practices, resulted in the greatest C storage among the simulated agricultural systems. Greater use and better management of trees with high C-storage potential can thus provide a low-cost means for mitigation of climate warming.

Impacts of climate change on tropical agroforestry systems: A systematic review for identifying future research priorities

“…This is congruent with robust evidence which suggests that drought could reduce soil biota productivity in TAFS, as indicated by declining soil CO 2 efflux, although only under severe drought (van Straaten et al, 2010). Similarly, model simulations suggested that increases in air temperature will drastically decrease soil C content, but only under a considerable temperature increase (+6 • C) as opposed to a marginal increase (+2 • C) (Russell and Kumar, 2019). In contrast, Andriamananjara et al (2019) suggested that temperature increase (+10 • C) will increase soil C and N content, possibly through increased soil biota activity and mineralization rates.…”

“…Whether these tree species increase or decrease in their aboveground carbon may also vary depending on the different future climate scenarios they are exposed to; however, in Kenya, all these tree species except Albizia gummifera may decline in aboveground carbon irrespective of the different climate scenarios. In contrast, similarly robust evidence suggests that aboveground carbon in TAFS in India could remain unchanged (Russell and Kumar, 2019), whilst in Nigeria forecasted declines in rainfall amounts during the hottest months could reduce the land suitable for supporting Garcinia kola by up to 35.8% based on LoE3 evidence (Agwu et al, 2020). These findings indicate that the future impacts of climate change could be positive, negative or have no effect on tree distribution and size.…”

“…The model considers that provisioning ecosystem services from TAFS and the wellbeing of smallholders are mainly influenced by the tree-soilcrop interactions, which in turn are mediated by (i) the state of the trees, soils, and water in the biophysical system, and (ii) the decisions made in the livelihoods and farm management system (e.g., which trees and crops are planted). We expect the provisioning of ecosystem services and the wellbeing of farmers, including their cultural values, health, and income, to decline under climate change due to impaired tree size and growth (Feng and Li, 2007;Vincent et al, 2009;Tamayo-Chim et al, 2012), declining soil productivity and nutrient cycling (van Straaten et al, 2010;Russell and Kumar, 2019;Lakshmi et al, 2021), reduced water availability (Blaser et al, 2018), lower crop pollination (Arnold et al, 2018) and farmer's decision to change their farm management, which can influence biodiversity (Landreth and Saito, 2014). These biophysical and social impacts would influence tree-soil-crop interactions that underpin smallholder farmers' crop production and wellbeing.…”

Impact of removal of rubber plantations for urbanization on CO2 mitigating capacity by the loss of carbon sink in Kerala state, India

“…reported that about 37.3 and 44.1 Mg C ha -1 could be sequestered through the maintenance of 50 year long green space project in Germany. Russell and Kumar (2019) reported that if the selection of trees has the capacity of increased carbon sequestration, like higher lignin composition, supplied with efficient management methods can achieve substantial carbon storage even in the simulated tree crop ecosystem and agricultural fields. Rubber trees also have higher lignin content, which can be selected for the selection of urban trees, and the rubber ecosystem is comparatively eco-friendly (Jacob, 2003b).…”