Modeling soil organic carbon dynamics under shifting cultivation and forests using Rothc model

Highlights

• The major land uses in the Northeast Himalayas are forest and jhum cultivation.

• RothC was used to simulate SOC stocks under the baseline and CC conditions.

• Simulations indicated that forest could not benefit from CC.

• SOC stocks decreased in jhum lands under the baseline and CC.

• Jhum cultivation under CC can be extended without large effects on SOC decreases.

Abstract

Shifting cultivation (jhum) and forest land are the main land uses in North Eastern region of Indian Himalaya, but in the long term this form of agriculture is not acceptable due to the soil degradation following the cutting of forest vegetation, and the consequent biodiversity loss, high erosion rates and nutrient loss through runoff. No information on soil organic carbon (SOC) dynamics and simulation studies are available, so an attempt was done using RothC model. The model was parameterized on measured SOC contents of forest and jhum sites, and average SOC stocks and changes were simulated for a period of 5 years in forest and jhum sites under the baseline and the projected climate change conditions available for Nagaland state (2021–2050). Forest sites under the baseline climate showed a steady-state condition, and simulated SOC decreased by 0.04 t C ha⁻¹ yr⁻¹during 5 years. In addition simulations indicated that forest land use could not benefit from climate change in a 10 years period (SOC changes showed a decreasing trend from 0.36 to 0.06 t C ha⁻¹ yr⁻¹). Jhum sites showed negative changes in SOC stocks both under the baseline (0.40 t C ha⁻¹ yr⁻¹) and the projected climate change conditions (0.50 t C ha⁻¹ yr⁻¹). Indeed, SOC decreases under climate change were inversely related to the duration of the jhum cropping cycle, almost linear in the first five years (from 0.65 to 0.41 t C ha⁻¹ yr⁻¹), and thereafter only slightly decreasing (from 0.39 to 0.32 t C ha⁻¹ yr⁻¹). We can conclude that under climate change conditions the jhum cropping cycle can be extended for a longer period without substantial effects on SOC decreases.

Introduction

Forests are one of the most important ecosystems of the earth due to their biodiversity, ecosystems services and capacity to offset climate change impact through carbon sequestration (Basu, 2009; Rahman et al., 2017). However, due to anthropogenic pressure many of the forests are under stress (Brandon, 2014). Conversion of forest land to agricultural land by slash and burn is known as “shifting cultivation”, and is locally called jhum cultivation (Singh et al., 2014), a common practice in Africa, Asia and Latin America and this contributes to 70, 50 and 16% of total deforestation, respectively (FAO, 1957; Inoue et al., 2010; Chaplot et al., 2010; van Vliet et al., 2012; Grogan et al., 2012). Jhum cultivation is an ancient practice which consists of repetitive cycles: cutting the forest vegetation, leaving the biomass in situ to dry, burning the slashed vegetation after drying, and growing annual and perennial crops for a variable period of time, depending on the region. The ash deposits after burning, helps to fertilize the soil. After the end of the cycle the field is abandoned and the natural vegetation will grow (secondary forest), while the farmer (jhumia) will move to another site.

Due to geographical position and biodiversity richness, the North Eastern region of Indian Himalaya (NEH) is considered as one of the twelve biodiversity hot spots in the world (Choudhury et al., 2016). It is covered by forests (65%), agricultural land (16%) and fallow for the rest (Saha et al., 2012). Approximately 86% of the total cultivated area of NEH is under the practice of jhum cultivation and also is the major source of livelihood for the local peoples (Patel et al., 2013; Yadav, 2013). However, during the last few decades, this practice has led to rapid change in land use, especially in Nagaland (Chase and Singh, 2014). Continuous jhumming and changes in land use has also aggravated the issues related to soil degradation, biodiversity loss, and climate change (Salehi et al., 2008; Chase and Singh, 2014).

A wide number of studies have been done throughout the world, using different models and land uses, to understand the soil carbon dynamics at different temporal scales. Campbell and Paustian (2015) and Brilli et al. (2017) recently reviewed and discussed different simulation models available worldwide, commonly used for studies on SOC dynamics, GHGs emissions and climate change mitigation since simulated results provide information on the global carbon cycle, including the changes in SOC over time and soil carbon dioxide emissions. Models differ in the complexity and requirements of input information (Peltoniemi et al., 2007), and simple models need less complicated and less detailed input information than complex models. For example, RothC (Coleman and Jenkinson, 2014) requires only basic input data, whereas CENTURY (Parton et al., 1987) is more complex and the input data requirement is high. Both models have a similar structure, containing pools with rapid, moderate, and slow turnover.

RothC has been used in different countries and ecosystems including grassland, agriculture and forest in the UK and Iran (Coleman et al., 1997; Farzanmanesh et al., 2016); forests in Austria (Palosuo et al., 2012), Australia (Paul et al., 2003), Brazil (Cerri et al., 2007), Iran (Soleimani et al., 2017), Spain (Romanya et al., 2000) and Zambia (Kaonga and Coleman, 2008); olive groves in Spain (Nieto et al., 2010); land use and land use change in Italy (Francaviglia et al., 2012; Farina et al., 2017); arable crops in Australia (Senapati et al., 2014), China (Guo et al., 2007; Ludwig et al., 2010; Li et al., 2016), Germany (Ludwig et al., 2007) and Kenya (Kamoni et al., 2007).

Unfortunately, neither information related to SOC dynamics nor simulation studies are available for the North Eastern region of Indian Himalaya (NEH). Thus, we used the RothC model in this study to simulate the patterns of SOC stocks in two major land uses (forest and jhum lands) of this region, evaluate the response to future climate change projections, and provide better insights for climate change mitigation in the region as well as assistance in the management strategies in a long-term perspective.