Limited role of shifting cultivation in soil carbon and nutrients recovery in regenerating tropical secondary forests

Abstract

Shifting cultivation is a dominant land-use in the tropical forest-agriculture frontier in Southeast Asia and is blamed for much of the environmental degradation in the region. We examined the distribution and availability of four soil macronutrients—i.e., soil organic carbon (SOC), total nitrogen (N), phosphorus (P) and potassium (K), in secondary forests regenerating after shifting cultivation abandonment. Soil samples were collected along an upland fallow gradient on Leyte Island in the Philippines. The effect of site environmental attributes on the availability of SOC and nutrients was investigated using linear mixed-effect models. We found relatively higher concentrations of SOC and P in the oldest fallows and higher N concentration in the youngest fallow secondary forest. There was no significant difference in SOC and other macronutrients within sites of different fallow categories and soil depths, except in the case of soil K, which was highest in our control old-growth forest. Patch size together with slope of the site and fallow age were the most influential factors in explaining the variability in SOC and nutrients availability in secondary forests recovering after shifting cultivation abandonment. Our study suggests that shifting cultivation may not be detrimental to soil quality, at least on the soil parameters and soil type we studied in the Philippines upland.

Drivers of soil organic carbon stock during tropical forest succession

“…The initial differences of soil quality may influence farmers' land use decision and leads to a bias of the space-for-time approach used in our study (a negative trend of SOC stock across forest successional gradients). However, recent studies have suggested that soil fertility recovers to 90% of oldgrowth forest values within 10 years of land abandonment from agriculture activities (Poorter et al, 2021), and the highest rate of soil no-change (Bruun et al, 2021), gain (Gogoi et al, 2020) and loss (Sugihara et al, 2019) or fluctuation with fallow age (Chan et al, 2016;Mukul et al, 2022), but SOC tends to recover rapidly during the first 2 years of a fallow period (Lungmuana et al, 2017). Our models did not detect significant direct effects of forest succession on SOC stock (Figure 4).…”

“…However, recent studies have suggested that soil fertility recovers to 90% of old‐growth forest values within 10 years of land abandonment from agriculture activities (Poorter et al, 2021), and the highest rate of soil carbon sequestration occurs during the first 15 years (Bautista‐Cruz & del Castillo, 2005). Scientists hypothesized that SOC stock increases with forest age (Powers & Marín‐Spiotta, 2017), but evidence from field studies on shifting cultivation systems varies and includes no‐change (Bruun et al, 2021), gain (Gogoi et al, 2020) and loss (Sugihara et al, 2019) or fluctuation with fallow age (Chan et al, 2016; Mukul et al, 2022), but SOC tends to recover rapidly during the first 2 years of a fallow period (Lungmuana et al, 2017). Our models did not detect significant direct effects of forest succession on SOC stock (Figure 4).…”

Physical and chemical soil quality and litter stock in agroforestry systems in the Eastern Amazon

“…Cecilio Rebola et al 2021;Mukul et al 2022;Primo et al 2023), highlighting the potential of AFSs to restore functional aspects in the Amazon. The practice of burning plant residues and the use of mineral fertilizers may have contributed to the increase in soil acidity over time, as these practices reduce soil pH and favor the release of hydrogen ions (H+) and aluminum (Al + 3) (Chaves et al 2020).…”