Abstract
Shifting cultivation dominates many tropical forest regions. It is expanding into old‐growth forests, and fallow period duration is rapidly decreasing, limiting secondary forest recovery. Shifting cultivation is thus a major driver of carbon emissions through deforestation and forest degradation, and of biodiversity loss. The impacts of shifting cultivation on carbon stocks have rarely been quantified, and the potential for carbon‐based payments for ecosystem services (PES), such as REDD+, to protect carbon in shifting cultivation landscapes is unknown. We present empirical data on aboveground carbon stocks in old‐growth forest and shifting cultivation landscapes in northeast India, a hotspot of threatened biodiversity. We then model landscape‐level carbon stocks under business‐as‐usual scenarios, via expansion into the old‐growth forest or decreasing fallow periods, and intervention scenarios in which REDD+ is used to either reduce deforestation of primary or secondary forest or increase fallow period duration. We found substantial recovery of carbon stocks as secondary forest regenerates, with a 30‐yr fallow storing about one‐half the carbon of an old‐growth forest. Business‐as‐usual scenarios led to substantial carbon loss, with an 80% reduction following conversion of old‐growth forest to a 30‐yr shifting cultivation cycle and, relative to a 30‐yr cultivation landscape, a 70% reduction when switching to a 5‐yr cultivation cycle. Sparing old‐growth forests from deforestation using protected areas and intensifying cropping in the remaining area of shifting cultivation is the most optimal strategy for carbon storage. In areas lacking old‐growth forest, substantial carbon stocks accumulate over time by sparing fallows for permanent forest regeneration. Successful implementation of REDD+ in shifting cultivation landscapes can help avert global climate change by protecting forest carbon, with likely co‐benefits for biodiversity.
Highlights
Deforestation and forest degradation in the tropics contribute significantly to biodiversity loss and generate 12% of global annual anthropogenic carbon emissions (van der Werf et al 2009, Barlow 2016)
The best model included both habitat type and elevation along with an interaction term between habitat type and elevation. This suggests that differences in live carbon stock across habitat types increased with elevation
Dead carbon stock showed no significant difference across habitat types
Summary
Deforestation and forest degradation in the tropics contribute significantly to biodiversity loss and generate 12% of global annual anthropogenic carbon emissions (van der Werf et al 2009, Barlow 2016). Shifting cultivation is the dominant land use across 2.6 million km in the tropics, of which only 6–19% is cleared annually for crop production (Silva et al 2011) While this provides subsistence for 200– 300 million people across 64 developing countries (Mertz et al 2009, Li et al 2014), it is a major driver of carbon emissions (Fearnside 2000) and biodiversity loss (Ogedegbe and Omoigberale 2011, Ding et al 2012). Crops are grown on the cleared land for a few seasons (normally one or two), after which the farmland is left fallow for vegetation regeneration (Mertz 2009). The fallow period lasted for 20–30 yr allowing complete regeneration
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