Converting forests into rubber plantations weakened the soil CH₄ sink in tropical uplands

Abstract

Large‐scale conversion of natural forest to rubber plantations has taken place for decades in Southeast Asia, help to make it a deforestation hot spot. Besides negative changes in biodiversity, ecosystem water, and carbon budgets, converting forests to plantations often reduced CH4 uptake by soils. The latter process, which might be partly responsible for resumed increase in the growth rate of CH4 atmospheric concentrations since 2006, has not been adequately investigated. We measured soil surface CH4 fluxes during 2014 and 2015 in natural forests and rubber plantations of different age and soil textures in Xishuangbanna, Southwest China—a representative area for this type of land‐use change. Natural forest soils were stronger CH4 sinks than rubber soils, with annual CH4 fluxes of −2.41 ± 0.28 and −1.01 ± 0.23 kg C ha−1 yr−1, respectively. Water‐filled pore space was the main factor explaining the differences between natural forests and rubber plantations, even reverting rubber soils temporarily from CH4 sink into a methane source during the rainy season in older plantations. Soil nitrate content was often lower under rubber plantations. Added as a model covariate, this factor improved explanation power of the CH4 flux—water‐filled pore space regression. Although soils under rubber plantation were more clayey than soils under natural forest, this was not the decisive factor driving higher soil moisture and lower CH4 uptake in rubber soils. Thus, the conversion of forests into rubber plantations exerts a negative impact on the CH4 balance in the tropics and likely contributes to global climate.

Changes in soil greenhouse gas fluxes by land use change from primary forest

“…Our results indicated that land use change from primary forest decreased soil CH 4 oxidation through modifying soil properties. Insufficient air constrained methanotroph activity due to the increase in soil bulk density and soil water filled pore space (Fest, Wardlaw, Livesley, Duff, & Arndt, ; Gutlein, Gerschlauer, Kikoti, & Kiese, ; Lang et al, ). Although there was negative effect of primary forest conversion on soil water holding capacity, illustrated by decreased soil moisture and organic matter, its positive impact on CH 4 oxidation might be overridden by other moderators that constrain CH 4 uptake.…”

Implementing a New Rubber Plant Functional Type in the Community Land Model (CLM5) Improves Accuracy of Carbon and Water Flux Estimation

“…Ray et al [19] found more areas would be suitable for rubber tree plantation in the NE region, whereas further expansion would be limited in the WG region under the projected climate scenario for 2050. Using a statistical regression model (SRM), Lang et al [20] disentangled the links between soil water content, soil texture, and mineral nitrogen in rubber plantations and assessed the impacts of land-use change on methane flux. Land surface models are also increasingly adopted to investigate the impact of land-use change on carbon and energy fluxes at various temporal and spatial scales [21][22][23].…”

Asymmetric response of soil methane uptake rate to land degradation and restoration: Data synthesis

“…Whereas the capacity of soil CH 4 uptake increased with the time since land use change under land restoration (Figures 3 and 6f). These results suggested that the capacity of CH 4 oxidation could lose rapidly and recover slowly in response to land degradation and restoration, respectively (Bárcena et al, 2014;Lang et al, 2019;Levine et al, 2011;Petitjean et al, 2019). Land degradation, such as the natural forest converted to plantation or cropland, is always associated with the clear-cutting, fertilization, and other intensive disturbances.…”

“…Surprisingly, the effect of land degradation on soil CH 4 uptake rate seems to be independent of the time since land use change. For instance, the conversion of natural forest to other land use types can significantly decrease soil CH 4 uptake rate in a very short time interval (less than 10 years; Lang et al., 2019; Petitjean et al., 2019). However, it is unclear whether this phenomenon is common in various terrestrial ecosystems worldwide.…”

“…These factors are inevitably influenced by land degradation and restoration. For instance, the natural forest converted to rubber plantations significantly increased the water‐filled pore space (WFPS; Lang et al., 2019), and hence limited the diffusion of atmospheric CH 4 into soils (Lang et al., 2020), ultimately weakened the soil CH 4 sink in the tropical uplands. On the contrary, the conversion of pasture to plantation increased soil CH 4 sink primarily due to the reduced soil water content (Hiltbrunner, Zimmermann, Karbin, Hagedorn, & Niklaus, 2012).…”