Logging disturbance shifts net primary productivity and its allocation in Bornean tropical forests

Abstract

Tropical forests play a major role in the carbon cycle of the terrestrial biosphere. Recent field studies have provided detailed descriptions of the carbon cycle of mature tropical forests, but logged or secondary forests have received much less attention. Here, we report the first measures of total net primary productivity (NPP) and its allocation along a disturbance gradient from old-growth forests to moderately and heavily logged forests in Malaysian Borneo. We measured the main NPP components (woody, fine root and canopy NPP) in old-growth (n = 6) and logged (n = 5) 1 ha forest plots. Overall, the total NPP did not differ between old-growth and logged forest (13.5 ± 0.5 and 15.7 ± 1.5 Mg C ha year respectively). However, logged forests allocated significantly higher fraction into woody NPP at the expense of the canopy NPP (42% and 48% into woody and canopy NPP, respectively, in old-growth forest vs 66% and 23% in logged forest). When controlling for local stand structure, NPP in logged forest stands was 41% higher, and woody NPP was 150% higher than in old-growth stands with similar basal area, but this was offset by structure effects (higher gap frequency and absence of large trees in logged forest). This pattern was not driven by species turnover: the average woody NPP of all species groups within logged forest (pioneers, nonpioneers, species unique to logged plots and species shared with old-growth plots) was similar. Hence, below a threshold of very heavy disturbance, logged forests can exhibit higher NPP and higher allocation to wood; such shifts in carbon cycling persist for decades after the logging event. Given that the majority of tropical forest biome has experienced some degree of logging, our results demonstrate that logging can cause substantial shifts in carbon production and allocation in tropical forests.

Logging and soil nutrients independently explain plant trait expression in tropical forests

“…Therefore, the effect of logging on the expression of functional traits is likely to pervade tropical forest landscapes and impact ecosystem processes with cascading effects on other trophic levels. Moreover, logging-associated changes in forest structure and CWM traits drive altered patterns of productivity in tropical forests (Pfeifer et al, 2016;Riutta et al, 2018).…”

“…FD was more variable among logged forests than among old-growth forests (Fig. 4), probably owing to variation in logging history and intensity, which affect forest structure (Cannon et al, 1994;Berry et al, 2008), microclimatic conditions (Hardwick et al, 2015) and ecosystem functions (Mayfield et al, 2006;Both et al, 2017;Riutta et al, 2018). The substantial variance in FD among the disturbed plots highlights the challenge of predicting the impacts of anthropogenic modification on FD in environments where the outcomes may be highly context-dependent (Costantini et al, 2016).…”

“…Logging creates a spatially patchy disturbance, with gaps and skid trails characterized by high light and temperature distributed among fragments of relatively unmodified forest (Johns, 1997). The selective removal of target species, logging-induced mortality and recruitment of pioneer species in disturbed areas affect tree species composition and the pools and fluxes of biomass and nutrients (Cannon et al, 1998;Verburg & van Eijk-Bos, 2003;Pfeifer et al, 2016;Riutta et al, 2018). Although the magnitude of anthropogenic disturbance is much greater in forests in Southeast Asia than in South America, they have received far less attention regarding the modification of plant functional traits.…”

Forest biomass, productivity and carbon cycling along a rainfall gradient in West Africa

“…This study presents the largest NPP dataset collected to date from tropical forests in Africa. Comparable datasets have recently emerged from South America and Southeast Asia that have explored patterns in NPP, GPP and CUE (Malhi et al., ; Riutta et al., in review; Slik et al., ), but until now carbon budget studies from African tropical forests have focused only on patterns of AGB and forest structure (e.g. Lewis et al., , ).…”

Multiple stages of tree seedling recruitment are altered in tropical forests degraded by selective logging

“…The forest at MBCA (a 588.4 km 2 protected area) represents the nearest topographically matched primary forest to the logged forest in KFR (Ewers et al, 2011;Struebig et al, 2013). The two sites are also similar in terms of soil nutrient profiles and physical properties (Riutta et al, 2018). The MBCA serves as the unlogged control site of the SAFE Project (Ewers et al, 2011).…”