The effect of insect disturbance on forest carbon flux: a multisite analysis

Insect outbreaks have a substantial effect on forest carbon cycle, including turning forests from carbon sink to carbon source. However, there is still lack of evaluation of the impact of insect disturbance on forests carbon cycle across different forest types at the global scale. Hence, we conducted a multi-site analysis to compare ecosystem CO2 fluxes’ change after an insect outbreak by compiling flux data from the literature or flux database. The final database consists of 21 site-years of eddy covariance data from 17 forest sites among diversity of forest types, namely temperate forest, mangrove, larch forest, etc. Our research showed that insect outbreak had significant negative effects on GEP that GEP reduces -186 gCm-2y-1 on average, as well as NEP reducing -146 gCm-2y-1 while had no significant positive effect on Re. Additionally, similar conclusion was gained when analyzing the recovery procedure that GEP increases with time at the slope of 67.6 gCm-2y-2 and NEP increases at slightly lower rate of 49.2 gCm-2y-2. But there is no evidence that Re will increase. As insects cause more severe damage to forests, all three carbon variables share negative correlation that GEP drops at the slope of -6.7 gCm-2y-1 and NEP also decreases in relatively similar rate at 66.3 gCm-2y-1 with Re decreasing by -3.4 gCm-2y-1. Also, it was found that girdling experiments has different impact on carbon budget from normal insect outbreaks while drought could dampen the damage to GEP followed with a greater recovery rate.