Global Tiger Density Linked With Forest Carbon Stock, Top-Down and Bottom-Up

Abstract

Tiger (Panthera tigris) survival, as apex predators in forest ecosystems, largely depends on abundant prey in healthy, intact forests. Because large herbivore prey are drivers of plant biomass, we reasoned that tiger distribution and density are probably also closely linked with forest carbon (C) stock, the management of which is critical for mitigating climate change. However, whether tigers exert top-down control of forest C stocks or are passive surrogate C indicators bottom-up is a salient unanswered question in conservation and management, particularly in trophic rewilding. Here, we compiled estimates of global tiger presence and density to test the top-down effects of tigers on forest C stocks and tiger-carbon relationships along a gradient from “empty forests” without tigers to “target state” ecosystems with tigers living at different abundances. Our results showed that tiger presence was associated with higher forest vegetation C stocks, lower C emissions, and higher C inputs globally. Top-down effects via ungulate biomass were stronger in less established forests. Furthermore, forest vegetation or soil C stocks increased with tiger density or reached tiger-carbon peaks in four forest habitat types covering most of the tiger range. Our findings reveal that tigers, represented by their presence and density, are both an indicator and a driver of forest ecosystem C stocks, depending on underlying ecological conditions, and could safeguard forests against future C emissions and improve our understanding of climate-C cycle feedback.