Interspecific variation in post-disturbance growth responses of a savanna tree community and its implications for escaping the fire trap

Vegetation states in savannas are highly sensitive to tree growth rates, which determine whether individual trees can escape periodic disturbances. Resprouting trees have lopsided shoot:root ratios and are often multi-stemmed, and these variables can modify post-disturbance growth rates and therefore the probability of escape. To date, few studies have systematically examined the implications of interspecific variation in these factors for escape. We conducted a two-year field experiment across 16 tree species in a South African lowveld savanna to quantify growth metrics following topkill. We examined the dependence of growth on pre-disturbance stem size and the relationship between growth rate and the tendency of trees to produce a few large vs. many small resprouts following disturbance. We found that resprout growth was strongly influenced by pre-disturbance size, but the strength of this relationship did not vary across species. In contrast, our results showed that fast-growing species tended to allocate resources toward a few dominant stems, while slow-growing species allocated new biomass towards many smaller stems. Tree species that produced a few large stems also tended to produce individual stems that were tall and thin, further suggesting that the few large vs. many small axis is linked to intrinsic species attributes. These findings have implications for understanding how interspecific variation in savanna tree communities may influence their ability to escape disturbance traps.

Automated summary

In savannas, vegetation states are highly sensitive to tree growth rates, which can determine the ability of individual trees to survive disturbances. This study found that tree resprout growth is strongly influenced by pre-disturbance stem size, and that fast-growing species tend to allocate resources to a few dominant stems while slow-growing species allocate new biomass to many smaller stems. These findings suggest that interspecific variation plays a key role in influencing the ability of savanna tree communities to escape disturbance traps.