Under the global context of climate change, forest ecosystems are facing increasingly frequent and severe drought threats, leading to a significant rise in tree mortality worldwide. 

Numerous studies have explored drought impacts on tree mortality in forest ecosystems, however, the relative importance of leaf habit, plant size, species richness, and diversity in drought-induced mortality remains unclear.

In a study published in Journal of Forestry Research, researchers from Xishuangbanna Tropical Botanical Garden (XTBG) of the Chinese Academy of Sciences identified leaf habit and plant height as critical predictors of tree and shrub survival during extreme drought, and that these two factors are more decisive than species diversity.

Researchers analyzed mortality patterns of tree and shrub species in a 1-ha plot in a savanna ecosystem of Southwest China during the extreme drought of 2019. They calculated species richness and diversity indices using 10 × 10 m quadrats within the plot and measured leaf and wood traits, seasonal minimum water potential, hydraulic safety margins and plotted xylem vulnerability curves.

Researchers found that deciduous species exhibited lower hydraulic safety margins compared to evergreen species, resulting in higher mortality risks during extreme drought. They also found that taller plants with deeper root systems demonstrated significantly lower mortality rates, leveraging soil moisture reserves inaccessible to shallow-rooted neighbors. 

Besides, researchers revealed that species richness and diversity showed no significant correlation with survival rates, challenging conventional biodiversity resilience assumptions.

"This study isn't just about plant physiology, it provides insights into plant community dynamics under drought conditions and a roadmap for ecological restoration," said ZHANG Shubin from XTBG. "It suggests that prioritizing deep-rooted evergreen trees can boost survival rates by up to 40% in reforestation projects."