Understanding how vegetation composition may change under climate change is one of the main preoccupations of plant ecologists nowadays. In already arid conditions, a particularly interesting aspect is how climate-change expected extremes may reshape vegetation patterns. How extreme is a drought-extreme for plants already adapted to dry conditions? To what extent these droughts relate ecosystem stability with current climate ?
In this paper led by my collaborator Maria Angles Perez Navarro she showed how an extreme event reshaped vegetation patterns in a semi-arid scrubland community of South Eastern Spain after an extreme drought.
To study such extreme localized events you either need to have a long-term monitoring plots (yay to all LTER-based ecology, NEON and alike !), and you need to be lucky. That is, the extreme event needs to occur at your already measured plots so you have a pre- and post- extreme event measurement. Unfortunately, extreme events will tend to be more frequent in the near future, so we may be more “lucky” in that regard, but in semi-arid scrublands pre- and post- plot measurement conditions is hard for a main reason: traditionally semi-arid scrublands have not been intensely monitored compared to, for instance, forests.
Another option is to visit the plots after the event, but how do you do you assess the impacts of drought in a system where species are already adapted to drought? For instance, typical measures of defoliation may only indicate plant strategies to cope with drought, but they may not imply community reorganization. MariaAngeles used a multiple-evidence approach to measure the impact of extreme drought in semi-arid scrublands. She set up 5x5m vegetation plots and measured how the drought impacted different species in such communities under different environmental conditions, and measured three conditions on species individuals: 1) lack of green leaves, 2) presence of thin branches, 3) presence of standing dry leaves in the plant or over the ground. While qualitative, these indicators helped her understand how species where differentially affected in the system.
She found that the extreme drought had an important filtering effect of species who were more sensitive to drought, thus reducing the number of more mesic species species in the community and aligning vegetation to the expected dryer climate change in the region. Interestingly, she also found that other microsite characteristics did not buffer against such an extreme drought event. This seems to be in accordance with other disturbance related dynamics, where extreme fire events may blur important factors of variability such as topography.
Still much to be learned on how extreme events shape vegetation, and what are the biotic and abiotic conditions that may buffer against them, but Maria Angeles brings here a new piece of information on how dryland vegetation composition is getting progressively filtered by these extreme events.
Read the full paper
Pérez‐Navarro, M. Á., Serra‐Diaz, J. M., Svenning, J. C., Esteve‐Selma, M. Á., Hernández‐Bastida, J., & Lloret, F. (2021). Extreme drought reduces climatic disequilibrium in dryland plant communities. Oikos.
And check out her profile here