Understanding the Complex Interplay of Multiple Stressors on Plant Populations

In a rapidly changing world, understanding how multiple stressors affect plant populations is crucial for effective conservation strategies. A recently published paper by Meredith Zettlemoyer in AoB PLANTS sheds light on this complex issue. Zettlemoyer illuminates how different anthropogenic stressors can interact to have significant effects on plant populations, potentially leading to novel insights for long-term biodiversity conservation. This work, which combines individual responses to stressors into a population growth model, aims to yield more informed predictions for species’ survival amidst multiple forms of anthropogenic change.

Central to Dr Zettlemoyer’s research is the role of demographic modelling, which she posits as an effective tool to weave individual plant responses to various stressors into population growth estimates. She argues that a sole focus on single stressors, though simpler, may yield a skewed view of population ecology. Instead, multifactorial investigations can better simulate present and future environmental conditions. Dr Zettlemoyer’s analysis not only emphasizes the crucial necessity of understanding the combined effects of stressors but also proposes four research priorities aimed at introducing more realism into such studies.

Zettlemoyer proposes tackling multiple stressors through four research priorities, including factorial experiments, stressor removal, stressor gradients, and long-term demographic data. These steps aim to incorporate multiple variables and investigate them simultaneously, mimicking the complex real-world conditions plants face.

While it might seem that climate change and biodiversity loss are deeply interwined, it would be a mistake to consider them the same thing. Over-exploitation of land, pollution and invasive species are all contributing to biodiversity loss, on top of warming temperatures. These factors may combine to increase problems, or else may mitigate issues species face in unexpected ways. In her article Dr Zettlemoyer says:

Assessing the additive vs. non-additive effects of multiple interacting threats on population dynamics will therefore help prioritize conservation efforts under future combinations of novel conditions. For example, climate warming threatens the viability of a rare forb, Eurybia furcata (forked aster), but only when site-level woody encroachment and deer herbivory are high (Bernardo et al. 2018). This suggests that management at a local scale (e.g. woody invasive species removal) could reduce this species’ extinction risk under warming. Similarly, invasive species removal is an important management strategy for the rare orchid Cypripedium candidum (white lady’s slipper) under moderate climate change scenarios. However, as drought stress increases, protecting groundwater recharge zones in sites near this hydrologically sensitive species becomes increasingly important (Phillips-Mao et al. 2016). Both of these studies inform conservation decision-making by assessing multiple interacting stressors and identifying the most important stressor. Applying this process to prioritize management under climate change is critical because while stressors like invasion can exacerbate the negative effects of climate change, their removal provides a ‘low-risk’ short-term management strategy. These low-risk strategies can be important initial actions to reduce the impact of climate change on vulnerable populations (Galatowitch et al. 2009), especially given the often-inadequate resources for conservation of rare plant populations (Heywood 2017; Westwood et al. 2021).

Zettlemoyer 2023