Trait selection and community weighting are key to understanding ecosystem responses to changing precipitation regimes

What is it about?

Rising global temperatures are expected to change rainfall patterns around the world leading to more extreme weather events, such as drought. Given this, we must understand how ecosystems and the valuable services they provide, such as plant growth and carbon storage, will respond to such changes. To do this, however, we need accurate predictions of which species of plants will respond positively or negatively to climate change, and the relative influence that those species have on the functioning or well being of the ecosystem in question. Ecologists have long used the characteristics, or traits, of plants to describe how and where individual species might grow. But the traits used are often those most easily measured such as plant height or leaf area. However, across large geographic scales, these basic plant traits are not related to average rainfall amount, making them not very useful for predicting plant responses to changing water availability. In this study, we review over 500 studies that survey plant traits in relation to water availability to identify ways in which trait measurements might be improved. We discovered two main gaps in this field of research that must be addressed if plant traits are to be useful for understanding ecosystem responses to climate change. First, traits must be measured for all plants in a community, and average trait values for the whole community should reflect the abundance of each species in the community (only 4% of surveyed studies do this). Community-scale trait surveys allow ecologists to correct for the high variability of traits within a community and determine a trait value that more closely reflects the average precipitation amount for the ecosystem. Secondly, these community-scale surveys must move away from basic measurements of plant structure (height and leaf area) and towards traits relevant to water transport and drought tolerance (i.e. hydraulic traits). While hydraulic traits are inherently more difficult to measure, they are more appropriate for understanding how changes in rainfall will impact where species can grow. Incorporating these suggestions into future surveys of plant traits will greatly improve predictions of plant, and ecosystem, response to climate change.

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