Why Functional Traits Do Not Predict Tree Demographic Rates

Foundational to trait-based community ecology is the expectation that functional traits determine demographic outcomes. However, trait-demographic rate relationships are frequently weak, particularly in tree communities. The foundation of trait-based tree community ecology may, therefore, appear to be unstable. Here we argue that there are three core reasons why trait-demographic relationships are generally weak in tree communities. Specifically, important contextual information is frequently ignored, there is too much focus on species relative to individuals, and there are dimensions of tree function that are critical for determining tree demographic rates that are not captured by easily measured functional traits. Rather than being evidence that trait-based community ecology is fundamentally flawed, these issues elucidate a pathway towards a more robust research program.