Multifunctionality in practice: Measuring differences in urban woodland ecosystem properties via functional traits

Abstract

The ability of urban woodlands to regenerate and provide ecosystem services depends on the maintenance of a range of ecosystem functions and processes (i.e. multifunctionality). Many conservation decisions are made by local land stewards and rely on taxonomic characterization of woodlands to infer ecosystem properties, but there is reason to doubt this approach. Can functional traits provide better information on ecosystem multifunctionality? We compare three methods for capturing differences in urban woodland multifunctionality. We ask whether differences in (1) species composition, (2) traits associated with urbanization (urbanization markers) or (3) traits associated with specific ecosystem properties (functional markers) best capture actual differences in colonisation, water infiltration and decomposition in woodlands across a rural-urban gradient (Montreal, Canada). We use Procrustes superimposition and Mantel tests to compare the fit of each method. We propose the functional Mahalanobis distance to measure the distance of an urban woodland from a reference range of multifunctionality.All three methods were significantly congruent with actual differences in ecosystem multifunctionality, but the strength of the rank-order correlations varied widely. Species composition and urbanization markers had a similar but weak correlation with differences in multifunctionality. Importantly, the mismatch between species composition and multifunctionality increased with urbanization. Functional markers captured ecosystem multifunctionality better than either species composition or urbanization markers.Commonly used species- and general trait-based approaches were poor measures for multifunctionality in our urban woodlands. Functional markers rely on vegetation inventories already routinely collected by land stewards and openly available trait information: they may provide a cost-effective way of capturing multifunctionality in urban systems. More broadly, the functional Mahalanobis distance provides a quantitative measure of site-level multifunctionality that allows land stewards to compare woodlands with a reference range of variability in a format that can directly inform conservation decisions.