Climatic Seasonality and Topographic Complexity Shape Canary Islands Plant Growth Form Distributions

Abstract Plant growth forms reflect the environmental conditions under which they evolved and persist. Yet, previous studies linking environmental conditions with growth form have overlooked that different growth form types arose through distinct evolutionary pathways; some woody angiosperm lineages evolved woodiness from a herbaceous ancestor, whereas others have retained their woodiness throughout evolutionary history. The Canary Islands are a global hotspot of insular woodiness (woodiness evolved on islands from herbaceous colonisers), raising the question of whether insular woody species occur in different environmental conditions than other growth forms. Here, we use a custom-built pipeline to extract and filter spatial data to analyse the environmental correlates of growth forms in the Canary Islands non-monocot angiosperm flora, accounting for their distinct evolutionary histories and differences in life span. To assess whether and how five growth forms (annual herbaceous, perennial herbaceous, ancestral woodiness, derived woodiness, and insular woodiness) differ in environmental niche space, we applied phylogenetic PCAs to a dataset of ∼600 native non-monocot Canary Island angiosperm species. Unexpectedly, herbaceous and woody growth forms highly overlap in niche space, with subtle differences explained mostly by climatic seasonality (temperature and precipitation) and topographic complexity. Using phylogenetic ANOVAs, we identified significant pairwise differences between growth forms across five environmental variables, with differentiation between combined woody and herbaceous niches, and between the three woody growth forms. Our phylogenetically inferred macroecological approach identifies terrain rugosity as a key environmental variable influencing niche space, and suggests aridity may be less important for determining insular woodiness distributions than previously hypothesised.