Geographic variation of leaf form among indigenous woody angiosperms in New Zealand

Correlations of non-monocot woody angiosperm leaf traits to macroclimate are often used to reconstruct terrestrial paleoclimate under the assumption that macroclimate correlates with leaf phenotype are globally uniform, regardless of evolutionary history. Here, we evaluate if global trends in leaf trait variation with macroclimate are observed in the predominantly evergreen indigenous flora of New Zealand. A dataset of 557 indigenous woody dicot species and over 100,000 occurrences was employed to investigate community-level relationships of four leaf characters (leaf pubescence, margin teeth, area and length-to-width ratio) with geographic variation in temperature, precipitation, water deficit and solar radiation. Leaf area and the frequency of toothed leaves decline at higher latitudes in New Zealand. Variation in leaf pubescence and leaf teeth is associated primarily with measures of water availability, such as annual rainfall and annual water deficit; whereas leaf size is associated primarily with temperature. Variation in leaf length-to-width ratio was weakly correlated to climate parameters. The New Zealand relationship of leaf area with temperature aligns with global patterns, highlighting the importance of small leaves in limiting night-time chilling. The global negative correlation of leaf teeth with temperature is apparent in New Zealand trees and vines, but not in shrubs or all woody dicots combined. However, the primary correlate of leaf teeth in New Zealand is water availability, showing that the response of this trait to macroclimate is not globally uniform. The high occurrence of pubescent leaves in low rainfall and drought-prone environments in New Zealand suggests that the trait is associated with water retention in drier climates.