Comparative leaf morphology spectra of plant communities in New Zealand, the Andes and the European Alps

Abstract

Leaf morphology of native vegetation has often been interpreted as a sensitive indicator of environmental conditions, presumably as a result of natural selection. If environmental pressures act as a selective force on community leaf morphology, then we would expect a high degree of similarity in similar environments, regardless of biogeographic origin of the flora. A comparative study of full regional floras of alpine vascular plants was undertaken to test the sensitivity of leaf morphology to macro‐environmental conditions. Five alpine sites and one lowland (control) site were selected in southern New Zealand spanning 1.5° latitude and 2323 m. Three sites with equivalent alpine environments were selected in South America across a 60° latitudinal and 4200 m altitudinal span with subtropical forest used as a control. A further alpine site from the European Alps was included as an outlier. Twenty leaf parameters were obtained for 2143 taxonomic entities x sites. Both the mean and the frequency distribution of leaf size and shape parameters were distinctive for each locality. Several morphological trends were found. Means of New Zealand contiguous low‐alpine and high‐alpine site pairs differed in: length ‐33%, width ‐14%, length/width ‐20%, leaf area ‐44%, entire margin ‐2% (variable), coriaceousness ‐18%, folded +22%, pubescence +40%. At higher elevations, leaves become smaller but rounder, considerably softer, are more often folded into crypts or similar structures and are more often pubescent. These changes corresponded to reductions of 2–3°C in mean annual air temperature, c. 10% in mean minimum relative humidity and 7% in CO₂ partial pressure. Despite the biogeographic and environmental differences, New Zealand and South American low‐alpine sites were consistently similar in their morphological parameters and consistently different from high‐alpine sites (except in Tierra del Fuego). High alpine sites were also consistently similar across the Pacific. Several parameters were found to have multimodal frequency distributions that were not significantly different in widely separate localities with different floras. The results suggest that plant community morphology is an emergent property, the magnitude of which is environmentally constrained.