Phytophthora and Vascular Plant Species Distributions along a Steep Elevation Gradient

A diverse Phytophthora community was detected in recent surveys conducted in alpine and subalpine areas, previously considered Phytophthora free. The current study was conducted to determine patterns of Phytophthora species richness and distribution along a steep elevation gradient, and to compare these patterns with those of vascular plant species. Phytophthora and vascular plant species were recorded over a wide range of elevation gradient (410–2125 m) and across a disturbance boundary. Vascular plant species exhibited a monotonic decline with increasing elevation. With the exception of native Phytophthora species isolated by baiting, Phytophthora species richness was invariant in relation to elevation and had higher elevational ranges than vascular plant species. Vascular plants occurred in discrete plant communities with introduced species more frequently recorded in road habitat and native species more frequently recorded in natural vegetation habitat. Both native and introduced Phytophthora species occurred with equal frequency in road and natural vegetation habitat. Phytophthora species were absent from one-third of sample plots and plots with no Phytophthora species were randomly distributed across landscapes. Only two Phytophthora species repeatedly occurred with a particular plant community. Our findings show that Phytophthora species are habitat generalists, being widely distributed across elevation and disturbance gradients, while vascular plant species are mostly habitat specialists, being confined to particular environments within narrow elevation bands. The effect of Phytophthora species on vascular plant species is largely unknown but the fact that Phytophthora species are already present throughout the elevation and disturbance gradients warrants closer examination of plant-pathogen relationships.