The MIREN global network of elevational transects has clearly shown declines in species richness of non-native plants with increasing elevation and with increasing distance from road disturbance. Even native plants tend to decline in species richness with increasing elevation. Could other organisms display such patterns, especially organisms that are intricately associated with plants?
A recent study from Australia has shown that a group of plant pathogens of the genus Phytophthora do not display similar patterns in species richness in relation to elevation and disturbance. As the MIREN plots in Kosciuszko National Park (New South Wales) were being sampled in 2016 / 17, Ihsan Khaliq, a PhD candidate from Murdoch University in Western Australia, sampled soils from the road and natural vegetation plots. He found that Phytophthora species had a patchy distribution but most occurred across the range of elevations and equally in road and natural habitats, whether they were native or introduced. Very few preferred particular plant communities, suggesting that they are pathological generalists, probably infecting a very broad range of hosts. Their broad distribution will make them very difficult to manage, if that is required.
Phytophthora species are amongst the world’s most destructive plant pathogens. They are not renowned as mountain species but one, Phytophthora gregata, has recently been found to cause severe dieback in a narrow endemic subalpine shrub in Kosciuszko National Park. With warming conditions and greater use of mountains for recreation, more Phytophthora species are likely to arrive in the future. Unlike most non-native vascular plants, they are not going to remain on roadsides for long, and are generally impossible to eradicate once present.
Khaliq, I., Burgess, T.I., Hardy, G.E.StJ., White, D. and McDougall, K.L. (2021) Phytophthora and vascular plant species distributions along a steep elevation gradient. Biological Invasions 23: 1443-1459.
Pimelea bracteata (Family Thymelaeaceae), a small shrub that is killed by Phytophthora gregata in Kosciuszko National Park, Australia.