How pathogens affect woodland diversity?

Woodland trees are dying at an increasingly alarming rate due to rising numbers of pests and pathogens damaging the trees. Some of the more commonly associated, and more damaging pathogens affecting these are Phytophthoras and Chalara.

Phytophthoras is a genus of Oomycetes and is the name given to a large group of pathogens which most frequently affects Larch and Rhododendron. It spreads by water-based spores between soil particles in short distances but can produce longer-lasting spores from the roots of decaying, infected trees which will infect an entire area. Symptoms of the disease include wilting, sparse foliage and branch dieback along with deteriorating roots.

Chiara ash dieback affects Ash trees and is caused by a fungus called Hymenoscyphus fraxineus. It was first confirmed in 2012 in the UK and causes leaf loss, bark lesions, and crown dieback; it is usually fatal and makes the trees more susceptible to the effects of other pests and pathogens but appears to have less of an effect on older trees. Chiara spread is difficult to contain because it can spread in a close range by wind or by the transportation of affected timber. The loss of Ash could massively alter ecosystems. Ash trees are very versatile to provide a nutrient-rich leaf litter which breaks down to form brown earth soil, allowing the growth of many other plant species.  There are over 1000 species identified a being associated with Ash trees so the death of these trees could be vital to a loss in species diversity.