Spatial Distribution of Armillaria and its effect on a Douglas-fir/Western hemlock forest

Armillaria root disease occurs in both temperate and tropical areas of the world. This root disease is caused by pathogenic fungus from the Armillaria genus. These fungus are commonly known as Honey Fungus. They infect both hardwood and conifer tree species including the Western Hemlock and Douglas fir. The Wind River Forest Dynamics Plot is part of an old growth Douglas fir/Western Hemlock forest. The plot area is 25.6 hectare (320 m x 800 m) with approximately 1300 trees per hectare. The plot contains 26 separate species, many of these species are susceptible to being infected by many Armillaria species such as Armillaria ostoyae and Armillaria mellea. In 2010, there were 31,301 live woody stems ≥ 1 cm dbh mapped and measured. The plot was divided into 680 (20 m x 20 m) quadrants and mortality data was collected. 363 of these quadrants had trees with their mortality associated to Armillaria root disease suggesting that 52 % of the quadrants are infected with Armillaria. Armillaria root disease can spread through the interaction of infected roots with uninfected roots. Since establishment, 656 tree mortalities where associated with Armillaria constituting 22% of all mortality. Unfortunately, this is an underestimate of the actual extent of the disease. In order to determine the extent of the disease, an estimate of crown width was determined for each infected tree. This was done using a quadratic formula in order to estimate the circumference of coarse roots. Using Arc GIS and Arc Map, we mapped a circle around each tree based off this circumference. After doing this, we then calculated the coarse root circumference of adjacent trees and assumed that if a trees estimated root circumference overlapped with an infected tree that the other tree was also infected. The total infected area was calculated from this