Variables related to EAB occurrences in China
Seven variables, including degree of EAB infestations, host tree species, host tree age, host tree size, habitat, latitude, and altitude, were recorded during field surveys in 11 regions of China from 2003 to 2019. Host tree size was measured as the diameter at breast height (DBH). The degree of EAB infestation was graded on a scale of 0-4 based on the percentage of infested ash trees: 0 = undamaged; 1 = slightly damaged, with less than 10% of ash trees infested; 2 = moderately damaged, with 10%-50% of ash trees infested; 3 = seriously damaged, with 50%-90% of ash trees infested; 4 = very seriously damaged, with over 90% of ash trees infested. Habitats were divided into three categories: (i) street trees: trees on roadsides; (ii) plantations: trees in parks, courtyards, neighborhoods, university campuses or nurseries; (iii) semi-natural conditions: trees growing in natural ecosystems or natural regenerations.
From 2012 to 2013, complementary field surveys were conducted in the Oleaceae Common Garden at the Institute of Botany, Chinese Academy of Sciences (39.99°N, 116.22°E) which contained both native and non-Asian ash species. All of the 39 native and 71 non-Asian ash trees in the 2.5 ha Oleaceae Common Garden were investigated and data were collected on the same seven variables as well as canopy condition and presence of bark splits on individual trees. Canopy condition was assigned an index on a scale with 5 levels: 1 = over 80% live crown; 2 = 60%-79%; 3 = 40%-59%; 4 = 20%-39%; 5 = below 20%. Presence of bark splits was recorded based on presence/absence: 1 = present; 0 = absent. In addition, we reviewed and extracted data on the same seven variables from the 17 recovered publications that contained detailed data about EAB infestations from 1900 to 2019. All data were analyzed to determine correlations between degrees of EAB infestation, host trees, and related environmental variables.