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.