Supplement description of qualitative analysis
Qualitative analysis was based on the calculation of the prevalence of tree species with a root range that intersected with the root range of diseased trees. Calculation of the prevalence of tree species with a root range that intersected with the root range of diseased trees includes the following steps. Firstly, we determined whether a tree’s root range intersects with the root range of diseased trees. Then, for each tree species, we calculated the number of recordable infected trees (disease severity 1~3) and total number of trees, excluding trees whose root ranges does not intersect with the root range of diseased trees. Finally, we calculated the prevalence of brown root rot in tree species. It was calculated as follows: Number of recordable infected trees / total number of trees.
Whether a tree’s root range intersects with the root range of diseased trees was judged by comparing the distance (L) between the target tree and diseased tree and the sum of their root radiuses (R, r) (Fig. 1). When L＜R+ r, target tree’s root range intersects with the root range of diseased trees; when L＞R+ r, target tree’s root range doesn’t intersect with the root range of diseased trees. The distance (L) between target trees and diseased trees were calculated according to their position (x, y coordinates) within the transect.
The root radiuses of trees were calculated from their crown radius. A study of root systems in Dinghushan, a subtropical forested area in southern China (112°30′–112°33′ E longitude, 23°09′–23°11′ N latitude, which is similar to the longitude and latitude of Colina da Guia), found that the root radius of most trees was approximately 1 to 2 times that of the crown radius (Hao 2005). To ensure that all the trees in the study can connect to the roots of diseased trees, we selected the minimum proportion of root radius to crown radius, that is to say, in this study we assumed the root radius:crown radius for the trees in the transects on Colina da Guia Hill = 1:1. In this way, we could determine the minimum root range of a tree by recording the tree’s crown radius, and therefore prevent overestimation the connection of health tree and diseased root.
Fig. 1 Sketch of qualitative analysis
Note: L indicates the distance between target tree and diseased tree; R indicates the root radius of diseased tree; r indicates the root radius of target tree.
Reference
Hao, Y. R. (2005). A study on the root system of vegetation at Dinghushan in forest succession. Dissertation, Graduate School of the Chinese Academy of Science