Adaptations of Casuarina windbreak stands to land subsidence on the southwestern coast of Taiwan.

In this study, we investigated the adaptive behavior of Casuarina windbreak stands along the southwestern coast of Taiwan to land subsidence. Based on surveys and measurements of 17 indicators, such as soil factors, the external appearance of individual trees, damage sustained by individual trees etc., we applied a maximum variance reciprocal matrix method of a factorial analysis to obtain sets of reciprocal matrices, together with weighting factor adjustments, and then we derived the state of health of the stands. The analytical results indicated that the vitality of the tree crowns, soil salinity, soil pH, tree diseases, tree flowering, and root damage were the 6 major factors affecting differences in the adaptive performance of Casuarina windbreak stands. Finally, the maximum variance reciprocal matrices of the factorial analysis identified 3 factors of tree status, crown vitality, and changes in the soil environment as influential indicators. Furthermore, the analysis indicated that there was a seasonal fluctuation in the tree health status with a decrease observed in summer and autumn compared to winter and spring. This study confirmed that coastal Casuarina windbreak stands of southwestern Taiwan have already been affected by land subsidence, and the adaptive characteristics of injured trees and a seasonal fluctuation of their health status were observed.