Wind and salt spray alter tree shape and dry mass density in Casuarina equisetifolia L.

Abstract

Wind, salt spray, and the proximity to the coastline significantly caused the variation of tree shape and dry mass density of Casuarina equisetifolia L. planted in coastal areas. Despite negative effects of exotic plants, they play an important role in the erosion control and the accumulation of wind-borne deposits in coastal areas. Identifying the adaptive strategies of exotic species and predicting their ability for stress adaption are of great interest to improve the management and regeneration of coastwise protective forests. We studied Casuarina equisetifolia L., an introduced tree planted successfully for dampening wind speed and preventing coastal soil erosion in coastal regions of southern China, 450–1400 m from the coastline in Taiwan Strait. Morphological and functional traits were measured on the windward and leeward sides of each of 48 trees of identical age and diameter. Coastal stress was measured by wind speed and salt spray. Traits were summarized using the Principal Component Analysis (PCA), and PC scores were related to coastal stress and to other environmental effects. Morphological traits were summarized as PCs describing tree shape, branch supporting capacity, and branching pattern. Coastal stress significantly influenced tree shape, but not branch supporting capacity and branching pattern. Tree shape was also affected by other environmental factors. Functional traits were summarized by PCs describing dry mass density, dry matter content, and water balance, but only dry mass density was influenced by coastal stress or other environmental factors. Our study indicated that C. equisetifolia adapts to coastal stress by altering its tree shape and dry mass density. Our results provide useful information for the selection of adequate species for the erosion control and management of coastal areas.