Wind affects the growth, root anchorage and tensile strength of Australian pine (<i>Casuarina equisetifolia</i>) seedlings

Abstract

Australian pine (Casuarina equisetifolia Forst.) is an important introduced reforestation species in windbreaks for agroforestry and ecological engineering. Nevertheless, the adaptive mechanism of its roots to withstand wind has not yet been fully investigated. In this study, a wind tunnel test was applied to investigate the effects of wind on growth, root architecture, root anchorage and tensile strength of Australian pine seedlings using root excavation method, pullout test and tensile test. After eight months of treatment with simulated wind load (8.2 m s−1) during the day, the non-wind-stressed control seedlings developed taller height (118%), larger stem base diameter (110%), root biomass (100%), shoot biomass (228%), and longer taproot length (56%) than those of wind-stressed seedlings. Furthermore, the wind-stressed seedlings distributed more roots at the windward side than at the leeward side, whereas the control seedlings distributed their root systems in all directions. The average maximum pullout resistance (0.25 ± 0.11 kN) of the control seedlings was significantly higher than that of the wind-stressed ones (0.08 ± 0.04 kN). Additionally, the control seedlings had significantly higher root tensile strength than the wind-stressed ones in 0–1, 1–2 and 2–5 mm root diameter classes, respectively. These results demonstrate that wind stress significantly decreases growth performance, root anchorage capability and tensile strength of Australian pine seedlings.