Artificial microtopography and herbivory protection facilitates wetland tree (Thuja occidentalis L.) survival and growth in created wetlands

摘要

Northern white-cedar (Thuja occidentalis L.) wetlands are highly valuable both commercially and as wildlife habitat. However, northern white-cedar forested wetlands are declining in area from forestry activities and development, with mitigation efforts often failing to reproduce these ecosystems. For this reason, the goal of this project was to determine the feasibility of creating a northern white-cedar forested wetland as a wetland mitigation option. Microtopography has been shown to be important for northern white-cedar establishment and recruitment, so a series of hummocks and flat areas were created and planted with northern white-cedar seedlings in two created wetlands in northern Michigan, USA. We examined the influence of microtopography and exposure to deer browse on white-cedar survivorship and height growth, 2 and 5 years after establishment. Hummock microtopography increased both tree survival and height growth. Percent survival after 5 years in protected fenced areas was 75 % on hummocks, while percent survival was only 15 % in protected fenced flat areas. Height growth rates were also greater on fenced hummocks, averaging 30 cm per year, compared to an average of 8 cm per year on fenced flat areas. Protection from browsing also improved white-cedar survival and height growth. Fenced white-cedar had 15-20 % greater survival compared to unfenced white-cedar and had 25-100 % greater growth rates. Our results indicate that incorporating microtopography and protection from browsing into future restoration or regeneration projects involving northern white-cedar should be considered as a viable option where high or variable water tables are expected.