Sveinbjörnsson Bjartmar, Hofgaard Annika, Lloyd Andrea
Department of Biological Sciences, University of Alaska Anchorage, 3211 Providence Drive, Anchorage, AK 99508, USA.
Ambio. 2002 Aug;Spec No 12:23-9.
The tundra-taiga interface is characterized by a change in tree cover or density, tree size and shape, tree growth, and reproduction. Generally, trees get denser, taller, and less damaged as one moves from the tundra into the taiga proper. The environmental covariates and possible mechanisms resulting in these patterns are addressed in the paper. Low seed rain density, lack of safe sites caused by microclimatic variation, low surface substrate moisture, and low soil nutrient availability may limit the density of the tree species. Tree growth may be limited by a short growing season and further diminished, by shoot and root damage reducing carbon and nutrient stores as well as by reducing carbon and nutrient uptake capacities. Positive and negative feedbacks of tree density on tree growth exist at treeline. Increased tree density leads to increased air temperature and decreased wind damage, but also to lower soil temperature, reduced nutrient availability, and greater nutrient competition.
苔原与泰加林的交界地带的特点是树木覆盖或密度、树木大小和形状、树木生长及繁殖方面的变化。一般来说，当从苔原向真正的泰加林过渡时，树木会变得更加密集、更高，且受损更少。本文探讨了导致这些模式的环境协变量及可能机制。种子雨密度低、微气候变异导致缺乏安全地点、地表基质湿度低以及土壤养分有效性低，可能会限制树种的密度。树木生长可能受生长季短的限制，而枝条和根系受损会减少碳和养分储备以及降低碳和养分吸收能力，从而进一步抑制生长。在树线处，树木密度对树木生长存在正负反馈。树木密度增加会导致气温升高和风害减少，但也会使土壤温度降低、养分有效性降低以及养分竞争加剧。
