Artificial Communities Seedling Growth: Bonanza Creek Experimental Forest (planted in 1989; measured in 1992, 1995, and 2002).

This study considers the relative role of competition and facilitation in primary succession of the boreal forest floodplain of Bonanza Creek Experimental Forest. Alder (Alnus tenuifolia Nutt.) is an early colonist of young floodplain sites, where it contributes greatly to soil development through the addition of nitrogen to the soil. White spruce (Picea glauca (Moench.) Voss) typically colonizes such sites later; it becomes established beneath a canopy of alder and willow (Salix spp.) which is sometimes overtopped by young balsam poplar (Populus balsamifera L.). The alder may potentially influence white spruce both positively and negatively. Possible facilitative effects include protection of small seedlings from excess heat or heavy siltation accompanying flooding and addition of soil nitrogen, an effect that may extend for many years. Competition for light (and other resources) before the white spruce has overtopped the alder canopy may prove to be a major negative effects. This study seeks to determine the net balance of these effects on the floodplain successional sequence by planting spruce seedlings with and without the presence of alder. Plots of white spruce seedlings were planted in 1989 on an early successional silt bar with and without alder in the Bonanza Creek Experimental Forest. Biomass by species and carbon and nitrogen pools of plants and soils were measured in 2002. Height and survivorship of spruce seedlings were measured in 1992, 1995, and 2002. White spruce grew more rapidly in the presence of alder during the first six years. After 13 years, however, seedlings planted with alder experienced high mortality due to intensive browsing by snowshoe hares. Alder resulted in greater total biomass and larger carbon and nitrogen pools in plants and soils.本研究旨在探讨博纳扎溪实验森林（Bonanza Creek Experimental Forest）北方林洪泛平原原生演替过程中，竞争与促进作用的相对地位。细叶桤木（Alnus tenuifolia Nutt.）是年轻洪泛平原生境的早期拓殖物种，可通过向土壤中添加氮素极大地促进土壤发育。白云杉（Picea glauca (Moench.) Voss）通常较晚拓殖此类生境，多在桤木与柳属（Salix spp.）的冠层下定植，有时会被幼年香脂杨（Populus balsamifera L.）的冠层覆盖。桤木对白云杉的作用可能兼具正向与负向效应：其潜在的促进作用包括保护幼苗免受过度受热或洪水伴随的过量淤积影响，以及向土壤添加氮素，这类效应可延续多年；而在白云杉超越桤木冠层之前，二者对光照（及其他资源）的竞争可能是主要的负向效应。本研究通过设置有/无桤木共存的白云杉幼苗样地，旨在明确洪泛平原演替序列中这些效应的净平衡。1989年，研究人员于博纳扎溪实验森林的一处早期演替粉砂沙洲上，分别设置有桤木与无桤木的白云杉幼苗样地。2002年，测定了各物种的生物量以及植物与土壤的碳、氮库。分别于1992年、1995年与2002年测定了白云杉幼苗的株高与存活率。前六年，有桤木共存的白云杉生长速率更快；但在种植13年后，与桤木伴生的幼苗因雪鞋兔（snowshoe hares）的高强度啃食出现了高死亡率。桤木的存在可使植物与土壤的总生物量及碳、氮库规模更高。