Artificial Communities Experiment: Predictor Variables

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.本研究旨在探究博纳扎溪实验林（Bonanza Creek Experimental Forest）北方森林洪泛平原原生演替过程中，竞争与促进作用的相对功能。细叶桤木（Alnus tenuifolia Nutt.）为年轻洪泛平原生境的早期拓殖物种，可通过向土壤输入氮素显著促进土壤发育。白云杉（Picea glauca (Moench.) Voss）通常较晚定植于此类生境，多在桤木与柳属植物（Salix spp.）的冠层下成功定植，有时其冠层会被幼年香脂杨（Populus balsamifera L.）所覆盖。桤木对白云杉可能同时产生正向与负向调控作用。潜在的促进效应包括保护幼苗免受极端高温或洪水裹挟的过量泥沙淤积伤害，以及土壤氮素输入，此类效应可延续多年；而在白云杉冠层超越桤木冠层之前，二者对光照（及其他资源）的竞争可能构成主要的负向效应。本研究旨在明确洪泛平原演替序列中这些效应的净平衡状态。