Light environments occupied by conifer and angiosperm seedlings in a New Zealand podocarp-broadleaved forest
Light environments occupied by conifer and angiosperm seedlings in a New Zealand podocarp-broadleaved forest
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新西兰罗汉松阔叶林中针叶树和被子植物幼苗所占据的光环境
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发表时间：
2009
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通讯作者：
P. Bellingham
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作者：
C. Lusk;R. Duncan;P. Bellingham
新西兰罗汉果树阔叶林中针叶植物和被子植物之间的相互作用是一个持久感兴趣的话题。我们的目的是要确定通常不连续的再生是否可以归因于它们的幼苗比被子植物树冠树的耐荫性更差和/或占用的光环境范围更窄。我们量化了新西兰北岛中部一片古老的罗汉果阔叶林中这两种针叶树和五种共生被子植物的大幼苗(50-200厘米高)自然占据的光环境(漫反射光可获得性百分比)。随机化被用来比较每个物种所占据的光环境的平均值和方差与森林林下的光环境分布的平均值和方差。还计算了分布的第10个百分位数，作为每个物种所能容忍的最深阴影的指标。这些参数表明，与被子植物Beilschmiedia tawa一样，Cupressinum基本上是随机分布的。尽管另一种针叶树--铁皮针叶树的平均光环境也是如此，但有轻微的重要证据表明，在最阴暗的微型场所，该物种的代表性不足。相比之下，被子植物杜鹃花和总状花序植物表现出强烈的非随机格局，占据的最低和平均光环境明显比偶然预期的要亮得多。因此，在许多森林中，罗汉果种群结构的不连续似乎不太可能是由于在大苗期不耐受遮荫造成的。此外，西洋参和铁锈菌所占据的光环境范围的相似性表明，这些物种在种群结构和演替地位上的差异不是由于幼苗耐荫性的差异。
Interaction between conifers and angiosperms in New Zealand's podocarp-broadleaved forests is a topic of enduring interest. We aimed to determine if the often discontinuous regeneration of the podocarps Dacrydium cupressinum and Prumnopitys ferruginea can be attributed to their seedlings' tolerating less shade than those of angiosperm canopy trees and/or to occupying a narrower range of light environments. We quantified the light environments (% diffuse light availability) naturally occupied by large seedlings (50-200 cm tall) of these two conifers and five co-occurring angiosperms, in an old-growth podocarp-broadleaved forest in the central North Island of New Zealand. Randomisation was used to compare the mean and variance of the light environments occupied by each species with those of the distribution of light environments in the forest understorey. The 10th percentiles of distributions were also calculated as an indicator of the deepest shade tolerated by each species. These parameters showed D. cupressinum to be essentially randomly distributed in relation to light availability, like the angiosperm Beilschmiedia tawa. Although this was also true of the mean light environment of the other conifer, P. ferruginea, there was marginally significant evidence that this species was underrepresented at the shadiest microsites. In contrast, the angiosperms Elaeocarpus dentatus and Weinmannia racemosa showed strongly non-random patterns, occupying significantly brighter minimum and mean light environments than would be expected by chance. It therefore seems unlikely that the discontinuous population structures of podocarps in many forests result from an intolerance of shade at the large seedling stage. Furthermore, the similarity of the ranges of light environments occupied by D. cupressinum and P. ferruginea suggests that reported differences in population structure and successional position of these species are not attributable to differences in seedling shade tolerance.