School of Biological Sciences, University of Tasmania Hobart, TAS, Australia.
Front Plant Sci. 2014 Jun 5;5:260. doi: 10.3389/fpls.2014.00260. eCollection 2014.
We tested the hypothesis that the effect of forest basal area on tree growth interacts with macro-ecological gradients of primary productivity, using a large dataset of eucalypt tree growth collected across temperate and sub- tropical mesic Australia. To do this, we derived an index of inter-tree competition based on stand basal area (stand BA) relative to the climatically determined potential basal area. Using linear mixed effects modeling, we found that the main effects of climatic productivity, tree size, and competition explained 26.5% of the deviance in individual tree growth, but adding interactions to the model could explain a further 8.9%. The effect of competition on growth interacts with the gradient of climatic productivity, with negligible effect of competition in low productivity environments, but marked negative effects at the most productive sites. We also found a positive interaction between tree size and stand BA, which was most pronounced in the most productive sites. We interpret these patterns as reflecting intense competition for light amongst maturing trees on more productive sites, and below ground moisture limitation at low productivity sites, which results in open stands with little competition for light. These trends are consistent with the life history and stand development of eucalypt forests: in cool moist environments, light is the most limiting resource, resulting in size-asymmetric competition, while in hot, low rainfall environments are open forests with little competition for light but where the amount of tree regeneration is limited by water availability.
我们利用在澳大利亚温带和亚热带湿润地区收集的大量桉树生长数据，检验了森林基面积对树木生长的影响与主要生产力宏生态学梯度相互作用的假设。为此，我们根据林分基面积相对于气候决定的潜在基面积，得出了一个树木间竞争指数。通过线性混合效应模型，我们发现气候生产力、树木大小和竞争的主要效应解释了个体树木生长差异的 26.5%，但在模型中加入相互作用可以进一步解释 8.9%。竞争对生长的影响与生产力梯度相互作用，在低生产力环境中竞争的影响可以忽略不计，但在最具生产力的地点则产生明显的负面影响。我们还发现树木大小和林分基面积之间存在正相互作用，在最具生产力的地点最为明显。我们将这些模式解释为反映了在生产力较高的地方，成熟树木之间对光的激烈竞争，以及在低生产力地区地下水分限制，导致光竞争很少的开阔林分。这些趋势与桉树森林的生活史和林分发育一致：在凉爽潮湿的环境中，光资源是最受限制的，导致大小不对称竞争，而在炎热、低降雨量的环境中，林分开阔，光竞争很少，但树木再生的数量受到水分供应的限制。
