Classical tree neighbourhood models use size variables acting at point distances. In a new approach here, trees were spatially extended as a function of their crown sizes, represented impressionistically as points within crown areas. Extension was accompanied by plasticity in the form of crown removal or relocation under the overlap of taller trees. Root systems were supposedly extended in a similar manner. For the 38 most abundant species in the focal size class (10 - <100 cm stem girth) in two 4-ha plots at Danum (Sabah), for periods P1 (1986-1996) and P2 (1996-2007), stem growth rate and tree survival were individually regressed against stem size, and neighbourhood conspecific (CON) and heterospecific (HET) basal areas within incremented steps in radius. Model parameters were critically assessed, and statistical robustness in the modelling set by randomization testing. Classical and extended models differed importantly in their outcomes. Crown extension weakened the relationship of CON effect on growth versus plot species abundance, showing that models without plasticity over-estimated negative density dependence. A significant negative trend of difference in CON effects on growth (P2 - P1) versus CON or HET effect on survival in P1 was strongest with crown extension. Model outcomes did not then support an explanation of CON and HET effects being due to (asymmetric) competition for light alone. An alternative hypothesis is that changes in CON effects on small trees, largely incurred by a drought phase (relaxing light limitation) in P2, and following the more shaded (suppressing) conditions in P1, were likely due to species-specific (symmetric) root competition and mycorrhizal processes. The very high variation in neighbourhood composition and abundances led to a strong "neighbourhood stochasticity", and hence to largely idiosyncratic species responses. A need to much better understand the roles of rooting structure and processes at the individual tree level was highlighted.

中文翻译：

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在婆罗洲雨林邻里竞争效应评价中包括树木空间扩展

经典的树邻域模型使用作用于点距离的大小变量。在这里的一种新方法中，树木根据树冠大小在空间上扩展，在印象上以树冠区域内的点表示。伸展伴随着高大树木重叠的树冠去除或重新安置形式的可塑性。根系统应该以类似的方式扩展。P1（1986-1996）和P2（1996-2007）期间，在Danum（沙巴州）的两个4公顷地块中，在焦点大小等级上最丰富的38个物种（茎周长10-<100 cm），茎生长比率和树木成活率分别根据茎的大小和半径递增步长内的邻域同种（CON）和异种（HET）基础区域进行回归分析。模型参数经过严格评估，随机测试在建模集中的统计稳健性。经典模型和扩展模型的结果差异很大。冠冠延伸减弱了CON对生长与田间物种丰度的关系，表明没有可塑性的模型高估了负密度依赖性。CON对生长的影响（P2-P1）与CON或HET对P1生存的影响之间的显着负趋势在冠延长时最强。然后，模型结果不支持对CON和HET效应的解释，这是由于光的非对称竞争所致。另一种假设是，CON对小树的影响发生变化，这主要是由P2中的干旱阶段（放松光照限制）引起的，并且随着P1中的阴影（抑制）条件的出现，可能是由于特定物种（对称）的根竞争和菌根过程。邻域组成和丰度的高度变化导致强烈的“邻域随机性”，从而导致特异种的反应。强调了需要更好地了解单个树级别的生根结构和过程的作用。