We examined forest and tree responses to decreasing nutrient availability with soil aging in a species-rich tropical montane rain forest on Mount Kinabalu, Borneo. Community composition and structure and tree growth rates were compared between two 1 ha plots on nutrient-rich young soil versus nutrient-deficient old soil. Myrtaceae and Fagaceae dominated both plots. With soil aging, the dominance of Lauraceae, stem density, basal area and aboveground biomass decreased, and the forest understory became brighter. Some dominant taxa on the old soil (Podocarpaceae and the genus Tristaniopsis in Myrtaceae) were virtually absent on the young soil; this was attributed to light limitation in the understory. Growth rates of understory trees were lower on the young soil, whereas those of canopy trees were lower on the old soil. This suggested that the growth of understory trees was limited by light on the young soil, whereas that of canopy trees was limited by nutrients on the old soil. Of the eight species that were abundant in both plots, the dominance of five species was considerably lower on the old soil, four of which also exhibited decreased maximum sizes and lower growth rates. The remaining three species showed similar dominance across plots without a decline in growth rates, although they exhibited decreased maximum sizes on the old soil. These analyses demonstrated divergent responses of species to the soil-age gradient. We suggest that the differential responses of species to decreasing nutrient availability with a concomitant increase in understory light levels explain floristic turnover with soil aging.

我们在婆罗洲基纳巴卢山物种丰富的热带山地雨林中研究了森林和树木对土壤老化导致养分供应减少的反应。对营养丰富的新土和营养缺乏的老土上的两个 1 公顷地块的群落组成和结构以及树木生长率进行了比较。桃金娘科和壳斗科在这两个地块中均占主导地位。随着土壤老化，樟科植物优势度、茎密度、断面积和地上生物量下降，林下植被变亮。老土壤上的一些优势类群（罗汉松科和桃金娘科中的Tristaniopsis属）在新土壤上几乎不存在；这是由于林下的光照限制造成的。年轻土壤上林下树木的生长速度较低，而老土壤上林冠树木的生长速度较低。这表明林下树木的生长受到新土壤上光线的限制，而冠层树木的生长则受到老土壤上养分的限制。在这两个地块中丰富的八个物种中，有五个物种在旧土壤上的优势度相当低，其中四个物种的最大尺寸也减少了，生长速度也降低了。其余三个物种在不同地块上表现出类似的优势，但生长率没有下降，尽管它们在旧土壤上表现出最大尺寸减小。这些分析表明物种对土壤年龄梯度的不同反应。我们认为，物种对养分有效性下降以及林下光照水平随之增加的不同反应解释了土壤老化引起的植物区系更替。