Data from: Transient dominance in a central African rain forest

The large-crowned emergent tree Microberlinia bisulcata dominates rainforest groves at Korup, along with two co-dominants Tetraberlinia bifoliolata and T. korupensis. M. bisulcata has a pronounced modal size frequency distribution around ~110 cm stem diameter: its recruitment potential is very poor. It is a long-lived light-demanding species, one of many found in African forests. Tetraberlinia species lack modality, are more shade-tolerant and recruit better. All three species are ectomycorrhizal. M. bisulcata dominates grove basal area, even though it has similar numbers of trees (≥ 50 cm stem diameter) as each of the other two species. This situation presented a conundrum which prompted a long-term study of grove dynamics. Enumerations of two plots (82.5 and 56.25 ha) between 1990 and 2010 showed mortality and recruitment of M. bisulcata to be very low (both rates ~0.2 %/yr) compared with Tetraberlinia (2.4, 0.8 %/yr), and M. bisulcata grows twice as fast as the Tetraberlinia. Ordinations indicated that these three species determined community structure by their strong negative associations whilst other species showed almost none. Ranked species abundance curves fitted the Zipf-Mandelbrot model well, and allowed ‘over-dominance’ of M. bisulcata to be estimated. Spatial analysis indicated strong repulsion by clusters of large (50 – < 100 cm) and very large (> 100 cm) M. bisulcata of their own medium-sized (10 – < 50 cm) trees and all sizes of Tetraberlinia. This was interpreted as competition by M. bisulcata increasing its dominance, but also inhibition of its own replacement potential. Stem coring showed a modal age of ~200 year for M. bisulcata, but with large size variation (50 – 150 cm). Fifty-year model projections suggested little change in medium, decreases in large, and increases in very large trees of M. bisulcata, accompanied by overall decreases in medium and large trees of Tetraberlinia species. Realistically increasing very-large-tree mortality led to grove collapse without short-term replacement. M. bisulcata most likely depends on climatic events to rebuild its stands: the ratio of disturbance interval to median species’ longevity is important. A new theory of transient dominance explains how M. bisulcata may be cycling in abundance over time and displaying non-equilibrium dynamics.冠幅宽大的顶极上层乔木双槽微柏林木（Microberlinia bisulcata）主导着科鲁普（Korup）地区的雨林群落斑块，与之同为优势种的还有两种四柏林木属（Tetraberlinia）植物：双叶四柏林木（Tetraberlinia bifoliolata）与科鲁普四柏林木（T. korupensis）。双槽微柏林木的茎径频率分布存在显著的众数，峰值约为110厘米，但其更新潜力极差。该物种为长寿命、喜光性树种，是非洲森林中常见的类群之一。四柏林木属植物则无明显的径级分布众数，耐阴性更强，更新表现更佳。上述三个物种均为外生菌根（ectomycorrhizal）植物。尽管双槽微柏林木的立木数量（茎径≥50厘米个体）与另外两个物种大致相当，但其主导着群落斑块的断面积总和。这一现象构成了一个科学谜题，推动了针对该群落斑块动态的长期研究。1990年至2010年间对两块样地（面积分别为82.5公顷与56.25公顷）的调查显示，双槽微柏林木的死亡率与更新率均极低（二者年均速率均约为0.2%），而四柏林木属植物的对应速率分别为2.4%与0.8%；同时双槽微柏林木的生长速率是四柏林木属植物的两倍。排序分析表明，这三个物种通过强烈的负关联塑造了群落结构，而其余物种则几乎无此类关联。物种相对多度排序曲线与齐夫-曼德布罗特模型（Zipf-Mandelbrot）拟合度极佳，借此可估算双槽微柏林木的‘过度优势度’。空间分析结果显示，大径级（50厘米≤茎径<100厘米）与超大径级（茎径>100厘米）的双槽微柏林木集群，对自身的中径级个体（10厘米≤茎径<50厘米）以及所有径级的四柏林木属植物均表现出强烈的排斥效应。该现象被解读为：双槽微柏林木通过种内与种间竞争强化自身优势，但同时也抑制了自身的更新替代潜力。茎干钻芯分析显示，双槽微柏林木的年龄众数约为200年，但茎径存在较大变异范围（50厘米至150厘米）。基于模型的50年预测结果显示，双槽微柏林木的中径级个体数量变化极小，大径级个体数量下降，而超大径级个体数量上升；与此同时，四柏林木属植物的中径级与大径级个体数量均呈整体下降趋势。若考虑到超大径级个体死亡率的实际上升趋势，则该群落斑块将在短期内缺乏更新替代的情况下发生崩溃。双槽微柏林木大概率依赖气候干扰事件来重建种群：干扰间隔与该物种中位寿命的比值是关键影响因素。一种全新的‘暂时性优势’理论，解释了双槽微柏林木的多度如何随时间周期性波动，并呈现出非平衡群落动态特征。