Williams Laura J, Bunyavejchewin Sarayudh, Baker Patrick J
Australian Centre for Biodiversity, School of Biological Sciences, Monash University, Melbourne, VIC 3800, Australia.
Oecologia. 2008 Mar;155(3):571-82. doi: 10.1007/s00442-007-0938-1. Epub 2008 Jan 10.
Seasonal tropical forests exhibit a great diversity of leaf exchange patterns. Within these forests variation in the timing and intensity of leaf exchange may occur within and among individual trees and species, as well as from year to year. Understanding what generates this diversity of phenological behaviour requires a mechanistic model that incorporates rate-limiting physiological conditions, environmental cues, and their interactions. In this study we examined long-term patterns of leaf flushing for a large proportion of the hundreds of tree species that co-occur in a seasonal tropical forest community in western Thailand. We used the data to examine community-wide variation in deciduousness and tested competing hypotheses regarding the timing and triggers of leaf flushing in seasonal tropical forests. We developed metrics to quantify the nature of deciduousness (its magnitude, timing and duration) and its variability among survey years and across a range of taxonomic levels. Tree species varied widely in the magnitude, duration, and variability of leaf loss within species and across years. The magnitude of deciduousness ranged from complete crown loss to no crown loss. Among species that lost most of their crown, the duration of deciduousness ranged from 2 to 21 weeks. The duration of deciduousness in the majority of species was considerably shorter than in neotropical forests with similar rainfall periodicity. While the timing of leaf flushing varied among species, most ( approximately 70%) flushed during the dry season. Leaf flushing was associated with changes in photoperiod in some species and the timing of rainfall in other species. However, more than a third of species showed no clear association with either photoperiod or rainfall, despite the considerable length and depth of the dataset. Further progress in resolving the underlying internal and external mechanisms controlling leaf exchange will require targeting these species for detailed physiological and microclimatic studies.
季节性热带森林呈现出多种多样的叶片更替模式。在这些森林中，叶片更替的时间和强度变化可能发生在个体树木和物种内部及之间，也可能随年份而变化。要理解这种物候行为多样性的产生原因，需要一个包含限速生理条件、环境线索及其相互作用的机理模型。在本研究中，我们调查了泰国西部一个季节性热带森林群落中共存的数百种树木中很大一部分的长期叶片萌发模式。我们利用这些数据来研究群落范围内落叶程度的变化，并检验了关于季节性热带森林中叶片萌发时间和触发因素的相互竞争的假设。我们开发了指标来量化落叶的性质（其程度、时间和持续时间）以及在调查年份之间和一系列分类水平上的变异性。树种在种内和跨年的落叶程度、持续时间和变异性方面差异很大。落叶程度从完全树冠落叶到无树冠落叶不等。在失去大部分树冠的物种中，落叶持续时间从2周到21周不等。大多数物种的落叶持续时间比降雨周期相似的新热带森林中的要短得多。虽然不同物种的叶片萌发时间不同，但大多数（约70%）在旱季萌发。在一些物种中，叶片萌发与光周期变化有关，而在其他物种中与降雨时间有关。然而，尽管数据集的长度和深度可观，但超过三分之一的物种与光周期或降雨均无明显关联。要进一步解析控制叶片更替的潜在内部和外部机制，需要针对这些物种进行详细的生理和微气候研究。
