Deciduousness in a seasonal tropical forest in western Thailand: interannual and intraspecific variation in timing, duration and environmental cues

Abstract

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 cooccur 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 Communicated by

Mapping Distinct Forest Types Improves Overall Forest Identification Based on Multi-Spectral Landsat Imagery for Myanmar’s Tanintharyi Region

“…Although forests in much of the region are broadleaf evergreen, certain areas contain mixtures or mosaics of evergreen and deciduous tree species. In monsoon areas of Southeast Asia, leaf drop occurs during the dry season for deciduous tree species, but can be highly variable among years, species, and locations [29,30]. For this study, we group forests in Tanintharyi into one of four major ecological types: (1) mangrove forest; (2) lowland evergreen forest; (3) upland evergreen forest; and (4) …”

Mapping Clearances in Tropical Dry Forests Using Breakpoints, Trend, and Seasonal Components from MODIS Time Series: Does Forest Type Matter?

“…Dry season leaf senescence can cause confusion in forest change analysis which can lead to higher error frequently reported in deciduous classes [57][58][59]. Besides seasonal variation in reflectance increasing with forest deciduousness [60], there can also be considerable natural inter-annual variation linked to changing climate and variable rainfall patterns [61][62][63]. This presents a major challenge for methods that use ridged seasonal models as they often model a constant average seasonality, failing to capture the natural variation.…”

Seasonal coupling of canopy structure and function in African tropical forests and its environmental controls

“…For example, the impact of radiation has been hypothesized to be mediated either through daylength (Rivera and Borchert 2001, Rivera et al 2002, Elliott et al 2006, Williams et al 2008), timing of sunrise or sunset (Borchert et al 2005), or insolation thresholds (van Schaik et al 1993, Wright and van Schaik 1994, Yeang 2007a, 2007b, Calle et al 2009, 2010. The insolation threshold pertains to solar radiation intensity at the top of the atmosphere (i.e., shortwave downward radiation at the top of atmosphere, ''SWTOA'' hereafter).…”

“…Many tropical forests have well-established drought-adaptive mechanisms linking the seasonality of growth with the seasonality of water availability. These strategies include deploying deep roots to access soil water reserves, which potentially allows them to grow in the dry season (Nepstad et al 1994, Dawson 1996, Borchert 1998, Meir et al 2009, Markewitz et al 2010, or by timing leaf flushing to precede the onset of the rainy season (Williams et al 2008).…”