Abstract
Abstract. The seasonality of litter inputs in forests has important implications for understanding ecosystem processes and biogeochemical cycles. We quantified the drivers of seasonality in litterfall and leaf decomposability using plots throughout the Australian wet tropical region. Litter fell mostly in the summer (wet, warm) months in the region, but other peaks occurred throughout the year. Litterfall seasonality was modelled well with the level of deciduousness of the site (plots with more deciduous species had lower seasonality than evergreen plots), temperature (higher seasonality in the uplands), disturbance (lower seasonality with more early secondary species) and soil fertility (higher seasonality with higher N : P/P limitation) (SL total litterfall model 1 = deciduousness + soil N : P + early secondary sp.: r2 = 0.63, n = 30; model 2 = temperature + early secondary sp. + soil N : P: r2 = 0.54, n = 30; SL leaf = temperature + early secondary sp. + rainfall seasonality: r2 = 0.39, n = 30). Leaf litter decomposability was lower in the dry season than in the wet season, driven by higher phenolic concentrations in the dry, with the difference exacerbated particularly by lower dry season moisture. Our results are contrary to the global trend for tropical rainforests; in that seasonality of litterfall input was generally higher in wetter, cooler, evergreen forests, compared to generally drier, warmer, semi-deciduous sites that had more uniform monthly inputs. We consider this due to more diverse litter shedding patterns in semi-deciduous and raingreen rainforest sites, and an important consideration for ecosystem modellers. Seasonal changes in litter quality are likely to have impacts on decomposition and biogeochemical cycles in these forests due to the litter that falls in the dry season being more recalcitrant to decay.
Highlights
Litterfall is an important component of forest function, and is inherently linked to net primarily productivity (NPP) and global biogeochemical cycles (Clark et al, 2001a; Aragão et al, 2009)
Other peaks occurred in the dry season for some plots (July–October), and in some cases bimodal peaks occurred around December and February–March (Supplement Fig. S1)
The seasonality of litterfall shows diverse patterns globally; in tropical forests, peaks most often occur in the dry season months, potentially as a response to moisture stress (Zhang et al, 2014)
Summary
Litterfall is an important component of forest function, and is inherently linked to net primarily productivity (NPP) and global biogeochemical cycles (Clark et al, 2001a; Aragão et al, 2009). Understanding of the seasonality of litter inputs in forested ecosystems is a limiting factor in ecosystem models, especially for tropical forests (De Weirdt et al, 2012), which represent a large portion of global litter inputs and NPP (Clark et al, 2001b). Understanding of how litter quality varies within years and between environments is essential in comprehending plant phenology, responses to the environment, and the effects on ecosystems and global cycles
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