Abstract
Due to their destructive and sporadic nature, it is often difficult to evaluate and predict the effects of typhoon on forest ecosystem patterns and processes. We used a 21-yr record of litterfall rates to explore the influence of typhoon frequency and intensity, along with other meteorological variables, on ecosystem dynamics in a subtropical rainforest. Over the past half century there has been an increasing frequency of strong typhoons (category 3; >49.6 m s−1; increase of 1.5 typhoons/decade) impacting the Fushan Experimental Forest, Taiwan. At Fushan strong typhoons drive total litterfall mass with an average of 1100 kg ha−1 litterfall typhoon−1. While mean typhoon season litterfall has been observed to vary by an order of magnitude, mean litterfall rates associated with annual leaf senescence vary by <20%. In response to increasing typhoon frequency, total annual litter mass increased gradually over the 21-year record following three major typhoons in 1994. Monthly maximum wind speed was predictive of monthly litterfall, yet the influence of precipitation and temperature was only evident in non-typhoon affected months. The response of this subtropical forest to strong typhoons suggests that increasing typhoon frequency has already shifted ecosystem structure and function (declining carbon sequestration and forest stature).
Highlights
Litterfall production and decomposition are important ecosystem processes closely linked to terrestrial ecosystem structure and function e.g., primary productivity[1, 2]
Several recent studies indicate that the number of intense tropical cyclones are likely to increase and other studies suggest an overall increase in tropical cyclone frequency[20,21,22,23]
The importance of typhoon disturbance on litterfall dynamics is evident in the role that Windmax played in predicting litterfall when typhoon affected months were excluded from the cross-correlations and ARIMA models, shifting from the most important predictor to providing no predictability
Summary
Litterfall production and decomposition are important ecosystem processes closely linked to terrestrial ecosystem structure and function e.g., primary productivity[1, 2]. A study of litterfall among 34 Finnish Scots pine forests reported that climate factors explained 70% of the variation in inter-site litterfall[4]. Gradual changes in temperature and precipitation, the most widely studied aspects of climate change, can have major impacts on litterfall through their effects on NPP. In addition to temperature and precipitation, changes in the intensity and frequency of extreme weather events can have major impacts on key ecosystem processes, including litterfall[18, 19]. Few studies have examined the effect of changes in tropical cyclone frequency and intensity on forests and litterfall in particular. A study in the Northwest Pacific indicates that intense tropical cyclones disproportionally influence litterfall rates[11], suggesting that any change in cyclone frequency and/or intensity could impact the structure and function of the impacted forests
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