Abstract
Insights on tree species and competition effects on seasonal stem growth are critical to understanding the impacts of changing climates on tree productivity, particularly for eucalypts species that occur in narrow climatic niches and have unreliable tree rings. To improve our understanding of climate effects on forest productivity, we examined the relative importance of species, competition and climate to the seasonal stem growth of co-occurring temperate eucalypts. We measured monthly stem growth of three eucalypts (Eucalyptus obliqua, E. radiata, and E. rubida) over four years in a natural mixed-species forest in south-eastern Australia, examining the relative influences of species, competition index (CI) and climate variables on the seasonal basal area increment (BAI). Seasonal BAI varied with species and CI, and was greatest in spring and/or autumn, and lowest in summer. Our study highlights the interactive effects of species and competition on the seasonal stem growth of temperate eucalypts, clearly indicating that competitive effects are strongest when conditions are favourable to growth (spring and autumn), and least pronounced in summer, when reduced BAI was associated with less rainfall. Thus, our study indicates that management to reduce inter-tree competition would have minimal influence on stem growth during less favourable (i.e., drier) periods.
Highlights
Knowledge of relationships between tree growth and climate variation is essential to understand the impacts of climate change on forest ecosystems [1]
Our study demonstrates that temperate eucalypt stems in natural mixed-species evergreen forests grow in all seasons, this growth varies with species, competition, season and year
Favourable growing conditions in spring and autumn were important periods of stem growth, for those trees in less competitive environments. This demonstrated that competition interacted with seasonal climate to drive stem growth and was most important when climactic conditions were favourable
Summary
Knowledge of relationships between tree growth and climate variation is essential to understand the impacts of climate change on forest ecosystems [1]. Impacts of climate on tree productivity are difficult to quantify due to the strong influences of short-term and localized variations [2]. Climate change is expected to shift the length of seasons, alter rainfall patterns, and increase the frequency and intensity of extreme weather events within forests [3,4]. These climatic changes are expected to impact both tree productivity [5] and tree mortality [6], affecting the carbon storage capacity of forests. Much remains unknown about climate impacts on forest productivity due to the myriad influences on tree growth, including species form and growth traits, within-stand growth environment, and multiple, ever-changing weather patterns [8]
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