Climatic information improves statistical individual-tree mortality models for three key species of Sichuan Province, China

Abstract

Climate variables improve individual-tree mortality models for fir, oak and birch. Climate is considered as an important driver of tree mortality, but few studies have included climate factors in models to explore their importance for modelling individual-tree mortality. To measure the performance of climate-based models, we built individual-tree mortality models using individual, stand, and climate variables for fir (Abies faxoniana Rehd. et Wils.), oak (Quercus aquifolioides Rehd. et Wils.), and birch (Betula albo-sinensis Burk.) in Southwest China, and explored the corresponding effects on tree death. We developed tree mortality models based on 287 permanent plots from the Sichuan Forest Inventory data, and compared the models based on variables of individual (I), stand (S), and climate (C) levels, and different combinations (I + S, I + C, S + C, I + S + C) among these groups to improve model performance. We employed relative Akaike information criterion (AIC), area under receiver operating characteristic curve (AUC), and Hosmer-Lemeshow’s goodness-of-fit statistic for model evaluation and validation. We found that tree mortalities of the three species could be better predicted (AUC > 0.8) by carefully selecting variables at three ecological scales (individual, stand, and regional climate). Our results suggest that the higher mortality of the object trees occurs when they endure lower radial growth of the previous years, more intensive competition, and moderate canopy cover (for birch), while lower mortality was seen in an appropriate range of climate conditions and at higher stand canopy cover (for fir and oak). The results have significance for incorporating the effects of a changing climate into mortality models.