An evaluation of how coarse woody debris (CWD) changes in quantity and quality during stand development was conducted using a 426-year chronosequence of 71 stands in sub-boreal forests in British Columbia. Additional characteristics of CWD were determined in 14 of the stands. Most stands are fire initiated and input from the predisturbance stand is critical in controlling the amounts and characteristics of CWD within young stands. Log volume declines from over 100 m3/ha in young stands (0-50 years) to just over 60 m3/ha in stands from 51 to 200 years old, and then increases to greater than 140 m3/ha in the oldest (>= 400-year-old) stands. Mean snag basal area is highest (31.6 m2/ha) in young, postfire stands, decreases to a very low value (2.0 m2/ha) in stands 51-100 years old, and then reaches a second maximum (12.1 m2/ha) in stands that are 201-250 years old; it declines slightly in very old stands. The high snag basal area in stands 201-250 years old coincides with the successional transition from lodgepole pine (Pinus contorta Dougl. ex Loud. var. latifolia Engelm.) to stands dominated by subalpine fir (Abies lasiocarpa (Hook.) Nutt.) and interior spruce (hybrids of Picea glauca (Moench) Voss and Picea engelmannii Parry). Stand age, characteristics of the predisturbance forest, and the disturbance history of stands subsequent to stand initiation all appear to be very important in determining variation in both the quality and quantity of CWD in these sub-boreal forests.

Abstract& Key message Climate variables improve individual-tree mortality models for fir, oak and birch. & Context 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 individualtree mortality.& Aims 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. & Methods 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. & Results 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). & Conclusion The results have significance for incorporating the effects of a changing climate into mortality models.