Short-term dynamic shifts in woody plants in a montane mixed evergreen and deciduous broadleaved forest in central China

摘要

The composition and structure in many forests is drifting across the world, although the causes of these changes remain unclear. We studied species turnover, mortality and recruitment, and population dynamism for different successional groups based on three datasets collected between 2001 and 2010 from a permanent 120mc80m plot in a Fagus englerianaCyclobalanopsis multinervis mixed forest patch in central China, to identify trends in forest change and explore the possible effects of ice storm in 2008 on forest dynamics. The majority of woody species in this forest belonged to early- and late-successional species and the proportion of evergreen species was lower than that of deciduous in terms of species richness. Floristic composition showed minor structural and compositional changes with no shift in the rank of importance value index among different successional groups, over the study periods, whereas stem density and basal area changed markedly between 2006 and 2010, probably as a consequence of the ice storm in 2008. Size distributions of living individuals were similar between census intervals for all successional groups, approximating an inverse J-shaped distribution for early- and late-successional species groups and a bell-shaped distribution for pioneer species, whereas size distributions of dead individuals varied significantly for all successional groups. Furthermore, patterns of mortality and recruitment displayed disequilibrium behaviors over the investigated period with mortality surpassing recruitment for all successional groups during the final census. Surprisingly, diameter growth rates reached a maximum during the final census interval (20062010) among all successional groups. All successional groups also showed size-dependent growth with maximal growth rates attained among the largest-sized classes except for pioneer species, which exhibited the highest growth rates at mid-sized classes. Moreover, ice-storm in 2008 also accelerated dynamisms among successional groups to different extents. The dynamism gauged by stem density was significantly lower than that based on basal area among successional groups during 20012006 but the reverse situation was observed in the later census interval, demonstrating the divergence in diameter growth rate but not in recruitment individuals between the two census intervals made large contribution to this observation. Taken together, these results indicate that despite the 2008 ice-storm this forest was generally resilient, undergoing only minor structural and compositional shifts, although an accelerated rate of forest dynamism among successional groups was linked to the period that included the ice storm. Therefore, long-term observation is needed to further reveal direct evidence of relationships between disturbance and forest dynamics.