• Energy Research

The occurrence of deadwood is inevitable during the process of plantation conversion, but the influences of conversion and the potential environmental effect on deadwood species diversity remain unclear. We established two fixed plots in Chinese fir thinned forest (TF) and Chinese fir and Michelia macclurei Dandy mixed forest (MF) (100 × 80 and 120 × 60 m2, respectively). We classified the deadwood into groups based on origin and by status, and analyzed deadwood species diversity using four common diversity indices. We also investigated the contribution of topographic factors to tree mortality using redundancy analysis. The species composition of deadwood differed markedly between the MF and TF. The species diversity and variety of deadwood status were greater for the TF than MF, although abundance was lower. Topography was poorly correlated with deadwood in the MF, while in the TF, altitude was strongly correlated with deadwood from Chinese fir, shade-intolerant late-coming populations, and fallen wood. Slope was negatively correlated with late-coming populations and fallen wood, but deadwood correlations with convexity were weak. These results indicate that cultivation methods strongly alter the species composition, status, abundance and diversity of deadwood in plantations. Topographic factors and targeted cultivation practices promote the formation of deadwood.

More than 60% of the total area of tree plantations in China is in subtropical, and over 70% of subtropical plantations consist of pure stands of coniferous species. Because of the poor ecosystem services provided by pure coniferous plantations and the ecological instability of these stands, a movement is under way to promote indigenous broadleaf plantation cultivation as a promising alternative. However, little is known about the carbon (C) stocks in indigenous broadleaf plantations and their dependence on stand age. Thus, we studied above- and below-ground biomass and C stocks in a chronosequence of Mytilaria laosensis plantations in subtropical China; stands were 7, 10, 18, 23, 29 and 33 years old. Our assessments included tree, shrub, herb and litter layers. We used plot-level inventories and destructive tree sampling to determine vegetation C stocks. We also measured soil C stocks by analyses of soil profiles to 100 cm depth. C stocks in the tree layer dominated the above-ground ecosystem C pool across the chronosequence. C stocks increased with age from 7 to 29 years and plateaued thereafter due to a reduction in tree growth rates. Minor C stocks were found in the shrub and herb layers of all six plantations and their temporal fluctuations were relatively small. C stocks in the litter and soil layers increased with stand age. Total above-ground ecosystem C also increased with stand age. Most increases in C stocks in below-ground and total ecosystems were attributable to increases in soil C content and tree biomass. Therefore, considerations of C sequestration potential in indigenous broadleaf plantations must take stand age into account.