Changes in plant debris and carbon stocks across a subalpine forest successional series

Background:As a structurally and functionally important component in forest ecosystems,plant debris plays a crucial role in the global carbon cycle.Although it is well known that plant debris stocks vary greatly with tree species composition,forest type,forest origin,and stand age,simultaneous investigation on the changes in woody and non-woody debris biomass and their carbon stock with forest succession has not been reported.Therefore,woody and non-woody debris and carbon stocks were investigated across a subalpine forest successional gradient in Wanglang National Nature Reserve on the eastern Qinghai-Tibet Plateau.Results:Plant debris ranged from 25.19 to 82.89 Mg∙ha−1 and showed a global increasing tendency across the subalpine forest successional series except for decreasing at the S4 successional stage.Accordingly,the ratios of woody to non-woody debris stocks ranged from 26.58 to 208.89,and the highest and lowest ratios of woody to non-woody debris stocks were respectively observed in mid-successional coniferous forest and shrub forest,implying that woody debris dominates the plant debris.In particular,the ratios of coarse to fine woody debris stocks varied greatly with the successional stage,and the highest and lowest ratios were found in later and earlier successional subalpine forests,respectively.Furthermore,the woody debris stock varied greatly with diameter size,and larger diameter woody debris dominated the plant debris.Correspondingly,the carbon stock of plant debris ranged from 10.30 to 38.87 Mg∙ha−1 across the successional series,and the highest and lowest values were observed in the mid-coniferous stage and shrub forest stage,respectively.Most importantly,the carbon stored in coarse woody debris in later successional forests was four times higher than in earlier successional forests.Conclusions:The stock and role of woody debris,particularly coarse woody debris,varied greatly with the forest successional stage and dominated the carbon cycle in the subalpine forest ecosystem.Thus,preserving coarse woody debris is a critical strategy for sustainable forest management.

Effect of spot burning of logging residues on the properties of mountain forest soils and the occurrence of ground beetles(Coleoptera, Carabidae)

We investigated the relationships between dehydrogenase activity and the physicochemical properties of mountain soils over three and five years from Norway spruce(Picea abies L. Karst) logging residue spot burning and the occurrence of epigeic carabid beetles. Six study sites were utilised, including18 study plots(nine plots in a mixed coniferous mountain forest site and nine plots in a mixed broadleaf mountain forest site), with five replicate pitfall traps at each site located in southern Poland.Soil samples from the organic horizon were taken for p H, organic carbon, nitrogen, base cation content,acidity and dehydrogenase activity determination.Carabid beetles were monitored in weekly intervals during the period of July to August 2016. The burning of logging residues led to modified soil properties,especially the dehydrogenase activity. In all the tested variants, the activity was higher in soil samples after the burning in comparison to the control variants. We show no positive correlation between dehydrogenase activity and the number of carabid specimens. The preferences of dominant predatory hygrophilous carabids to acid habitats with weakly decomposed organic matter were proven. Simultaneously, the soil organic matter content was positively related to the carabid abundance. The significant impact of forest site conditions and the date of logging residue burning on the number of caught specimens were confirmed. In contrast, no relationships between the species richness, species diversity, mean individual biomass and spot burning effect were found. This work supports the recommendation of spruce fine woody debris utilisation by spot burning on mountain regions with rich habitats presenting moderate wet conditions and small land falls.