Thermodegradation of naturally decomposed forest logging residues: Characteristics, kinetics, and thermodynamics.

Combustion and pyrolysis characteristics, kinetics, and thermodynamics of naturally decomposed softwood and hardwood forest logging residues (FLR) were investigated using thermogravimetric analysis. Results showed that calorific values of fresh red pine, two-year decomposed, four-years decomposed, fresh red maple, two-year decomposed, and four-years decomposed were 19.78, 19.40, 20.19, 20.35, 19.27, and 19.62 MJ/kg, respectively. Hemicellulose pyrolysis peak only occurred in the hardwood thermodegradation process. Softwood had a higher pyrolysis yield of solid products (16.08-19.30%) than hardwood (11.19-14.67%). The average pyrolysis activation energy (Ea) of hardwood residue increased with the year after harvest, whereas softwood samples decreased. The average combustion Ea of hardwood samples increased first, then decreased, while that of softwood samples decreased continuously. Enthalpy (ΔH), entropy (ΔS), and Gibbs free energy (ΔG) were also investigated. This research will aid in understanding the thermal decomposition properties of naturally decomposed FLR from various years after harvest.

Local community assembly mechanisms shape soil bacterial ß diversity patterns along a latitudinal gradient.

Biodiversity patterns across geographical gradients could result from regional species pool and local community assembly mechanisms. However, little has been done to separate the effects of local ecological mechanisms from variation in the regional species pools on bacterial diversity patterns. In this study, we compare assembly mechanisms of soil bacterial communities in 660 plots from 11 regions along a latitudinal gradient in eastern China with highly divergent species pools. Our results show that ß diversity does not co-vary with γ diversity, and local community assembly mechanisms appear to explain variation in ß diversity patterns after correcting for variation in regional species pools. The variation in environmental conditions along the latitudinal gradient accounts for the variation in ß diversity through mediating the strength of heterogeneous selection. In conclusion, our study clearly illustrates the importance of local community assembly processes in shaping geographical patterns of soil bacterial ß diversity.

Natural forests exhibit higher carbon sequestration and lower water consumption than planted forests in China.

Large-scale planted forests (PF) have been given a higher priority in China for improving the environment and mitigating climate change relative to natural forests (NF). However, the ecological consequences of these PF on water resource security have been less considered in the national scale. Moreover, a critically needed comparison on key ecological effects between PF and NF under climate change has rarely been conducted. Here, we compare carbon sequestration and water consumption in PF and NF across China using combination of remote sensing and field inventory. We found that, on average, NF consumed 6.8% (37.5 mm per growing season) less water but sequestered 1.1% (12.5 g C m-2  growing season-1 ) more carbon than PF in the period of 2000-2012. While there was no significant difference in water consumption (p = 0.6) between PF and NF in energy-limited areas (dryness index [DI] < 1), water consumption was significantly (p < 0.001) higher in PF than that in NF in water-limited regions (DI > 1). Moreover, a distinct and larger shift of water yield was identified in PF than in NF from the 1980s to the 2000s, indicating that PF were more sensitive to climate change, leading to a higher water consumption when compared with NF. Our results suggest NF should be properly valued in terms of maximizing the benefits of carbon sequestration and water yield. Future forest plantation projects should be planned with caution, particularly in water-limited regions where they might have less positive effect on carbon sequestration but lead to significant water yield reduction.