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.

Recovery of saturated hydraulic conductivity along a forest successional series from abandoned land to mature, evergreen broad-leaved forest in eastern China

Saturated hydraulic conductivity (Ks) can be used to indicate changes in soil hydrology resulting from vegetation succession. A constant-head permeameter was used to investigate differences in Ks at five soil depths (10, 20, 40, 60, and 80 cm) along a successional sequence of 155 years in evergreen broad-leaved forest at Tiantong National Forest Park, eastern China. The following six forest successional classes were studied: climax evergreen broad-leaved forest (CE), sub-climax evergreen broad-leaved forest (SE), evergreen broad-leaved mixed coniferous forest (MF), coniferous forest (CF), secondary shrub (SS), and abandoned land (AL). Surface Ks (the geometric mean of Ks at 10 and 20 cm soil depths) significantly increased from AL to CE but declined in CF. The surface Ks value under CE was higher than under other successional stages (CE 271 mm h–1, AL 58 mm h–1, SS 124 mm h–1, CF 90 mm h–1, MF 170 mm h–1, SE 231 mm h–1), and was 4.7 times greater than under AL, 2.2 times greater than under SS, and 3.0 times greater than under CF, but showed no significant difference from SE (P > 0.05). Vertical difference of Ks was detected up to a soil depth of 40 cm along forest successional series. Macroporosity was the main determining factor and played an important role in the process of Ks recovery. The likelihood of overland flow generation was inferred by comparing Ks at soil depths of 10, 20, 40, and 60 cm under the various successional stages at prevailing storm intensities. Overland flow was most likely to occur in the early successional stages. This study suggests that Ks could be restored to climax forest levels along forest successional series, but the recovery time could be as long as 95 years.

Scarcity of sites suitable for nesting promotes plesiobiosis in ants (Hymenoptera: Formicidae)

Plesiobiosis is a rudimentary form of social symbiosis. It consists of the close proximity of nests of different social insect species. Numerous cases of plesiobiosis between ant species observed in a successional series of rocky habitats in S Finland are listed and themost interesting of them are described in detail. Among all Lasius colonies found within the whole successional series studied, as many as 8.4% were plesiobiotically associated with other ants. In the two earliest successional stages: the shoremeadow and the open rocky outcrop, the proportion was nearly 12% and 10% respectively. The finding of numerous plesiobiotically related nests there is discussed in the context of the unique local habitat conditions.