[Effects of human disturbance on coarse woody debris of Larix gmelinii forest on northern slope of Greater Hinggan Mountains].

An investigation was conducted on the living tree volume, coarse woody debris (CWD) loading, and composition of Larix gmelinii forest along a human disturbance gradient, i.e., no disturbance (natural larch forest), one-time disturbance (natural forest was disturbed once only), and two-time disturbance (natural forest was disturbed two times consecutively), on the northern slope of Greater Hinggan Mountains. The results showed that under no disturbance, one-time disturbance, and two-time disturbance, the average living tree volume of L. gmelinii forest was 161.6, 138.3, and 114. 8 m3 x hm(-2), and the average CWD loading was 69.77, 36.64 and 32.61 m3 x hm(-2), respectively. In natural L. gmelinii forest, most of CWD was of 20-40 cm diameter class, among which, fallen logs occupied 72%, and snags and stumps occupied 28% ; while in one-time and two-time disturbance L. gmelinii forests, most CWD was of 10-30 cm diameter class, with the fallen logs, snags, and stumps occupied 70%, 14% and 16%, and 57%, 15% and 28%, respectively. Human disturbance reduced the CWD loading of L. gmelinii forest and altered the composition of the CWD.

[Effects of heavy machinery operation on the structural characters of cultivated soils in black soil region of Northeast China].

With the cultivated soils in black soil region of Northeast China as test objects, this paper measured their structural characters such as soil strength, bulk density, and non-capillary porosity/capillary porosity (NCP/CP) ratio before and after heavy and medium-sized machinery operation, aimed to study the effects of machinery operation on the physical properties of test soils. The results showed that after machinery operation, there existed three distinct layers from top to bottom in the soil profiles, i.e., plowed layer, cumulative compacted layer, and non-affected layer, according to the changes of soil strength. Under medium-sized machinery operation, these three layers were shallower, and there was a new plow pan at the depth between 17.5 and 30 cm. Heavy machinery operation had significant positive effects on the improvement of topsoil structure (P < 0.05). After subsoiling and harvesting with heavy machinery, the bulk density of topsoil decreased by 7.2% and 3.5%, respectively, and NCP/CP increased by 556.6% after subsoiling, which would benefit water infiltration, reinforce water storage, and weaken the threat of soil erosion. The main action of heavy machinery operation was soil loosening, while that of medium-sized machinery operation was soil compacting.