[Spatial structure characteristics of plain ecological plantation in Tongzhou District, Beijing, China]. / 北京通州平原生态林空间结构特征.

Forest spatial structure (FSS) directly reflects resource competition and growth space distribution among different trees. The characteristics of FSS play an important role in mastering the growth status of ecological forest, formulating stand structure regulation measures, and improving forest quality and ecological services. In this study, seven plain ecological plantations including Pinus tabuliformis, Fraxinus chinensis, Salix matsudana, Populus tomentosa, Sophora japonica, Robinia pseudoacacia, and Salix babylonica in Tongzhou District, Beijing were selected as the research objects. The spatial structure characteristics of plain ecological plantations were evaluated by aggregation degree, angle index, neighborhood comparison, open degree, canopy index, competition index, edge benefit, and spatial structure comprehensive index. The horizontal distribution pattern of stand was well, with the aggregation degree of 0.32-1.41, the angle index of 0.4, and the neighborhood comparison mainly around 0.5. The vertical distribution pattern of stand was not well and needed to be improved, with the open degree of 0.19-0.52, most canopy indexes of about 0.7. The competition index presented a high competitive status with the all values of >50. Except the comprehensive evaluation index of R. pseudoacacia plantation presented in grade Ⅲ, the other six kinds of plain ecological plantations fell to grade Ⅱ, with low stand openness and low vitality. The comprehensive evaluation indices of FSS followed the order of R. pseudoacacia > S. babylonica > P. tabuliformis > S. matsudana > F. chinensis > S. japonica > P. tomentosa.

Effects of soil water and heat relationship under various snow cover during freezing-thawing periods in Songnen Plain, China.

In this study, the spatial variations of soil water and heat under bare land (BL), natural snow (NS), compacted snow (CS) and thick snow (TS) treatments were analyzed. The relationship curve between soil temperature and water content conforms to the exponential filtering model, by means of the functional form of the model, it was defined as soil water and heat relation function model. On this basis, soil water and heat function models of 10, 20, 40, 60, 100, and 140 cm were established. Finally, a spatial variation law of the relationship effect was described based on analysising of the differences between the predicted and measured results. During freezing period, the effects of external factors on soil were hindered by snow cover. As the snow increased, the accuracy of the function model gradually improved. During melting period, infiltration by snowmelt affected the relationship between the soil temperature and moisture. With the increasing of snow, the accuracy of the function models gradually decreased. The relationship effects of soil water and heat increased with increasing depth within the frozen zone. In contrast, below the frozen layer, the relationship of soil water and heat was weaker, and the function models were less accurate.