江西千烟洲试验区大气降雨及人工林树干茎流特征

对中国科学院千烟洲试验区大气降水特征及人工林树干茎流进行了研究,结果表明:年降雨量大部分集中在3～9月份,其中以5月份最大,日降雨量低于5.0mm的小雨较多。以木荷林的干流量最大,为100.54mm,其次是蓝桉,为66.96mm,其它的顺序分别是:枫香41.21mm、喜树36.73mm、苦楝28.26mm,湿地松最小,为15.97mm。6种森林类型干流量的月际变化基本上都是随着降水量增加而增加,其中以木荷林较为明显。但是各森林类型的干流率则大致相同,有时降水量增大干流率反而减少,如2月份降水量仅8.3mm,6种森林类型的干流量分别只有0.57mm、0.39mm、0.03mm、0.16mm、0.12mm和0.41mm,干流率却分别达到6.87%、4.60%0.36%、1.93%、1.45%和4.94%;4月份的降水量达到了218.9mm,干流率却分别只有6.03%、2.61%1.05%、2.45%、1.87%和4.33%。

Changes of community characteristics of a broad-leaved-conifer mixed forest after selection cutting

The modification in structure, composition, and diversity, shrub, as well as herb strata ofPinus koraiensis-Tilia amurensis-Abies nephrolepis forest after 16a of selection cutting in northeastern China was studied. In the selection cutting forest, individuals with small DBH classes characterized size distribution. The virgin forest, on the other hand, was mainly composed of individuals having larger DBH classes. The density of dominant species and the species diversity at tree stratum in the selection-cutting stand was significantly larger than that of in the primeval forest. The shrub layer also showed a similar result. However, the herb layer had comparatively low species diversity. Large growing space and strong light in the artificial gaps must have provided opportunities for the species of shade tolerance or shade intolerance to establish on the stand. The juveniles of non-pioneer species, which were hardly found in highly shaded virgin forest, were also released by the disturbance. Regeneration in the selection-cutting stand was prompted by the disturbance, where the density of saplings occurred nearly 3 times as much as that in the virgin stand. The growth of shrub layer was improved due to the alteration in light condition. The projection volume of the herb layer was less affected. Restoration of a semi-virgin forest to the original status after selection cutting could be possible in several decades. However, for those subjected to clear cutting, it might take several centuries. In order to promote biodiversity, it is reasonable to practice selection cutting in communities for consisting of species with various levels of shade tolerance.

Structure and changes of broad-leaved-conifer-Korean pine mixed forest in Northeast China

The structure and species composition as well as their changes in a climax forest, dominated byPinus koraiensis-Tilia amurensis andFraxinus koraiensis, were observed with an interval of 10 years. The number of tree species was 16 in 1981, which was kept unchanged. Density was increased from 510 to 535 stems/hm2, and basal area from 35.19 to 38.17 m2/hm2. Average stand DBH remained nearly unchanged. The total mortality of the stand was very low, 0.61% per year.Fraxinus andPinus were declining in population size, the highest mortality rate for the former, and the largest death number for the latter.Tilia showed a rapid increasing of 14.9%, and the density of saplings (DBH 3-8 cm) was 71 stems/hm2, led the top among canopy-layer species.Acer mono, similar toTilia, showed a type of continuous regeneration which was represented by the reverse J-shape of DBH distribution and compensation ability to mortality. Sub-canopy species such asAcer pseudo-sieboldianum, Maackia amurensis etc. presented a stable status by self-maintenance. Based on the fact of the decreasing of dominant populations, it is predicted that the composition of the community was changing gradually, the rising of broad-leaved components versus the declining of coniferous species.