不同强度间伐对北京山区油松生长及其林下植物多样性的影响

Effects of Thinning on the Growth and the Diversity of Undergrowth of Pinus tabulaeformis Plantation in Beijing Mountainous Areas

2005年和2006年夏季,对北京密云水漳村和昌平小宫门低山阴坡厚土油松人工林林分的生长及其林下植物多样性变化情况进行抚育间伐后的调查研究。结果表明:间伐后第1、2年,油松林分平均胸径、树高、冠幅、单株材积和蓄积量显著高于对照,但各强度间伐林分之间生长差异不显著;而间伐后第6年,油松林的各项生长指标均表现为强度间伐>中度间伐>弱度间伐>对照,且中度、强度间伐显著大于对照和弱度间伐,强度间伐后林分生长效果最好;林下植物种类、数量、多样性指数、均匀度指数和林下植物总生物量在间伐后第1、2年都随着间伐强度的增加而升高,间伐后第6年,不同强度间伐下油松林的植物种类、多样性指数、均匀度指数均比间伐后第1、2年有所降低,弱度、中度、强度间伐后的林下植物种类比对照分别增加了5、10和18种,多样性指数仍表现为强度间伐>中度间伐>弱度间伐>对照;各强度间伐后林下植物的密度较间伐初期有所减少,植物盖度仍随间伐强度加大而增加,强度间伐后,可明显看出林下植物的结构层次;中度、强度间伐使林下需水性强的植物比例增加,促使油松人工林林下植物向中旱生、中生植物转变;随着间伐强度的增大,油松林林下植物总生物量也增加,且各强度间伐的林下植物总生物量表现为间伐后第6年>第2年>第1年;间伐后第6年,弱度、中度和强度间伐的林下植物总生物量与对照相比,分别增加了29.1%、45.2%和70.9%。间伐对油松林分的生长及其林下植物多样性的影响是显著的,对于北京低山阴坡厚土35～37年生密度为3200～3467株.hm-2的油松人工林而言,强度间伐最有利于林分的生长和林下植物多样性的提高,经营密度宜为1240～1500株.hm-2。

The Pinus tabulaeformis plantation is a low and middle hill type of the zonal vegetation and is distributing in the low hill shade slope and half shade slope in Beijing mountainous areas. Due to a generally high stand density and the lag of tending, the forests could not grow well and the general quality of the stand is in poor condition. The ecological functions of the plantation therefore cannot be fulfilled. In order to investigate the dynamic variance of the undergrowth and to provide reference for reasonable thinning, in 2000 and 2004, 24 sample plots in the low hill shade slope with thick soil were selected in Beijing mountainous areas and the light, medium and heavy thinning, pruning, and bushing were conducted on each sample plots respectively. In the summers of 2005 and 2006, the changes of the growth and the undergrowth diversity of the P. tabulaeformis were investigated and analyzed. The results showed： In the 2^nd year after thinning, the DBH, height, crown length, individual volume and stocking of the tending group were significantly higher than that of the control group, while no clear evidence was observed regarding the variance on growth of the P. tabulaeformis among the light thinning, medium thinning and heavy thinning groups. In the 6^th year after thinning, the growth of the P. tabulaeformis of the 3 groups were ranked in such order： heavy thinning 〉 medium thinning 〉 light thinning; the growth of medium and heavy thinning groups were much better than that of the light thinning group and the control group; and the heavy thinning group obtained the best growth; In the first 2 years of thinning, the species and quantity of the undergrowth, Simpson index, Shannon-Wiener index, Evenness index and the total amount of the undergrowth biomass all increased along with the enhancing of the thinning; In the 6th year after thinning, The species, Simpson index, Shannon-Wiener index and Evenness index all depressed and the species number increased 5, 10 and 12 respectively ; For the Simpson index and Shannon-Wiener index, the 3 groups were ranked under the order： heavy thinning 〉 medium thinning 〉 light thinning. Compared with the first 2 years after thinning, the quantity of the undergrowth was decreased for every group, but the undergrowth eoverage was increased as the thinning was enhancing, and the eommunity vertieal strueture became much clearer for the heavy thinning group. Besides, the medium and heavy thinning increased the ratio of the highly water demanded plants, and had an effect of turning the undergrowth to meso-xerophytes and mesophytes; After the thinning, the total amounts of the undergrowth biomass were increased as the thinning was enhancing and were ranked in sueh order： 6^th year 〉 2^sd year 〉 1^st year. In the 6^th year after thinning, the undergrowth biomass are increased by 29.1% , 45.2% and 70.9% respectively for the light thinning group, medium thinning group and heavy thinning group; Thinning has a significant effect on the growth and diversity of undergrowth of the P. tabulaeformis plantation; It would improve the plantations in Beijing mountainous area turning to a sustainable development pattern. For inereasing the growth and diversity of undergrowth, the heavy thinning has the best effect, and the appropriate stand density for the Pinus tabulaeformis plantations, on 35 -37 a shady slope with thick soil and an original density of 3 200 - 3 467 tree· hm^- 2, is 1 240 - 1 500 tree· hm^- 2.