陕北刺槐林木生长及林下植被与土壤水分对种植密度的响应特征

Response Characteristics of Locust Growth,Understory Vegetation and Soil Moisture on Planting Density in Northern Shaanxi

以陕西省安塞县2000年左右退耕栽植的5种不同密度(830~3 330株/hm^2)刺槐林地为研究对象,分析不同栽植密度对刺槐林木生长、林下植被及土壤水分的影响,为黄土高原丘陵沟壑区刺槐人工林合理栽植密度的确定以及可持续经营提供理论依据。结果表明:(1)阳坡中不同密度间刺槐林木的胸径、树高、冠幅均差异显著;阴坡中2 500株/hm^2的刺槐林木平均胸径、树高与两个低密度林的差异显著,且平均冠幅与1 670株/hm^2差异显著,与2 000株/hm^2差异不显著。(2)当栽植密度为1 670株/hm^2时,刺槐林地水分含量相对较高,林下植被平均盖度及物种多样性也较高。(3)各栽植密度刺槐林地0~500cm土壤含水量均低于该地区土壤稳定湿度(12%)。(4)阳坡中3 330株/hm^2的林地0~500cm土层含水量仅为4.5%,土壤干旱化严重,而830株/hm^2的刺槐林地土壤水分为7.8%;阴坡中栽植密度为1 670~2 000株/hm^2的刺槐林地土壤含水量较高,为7.5%~8.2%。研究表明,在陕北黄土高原丘陵沟壑区,刺槐初始造林密度不宜超过1 670株/hm^2(株行距2m×3m),在进入刺槐生长高峰期后,应采取间伐管理以调整林分密度,使其维持刺槐人工林林地的稳定性与可持续性。

In order to explore the impact of planting density on the locust growth,understory vegetation and soil moisture on the Hillygullied Loess Plateau in northern Shaanxi,we observed and analyzed the locust woodland planted around2000with five different planting densities.The results show that:(1)in sunny aspect,the average DBH,tree height and crown between different densities were significantly different(P<0.05).In shady aspect the average DBH and tree height in the density of2500plants/hm2were significantly different from the another two lower densities.The average crown was significantly different from1670plants/hm2while insignificantly from2000plants/hm2(P>0.05).(2)Woodland soil moisture,cover of understory vegetation and species diversity were relatively higher under the density of1670plants/hm2.(3)Soil moisture in0~500cm depth of locust woodland with each density was lower than that of stable soil moisture(12%)in the study area.(4)In sunny aspect,soil moisture in0~500cm depth with density of3330plants/hm2was only4.5%,while the density of830plants/hm2reached7.8%,and the soil moisture with density of1670plants/hm2and2000plants/hm2was relatively higher in shady aspect,which was7.5%~8.2%.The study suggests that the initial planting density of locust should not be more than1670plants/hm2(spacing of2m×3m)in the hillygullied loess area and thinning management should be taken to adjust the stand density after entering the peak growth period in order to maintain the stability and sustainability of locust plantation.