黄土丘陵半干旱区柠条林密度对土壤水分和柠条生长的影响

研究密度对土壤水分和植物生长的影响对森林植被恢复和生态建设具有重要的意义。以黄土丘陵半干旱区人工柠条为研究对象,对相同立地条件下不同密度柠条林生长与林地土壤水分进行了长期定位观测和分析。研究表明,1—5年生柠条不同密度林地土壤水资源量差异显著,从第3年开始,土壤水资源量随着密度增加而增加;10—12年生柠条密度越低土壤水资源量越高(Treatment4除外,T4),不同密度之间水资源量差异不显著。1—3年生柠条密度越高会促进其株高生长;从第四年开始,柠条密度过高会抑制其株高生长;1—5年生柠条密度越高基径生长越快,不同密度生长差异不显著;10—12年生密度过高(Treatment1,T1)或过低(T4)均会抑制柠条株高与基径生长。在柠条播种后第5年,高密度试验小区(T1和Treatment2,T2)柠条林地最大入渗深度土壤水资源量降到水资源利用限度,此时需要依据土壤水分植被承载力通过平茬来降低林分密度,以达到减少土壤水分消耗和可持续利用土壤水资源之目的。

The effects of plant density on soil water and plant growth on semi-arid loess hilly region

Caragana korshinskii Kom. is widely distributed on the Loess Plateau, China, and it is a very ecologically adaptable shrub with an extensive root system capable of adsorbing large amounts of water and resistant to adverse environmental conditions. Moreover, Caragana korshinskii Kom. is the main shrub species for semi-arid loess hilly region to create of soil and water conservation forest. Therefore, it is necessary to explore the influence of Caragana korshinskii Kom. on the soil water resources in semi-arid loess hilly region. Plant density is one of the most important factors affecting the soil water resources, there are many studies on relationship between plant density and soil water resources, and also some researches about the effect of plant density on plant growth. However, rather less attention has been paid to the effect of plant density both on plant growth and soil water resources. The influence of density on soil water and plant growth has great significance on forest vegetation restoration and ecological construction. The effects of Caranaga korshinskii Kom. forest density on plant growth and soil water volumetric content under the same site condition were conducted by long-term in-situ observation and analysis. The results showed that there are significant differences between the different density treatments of 1 to 5-year-old Caranaga korshinskii Kom. woodland. The soil water resources increased with the increase of plant density from the third year. However, the Soil water resources were negatively correlated to plant density of 10 to 12-year-old Caranaga korshinskii Kom. treatment (except Treatment 4,T₄) and the differences between the different density treatments were not significant. The plant height growth was positively correlated to plant density for 1 to 3-year-old Caranaga korshinskii Kom. treatments. The excessive high density restrained the plant height growth from the fourth year. The basal diameter increased with increasing density of the 1 to 5-year-old Caranaga korshinskii Kom. woodland, but the differences caused by density were not significant. The plant height and basal diameter growth were both restrained under the condition of excessive high(Treatment1,T₁) or low density(T₄) of 10 to 12-years-old Caranaga. The soil water resources of the maximum infiltration depth layer in high-density experimental treatment (both T₁ and Treatment 2,T₂) dropped to the soil water resource use limit at the fifth year of Caranaga korshinskii Kom. growth, meanwhile, the plant density should be reduced by cutting according to the soil water carrying capacity for vegetation in order to reduce the soil water consumption and realizing the sustainable utilization of soil water resources in this situation.