降水、土壤水分和结皮对人工梭梭(Haloxylonammodendron)林的影响

通过对石羊河下游沙井子地区不同立地类型、不同林龄人工梭梭林的大范围调查和定位观测研究，分析了主要生态因子降水、土壤水分和结皮对人工梭梭种群及其群落的影响。结果表明，梭梭对降水下限要求不严，但对降水上限有较为严格的要求，180mm降水量是建立人工梭梭林的上限；石羊河流域现存人工梭梭林基本依靠降水生存，但非连续同向的年际降水波动变化，对人工梭梭种群无明显影响，却显著影响梭梭林中草本植物物种组成、种群数量和生物产量。土壤水分是影响人工梭梭林最关键、最直接的生态因子，风沙土土壤含水率低于0．824％，梭梭死亡，介于0．824％-1．30％之间，处于退化状态，高于1．30％，生长正常；土壤水分限制梭梭生长，而梭梭生长又会进一步加剧土壤水分下降，梭梭造林8a后土壤含水率降低到1．30％，14a后降至土壤调萎系数之下，30a后又恢复到1．30％并保持稳定，残存梭梭种群生长趋于正常。结皮在起到固沙和保护梭梭免遭风蚀的同时，明显限制水分下渗并引起土壤干旱，加速了人工梭梭林的退化，破坏结皮后土壤含水率逐渐增加；同时，结皮还改变了1年生植物的种类组成及其数量。

Effects of precipitation, soil water content and soil crust on artificial Haloxylon ammodendron forest

Based on the large-scale survey and positioning observation of Haloxylon ammodendron forest with various ages growing under different site conditions in Shajingzi region at the downstream of Shiyang River,this paper studied the effects of ecological factors as precipitation,soil water content and soil crust on the artificial H.ammodendron population and communities.Result shows that H.ammodendron is not restricted by the minimum threshold of precipitation,while restricted by the maximum threshold of precipitation,180mm.At present,artificial H.ammodendron in the downstream of Shiyang River is basicly relying on precipitation.However,the annual discontinuous rainfall with similar intensity will not apparently affect the growth of artificial H.ammodendron population,whereas will significantly affect species composition,quantity of plant population and biomass of herbs in H.ammodendron forest.Soil water content is the essential ecological factor affecting artificial H.ammodendron forest.H.ammodendron will die when water content in aeolian sandy soil is less than 0.824%;and degenerate when water content is between 0.824% to 1.30%;and grow normally when water content is above 1.30%.The growth of H.ammodendron,restricted by soil water content,will aggravate the loss of soil water.Soil water content reduced to 1.3% after 8 years of afforestation of H.ammodendron;reduced to less than the wilting coeffcient 14 years later;but increased to 1.30% 30 years later,when the remaining H.ammodendron population can grow normally.Soil crust,especially physical crust,played an important role on fixing sand and protecting H.ammodendron from erosion,but simultaneously,it restricts infiltration,which will result in soil drought,and accelerate degeneration of artificial H.ammodendron.With undermined soil crust,soil water content will increase gradually.Comparing with bare mobile sand dunes,soil crust has significantly changed the composition and the quantity of species in H.ammodendron forest.