黄土高原沟壑区不同树种的水土保持效益及其适应性评价

Soil and water conservation benefits and suitability of different forestation trees in tableland-gully area of the Loess Plateau

【目的】研究黄土高原沟壑区不同树种幼林的水土保持效益及其适应性。【方法】以草地为对照，对黄土高原沟壑区刺槐、油松、沙棘、侧柏纯林及其混交林径流小区的产流产沙情况、土壤水分状况及各树种的生理特性进行了分析。【结果】造林初期，各树种及其不同造林方式的水土保持效益均比较差，处于水土保持功能低下阶段，土壤侵蚀的差异主要是由植被的不同覆盖度引起的，二者呈二次多项式关系；回归分析表明，当覆盖度达53％时土壤侵蚀较为轻微。草地和各树种林下0-250cm土层土壤水分变化较大，其中以刺槐消耗土壤水分最多，其次是侧柏，油松、沙棘和草地之间差异不明显；刺槐纯林与其混交林下土壤水分的差异比较明显，而其他树种不同造林方式下的土壤水分无明显差异。各树种叶片的水分利用效率表现为侧柏〉油松≈沙棘〉刺槐，油松与沙棘混交造林后两者的水分利用效率都有显著提高；各树种叶片的蒸腾速率表现为刺槐≈沙棘〉油松〉侧柏，沙棘与油松或刺槐混交后，油松与刺槐的蒸腾速率均有所降低，而沙棘变化不显著。【结论】综合考虑树种的水保效益及其适应性可以发现，沙棘与油松混交可能是黄土高原沟壑区较为适宜的一种造林方式。

[Objective] Soil and water conservation benefits and suitability of different young afforested trees were evaluated in tableland-gully area of the Loess Plateau. [Method] The runoff, soil erosion, soil water content and physiological characteristics of, mono-species of R. pseudoacacia, P. tabulaeforrnis, 19. orientalis, H. rhamnoides and their mixtures in vegetated runoff plots were analyzed taking grassland as a control. [Result] The results demonstrated that in the early stage of afforestation, the benefits of water and soil conservation were relatively poor for all afforested tree species and afforestation methods. The differences of soil erosion amounts between each tree species under monoculture or biculture resulted from differences in vegetation cover. The relationship between soil erosion and vegetation cover could be expressed by a quadratic function. Regression analysis showed that soil erosion was not severe when vegetation cover was more than fifty percent. Soil water content varied with the soil depth within the top 250 cm in grassland and each woodlot,but it became more or less constant below the 250 cm depth. R. pseudoacacia consumed most soil water,followed by P. orientalis, P. tabulaeformis,and H. rhamnoides with the last two being similar to the grassland. There were no significant differences in soil water contents between monospecies and its binary mixtures,except for R. pseudoacacia and its mixtures. Water use efficiency followed the order of： P. orientalis 〉 P. tabulaeformis ≈H. rhamnoides 〉 R. pseudoacacia. The leaf water use efficiencies of both P. tabulaeformis and H. rhamnoides in the mixture were significantly increased compared to the monocultures. The leaf transpiration rates followed the order of：R. pseudoacacia ≈H. rhamnoides 〉 P. tabulae-formis 〉 P. orientalis. Compared to their monocultures, the leaf transpiration rates of P. tabulaeformis and R. pseudoacacia decreased in their biculture mixed with H. rhamnoides, while the transpiration rates of H. rhamnoides remained relatively constant. [Conclusion] Considering soil and water conservation benefits and adaptability of each tree species,we could conclude that the biculture of H. rhamnoides and P. tabulae-formis is very likely suitable for afforestation in tableland-gully areas of the Loess Plateau.