地形对陕北黄土区衰退沙棘人工林天然更新的影响

Modeling the Effects of Topography on the Natural Renewal of Declining Sea-buckthorn Forest in Loess Plateau of Northern Shaanxi Province

[目的]为揭示陕北黄土区衰退沙棘人工林天然更新的地形适生范围。[方法]通过调查陕西省吴起县沙棘人工林大面积衰退及死亡后的天然更新状况,以68个样方的更新率、成林率及每木数据(株高、地径等)作为更新恢复能力的衡量指标,运用方差分析、回归拟合及系统聚类分析等方法,分析了沙棘更新恢复能力与各地形因子的关系。[结果](1)各坡向沙棘更新率差异显著(P=0.018),沙棘更新率均值阴坡>半阴坡>半阳坡>阳坡,阴坡更新生长状况最好,半阴坡更新幼株数量大,存活率较高;(2)坡度对更新率无显著影响,但更新率在阴坡缓坡、极陡坡范围内出现峰值,在阳坡条件下随坡度上升而减小;(3)总体上衰退沙棘人工林天然更新的地形条件是阴坡、半阴坡;(4)坡面微地形对衰退沙棘人工林更新具有显著影响(P=0.038),缓台较好,陡坎较差。[结论]半干旱黄土区部分衰退沙棘人工林可自行完成天然更新,部分恢复困难,需人工辅助或重新栽植适合的树种。阴坡、半阴坡的衰退沙棘幼株种群生长状况较好且基本能更新成林,阳坡、半阳坡的生长状况较差且难以更新成林;阴坡坡向条件下,坡度对沙棘更新率的影响程度随着坡度上升而变小,阳坡坡向条件下坡度对更新率的影响较小。衰退沙棘人工林更新率因所处微地形不同而存在差异。处于缓台的衰退沙棘幼株种群基本能更新成林,浅沟的沙棘幼株种群与所处的原状坡面上的更新状况相似,部分能更新成林,处于陡坎的沙棘幼株种群基本不能更新成林。

To illustrate the topographic condition of natural renewal of declining Sea-buckthorn （Hippophae rhamnoides） forest in Loess Plateau of northern Shaanxi Province.[Method]The relations between recovery ability of sea-buckthorn and terrain factors were analyzed based on an investigation of natural regenerative condition of Sea-buckthorn forest after large-area death in Wuqi County, Shaanxi Province, by using renewal rate, reforestation percentage and tally data （height and basal diameter） from 68 quadrates as standard to measure the value of recovery ability, and also by using one-way Anova method of square-deviation （SD）, regression fitting and systematical clustering method.[Result]（1）The renewal rate of sea-buckthorn showed significant different in various slopes （P=0.018）. The average of renewal rate may be ranked in the order of shady slope 〉 semi-shady slope 〉 semi-sunny slope 〉 sunny slope. The best growth status of seeding population was in shady slope while the condition with a high survival rate and a huge amount of renewal young trees were in semi-shady slope. （2） Gradient has no significant effect on renewal rate. The renewal rate of sea-buckthorn showed the first peak （gentle slope） and the second peak （extremely steep slope） on shady slope, while the renewal rate gradually decrease with the grade increase of slope on sunny slope. （3） The topographic conditions of natural renewal of declining Sea-buckthorn forest were shady slope and semi-shady slope. （4） Micro-relief has a significant impact on natural renewal of declining Sea-buckthorn forest （P=0.038）, platform was better while scarp was poor. [Conclusion]A portion of declining sea-buckthorn populations are difficult to recover spontaneously while they require manual assistance or alternative plants instead in Loess Plateau.