降水量对商州飞播油松成苗效果影响

陕南秦巴山地立地条件复杂，降水量对飞播成苗效果作用表现各异。在汉中和安康降水量与飞播油松成苗效果关系研究的基础上，利用1997年商州飞播油松成苗期有苗样方频度和成苗量调查数据，采用相关分析法和逐步回归模型分析法，分析成苗效果与降水量的关系。结果表明，春夏连旱频发掩盖了年降水量的作用，使商州油松成苗效果与年降水量无显著性相关。冬季土壤表层结冻导致油松幼苗生理缺水使成苗效果与月降水量呈负相关。春季林木开始生长，对水分需求增加，而降水量少，成苗效果与月降水量呈正相关；植被和土壤类型差异导致相关度产生地域变化。造林成苗效果与3月和5月降水量呈极显著正相关，与4月降水量相关不显著。暴雨和伏旱发生频次及强度是盛夏季节油松成苗效果与降水量关系变化的主要原因。成苗效果与6月降水量均呈极显著负相关，与8月降水量极显著正相关。因秋季多雨，土壤水分满足苗木生长，成苗效果与降水量多呈极显著负相关。说明飞播油松成苗效果不仅取决于年降水量，而且与当地降水量的分布密切相关。在当地降水量范围内，多效抗旱驱鼠剂（RPA）拌种处理的模型值均大于对照，证明RPA拌种能提高单位降水量的油松有苗样方频度和成苗量，且作用稳定。

Influence of Rainfall on Effective Grown-up Seedlings of Pinus tabulaeformis for Aerial Seeding in Shangzhou County

Site conditions in Qinba Mountains in Southern Shaanxi were complex,after aerial seeding,the precipitation effects on the grown-up seedlings were different.Previously,we reported the relationship between precipitation and effective grown-up seedlings for Pinus tabulaeformis after the aerial seeding in two places: Hanzhong and Ankang.In present study,we now reported the relationship between precipitation and effective grown-up seedlings for Pinus tabulaeformis after the aerial seeding in Shangzhou by using the data of the frequentness of sample plots with available seedlings and the quantity of available seedlings of Pinus tabulaeformis during grown-up seedlings period in 1997 after aerial seeding.Correlation analysis method and the stepwise regression model analysis method were adopted.The results showed that the effect of precipitation was covered by the frequent spring and summer drought,as a result,the effective grown-up seedlings of P.tabulaeformis correlated with annual precipitation was not significant in Shangzhou.In winter,soil surface freezing caused the physiological water scarcity of P.tabulaeformis seedlings which resulted in the negative correlation between effective grown-up seedlings and monthly rainfall.Trees started to grow in the spring,which led to the increase of demand for water,and less precipitation,effective grown-up seedlings and monthly precipitation were positively correlated.However,vegetation and soil type differences led to relevant geographical changes.In Shangzhou and Ankang,effective grown-up seedlings were most significantly and positively correlated with precipitation in March and May,and not significant in April.In Hanzhong,March to May were highly significantly positive correlation was found between grown-up seedlings and precipitation during March to May.In the season of midsummer,heavy rain and summer drought occurrence frequency and intensity were the main reason that changed the correlationship of effective grown-up seedlings and rainfall.In three places,effective grown-up seedlings was most significantly and negatively correlated with precipitation in June.In Shangzhou,positive correlation with precipitation in August was significant,in Hanzhong,were highly significant positive correlation with precipitation in July and August was found.In autumn,rainfall was rich,soil moisture content could meet seedlings growth,effective grown-up seedlings and precipitation showed significantly negative correlation mostly.The results demonstrated clearly that effective grown-up seedlings of P.tabulaeformis with aerial seeding not only depended on the local annual precipitation,but also closely related with the local precipitation distribution.In three places,the RPA model values were larger than the control,which proved that seeds dressed by RPA could improve of the frequentness of sample plots with available seedlings and the quantity of available seedlings of P.tabulaeformis in the unit precipitation,and its effect was stable.