岷江上游花椒地/林地边界土壤水分影响域的定量判定

Quantitative determination of the depth of edge influence on soil moisture in pepper-forest boundary of Minjiang River upper reaches.

在岷江上游干旱河谷区，选取典型的花椒地／林地边界，利用TDR仪测定干旱条件下、雨后和每月0～15cm土层水分含量，并用移动窗口法判定土壤水分的边界影响域，结果表明，若用移动窗口法对土壤水分的边界影响域进行判定，当窗口宽度为8—12时，边界影响域较易判定．年内土壤水分随时间变化而变化．这种变化可分为土壤水分上升期、高峰期和消退期3个时期．干旱条件下土壤水分的边界影响域较小，其宽度约从花椒地6m到林地2m；雨后土壤水分的边界影响域有较大增加，其宽度约从花椒地12m到林地2m；年内土壤水分的边界影响域宽度约从花椒地10m到林地2m之间变化．不同季节土壤水分的边界影响域不同，并随着季节的变化呈动态变化．从生态学意义上讲，岷江上游地区目前进行的将花椒地退耕成林地、栽植树苗的措施是不可取的，该区退耕还林的最好方法应该是退耕，使其灌木林或草本植物自然生长．

A typical pepper-forest boundary was selected in the arid valley of Minjiang River upper reaches, and the moisture content in 0-15 cm soil layer was determined by time-domain reflectometry （TDR） during drought, after rain, and different seasons. Moving split-window techniques （MSWT） was employed to detect the depth of edge influence （DEI） on soil moisture and its dynamic variation with time. The results showed that the changes of squared Euclidean distance （SED） curve on the graph tended to become stable when the window width reached 8 - 12, and DEI could he detected. The seasonal variation of soil moisture could be divided into three periods, i. e. , rising period （January to April）, peak period （May to October）, and lessen period （November to December）. DEI was smaller during drought, and increased after rain. The DEI on soil moisture ranged from 6 m in pepper field to 2 m in forest during drought and from 12 m in pepper field to 2 m in forest after rain, but ranged from 10 m in pepper field to 2 m in forest field within a year. DEI was different in different seasons, and was dynamic. Under such condition of soil moisture, tbe forest restoration from pepper land and the seedling planting were not ecologically reasonable. Reducing human disturbance and revegetating with natural shrubs and meadows could be more effective for vegetation conservation in the arid valley of Minjiang River upper reaches.