[Analysis on Spatial-temporal Characteristics and Driving Factors of PM in Heilongjiang Province in the Past 20 years].

PM is an important indicator for measuring the degree of air pollution. Studying the space-time variation and the driving factors of spatial heterogeneity is important for controlling air pollution and improving regional air quality. Based on PM remote sensing data from 2000 to 2021, the Theil-Sen Median trend analysis, Mann-Kendall significant inspection, and spatial auto correlation were used to analyze the characteristics of space-time changes in PM concentration, and geographical detectors were combined with a multi-scale geographical weighted regression model to explore the key driver factor and its influence and direction of the impact and role of PM spatial differences.

[Rainfall redistribution traits of three main forest types in Dagangshan Mountains of Jiangxi Province, China].

The redistribution processes of rainfall due to the canopy were studied on three typical forest types (Chinese fir forest, evergreen broad-leaved forest and Phyllostachys pubescens forest) in Dagangshan Mountains of Jiangxi Province. The results showed that from April to June, 2012, the total precipitation was 531.6 mm, with the maximum single rainfall of 61.

[Estimation of forest canopy closure by using partial least square regression].

Based on remote sensing and forest resources inventory data, this paper approached the feasibility of using Bootstrap approach to select optimal variables and using partial least square (PLS) regression to build a model for estimating forest canopy closure. The results showed that whether using a model built with all variables or a model with the optimal variables selected by Bootstrap approach, the relative deviation in estimating forest canopy closure was about 5%. The optimal variables selected in this paper differed greatly with those in the studies for other areas, suggesting that besides selection method, zonal vegetation and terrain could also induce the differences of selected optimal variables for the estimation of forest canopy closure.

[Quantitative estimation of vegetation coverage in Mu Us sandy land based on RS and GIS].

On the basis of oriented field investigation data and corresponding RS and GIS information, and by the method of ridge estimation, this paper studied the estimation model of vegetation coverage and its affecting factors in Yijinholo County of northeast Mu Us sandy land. The results showed that the vegetation coverage was affected by NDVI, and closely linked with such RS and GIS information as, TM7, TM2, TM 4/3 and gradient. Ridge estimation method could obviously improve the limitation of Least Square method, eliminate the adverse effects caused by existing complex estimation relation towards uncoiling undetermined parameter among the variables, and improve the estimate precision.

[Effects of forest harvesting on river runoff in Xiaoxing'anling].

By the method of runoff determination in large basin combined with contrast experiment in small watershed, and based on the runoff and forest resources data in past 35 years, this paper studied the serial changes of river runoff in Xiaoxing'anling after forest harvesting. The results showed that the river flow was increased in the early 10 years after forest harvesting, but decreased gradually with the growth and crown closure of artificial larch forest, tended towards or even lower than the level before harvesting. The river runoff had a close correlation with annual rainfall and the areas of forest harvesting and regeneration.