Estimating Stem Volume Using QuickBird Imagery and Allometric Relationships for Open Populus xiaohei Plantations

There has been a great deal of interest in studying the crown of trees using remote sensing data. In this study, crown width was extracted from high-resolution QuickBird images for open Populus xiaohei plantations. Regression models for predicting the individual stem volumes of Populus xiaohei were established using extracted crown width, as well as estimated tree parameters （i.e. diameter at breast height [DBH] and tree height） as predictors. Our results indicated that crown width could be accurately extracted from QuickBird images using a multi-scale segmentation approach with a mean relative error of 5.74%, especially for wide-spacing stands. Using either extracted crown width alone or with estimated DBH and tree height can successfully estimate individual stem volume of Populus xiaohei with the R2 value ranging from 0.87 to 0.92 depending on different model forms. In particular, the two second-order polynomial models （model 2 and model 6）, based on QuickBird image-derived crown widths and estimated DBH and tree heights, respectively, were the best at describing the relationship between stem volume and tree characteristics.

Changes in and evaluation of surface soil quality in Populus×xiaohei shelterbelts in midwestern Heilongjiang province,China

To examine changes in surface soil quality over time in Populus×xiaohei shelterbelts,we collected soil samples from five shelterbelts of different ages and also from former cropland left fallow for 25 years.Twenty-one surface soil(0–20 cm)properties were measured,and variation in soil quality was assessed using one-way ANOVAs and multiple comparison tests.Based on this analysis,16 soil indexes were used in a model evaluating soil quality,with each index given weight as determined by the correlation coefficient.Compared with the control,the postmature forest had greater soil moisture content but lower bulk density(P<0.05).The mature forest also had higher soil pH,total organic carbon,alkali-hydrolyzed nitrogen,available phosphorus,and biomass nitrogen content,but reduced nitrate-nitrogen and total phosphorus content than the control(P<0.05).Total porosity was highly positively correlated with aeration,nitrate-nitrogen,alkali-hydrolyzed nitrogen,available phosphorus,microbial biomass carbon and microbial biomass nitrogen.Soil total organic carbon,ammonium nitrogen,nitrate-nitrogen,alkali-hydrolyzed nitrogen,total nitrogen,available phosphorus,microbial biomass carbon and microbial biomass nitrogen were all strongly correlated.In the soil quality evaluation model,total organic carbon was assigned the highest weight and total potassium content the lowest.The soil quality index was lowest in the near-mature forest and greatest in the postmature forest.Generally,soil quality in P opulus×xiaohei shelterbelts varied with age and was higher in the 10–20 cm versus 0–10 cm soil layer.After a single forest generation,surface soil quality was significantly improved.