Seamless integration of above-and undercanopy unmanned aerial vehicle laser scanning for forest investigation

Background:Current automated forest investigation is facing a dilemma over how to achieve high tree-and plotlevel completeness while maintaining a high cost and labor efficiency.This study tackles the challenge by exploring a new concept that enables an efficient fusion of aerial and terrestrial perspectives for digitizing and characterizing individual trees in forests through an Unmanned Aerial Vehicle(UAV)that flies above and under canopies in a single operation.The advantage of such concept is that the aerial perspective from the above-canopy UAV and the terrestrial perspective from the under-canopy UAV can be seamlessly integrated in one flight,thus grants the access to simultaneous high completeness,high efficiency,and low cost.Results:In the experiment,an approximately 0.5 ha forest was covered in ca.10 min from takeoff to landing.The GNSS-IMU based positioning supports a geometric accuracy of the produced point cloud that is equivalent to that of the mobile mapping systems,which leads to a 2–4 cm RMSE of the diameter at the breast height estimates,and a 4–7 cm RMSE of the stem curve estimates.Conclusions:Results of the experiment suggested that the integrated flight is capable of combining the high completeness of upper canopies from the above-canopy perspective and the high completeness of stems from the terrestrial perspective.Thus,it is a solution to combine the advantages of the terrestrial static,the mobile,and the above-canopy UAV observations,which is a promising step forward to achieve a fully autonomous in situ forest inventory.Future studies should be aimed to further improve the platform positioning,and to automatize the UAV operation.

Effect of microenvironmental quantitative regulation on growth of Korean pine trees planted under secondary forest

Korean pine（Pinus koraiensis） and broadleaved mixed forest in Northeast China has been changed regressively into secondary forest with almost no conifers.Planting Korean pine trees under the canopy of secondary forest is a feasible approach for recovering Korean pine and broadleaved mixed forest.For establishing an effective growth promotion method for under-canopy planted young Korean pine trees,two stands were selected as the experiment plots,Stand A（planted in 1989） and Stand B（planted in 1982）,and an experiment of microenvironment regulation was conducted relying mainly on Opening degree（K=1,K=1.5,K=2,CK） in 2004.The results were shown that the adjustment had promoted growth of diameter and height of Korean pine planted in Stand A and Stand B,and had a significant influence on the growth rate of basal diameter,diameter at breast height and height in the two growth stands.The four years periodic increment of mean diameter and height of Korean pine planted in 1989 and in 1982 after regulation in K=1 level were 63.4%（D0） and 82.7%（H）,64.8%（D1.3） and 69.7%（H） higher than that of control respectively.Quantitative regulation had significant influence on specific leaf area of Korean pine planted in 1989,and the current year specific leaf area（SLA） was lager than perennial year SLA.Quality indexes of natural pruning capacity,normal form quotient and crown size was not significantly changed but shown a positive tendency.The regulation scheme of Opening degree K=1 might be proper for adjusting the microenvironment of Korean pine trees planted under the canopy of secondary forest when the Korean pine trees were in the growth period of 15 to 26 years old in the experiment region.