Background The understory natural environment is critical in affecting the succession and recovery process of vegetation, stand structure, and species composition of forest. The thinning intensity could significantly change the forest microclimates and soil properties, therefore, to analyze the effects of thinning intensity on the understory natural environment of forest is of important significance for promoting the ecological benefits of thinning. Methods A total of 16 fixed sample plots with different thinning intensities were established in the mixed broadleaf-conifer forest in Jiaohe, situated in Changbai Mountain area, Northeast China, and the forest microclimates and soil properties were investigated after 4 years since the establishment of the sample plots. Results The results showed that the high intensity thinning significantly decreased the leaf area index from 4.13 (unthinned plot) to 2.21 (high intensity thinned plot), and the air temperature was increased by thinning from May to July. Comparing with the unthinned plot, thinning caused a rise of temperature (ranging from 2.11 to 6.74 °C, depending on the intensity of thinning) in May. However, it showed cooling effect in September and October. Besides, the air moisture of thinning plots was lower than the control plot in May and October, when the density of leaves is lower in the forest, and it even decreased 20.27% after thinning. The thinning intensity had no significantly effect on water content and organic carbon in forest soils, and only the bulk density in the top-layer soils in high intensity thinning plot was remarkably increased. Total nitrogen in soil was increased by different intensities of thinning, and the availability of nutrients for nitrogen, phosphorus and potassium in some soils were also affected.

Vaccinium uliginosum (VU) is one of the most precious wild berry plants distributed in the Changbai Mountain region in northeast China. Eight key morphological traits of VU were analyzed to examine the variation among and within five natural populations at different altitudes, as well as their response to environmental factors. The study results showed an increasing trend of variation among populations with ascending altitudes, but the range variation within populations exhibited a decreasing trend. The diversity level among populations was found to be higher than that within populations, and the five populations of VU were classified into four groups. Except for leaf width and twig length, all other morphological traits demonstrated significant or extremely significant correlations. Generally, with increasing altitude, leaf length decreased, while plant height, clear bole height, and basal diameter decreased significantly, and similar trends were observed with moisture factors, while a significant positive correlation was found with temperature factors. Among them, the morphological traits of clear bole height and basal diameter exhibited the strongest correlation with environmental factor variations. Overall, these findings indicate extensive variation in the morphological traits of VU within and among populations at different altitudes, with clear responses to changes in environmental factors.