Amur tigers are at the top of the food chain and play an important role in maintaining the health of forest ecosystems. Scientific and detailed assessment of the habitat quality of Amur tigers in China is the key to maintaining the forest ecosystem and also addressing the urgent need to protect and restore the wild population of Amur tigers in China. This study used the random forest method to predict the potential habitat of Amur tigers in Heilongjiang and Jilin provinces using animal occurrence sites and a variety of environmental variables. Random forests are a combination of tree predictors such that each tree depends on the values of a random vector sampled independently and with the same distribution for all trees in the forest. The generalization error for forests converges to a limit as the number of trees in the forest becomes large. The generalization error of a forest of tree classifiers depends on the strength of the individual trees in the forest and the correlation between them. The results showed that the AUC value of the test set was 0.955. The true skill statistic (TSS) value is 0.5924, indicating that the model had good prediction accuracy. Using the optimal threshold determined by the Youden index as the cutoff value, we found that the suitable habitat for Amur tigers in the field was approximately 107,600 km², accounting for 16.3% of the total study areas. It was mainly distributed in the Sino-Russian border areas in the south of the Laoyeling Mountains at the junction of Jilin and Heilongjiang provinces, the Sino-Russian border areas of Hulin–Raohe in the eastern part of the Wanda Mountains, and the Lesser Khingan Mountain forest region. The habitat suitability of the Greater Khingan Mountain and the plain areas connecting Harbin and Changchun was relatively low. Prey potential richness was the most critical factor driving the distribution of Amur tigers. Compared with their prey, the potential habitats for Amur tigers in Heilongjiang and Jilin provinces were small in total areas, sporadically distributed, and had low continuity and a lack of connectivity between patches. This indicates that some factors may restrict the diffusion of the Amur tiger, whereas the diffusion of ungulates is less restricted. The Amur tigers in this area face a serious threat of habitat fragmentation, suggesting that habitat protection, restoration, and ecological corridor construction should be strengthened to increase population dispersal and exchange. We provide a reference for future population conservation, habitat restoration, construction of ecological migration corridors, and population exchange of Amur tigers.

This study focuses on the Siberian roe deer population in the Greater Khingan Mountains, Northeast China. The cold temperate forest ecosystem in this area is distinctive. The Siberian roe deer is a crucial ecological indicator species, and its living conditions hold significant importance for ecological balance. From the winter of 2019 to 2022, 269 fecal samples of Siberian roe deer were collected from four protected areas in the northern part of the Greater Khingan Mountains, Heilongjiang Province. These samples were comprehensively analyzed using mitochondrial DNA and microsatellite markers, combined with conservation genetics evaluation methods. The results revealed that 244 individuals were identified in the fecal samples. The results of a Cyt b genetic analysis of the samples indicated that the haplotype and nucleotide diversity were 88.1% and 20.3%, respectively. The evaluation of 14 pairs of microsatellite loci showed that the average number of alleles was 11.2, and the average expected and observed heterozygosity were 0.672 and 0.506, respectively. Therefore, the overall genetic diversity level is high, but some populations of Siberian roe deer are at risk. AMOVA analysis and STRUCTURE Bayesian clustering confirmed the existence of obvious genetic differentiation among the populations. Historical studies have shown that the HZ and SH populations underwent the earliest diffusion events, and the BJC and SL populations also exhibited related signs (HZ: Huzhong Nature Reserve in the Greater Khingan Mountains; SH: Shuanghe National Nature Reserve in Heilongjiang Province; BJC: Heilongjiang Beijicun National Nature Reserve; SL: Songling District in Heilongjiang Province). Mismatch distribution and neutral tests indicated no expansion events or bottleneck effects in the population, and the inbreeding coefficient was positive, suggesting the possibility of inbreeding. The development potential of the population in the future varies among the various local populations. This study supports the biodiversity of Siberian roe deer at the genetic level to save the population and provides important scientific basis and reference for the protection and management of Siberian roe deer.