Ecological niches remain central to explaining community structure, and niche-based studies have helped us to better understand species interactions, distributions, coexistence and associated mechanisms.Quercus wutaishanseapopulations on Loess Plateau are currently expanding their dominance in natural secondary forest types. In the present paper, we focused on the dynamic changes of niches and interspecific association among different changed stages. The overall interspecies association of the three communities exhibited positive association for Variance Ratio (VR) >1; the value of χ²significance test further revealed that the overall association had reached the level of significant association. Among the total of 45 species pairs composed of 10 dominant species, in thePinus tabulaeformisforest, the ratio of positive and negative associations was below 1, which 19 pairs showing positive association, 25 pairs showing negative association, and 1 pair showing no association; in contrast, in another forests, the ratios of positive and negative associations were above 1. The timing and consequences of these associations may illuminate how interaction mechanisms such as competition and alleopathy, structure changes. Then differences of species features in niches and associations should receive greater attention when planning forest management and developing restoration strategies.

Regional habitat quality is an important reflection of ecosystem services and ecosystem health. Exploring the characteristics of habitat quality changes and revealing the vulnerability of regional ecosystems caused could provide reference for the improvement of ecological service functions and the protection of regional ecological environment. Based on remote sensing data of Shaanxi Province from 2000 to 2015, InVEST model and grid analysis were used to analyze the evolution characteristics of habitat quality and landscape pattern, and spatial autocorrelation was also used to analyze the spatial correlation and temporal evolution characteristics. The results showed: (1) Arable land, grassland, and forest land were the main landscape types in Shaanxi province, accounting for more than 94% of the total area, and the arable land and unused land showed a decreasing trend, while the grassland and forest land showed an increasing trend, and the proportion of construction land continued to increase with the rapid economic development from 2000 to 2015; (2) The spatial distribution characteristics of habitat quality was similar to land use cover change, which was “high in the southern and central forest areas, low in the northern sandy land and central urban agglomeration”, and habitat quality value showed a steady increase, indicating that the habitat quality was getting better; (3) The landscape pattern index values of Guanzhong Plain urban agglomeration changed significantly, which tended to be fragmented, and the landscape types were more diverse and uniform; (4) There were obvious spatial correlation between habitat quality and landscape pattern, and the spatial differentiation of clustering was obvious, and the clustering effect of habitat quality and landscape pattern characteristics would weaken with the increase in urbanization degree. The analysis of the spatial association between habitat quality and landscape pattern could provide scientific support for ecological protection and landscape planning.

As ecological and environmental issues have received continuous attention, forest transition has gradually become the frontier and a hot issue, which have implications for biodiversity and ecosystem functioning. In this study, the spatial-temporal dynamics and the spatial determinants of forest quality were investigated using spatial econometric regression models at the province level, which contained 31 provinces, autonomous regions, and municipalities in China. The results showed that forest area, forest volume, forest coverage, and forest quality have greatly increased as of 2018, but uneven forest distribution is an important feature of forest adaptation to the environment. The global Moran’s I value was greater than 0.3, and forest quality of the province level had a positive spatial correlation and exhibited obvious spatial clustering characteristics. In particular, the spatial expansion of forest quality had shown an accelerated concentration. The most suitable model for empirical analysis and interpretation was the Spatial Durbin Model (SDM) with fixed effects. The average annual precipitation and the area ratio of the collective forest were positively correlated with forested quality (significance level 1%). Ultimately, this framework could guide future research, describe actual and potential changes in forest quality associated with forest transitions, and promote management plans that incorporate forest area changes.

Determining the optimal rotation period was a crucial component of forest sustainable management strategies, especially under climate change. This paper had two objectives: (1) to determine the economic benefits and optimal rotation periods for timber production when coupled to carbon sequestration, as predicted by time series prediction models for Pinus tabulaeformis plantations in China; and (2) to evaluate how different carbon prices and interest rates affected optimal rotation periods using the forest land expectation value. The results suggested that time series prediction models were valuable for estimating timber volumes and carbon sequestrations based on surveys of different-aged stands. Importantly, since integrating carbon sequestrations into timber production benefits did not increase optimal rotation periods, this should promote P. tabulaeformis plantation management. In the sensitivity analysis, a higher carbon price increased the profitability of carbon sequestration and timber production, but not optimal rotation periods, though they were reduced under higher interest rates. In conclusion, incorporating both timber production and carbon sequestration benefits would sharply increase forest-based revenues, while realizing the carbon sequestration potential of P. tabulaeformis plantations. This approach was clearly useful to the development of reforestation/afforestation projects trying to mitigate climate change and also provided a theoretical basis for sustainable forest management.