Predicting crown width using nonlinear mixed-effects models accounting for competition in multi-species secondary forests.

Crown width (CW) is an important tree variable and is often used as a covariate predictor in forest growth models. The precise measurement and prediction of CW is therefore critical for forest management. In this study, we introduced tree species as a random effect to develop nonlinear mixed-effects CW models for individual trees in multi-species secondary forests, accounting for the effects of competition. We identified a simple power function for the basic CW model. In addition to diameter at breast height (DBH), other significant predictor variables including height to crown base (HCB), tree height (TH), and competition indices (CI) were selected for the mixed-effects CW model. The sum of relative DBH (SRD) was identified the optimal distance-independent CI and as a covariate predictor for spatially non-explicit CW models, whereas the sum of the Hegyi index for fixed number competitors (SHGN) was the optimal distance-dependent CI for spatially explicit CW models, with significant linear correlation (R 2 = 0.943, P < 0.001). Both spatially non-explicit and spatially explicit mixed-effects CW models were developed for studied secondary forests. We found that these models can describe more than 50% of the variation in CW without significant residual trends. Spatially explicit models exhibited a significantly larger effect on CW than spatially non-explicit ones; however, spatially explicit models are computationally complex and difficult and can be replaced by corresponding spatially non-explicit models due to the small differences in the fit statistics. The models we present may be useful for forestry inventory practices and have the potential to aid the evaluation and management of secondary forests in the region.

[Spatial distribution and interspecific associations of regenerating saplings in karst secondary forests.] / å–€æ–¯ç‰¹æ¬¡ç”Ÿæž—å¹¼æ ‘æ›´æ–°ç©ºé—´åˆ†å¸ƒæ ¼å±€åŠç§é—´å ³è”æ€§.

A 140 m×120 m plot was set in a secondary forest with more than 30 years natural reco-very after abandonment in Ziyun Miao and Buyi Autonomous County, a typical karst area in Guizhou Province. We investigated the spatial distribution and interspecific associations of regenerating sapling population using spatial point pattern analytical method. There were 1291 saplings with 39 tree species. Betula luminifera, Platycarya strobilacea, Liquidambar formosana, Pinus massoniana and Populus davidiana were the dominant populations of regenerating saplings, accounting for 83.7% of the saplings and 77.8% of the total importance value. The spatial distributions of B. luminifera, P. strobilacea and L. formosana were strongly aggregated at a spatial scale of 0-60 m, while the spatial distributions of P. massoniana and P. davidiana were aggregated at small scale and randomly distributed at large scale. The spatial associations among those dominant populations were mostly positively correlated, with positive correlations of P. massoniana with L. formosana and P. davidiana at small scale but no associations at large scale. In conclusion, the spatial distributions and interspecific associations differed among the dominant sapling populations, due to the different biological characteristics of different tree species, habitats and uses of spatial resources. Most of the stands investigated were dominated by pioneering species, with poor stand quality and unstable community structure. A mixed forest dominated by P. massoniana and B. luminifera would be the next stage of succession. We recommended that measures of forest management should be adopted to accelerate vegetation restoration.

Changes in Species Diversity Patterns and Spatial Heterogeneity during the Secondary Succession of Grassland Vegetation on the Loess Plateau, China.

Analyzing the dynamic patterns of species diversity and spatial heterogeneity of vegetation in grasslands during secondary succession could help with the maintenance and management of these ecosystems. Here, we evaluated the influence of secondary succession on grassland plant diversity and spatial heterogeneity of abandoned croplands on the Loess Plateau (China) during four phases of recovery: 1-5, 5-10, 10-20, and 20-30 years. The species composition and dominance of the grassland vegetation changed markedly during secondary succession and formed a clear successional series, with the species assemblage dominated by Artemisia capillaris→ Heteropappus altaicus→ A. sacrorum. The diversity pattern was one of low-high-low, with diversity peaking in the 10-20 year phase, thus corresponding to a hump-backed model in which maximum diversity occurring at the intermediate stages. A spatially aggregated pattern prevailed throughout the entire period of grassland recovery; this was likely linked to the dispersal properties of herbaceous plants and to high habitat heterogeneity. We conclude that natural succession was conducive to the successful recovery of native vegetation. From a management perspective, native pioneer tree species should be introduced about 20 years after abandoning croplands to accelerate the natural succession of grassland vegetation.

A comparison of species composition and community assemblage of secondary forests between the birch and pine-oak belts in the mid-altitude zone of the Qinling Mountains, China.

The mid-altitude zone of the Qinling Mountains in China was once dominated by birch and pine-oak belts but are now mainly covered by secondary growth following large-scale deforestation. Assessing the recovery and sustainability of these forests is essential for their management and restoration. We investigated and compared the tree species composition and community assemblages of secondary forests of the birch and pine-oak belts in the Huoditang forest region of the Qinling Mountains after identical natural recoveries. Both types of belts had rich species compositions and similar floristic components but clearly different community structures. Tree diversity was significantly higher for the birch than the pine-oak belt. Niche and neutral processes simultaneously influenced the species distribution and community dynamics of the belts, and these forests were able to maintain stable development during natural recoveries. The conservation and management of these forests should receive more attention to protect biodiversity and the forest resources in the Qinling Mountains.

Interspecific associations of dominant tree populations in a virgin old-growth oak forest in the Qinling Mountains, China.

BACKGROUND: Understanding interspecific associations in old-growth forests will help to reveal mechanisms of interspecific replacement in the process of forest development and provide a theoretical basis for vegetation restoration and reestablishment. In this study, we analyzed interspecific associations of eleven dominant tree populations of varying development stages in an old-growth oak forest stand in the Qinling Mountains, China. We examined overall interspecific associations (multiple species) and pairwise interspecific associations (two species). RESULTS: Interspecific competition was intense during forest development and was the main factor driving succession. Community structure appears to become more stable over time which supports the harsh-benign hypothesis that interspecific competition is more common in stable sites. CONCLUSION: Old growth oak (Quercus spp.) forests are distributed widely around the world in part due to oak being a typical K-selected species. K-selected species produce fewer, high-quality offspring with higher survival rates, strong competitive ability, and longevity. The resulting distribution shifted from clumped to random, likely as a result of intense interspecific competition creating ecological niche differentiation.