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The spatial pattern of herbaceous plants is closely associated with the reestablishment of species diversity as well as other ecological benefits in restored vegetation communities. However, it is still not clear how the distribution of herbaceous understory plants occur after the vegetation restoration. Additionally, the relationship between spatial heterogeneity index and number of herbaceous plants in semi-arid areas are still not well-understood. We selected two types of 35-year-old afforested lands and one type of grassland with areas of 50 × 50 m in Ansai County, Northern Shaanxi, Loess Plateau of China (36°46′42″–36°46′28″ N, 109°13′46″–109°16′03″ E). Each plot was evenly divided into a total of 100 (5 × 5 m in size) cells. The herbaceous plants in each cell were surveyed in three randomly selected 1 m×1 m S-quadrats. The power law model was used to define the relationship among the variance in the number of plants for species i (vi) and the mean total number of plants (mi) to reflect the spatial heterogeneity index. Results indicated that the relationship between vi and mi in afforested land and grassland demonstrated good fit with the power law model (R2 > 0.85). The spatial heterogeneity indexes of all herbaceous species in the three plots were >0, and the regression lines of the power law model were significantly above the y = x. The species number, Shannon index, and overall spatial heterogeneity indexes of the afforested land were greater than those of the restored grassland. There was a positive correlation between spatial heterogeneity index and mean number of plant individuals. Additionally, there was a negative correlation between overall spatial heterogeneity index and total number of herbaceous plant individuals. These results indicated that afforestation has positive effects on the reestablishment of diversity for herbaceous species. The herbaceous species in afforested land and restored grassland communities exhibited an aggregated distribution in the Loess Plateau. [ABSTRACT FROM AUTHOR]

Abstract: It is not known if the species composition of herbaceous plant assemblies within tree-fall gaps is determined stochastically or whether it follows species-specific and environmentally-determined patterns. We applied three methods, fitting species abundance distribution models, comparing community similarities, and testing species–environmental variable association, to evaluate the relative importance of chance and deterministic rules in controlling herbaceous composition within canopy gaps in the Abies–Betula forests of Mt. Taibai, Central China. Herbaceous species abundance within canopy gaps was well fit by a neutral model, showing that relative abundance was qualitatively consistent with stochastic processes. Although species composition in gaps significantly differed from closed canopy sites (ANOSIM, R =0.509, p =0.001), there were no significant differences among gaps of different age groups (ANOSIM, R =0.035, p =0.191) or gaps of different size groups (ANOSIM, R =0.089, p =0.057). Similarly, gaps of similar age and size did not show significantly higher similarity (χ 2 =2.30, df =3, p =0.513) in species composition than gaps of distinct age or size. Moreover, there were only eight species, including two light-demanding species, confined to larger gaps among the 69 species, and only an additional seven species found more commonly in larger gaps, whereas most herbaceous species were gap size generalists. Canonical correspondence analysis and random permutation tests suggested that only 27% of species with abundance ⩾5 were associated with environmental variables in gaps. In summary, the species composition in gaps was not constrained significantly by gap traits; rather species were distributed stochastically, likely through by random dispersal and recruitment limitation of species from the surrounding available species pool. Measures that introduce gap disturbance, such as selective harvesting, are still recommended when the maintenance of total biodiversity in forests is a concern. [Copyright &y& Elsevier]