The effects of land degradation on plant community assembly: Implications for the restoration of the Tibetan Plateau

Abstract

Understanding how biotic and abiotic filters drive plant distributions is critical for informing restoration efforts of degraded lands. However, it remains unclear whether or not it is possible to develop efficient restoration strategies that are based on field investigations? Here, we conducted a field-based investigation along a land degradation gradient on the Tibetan Plateau. Along this gradient, we compared species composition, Pianka's niche overlap, and total aboveground biomass among grasses, sedges, legumes, and forbs. We also used Faith's (1992) phylogenetic diversity index (PD) and the net relatedness index (NRI) to measure community phylogenetic patterns. To understand the effects of abiotic filtering, we measured soil pH, moisture, electrical conductivity, total soil organic carbon, microbial biomass carbon, and microbial biomass nitrogen. Our results show that grasses replaced sedges and mesoxerophytes replaced mesohydrophytes with increasing land degradation. We also found that niche overlap declined with increasing degradation intensity. Furthermore, grass biomass increased, while sedges and legumes decreased, and forb biomass showed a hump-shaped relationship with degradation intensity. In addition, the communities transitioned from a clustered to a more random phylogenetic pattern. Soil conditions changed from acidic to alkaline and from fertile to harsh (p < .05). High niche overlap indicates a high biotic filtering at lightly degraded land where abiotic filtering is less stressful. However, when degradation is intense, abiotic filtering is apparent, as indicated by low levels of niche overlap. Overall, we suggest that distantly related, arid tolerant and hardy plants, and soil reclamation should be considered in degraded alpine lands restoration.

Response of the plant–soil system to desertification in the Hulun Buir Sandy Land, China

“…With the increasing desertification, grassland herbs are gradually replaced by shrubs, semi‐shrubs, and forbs, and the dominant species finally changed into sparsely distributed drought‐ and barren‐tolerant annual sandy plants (Li, Jia, & Dong, 2006; Schlesinger et al, 1990). During this process, niche overlap decreases with increasing desertification severity (Luo et al, 2020), accompanied by decreasing plant productivity and diversity (Li, Zhao, et al, 2006). For example, previous studies in Ethiopia suggested that the soil seed bank would be reduced with the strengthening of degradation, and the severely degraded ecosystem could not even maintain an adequate soil seed bank (Kassahun et al, 2009).…”

Land Degradation Changes the Role of Above- and Belowground Competition in Regulating Plant Biomass Allocation in an Alpine Meadow

“…Land degradation increased the R/S ratio of alpine meadows in the QTP due to a significant decrease in aboveground biomass and a weak change in belowground biomass (Zhang et al, 2019). Moreover, the negative effects of land degradation on plant species richness, plant composition, and plant competition have been widely studied in the QTP (Wang et al, 2014;Tang et al, 2015;Luo et al, 2020;Peng et al, 2020). However, it is still unclear whether the land degradation would change the role of aboveand belowground competition in regulating the R/S ratio.…”