Abstract
Plant functional groups (PFGs) have been increasingly introduced in land degradation (LD) studies; however, it is unclear whether PFGs can indicate LD. Here, we selected five different degraded lands (i.e., pristine and, lightly, moderately, seriously and extremely degraded) higher than 4650 m on the Tibetan Plateau. In addition, we investigated floristic metrics (i.e., composition, height, cover, biomass and abundance) and soil conditions (e.g., moisture, temperature and gravel ratio) by sampling 225 subplots. We found 75 vascular plants that consist of sedges (Cyperaceae), grasses (Gramineae), legumes, forbs, cushion plants and shrubs PFGs. LD dramatically deteriorated soil conditions, vegetation cover and productivity, however, improved species diversity. Moreover, cover and productivity showed a hump-shaped relationship with LD intensification in legumes, grasses and forbs and decreased mainly in sedges. Productivity increased considerably in cushion plants and shrubs on the extremely degraded land. Major characteristics of the LD process were the replacement of Kobresia spp. by Carex spp. in sedges; cushion plants significantly expanded, and shrubs appeared on the extremely degraded land. We, thus, confirm that the PFG variations are likely to indicate a LD process and demonstrate ways of using PFGs to assess LD status on the Tibetan Plateau.
Highlights
Land degradation (LD) is a global concern because of its greatly negative influence[1,2,3]
Seventy-five vascular plant taxa distributed in 49 genera and 20 families of angiosperms were recorded in 225 subplots across the 5 communities (I = pristine land, II = lightly degraded land, III = moderately degraded land, importance value (IV) = seriously degraded land and V = extremely degraded land) (Table S1)
The floristic composition in sedges presented a qualitative change in that Kobresia spp. (e.g., K. humilis, K. tibetica, and K. royleana) were replaced by Carex spp. (e.g., C. montis-everestii and C. moorcroftii) from I to V
Summary
Land degradation (LD) is a global concern because of its greatly negative influence[1,2,3]. Previous studies have focused on vegetation productivity or vegetated cover[12,13], community species diversity[14,15], or soil nutrients[14,16,17] in degraded lands. Knowledge of the indicative plant functional group (PFG) in degraded alpine meadows is still rare[2]. Evidence suggests that a PFG investigation is crucial for degraded grassland community structure or function research[9,20], such as in a Siberian lowland tundra, where the shrubs (e.g., Betula nana), grasses (e.g., Arctagrostis latifolia), and sedges (e.g., Eriophorum spp.) cover ratio showed a close relationship with LD, resulting in thaw pond formation[21]. Experimental sites were selected in an area undergoing a degradation process and the design followed a comprehensive ecological field experiment in the Tibetan Plateau alpine meadow region. A floristic composition investigation (identification, height, cover, abundance and aboveground biomass of vascular plants) was conducted, and the topsoil layer conditions (water content, temperature and gravel ratio) were measured
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