Grazing exclusion altered the pattern of the soil seed bank but not the aboveground vegetation along an altitudinal gradient in alpine grassland

Abstract

Grazing exclusion by fencing is the principal option to restore degraded grassland, but its effects on recovery and succession of vegetation are not clear, especially in high mountain areas. In this study, we aimed to fill this gap by assessing the effect of seven-year grazing exclusion on vegetation and soil seed bank along an altitudinal gradient in northern Tibet, China. Species richness, Shannon-Wiener index and Simpson's diversity index of vegetation and soil seed bank, seed density, and the Sørensen index all displayed a mid-domain (hump-shaped) pattern with increasing altitude, except for the Shannon-Wiener and Pielou indices of soil seed bank in fenced grasslands. These results demonstrated that the impact of grazing exclusion on the patterns of vegetation and soil seed bank change with altitude but are not synchronous.Grazing exclusion increased vegetation coverage but decreased soil seed bank density, and species diversity of vegetation and soil seed bank. The Sørensen index (0.03-0.2) and non-metric multidimensional scaling (NMDS) analysis indicated that the species composition differed between vegetation and soil seed bank, but no difference was found between fenced and grazed grasslands. The low similarity suggests that the soil seed bank contributes little to vegetation recovery in alpine grassland. Seven-year grazing exclusion had no effect on either vegetation succession or species composition of soil seed bank in alpine grassland. Overall, our findings suggest reconsidering the use of long-term grazing exclusion to restore degraded grassland at high altitudes (above 4400 m above sea level) on the Tibetan Plateau.

Grazing intensity effects on rangeland condition and tree diversity in Afar, northeastern Ethiopia

“…Lower species diversity in the present study in general and at the moderate and heavily grazed sites in particular suggests that the impacts of intensive grazing and trampling is likely prevented species occurrence. Selection of palatable plants and trampling damage during early stages of the plants may have also reduced the woody vegetation cover and richness [ 43 ]. Suppressive effects of livestock grazing on woody species diversity have been observed in other semi-arid rangelands of Ethiopia [ 44 ].…”

Estimating the effects of grazing exclusion on the seed bank in Icelandic rangelands

“…Soil seed banks are an essential resource for vegetation regeneration (Ma et al 2018, Huang et al 2022, as viable seeds can help maintain plant populations and increase the resilience of vegetation to disturbances (Kiss et al 2018). Despite the potential relevance of seed banks for natural recovery of degraded rangelands, very little research has been conducted on this topic in Iceland (Magnússon 1994, Marteinsdóttir et al 2010.…”

“…Land degradation and soil erosion are main environmental issues in Iceland, and extensive grazing has been pointed out as one of the key drivers of degradation (Arnalds et al 1987). In other degraded rangelands, grazing exclusion has been suggested as a potential strategy to strengthen soil seed banks (Huang et al 2022). In Iceland, the lack of seed sources has been proposed as one of the reasons for the slow natural revegetation of eroded areas (Arnalds et al 1987), but the effects of grazing exclusion on vegetation recovery from soil seed banks have not been extensively studied.…”

“…Seedling emergence methods are well established for estimating the number of viable seeds in the soil (Gross 1990). The degree of similarity between soil seed banks and aboveground vegetation has been suggested as an indicator of the role of seed banks in plant community regeneration (Huang et al 2022), with high similarity interpreted as a strong contribution of soil seed banks to vegetation recovery. We collected soil samples and measured vegetation in an ongoing field experiment.…”

“…We excluded sheep grazing at two sites in two habitats, a moderately-degraded heathland and a heavily-degraded, gravelly desert (Mulloy et al 2019). Given that the vegetation in the highlands is dominated by perennial species, we expected little effect of grazing exclusion on soil seed banks (Huang et al 2022). In the heavily-degraded, gravelly desert, where soil seed banks could contribute more to vegetation regeneration, plant species Short communications represented in soil seed banks should be more similar to those present in aboveground vegetation (Huang et al 2022).…”