Abstract:

Enclosure （fencing） is a key measure to restore degraded grasslands. Investigating the dynamic changes in plant community characteristics under different durations of fencing is crucial to evaluate the effectiveness of fencing for optimizing ecological engineering management. In this study， we focused on the desert grassland of Liuyangbu in Yanchi County， Ningxia. We selected a grassland area that was divided into a long-term fully enclosed core plot （completely enclosed since 1991， 31 years continuous）， a short-term fully enclosed edge plot （completely enclosed since 2002， 20 years continuous）， and a short-term incompletely enclosed peripheral plot （incompletely enclosed since 2002， subject to light grazing disturbance）； i.e.， three zones that differed in terms of their fencing duration and disturbance levels. Based on field vegetation surveys conducted in 2010， 2015， 2020， and 2022 （a total of 120 plots） and concurrent meteorological data， we analyzed dynamic changes in species importance values and species diversity （Shannon-Wiener index， Pielou index， species richness， Simpson’s index）， and their relationships with precipitation and temperature during long-term fencing. We also assessed the stability of the plant community （characterized by the inverse of the coefficient of variation in species density， ICV）. The results show that： 1） Long-term complete enclosure weakened the dominant position of original dominant species such as Aster altaicus and Salsola ruthenica， leading to increased fluctuations in the importance values of other species and changes in community structure； 2） Species richness and evenness were significantly higher in the edge plot （20 years of complete enclosure） and the peripheral plot （20 years of incomplete enclosure） than in the core plot （31 years of complete enclosure）； 3） Increased precipitation in the current and previous years significantly promoted species diversity， whereas increases in annual mean temperature had no significant effect on species diversity， indicating that the species composition and diversity of plant communities is jointly regulated by precipitation in the current and previous years； 4） Community stability was manifested as peripheral plot （ICV=2.13）>edge plot （ICV=2.00）>core plot （ICV=1.74）， reflecting the positive effects of moderate disturbance and the potential risks of long-term enclosure. In summary， long-term complete enclosure is detrimental to the maintenance of plant community stability and the enhancement of species diversity. It is recommended to implement an alternating “enclosure-utilization” management cycle for long-term complete enclosed areas （such as the core plot in this study， with enclosure periods exceeding 30 years）. This approach aims to break habitat homogenization through moderate human disturbance， which suppresses the excessive expansion of dominant species and promotes seed dispersal and soil seed bank renewal. Consequently， this approach will enhance species diversity and long-term stability while preserving ecosystem restoration outcomes. Our findings provide a scientific basis for the sustainable management of grasslands in arid and semi-arid regions.

Key words: enclosure, community characteristics, community stability, precipitation, temperature