Long‐term livestock exclusion facilitates native woody plant encroachment in a sandy semiarid rangeland

Abstract

The role of livestock grazing in regulating woody cover and biomass in grass-dominant systems is well recognized. However, the way in which woody plant populations in respond when livestock are removed from grazing in the absence of other disturbances, such as fire, remains unclear.We conducted a 10-year, replicated fencing experiment in a sandy semiarid rangeland in northern China (which has a mean annual rainfall of 365 mm), where fires have been actively suppressed for decades.Fencing dramatically influenced the growth and age structure of the native tree species, Ulmus pumila, which is the sole dominant tree in the area. After a decade, the density of the U. pumila tree population in the fencing plots increased doubly and canopy cover increased triply. The proportion of both saplings (U2) and young trees (U3) increased in fencing plots but decreased in grazing plots after the 10-year treatment period. The effects of fencing on U. pumila trees varied by age class, with potential implications for the future structure of the U. pumila tree community. Decadal fencing led to approximately 80-fold increase in recruitment and a nearly 2.5-fold decrease in the mortality of both U2 and U3. Further, livestock grazing generated a “browsing trap” to the recruitment of both U2 and U3, and had a small impact on the mortality of old trees. A long-term, fencing-driven shift in woody species composition was mediated via its effects on both recruitment and mortality rates.Synthesis and applications. Our results demonstrate that in the long-term absence of both fire and livestock, native woody plant encroachment tends to occur in sandy rangelands, transforming the woody plant demography in the process. The feasibility of full livestock exclusion in sandy rangelands requires further discussion. A balanced amount of livestock grazing may provide critical ecosystem services by regulating woody cover and mediating woody plant encroachment.

Sand and Dust Storms: Impact Mitigation

“…The GGW program has greatly improved vegetation cover and effectively reduced dust storm intensity in parts of northern China [8], but other researchers point to warmer temperatures and greater rainfall as being more important drivers of greening trends in the area [146], and the value of large-scale afforestation in controlling desertification and soil erosion in China has been questioned due to low tree survival rates [147]. Huang et al [148] report that rangeland restoration programs have resulted in a systematic increase in the area of grassland in most northern and western regions, but Su et al [149] warn that bush encroachment is an unexpected outcome of the grazing ban on sandy rangelands in Inner Mongolia.…”

Effects of different fencing regimes on community structure of degraded desert grasslands on Mu Us desert, China

“…However, because of lacking in human interference, the fierce competition of plants, caused by limited resources, may induce intense intra-and interspecific competition in exclosure grasslands (Angassa & Oba, 2010;Catford et al, 2012;Connell, 1979;Oba, Vetaas, & Stenseth, 2001). This may lead to a loss of biodiversity and ultimately cause redegradation of ecosystem after long-term fencing (Shang et al, 2010;Su, Liu, Xu, Wang, & Li, 2015).…”

“…Recent studies focused on the effects of grazing bans/exclosure mostly concentrated on plant community characteristics (Deng, Zhang, & Shangguan, 2014;Li, Zhang, et al, 2017;Li, Cao, et al, 2017;Liu et al, 2015;Rooyen et al, 2014;Wal, Bardgett, Harrison, & Stien, 2004;Wu et al, 2009) and soil properties (Li, Zhang, et al, 2017;Li, Cao, et al, 2017;Mekuria & Aynekulu, 2013;Zhu et al, 2016;Zou et al, 2016). Plenty studies have focused on the evaluation of aboveground vegetation and soil based on different restoration time or management types (Su et al, 2015;Zhu et al, 2016).…”

Grazing Effect on Floristic Diversity and Structure in Arid Rangelands of Algeria.

“…Grazing has a role in changing the composition of plant communities by reducing the abundance of palatable plants and promoting ephemeral plants (Milton & Hoffman 1994). Heavy grazing can lead to the deterioration of the vegetation cover by consuming plant species and trampling (Su et al 2015). The reduction of vegetation cover and its replacement by annual plants makes the soil more susceptible to wind and water erosion in consequence, the processes of desertification.…”