Shrub encroachment impaired the structure and functioning of alpine meadow communities on the Qinghai–Tibetan Plateau

Abstract

Shrub encroachment has been rapidly occurring due to climate change, with profound ecological consequences for the alpine meadows of the Qinghai-Tibetan Plateau. Here, we conducted field surveys along a shrub coverage gradient to examine the effects of shrub encroachment on the structure and functioning of alpine meadows' plant communities. Our results showed that the overall coverage, density, aboveground biomass, species richness, and diversity of meadow community gradually declined with increasing levels of shrub encroachment, especially when shrub coverage exceeded 60%. Aboveground ecosystem multifunctionality also decreased along the shrub coverage gradient. With 90% shrub coverage, the relative importance value of the forbs functional group significantly increased while the Cyperaceae functional group showed the opposite trend: the originally dominant sedges Carex moorcroftii and Kobresia myosuroides were replaced by the forbs Androsace umbellate and Polygonum sparsipilosum. Additionally, shrub encroachment had a strong effect on nonrandom herb species extinction and colonization. At shrub coverages higher than 60%, there were 9 herb species absent and 18 new species colonizing-7 of which were only observed in meadows with 90% shrub coverage. Rare species and those with lower stature were more likely to go extinct, while taller and shadetolerant species tended to colonize areas with increasing shrub coverage. Overall, our results indicate that shrub encroachment negatively affects herbaceous community structure and functioning, which has important implications for the management of alpine meadows of the Qinghai-Tibetan Plateau under ongoing climate change.

Divergent responses of above- and belowground ecosystem functioning to shrub encroachment in the Tibetan semi-arid alpine steppes

“…These encroaching shrubs can create a microhabitat favoring growth of herbaceous plants through buffering of extreme soil temperatures and drought stress and increasing in soil nutrients availability, contributing to the increase of biodiversity and ecosystem functioning (Cui et al, 2023;Zhao et al, 2023). However, species richness, diversity, and productivity of herbaceous plants in the encroached areas also could be lower due to the encroaching shrub species competing for soil nutrients and shading light resources (Zhang et al, 2022). Therefore, the net impacts of shrub encroaching on biodiversity and ecosystem functioning often depend greatly on its facilitation and inhibition effects.…”

“…This may be because the climate in this region is relatively dry, and shrub encroachment-induced increase in soil nutrients may just slightly promote the growth of herbaceous plants in the semi-arid alpine steppes. In addition, in semi-arid region, most of these herbaceous plants with a shallow root system might be more sensitive to water rather than nutrients availability, and the shallow roots also makes them less advantageous in competing for water and nutrient resources with the deep-rooted Leguminosae shrub (Zhang et al, 2022). Such mechanisms also could explain why there was a neutral response of the AEMF in semi-arid alpine steppes after the encroaching of both shrub species.…”

“…Shrub encroached into alpine grassland ecosystems can increase biodiversity, soil fertility, soil infiltration processes, ultimately attributing to strengthen ecosystem functioning (Butterfield et al, 2016;Cai et al, 2020). Nevertheless, neutral or even negative ecosystem individual and multiple functioning response to shrub encroachment also existed in alpine ecosystems (Zhang et al, 2022;Yang et al, 2023). Thus, the ecological impacts of shrub encroachment are expected to affect biodiversity and even lead to the shifts of ecological functioning in alpine ecosystems, which depend on a variety of factors, including shrub traits, edaphic condition, and local climate (Brandt et al, 2013;Collins et al, 2020).…”

Aridity and soil properties drive the shrub-herb interactions along drought gradient in desert grassland in Inner Mongolia

“…During the past few years, the ecological consequences of shrub encroachment have been controversial. Shrubencroachment are considered could decrease the richness, abundance and aboveground biomass of herbs, that has a negative impact on the structure and diversity of herbs plant communities (Zhang et al 2022;Zhou et al 2019). On the contrary, shrub in our study has a positive impact on the composition and structure of herbs communities in desert steppe.…”

Divergent responses of above‐ and belowground ecosystem functioning to shrub encroachment in the Tibetan semi‐arid alpine steppes

“…Shrub encroaches into alpine grassland ecosystems can increase biodiversity, soil fertility, soil infiltration processes, and ultimately attributing to strengthen ecosystem functioning (Butterfield et al, 2016;Cai et al, 2020). Nevertheless, neutral or even negative ecosystem individual and multiple functioning response to shrub encroachment also exist in alpine ecosystems (Liu et al, 2022;Yang et al, 2023;Zhang et al, 2022). Thus, the ecological impacts of shrub encroachment are expected to affect biodiversity and even lead to the shifts of ecological functioning in alpine ecosystems, which greatly depend on a variety of factors, including shrub traits, edaphic condition, and local climate (Brandt et al, 2013;Collins et al, 2022).…”