Restoration of Degraded Alpine Meadows Improves Pollination Network Robustness and Function in the Tibetan Plateau

Abstract

Ecological restoration is widely used to mitigate the negative impacts of anthropogenic activities. There is an increasing demand to identify suitable restoration management strategies for specific habitat and disturbance types to restore interactions between organisms of degraded habitats, such as pollination. In the Tibetan Plateau, alpine meadows have suffered severe degradation due to overgrazing and climate change. Protecting vegetation by fencing during the growing season is a widely applied management regime for restoration of degraded grasslands in this region. Here, we investigated the effect of this restoration strategy on plant–pollinator communities and plant reproduction in the eastern Tibetan Plateau. We collected interaction and seed set data monthly across three grazed (grazed all year) and three ungrazed (fenced during growing season) alpine meadows in growing seasons of two consecutive years. We found ungrazed meadows produced more flowers and attracted more pollinator visits. Many common network metrics, such as nestedness, connectance, network specialization, and modularity, did not differ between grazing treatments. However, plants in ungrazed meadows were more robust to secondary species extinction than those in grazed meadows. The observed changes in the networks corresponded with higher seed set of plants that rely on pollinators for reproduction. Our results indicate that protection from grazing in growing seasons improves pollination network stability and function and thus is a viable restoration approach for degraded meadows.

Meadow transformations alter above‐ and below‐ground ecological networks and ecosystem multifunctionality

“…Parnassia trinervis , Pedicularis longiflora ). By contrast, dominant flowers in alpine meadows were relatively generalized species with easily accessible floral structures (e.g., Ranunculus tanguticus , Gentiana aristate ) (Table S5; Gao et al, 2021). Importantly, more generalized pollination networks in alpine meadow indicate lower mutual dependencies, which suggests overall higher network robustness (Kaiser‐Bunbury et al, 2017).…”

“…Meadow types that do not share a letter on top of their boxes are statistically different from each other (adjusted p < 0.05, statistics are shown in Table S4). S5; Gao et al, 2021). Importantly, more generalized pollination networks in alpine meadow indicate lower mutual dependencies, which suggests overall higher network robustness (Kaiser-Bunbury et al, 2017).…”

Increasing flower species richness in agricultural landscapes alters insect pollinator networks: Implications for bee health and competition

“…In agricultural areas, seed mixes for WFS are designed to meet the dietary needs of mostly generalist bees, with high flower density and enhanced flower species richness. One can hypothesize that higher flower species richness will expand the foraging spectrum of pollinators, as observed in Kaiser-Bunbury et al (2017) and Gao et al (2021), and in consequence may increase competition between pollinators when foraging niches overlap. Increasing the number of insect species visiting the same plants by promoting niche overlap and connectance can be beneficial for network robustness (the resilience of networks following the loss of species), and hence is often a goal in pollinator restoration (e.g., Cusser & Goodell, 2013).…”

“…Kaiser‐Bunbury et al (2017) showed a diversification of interactions in restored tropical plant‐pollinator networks, as higher plant species richness increased pollinator diet breadth (i.e., the number of visited flower species). Gao et al (2021) showed moreover that restored networks with more diverse interactions are more stable and robust to perturbations and species loss, as measured by network connectance. In contrast, heathland restoration in England led to a reduction in insect pollinator network connectance, independent of plant species richness (Forup et al, 2007).…”

The effects of changes in flowering plant composition caused by nitrogen and phosphorus enrichment on plant–pollinator interactions in a Tibetan alpine grassland

“…Here, we experimentally manipulated the addition of nutrients to investigate whether and how the addition of P and N affected flowering plant communities, pollinator assemblages, and plant–pollinator interactions ( Figure 1 ). In addition, we used a network approach to describe the interaction networks between plants and pollinators, which is commonly used to study changes in plant–pollinator interactions in communities ( Kaiser-Bunbury et al, 2017 ; Gao et al, 2021 ; Villa-Galaviz et al, 2021 ). Previous research showed that nutrient addition reduced the diversity of plants in grasslands ( Stevens et al, 2018 ; Xiao et al, 2020 ; Villa-Galaviz et al, 2021 ).…”