Grassland Restoration Drives Strong Multitrophic Biodiversity Recovery, but Climate Extremes Jeopardize Drought-Sensitive Species

Abstract

Semi-natural grasslands, Europe's most biodiverse ecosystems, are rapidly declining due to agricultural intensification, abandonment, and afforestation, leading to biodiversity loss and reduced ecosystem function. Despite their ecological value, grasslands are often overlooked, while afforestation, for instance, is prioritized for climate mitigation. This study assessed the effects of grassland abandonment, afforestation, and ecological restoration on multitrophic species richness and soil conditions. We used Estonian semi-natural calcareous grasslands (alvars) as a model system. Results showed that historically overgrown and afforested grasslands recover fast and rapidly become species-rich after woody plant removal and low-intensity grazing reinstatement. These grasslands also serve as stable carbon sinks, storing soil carbon at levels comparable to afforested grassland areas, with restoration having no negative impact on carbon storage. Multitrophic species richness responded to restoration in three main ways: fast responders (plants, pollinators, birds) recovered relatively quickly, slow responders (lichens, bryophytes, soil fungi) showed little to no short-term change, and drought-sensitive species (ground-dwelling arthropods) declined due to prolonged drought, which also potentially overshadowed the impact of restoration. Grassland restoration is vital for biodiversity, the sustainable supply of ecosystem services, and climate resilience, with long-term monitoring needed to track recovery.

Keywords: carbon storage; drought impact; grassland abandonment; grassland afforestation; grassland restoration; multitrophic species richness; soil condition.

FIGURE 1

Study sites: positioning of grassland restoration and unrestored comparison sites in western Estonia (above), and example of positioning of the subsites before and after restoration in Paope restoration site with aerial photo comparison (Estonian Land and Spatial Development Board) showing the restoration impact (below). Yellow dashed polygons indicate the boundaries of the LIFE to Alvars restoration project. Map lines delineate study areas and do not necessarily depict accepted national boundaries.

FIGURE 2

Changes in multitrophic species richness (standardized richness) in relation to alvar grassland restoration. Left panel, restoration sites, and right panel, unrestored comparison sites before and after restoration. Significance values are indicated as follows: ***p ≤ 0.001, **0.001 < p ≤ 0.01; *0.01 < p < 0.05, ns p ≥ 0.05.

FIGURE 3

Changes in the vascular plant community in relation to alvar grassland restoration. (A) Vascular plant community composition reflected by nonmetric multidimensional scaling (stress value 0.23), ellipses with standard error and confidence value of 0.99 are indicated. Both ordination figures are based on the same NMDS, positions of restoration sites are illustrated on the left figure, and positions of unrestored comparison sites on the right figure. (B) Vascular plant species richness before and after restoration in different subsites. Significance values are indicated as follows: ***p ≤ 0.001, **0.001 < p ≤ 0.01; *0.01 < p < 0.05, ns p ≥ 0.05.

FIGURE 4

Changes in bryophyte community in relation to alvar grassland restoration. (A) Bryophyte community composition reflected by nonmetric multidimensional scaling (stress value 0.25), ellipses with standard error and confidence value of 0.99 are indicated. Both ordination figures are based on the same NMDS, the positions of restoration sites are illustrated on the left figure, and the positions of unrestored comparison sites on the right figure. (B) Bryophyte species richness before and after restoration in different subsites. Significance values are indicated as follows: ***p ≤ 0.001, **0.001 < p ≤ 0.01; *0.01 < p < 0.05, ns p ≥ 0.05.

FIGURE 5

Changes in the bumblebee community in relation to calcareous grassland restoration. (A) Bumblebee community composition reflected by nonmetric multidimensional scaling (stress value 0.22), ellipses with standard error and confidence value of 0.99 are indicated. Both ordination figures are based on the same NMDS, the positions of restoration sites are illustrated on the left figure, and the positions of unrestored comparison sites on the right figure. (B) Bumblebee species richness before and after restoration in different subsites. Significance values are indicated as follows: ***p ≤ 0.001, **0.001 < p ≤ 0.01; *0.01 < p < 0.05, ns p ≥ 0.05.

FIGURE 6

Changes in bird community in relation to alvar grassland restoration. (A) Bird community composition reflected by nonmetric multidimensional scaling (stress value 0.19), ellipses with standard error and confidence value of 0.99 are indicated. Both ordination figures are based on the same NMDS, positions of restoration sites are illustrated on the left figure, and positions of unrestored comparison sites on the right figure. (B) Overall bird species richness and C: Open habitat specialist bird species richness before and after restoration in different subsites. Significance values are indicated as follows: ***p ≤ 0.001, **0.001 < p ≤ 0.01; *0.01 < p < 0.05, ns p ≥ 0.05.

FIGURE 7

Changes in ground‐dwelling spider community in relation to alvar grassland restoration in Estonia. (A) Ground‐dwelling spider community composition reflected by nonmetric multidimensional scaling (stress value 0.21), ellipses with standard error and confidence value of 0.99 are indicated. Both ordination figures are based on the same NMDS, positions of restoration sites are illustrated on the left figure, and positions of unrestored comparison sites on the right figure. (B) Ground‐dwelling spider species richness before and after restoration in different subsites. Significance values are indicated as follows: ***p ≤ 0.001, **0.001 < p ≤ 0.01; *0.01 < p < 0.05, ns p ≥ 0.05.