Enhancing diversity of species‐poor grasslands: an experimental assessment of multiple constraints

Abstract

Summary 1.Many grasslands in north-west Europe are productive but species-poor communities resulting from intensive agriculture. Reducing the intensity of management under agrienvironment schemes has often failed to increase botanical diversity. We investigated biotic and abiotic constraints on diversification by manipulating seed and microsite availability, soil fertility, resource competition, herbivory and deficiencies in the soil microbial community. 2. The effectiveness of 13 restoration treatments was investigated over 4 years in a randomized block experiment established in two productive grasslands in central-east and south-west England. 3. Severe disturbance involving turf removal followed by seed addition was the most effective and reliable means of increasing grassland diversity. Disturbance by multiple harrowing was moderately effective but was enhanced by molluscicide application to reduce seedling herbivory and by sowing the hemiparasite Rhinanthus to reduce competition from grasses. 4. Low-level disturbance by grazing or slot-seeding was ineffective in increasing diversity. Inoculation with soil microbial communities from species-rich grasslands had no effect on botanical diversity. Nitrogen and potassium fertilizer addition accelerated off-take of phosphorus in cut herbage but did not cause a reduction in soil phosphorus or increase botanical diversity. 5. Different grazing management regimes had little impact on diversity. This may reflect the constraining effect of the July hay cut on species dispersal and colonization. 6. Synthesis and applications. Three alternative approaches to grassland diversification, with different outcomes, are recommended. (i) High intervention deturfing, which would create patches with low competitive conditions for rapid and reliable establishment of the target community. For reasons of cost and practicality this can only be done over small areas but will form source populations for subsequent spread. (ii) Moderate intervention (harrowing or slot-seeding) over large areas, which would establish a limited number of desirable, generalist species that perform well in restoration. This method is low cost and rapid but the increases in biodiversity are less predictable. (iii) Phased restoration, which would complement the above approaches. Productivity and competition are reduced over 3-5 years using Rhinanthus or fertilizers to accelerate phosphorus off-take. After this time harrowing and seeding should allow a wide range of more specialist species to establish. However, further research is required to determine the long-term effectiveness of these approaches.

A spatial scale assessment of habitat effects on arthropod communities of an oceanic island

“…Thus, with the purpose of improving conditions necessary for the spreading of native and endemic species, intensively managed pastures should be replaced by semi-natural pastures, and most preferably, the increase of tree and shrub vegetation cover should be strongly encouraged. Grassland restoration is a complex issue (Pywell et al, 2007) and much evidence suggests that it is difficult, if not impossible, to re-establish the natural ancestral condition (Hobbs et al, 2006;Whittingham, 2007). However, it has been observed multiple times in the Azores that when grazing intensity decreases, the semi-natural pastures are easily invaded by the endemic shrub Erica azorica.…”

Enhancing floral resources for pollinators in productive agricultural grasslands

“…While the minimum tillage approach has low fuel requirements, uses no herbicides and helps maintains soil carbon stocks, it is relatively ineffective in terms of controlling competitive weed species (Edwards, et al, 2007;Morris, et al, 2010). This limits the window of opportunity for small seeded, slow-growing wildflowers to establish (Edwards, et al, 2007;Pywell, et al, 2007).…”

“…Indeed, such an approach would not only benefit insect pollinators, but would re-establish threatened grassland types to the benefit of native wildlife and a range of ecosystem services in general (Bullock, et al, 2011;Littlewood, et al, 2012). However, restoration of grasslands is technically hard to achieve, time consuming and expensive (Bullock, et al, 2011;Pywell, et al, 2007). Where soils have become enriched with nutrients, typically following the application of inorganic fertilisers (Edwards, et al, 2007;Pywell, et al, 2007) or as a result of atmospheric nitrogen deposition (Payne, et al, 2013), re-establishing stress-tolerant species often meets within limited success.…”

“…However, restoration of grasslands is technically hard to achieve, time consuming and expensive (Bullock, et al, 2011;Pywell, et al, 2007). Where soils have become enriched with nutrients, typically following the application of inorganic fertilisers (Edwards, et al, 2007;Pywell, et al, 2007) or as a result of atmospheric nitrogen deposition (Payne, et al, 2013), re-establishing stress-tolerant species often meets within limited success. Furthermore, such restoration is a form of land sparing which results in the loss of agriculturally-productive land (Rey Benayas and Bullock, 2012).…”

“…We test how seed bed preparation, management (cattle grazing or cutting) and its intensity affect the persistence of these plants and so the provision of pollen and nectar resources. We hypothesised that: H1) Wildflowers require the creation of a large amount of bare ground to establish in grassland (Bullock, et al, 2001;Pywell, et al, 2007) and so inversion tillage (conventional ploughing) in combination with application of non-selective herbicide is a more effective means of creating a seed bed to establish wildflowers when compared with non-inversion, minimum tillage alone. This reflects the value of inversion tillage and herbicide in controlling competitive and undesirable species (Morris, et al, 2010;Pywell, et al, 2007);…”