Long-Term Land Use Change on the Machair and its Impact on Biodiversity

Published on 3 May 2012 in Sustainability and Communities , Ecosystems and biodiversity

Introduction

Machair is a distinctive type of coastal grassland restricted to about 25,000 ha in world-wide extent; 17,500 ha of this resource are in Scotland. Machair develops on calcareous sands deposited by onshore winds on exposed, western coasts, is comparatively plant species-rich and hosts a number of rare plant, invertebrate and bird species. It is a Priority Habitat within the UK Biodiversity Action Plan and included in Annex 1 of the EC Habitats Directive.

It is acknowledged that the high nature value derives from its continued use for low-intensity agriculture and a land ownership structure which often includes crofting tenants who, to varying extents, manage the land communally within township units.

National monitoring schemes miss out rare habitats or are not designed to look at changes over time. They also fail to quantify the drivers of change and infer them from analysis of the data. The project reported here used a combination of a resurvey of vegetation records, a sociological investigation of changes in land use practices and analysis of agricultural statistics to determine if changes in land use practices have had an impact on vegetation diversity, composition and function.

The study was funded by the Esmée Fairbairn Foundation and the Scottish Government.

Key Points

Many of the concerns over changes in machair management were confirmed by the interviews with land managers and the Agricultural Census data. Specifically these were:

A near restriction of arable cropping to North and South Uist, and on these islands a reduction in the area cropped.
A reduction in the use of strip cultivation, so that land is managed in large blocks leading to homogenisation of the landscape.
A switch from dependency on seaweed as a fertiliser to inorganic fertilisers and an increase in plough depths.
A switch from hay to silage cropping and a near abandonment of cropping on the in-bye ground.
A reduction in the number of active crofters. This was nearly universal across the sites studied and approximated to a 50 % reduction in their numbers in c. 35 years.

Changes that have not been previously identified included:

A greater stability in land use within farms than within crofting areas. Improvements/intensification on the farms had largely occurred prior to the 1970s.
A shift in summer grazing from the hill ground to the in-bye close to habitation, reducing the area cut for winter fodder.
A substantial reduction in the use of hill ground in all areas.
Substantial falls in both cattle and sheep numbers. Cattle numbers have dropped faster, so the ratio of sheep to cattle has increased.

In terms of the impacts of land use change on the vegetation of the machair overall and for machair grasslands specifically there were considerable differences between islands and regions:

Increased species richness was seen in both machair and machair grassland Barra, Coll, Colonsay, Islay, South Uist and Tiree.
Declines in species richness were observed for Harris, Lewis, Monach Isles, North Coast (machair only), North Uist (machair only) and Shetland.
Analysis of changes in the vegetation by assessing changes in species, functional groups and indicator values suggested that decreased grazing intensity and decreased cultivation are the main drivers of declines in species richness – as grazing falls many shorter species are shaded out and a dense moss layer can develop which prevents species regeneration of shorter-lived species.
The increased species richness seen for many of the areas seems to be in line with an increase in species that prefer grazing. These areas include many of the islands with farms rather than crofts, suggesting that land use in farmed areas is more stable than in crofting ones.
Not in line with these results was Shetland, where a decline in species richness was associated with an increase in grazing, possibly the grazing has reached a point where grazing sensitive species are being eliminated, and Sanday, where no change in richness was observed but management intensity had increased.
There was some indication of enrichment for Islay, Sanday and Shetland as indicator values for nitrogen rose. This suggests these areas have seen significant shifts to species preferring more nutrient-rich habitats not characteristic of traditional machair management.
Assessing change using species indicator groups from Common Standard Monitoring suggested a decline in quality of machair in terms of desirable and undesirable species in Barra, Benbecula, Monach Isles, North Uist and Shetland.

Overall, these results are in line with the land use change results. Declines in management intensity in many crofting areas are detectable in shifts in species richness and composition. This appears to be of particular concern for Barra, Harris, Lewis, North Coast and North Uist. The unpopulated Monach Isles are also of concern, but it is unlikely that management can be changed on this remote set of island. There is also concern for intensification in management having impacts on Islay, Sanday and Shetland.

Research Undertaken

From 1975 to 1977 a large-scale vegetation survey of all major sand dune sites around Scotland was carried out. During 2009 and 2010, 56 sites were revisited, covering almost all of this resource in Scotland. Quadrat locations were relocated and changes in plant diversity, composition and functional attributes analysed.

Parallel to this investigation, interviews with 79 crofters, farmers and township clerks were carried out. These were aimed at identifying changes in land management over the same time period as the two surveys for the machair areas, and associated in-bye land and common grazings. Agricultural Census data was examined to reveal parish level trends in stocking rates and in cropping practices for the same period.

Policy Implications

All the areas with a decreased intensity of management are crofting areas which have seen a substantial reduction in the numbers of crofters between the surveys as well as a reduction in the number of grazing animals and the amount of cropping carried out.

The major land use changes were a retraction of arable cropping to the Uists (and even here it declined in frequency), increased use of inorganic fertilisers and deeper ploughing, and a shift in grass management from hay cropping to silage making, particularly on the in-bye land. The current Machair LIFE+ project has the aim of extending the area under arable cultivation. However, the changes on the in-bye land and the reduction in hill grazing indicate that concern about this habitat should be widened from the narrow focus on machair grasslands to the whole land use system.

The long-term health of this resource appears intrinsically linked to the numbers of active crofters and hence altering agri-environment payments to focus on different aspects of habitat management is unlikely to have a great impact on conservation unless this reduction in active management is addressed as well. Adjusting agri-environment payments may help prevent further declines in quality in the farming areas.

Author

Professor Robin Pakeman robin.pakeman@hutton.ac.uk

Topics

Sustainability and Communities , Ecosystems and biodiversity