Investigating the drivers of spatial and temporal biodiversity patterns of the Machair

• Main Author: Lewis, Robert
• Other Authors: Marrs, R. H. M.; Pakeman, R. J. P.; Lennon, J. J. L.
• Published: University of Liverpool 2012
• Subjects: 333.95; Q Science (General)
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.564270

In plant ecology, understanding which species live where and why is fundamental for ensuring successful conservation management with the aim of maintaining biodiversity and ecosystem services. Biodiversity patterns in space can be empirically linked to spatially scaled environmental processes, providing a greater understanding to how plant species assemblages change along differing environmental gradients. In the same way, biodiversity patterns in time can be linked to temporal trends in the environment, empirically linking changes in vegetation to changes in the external environment. This furthers understanding of how plant communities are likely to respond to future scenarios of environmental change, providing an insight into future shifts in biodiversity patterns and, in turn, how his may influence valuable ecosystem functions and services upon which humans ultimately depend. Trends in human land use have been shown to be the single most influential driver of current global biodiversity change to date. This, coupled with a changing climate, suggests vegetation communities on a global scale are under increasing pressure to adapt to multiple dynamically changing environmental constraints. This thesis focuses on a globally-rare semi-natural, coastal grassland habitat termed ‘Machair’, renowned for its high biodiversity and cultural heritage importance. Confined solely to the north-western fringe of Europe, the Machairs have formed through unique combinations of geo-physiological and climatic conditions, and even more importantly, century-long associations with human land use through which the low-intensity intermediate disturbance is considered to be vital in maintaining its biodiversity value. However, change in the management of the Machairs alongside other environmental drivers of change, particularly climate, provides major concerns for the biodiversity value of this habitat. In this thesis, spatial and temporal biodiversity patterns of Machair vegetation are investigated to assess the major drivers of change and identify regions which may require future conservation efforts to restore and/or maintain the future biodiversity value of this globally-rare habitat. To achieve this, a spatio-temporal dataset of Scottish Machair vegetation first collected in 1976-77 and then re-surveyed in 2009-10 was used. Analyses found both climate and land use management to influence spatial and temporal vegetation patterns of Scotland’s Machair and Machair grassland. Climate was shown to operate at relatively broad scales (>50km), while the influence of different measurable components of climate was also found to significantly affect temporal turnover patterns of Machair grassland assemblages. Land use management, predominantly at a relatively fine scale (<1.5km), is shown to be the single most influential driver of spatial turnover patterns among both the national extent of Scotland’s soft coast habitats (i.e. low lying coastal areas composed of sand, shingle or mud) and Machair. This indicates the relative importance of land use management in maintaining the high habitat heterogeneity and a high proportion of edge habitat believed to be vital for maintaining the high biodiversity value typical of these habitats. Considerable change in Machair biodiversity for many of Scotland’s regions was observed, much of which could be reasonably well linked to reported shifts in land use, particularly shifts towards increased use of inorganic fertilisers and either increased or decreased agricultural intensification. Not all change was deleterious, many regions which were once included in government incentivised schemes specific to the protection and biodiversity maintenance of Machair grassland displayed higher biodiversity, including species of conservation importance. This highlights the importance of financial incentives to encourage environmentally sensitive land use management more inline with traditional practices, which are increasingly becoming socially and economically unviable. The analyses used were deliberately targeted to identify the community assembly processes by which the Machair communities are governed at local, regional and national scales. It is evident that these communities are governed by environmental filtering at relatively broad regional scales principally through climatic constraints, and similarly at relatively fine local scales through constraints imposed by land use management. It is also evident that community assembly processes are not mutually exclusive and operate simultaneously, at hierarchical scales. Biotic processes at extremely fine scales certainly operate to govern the vegetation communities of Machair grasslands, evident through functional trait divergence. Furthermore, shifts in land use management are shown to impact on these assembly processes, displaying for several regions, an increase in constraints through environmental filtering and reduced resilience through reduced niche differentiation. This study makes a valuable contribution to knowledge of how land use and climate impact on spatial and temporal biodiversity patterns among Machair vegetation, identifying the relative importance of climate and land use determinants, the scale at which they operate, and, how current trends are influencing the biodiversity value of the Machairs at national and regional scales. Furthermore this research demonstrates the utility of different methodological advances and techniques in investigating patterns of biodiversity change for a better understanding of the patterns and processes that govern plant communities.