Climate drives temporal replacement and nested‐resultant richness patterns of Scottish coastal vegetation

Beta diversity quantifies spatial and/or temporal variation in species composition. It is comprised of two distinct components, species replacement and nestedness, which derive from opposing ecological processes. Using Scotland as a case study and a β-diversity partitioning framework, we investigate temporal replacement and nestedness patterns of coastal grassland species over a 34-yr time period. We aim to 1) understand the influence of two potentially pivotal processes (climate and land-use changes) on landscape-scale (5 × 5 km) temporal replacement and nestedness patterns, and 2) investigate whether patterns from one β-diversity component can mask observable patterns in the other.

We summarised key aspects of climate driven macro-ecological variation as measures of variance, long-term trends, between-year similarity and extremes, for three important climatic predictors (minimum temperature, water-balance and growing degree-days). Shifts in landscape-scale heterogeneity, a proxy of land-use change, was summarised as a spatial multiple-site dissimilarity measure. Together, these climatic and spatial predictors were used in a multi-model inference framework to gauge the relative contribution of each on temporal replacement and nestedness patterns.

Temporal β-diversity patterns were reasonably well explained by climate change but weakly explained by changes in landscape-scale heterogeneity. Climate was shown to have a greater influence on temporal nestedness than replacement patterns over our study period, linking nestedness patterns, as a result of imbalanced gains and losses, to climatic warming and extremes respectively. Important climatic predictors (i.e. growing degree-days) of temporal β-diversity were also identified, and contrasting patterns between the two β-diversity components revealed.

Results suggest climate influences plant species recruitment and establishment processes of Scotland's coastal grasslands, and while species extinctions take time, they are likely to be facilitated by climatic perturbations. Our findings also highlight the importance of distinguishing between different components of β-diversity, disentangling contrasting patterns than can mask one another.

How simple grazing rules can lead to persistent boundaries in vegetation communities.

Natural landscape boundaries between vegetation communities are dynamically influenced by the selective grazing of herbivores. Here we show how this may be an emergent property of very simple animal decisions, without the need for any sophisticated choice rules etc., using a model based on biased diffusion. Animal grazing intensity is coupled with plant competition, resulting in reaction-diffusion dynamics, from which stable boundaries spontaneously emerge. In the model, animals affect their resources by both consumption and trampling. It is assumed that forage consists of two heterogeneously distributed competing resource species, one that is preferred (grass) over the other (heather) by the animals. The solutions to the resulting system of differential equations for three cases a) optimal foraging, b) random walk foraging and c) taxis-diffusion are presented. Optimal and random foraging gave unrealistic results, but taxis-diffusion accorded well with field observations. Persistent boundaries between patches of near-monoculture vegetation were predicted, with these boundaries drifting in response to overall grazing pressure (grass advancing with increased grazing and vice versa). The reaction-taxis-diffusion model provides the first mathematical explanation for such vegetation mosaic dynamics and the parameters of the model are open to experimental testing.

Numerical analysis of surface and fossil pollen spectra from northern Fennoscandia

Aim Determination of the main directions of variance in an extensive data base of annual pollen deposition, and the relationship between pollen data from modified Tauber traps and palaeoecological data. Location Northern Finland and Norway. Methods Pollen analysis of annual samples from pollen traps and contiguous high-resolution samples from a peat sequence. Numerical analysis (principal components analysis) of the resulting data. Results The main direction of variation in the trap data is due to the vegetation region in which each trap is located. A secondary direction of variation is due to the annual variability of pollen production of some of the tree taxa, especially Betula and Pinus. This annual variability is more conspicuous in ‘absolute’ data than it is in percentage data which, at this annual resolution, becomes more random. There are systematic differences, with respect to peat-forming taxa, between pollen data from traps and pollen data from a peat profile collected over the same period of time. Main conclusions Annual variability in pollen production is rarely visible in fossil pollen samples because these cannot be sampled at precisely a 12-month resolution. At near-annual resolution sampling, it results in erratic percentage values which do not reflect changes in vegetation. Profiles sampled at near annual resolution are better analysed in terms of pollen accumulation rates with the realization that even these do not record changes in plant abundance but changes in pollen abundance. However, at the coarser temporal resolution common in most fossil samples it does not mask the origin of the pollen in terms of its vegetation region. Climate change may not be recognizable from pollen assemblages until the change has persisted in the same direction sufficiently long enough to alter the flowering (pollen production) pattern of the dominant trees.

Vegetation history at the multi-period prehistoric complex at Ballynahatty, Co. Down, Northern Ireland.

Palaeoecological methods can provide an environmental context for archaeological sites, enabling the nature of past human activity to be explored from an indirect but alternative perspective. Through a palynological study of a small fen wetland located within the catchment of a multi-period prehistoric complex at Ballynahatty, Co. Down, Northern Ireland, we reconstruct the vegetation history of the area during the early prehistoric period. The pollen record reveals tentative evidence for Mesolithic activity in the area at 6410-6220 cal. BC, with woodland disturbance identified during the Mesolithic-Neolithic transitional period ca. 4430-3890 cal. BC. A more significant impact on the landscape is observed in the Early Neolithic from 3944-3702 cal. BC, with an opening up of the forests and the establishment of a mixed agricultural economy. This activity precedes and continues to be evident during the Mid-Neolithic during which megalithic tombs and related burial sites were constructed at Ballynahatty. Due to chronological uncertainties and a possible hiatus in peat accumulation in the fen, the contemporary environment of the Ballynahatty timber circle complex (constructed and used ca. 3080-2490 cal. BC) and henge (dating to the third millennium cal. BC) cannot certainly be established. Nevertheless, the pollen record suggests that the landscape remained open through to the Bronze Age, implying a long continuity of human activity in the area. These findings support the idea that the Ballynahatty prehistoric complex was the product of a gradual and repeated restructuring of the ritual and ceremonial landscape whose significance continued to be recognised throughout the early prehistoric period.

Postglacial vegetation and climate dynamics in the Seymour-Belize Inlet Complex, central coastal British Columbia, Canada: palynological evidence from Tiny Lake.

A pollen-based study from Tiny Lake in the Seymour-Belize Inlet Complex of central coastal British Columbia, Canada, permits an evaluation of the dynamic response of coastal temperate rainforests to postglacial climate change. Open Pinus parklands grew at the site during the early Lateglacial when the climate was cool and dry, but more humid conditions in the later phases of the Lateglacial permitted mesophytic conifers to colonise the region. Early Holocene conditions were warmer than present and a successional mosaic of Tsuga heterophylla and Alnus occurred at Tiny Lake. Climate cooling and moistening at 8740?±?70 14C a BP initiated the development of closed, late successional T. heterophylla–Cupressaceae forests, which achieved modern character after 6860?±?50 14C a BP, when a temperate and very wet climate became established. The onset of early Holocene climate cooling and moistening at Tiny Lake may have preceded change at more southern locations, including within the Seymour-Belize Inlet Complex, on a meso- to synoptic scale. This would suggest that an early Holocene intensification of the Aleutian Low pressure system was an important influence on forest dynamics in the Seymour-Belize Inlet Complex and that the study region was located near the southern extent of immediate influence of this semi-permanent air mass.

Vegetation and climate c. 12 300-9000 cal. yr BP at Andoya, NW Norway

Owing to proximity of the North Atlantic Stream and the shelf, the And circle divide ya biota are assumed to have responded rapidly to climatic changes taking place after the Weichselian glaciation. Palynological, macrofossil, loss-on-ignition, tephra and C-14 data from three sites at the northern part of the island of And circle divide ya were studied. The period 12 300-11 950 cal. yr BP was characterized by polar desert vegetation, and 11 950-11 050 cal. yr BP by a moisture-demanding predominantly low-arctic Oxyria vegetation. During the period 11 050-10 650 cal. yr BP, there was a climatic amelioration towards a sub-arctic climate and heaths dominated by Empetrum. After 10 650 cal. yr BP the Oxyria vegetation disappeared. As early as about 10 800 cal. yr BP the bryozoan Cristatella mucedo indicated a climate sufficient for Betula woodland. However, tree birch did not establish until 10 420-10 250 cal. yr BP, indicating a time-lag for the formation of Betula ecotypes adapted to the oceanic climate of And circle divide ya. From about 10 150 to 9400 cal. yr BP the summers were dry and warm. There was a change towards moister, though comparatively warm, climatic conditions about 9400 cal. yr BP. The present data are compared with evidence from marine sediments and the deglaciation history in the region. It is suggested that during most of the period 11 500-10 250 cal. yr BP a similar situation as in present southern Greenland existed, with birch woodland in the inner fjords near the ice sheet and low-arctic heath vegetation along the outer coast.

Efficacy of sod removal in regenerating fen vegetation for the conservation of the marsh fritillary butterfly Euphydryas aurinia, Montiaghs Moss Nature Reserve, County Antrim, Northern Ireland.

The efficacy of ‘sod removal’ as a fenland restoration technique was tested using an experimental approach at Montiaghs Moss Nature Reserve, Northern Ireland, from 2006 to 2008. The site suffered from rank growth of purple moor-grass Molinia caerulea which was out-competing herbaceous species. Soil was removed up to a depth of 15 cm completely denuding vegetation in the experimental plot exposing bare peat. By July 2007, 15.2% of sod-removal areas were revegetated; by October 2008 cover had risen to 64.6%. Of this cover, purple moor-grass accounted for only 9-11% compared to 78- 79% on control plots. Cover of other rank-forming grass species was also significantly reduced. Sod removal significantly increased the cover of species characteristic of fenlands including sedges Carex spp., rushes Juncus spp., marsh pennywort Hydrocotyle vulgaris and lesser spearwort Ranunculus flammula. It seems likely that sod removal, which lowered the surface of the peat, restored minerotrophic conditions and exposed the historical seed bank stimulating regeneration of some fenland specialists and pioneer species; this resulted in significantly higher species richness on sod removal plots than control plots two years after treatment. There was no demonstrable effect of sod removal on abundance of devil’s-bit scabious Succisa pratensis, the larval food plant of the Annex II listed marsh fritillary butterfly Euphydryas aurinia. We recommend that consideration should be given to artificially seeding devil’s-bit scabious soon after sod removal treatment to promote early recolonisation and to increase plant abundance on the site.