Climate change impacts on ecosystem functioning: evidence from an Empetrum heathland

Abstract

Summary• The extent to which plants exert an influence over ecosystem processes, such as nitrogen cycling and fire regimes, is still largely unknown. It is also unclear how such processes may be dependent on the prevailing environmental conditions.• Here, we applied mechanistic models of plant-environment interactions to palaeoecological time series data to determine the most likely functional relationships of Empetrum (crowberry) and Betula (birch) with millennial-scale changes in climate, fire activity, nitrogen cycling and herbivore density in an Irish heathland.• Herbivory and fire activity preferentially removed Betula from the landscape. Empetrum had a positive feedback on fire activity, but the effect of Betula was slightly negative. Nitrogen cycling was not strongly controlled by plant population dynamics. Betula had a greater temperature-dependent population growth rate than Empetrum; thus climate warming promoted Betula expansion into the heathland and this led to reduced fire activity and greater herbivory, which further reinforced Betula dominance.• Differences in population growth response to warming were responsible for an observed shift to an alternative community state with contrasting forms of ecosystem functioning. Selfreinforcing feedback mechanisms -which often protect plant communities from invasionmay therefore be sensitive to climate warming, particularly in arctic regions that are dominated by cold-adapted plant populations.

To what extent did changes in July temperature influence Lateglacial vegetation patterns in NW Europe?

“…North of 55 N, percentages were much lower, around 2e5%. The low percentages at Lough Nadourcan in NW Ireland are probably depressed due to the very high Empetrum and Cyperaceae percentages there (Watts, 1977;Jeffers et al, 2011a).…”

“…There is no macrofossil evidence from Fiddaun, but it is likely that R. acetosa was common in the Irish 'Rumex-Juniperus assemblage' (Watts, 1977) during the first part of the interstadial. Rumex pollen attains 15% in the Glenveagh diagram of Watts (1977) from Lough Nadourcan, but it is not on the pollen diagram from there by Jeffers et al (2011a). As that area was dominated by Empetrum heath, even in the early interstadial, and the climate was probably wet, the likely Rumex species is R. acetosa.…”

Using dung fungi to interpret decline and extinction of megaherbivores: problems and solutions

“…In northeastern North America, influx rates were in the range 30e180 spores cm À2 yr À1 at Appleman Lake, Indiana (Gill et al, 2009), and around 1500 at Silver Lake, Ohio (Gill et al, 2012). In the British Isles, accumulation rates were in the range of 200e1000 spores cm À2 yr À1 at Quidenham Mere, Norfolk, England (Jeffers et al, 2011), and varied over a similar range at Lough Nadourcan, Donegal, Ireland (Jeffers et al, 2012) [Both studies by Jeffers et al refer to 'dung-fungus accumulation rates' so could include taxa other than Sporormiella, but Jeffers et al (2012) imply that only Sporormiella was counted]. Table 1 Correlations of variation in spore influx rates among taxa of dung fungi.…”

“…For these reasons, spores of dung fungi are becoming widely used to interpret dynamics of mega-herbivores in the late Quaternary (Davis, 1987;Davis and Shafer, 2006;Jeffers et al, 2011Jeffers et al, , 2012Baker et al, 2013), and to reconstruct changes in the densities and distribution of domestic livestock during the Holocene (Mazier et al, 2009;Cugny et al, 2010;Schofield and Edwards, 2011). Studies using the dung fungus Sporormiella in Madagascar, New Zealand, North America and Australia have been especially valuable in revealing the fine temporal structure of megafaunal extinction in relation to other environmental shifts, and so indicating mechanisms that might (or could not) have been involved (Burney et al, 2003;Robinson et al, 2005;Gill et al, 2009Gill et al, , 2012Wood et al, 2011;Rule et al, 2012).…”

POLLEN METHODS AND STUDIES | Numerical Analysis Methods

“…Statistical techniques such as constrained ordination (e.g., RDA ¼ reduced-rank multivariate regression, CCA, DCCA) and associated Monte Carlo permutation tests can be used to assess the statistical relationships between pollen data ('responses') and external forcing factors ('predictors'), for example, to assess the relative impacts of climatic change and volcanic tephra deposition on pollen assemblages and hence on past vegetation (Lotter and Birks, 1993) or the role of fire on vegetation dynamics (Feurdean et al, 2009). This remains a major challenge in the interpretation of all Quaternary pollen-analytical data -see Birks (1993, 2003), Mitchell (2004), and Jeffers et al (2011Jeffers et al ( , 2012 for examples of different approaches to hypothesis testing in Quaternary pollen analysis. This remains a major challenge in the interpretation of all Quaternary pollen-analytical data -see Birks (1993, 2003), Mitchell (2004), and Jeffers et al (2011Jeffers et al ( , 2012 for examples of different approaches to hypothesis testing in Quaternary pollen analysis.…”