Plant community responses to experimental climate manipulation in a Welsh ombrotrophic peatland and their palaeoenvironmental context.

We test whether vegetation community composition from a 10-year climate manipulation experiment on a Welsh peat bog resembles vegetation communities during periods of climate change inferred from a peat core. Experimentally warmed and combined warmed and droughted treatments drove significant increases in ericaceous shrubs but Sphagnum was unaffected. Similarly, Calluna vulgaris seeds increase during inferred warmer periods in the palaeoecological record. Experimental short-term episodic drought (four 4-week drought treatments) did not affect vegetation. Plant community composition has undergone several abrupt changes throughout the past c. 1500 years, often in response to human disturbance. Only slight changes occurred during the Medieval Climate Anomaly (c. 950-1250 Common Era [CE]) in vegetation and hydrology, while abrupt changes occurred during the Little Ice Age (c. 1300-1850 CE) when water tables were highest, suggesting that these shifts were driven by changes in water table, modulated by climate. A period of water table drawdown c. 1800, synchronous with historical records of increased drainage, corresponds with the development of the present-day vegetation community. Modern analogues for fossil material, characterized by abundant Rhynchospora alba and Sphagnum pulchrum, are more common after this event. Vegetation changes due to climate inferred from the palaeo record differ from those observed in the experiments, possibly relating to differences in the importance of drivers of vegetation change over varying timescales. Whereas temperature is frequently identified as the dominant driver of plant community change in experiments, sustained changes in water table appear to be more important in the long-term record. We find evidence that recent climate change and other anthropogenic stressors (e.g. drainage, heavy metal and nitrogen pollution) may promote the development of novel plant communities without analogues in the fossil record. These communities may be poorer at sequestering carbon and may respond differently to future climate change.

Annual gaseous carbon budgets of forest-to-bog restoration sites are strongly determined by vegetation composition.

Large areas of naturally open peatland in western Europe were drained and planted with non-native conifers in the twentieth century. Efforts are currently underway to restore many of these sites. Ultimately, forest-to-bog restoration aims to bring back functional peatlands that can sequester carbon but there is a lack of empirical evidence for whether current approaches are effective. Using a chronosequence design, we compared the annual gaseous carbon balance of two forest-to-bog restoration areas with an open area not subject to afforestation. A closed chamber method was used to determine gas fluxes (Net Ecosystem Respiration, Gross Primary Productivity, Net Ecosystem Exchange (NEE) and methane (CH4)) over a twelve-month period for locations spanning the range of peatland microtopography and vegetation communities. Relationships between gas fluxes, vegetation/cover and environmental factors were analysed and regression models used to estimate annual CO2 and CH4 budgets. During the study period, NEE estimates (total gaseous C expressed as CO2-eq) showed a net sink for the unafforested (-102 g C m-2 yr-1) and oldest (-131 g C m-2 yr-1) restoration area (17 years post-restoration 'RES 17 YRS'), whilst the youngest restoration area (6 years post-restoration 'RES 6YRS'), was a net source (35 g C m-2 yr-1). We observed significantly higher CH4 emissions from restoration areas dominated by Eriophorum angustifolium compared with other peatland vegetation types. Sampling points with higher cover of Sphagnum were found to be most effective for C sequestration. Overall, vegetation composition/cover was observed to be an important factor determining C emissions from forest-to-bog restoration areas. These results suggest that restoration is effective in returning the carbon sink function of peatlands damaged by commercial forestry and - depending on restoration techniques - timescales of >10 years may be required.

Ecological and environmental transition across the forested-to-open bog ecotone in a west Siberian peatland.

Climate change may cause increasing tree cover in boreal peatlands, and the impacts of this encroachment will be noted first at forested-to-open bog ecotones. We investigate key metrics of ecosystem function in five such ecotones at a peatland complex in Western Siberia. Stratigraphic analysis of three cores from one of these transects shows that the ecotone has been dynamic over time with evidence for recent expansion of forested peatland. We observed that the two alternative states for northern boreal peatlands (forested/open) clearly support distinct plant and microbial communities. These in turn drive and respond to a number of feedback mechanisms. This has led to steep ecological gradients across the ecotones. Tree cover was associated with lower water tables and pH, along with higher bulk density, aquatic carbon concentrations, and electrical conductivity. We propose that the conditions found in the forested peatland of Western Siberia make the carbon sink more vulnerable to warmer and drier conditions.