There and back again : Forty years of change in vegetation patterns in Irish peatlands

Northern peatlands play a disproportionally large role in the global carbon balance due to the massive amount of carbon stored in peat and ongoing sequestration. Vegetation composition and structure are recognised indicators for carbon sequestration and storage potential in these ecosystems, but decadal dynamics and roles of autogenic succession, climate, and land-use herein remain poorly understood. We assessed vegetation changes in the least disturbed centre of twelve Irish peatland reserves sampled across a gradient in temperature and precipitation between 1978(1983)–2021, combining re-classified traditional high-resolution vegetation maps with recent very high-resolution drone imagery. Specifically, we tested whether microform proportions of open water, wet hollow, moist lawn, and dry hummock had changed and explored to what extent changes were related to climate and land-use drivers. Results revealed that the studied peatlands underwent an overall unidirectional surface drying trend, with dry hummocks expanding at the expense of open water and wet hollow, while moist lawns remained approximately equal in proportions. The degree of change varied between the studied peatlands, with western blanket bogs and unrestored raised bogs experiencing more surface drying than mountain blanket bogs and raised bogs under hydrological restoration. While our results indicated climate and/or land-use as drivers of surface drying, our sample size was too small to make definitive conclusions about their exact role. The overall change from wet to dry surface conditions between 1978 and 2021 occurred at a much faster rate than hitherto reported for these slow-changing ecosystems. This raises concern for the future resilience of peatlands to changes in climate and land-use, as well as their potential impact on the peatland carbon balance.