Carbon accumulation rates of Holocene peatlands in central–eastern Europe document the driving role of human impact over the past 4000 years

Peatlands are one of the largest terrestrial carbon sinks on the planet, yet little is known about the carbon accumulation rates (CARs) of mountainous peatlands. The long-term variability in the size of the associated carbon sink and its drivers remain largely unconstrained, especially when the long-term anthropogenic impact is also considered. Here, we present a composite CAR record of nine peatlands from central–eastern Europe (Romania and Serbia) detailing variability in the rates of carbon accumulation during the Holocene. We show examples of extremely high long-term rates of carbon accumulation (LORCA>120 gCm-2yr-1), indicating that mountain peatlands constitute an efficient regional carbon sink at times. By comparing our data to modelled palaeoclimatic indices and to measures of anthropogenic impact we disentangle the drivers of peat carbon accumulation in the area. Variability in early- and mid-Holocene CARs is linked to hydroclimatic controls, with high CARs occurring during the early Holocene and lower CARs associated with the transition to cooler and moister mid-Holocene conditions. By contrast, after 4000 years (calibrated) before present (years BP), the trends in CARs indicate a divergence from hydroclimate proxies, suggesting that other processes became the dominant drivers of peat CARs. We propose that enhanced erosion following tree cover reduction as well as increased rates of long-distance atmospheric dust fallout might have played a role, as both processes would result in enhanced mineral and nutrient supply to bog surfaces, stimulating peatland productivity. Surprisingly though, for the last 1000 years, reconstructed temperature is significantly correlated with CARs, with rising temperatures linked to higher CARs. Under future climate conditions, which are predicted to be warmer in the region, we predict that peat growth may expand but that this is entirely dependent upon the scale of human impact directly affecting the sensitive hydrological budget of these peatlands.

Carbon accumulation rates of Holocene peatlands in central-eastern Europe document the driving role of human impact for the past 4000 years

Peatlands are one of the largest terrestrial carbon sinks on the planet, yet little is known about carbon accumulation rates (CARs) of mountainous examples. The long-term variability in the size of the associated carbon sink and its drivers remain largely unconstrained, especially when long-term anthropogenic impact is also considered. Here we present a composite CAR record of nine peatlands from central-eastern Europe (Romania and Serbia) detailing variability in rates of carbon accumulation across the Holocene. We show examples of extremely high long-term rates of carbon accumulation (LORCA > 120 g C m−2 yr−1), indicating that at times, mountain peatlands constitute an efficient regional carbon sink. By comparing our data to modelled palaeoclimatic indices and to measures of anthropogenic impact we disentangle the drivers of peat carbon accumulation in the area. Variability in early and mid-Holocene CARs is linked to hydroclimatic controls, with high CARs occurring during the early Holocene and lower CARs associated with the transition to cooler and moister mid-Holocene conditions. By contrast, after 4000 years (calibrated) before present (yr BP) the trends in CARs indicate a divergence from hydroclimate proxies, indicating that other processes became the dominant drivers of peat CARs. We suggest that enhanced erosion following tree cover reduction as well as enhanced rates of long-distance atmospheric dust fallout might have played a role as both processes would result in enhanced mineral and nutrient supply to bog surfaces, stimulating peat land productivity. Surprisingly though, for the last 1000 years, reconstructed temperature is significantly correlated with CARs, with rising temperatures linked to higher CARs. We suggest under future climate conditions, predicted to be warmer in the region, peat growth may expand, but that this is entirely dependent upon the scale of human impact directly affecting the sensitive hydrological budget of these peatlands.

Constructive criticism of “Misinterpreting carbon accumulation rates in records from near-surface peat” by Young et al: Further evidence of charcoal impacts in relation to long-term carbon storage on blanket bog under rotational burn management

t is with great interest that we read the recent paper by Young et al. entitled “Misinterpreting carbon accumulation rates in records from near-surface peat”. However, we have some concerns about: (i) the use of an unvalidated deep drainage model to criticise studies investigating the impact of heather burning; (ii) the model scenarios and underlying model assumptions used; and (iii) misleading claims made about net C budgets and deep C losses. We feel that these issues require clarification and, in some cases, correction, especially as Young et al. has been used by a leading peatland policy and conservation body (IUCN UK Peatland Programme) to incorrectly characterise two recent studies by Heinemeyer et al. and Marrs et al. as having “presented misleading conclusions”. We strongly believe that one of the main ways to increase our scientific understanding is through vigorous and factual debate. Whilst we are open to and welcome criticism, such criticism needs to be accurate, balanced and evidence-based. Criticism must avoid unfounded or speculative accusations, especially when based on unrelated and unvalidated model scenarios. Indeed, study aims, hypotheses and discussion sections all need to be considered to ensure any criticism is applicable. We accept that deep C losses can be caused by peatland drainage and that this can lead to the misinterpretation of peat surface C accumulation rates or peatland C budgets. But these issues do not apply to the Heinemeyer et al. study, which investigated two specific and clearly stated burn-related hypotheses (charcoal impacts on peat properties and thus peat C accumulation), which only required comparisons of C accumulation rates within recent peat layers. Moreover, using peat core data collected by Heinemeyer et al., we provide strong evidence that the accusations of deep C losses by Young et al. are unfounded. However, the peat core data from Heinemeyer et al. does highlight the value of the Young et al. model scenarios for predicting short-term C loss caused by recent drainage. Finally, we also highlight the value of a detailed peat layer organic C content (%Corg) assessments to detect potential management (i.e. drainage) induced deep peat C loss.

First-Decade Biomass and Carbon Accumulation, and Woody Community Change after Severe Wind Damage in a Hemlock-White Pine Forest Remnant

Studies of biomass and carbon dynamics and community composition change after forest wind disturbance have predominantly examined trends after low and intermediate severity events, while studies after very severe wind disturbance have been few. This study documents trends in aboveground biomass and carbon across 10 years of forest recovery after severe wind disturbance. In July 1989, a tornado struck mature Tsugacanadensis-Pinusstrobus forest in northwest Connecticut, USA, causing damage across roughly 8 ha. Canopy tree damage and regeneration were surveyed in 1991 and 1999. Two primary hypotheses were tested, both of which derive from regeneration being primarily via the release of suppressed saplings rather than new seedling establishment: (1) Biomass and carbon accumulation will be faster than accumulation reported from a similar forest that experienced similar severity of wind disturbance; and (2) The stand will experience very little change in species composition or diversity. Estimated immediate post-disturbance (1989) aboveground live-tree carbon was 20.7 ± 43.9 Mg ha−1 (9.9% of pre-disturbance) Ten years after the disturbance, carbon in aboveground live tree biomass increased to 37.1 ± 47.9 Mg ha−1; thus for the first decade, annual accumulation averaged 1.6 Mg ha−1 of carbon; this was significantly faster than the rate reported in a similar forest that experienced similar severity of wind disturbance. The species diversity of woody stems ten years after the disturbance was significantly higher (nonoverlapping confidence intervals of rarefaction curves) than pre-disturbance canopy trees. Thus, hypothesis 1 was confirmed while hypothesis 2 was rejected. This study augments the limited number of longer-term empirical studies that report biomass and carbon accumulation rates after wind disturbance, and can therefore serve as a benchmark for mechanistic and modeling research.