Persistent versus transient tree encroachment of temperate peat bogs: effects of climate warming and drought events

Abstract

Peatlands store approximately 30% of global soil carbon, most in moss-dominated bogs. Future climatic changes, such as changes in precipitation patterns and warming, are expected to affect peat bog vegetation composition and thereby its long-term carbon sequestration capacity. Theoretical work suggests that an episode of rapid environmental change is more likely to trigger transitions to alternative ecosystem states than a gradual, but equally large, change in conditions. We used a dynamic vegetation model to explore the impacts of drought events and increased temperature on vegetation composition of temperate peat bogs. We analyzed the consequences of six patterns of summer drought events combined with five temperature scenarios to test whether an open peat bog dominated by moss (Sphagnum) could shift to a tree-dominated state. Unexpectedly, neither a gradual decrease in the amount of summer precipitation nor the occurrence of a number of extremely dry summers in a row could shift the moss-dominated peat bog permanently into a tree-dominated peat bog. The increase in tree biomass during drought events was unable to trigger positive feedbacks that keep the ecosystem in a tree-dominated state after a return to previous 'normal' rainfall conditions. In contrast, temperature increases from 1 °C onward already shifted peat bogs into tree-dominated ecosystems. In our simulations, drought events facilitated tree establishment, but temperature determined how much tree biomass could develop. Our results suggest that under current climatic conditions, peat bog vegetation is rather resilient to drought events, but very sensitive to temperature increases, indicating that future warming is likely to trigger persistent vegetation shifts.

Phylogenetic or environmental control on the elemental and organo-chemical composition of Sphagnum mosses?

“…But, as long as species replacement occurs within taxonomic section, the consequences for peat accumulation may be limited as microtopography, and thereby overall hydrologic functioning, will be maintained (Bohlin et al 1989;Belyea and Clymo 2001). Assuming our inferences above are correct, the phylogenetically conserved carbohydrate chemistry thus likely reinforces the strong control exerted by Sphagnum species on their environment, contributing to the resilience of peatlands to environmental change (Belyea 2009;Turetsky et al 2012;Heijmans et al 2013). …”

Behind the stability of boreal bog carbon sink: Compositional and functional variation of vegetation across temporal and spatial scales

“…Peatlands are currently considered as complex adaptive systems, which are resilient to environmental changes to some degree, but capable of rapid transformation to an alternative stable state at higher level of perturbation (Belyea and Baird, 2006;Dise, 2009;Heijmans et al 2013). The spatial surface patterning typical for bog state emerges as a result of selforganizing process (Belyea and Baird, 2006).…”

The Impact of Experimental Temperature and Water Level Manipulation on Carbon Dioxide Release in a Poor Fen in Northern Poland

“…Many studies documented that main factors impacting soil respiration (R ECO ) and therefore carbon emissions are air temperature (Bubier et al 1998;Bortoluzzi et al 2006;Davidson et al 2006;Heijmans et al 2013) or peat temperature (Chapman and Thurlow 1996;Silvola et al 1996;Lafleur et al 2005;Juszczak et al 2013;D'Angelo et al 2016). Approximate 1°C temperature increase at subarctic peatlands resulted in increases of R ECO values and mobilization of carbon that was located in deeper peat layers (Dorrepaal et al 2009).…”