Speaker
Description
European heathlands are unique natural landscapes, providing a wide range of ecosystem services, however ongoing climate change threatens plant health and ecosystem functioning. Without conservation management, heathlands would slowly be replaced by successional forests. However, under high N deposition, heather (Calluna vulgaris) dieback has been followed by increased growth of pioneer grass species including Molinia caerulea shifting from a shrub-dominated to a grass-dominated ecosystem. M.caerulea litter is less lignified than C.vulgaris litter and has lower C:N ratios making it easier decomposable. Pioneer species often have a lower nutrient use efficiency, further enhancing potential nutrient losses. It remains unclear how future climatic conditions will affect heathlands, potential succession, and their ecosystem functioning.
To investigate the effect of climate change on heathland ecosystem dynamics, a long-term experiment was established in the Ecotron Research Facility of Hasselt University, Belgium. Six heathland monoliths (2 m diameter, 1.5 m depth) were extracted from the Hoge Kempen national park in Belgium and subjected to a gradient of distinct past or future climate scenarios ranging from 1950 to 2070. Carbon, nutrient and water cycles, and vegetation ecophysiology of heathland ecosystem were continuously monitored.
We observed heather dieback in one experimental unit in the middle of the climate gradient after a period characterized by particularly high rainfall followed by high continentality. C.vulgaris died and M.caerulea filled the gaps in the vegetation until the whole monolith was dominated by grasses. No changes in vegetation were documented in the other units, indicating that reasons for vegetation shifts were more complex than increased climate forcing. In the shifting unit, the change in vegetation was further visible in root images acquired with minirhizotrons where grass roots appeared thicker and mainly in the upper soil layer (10 cm), while heathland-dominated units were characterized by dense fine root networks to depths of 35 cm.
We further assessed how this vegetation shift affected ecosystem functioning including C fluxes, soil water nutrient concentrations, litter decomposition rates, and microbial communities. In this presentation, we will present the main results of this long-term experiment and discuss their potential implications for our understanding on tipping points.
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