Dieback of Calluna vulgaris in a Coastal Heathland After the 2018 Extreme Drought

Abstract

Aims

Central and northern Europe experienced extremely dry conditions in 2018, which caused dieback events in many ecosystems, including coastal heathlands. Our aim was to determine the causes of the varying drought responses observed in Calluna vulgaris on the Baltic island of Hiddensee after this extreme drought.

Location

Island of Hiddensee, Baltic Sea, NE Germany.

Methods

We assessed heathland community damage in autumn 2018 and 2019 with drone-based remote sensing. In addition, we measured water table depths and excavated root samples of C. vulgaris. In 2019, we sampled neighboring C. vulgaris individuals showing contrasting vitality statuses (dead, weakened or healthy), measured their height and canopy width, and prepared cross-sections of the main stem at the root collar or soil surface level to count and measure their xylem rings. We also assessed climate-growth correlations in these individuals.

Results

An 8.0% of all heathland plants showed damage in 2018, while this value decreased to 6.6% in 2019. Only 18% of the plants showing damage in 2018 recovered in 2019. Plant damage was positively related to elevation. Groundwater measurements showed that water table depth dropped below C. vulgaris rooting depth during 2018 and 2019. Healthy plants were taller and had a larger crown area than neighboring weakened and dead individuals, but they did not differ in age nor in previous years' growth. C. vulgaris growth was positively correlated with June and July precipitation.

Conclusions

Our study evidences the negative impacts of extreme droughts on C. vulgaris in coastal heathlands, especially in individuals growing in elevated areas and/or relatively small-sized a, and emphasizes the need for adapting heathland management planning accordingly.