Drought and successional stage affects leaf and flower phenology

Due to climate change there have been major shifts in weather events, with a predicted increase in extreme drought events in Western Norway. These events in combination with land-use change, are putting the red-listed ecosystem coastal heathlands under high pressure. In Norway, there has been a loss of 90% of coastal heathland cover over the last decades, with the remaining 10% being dominated by the mature successional stage.

In recent years, there has been research highlighting how the mature heathlands are vulnerable to drought. This includes a higher input of litter into the system and also less seeds seeds, which are of lower quality when exposed to drought. These results indicate an effect on the leaf and flower phenology of the dominant species in coastal heathlands.

To expand our knowledge, this project has investigated the responses to drought through leaf and flower phenology for the dominating dwarf-shrub species in coastal heathlands; Calluna vulgaris, Empetrum nigrum, Vaccinium myrtillus and Vaccinium vitis-idaea. The project was conducted from April 2023 until May 2024 using the DroughtNet rainout shelters established at Lygra in 2017. This experiment is one of few long term drought experiments in coastal heathlands. Within the site there are 3 successional stages (young, intermediate, mature), with 3 drought treatments (control, 60% and 90% roof coverage), which is replicated by 3, resulting in 27 plots. Within each plot a replica of 5 for each species were subjected to phenology measurements: plant height, branch length and thickness, flowering time, number of flowers, and number, length, and colouration of leaves. 

Our results show an earlier flowering in the mature stage, with less flowers with increasing drought. The number of leaves seems to be less affected by drought, except in the mature stage, where the leaf count is overall lower, especially in the extreme drought treatment (90% roof coverage). Our results build upon previous research and confirms that the older mature successional stage is more sensitive to drought.