Nitrogen Deposition Increases Spontaneous Forest Establishment and Loss of Lichen Vegetation in Inland Dune Areas Across the Netherlands

Questions

(1) How much of the inland dune habitat has been transformed into spontaneous forest across the Netherlands between 2007 and 2018? (2) Is there a spatial correlation between nitrogen deposition and changes in vegetation? (3) What changes could be observed in the cover of lichen vegetation and the invasive bryophyte Campylopus introflexus within this period? (4) What measures can be taken to counteract the effect of spontaneous forest establishment?

Location

Inland dune sites across the Netherlands are primarily located in the eastern part of the country.

Methods

Comparative analysis of vegetation maps made in 2007 and 2018. Lichen species trends were estimated based on a study with 75 permanent plots over the period 1999–2023.

Results

Our study shows that, with increasing N deposition, the spontaneous forest establishment rate doubles. The Netherlands loses 118 ha (0.7%) of inland dune vegetation to spontaneous forest establishment annually, which is largely compensated by nature restoration measures. Increasing nitrogen deposition causes a stronger dominance of Campylopus introflexus. This resulted in a 40% decrease in the abundance of terrestrial lichen species, and consequently in a decrease in overall habitat quality.

Conclusions

N deposition has a positive effect on spontaneous forest establishment in inland dune areas across the Netherlands. In total, site management would have to fell a minimum of 118 ha of Scots pine annually as a restoration measure to combat the spontaneous establishment rate and maintain the current open area inland dune habitat. Habitat quality was negatively affected and visible as a strong decline in lichen abundance and an increase in the invasive moss Campylopus introflexus.