Response of inland dune vegetation to increased nitrogen and phosphorus levels

Question: How does pioneer vegetation of acid inland dunes respond to addition of nitrogen (N) and phosphorus (P)? Location: Two inland dune reserves in The Netherlands with low and high N deposition. Methods: During 2.5 yr, N and P addition (control, N, P, NP) took place in three different vegetation types of inland dunes (Polytrichum piliferum mats, Campylopus introflexus mats and lichen-dominated vegetation). In each site, changes in the vegetation were recorded in three replicate quadrats of 1 m × 1 m per treatment. Differences in element content of grasses and lichens were recorded, together with vegetation parameters, including cover and height of grasses, bryophytes and lichens. Results: In the site with high N deposition, grasses were taller, had higher N:P ratios and a generally lower lichen cover than in the low-deposition area. Experimental N application resulted in higher N and lower base metal concentrations in grasses and an increase in grass cover and size. In contrast, lichens showed a general decline in the N treatment and the lichen:grass ratio decreased. The effect of N addition was larger in the low-deposition area. The P treatment had an opposite effect: lichens increased in size and cover and overgrew grasses, especially when reindeer lichens were present. This suggests that the cryptogam layer was P-limited even in the low N deposition site. Conclusions: Pioneer vegetation in inland dunes is susceptible to N and P addition. The results provide evidence for a decrease in lichen cover due to increased N deposition.