Successful recovery of grey dunes after shallow sod cutting and wildfire

In the second half of the 20th Century coastal dune grasslands in the Netherlands, belonging to the grey dunes, have suffered from severe grass and shrub encroachment, mainly due to prolonged stabilisation, nitrogen deposition and rabbit decline. The loss of biodiversity is counteracted by different nature conservation measures, such as cattle grazing, mowing, sod cutting and the restoration of blow outs. Besides, wild fire might also be considered as an opportunity in order to restore grey dunes. In the Amsterdam Water supply Dunes in 2002 shallow sod cutting was experimentally applied in degraded grey dunes. Research mainly focussed on the effects of sod cutting on soil parameters and vegetation composition in plots before and after sod cutting, grass encroached control plots and well developed grey dune plots. Besides, some insect groups such as butterflies and grasshoppers were investigated. In 2004 a wildfire destroyed a small thicket of Hippophae rhamnoides in an environment of Taraxaco-Galietum veri grey dunes. Vegetation and soil parameters were studied in 2011. Small plots were situated in burnt scrub and unaffected scrub (control), and were compared with adjacent grey dunes. In dune grasslands of the Taraxaco-Galietum veri shallow sod cutting led to a successful recovery of the vegetation and come-back of rabbits and characteristic butterfly and grasshopper species within a period of eight years. The degraded Phleo-Tortuletum ruraliformis grey dunes also show a recovery but they respond more slowly to sod cutting, probably due to temporarily higher rabbit numbers and lower nutrient availability. The coverage of ruderal species significantly decreased on both sites. In burnt scrub Hippophae rhamnoides did not return. The average number of grey dune species was significantly higher in comparison with the unaffected scrub, but not as high as in the adjacent grey dune plots. The success parameters of the shallow sod cutting are a small scale approach, the presence of well-developed relic populations of grey dune vegetation with the accompanying fauna species and the return of an open, varied vegetation with bare sand. The development after wildfire illustrates that Hippophae scrub can be converted into grey dune habitat by fire. Rabbits which are present in high numbers on all sites probably played a positive role in the recovery of grey dunes.