15.4 Overall Effectiveness of Restoration Measures in Dutch
Dune Areas
The case studies discussed above are some illustrations of well-monitored restoration projects over time periods exceeding 10 years. Long-term monitoring showed
that restoration may lead to short-term successes, such as in the sod-cutting
experiments in the dune slacks, but that long-term responses may be completely
different. Unfortunately, most restoration projects are not monitored at all or only for
a short time. Restoration of dry and wet dunes is not easy. In dry dunes, counteraction of grass encroachment by grazing is mainly successful in areas with low P
availability and low productivity of the vegetation. Also, with respect to Red List
species, a recent evaluation of 138 restoration projects, including both small areas of
a few hectares to large areas of more than 100 ha, showed that restoration projects in
dry dunes were generally less successful than those in wet dune slacks (Jansen et al.
2009). In dry dunes, a grazing regime generally led to more diverse vegetation,
which is in accordance with earlier findings. However, only 12 Red List species (out
of 66 for this habitat) in 11 projects responded positively to these measures (Jansen
et al. 2009). Renewed dune formation is possibly a much more effective way to
increase biodiversity in dry dunes again, because aeolian activity will transport
calcareous sand to areas that have been acidified and it will probably also help to
disperse seeds more effectively.
An evaluation of 126 restoration projects in wet dune slacks showed that sod
cutting was most successful in increasing populations of Red List species (Jansen
et al. 2009). More than 50 % of the Red List species (51 out of 95 for this habitat)
responded well to the measures. Moreover, 43 of these species have improved so
much that they could be removed from the list. Also, 10 of the endangered orchid
species responded slowly but positively to the restoration measures during the
period of observation (5–15 years). Long-term monitoring suggests that sod cutting in wet dune slacks may only be successful when hydrology has also improved,
and that soils are not loaded with P because of the former input of P-rich surface
water. Few species showed a negative response over a longer time span, which
could be because of their adaptation to pioneer habitats. They appear to be successful initially, but disappear again as succession proceeds and organic matter
accumulates in the habitat.
Jansen et al. (2009) showed that Red List species that were positively
responding to restoration measures did not usually have long-living seed banks,
especially not where seeds have been removed through the restoration measures.
This indicates that dispersal mechanisms in these projects were more important
than soil seed banks (Fig. 15.6), which is in accordance with Ozinga et al. (2009).
This may be true for less endangered species as well.
In the Moksloot area, we noticed that species diversity increased very rapidly
after sod cutting, although approximately 99 % of the soil seed banks had been lost
because of top soil removal (Grootjans et al. 2001). This explains the relatively
small contribution of species with long-living seeds.
15 Restoration of Dune Vegetation
249
Dune Areas
The case studies discussed above are some illustrations of well-monitored restoration projects over time periods exceeding 10 years. Long-term monitoring showed
that restoration may lead to short-term successes, such as in the sod-cutting
experiments in the dune slacks, but that long-term responses may be completely
different. Unfortunately, most restoration projects are not monitored at all or only for
a short time. Restoration of dry and wet dunes is not easy. In dry dunes, counteraction of grass encroachment by grazing is mainly successful in areas with low P
availability and low productivity of the vegetation. Also, with respect to Red List
species, a recent evaluation of 138 restoration projects, including both small areas of
a few hectares to large areas of more than 100 ha, showed that restoration projects in
dry dunes were generally less successful than those in wet dune slacks (Jansen et al.
2009). In dry dunes, a grazing regime generally led to more diverse vegetation,
which is in accordance with earlier findings. However, only 12 Red List species (out
of 66 for this habitat) in 11 projects responded positively to these measures (Jansen
et al. 2009). Renewed dune formation is possibly a much more effective way to
increase biodiversity in dry dunes again, because aeolian activity will transport
calcareous sand to areas that have been acidified and it will probably also help to
disperse seeds more effectively.
An evaluation of 126 restoration projects in wet dune slacks showed that sod
cutting was most successful in increasing populations of Red List species (Jansen
et al. 2009). More than 50 % of the Red List species (51 out of 95 for this habitat)
responded well to the measures. Moreover, 43 of these species have improved so
much that they could be removed from the list. Also, 10 of the endangered orchid
species responded slowly but positively to the restoration measures during the
period of observation (5–15 years). Long-term monitoring suggests that sod cutting in wet dune slacks may only be successful when hydrology has also improved,
and that soils are not loaded with P because of the former input of P-rich surface
water. Few species showed a negative response over a longer time span, which
could be because of their adaptation to pioneer habitats. They appear to be successful initially, but disappear again as succession proceeds and organic matter
accumulates in the habitat.
Jansen et al. (2009) showed that Red List species that were positively
responding to restoration measures did not usually have long-living seed banks,
especially not where seeds have been removed through the restoration measures.
This indicates that dispersal mechanisms in these projects were more important
than soil seed banks (Fig. 15.6), which is in accordance with Ozinga et al. (2009).
This may be true for less endangered species as well.
In the Moksloot area, we noticed that species diversity increased very rapidly
after sod cutting, although approximately 99 % of the soil seed banks had been lost
because of top soil removal (Grootjans et al. 2001). This explains the relatively
small contribution of species with long-living seeds.
15 Restoration of Dune Vegetation
249