De Levende Natuur nummer 4 van 2010 (English summary)


DLN 2010-4

Soil quality for habitat areas insufficient

G.W.W. Wamelink, M. van Adrichem & H.F. van Dobben

To preserve or enhance the quality of the habitat directive areas, the quality of the soil is one of the main factors. We assessed the soil quality for a large amount of habitat directive areas in the province of Gelderland in The Netherlands. We applied our newly developed indicator system for plant species to estimate the soil conditions based on the plant species composition for habitat directive areas. The abiotic demands of the habitat types were estimated as well, for e.g. soil pH, nitrogen content of the soil or groundwater table. The calculated abiotic conditions of the soil were compared with the demands of the habitat types, thus giving the suitability for a habitat type. This revealed that for all habitat directive areas at least for one of the assessed abiotic parameters the quality was insufficient. For instance the estimated soil pH was outside the range for the designated habitat vegetation type. For many areas the calcium content on the dry sandy soils was too low and the total nitrogen and phosphorus content too high. For the wet habitat types the groundwater table was too low.

Nitrogen deposition in lime-rich and lime-poor dunes: is there really an improvement?

A.M. Kooijman, A. van Hinsberg, H. Noordijk, M. van Til & C. Cusell

According to the Dutch government, coastal dunes are no longer threatened by high atmospheric N-deposition. Already in 2003, N-deposition was supposed to be lower than the critical loads in 75% of the dune area. However, ammonia concentrations, measured to callibrate modelled N-deposition, were twice to four times higher than expected, which implies that actual N-deposition is much higher. Also, critical values may have been overestimated for grey dune areas, and the actual non-threatened area is probably much lower than 75%. In addition, high atmospheric deposition in the past has possibly led to almost double rates of acidification, dissolution of calcium phosphates and succession. Acid dunes are probably more sensitive than calcareous dunes, because low microbial N-demand may lead to relatively high allocation of (excess) N to the vegetation, and stimulation of grass-encroachment. Also, except for iron rich soils low in organic matter, acid soils have no mechanisms for P-fixation. In calcareous soils, however, microbial N-demand is high, which may lead to storage of N in microbes and soil, rather than in vegetation. Also, calcareous soils have low P-availability, due to P-fixation in calcium phosphates. Grass-encroachment is less severe, and easier to keep under control.

The Tree Grayling almost gone?

J.H. Bouwman, N.G. Peet, R. Ketelaar & L. Soerink

The Tree Grayling is one of the rarest butterflies in the Netherlands; nowadays it can only be found at Kootwijkerzand in the Province of Gelderland. The numbers of this species are so low that it is not unlikely to disappear in the Netherlands within a couple of years. The Tree Grayling lives in inland sand dunes with a Corynophorus-vegetation and adjacent heath of Calluna vulgaris. The area of active sand dune systems is on a historically extreme low point. To prevent the disappearance of the Tree grayling in the Netherlands it is necessary act rapidly. The most important threat for the Tree grayling is this loss of suitable habitat. The long term survival of the species requires large scale restoration of sand dunes. The most promising locations to reactivate the fossilized sand dunes are those close to the only recent population. For this extreme rare and threatened species, that can only be saved by large scale and thus expensive measures, one could raise the question of conservation efficiency. In this case however, we think that by safeguarding the habitat of the Tree grayling many other species will be helped. Furthermore, enlarging existing sand dune systems will stimulate essential natural processes like erosion, sedimentation and accompanying vegetation..

Public acceptability of wildlife management interventions

M.H. Jacobs, M.T.J. Sijtsma & J.J. Vaske

Wildlife management raises public concern and can be a cause of conflict, as media coverage in The Netherlands continuously demonstrates. We studied the Dutch population’s acceptance of various wildlife management interventions, and tested the predictive power of wildlife value orientations for the acceptance of interventions. Many wildlife management interventions are controversial in The Netherlands. Hunting geese and deer that cause damage is deemed acceptable by approximately half of the population, while unacceptable by the other half. Not taking measures in this situation is controversial as well. Interventions in situations without a human-wildlife conflict, and concerning no harm to wildlife, are generally accepted. Amongst people with a mutualism wildlife value orientation (who believe that humans and wildlife should co-exist and live in harmony), interventions that do not harm animals are more acceptable than amongst people with a dominate orientation (who believe that wildlife should be managed for human benefit). Amongst the latter, interventions that do harm animals are more acceptable. The general wildlife value orientations substantially predict specific opinions in specific contexts, and thus reveal an underlying mental structure that explains people’s reasoning about wildlife and wildlife interventions. Our findings can inform wildlife policy makers and managers about public support for wildlife management and indicate potential conflicts about wildlife.

Will the honeybee survive civilization?

Pollinating insects are in decline, probably world wide. This may imply a pollination crisis, for (food) crops as well as wild plants. Eventually this decline might result in great economic losses, a human food crisis and loss of natural biodiversity. Although the world population of honeybee colonies still increases (despite decreases in many countries) it is urgently needed to look after bees and other pollinators.

Possible drivers for the decline of insect pollinators in general are (1) habitat loss and intensive land use, (2) globalization and introductions of foreign species, (3) pollution including pesticides, (4) climate change. For honeybees to this adds (5) world wide presence of the invasive parasitic mite Varroa destructor (as a consequence of (2)), (6) introduction and spread of other (new) parasites, (7) loss of the honey bee’s genetic diversity and (8) detrimental beekeeping practices. Simultaneously the beekeeping sector in many countries is vanishing for demographical reasons and a lack of incentives for beekeeping.

Beekeeping in The Netherlands almost fully depends on hobbyists, which results in little professional education and the absence of a professional extension service. Nevertheless the beekeeping standard has to improve in order to help the beekeeping sector to cope with the upcoming challenges and to safeguard the professional agricultural need for pollination.