De Levende Natuur nummer 5 van 2011 (English summary)


DLN 2011-5

Rabbit and Juniper

Marijke Drees, Thomas Stolz & Chris Smit

Recruitment failure forms an important threat to the long-term persistence of the remaining populations of Juniper (Juniperus communis) in most Western European countries. Suggested causes for this recruitment failure are variable and include pollination limitation (due to air pollution), poor viability of the seeds (related with the old age of the populations), limited seed dispersal, and seedling mortality due to drought (climate change) and herbivory. We focused on the impact of Rabbits on Juniper recruitment and performed a preliminary study in two sites in the province of Drenthe, the Netherlands. Firstly we revisited locations at the Dwingelderveld where recruitment had been observed in 2004. We estimated the year of establishment from diameter and height measurements of the retrieved 137 seedlings, and related seedling establishment to the number of observed rabbits in those particular years. Our results show that the number of rabbits declined until 2005 - probably due to Rabbit Hemorrhagic Disease (RHD) - which seemed to correspond with an establishment peak in 2006. Secondly we transplanted small (1-5 cm) and larger (10-15 cm) Juniper cuttings in the Mantingerzand, near and away from Rabbit burrows, with and without a small fence, and followed their performance for a few weeks. The small cuttings remained untouched by Rabbits and finally desiccated. The larger cuttings were repeatedly browsed by the Rabbits, leading to a height reduction of 80% in 5 weeks. It seems that only from a certain height onwards Juniper seedlings become apparent to Rabbits and run the risk of being browsed. This finding would correspond with the observed ‘delay-effect’ of 1 year of the descriptive study, but we are careful with the interpretation of our data due to the short period of study and limited repetition. We are currently looking for funding to repeat our study on a larger spatial and temporal scale to investigate the impact of Rabbits, and other herbivores, on the recruitment of Juniper.

Breeding birds in a nature development area in ‘De Wieden’ 1989-2010

Obe Brandsma

The ‘De Wieden’-wetland is a peat-bog area consisting of lakes, pools, swamps, woods and grasslands, located in the northwest of the province Overijssel. At the east side of this area a agricultural re-allotment has been realised with low water tables. As a consequence water of the nature reserve with high water table, flows to the adjacent agricultural area. To prevent this, a high water level zone with a water level of 30 cm above the level in the nature reserve was established between the nature reserve and the agricultural area. In this zone a variety of grassland types, ditches and small copses developed into a swamp area with sedges, Reed, willows and water. In this small area (86 hectares) a remarkable great number of marshland species has shown up as Marsh Harrier, Bittern, Purple Heron, Spoonbill, Greylag Goose, Water Rail, Blue Throat and Savi’s Warbler. Even 15-20 years after the project was initiated, it still is a very important area for several Red List species. Probably the great diversity in habitats at a small spatial scale and the inaccessibility to ground predators are responsible for this effect, especially for Purple Heron and Spoonbill. But beware of the strength of wind and waves, for they can be stronger than succession.

Early establishment of wooded meadows

Jan Bakker, Yzaak de Vries & Chris Smit

A former arable field (9 ha) was abandoned in 1982 and grazed by 12 cattle from May till November. Initially, tall vegetation and shrubs were mown. Since 1989, 3-5 Scottish Highland cattle graze the area year round and patches of spiny shrub could freely establish. These spiny shrub species all carry fleshy fruits, hence it is likely that dispersal took place through frugivorous birds. Characteristic breeding birds such as Common stonechat and Red-backed shrike have established. Inside the protecting spiny shrubs other woody plant species without spines can emerge. Hence, we witness the early establishment of a wooded meadow. Most of the area showed succession from initial large proportion of annual arable field species and species of nutrient-rich soil conditions towards species of moderate nutrient-rich soil conditions. In a small area (0.5 ha) the topsoil (10 cm) has been removed. Apart from the aforementioned succession, also species of nutrient-poor soil conditions have established.

Can policy make a difference?  Flanders’ nature outlook

Anik Schneiders, Toon Van Daele, Luc De Bruyn, Myriam Dumortier, Maarten Hens, Johan Peymen & Wouter Van Reeth

The EU has missed its 2010 target of halting biodiversity decline. A continuing challenge is to develop realistic strategies to stop this decline.Flanders is densely populated and autonomous socio-economic development dominates the main land-use changes. Question is if nature conservation measures can counteract and which measures would return highest benefit.

We evaluated six policy scenarios. The impact of the autonomous socio-economic development is combined with two environmental (abiotic) scenarios. Compared to the ‘Business-as-usual’, the Europe scenario takes all measures necessary to achieve European environmental targets. These two environmental scenarios are combined with three nature conservation scenarios. Under the ‘Separation’ scenario, nature policy is to a large extend separated from other land use (e.g. focuses on nature reserves). Under the ‘Integration’ scenario, the interests of nature and other land uses are closely knit (multifunctional). The ‘Reference’ scenario depends to a large extend on local management initiatives. A budget constraint makes that all six scenario’s will cost the same amount of money. The target year is 2030.

Our model showed that urban sprawl persists in the future and many small remnants of open space will disappear. However, due to decreasing agricultural development, the area of land used for agriculture will drop, creating new opportunities for nature expansion. Under the European environmental scenario, nitrogen deposition declines and habitats sensitive to eutrophication can reach European conservation goals more easily than under ‘Business-as-usual’. Climate changes may hamper the positive development due to changes in temperature and precipitation.

Each nature policy scenario demonstrates specific benefits. The ‘Separation’ scenario mainly benefits heath- and marshland species, including many species of European interest. On the other hand, farmland species benefit more from the ‘Integration’ scenario. The ‘Reference’ scenario returns more opportunities for meadow birds and forest species.

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