Experimental wet heath translocation in Dorset, England

Abstract

Heathland has become fragmented throughout its European range with many countries losing 60–90% of their heathland area during the 20th century. A small, isolated area of wet heathland within permitted ball clay workings in Dorset (England) was translocated in October 1993 to an engineered receptor cell fed by groundwater and direct precipitation in order to mitigate the otherwise total loss of the wet heath. The aims were to rescue the wet heathland and to re-establish a community type similar to the wet heath that originally occurred at the donor site prior to the recent development of vegetation communities and birch colonisation associated with drier conditions. Vegetation monitoring over 12 years up to 2005 indicated that the experimental translocation successfully fulfilled the aims for a period of 7 years when the hydrological regime of the receptor site was actively managed. There was development of a mosaic of wet heath and mire vegetation community types including Sphagnum lawns and open bog pools. However, when active management ceased, the receptor site became drier and species were lost. Multivariate analysis revealed a trajectory of progressive rapid chronological change during 1994 and 1995 followed by a period of relative stability between 1996 and 2000 which coincided with greater species density. Subsequently up to 2005, the plant community became less species-rich and the plant community reverted to a species structure similar to that which occurred in 1994/1995. The importance of hydrological regime for plant community structure was tested using fixed-quadrat data and the water level measurements made in the period 1995–1998. Canonical Correspondence Analysis (CCA) multivariate analysis revealed a hydrological gradient with a significant seasonal effect of water table depth in the first half of the year and close association of the least wet quadrat location and non-mire species. Overall, the results support the use of translocation as a means of rescuing wet heath habitat which would otherwise be lost due to change in land use. There is a risk of failure when translocating a complex ecosystem such as wet heath but ecological engineering provides an insight into defining the risk. Our results demonstrated that an ecologically acceptable outcome for a wet heath translocation can be achieved with careful design and implementation and sensitive management of the receptor site. However, it is essential to secure long-term hydrological and vegetation management in order to provide a sustainable outcome for long-term survival of a target wet heath community.