Wind, P. & Nygaard, B. 2018. Monitoring the vegetation recovery in Østerild Plantage 2017. Part 3. Aarhus University, DCE – Danish Centre for Environment and Energy, 170 pp. Technical Report from DCE – Danish Centre for Environment and Energy No. 118 http://dce2.au.dk/pub/TR118.pdf
The overall objective of the monitoring program running from 2011 to 2021 is to document the direction of the recovery of open dune habitats after the clear-cutting of the dune plantations in the National Test Centre facility established at Østerild in 2011. Aarhus University, Danish Centre for Environment and Energy (DCE), has developed the monitoring program in 2011.
Within the framework of the monitoring program, as a first phase, the vegetation composition and the soil condition prior to the clear-cutting of the dune plantations (baseline monitoring) was recorded. The next phase involved a systematic recording of the development of the vegetation composition and soil conditions (post-construction monitoring) during the first 10 years after the clear-cutting in order to follow the changes from the baseline conditions towards recovery of open dune habitats. The establishment of the project’s 12 monitoring sites and the 100 monitoring plots followed a stratified random design in order to span the different times of planting of the different conifer stands and the applied regeneration measures. The baseline condition (forest type), the planned post-cutting treatments of the litter layer and the hydrology, the expected management regimes, the distance to appropriate seed sources and the topography were important parameters for the stratification.
Conifers are the dominant tree species in the Østerild area including the Østerild Plantage itself and the neighbouring Hjardemål Plantage in the north, which are both afforested plantations located in state-owned areas. The introduced coniferous species Picea sitchensis (Sitka Spruce), Pinus contorta (Lodgepole Pine) and Pinus mugo (Mountain Pine) together with the native Pinus sylvestris (Scots Pine) were the main conifers present in the afforested areas where the National Test Centre facility for wind turbines was established and inaugurated in 2012. Before the clear-cutting, the assumption was that the starting conditions would have a major impact on the succession following deforestation. Thus, the twelve monitoring sites were established in stands of three of the coniferous species. Hundred monitoring plots were established in the monitoring sites of which 20 were laid down in the P. mugo, 30 in the P. sylvestris and 50 in the P. sitchensis stands.
Various post-cutting treatments of hydrology and accumulated soil organic matter were planned in order to facilitate the recovery of the vegetation cover of grey dunes (habitat type 2130), dune heaths (habitat type 2140) and humid dune slacks (habitat type 2190). One of the aims of the monitoring program was to assess the effect of these treatments on the rate and direction of vegetation development towards the target communities. Unfortunately, not all the planned treatments were accomplished and 35 new monitoring plots were therefore established in 2017 in clear-cut areas not previously surveyed. Five of them were placed close to the main unpaved field road, partly covering the verge.
Prior to afforestation in the late 1800 and in the beginning of the 20th century, the dune areas in the Østerild area were characterised by a high-level, presumably fluctuating, water table. Consequently, moist and wet habitats were widespread in the area.
Therefore, successful regeneration of moist dune heaths (habitat type 2140) and humid dune slacks (habitat type 2190) required recovery of the original hydrological regime. Thus, one of the implemented initiatives was to close drainage ditches and allow temporary pools and shallow waterbodies to develop or expand. One of the aims of the monitoring program was to follow the succession in dry and moist dune habitats, including areas with seasonal flooding.
In August 2017, DCE carried out a survey of the 65 monitoring plots established in 2011 and of the 35 new plots established in 2017. The composition and vegetation structure of the plant species were investigated using a pinpoint frame (0.5 * 0.5 m2) and a documentation circle with a radius of 5 m in each of the 100 monitoring plots, with the pinpoint frame as the centre. All vascular plant species, bryophytes and lichens were recorded. Besides, the total area of coverage of bryophytes, lichens, bare soil and sand, the amount of dead wood and the free water surface in the 5 m circles were estimated and the general inclination of the monitoring plot was measured. A digital photo was taken of all of the 100 monitoring plots. All vascular plant species and some characteristic bryophytes and lichens were determined in the field. The remaining bryophytes and lichens were collected for determination in the laboratory. Specialists subsequently confirmed the determination of the collected specimens. The names of the species, the collected data and the digital photos were compiled in the annexes of this report.
During the fieldwork in 2017, 165 taxa were recorded in the 100 monitoring plots – 87 dicots and 38 monocots, including 16 grasses and 11 sedges and rushes, respectively. Gymnosperms contributed with 5 species, and ferns and fern allies with 7 species. The cryptogam flora included 17 determinable taxa of bryophytes, 4 hepatics, and 7 lichen taxa.
Of the 65 monitoring plots previously surveyed, the most species-poor plot was found in the former Pinus mugo stand and contained 4 taxa. The highest number of species, 38, was recorded in a monitoring plot in the former Picea sitchensis stand. Among the new 2017 plots, the minimum and maximum species numbers were 9 and 26, respectively. In the five plots established at the unpaved main field road, the species number ranged between 22 and 40.
The dwarf shrub Calluna vulgaris was the most abundant species, being recorded in 92% of the monitoring plots followed by the grasses Avenella flexuosa and Molinia caerulea with abundances of 89% and 85%, respectively. Hypochaeris radicata, Holcus lanatus, Carex arenaria and Rumex acetosella were also abundant and appeared in 73%, 64%, 59% and 59% of the plots, respectively. Another 7 taxa, Erica tetralix, Hypnum cupressiforme/H. jutlandicum, Juncus effusus, Agrostis capillaris, Dicranum scoparium and Pleurozium schreberi, were recorded in more than 50% of the plots.
The quoted species are also the most widespread as they were recorded in all monitoring sites, except for Carex arenaria, which was not found in any of the five plots, including the verge of the main unpaved field road. However, the influence of the field road is obvious as some species either were the most frequent or only recorded in the vegetation cover in the verge next to the road.
The clear-cutting of trees in the project area has led to exposure of the bottom layer. The improved light penetration to the bottom layer has facilitated the spread of vascular plants, bryophytes and lichens to the former afforested areas. Especially dwarf shrubs like Calluna vulgaris, Empetrum nigrum, Erica tetralix and Vaccinium uliginosum and a number of prominent grass species such as Agrostis capillaris, Avenella flexuosa, Holcus lanatus and Molinia caerulea have benefitted from the improved light conditions. No invasive alien species have so far been recorded, although clear-cutting in other parts of Denmark has been observed to lead to such species invasion.
The altered water regime has created new not previously present habitats in the project area. These newly formed habitats have become home to species that have not been recorded in the Østerild area before. Some of the species are less frequent in Denmark and depend on fluctuating water coverage, changing moistness, nutrient-poor conditions and open vegetation cover. Examples are Drosera rotundifolia, Lycopodiella inundata, Eleocharis multicaulis and Potamogeton polygonifolius. Besides, the clubmoss Lycopodium clavatum has appeared in two monitoring plots in the former Pinus mugo stand in the Hjardemål Klitplantage. The latter species was not recorded in the previous surveys in 2011, 2013 and 2015 in the P. mugo monitoring sites.
The primary objective of the clear-cutting of the former afforested areas in the project area was to establish the National Test Centre giving the opportunity to direct the vegetation succession on areas not directly affected by the establishment of the wind turbine facilities towards the target communities – dry and wet heathland and dune slacks. Secondly, the project aims to improve the diversity of natural species compared with the situation before the deforestation of the project area by creating suitable habitats for light-preferring and low growing species, species demanding nutrient-poor conditions and species depending on a fluctuating water table and changing moistness. The results of the 2017 survey of the 100 monitoring plots indicate that the vegetation succession fulfils the aim of the entire vegetation recovery project. The conclusion is preliminary, however, as a more in-depth analysis of the all the gathered vegetation data will be performed after the completion of the project in 2021.
