Date Published: February 19, 2019
Publisher: Public Library of Science
Author(s): Louise C. Ross, James D. M. Speed, Dag-Inge Øien, Mateusz Grygoruk, Kristian Hassel, Anders Lyngstad, Asbjørn Moen, Christopher Carcaillet.
Low-frequency mowing has been proposed to be an effective strategy for the restoration and management of boreal fens after abandonment of traditional haymaking. This study investigates how mowing affects long-term vegetation change in both oceanic and continental boreal rich-fen vegetation. This will allow evaluation of the effectiveness of mowing as a management and restoration tool in this ecosystem in the face of climate change. At two nature reserves in Central Norway (Tågdalen, 63° 03’ N, 9° 05 E, oceanic climate and Sølendet, 62° 40’ N, 11° 50’ E, continental climate), we used permanent plot data from the two sites to compare plant species composition from the late 1960s to the early 1980s with that recorded in 2012–2015 in abandoned and mown fens. Changes in species composition and frequency were analysed by multivariate and univariate methods in relation to environmental variables and modelled climate and groundwater data. Mowing resulted in a decline in shrub and Molinia caerulea cover at the continental and oceanic sites respectively, and the total cover of specialist fen species had increased to a significantly greater extent in the mown plots than the unmown at the continental site. However, mowing did not have an effect on the cover of specialist bryophyte species, and some specialist species declined regardless of mowing treatment. Temperature sums had increased at both sites, but precipitation had not changed significantly. Mowing was shown to be the most important determinant of plant community composition at both sites, with local environmental conditions being of secondary importance. In conclusion, the abandonment of traditional management practices results in the loss of characteristic fen species. In order to encourage the restoration of typical rich-fen vegetation, particularly in oceanic areas, additional management measures, such as more intensive mowing, may be required.
Many ecosystems of high conservation value have been shaped by human activity, and rely heavily on the continuation of traditional management methods, particularly in grasslands and wetlands [1, 2]. Mowing is widely held to promote plant species diversity by increasing accessibility of light and heat [3, 4]. Fens are among the most diverse ecosystems in the boreal region , and are priority habitats for conservation that harbour a high number of specialised and endangered species [2, 6]. For centuries, fens were important for hay production and as pastures for livestock grazing throughout Europe. Regular harvesting turned large areas of fen vegetation into open semi-natural landscapes [7–11]. However, the widespread traditional use of fens ended many decades ago across most of Europe. The cessation of management often results in the displacement of specialist fen species following secondary succession of competitive species, particularly by graminoids and shrubs, and subsequent biomass accumulation [3, 6, 11, 12]. The grass Molinia caerulea is a particularly strong competitor in fens and can invade rapidly, causing a reduction in species richness . Thus, traditionally-managed hay fens are threatened all over Europe, including Norway , where 105 of 246 Red-Listed vascular plant species (ca. 43%) are found primarily in semi-natural habitats . Despite this, only 200 ha out of more than 300 000 ha of former hay fens are mown as a management measure . There is, therefore, a clear need for restoration measures in this valuable habitat in order to increase the abundance of specialist fen species, both vascular plants and bryophytes, to maintain viable populations, and more research to facilitate evidence-based management for fen restoration.
The results of the linear mixed models show that specialist bryophyte species cover is not affected by mowing (Table 2). However, mowing resulted in a decline in shrub cover, and an increase in specialist fen vascular plant species cover at the continental site, and a decline in M. caerulea cover at both sites, particularly the oceanic site (see also Fig 2). There was also a significant interaction between mowing treatment and time for the change in M.caerulea cover.
This study used historical botanical and environmental data to highlight the importance of land management in restoring boreal rich-fen vegetation in a changing climate. The changes detected here can therefore be interpreted with confidence, in contrast to multiple short-term studies that may fail to detect important trends . Our results suggest that the effect of mowing is an important factor in determining vegetation composition at these rich fens in Central Norway. In the period between the initial survey and re-survey of these two rich fen study areas, concurrent climate change has occurred, with significant increases in temperature sums. Local environmental conditions differ markedly between regions, but play a secondary role. Vegetation change since the beginning of the experiment appears to be greater at the continental site than the oceanic, and in the mown than the unmown plots. However, although mowing prevents the encroachment of M. caerulea and Betula species, this practice may not be sufficient to over-ride the effect of other environmental drivers, including climate change, on all fen specialist species.