Prescribed burning of northern heathlands: Calluna vulgaris germination cues and seed-bank dynamics

Abstract

The European coastal heathlands are important habitats for international conservation. Today, these low-intensity farming systems are threatened by the cessation of traditional management regimes, such as grazing and prescribed burning. In natural systems, the effects of fire on germination responses are often explained by adaptation to fire over extended periods of time. However, Northern heathlands are semi-natural systems with only a limited fire history. We investigated whether and how the keystone species in this system, Calluna vulgaris, responded to prescribed burning, based on previous findings where Calluna germinable seedbank densities showed a pronounced peak right after fire. Our main findings were (i) an ecophysiological response to smoke; (ii) a potential explanation for this pattern, revealed by a seed-bank experiment where we managed to re-create the germination pattern experimentally by using an aqueous plant-derived smoke solution; and (iii) a history of anthropogenic use of fire and the development of heathlands in the region documented through palaeoecological investigations.

Management-driven evolution in a domesticated ecosystem

“…Smoke-induced germination is known from Calluna populations in anthropogenic coastal heathlands [17,18], where it increases recruitment from seedbanks in newly burnt heath [19,20]. We document that the trait is not universally present in Calluna; instead, it is lacking in the species' range outside the culturally fire-prone coastal heathlands.…”

“…Major expansion occurred from ca 5000 BP (before present) in Jutland, Denmark [12], and at 3300-1000 BP in western Norway [11,13]; and although studies are scarce in the north, there is evidence of anthropogenic coastal heathland 4700-3300 BP in central Norway [14], and 3800-1800 BP in northern Norway [15]. Burning cycles of [10][11][12][13][14][15][16][17][18][19][20] traditional throughout the coastal heathland region [10,16]. Smoke-stimulated germination responses in heathland species, e.g.…”

“…Smoke-stimulated germination responses in heathland species, e.g. Calluna vulgaris [17,18], have ecological consequences: for example, germination rate and final percentages increase in smoke-exposed seedbanks [17,19,20]. As 6000 years of human influence affords scope for evolutionary change, we ask: is this a trait that Calluna brought into the heathlands or has it evolved there?…”

“…Black circles and white squares indicate seed-sampling sites along the latitudinal and elevational gradient, respectively. Inset shows a microfossil record from site B over the past 6000 years (reprinted with permission from [17]). See the electronic supplementary material, table S1 for site information.…”

Wall Vegetation in Old Royal Mining Towns in Central Slovakia

“…As a result of such development, the stands of Calluna vulgaris have almost disappeared in a number of localities. The use of controlled fire is recognized to be one of the most effective tools for the conservation management of this type of vegetation (Sedláková & Chytrý 1999, Mohamed et al 2006, Klein et al 2009, Davies et al 2010, Måren et al 2010, Harris et al 2011. Nevertheless, Calluna regeneration after fire may be modified by the local environment (Vandvik et al 2005) and also by interactions with encroaching woody species (Manning et al 2004).…”