The regeneration of bryophytes after the burning of dry and wet heath; a literature review and a field study conducted on the North York Moors

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The age at which heather is burnt influences the amount of dry matter ignited, the fire temperature and subsequent re-colonisation by both heather and the bryophyte community. On moorland managed by controlled burning, a balance needs to be reached between having a burning cycle long enough to allow re-colonisation and development of the bryophyte community without allowing too much dry matter to accumulate. If this balance is achieved, damage to the peat surface and the level of peat erosion will be kept at a minimum, whilst allowing the survival of refugia of bryophytes and encouraging post fire bryophyte recolonisation.

To investigate the regeneration of bryophytes following heather burning, including a review of the literature review and fieldwork, and try to establish an indicator to inform the decision as to when burning should occur, that is easy to apply, and will be accurate and consistent when applied.

Studies evaluating the regeneration of bryophytes after wild or managed fires were sought for the literature review by searching the electronic database Web of Science and the contents pages of relevant journals. Studies were grouped according to the pre-fire vegetation type; sand/alluvial deposits, grassland, forest/woodland and heathland.

The field study was conducted on Spaunton Moor, North York Moors. Four H12a dry heath sites were selected, with plots 1, 3, 5, 7, 10, 15, 20, and >25 years post-burn. Three M16d wet heath sites were selected with plots 3, 7 and 25 years post-burn on each site. Other ages at the wet heath sites included 10 years (1 site), 15 years (2 sites), and 20 years (2 sites) post-burn. Firstly, eight 10x10cm quadrats were surveyed on each plot. Vegetation height, percentage cover of vascular plants, and the number of growing tips and percentage cover of bryophytes were recorded. Secondly, the presence of bryophyte species was recorded every metre along three 10m transects in each plot. Species abundance was analysed using the Friedman test and principal components analysis. The presence and absence of species was analysed using TWINSPAN (Hill and Smilauer 2005). Relationships between vascular plant height (mainly heather) and abundance and bryophyte abundance were analysed using Spearman‟s rank correlation.

Literature review
Twenty four studies were identified, one conducted on alluvial deposits/sand, two on grassland, twelve in forest/woodland, and nine on heathland. The most commonly recorded post burn coloniser was Ceratodon purpureus, being recorded in thirteen of the studies. Other commonly recorded species were Funaria hygrometrica (ten studies), Polytrichum species (nine studies), and Bryum species (seven studies). Pohlia was a colonising species in four studies, all of which were carried out on heathlands. Other species specific to heathland recolonisation were Campylopus species (three studies) and Dicranum scoparium (one study).

Field study
H12a dry heath Twenty three bryophyte species were recorded on the H12a sites. Campylopus introflexus was the most abundant bryophyte species one year post-fire. Campylopus pyriformis, Cephaloziella divaricata and Ceratodon purpureus were also prominent. Species restricted to younger plots were Bryum capillare, Leptodontium flexifolium and Polytrichum juniperinum. Dicranum scoparium and Hypnum jutlandicum were most abundant in older heather stands. Species restricted to older plots were Barbilophozia floerkei, Campylopus flexuosus, Lophocolea bidentata, Mnium hornum, Plagiothecium undulatum and Rhytidiadelphus squarrosus.

Hypnum jutlandicum significantly increased in abundance with the age of heather (p=0.002), whereas Campylopus introflexus (p=0.006), Campylopus pyriformis (p=0.041), and Cephaloziella divaricata (p=0.028) significantly decreased in abundance. TWINSPAN divided the H12a sites into two main groups, one predominantly of plots ten years and older, and the other mainly of plots of seven years and younger.

The height of the vascular plant canopy was negatively correlated with the number of stems of Campylopus introflexus (p<0.001), Campylopus pyriformis (p<0.001), Cephaloziella divaricata (p=0.004). The greatest number of stems of Campylopus introflexus (and acrocarpous mosses in general) were recorded when the canopy height was below 30 cm. The height of the vascular plant canopy was positively correlated with the number of stems of Hypnum jutlandicum (p=0.008), with the abundance of this species (and pleurocarpous mosses in general) increasing once the canopy height reached 30 cm, appearing more consistently at canopy heights over 40 cm and declining once the canopy height reached approximately 55 cm.

M16d wet heath Thirty species were recorded on the M16d sites. Sphagnum was most the most abundant bryophyte genus three years after burning; Odontoshisma sphagni and Campylopus introflexus were also prominent. Species restricted to younger plots were Campylopus pyriformis, Calypogea fissa, Cephalozia connivens, and Kurzia pauciflora. Species restricted to older plots were Polytrichum commune, Pleurozium schreberi, Rhytidiadelphus squarrosus, and Pseudoscleropodiu purum. Hypnum jutlandicum was present throughout the age range of heather, although it was more abundant in older stands.

Odontoshisma sphagni showed significant effect of the stage of heather development on abundance (p=0.048), with the greatest number of stems at the building stage. TWINSPAN divided the sites into two main groups, one generally of younger sites where Sphagnum was recorded, and the other older sites generally without Sphagnum. There was a significant correlation between the height of the vascular plant canopy and the number of stems of Odontoschisma sphagni (p=0.001), Sphagnum section Subsecunda (p=0.008), Sphagnum section Cuspidata (p=0.002), and Hypnum jutlandicum (p=0.012).

Sphagnum species and Odontoshisma sphagni were recorded in the greatest numbers when the canopy height was below 30 cm. H. jutlandicum started to increase in abundance once the canopy height reached approximately 20 cm, with the maximum abundance achieved at a canopy height of approximately 50 cm. The height of the canopy where both Sphagnum and Hypnum jutlandicum were represented, ranged from approximately 20 cm to 35 cm.

On both the dry and wet heath sites, the narrow range of canopy heights at which the bryophyte species characteristic of these habitats were present, were recorded in a wide range of ages and stages of development of heather, indicating that canopy height is a better indicator of the bryoflora than either the age or stage of heather development.

Implications for management
The benefit of a developed bryoflora in an area to be burnt is their water holding capacity, which moistens the bases of the heather stems, producing a cooler burn. This in turn may reduce damage to the peat surface and increase the likelihood of survival of some of the pre-burn bryophyte community, increasing the speed of recovery of the bryoflora, and limiting the colonisation of less desirable invasive species, such as C. introflexus. The current study highlighted the potential for promoting the spread of Campylopus introflexus with repeated burning, and the relationship between characteristics of the vascular plant canopy and the bryoflora. The 10-year post-burn increase in species characteristic of a mature H12a heathland is most likely an indicator to the start of the the recovery of this habitat, rather than a widespread recovery, as C. introflexus persists in older plots and desired species characteristic of a mature heathland were still absence. Age and stage of heather development do not seem to be good indicators of bryoflora composition. Canopy height may be a more reliable indicator to inform practice regarding a sustainable burning cycle.

Recommendations for future research
Further research is required to determine whether the canopy heights indicating a recovered bryoflora at Spaunton Moor can be extrapolated to other moors in the North York Moors and elsewhere in England. It seems promising that the same canopy height is related to a high abundance of H. jutlandicum on both the H12a and M16d sites. However, until this is tested experimentally on other vegetation types, and moorlands in other areas with different environmental conditions, it would be unwise to apply the results of this study to other areas.
Original languageEnglish
PublisherNatural England
Commissioning bodyNATURAL ENGLAND
Number of pages114
Publication statusPublished - 2009

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