Colin J. Legg

The ecology of severe moorland fire on the North York Moors: effects of the 1976 fires, and subsequent surface and vegetation development.

At the end of the dry summer of 1976, severe fires destroyed the surface vegetation and caused major alterations of the underlying soils and peats of over 600 ha of Calluna-dominated moorland at Rosedale Moor, c. 330-400 m a.s.l. on the central plateau of the North York Moors. The fire burnt deeply into blanket peats, and largely destroyed thinner peats and the organic horizons of neighbouring stagnohumic gley and podzolic soils, reducing them, in the most extreme cases, to a layer of ash. (...)

The ecology of severe moorland fire on the North York moors : seed distribution and seedling establishment of Calluna vulgaris

1. Regeneration of Calluna vulgaris following normal heath fires is from surviving stem bases or, where survival is poor, from a seed bank. Severe fires causing ignition of surface organic horizons kill stem bases and cause a serious depletion of the seed bank, most of which (up to 10 6 seeds m −2 ) lies in the litter and upper 2-3 cm of soil or organic material. Germinable seeds were detected in appreciable numbers down to 6 cm beneath the boundary of the F/O soil horizons in soil cores from mature heath vegetation on a blanket peat and peaty stagnopodzol. However, severe fires in which more than 10 cm of peat is ignited will destroy all of the viable seed bank

SEED DYNAMICS IN CALLUNA-ARCTOSTAPHYLOS HEATH IN NORTH-EASTERN SCOTLAND

(1) Estimates were made of seed production, dispersal and storage in the soil in Calluna-Arctostaphylos heath in N.E. Scotland. Germination and seedling establishment in recently burned areas were also studied. (2) Seed production and dispersal by individual species were found to follow the abundance of the species in each stand, though the performance of some species declined as the Calluna canopy closed. Little seed input occurred from surrounding areas into closed or recently burned stands. (3) The amount of seed stored in the soil varied according to stand age. Seeds of Calluna vulgaris and Carexpilulifera increased in abundance with stand age. Stored seed of most other species decreased in numbers though in some there was a slight increase in the degenerate Calluna vulgaris phase. (4) The number of seedlings establishing after fire was far fewer than would be expected from the soil seed store, and is correlated with the type of substrate left by the fire. (5) Seed budgets are estimated for a 15 year fire rotation for the major species studied.

Markov models and initial floristic composition in heathland vegetation dynamics

A simple Markov model is used to test the hypothesis that the floristic composition of vegetation colonizing bare ground immediately after burning is the major factor influencing post-fire development in heathland vegetation. Data are taken from stands of different ages at time of burning in a species-rich Calluna-Arctostaphylos heath in NE Scotland. It is shown that variation in the initial floristic composition of the stands is not, in itself, sufficient to produce model simulations which match observed trends, although altering the probabilities of transition from bare ground to other states allows more successful simulations. The model supports the hypothesis that stand age before burning influences the post-fire development through the process of colonization of bare ground. After a very severe fire post-fire development may initially depend on the formation of a moss cover, although this requires further study. It is concluded that simple Markov models can provide the basis for examining successional processes when used in a comparative way.

Using visual obstruction to estimate heathland fuel load and structure

We present a simple non-destructive technique for assessing fuel load and critical aspects of vegetation structure that play important roles in determining fire behaviour. The method is tested in a Scottish Calluna vulgaris (L.) Hull heathland but could be applied to any vegetation up to ~1 m high. Visual obstruction of a banded measurement stick (the FuelRule) placed vertically through a stand of vegetation is governed by a combination of the height of the vegetation and its density. The vertical distribution of visual obstruction is calibrated to give estimates of total fuel loading, the loading of separate size categories and the vertical distribution and horizontal heterogeneity of fuels. The present paper provides a quick and simple method for estimating total aboveground biomass and structure that may be useful not just in studies of fire behaviour but where non-destructive assessment of biomass, vegetation density or canopy structure is needed. Calibration equations can be rapidly created for use in other vegetation or fuel types.

Pitfall trapping bias and arthropod body mass

Abstract.  1. Pitfall trapping is one of the most widely used arthropod sampling techniques. However, relative species abundance in pitfall trap catches differs from that found using quadrat samples. This difference, here termed bias, reflects the fact that pitfall trap catch is influenced not only by abundance but also by other factors, including activity, which may be linked to body size. Here, we investigate whether the bias affecting pitfall trap catches of a particular species is related to the typical body mass of individuals of that species.

The effect of traditional management burning on lichen diversity

ABSTRACT Question: How does regular management burning of a northern, Calluna vulgaris-dominated heathland affect the lichen diversity at the patch and landscape scale? Location: Mar Lodge Estate, Scottish Highlands, United Kingdom. Methods: 26 fire sites of different ages and 11 long-term unburnt stands were surveyed to create a chronosequence of changing lichen diversity following burning. Data were analysed graphically, with a GLM and using a CCA. Results: Though the immediate effect of fire was to significantly reduce lichen diversity, it generally recovered within 20 years. There was a significant difference in the population dynamics between wet and dry moorland areas with terricolous lichens in the former site being replaced by pleurocarpous mosses. Older stands, unburnt for 25 years or more, generally had lower diversity than stands 10 to 15 years old. Changes in lichen diversity and community composition can be attributed to the development of Calluna stand structure following burning. Conclusions: Fire can be seen to play an important role in maintaining the diversity of lichens in heathland areas by providing a variety of stand-structures and ages across the landscape that favours the development of greater beta-diversity. Nomenclature: Dobson (2005) for lichens; Smith (2004) for bryophytes and Stace (1997) for vascular plants.

Winter desiccation and rapid changes in the live fuel moisture content of Calluna vulgaris

Background: Dramatic reductions in early-spring Calluna vulgaris moisture content have been linked to extreme fire hazard and plant die-back. Aims: To investigate spatial and temporal variation in the fuel moisture content of Calluna vulgaris. Methods: Calluna vulgaris plants were sampled in different sites and seasons to examine vertical profiles in moisture content. Live moisture content was monitored throughout autumn 2003 and spring 2004. Changes were compared to trends in temperature, soil resistance and rainfall. The effect of exposure was examined by comparing shoot moisture content in sheltered and exposed locations. Results: Significant spatial and temporal variation in moisture content was observed. In spring rapid fluctuations in moisture coincided with periods of dry weather, low temperatures and frozen ground. Shoots from exposed locations had significantly lower moisture content when the ground was frozen. Conclusions: Significant declines in the live fuel moisture content of Calluna vulgaris are associated with physiological drought caused by cold, clear conditions and frozen ground. Over-winter damage to leaf cuticles reduces the ability of the plant to regulate water loss. Changes in moisture content can be rapid, and managers should be aware of the potential for extreme fire behaviour.

Effect of nitrate and phosphate on weight losses of pine and oak wood caused by aquatic and aero-aquatic hyphomycetes

The effect of enriching river water with ecologically probable amounts of nitrate and phosphate on the decay of pine and oak wood caused by aquatic and aero-aquatic hyphomycetes was investigated. Decay was of the typical soft-rot type with weight losses of pine wood consistently less than those of oak, but enrichment of the medium increased weight losses of pine more than oak. Nitrate utilization was found to be dependent on the availability of phosphate.

Assessment of Expert Opinion: Seasonal Sheep Preference and Plant Response to Grazing

Abstract Expert opinion was sought on 2 issues relating to herbivory: seasonal sheep preferences for plant species and seasonal plant response to grazing. Expert opinion is commonly used to parameterize models: it is therefore important to assess its quality. Understanding the limitations of expert knowledge can allow prioritization of future research. Nine experts in plant or grazing ecology from Scotland/Northern England were individually interviewed. The experts ranked sheep preferences for species in 4 rangeland vegetation types and provided categorical information on plant response to grazing. For both issues, seasonal information was collected. Uncertainty (unanswered questions) on plant responses was much higher than uncertainty on sheep preferences. Uncertainty on sheep preference was significantly negatively correlated with plant species commonness, but not with quantity of scientific literature. Uncertainty on plant responses was significantly negatively correlated with both plant commonness and literature. There was agreement among experts on sheep preferences; standardized seasonal information for selected plant species is presented. In general, experts considered graminoids to be preferred over dwarf shrubs, with forbs and other species groups intermediate. Seasonal variation in sheep preference was greater for heath and mire than for grasslands. There was limited agreement among experts on seasonal plant responses. Some experts considered grazing in summer to affect growth more than grazing in winter, whereas others thought season had little effect. Sufficient agreement was found at the species level to present results on plant responses. Experts considered graminoids more resilient to grazing than dwarf shrubs. Experts agreed on sheep preference at different times of year, and on the overall resilience of plant species to grazing. However, the experts held 2 paradigms on the impact of seasonal grazing. Further research is required to explore this, because seasonal grazing regimes are currently promoted as conservation management tools.