Vegetation dynamics following management burning of lowland heathland.
Management of the southern lowland heaths is usually for conservation, and aims to
create structural diversity, prevent succession to scrub and maintain the low nutrient status of
the system. The main aim of this study was to investigate the effects of burning, fire
temperature and intensity on seed banks, nutrients, vegetative regeneration and seedling
In the first experiment (1994), vegetation fuel loads were manipulated in stands
representing two different growth phases of vegetation (mature and degenerate) at two sites
(Arne in Dorset and Aylesbeare in Devon) to test the hypothesis that frre temperature and
intensity depend chiefly on fuel load rather than other factors associated with the pre-burn age
of the stand. There were two burning treatments of low and high fuel loads. Fire
temperatures were measured with temperature-sensitive paints on tiles ('pyrometers').
Intensity (the heat released per unit area) was highly correlated with fuel load. Fire
temperatures were higher in the high fuel load treatments than in the low fuel load treatments
at all stands except the Aylesbeare degenerate stand. where temperatures were low in both
In the second experiment (1995). paraffin was added to treatment plots at the mature
stand at Aylesbeare in an attempt to produce higher temperatures. but this aim was not
achieved. Thermocouples and pyrometers were used to measure temperatures and indicated
that these fires were hotter than the fires at the same stand in the first experiment.
There was no effect of burning or of temperature on the size of the seed banks in the
soil and litter in the frrst experiment. The litter seed bank of Erica tetralix was depleted by a
similar quantity in both treatments in the second experiment. There was no effect of burning
on the nutrients (P. Ca. K) in the humic soil in either of the experiments. The concentration of
nutrients was higher in the ash than in the litter of control plots after burning (except at the
Aylesbeare degenerate stand). There were significant but inconsistent effects of temperature
on the quantities of nutrients.
Vegetative regeneration after burning depended chiefly on the pre-bum age of the stand
and possibly on grazing. but fire temperature had no effect. There was rapid resprouting at
both the mature stands, but regeneration at the degenerate stands was sparse. Calluna rapidly
regained dominance at the Arne mature stand but was relatively less abundant at the
Aylesbeare mature stand after burning than it was before. Agrostis curtisii. Ulex gallii and
Erica tetralix were co-dominant in the regrowth at this stand. However. there was a decline in
the relative abundances of U. gallii and A. curtisii by the third growing season after burning.
At the mature stands. seedlings affected by resprouting vegetation were sheltered from
microclimatic extremes and experienced higher survivorship than seedlings in areas of bare
ground. However. seedling density under resprouts decreased over time as continued growth
of resprouts prevented seedling germination and establishment. Seedling populations on bare
ground at both types of stand oscillated widely, and there was a rapid turnover. Although
bare ground persisted at the degenerate stands, there was no invasion of non-heathland
species. A canopy of ericaceous species should eventually develop via gradual accumulation
of seedling density and vegetative spread from the few stem bases that were able to resprout.
The range of temperatures generated by the fuel loads tested did not have significant
effects on regeneration from seed or from stem bases. However. the removal of vegetation by
burning had a large impact on vegetation dynamics by enabling seedling emergence and
resprouting from stem bases. The balance between regcneration from seed and from stcm
bases depended on the pre-bum age of the stand.