Individual study: Effects of prescribed winter burning on heather Calluna vulgaris and wavy hair-grass Deschampsia flexuosa with reference to available nutrients, Lüneburg Heide, Niedersachen, Germany
Mohamed A., HÃ¤rdtle W., Jirjahn B., Niemeyer T. & von Oheimb G. (2007) Effects of prescribed burning on plant available nutrients in dry heathland ecosystems. Plant Ecology, 189, 279-289
Appropriate heathland management can counter increased atmospheric nutrient deposition as is occurring over much of Europe. This study undertaken on Lüneburg Heide in northwest Germany, assessed the effects of prescribed winter burning on nutrient availability in dry heathland soils and the nutrient content of the two common and competing heathland species, heather Calluna vulgaris and wavy hair-grass Deschampsia flexuosa, with particular reference to N and P.
Study area: The study was undertaken on Lüneburg Heide (Lueneburg Heath nature reserve) (53º15'N, 9º58'E; 105 m a.s.l.) in Lower Saxony, northwest Germany. It is the largest complex of heathlands (about 5,000 ha) in the region.
Experimental design: Within an area of 100 ha dominated by 10-12-year-old Calluna, 10, 20 m x 40 m plots were randomly selected. This stand age was chosen as prescribed burning is carried out on a 10-15 year cycle. Plant species composistion and average vegetation cover was: dwarf shrubs (i.e. C.vulgaris) 56%; graminoids (i.e. D.flexuosa) 19%; and cryptogams 42%. Each plot was divided into two subplots (20 m x 20 m; n = 20). Burning was applied to one subplot, the second served as a control.
Plots were burned in February 2001 during fine weather with low wind velocity. Winter burns usually result in low-temperature fires, as was the case here; the organic layer was thus unaffected. About 75% of the aboveground biomass of Calluna, and 20% of the biomass of Deschampsia and cryptogams, burned in the treatment plots. Calluna regenerated mainly by resprouting from the stem base.
Plant available nutrients and soil pH: Determination of plant available nutrients in the soil O- and A-horizons was carried out in five treatment plots and the corresponding controls.
Nutrient losses by leaching: Nutrient losses by leaching were determined using a lysimeter
Calluna and Deschampsia nutrient content: In all subplots, Calluna and Deschampsia were sampled before and 19 months after burning. For each subplot, 20 samples (at least 50 g) of young Calluna shoots and Deschampsia leaves were collected. The harvested material was analysed for nutrient content in the laboratory.
The prescribed late-winter burning mostly affected NH4+ availability in the soil O-horizon, increasing greatly from around 5 mg/l dry soil pre-burn, steadily rising to 60% by June, reaching a maximum of 65% in July and August, before declining to < 40% in September then remaining fairly constant at 10-15% until the end of the experiment (January 2002). There were only short-term and less pronounced effects for NO3−, PO43−, and Mg, and insignificant effects on the availability of other nutrients (K, Ca).
Due to the increased nutrient availability in the humus horizons and a limited nutrient uptake by plants after burning, leaching increased significantly for N, Ca, K and Mg. No significant changes were found in the foliar C:N ratios for Calluna or Deschampsia after burning, but Deschampsia exhibited increased deficiency in other nutrients, particularly P. In contrast, the nutrient content of Calluna changed little; it is assumed that water shortage as a result of microclimate changes was mainly responsible for the deterioration of the nutrient content of the grass. The outcome is that Calluna (usually the desired component species of such heathlands) has a competitive advantage, enabling it to out-compete Deschampsia on burned heaths, especially with respect to P-limitation.
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