Individual study: The effect of sulphur addition and weeding regimes on potted heather Calluna vulgaris plants, Craibstone, Aberdeenshire, Scotland
Lawson C.S., Ford M.A., Mitchley J. & Warren J.M. (2004) The establishment of heathland vegetation on ex-arable land: the response of Calluna vulgaris to soil acidification. Biological Conservation, 116, 409-416
Lowland heaths are a semi-natural habitat with high biodiversity conservation value. Conversion to arable farmland, reduction of grazing on remaining heaths (leading to succession to woodland), afforestation, and urbanisation has resulted in large scale loss of lowland heaths throughout Western Europe. Consequently, the re-establishment of lowland heathland is a priority within the UK Biodiversity Action Plan, with a 2005 target of creating 6,000 ha of heathland.
The conversion of agricultural land back to heathland may help achieve this target. However, simply abandoning arable land usually results in species-poor habitat dominated by common, competetive perennial grasses, which thrive in the nutrient-rich soil. Former arable land is often unsuitable for heathland regeneration because of such high levels of soil nutrients, and also because of a high pH (due to agricultural liming), and the presence already of agressive ruderals and weeds. In this study, the relationship between soil acidification using sulphur, the development of ruderal vegetation, and the establishment of heather Calluna vulgaris (a dominant and desirable heathland plant species) in arable-derived soil was investigated.
Study area & heather cultivation: 4 cm high cuttings of heather Calluna vulgaris were taken from Brimmond Hill, (National Grid Reference NJ858091) near the town of Aberdeen, northeast Scotland, during February 1994. These were planted in a 1:1 peat:sand mix under mist (to maintain moist conditions) in a glasshouse. In April 1994, the rooted cuttings were transferred to peat-filled pots (7.8 cm diameter, 9.4 cm deep), and in May 1994 these were moved outside. At this time, arable soil was taken from the Craibstone Estate, Aberdeen (National Grid reference NJ877115), and transferred into tubs (55 cm diameter, 45 cm deep) placed outside at Craibstone. This soil was a sandy loam podzol derived from granitic till, with a pH of 5.4 and an organic matter content of 8%. A single heather plant was transplanted into each tub and the treatment applied the following day.
Treatments: A total of six treatments were applied in a fully factorial design, with three treatment applications of elemental sulphur (0, 0.24 and 0.48 kg/m²), and the presence or absence of naturally regenerating weeds. Weed free treatments were hand weeded every two weeks. Each treatment was replicated seven times.
heather survival: The number of plants surviving was recorded every other week for 40 months. Four plants that died within the first four weeks were replaced, another two that died in the four weeks after this were removed from the experiment.
Heather growth: The length of the apical shoot and the length of the flowering zone on the apical shoot was recorded during August 1994, 1995 and 1996.
Soil conditions: Every three months for the first year and again in August 1996, soil pH was measured in each tub. In August 1994, soil moisture content was taken for each tub using fresh and dry soil weights.
Heather survival: 22 of the 40 heather plants had died within the 40 month duration of the experiment. There was greater mortality in unweeded (dead plants = 17 of 20) than weeded (5 of 20) treatments. Sulphur also had a significant effect on mortality: in weeded treatments both 0 and 0.24 kg/m² treatments had no deaths (survivors = 7 and 6 respectively), whereas five of seven plants in the 0.48 kg/m² treatment had died.
Heather growth: In August 1994, 1995 and 1996, the addition of sulphur had no effect on the growth of heather plants. By comparison, weeded plants grew significantly larger and flowered more than plants growing in unweeded pots.
Soil conditions: By August 1996, soil pH was reduced by the addition of sulphur. The control treatment ranged from pH 4.96 to 5.18, a small reduction from the original 5.40. In contrast, soil pH ranged from 3.52 to 4.75 in the 0.24 kg/m² sulphur treatment and from 3.39 to 4.13 in the 0.48 kg/m² sulphur treatment. This equated to an average pH reduction of 0.98 for the 0.24 kg/m² and 1.30 for the 0.48 kg/m² sulphur treatments. The addition of sulphur did not affect soil moisture. However, removal of weeds significantly increased soil moisture from an average of 8.96% in unweeded to 14.95% in weeded pots.
Conclusions: Heather grew well in the absence of competing plants. Additionally, a low amount of sulphur addition at the same time as planting also appeared beneficial to development, but too high an amount of sulphur addition resulted in high mortality. (See also Cases 358, 359 and 360).
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