The mineral nutrient status of Rubus chamaemorus L. in relation to burning and sheep grazing

Published source details Marks T.C. & Taylor K. (1972) The mineral nutrient status of Rubus chamaemorus L. in relation to burning and sheep grazing. Journal of Applied Ecology, 9, 501-511.
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Summary

In an experimental plot established in 1957 to follow long-term effects of sheep grazing and rotational burning on Calluneto-Eriophoretum blanket bog, a study of the response of cloudberry Rubus chamaemorus (a local upland plant in the UK) to these treatments was initiated in 1969. I the absence of grazing and recent burning, the above-ground cloudberry standing crop in 1969 was 5-times greater than in the equivalent grazed treatment. Where burned in the traditional manner in one of the fenced plots in the spring of 1965, average above-ground dry-matter yield was over 10 times that in the unburned and grazed treatment. Fruits were produced in the fenced area but not in those grazed. This paper describes the treatment differences on R.chamaemorus in terms of seasonal trends of nitrogen, phosphorus, potassium, calcium and magnesium in this experiment and seeks to determine whether the concentrations of these macro-nutrients may be limiting growth.

Study area: The study was undertaken on an area of bog on the east flank of Hard Hill (around 610 m) in Moor House-Upper Teesdale National Nature Reserve, Northumberland, northeast England.

Experimental design: The bog was burned in the spring 1954. Within this area in 1957, four blocks were demarcated in a series with increasing altitude. Each block included the same burning and grazing treatments in a restricted random 2 x 3 factorial arrangement in which the three ungrazed plots (30 m²) were included beside each other within a fenced area (30 x 90 m), with the unfenced treatments similarly arranged alongside. A similar pattern of response was found in each of the four blocks, and one block only was selected for more detailed investigation.

Treatments in each of a fenced and unfenced plot were: no further treatment; short rotation (burnt in 1965, to be burnt in 1976); long rotation to be burnt again in 1976.

Sampling and chemical analysis: Plant samples were taken at intervals during the growing season of 1969, dry weight, and nitrogen, phosphorus, potassium, calcium and magnesium content, were determined.

Nutrient content: As shoots developed from mid-May onwards, there was a rapid increase in plant N, P and K reflected by increases production of plants within plots burnt in 1965. The nutrient amount per unit area remained steady or slightly decreased as the season progressed. In plants from the other treatments, the increases in N, P, K and dry matter proceeded more slowly. Similarly, changes in Ca and Mg in all treatments were proportional to the rate of dry weight increase, except that Ca values were still increasing at the time of the final harvest.

Effect of treatment on cloudberry growth: The effect of removing the heather canopy was pronounced. In the fenced area shoot density in cut plots was about 20% greater at the end of the first season than in those uncut. By the end of the second growing season the average shoot number/m² was almost double that found in the burned and fenced treatment. The total number of fruits produced also increased in the cut plots in the second year.

Conclusions: Results suggest that availability of major mineral elements is not the cause of between-treatment differences in cloudberry growth. Some other aspect of the burning and sheep grazing treatments are considered to have produced the observed effects. Sheep grazing and trampling may modify the above-ground standing crop and ultimately the below-ground biomass. Grazing of plants will damage shoots and reduce the biomass. Fire, through the removal of the dwarf-shrub canopy alters the microclimate close to the ground and also presumably influences cloudberry growth.

Note: The compilation and addition of this summary was funded by the Journal of Applied Ecology (BES). If using or referring to this published study, please read and quote the original paper, this can be viewed at: http://links.jstor.org/sici?sici=0021-8901%28197208%299%3A2%3C501%3ATMNSOR%3E2.0.CO%3B2-Q