Effects of fertilization and cutting on the chemical composition of vegetation and soils of mountain heathlands in Spain

In the mountains of northern Spain, patches dominated by Calluna vulgaris are scarce and they may disappear or change as a result of continued lack of management and possibly increasing nutrient availability through atmospheric deposition. The effects in the soil properties and in the composition of Calluna vulgaris and Erica tetralix shoots on heathlands dominated by Calluna and Erica subjected to fertilization and experimental cutting were studied in three mountain passes in northern Spain. A total of 90 1-m² plots received different combinations of cutting and twice the estimated atmospheric deposition of nitrogen (5.6 g.m⁻⁻².yr⁻⁻¹) as ammonium nitrate. One of the dominant ericaceous species (Calluna and Erica) was selectively cut by hand at ground level and their nitrogen shoot content were compared in the presence or absence of the other. Treatments were carried out in April 1998. In each plot one soil sample was taken in the original situation and 12, 24 and 36 months after the treatments. Soil properties such as organic matter, total nitrogen, available phosphorus and pH were determined. In every plot five shoots of Calluna and Erica were also taken to analyse total nitrogen content in the original situation and 12, 24 and 36 mo after the treatments.Nitrogen addition does not necessarily lead to increased levels in the soil, and a clear pattern was not found in the three areas. A gradual decrease in available phosphorus content was detected in the three areas until two years after treatment, although values tend to recover in two of the areas in the third study year. An increase in organic matter content was observed in all areas. It is concluded that increased nutrients alone, at twice the rate of the estimated current atmospheric deposition for the area, which is relatively low, will not alter significantly the soil characteristics of the mountain heathland stands. A clear increase in plant N-content is observed in the fertilized plots in comparison with the non-fertilized ones and Calluna always has higher nitrogen content than Erica. This increase is most pronounced one year after the treatments started in one of the areas and after two years in the other two areas. In some cases the elimination of one species is seen to favour nitrogen increase in the other.