6). Within the open zone (Heath and Cal+M.c) soil pH was significantly greater (P < 0.05) in high density than in low density birch areas (Fig. 7). The soil water content varied between 15% and 60%, without any significant differences among the five vegetation types (Fig. 8). 4. Discussion The development phase of was one of the factors suggested to regulate the C. vulgaris expansion of in fact only the pioneer and building phases of (CalO) M. caerulea: C. vulgaris were colonized by this grass. The existence of bare soil in such areas enabled the establishment of contrasting with the mature phase in which high heather covers M. caerulea, all the soil. In the study area, two large areas with a high density of birch shoots were observed on different soil types, one within open low and discontinuous stands of (CalO) and C. vulgaris the other within high and continuous stands of (CalH). spp. can establish in C. vulgaris Betula gaps in the centre of mature or degenerate stands (Gong and Gimingham, 1984). C. vulgaris This prevents the repetition of the life cycle of heather (Gimingham, 1988), suggesting that after degeneration of heather in CalH areas, cyclical growth processes cannot be restarted and available spaces are instead colonized by other species (Fig. 9). Within open low and discontinuous stands of colonization by birch exerted C. vulgaris, significant effects on the expansion of In fact, the area where M. caerulea. M. caerulea appeared is an area of high density of old birch shoots. In this zone birch, that was cut every four years following prescribed management practices, later resprouted thereby creating a special microhabitat likely to counteract soil acidification (Gardiner, 1968). This influence is well explained by the relationship between the expansion of areas and soil types. M. caerulea
6). Within the open zone (Heath and Cal+M.c) soil pH was significantly greater (P < 0.05) in high density than in low density birch areas (Fig. 7). The soil water content varied between 15% and 60%, without any significant differences among the five vegetation types (Fig. 8). 4. Discussion The development phase of C. vulgaris was one of the factors suggested to regulate the expansion of M. caerulea: in fact only the pioneer and building phases of C. vulgaris (CalO) were colonized by this grass. The existence of bare soil in such areas enabled the establishment of M. caerulea, contrasting with the mature phase in which high heather covers all the soil. In the study area, two large areas with a high density of birch shoots were observed on different soil types, one within open low and discontinuous stands of C. vulgaris (CalO) and the other within high and continuous stands of C. vulgaris (CalH). Betula spp. can establish in gaps in the centre of mature or degenerate C. vulgaris stands (Gong and Gimingham, 1984). This prevents the repetition of the life cycle of heather (Gimingham, 1988), suggesting that after degeneration of heather in CalH areas, cyclical growth processes cannot be restarted and available spaces are instead colonized by other species (Fig. 9). Within open low and discontinuous stands of C. vulgaris, colonization by birch exerted significant effects on the expansion of M. caerulea. In fact, the area where M. caerulea appeared is an area of high density of old birch shoots. In this zone birch, that was cut every four years following prescribed management practices, later resprouted thereby creating a special microhabitat likely to counteract soil acidification (Gardiner, 1968). This influence is well explained by the relationship between the expansion of M. caerulea areas and soil types.