Results

The plots presented similar environmental characteristics, all having a canopy cover of 40-60% and an understory cover class between 6 and 8. Slope was one of the variables that offered more differences among all the plots (Table 1).

Forest stand characteristics showed more variability between plots. Measured by basal area, P. pinea was dominant in plots 2 and 5, while P. canariensis was dominant in the remaining plots (Table 2). Measured by density, P. pinea dominated only plot 5, while the rest of the plots were highly dominated by P. canariensis. Another tree species appeared in plot 4, Erica arborea, although its abundance was less than 1.6% of the total basal area of the plot.

Table 2. Trees (individuals of at least 2.5 cm dbh) basal area (PC: Pinus canariensis, PP: Pinus pinea, EA: Erica arborea) and density

Tree (m2/ha)

Density (ind/ha)

PC

PP

EA

PC

PP

EA

Plot 1

12.51

3.91

0.00

656.25

25.00

0.00

Plot 2

3.85

10.86

0.00

253.08

153.18

0.00

Plot 3

14.56

4.04

0.00

506.16

59.94

0.00

Plot 4

10.13

1.94

0.20

120.00

105.00

40.00

Plot 5

3.15

17.88

0.00

24.00

152.00

0.00

At the beginning of the study, Plot 4 had the highest number of individuals of Pinus canariensis, 768, while plot 3 presented the highest values for P. pinea, 40. At the end of the two year period, these plots were still the most abundant plots for both species respectively. The highest mortality was found in plot 2 for P.canariensis, and plot 3 for P. pinea (Annex I).

The percentage of survivorship after two years of monitoring of Pinus canariensis excluded from grazing was lower than the P. canariensis non-excluded (Fig. 2a), although differences were not significant (t=2.807, n=5, p=0.441). When we compared the percentage of survivorship among P.canarienis vs. Pinus pinea, the mean survivorship of P.pinea were higher, but the differences were not significant (t=1.067, n=5, p=0.638).

Annex I.- Monitoring of the individuals in five different periods, indicating the number of individuals that survive since the first sampling. a) Pinus canariensis excluded from grazing b) Pinus canariensis non excluded_

Rlotl

Plot2

Rlot3

Rlot4

Rlot5

Plot1

Plot2

Rlot3

Plot4

Plot5

Feb-0

2

12

10

89

6

Feb-06

52

54

184

598

33

Jun-01

2

12

10

85

5

Jun-06

52

53

184

584

33

Dec-0

2

11

10

82

4

Dec-06

52

49

177

546

32

Jun-0"

2

11

10

82

4

Jun-0"

52

49

177

548

32

Feb-0

2

11

10

82

4

Feb-08

52

49

175

547

32

c) Pinus pinea non excluded

Plot1

Plot2

Rlot3

Plot4

Plot5

Feb-0

2

7

40

23

5

Jun-06

2

7

40

23

5

Dec-0

2

7

36

22

5

Jun-07

2

7

34

22

5

Feb-0

2

7

34

22

5

% Basal Area plotl plot2 plot3 plot4 plot5

plotl plot2 plot3 plot4 plot5

Rnus canariensis Rnus pinea

% Density

plot1 plot2 plot3 plot4 plot5

% Density seedlings

mm plot1 plot2 plot3 plot4 plot5

Figure 2. a) Percentage of basal areas for Pinus canariensis and P. pinea in the five plots, b) percentage of density of both species and c) percentage of density for the seedlings class.

When the percentage of regeneration density (in the last sampling period) in each plot for Pinus canariensis and P. pinea was correlated with the percentage of basal area of trees of its own species (Fig. 2a and 2c), we found no significant relation among these values (p=0.400 in both cases, n=5, p>0.05). When the regeneration density was correlated with the percentage of density of the trees (Fig. 2a and 2b), this relationship was also non-significant (p=0.476 in both cases, n=5, p>0.05).

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