R ESULTADOS DE LA ENCUESTA

II.4.2.1 Pinus halepensis Models

In the understory study, annual precipitation for P. halepensis stands averaged 503 mm and ranged from 259 - 777 mm (Table 7). Elevation was 381 m on average with a range of 83 - 708 m. The number of hard and soft bedrock stands was 23 and 25, while the number of stands on both north and south facing aspects were 24 (Table 8). Overstory basal area had a mean of 9.9 m²/ha with a range of 2.8 - 19.4 m²/ha (Table 7). Stand age averaged 53 years and ranged 44 to 88.

Understory biovolume variables total, oak, and pine, averaged 0.169, 0.029, and 0.007 m³/m², respectively, with a range from 0 - 1.77, 0 - 0.58, and 0 - 0.25 m³/m², respectively (Table 9).

0 5 10 15 20 25 30 35 40 45 50

HT (m) DBH (cm) MBAI

(cm²/yr)

Density (tph/10)

BA (m²/ha) NDVI × 10 P. brutia P. halepensis

Abiotic factors accounted for 24%, 48% and 33% of the variation in understory pine (regenerating pines), oak (regenerating oaks), and total woody (trees, shrubs and vines) volumes. For understory pine volume, bedrock accounted for 78% of the explained variation within the model (Table 10). Hard bedrock supported significantly less pine volume than soft. The remaining 22% of explained variation within the pine volume model was accounted for by precipitation, although it did not reach the P < 0.05 threshold (P = 0.0594). For

understory oak volume, precipitation accounted for 45% and overstory BA for 32% of the explained variation (Table 10). Understory Oak volume increased with precipitation but decreased with overstory basal area. In addition, a bedrock × elevation was also found to be significant, however it was difficult to interpret this relationship as only 13 stands (7 hard bedrock stands, 6 soft bedrock stands) had any recordable oak volume and were poorly distributed along the elevation gradient. Variation in total understory volume was best described by precipitation and elevation (Table 10) accounting for 81% and 19% of the explained variation, respectively. Precipitation had a positive effect (Figure 8) and elevation had a negative effect on total understory woody volume.

Table 7. Continuous explanatory variable range, averages, and standard error for the understory dataset of Pinus halepensis and Pinus brutia forest stands examined in Israel.

Pinus halepensis Pinus brutia

Variable Range Mean Std.Err. Range Mean Std.Err.

Precipitation (mm) 259 - 777 504 21 432 - 714 588 11

Elevation (m) 83 - 708 381 28 58 - 734 300 35

Basal Area (m²/ha) 2.8 - 19.4 9.9 0.6 2.4 - 21.5 12.4 0.7

Table 8. Numbers of stands with the nominal explanatory variables for the undestory dataset comprised of Pinus halpepensis and Pinus brutia forest stands in Israel.

Pinus halepensis Pinus brutia

Aspect Aspect

Bedrock North South Bedrock North South

Soft 12 13 Soft 8 8

Hard 12 11 Hard 7 9

Table 9. Response variable range, average and standard error for the understory dataset of Pinus halepensis and Pinus brutia forest stands examined in Israel.

Pinus halepensis Pinus brutia

Variable Range Mean Std.Err. Range Mean Std.Err.

Total (m³/m²) 0 - 1.77 0.169 0.046 0 - 1.80 0.237 0.079 Oak (m³/m²) 0 - 0.58 0.029 0.016 0 - 1.35 0.117 0.051 Pine (m³/m²) 0 - 0.25 0.007 0.007 0 - 0.02 0.001 0.001

Figure 8. Relationship between total understory woody volume and precipitation for Pinus halepensis forests in Israel.

II.4.2.2 Pinus brutia Models

In the understory plot set up (32 plots), annual precipitation for P. brutia stands averaged 588mm and ranged from 432 - 714 mm (Table 7). Average elevation was 300 m with a range of 58 - 734 m. The number of stands on both hard and soft bedrock was 16, while the number of stands with north and south facing aspects was 15 and 17, respectively (Table 8).

Overstory basal area had a mean of 12.4 m²/ha with a range of 2.4 - 21.5 m²/ha (Table 7).

Stand age averaged 53 years and ranged 45 to 64.

-0.1 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9

200 300 400 500 600 700 800

Total Understory Vol. (m3 /m2 )

Precipitation (mm)

R² = 0.08 P = 0.0475 y = 4.4468x - 871.66

Table 10. Results from stepwise regression analysis of the effect of abiotic factors on understory volume in Pinus halepensis and Pinus brutia forests.

Tree Response Explanatory R² DF EV¹ SS F Ratio Prob > F P. halepensis Pine Precipitation 0.24 45 1009.03 3.7423 0.0594

Bedrock 0.78 3587.93 13.3068 0.0007(H<S)

Oak Precipitation 0.48 41 0.45 3832.45 25.4478 <.0001(+)

Bedrock 152.97 1.0157 0.3194

Elevation 73.79 0.4900 0.4879

Bedrock*Elevation 0.11 985.01 6.5406 0.0143

Basal Area 0.32 2723.52 18.0844 0.0001(-)

Age 0.10 826.23 5.4862 0.0241(+)

Total Precipitation 0.33 45 0.81 7860.82 21.3543 <.0001(+)

Elevation 0.19 1803.72 4.8999 0.0320(-)

P. brutia Pine No model produced

Oak Precipitation 0.13 29 1527.19 3.8963 0.0580

Aspect 1282.92 3.2731 0.0808

Total Precipitation 0.12 31 2073.00 4.3108 0.0465(+)

1EV = Explained Variation

Understory woody volume variables total, oak, and pine averaged 0.237, 0.117, and 0.001 m³/m², respectively, with a range from 0 - 1.80, 0 - 1.35, and 0 - 0.02 m³/m² (Table 9).

Understory vegetation development in P. brutia forests appeared to be less influenced by abiotic factors than in P. halepensis forests and insensitive to overstory canopy coverage or basal area. Abiotic factors accounted for 13% and 12% of the variation in understory oak and total woody volumes, but had no discernible effect on pine regeneration (Table 10).

Precipitation and aspect accounted for 13% of the variation in oak volume but neither factor was significant, although precipitation corresponded to a positive effect (P = 0.058).

Similarly, for total understory woody volume in P. brutia stands, precipitation accounted for 12% of the variation and had a significant positive effect with increasing precipitation (Table 10).

II.4.2.3 Combined Species Model

The total number of stands in the combined dataset was 64 with P. halepensis and P. brutia both having thirty-two stands. The reduced number of P. halepensis stands, from forty-eight to thirty-two was for the same reason as mentioned in the overstory combined dataset section. In this set up, AAP for P. halepensis stands was 586 mm with a range from 408 - 777 mm, average elevation was 384 m with a range from 83 - 697 m, number of stands on both hard and soft bedrock was 16, as well as 16 stands on both north and south facing aspects. Stand age averaged 53 years and ranged 44 to 88.

Overstory basal area had a mean of 11.1 m²/ha with a range of 4.0 - 19.4 m²/ha. Distribution for P. brutia stands was the same as previously described.

A significant difference in understory development between P. halepensis and P brutia stands was only found for understory pine volume (Appendix 4, Figure 9). A significant species × bedrock interaction on pine regeneration was found indicating that on soft bedrock pine regeneration was much higher in P. halepensis than in P. brutia stands while on hard

Figure 9. Average understory volume for Pinus halepensis and Pinus brutia forest stands in Israel. Error bars represent standard error of the mean.

bedrock it was similar among the two species. Notably for P. brutia, only five stands had pine in the understory.