Table 5. Statistical models for tree persistence.
For each model, the table shows the predictor variables entering the model (remaining variables did not enter), respective direction of association (positive + or negative -) with the response variable (presence of cork oak persistence), the AICc value, AICc differences (Δi) and Akaike weights (wi), and model fit (full model χ²) and area under curve (AUC±s.e.). Models are ordered by increasing Δi, with the best model having Δi=0 (model 1) and the worst model having Δi=29.0 (model 12). The type of model is also coded according to the method used: (a) separate models for each variable, (b) models for each set of biophysical and management variables, (c) stepwise models for each set of biophysical and management variables, (d) stepwise models with the whole set of variables. Codes for management variables: underst= understory management pre 1975; cuttree= tree cutting post 1975; afforest= tree planting post 1985.
| |
| |
|
|
Variables |
|
|
|
|
|
| |
|
Model |
aspect |
slope |
fire |
underst |
cuttree |
afforest |
AICc |
Δi |
wi |
χ² |
AUC |
|
1 d |
|
+ |
- |
- |
|
- |
22.618 |
0.000 |
0.759 |
34.45 |
0.98±0.019 |
|
2 d |
|
|
- |
- |
|
- |
24.922 |
2.304 |
0.240 |
29.41 |
0.95±0.035 |
|
3 c |
|
|
|
- |
|
- |
37.062 |
14.444 |
0.001 |
14.71 |
0.83±0.069 |
|
4 b |
|
|
|
- |
- |
- |
38.583 |
15.965 |
0.000 |
15.75 |
0.85±0.066 |
|
5 c |
|
+ |
- |
|
|
|
39.933 |
17.315 |
0.000 |
11.84 |
0.80±0.084 |
|
6 a |
|
|
|
- |
|
|
40.265 |
17.647 |
0.000 |
9.11 |
0.69±0.087 |
|
7 a |
|
|
- |
|
|
|
41.612 |
18.994 |
0.000 |
7.76 |
0.73±0.097 |
|
8 a |
|
|
|
|
|
- |
43.947 |
21.329 |
0.000 |
5.43 |
0.70±0.096 |
|
9 b |
- (S)† |
+ |
- |
|
|
|
44.481 |
21.863 |
0.000 |
12.59 |
0.81±0.080 |
|
10 a |
|
+ |
|
|
|
|
45.902 |
23.284 |
0.000 |
3.47 |
0.66±0.100 |
|
11 a |
|
|
|
|
- |
|
48.278 |
25.660 |
0.000 |
1.01 |
0.56±0.100 |
|
12 a |
- (S)† |
|
|
|
|
|
51.661 |
29.043 |
0.000 |
0.12 |
0.52±0.103 |
|
| |
† less probability of tree persistence in southern
exposures
|