Table 4. Models testing effect of growth parameters and neighboring competition on the tree response to the release (number of releases and mean growth change), and the accuracy of coppice detection from tree-ring analysis (expressed by sensitivity and PPP).
Significance was tested in generalized linear models using software R version 3.1.3. Best predictor variables were selected by stepwise model selection by Akaike’s Information Criterion using MASS package in R.
| Variables of initial models (No. releases and MGC): MGR; No. neighbors (all, oaks, hornbeam, other); DWBA (all, oaks, hornbeam, other); age | |||||
| Number of releases | Estimate | Std. Error | t value | Pr(>|t|) | |
| (Intercept) | -0.2987461 | 0.5185749 | -0.576 | 0.5657 | |
| age | 0.016471 | 0.0034024 | 4.841 | 4.29E-06 | *** |
| DWBA hornbeam | -0.0014463 | 0.0006678 | -2.166 | 0.0325 | * |
| No. hornbeam | 0.0226908 | 0.0116399 | 1.949 | 0.0538 | . |
| AIC: 328.19 | |||||
| Model I. for MGC | Estimate | Std. Error | t value | Pr(>|t|) | |
| (Intercept) | 7.46E-02 | 4.22E-02 | 1.768 | 0.0799 | . |
| MGR | -3.81E-04 | 1.88E-04 | -2.031 | 0.0447 | * |
| DWBA hornbeam | -6.19E-05 | 2.47E-05 | -2.505 | 0.0137 | * |
| No. all neighbors | 7.89E-04 | 4.40E-04 | 1.793 | 0.0757 | . |
| DWBA oak | -2.03E-05 | 1.45E-05 | -1.405 | 0.163 | |
| AIC: -326.59 | |||||
| Variables of initial model (MGC): MGR; No. neighbors (all, single-stemmed, multi-stemmed); DWBA (all, single-stemmed, multi-stemmed); age | |||||
| Model II. for MGC | Estimate | Std. Error | t value | Pr(>|t|) | |
| (Intercept) | 4.76E-02 | 2.84E-02 | 1.676 | 0.09662 | . |
| DWBA single-stemmed | -5.33E-05 | 1.86E-05 | -2.874 | 0.00487 | ** |
| No. single-stemmed | 3.03E-03 | 1.12E-03 | 2.706 | 0.00791 | ** |
| MGR | -2.57E-04 | 1.75E-04 | -1.465 | 0.14587 | |
| AIC: -331.18 | |||||
| Variables of initial models (sensitivity and PPP): MGC; No. releases; MGR; No. neighbors (all, oaks, hornbeam, other); DWBA (all, oaks, hornbeam, other); age | |||||
| Sensitivity | Estimate | Std. Error | t value | Pr(>|t|) | |
| (Intercept) | 0.914319 | 0.208031 | 4.395 | 2.60E-05 | *** |
| MGC | 2.512293 | 0.632153 | 3.974 | 0.000128 | *** |
| age | -0.002966 | 0.001243 | -2.385 | 0.018825 | * |
| No. oaks | -0.006481 | 0.003534 | -1.834 | 0.069373 | . |
| No. all neighbors | 0.003364 | 0.002191 | 1.535 | 0.127586 | |
| AIC: 104.73 | |||||
| PPP | Estimate | Std. Error | t value | Pr(>|t|) | |
| (Intercept) | 0.548567 | 0.0638904 | 8.586 | 7.02E-14 | *** |
| No. hornbeam | 0.0085018 | 0.0048387 | 1.757 | 0.0817 | . |
| MGC | 1.2113676 | 0.7090305 | 1.708 | 0.0904 | . |
| DWBA hornbeam | -0.0004111 | 0.0002778 | -1.48 | 0.1418 | |
| AIC: 132.47 | |||||
Signif. codes: 0 ‘***’0.001‘**’0.01‘*’0.05‘.’0.1‘ ‘1.
Abbreviations: DWBA—distance-weighted basal area of neighboring trees; MGC—mean growth change; MGR—mean growth rate; PPP—Positive Predictive Power.