*3.2. Thallus Growth*

Following one year of exposure, the transplants in the unlogged stand (both non-meristematic and meristematic) were characterized by larger surfaces and a comparable increase in the thallus area (by 25% and 21%, respectively). Transplants exposed in the logged stand showed a significantly lower (*p* < 0.05) growth in the case of non-meristematic fragments (their increase was about 6%). The growth of meristematic fragments (14%) did not significantly differ between the logged and unlogged stand. Irrespective of forest management, meristematic fragments showed higher growth rates (surface increase 0.16–0.18 cm<sup>2</sup> year<sup>−</sup>1) as compared with non-meristematic fragments (0.02–0.06 cm2 year<sup>−</sup>1). The presence of regeneration lobules along the cut edges of meristematic fragments was not observed (except for one case in the unlogged stand).

#### *3.3. Principal Component Analysis (PCA)*

A 3-dimensional solution was found both for meristematic and non-meristematic datasets, explaining 100% of the total variance (Table 1). Figure 4 shows the score plots of the first two axes, that explained >80% of the variance. Regarding meristematic fragments, the first two principal components (PC) cumulatively explained 80.44% of the total variance. PC1 (explained variance: 47.15%) showed an increasing gradient of vitality (delta fluo, *R*<sup>2</sup> = 0.706) and chlorophyll content (delta Chl, *R<sup>2</sup>* = 0.705) in relation to the meristematic thalli that were transplanted in the unlogged stand (26 out of the 35 samples, 74%). The growth was positively correlated with PC2 (explained variance: 33.29%), irrespective of forest management. Concerning non-meristematic fragments, the first two PC cumulatively explained 80.86% of the total variance. The fragments transplanted in the unlogged stand were distributed (26 out of the 33 samples, 79%) for negative values of PC1 (explained variance: 50.70%), showing an increasing gradient of growth rate (*R2* = −0.639) and vitality (delta fluo, *R2* = −0.658), while the values of chlorophyll content were highly related to the negative values of PC2 (explained variance: 30.16%).


**Table 1.** Matrix of variable loadings reporting the eigenvalues of the three principal components of the PCA ordinations (explained variance in brackets), which were performed separately for meristematic and non-meristematic thallus fragments. Values >0.5 are reported in bold.

**Figure 4.** Score plots of the Principal Component Analysis obtained for meristematic (ordination on the left) and non-meristematic fragments (on the right). Distribution of meristematic lobes in logged and unlogged stand: 40 and 35 samples, respectively; non-meristematic fragments: 49 and 33 samples, respectively.

#### *3.4. Multiple Linear Regression Models*

Considering the growth of meristematic fragments as the response variable, a non-significant model was obtained, thus showing that it was not affected by forest management and by photobiont vitality and chlorophyll content (Table 2 and Figure 5). The model for non-meristematic fragments was significant (*AdjR*2: 0.197; *p* < 0.001; Table 2), with an increasing gradient of growth with respect to fragments transplanted in the unlogged stand (*p* < 0.05), corresponding to an average of 0.142 cm estimated higher linear growth. The growth also was positively related to higher values of delta fluo (*p* < 0.01; Figure 5).

**Table 2.** Multiple Linear Regression Models describing the effects of logging and vitality on growth rates both in meristematic and non-meristematic fragments. Estimates, Standard Errors, *t* values and *p* values (\* *p* < 0.05; \*\* *p* < 0.01) are reported. Summary statistics also are reported for each model (*F* statistics and *p* values).


**Figure 5.** Fitted modeled relationships between growth rate and delta fluo, according to the linear models of Table 2, for meristematic (**left**; *p* > 0.05) and non-meristematic fragments (**right**; *p* < 0.01). Bands represent 95% confidence intervals. Solid line = logged, dashed line = unlogged.
