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Cork harvesting and stopper production represent a major forest industry in Sardinia (Italy). The target of the present investigation was to evaluate the ''classification tree'' as a tool to discover possible relationships between microsite characteristics and cork quality. Seven main cork oak (Quercus suber) producing areas have been identified in Sardinia, for a total of more than 122,000 ha. Sixty-three sample trees, distributed among different geographical locations and microsite conditions, were selected. A soil profile near each sample tree was described, soil samples were collected and analysed. After debarking, cork quality of each sample tree was graded by an independent panel of experts. Microsites where trees had more than 50% of the extracted cork graded in the best quality class, according to the official quality standard in Italy, were labelled as prime microsites, the others as nonprime microsites. Relationships between a binary dummy variable (0 for nonprime microsites, 1 for prime microsites) and site factors were investigated using classification tree analysis to select the relevant variables and to define the classification scheme. Prime quality microsites for cork production proved to be characterised by elevation, soil phosphorus content and sandiness. Results have been compared with those of the more conventional parametric approach by logistic regression. The work demonstrates the advantages of the classification tree method. The model may be appropriate for classifications at landscape and stand mapping levels, where it is possible to sample a number of microsites and to evaluate distributional characteristics of model output, while its precision is only indicative when estimating the prime quality of single microsites.

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Land cover change analyses are common and, especially in the absence of explanatory variables, they are mainly carried out by employing qualitative methods such as transition matrices or raster operations. These methods do not provide any estimation of the statistical significance of the changes, or the uncertainty of the model and data, and are usually limited in supporting explicit biological/ecological interpretation of the processes determining the changes. Here we show how the original nearest-neighbour contingency table, proposed by Dixon to evaluate spatial segregation, has been extended to the temporal domain to map the intensity, statistical significance and uncertainty of land cover changes. This index was then employed to quantify the changes in cork oak forest cover between 1998 and 2016 in the Sa Serra region of Sardinia (Italy). The method showed that most statistically significant cork oak losses were concentrated in the centre of Sa Serra and characterised by high intensity. A spatial binomial-logit generalised linear model estimated the probability of changes occurring in the area but not the type of change. We show how the spatio-temporal Dixon’s index can be an attractive alternative to other land cover change analysis methods, since it provides a robust statistical framework and facilitates direct biological/ecological interpretation.

Considering the very high socio economic value of cork oak (Quercus suber L.) in Mediterranean areas, a better knowledge of local genetic resources is necessary in order to reach a good balance between the conservation issues and the need of an efficient cork production network. In such frame, local germplasm of Q. suber from the main cork production areas of Sardinia was analysed for DNA and isozyme polymorphisms and for cork quality in relation to some environmental parameters. A total number of 24 sample stands of cork oak were selected, representing typical vegetation, sylvicultural and cork quality features within the eight identified cork growing areas in Sardinia. Considerable variation was found between cork oak stands of the different areas. Results of the principal component analysis performed on the cork quality data and environmental characters of the eight areas, showed that the first three components explain 72.2% of the variation. The major characters involved in this differentiation were cork quality characters such as dimensional recover, moisture and Mg content of the cork and also elevation of stands m a.s.l. for the first component. The second component appears to be determined by some climatic parameters (average annual temperature and average of the minimum temperatures of coldest month) and by the Fe and Zn in the cork. For the third component, major characters involved in differentiation are average annual rainfall, bark thickness and Ca content in the cork.

The cork oak shows a good resistance to fire events due to the properties of its bark and a high capacity to resprout after intense fire events from basal suckers. Two experimental trials aiming to evaluate post fire recovery techniques enclosing the influence of the grazing disturbance were conducted in Sardinia. In the first trial, where the experimental activities started in the 1985 in northern hills of Sardinia, a traditional coppicing of severe damaged cork oak trees was compared with the branch pruning.. The coppicing, suggested when high damage levels due to the fire occur, showed a percentage of recovered plants higher than 95%. The early sucker thinning did not produce any significant advantage. The branch pruning showed lower percentages of living trees, going from 20% to 77% in relation to the number of the bark stripping the plants have before the fire. The second case study (Sardinia, central hills) was mainly addressed to the evaluation of the grazing effects after fire. As in the first case, the fire event occurred two years after the bark stripping. The results reveal that the intense grazing after fire causes the death of all coppiced trees. On the other hand, almost all plants recovered after the fire in not grazed plots. The trials showed that a preliminary evaluation of the degree of the trees damage due to the fire is necessary before to apply any recovery technique. Finally, the results give useful information for the management of cork oak stands after fire events, a very common situation in the Mediterranean areas where cork oak is diffuse.

No abstract

Growth performance of cork oak plantations recently established on farmlands in Sardinia, Italy. Recently, significant forestry activities have taken place in Sardinia thanks to EU Regulation 2080/92 funds. Some 80% of the afforestated surface has been planted with holm oak and cork oak. The latter also characterizes 89% of the reforestation area. Given the funding source, plantations have been established on farmlands. Growth performances of these recent cork oak stands have been quantitatively evaluated and compared with the performances of two experimental plots. In Gallura (north-east of Sardinia), that is the traditional cork production area and still is economically the most important cork district of the island, these new cork oak plantations have an average size of 28 ha. They have been established on lands that, before plantation, were either pastures (30%) or arable lands (70%). Plantation failures are limited to 8.8% of the total (in term of mass) and seem independent of environmental factors or plantations species composition (conifers have been frequently used as secondary species). Average growth of the stem, measured above cork at collar height, is in the range 4 to 8mm/year with a mean value of 5.5mm/year. No correlation appears with either environmental conditions or species composition of the plantations. In the first experimental plot, soil management practices (natural vegetation removal vs its cutting and mulching) does not differentiate young plants growth trends. In the control subplots (no removal) stem collar diameter is 20% smaller. Localized manual hoeing around trunk base increased the diameters by 13% but reduced cork thickness by 21%. The second experimental plot allows comparisons among 27 Mediterranean proveniences of cork oak. The trial exhibits reduced genetic influence: diameters and heights growth are significantly different only among extreme groups. In conclusion, reduced growth performances of the plantations established in farmlands is due, to some extent, to the limitations inherent with private land management (constrained to costs minimization) and, on the other hand, to the generally very limited thickness of Gallura soils. Demand for good quality commercial cork is steadily raising. To sustain the request, in the short term, it would be necessary to extend financial support for plantations care, from 5 to 10 years, or even up to the first stripping (virgin cork). IntroduzioneOltre l'80% delle foreste di quercia da sughero italiane si trova in Sardegna, dove è anche presente la gran parte dell'industria di trasformazione in uno specifico distretto industriale che trova nel tappo il prodotto principale e il maggiore valore aggiunto. La fase espansiva globalmente registrata dai vigneti fa prevedere per il 2010 una richiesta di 24 miliardi di tappi di sughero a fronte degli attuali 19 miliardi, anche se la sempre più ampia diffusione di chiusure e contenitori alternativi delinea sul lungo periodo previsioni meno ottimistiche (Repetti 2005). Si può presumere una...