Effetti della consociazione con Alnus cordata sulla funzionalità di impianti di noce comune (Juglans regia L.) sottoposti a diradamento

Abstract

Abstract: Results about the effects of thinning and mixed plantations with Italian alder (Alnus cordata Loisel.) on growth and efficiency of common walnut (Juglans regia L.) plantations for wood production are reported. The study, carried out for six years on sixteen year old plantations, compared three theses: pure common walnut plantation (pure common walnut); 50% common walnut - 50% Italian alder plantation; 25% common walnut - 75% Italian alder plantation. Beyond annual surveys of girth at breast height, total height, stem volume and biomass, several variables, useful to describe canopy and foliage characteristics such as leaf area index (LAI), leaf biomass and photosynthetic active radiation below the canopy, were recorded. Data collected allowed to compare growth at individual and whole stand level, to calculate the net assimilation rate (NAR) and to compare the growth efficiency of the three theses. Mixed plantations performed results significantly higher than the pure plantation in terms of growth, LAI and leaf biomass both before and after experimental thinning. With reference only to common walnut, growth in mixed plantations was higher than the pure plantation with differences ranging from +40% to +100%. More relevant differences among pure common walnut, 50% common walnut and 25% common walnut at canopy and foliage characteristics were observed, with LAI values of 1.07, 3.96 e 4.35 m2 m-2 respectively. Results accounted for a general positive effect of Italian alder as accessory tree species on growth and efficiency of mixed plantations, mainly due to the good performances induced in common walnut trees. Such performances were enabled by the good ecological integration between the two species and by the positive effects of N-fixing activity of Italian alder. Experimental thinning applied, although heavy, did not biased the dynamics observed before thinning both in pure and mixed plantations. In addition, they had positive effects on common walnut growth and especially on radial increment, a very important matter being common walnut the target species with a very appreciated and valuable wood.