Ce travail se propose d'analyser les dynamiques forestières de deux peuplements de conifères d'origine artificielle, situés en Valchiusella (Province de Turin). En particulier, l'étude examine la présence et la distribution de la régénération naturelle sous l'angle de la couverture des deux reboisements, l'un avec Pinus strobus L. et l'autre avec Pseudotsuga menziesii (Mirb.) Franco. Les observations effectuées dans la futaie de Douglas (située à Meugliano) se concernent deux parcelles: l'une n'a, durant les 70 dernières années, reçu aucune intervention forestière, et l'autre a été éclairci durant l'hiver 2004-2005. Dans le bois a Pin blanc (à Alice Superiore), par contre, seulement une aire d'essai a été considérée, mais les informations dendrométriques ont été recueillies avant et après une intervention de éclaircissement forestière ayant eu lieu durant le printemps 2013. Les aires d'essai ont eu la dimension de 10x50 et 20x50 mètres. En outre, une section centrale de chaque aire d'essai, large de trois mètres, a été subdivisé en dix secteurs, pour relever la présence, l'état de développement et la distribution spatiale de la régénération spontanée. Les données recueillies ont été comparée avec les valeurs de radiation lumineuse parvenant au sol. Ces valeurs dérivent de l'interprétation de photographies hémisphériques prises dans chaque secteur; l'analyse digitale des photos a été effectuée par le logiciel Gap Light Analyzer©. Les espèces les plus fréquentes dans les groupes de régénération analysées sont Acer pseudoplatanus L. (n = 84; 25,45 %) et Fraxinus excelsior L. (n = 81; 24,55%). En examinant les données recueillies, on a pu établir le niveau de corrélation entre la modification des conditions de luminosité au sol, déterminée par les éclaircissement, et la distribution spatiale de la régénération naturelle. Les principales conclusions obtenues à l'issu cette recherche concernent les niveaux de radiation lumineuse parvenant au sol dans les trois sites: au-dessous du Pin blanc, la Site Openness % et la Transmitted Total % se sont avérées supérieures à celles des parcelles a Douglas, pou lesquelles les valeurs sont inférieurs également dans le site éclairci. Il s'avère donc que l'espèce prévalent du plan dominant conditionne fortement la disponibilité de lumière au sol et, donc, la présence de semis spontanés. Parallèlement, dans la parcelle de Douglas éclaircie les données relatives au photos hémisphériques mettent en évidence que, 8 ans après l'intervention, les chevelures sont à nouveau fermée, ce qui peut ralentir beaucoup le développement et l'affirmation de la régénération. Selon les tests statistiques exécutés, il apparaît que la distribution et la quantité de régénération sont corrélées, pour la plus parte, au gré de Transmitted Total %, en confirmant que la variabilité des climats lumineux a un rôle fondamental dans les dynamiques forestières. Dans la situation étudiée, donc, l'intervention sylviculturelle conseillée paraît être des éclaircissements prudents, réalisés en périodes inférieures aux huit années, en ayant soin de libérer les groupes de régénération. En alternative ils pourraient être exécuté des trous de petites dimensions, progressivement et prudemment agrandies, après les mêmes éclaircissements, au paraître de la régénération. Cette solution pourrait représenter un bon compromis entre les exigences de renaturation de l'aire et les aspects paysagers à sauvegarder.
The aim of this work is to analyze forest dynamics in two conifer stands, that have artificial origin, located in Valchiusella (Province of Turin). In particular, the study is about the presence and distribution of natural regeneration under the cover of two plantations, the first one of White pine, (Pinus strobus L.) and the other one of Douglas fir (Pseudotsuga menziesii (Mirb.) Franco). The survey conducted in two different representative units of high forest Douglas fir (in Meugliano): one where hasn't been significant forest interventions in the last 70 years, and another that was affected by thinning in the winter 2004-2005. In the White pine stand (in Alice Superiore), has been realized only one plot, but the dendrometric data collected refer both before and after a forest thinning, operated in the spring 2013. Furthermore, the central zone on each plot was divided into 10 sectors, in order to be able to observe the presence, the spatial distribution and the development of the natural regeneration. The data collected have been compared to the values of luminous radiation on the ground. Those values have been deducted by hemispheric photos, taken in each sector. The digital analysis of the photos has been made by the software Gap Light Analyzer©. The most common woody species analyzed in all regeneration units are Acer pseudoplatanus L. (n = 84; 25,45 %) and Fraxinus excelsior L. (n = 81; 24,55%). Examining the data collected, it has been possible to establish the correlation between the modification of the luminous climates on the ground, determined by thinning, and the spatial distribution of natural regeneration. The main conclusions that can be assumed are about the levels of light at the under storey in the different sites: as far as concerns White pine, the Site Openness % and the Transmitted Total % present higher values than Douglas fir, where these are lower even in the thinned site. So, the predominant species of the dominant level conditions light availability at ground and, as consequence, the presence of natural regeneration. According to statistic tests executed, it appears that distribution and quantity of seedlings is strictly connected with the value of Transmitted Total %. This information confirms that variability of light climates plays a primary role in forest dynamics. Meanwhile, in Douglas fir plot submitted to thinning, it appears that, after 8 years from the intervention, canopies are newly closed and they slow down regeneration development and affirmation. In the case of study, therefore, the counselled silvicultural intervention may be gap opening, preferably small and deferred in the time. Cautious thinnings, realized in periods no more longer than eight years, in correspondence of regeneration units may represent the correct compromise between rinaturalization exigencies and landscape aspects to be safeguarded.
Dinamiche forestali in rimboschimenti di conifere in Valchiusella (TO)
RAVETTO ENRI, SIMONE
2012/2013
Abstract
The aim of this work is to analyze forest dynamics in two conifer stands, that have artificial origin, located in Valchiusella (Province of Turin). In particular, the study is about the presence and distribution of natural regeneration under the cover of two plantations, the first one of White pine, (Pinus strobus L.) and the other one of Douglas fir (Pseudotsuga menziesii (Mirb.) Franco). The survey conducted in two different representative units of high forest Douglas fir (in Meugliano): one where hasn't been significant forest interventions in the last 70 years, and another that was affected by thinning in the winter 2004-2005. In the White pine stand (in Alice Superiore), has been realized only one plot, but the dendrometric data collected refer both before and after a forest thinning, operated in the spring 2013. Furthermore, the central zone on each plot was divided into 10 sectors, in order to be able to observe the presence, the spatial distribution and the development of the natural regeneration. The data collected have been compared to the values of luminous radiation on the ground. Those values have been deducted by hemispheric photos, taken in each sector. The digital analysis of the photos has been made by the software Gap Light Analyzer©. The most common woody species analyzed in all regeneration units are Acer pseudoplatanus L. (n = 84; 25,45 %) and Fraxinus excelsior L. (n = 81; 24,55%). Examining the data collected, it has been possible to establish the correlation between the modification of the luminous climates on the ground, determined by thinning, and the spatial distribution of natural regeneration. The main conclusions that can be assumed are about the levels of light at the under storey in the different sites: as far as concerns White pine, the Site Openness % and the Transmitted Total % present higher values than Douglas fir, where these are lower even in the thinned site. So, the predominant species of the dominant level conditions light availability at ground and, as consequence, the presence of natural regeneration. According to statistic tests executed, it appears that distribution and quantity of seedlings is strictly connected with the value of Transmitted Total %. This information confirms that variability of light climates plays a primary role in forest dynamics. Meanwhile, in Douglas fir plot submitted to thinning, it appears that, after 8 years from the intervention, canopies are newly closed and they slow down regeneration development and affirmation. In the case of study, therefore, the counselled silvicultural intervention may be gap opening, preferably small and deferred in the time. Cautious thinnings, realized in periods no more longer than eight years, in correspondence of regeneration units may represent the correct compromise between rinaturalization exigencies and landscape aspects to be safeguarded.| File | Dimensione | Formato | |
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https://hdl.handle.net/20.500.14240/44463