Free access
Issue
Ann. For. Sci.
Volume 63, Number 7, October-November 2006
Page(s) 739 - 747
DOI http://dx.doi.org/10.1051/forest:2006055
Published online 18 October 2006
Ann. For. Sci. 63 (2006) 739-747
DOI: 10.1051/forest:2006055

Human land-use, forest dynamics and tree growth at the treeline in the Western Italian Alps

Renzo Mottaa, Mariano Moralesb and Paola Nolac

a  Dep. Agroselviter University of Turin, Via Leonardo da Vinci 44, 10095 Grugliasco (TO), Italy
b  Dep. de Dendrocronología e Historia Ambiental, IANIGLA-CRICYT, CC330, CP 5500, Mendoza, Argentina
c  Dep. Ecoter University of Pavia, Via S. Epifanio 14, 27100 Pavia, Italy

(Received 5 October 2005; accepted 9 March 2006; published online 18 October 2006)

Abstract - Three plots were sampled along an altitudinal gradient in the upper Susa Valley (Piedmont, Italy) on a northeastern slope from 1800 to 2300 m a.s.l. In order to reconstruct recent dynamics at this altitudinal range various techniques were used. Dendroecological methods were used to reconstruct the age structures of tree populations. Growth dynamics were investigated both by observing Basal Area Increment (BAI) in old and dominant trees and by comparing the BAIs within a given cambial age class in different time periods. Historical documents were analyzed as an independent data source to explain changes in establishment rate. As far as the tree establishment at the forestline and at the treeline is concerned we observed three distinct periods: during the first one (1850-1930) larch establishment was reduced or prevented because of heavy grazing and the stone pine establishment was almost null because of the grazing and of the human anthropogenic removal. During the second one (1930-1960) the past heavy grazing followed by periods of moderate grazing favored the larch establishment; stone pine establishment was still prevented both by grazing and by anthropogenic removal. Finally the third period (1960-present) has been the period of massive stone pine regeneration. The growth rates of stone pine and larch have increased in the last decades: individuals in the 100-, 150- and 200-year age classes grow more rapidly in present times as compared to the previous two centuries. In the same time younger trees (1-50 years old) showed a decline in growth because the current stands are denser and the young and suppressed trees have worse growth conditions respect the previous open stands. An analysis of all the data taken together in the present study argues in favor of the fact that the tree establishment, and more in general the forest dynamic, has been mainly controlled by human land-use and that the tree growth has been mainly climatically controlled.


Résumé - Histoire de l'occupation du sol, et dynamique forestière à la limite supérieure des arbres dans la vallée de Suse (Piémont, Italie). Afin de reconstruire la dynamique récente de l'étage subalpin, la présente étude a mis en oeuvre plusieurs techniques. Des méthodes dendrochronologiques ont permis de reconstruire la structure d'âges des populations d'arbres. La croissance a été étudiée à la fois par l'observation de l'accroissement en surface terrière des vieux arbres dominants et en comparant les accroissements en surface terrière des classes d'arbres avec la même classe d'âge cambial à différentes périodes de temps. De plus, des documents d'archives ont été étudiés. On a observé trois phases distinctes d'établissement des arbres: la première (1850-1930) durant laquelle il n'y a pas d'établissement d'arbre à cause de la forte pression du pâturage, la deuxième (1930-1960) durant laquelle il y a établissement de mélèzes, car la pression du pâturage diminue et la troisième (1960-aujourd'hui) avec établissement de pins cembro où la pression du pâturage continue de diminuer et où le pin cembro n'est plus arraché systématiquement par l'homme. L'accroissement des arbres a montré une augmentation dans les dernières décennies parmi les arbres dominants et co-dominants tandis qu'une diminution de l'accroissement à été observée parmi les plus jeunes. Le pastoralisme semble être le facteur principal influençant la dynamique passée et récente des peuplements forestiers d'altitude, alors que les changements climatiques pourraient être responsables d'une augmentation de la vitesse de croissance des arbres.


Key words: dendroecology / Larix decidua / Pinus cembra / tree-rings / basal area increment (BAI) / herbivory

Mots clés : dendroécologie / Larix decidua / Pinus cembra / cernes / accroissement en surface terrière / pâturage du bétail

Corresponding author: renzo.motta@unito.it

© INRA, EDP Sciences 2006