Caratterizzazione dendrocronologica dei regimi di disturbo in una rete di faggete vetuste altimontane distribuite lungo un gradiente latitudinale
Author(s)
Ziaco, Emanuele
Date Issued
May 27, 2013
Type
Doctoral Thesis
Abstract
Frequency and intensity of disturbance events play a key role in influencing forest structural-ecological
processes and trees' auxological history, particularly inside unmanaged stands characterized by high degrees of
naturalness. Dendrochronology is a valid tool for quali-quantitatively describing disturbance regimes through
the analysis of ring-width series, where disturbance events are registered as abrupt growth releases which can be
recorded and dated. The goal of this work was the analysis of auxological histories and the characterization of
disturbance regimes of 9 high-mountain old-growth beech forests distributed along a latitudinal gradient from
the Austrian Alps to the Southern Apennines. The study was divided into 3 phases: i) development of
chronological indicators capable to discriminate different degrees of naturalness according to parameters linked
to the age of dominant trees and their history of growth; ii) identification of growth releases and reconstruction
of disturbance regimes according to the boundary lines release criteria and the analysis of plant response to
disturbances in terms of radial and basal growth and in relation to plant size and age; iii) identification of
relationships between growth variations associated to disturbance events and some important climatic patterns
of the Boreal hemisphere, as the Multidecadal Atlantic Oscillation (AMO) and the North Atlantic Oscillation
(NAO) through the wavelet and crosswavelet analysis of time series of plants' growth variations.
Chronological indicators of old-growthness showed the high degree of naturalness of studied stands, where
multi-centennial individuals are present (ages > 550 years). Chronological indicators provided coherent results
with the most common structural indicators of old-growthness (e.g. deadwood; density of large trees). The
reconstruction of disturbance regimes performed by using both a radial and basal boundary line uncovered the
prevalence of frequent low-intensity disturbance events, highlighting the importance of “gap dynamic” as a
driver of structural renovation processes in temperate environments. The possibility of plants to produce growth
releases up to remarkable dimensions (50-60 in diameter) and ages (even > 500 years) also emerged. A
periodicity of ~65-70 years in plants' growth oscillations and in the frequency of disturbance events was
observed, which surprisingly follows the periodicity of the AMO index, whose oscillations are responsible for
the frequency of cyclones over Southern Europe (during positive AMO phases) that make forest stands more
vulnerable to disturbance events.
Additional information
Dottorato di ricerca in Scienze e tecnologie per la gestione forestale e ambientale
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