Floristic and structural variability of the central apennines beech forests in relation to natural and anthropogenic determinants

Abstract

Forests are complex ecosystems, in which the floristic composition is the result of the combined effect of several factors, acting at different levels. Climate, lithology, geomorphology act at a broader scale, driving the forest's communities differentiation while, at a finer scale, the understory species composition is shaped by the forest stand structure that directly influences the environmental conditions (light, temperature, moisture) at the ground level. Fagus sylvatica forests are the most abundant broadleaved communities in central and southern Europe; in Italy they represent the typical montane vegetation in the Apennine chain, where these coenoses reach the highest elevations of their whole distributional range. Beech forests have been managed for centuries, prevalently as coppice, or coppice-with-standards (CWS), and high forest (HF). However, in recent decades deep socio-economical changes have led to the progressive abandonment of coppice cut and its conversion to high forest management. These two systems differ in cut intensity and severity (both higher in CWS): given that forest management impacts upon overstory structure and therefore determines the understory composition, management changes are likely to affect understory species composition and diversity. In this thesis I have analyzed the effect of the main environmental drivers on beech forests communities: I then focused on the management effects on understory species and 9210* Habitat diagnostic species richness and composition (sensu Habitat Directive 92/43 EEC), in order to understand the possible implications of the old CWS conversion on the floristic composition. The study was conducted in central Apennines, on the Montagne della Duchessa massif, where beech forests occupy a surface of more than 1200 ha; these forests have ceased to be managed since '60s, so the CWS have become older, and are destined to be converted to the HF cut. I studied the role of the environmental factors in differentiating the beech forests communities by using a dataset of 40 relevés randomly selected. The dataset obtained has been analyzed through a cluster analysis and a Indicator Species Analysis (ISA), in order to obtain groups of relevés and to characterize them in floristic terms; the groups obtained were then compared in terms of environmental and topographic variables, Ellenberg indicator values, life forms, Social Behaviour Types (SBT) and structural parameters. Results showed that the floristic and coenological variability is shaped by a climatic and edaphic gradient, that both contribute to define two main communities: a microthermal one, placed at higher altitudes and cooler aspects (Cardamino kitaibelii - Fagetum sylvaticae), and a termophilous one, lying at lower altitudes and warmer aspects (Lathyro veneti - Fagetum sylvaticae). Social Behaviour Types and structural parameters were useful for detecting the effects of the progressive reforestation process occurring inside the microthermal community at higher elevation. In order to investigate the differences between old CWS and HF stands in terms of understory richness and composition, I used 66 relevés, selected through a random-stratified method, so as to have a comparable number of relevés for each management category; old CWS and HF stands were compared in terms of structural attributes and floristic richness through a U Mann-Whitney test: the II results showed how management is the main factor responsible for differences in the tree layer's spatial aggregation pattern and vertical layering, and that therefore determines the amount of surface available for understory species. HF stands showed a higher mean richness of both understory and diagnostic species, these latter being more evenly distributed (higher species equitability) inside the community. This leads to the consideration that in HF stands the cut regime provided a constant canopy cover over time, and then maintained more stable microclimatic conditions favoring a higher abundance and evenness of the shade-tolerant and vernal species. Conversely, in old CWS the dense canopy negatively affected the understory richness by reducing the light-demanding species pool, while the shade-tolerant species have not yet had time to spread. In order to understand the implications of the old CWS conversion on beech forests ecosystem's ecological functions, the same dataset was analyzed through plant functional traits, by creating a relevés x traits matrix. A Redundancy Analysis (RDA) was performed to assess the relationship between traits states and management, while a U Mann-Whitney test was used to assess differences in traits states richness between the management types. The results were consistent with the previous findings based on habitat diagnostic species, as HF stands showed a higher affinity to traits typical of mature forests, while old CWS were more related to traits related to managed stands. Moreover, HF stands showed a higher abundance of those traits related to the natural forest's seasonal change, this indicating a good species distribution among the functional niches. Even in this case, old CWS was shown to be in a transitional stage, still represented by some traits related to management, where the mature forest traits are also present, but with lower abundance. Finally, given that in a forest ecosystem understory represent more than 90% of species richness, and is the most sensitive to disturbance, the modern silvi-cultural strategies should take into account the management effects on forest biodiversity, and adopt sustainable interventions able to favor the typical biodiversity of the ecosystems we want to manage. This thesis provides useful information for management purposes, as our findings show that, in the forests studied, the old CWS conversion to HF could be a good management strategy if our aim is the conservation over time of the species typically related to mature forest conditions.