Sandro Pignatti

Evolutionary Trends in Mediterranean Flora and Vegetation

The vegetation of the Mediterranean Basin was originally composed of evergreen forests; during the Pleistocene deciduous forests expanded, chiefly in the mountains. In historical time the forest belt was strongly reduced by human activity and substituted by anthropogenous vegetation types (macchia, garigue, weed-communities). The frequency of polyploids in the present vegetation types support this interpretation. Reciprocal relationships between the vegetational system and social system are discussed and a terminology is proposed. During ancient times and the middle ages a reciprocal control of vegetation and human activity was possible (cyclic system), stabilizing the vegetation in a steady state; the technological impact modified these conditions in a linear sense, and now the vegetation is menaced by irreversible changes.

On the concept of vegetation class in phytosociology

. The vegetation class is generally accepted as the highest category in vegetation taxonomy. Vegetation classes, following the tradition, are defined mainly on the basis of character species. However, these are sometimes relatively rare and not always really representative of the ecological conditions of plant communities included in the class. In the present study the possibilities are discussed for a more comprehensive definition of the class, including spatial structure and environmental characteristics of the vegetation and the geographical distribution of character species. These include criteria with practical value, in particular for the understanding of vegetation in tropical areas. Some cases of well-known vegetation classes are discussed; in most of them the ranges of single character species and the range of the class as a whole largely coincide.

Data-Processing in Phytosociology: Retrospect and Anticipation

The Working Group for Data-Processing in Phytosociology of the International Society for Vegetation Science is now to finish its activities. Through four conferences of the Working Group at Trieste (1969), the Netherlands (1971), Prague (1973) and Montpellier (1975), during the 14th Symposium of the Society which was devoted to Basic problems and methods in phytosociology and included 12 contributions from members of the Group (Van der Maarel & Tuxen 1972; see Van der Maarel 1971), during small meetings at the Society’s Symposia in Rinteln, as well as through numerous personal contacts, the Working Group largely achieved its original aim, viz. the assimilation of computer-based data-processing in Braun-Blanquet phytosociology. Furthermore, theories and new methods were developed which are of general interest for quantitative and theoretical plant ecology.

Impact of tourism on the mountain landscape of central Italy.

Abstract The mountain landscape of the Apennines in central Italy has been severly affected by tourism for decades. Field research was carried out in order to investigate if some general patterns of environmental changes could be detected. The vegetation of several places under ski-lifts was analysed on the basis of a careful floral survey. In all cases a strong decline of the floristic diversity was observed. On the lines of frequent transit, numbers of occurring species became reduced to about one half and species resistant to trampling (eventually present outside of the ski-lift trucks) expanded and became dominant. The parallel investigation of impacts on human artefacts dealt with architectural features of Leonessa town, a typical example of traditional architecture built at the end of the Middle Ages. Number, size and shape of windows and gates was studied. A comparison was made with the architecture of a modern tourist resort. The recent constructions appear to be characterized by dominance of few elements, general uniformity and normalization. From both examples it can be concluded that the undisturbed condition is in a state of high diversity which declines under the effects of heavy human impact.

Comparison of ecosystems in the Mediterranean Basin and Western Australia

A comparison between fire-prone ecosystems in the Mediterranean basin and Western Australia shows convergent adaptations in structure, life forms and flora evolution. Both areas have in common summer drought and winter rainfall. Reproductive biology is mainly correlated with fire ecology; the different length of human impact and history seem to be responsible for floristic divergency in both areas. The ecological significance of pollination by insects, birds and mammals and problems of the seed banks are discussed.

Ecological responses of plant species and communities to climate warming: upward shift or range filling processes?

The fate of alpine species in response to climate warming is still unclear. We analyze effects of climate warming on the composition of alpine plants communities and unravel the range filling of communities within a belt from long-term true upward shift processes. In the European Alps we re-sampled in 2003 the vegetation at sites studied in 1953 and analyzed the changes at intra- and inter-community level. Since 1953 all communities experienced a high species turnover, leading to an overall increase in species richness as new species exceeded species losses. The dominant species mainly declined allowing the potential expansion of competitors and/or of new species. The main recruitment sources are neighbor communities within the same elevation belt performing biotic exchanges with other plant communities in the same altitudinal belts. The changes of species distribution curves with elevation emphasized that more than half of the most widespread persisting species exhibited downward shifts instead of upward shifts. Upward shifts from lower elevation belts and of nonnative species were very limited. One third of the persisting species declined and could be used as a proxy to measure the extinction debt. Therefore the fate of plant communities will depend on the ability of the original species to persist and fill the available ecological gaps. Species persistence may be crucial in developing adaptation and environmental protection strategies.

Reliability and effectiveness of Ellenberg’s indices in checking flora and vegetation changes induced by climatic variations

Two methods are proposed to assess the significance of time-spanned local variations of Ellenberg’s indicator values in floristic and phytosociological data sets respectively. Both methods are based on frequencies and averages of the indicator values within and among data sets. Main goal of proposed methods is to determine the threshold above which the observed variations are to be considered significant. In order to relate the observed floristic variations to recent climatic changes, attention was focused on the Ellenberg’s indices dealing with the main climatic variables: heliophany, temperature and precipitation. Study-cases from Zannone Island (Pontine Archipelago, Mediterranean region), Inferno Valley (Rome, Mediterranean region) and Braulio Valley (Stelvio National Park, Alpine region) are reported. For Mediterranean data- sets, integration and adjustments to the Ellenberg’s indicator values have been adopted.

A system for coding plant species for Data-Processing in phytosociology

A first attempt to code plant names for use in phytosociological tables has been made during 1969. A mimeographed paper (4th Circular, Appendix 3 of the Working Group for Data Processing in Phytosociology) gave an account of the method proposed. Since this time, the method has been used subsequently for different tasks (storage of information, ordination, elaboration) without serious incovenience and it has become more and more complete. It is now known to members as the Trieste Code.

An application case of ecological indicator values (Zeigerwerte) calculated with a simple algorithmic approach

Abstract The vegetation of the study site near Rome (Castelporziano Estate), where different woodland types occur, was analysed on the basis of ecological indicator values (Zeigerwerte) for light, temperature, continentality of climate, soil moisture, soil pH and nitrogen. Indicator values were estimated with Hills reprediction algorithm for the flora of Central-Southern Italy relying on a database of 4,207 original relevés representing a balanced survey of the vegetation of this and surrounding areas. It was possible to obtain indicator values for an important fraction of the Italian Mediterranean flora. Results are ecologically reasonable, and it was possible to find strong correlation between the recalculated values and a few environmental variables. These correlations were not significant in an analogous test with subjectively derived scores of Ellenberg indicator values.

Syntaxonomy of the Sesleria Varia-Grasslands of the calcareous alps

The syntaxonomical status of theSeslerio-Semperviretum is discussed. This is a widespread association in the subalpine and alpine zone of the Alps, but does not possess characteristic species distributed all over its area. It is closely related to a series of associations from the Southern Alps which are localized in small territories (areas of refuge during the glacial era) and rich in endemic and characteristic species of their own. TheSeslerio-Semperviretum developed in the post-glacial era and is composed by different floristic elements: species of south-alpine associations, species of moist canyons and boreal species immigrated from the North.Sesleria varia, the most significant species, seems to be a hygrophyte, and only recently adapted to more or less xerophilous habitats in the subalpine and alpine zone. All these associations are closely related in their origin and it seems that they ought to be considered a unitary group (one single alliance in the conventional sense), although some important floristic differences make it possible to distinguish several subordinated groups. Auf Grund eines umfassenden Vergleiches und einer Datenverarbeitung durch den Computer wurden die Gültigkeit desSeslerio-Sempervire tums und die Beziehungen dieser Assoziation zu ähnlichen Vegetationstypen der Alpen überprüft. DasSeslerio-Semperviretum ist eine in der subalpinen und alpinen Stufe der Alpen weitverbreitete Gesellschaft, die aber keine über das Gesamtareal der Assoziation verbreitete Charakterarten besitzt. Die Blaugrashalden sind eng verwandt mit einigen Endemiten- und Charakterarten-reichen Rasengesellschaften, die auf jeweils kleine Gebiete am Alpensüdrand (Refugien während der Eiszeit) beschränkt sind. DasSeslerio-Semperviretum ist wohl postglazialen Ursprungs und aus der Mischung verschiedener floristischer Strömungen entstanden und zwar Arten aus südalpinen Rasengesellschaften, Arten aus feuchten Schluchten und boreale Elemente nordischer Herkunft.Sesleria varia, die bezeichnendste Art, scheint eine feuchtigkeitsliebende Pflanze zu sein, deren Anpassung an trockene Standorte der subalpinen und alpinen Stufe in relativ rezenter Zeit zustandegekommen ist. Der engen genetischen Verwandtschaft wegen, scheinen alle besprochenen Assoziationen, trotz deutlicher floristischer Unterschiede, einem einzigen Verband anzugehören.