Holocene Vegetation and Climate Dynamics in Ossola and Neighboring Mountain Ecosystems

Mountain ecosystems are very sensitive to climatic change, for instance at treeline trees exist at their lower limits of thermal tolerance. Therefore even small changes have marked effects on the species composition of high altitude forest communities. With climate change today's treeline is expected to shift to higher elevations, but the rate and extent of change are largely unknown. Similarly, in the lowlands species from warmer ecosystems may expand. Due to its extremely mild winter climate (only one frost day/year) and high summer precipitation (ca. 800 mm) Ossola, as entire Insubria, is particularly prone to invasions by evergreen broadleaved species from subtropical ecosystems (e.g. Trachycarpus fortunei, Cinnamomum camphora). In this study we combine paleoecological methods like pollen and macrofossil analysis, with dynamic landscape modeling to assess the impact of past climatic changes and human disturbance on the vegetation in Ossola and adjacent valleys.

We focus our study on lakes at different altitudes to gain a high resolution overview of vegetation dynamics. The highest lake in the study area Lago del Sangiatto is close to the border to Valais at about 2000 m a.s.l. Archeological findings point to an important mountain pass nearby that was used by humans since prehistory. We will analyse lakes located at intermediate altitudes (ca. 1000 m) and in the lowlands (e.g. Lago d’Orta in the neighboring Cusio area or Lago di Monate in the Varese area).

View on Lago Sangiatto in Ossola
View on Lago Sangiatto in Ossola. Located close to treeline, the most abundant tree species is Larix decidua. © Christoph Schwörer

The reconstruction of Holocene plant occurrence, abundance and diversity gives an indication of the potential natural vegetation and is therefore valuable in the development of nature conservation strategies in montane to alpine environments. In addition, by combining these paleorecords with a dynamic landscape succession model, we can test different hypotheses explaining mountain vegetation dynamics and differentiate between anthropogenic and climatic impacts on the ecosystem. Once validated with the pollen and macrofossil record, the succession model can ultimately be used to simulate the response of the vegetation to different future climate scenarios.

View on Lago Sangiatto in Ossola
© Christoph Schwörer


Christoph Schwörer, Erika Gobet, Lieveke van Vugt, Willy Tinner