The 8200-year vegetation history of an urban woodland as reconstructed from pollen and plant remains

Abstract

Data on the long term evolution of urban forests are rare. Using pollen and macrofossil analyses of a sediment core collected in a swampy forest hollow on Île aux Chats, an island in Bois-de-Saraguay woodland park in Montreal (Quebec), the postglacial history of a maple forest was reconstructed at a local spatial scale for the last 8200 years. Results show that after Île aux Chats emerged from the waters of Lake Lampsilis, it was rapidly colonized by a maple forest that was already diversified 8000 years ago. More than half of the vascular species identified in the macrofossil assemblages are absent from the local plant community today, notably coniferous species (Pinus resinosa, Larix laricina, Picea mariana). Other plants have multiplied their populations over time (Tilia americana, Tsuga canadensis, Acer rubrum). The maple forest was probably sustained by a small-scale gap dynamic caused by windthrow, fires having apparently been very rare. Fagus grandifolia, never abundant locally in the past, is observed to be currently expanding, and could eventually compete with Acer saccharum. This study constitutes not only a rare plurimillenial study of an urban woodland in eastern North America, but also of a maple forest at a local spatial scale.