Constellation, le dépôt institutionnel de l'Université du Québec à Chicoutimi

Résumé

Questions: Do early land survey records of the 'line description' type allow accurate reconstructions of pre-settlement forest composition? Did surveyors record all tree taxa in forest stands encountered along the surveyed lines? Were taxa ranked according to their relative importance in forest stands? What criteria did surveyors used to rank taxa in stands?

Location: Northern range limit of northern hardwoods, Lower St. Lawrence region, eastern Québec, Canada.

Methods: Validation of 1695 taxon lists recorded by surveyors in the 19th century through comparison of the number of stems by tree species and stem diameter classes recorded in 2790 old-growth plots over the same two regions during a 1930 forest inventory.

Results: Taxon prevalence and dominance (i.e. proportion of observations for which each taxon is dominant) are highly correlated between the pre-settlement surveys and the 1930 forest inventory data sets. Surveyors ranked taxa in decreasing order of relative importance, using criteria directly equivalent to basal area of stems in modern forest inventory plots. Taxon prevalence is more accurately reconstructed using relative metrics (i.e. ranks of taxon prevalence in a region), whereas taxon dominance is more accurately reconstructed using absolute metrics (percentage of dominant stands across landscapes). The early land surveys allow spatial patterns of forest composition to be reconstructed by computing relative taxon prevalence in cells of 3 km × 3 km. Prevalence of balsam fir (Abies balsamea) and white birch (Betula papyrifera) are underestimated in survey data, probably reflecting their low economic value in the 19th century.

Conclusions: Taxon lists of early surveyors can accurately reconstruct pre-settlement forest composition and spatial patterns using metrics of taxon prevalence and dominance across landscapes. Relative prevalence is a more comprehensive description of forest composition than dominance, but tends to underestimate some taxa. Absolute taxon dominance is a more robust metric than prevalence, but only reports on the abundance of the most dominant taxa.