MAPPING EVENTS: CAMBIUM PHENOLOGY ACROSS THE LATITUDINAL DISTRIBUTION OF BLACK SPRUCE

Abstract

This study used statistical models for describing the spatial patterns of variation in cambium phenology and xylem cell production across the entire latitudinal distribution of a species. The studied area extends over 600 km from the 48th to the 53rd parallel in the boreal forest of Quebec, Canada. Microcores were collected weekly from April to October 2012 from 50 Black spruce [Picea mariana (Mill.) BSP] trees in five stands. The dates of occurrence of the phases of cambium phenology were identified on histological sections and correlated to the latitude and altitude of the sites by means of linear and non-linear functions. The results were used to estimate the timings of xylem growth and cell production across the sampled region. Phenology was mostly represented by linear functions. The increase in latitude and altitude produced a proportional variation in the beginning and ending of xylem differentiation, thus leading to a shorter length of the period of wood formation. The phase of cell enlargement and cell production changed according to a non-linear pattern represented by a negative exponential curve. Latitude was the factor with the greatest impact on xylem phenology, while altitude had a slight or no effect, especially for nonlinear relationships. Xylem formation is a complex process composed of several phenological phases that change across a species distribution area according to either linear or non-linear patterns. Knowledge and quantification of these patterns are important for modelling the dynamics of tree growth across wide geographical areas and for predicting productivity of forest ecosystems under climate change scenarios.