Changes in growth of pristine boreal North American forests from 1950 to 2005 driven by landscape demographics and species traits

[摘要] In spite of the many factors that are occurring and knownfor positively affecting the growth of forests, some boreal forests acrossNorth America have recently felt the adverse impacts of environmentalchanges. Knowledge of causes for productivity declines in North Americanboreal forests remains limited, and this is owed to the large spatial andtemporal scales involved, and the many plant processes affected. Here, theresponse of pristine eastern boreal North American (PEBNA) forests toongoing climatic changes is examined using in situ data, community ecologystatistics, and species-specific model simulations of carbon exchangesforced by contemporary climatic data. To examine trends in forest growth, weused a recently acquired collection of tree-ring width data from 252 sampleplots distributed in PEBNA forests dominated by black spruce (Picea mariana [Mill.]B.S.P.) and jack pine (Pinus banksiana Lamb.). Results of linear trend analysis on the treegrowth data highlight a dominating forest growth decline in overmatureforests (age > 120 years) from 1950 to 2005. In contrast, improving growthconditions are seen in jack pine and mature (70–120 years) black sprucestands. Multivariate analysis of climate and growth relationships suggeststhat responses of PEBNA forests to climate are dependent on demographic andspecies traits via their mediation of temperature and water stressconstraints. In support of this hypothesis, the simulation experimentsuggests that in old-growth black spruce stands the benefit to growthbrought on by a longer growing season may have been low in comparison withthe increasing moisture stress and respiration losses caused by warmersummer temperatures. Predicted increases in wildfire frequency in PEBNAforests will likely enhance the positive response of landscape-level forestgrowth to climate change by shifting the forest distribution to younger ageclasses while also enhancing the jack pine component.

[学科分类] 地球化学与岩石