Growth-climate relationships of Acer saccharum (Aceraceae) along a latitudinal climate gradient in its western range

Acer saccharum (Marsh.) is an ecologically and economically important overstory tree species with a widespread distribution in eastern North America. As climate change is predicted to modify the temperature and precipitation regimes throughout the range of the species, it is important to understand how climate has impacted the growth of the species in the past to predict how it may be affected in the future. However, limited research has been conducted on the growth responses of A. saccharum to climate in the western half of the species range. Because climate varies substantially over the range of A. saccharum, becoming warmer and drier at sites in the west and south, there is a need for additional research in this portion of the range. A dendroecological study was conducted at sites in Michigan, Indiana, Kentucky, and Missouri to determine how past variation in temperature and precipitation has affected A. saccharum growth, and how these growth responses varied spatially and temporally. Acer saccharum radial growth correlated strongest with maximum temperature, precipitation, and Palmer Drought Severity Index during the months of June-August of the year the annual growth ring formed. The strength of the growth-climate correlations with June-August precipitation: maximum temperature ratios decreased over the last century. Climate had a stronger impact on radial growth at the study sites in the western part of its range compared to eastern populations examined in other studies. However, differences in growth-climate correlations across a latitudinal gradient did not show a consistent pattern of variation along the climate gradient. These results suggest that A. saccharum populations in the western part of the species range may be more vulnerable to increasing temperature, drought frequency, and drought intensity compared to populations in the eastern part of the species range.