U.S. Sugar Maple Tree Distribution Expands with Warmer Temperatures

One of the major concerns with forecast CO2-induced global warming is temperatures might rise so rapidly that many plant species will be driven to extinction, unable to migrate fast enough toward cooler regions of the planet to keep pace with the projected warming. The prospect of species demise and potential extinction have served as a rallying cry in calls for restricting CO2 emissions. But how much confidence should be placed in this climate-extinction hypothesis? Do real world data support these projections? Are plants really as fragile as model projections make them out to be? 

A new paper published in the research journal Botany investigates this topic as it pertains to sugar maple trees, and the findings do not bode well for climate alarmists. In this work, Hart et al. (2014) analyzed “the population dynamics of sugar maple (Acer saccharum Marsh.) trees through the southern portion of their range in eastern North America,” selecting this particular species for this specific task because its range “has been projected to shift significantly northward in accord with changing climatic conditions” by both Prasad et al. (2007) and Matthews et al. (2011).

The three U.S. researchers

analyzed changes in sugar maple basal area, relative frequency, relative density, relative importance values, diameter distributions, and the ratio of sapling biomass to total sugar maple biomass at three spatial positions near the southern boundary of the species’ range using forest inventory data from the USDA Forest Service’s Forest Inventory and Analysis program over a 20-year observation period (1990-2010),” during which time temperatures increased and summer precipitation declined.  

And what did they discover?

Range expansion (!). Hart et al. write that,

In contrast to a contraction of the sugar maple range, our results corroborate the pattern of increased mesophyte (including sugar maple) density and dominance that has been widely reported throughout the Central Hardwood Forest of the eastern US, including sites near the southern range boundary (e.g., Hart and Grissino-Mayer, 2008; Hart et al., 2008; Schweitzer and Dey (2011).

Or put another way, they say the results of their study indicate that (1) “over the past 20 years, the southern range boundary of sugar maple has neither contracted nor expanded,” and that (2) “when accounting for documented northern range boundary shifts (Woodall et al., 2009), these results indicate an expansion of the geographic distribution for sugar maple at this time attributed to the relatively stable southern range boundary.”

Clearly, the rise in temperature and decline in precipitation observed across the study area has had no negative impact on sugar maple populations, despite model projections to the contrary.  Rather, the observed response has been positive, and largely so as evidenced by increased sugar maple density, dominance and range expansion. To most rational people, these observations represent benefits. To climate alarmists, they are problematic, inconvenient truths which they tend not to  acknowledge.

References

Hart, J.L. and Grissino-Mayer, H.D. 2008. Vegetation patterns and dendroecology of a mixed hardwood forest on the Cumberland Plateau: implications for stand development. Forest and Ecology Management 255: 1960-1975.

Hart, J.L., Oswalt, C.M. and Turberville, C.M. 2014. Population dynamics of sugar maple through the southern portion of its range: implications for range migration. Botany 92: 563-569.

Hart, J.L., van de Gevel, S.L. and Grissino-Mayer, H.D. 2008. Forest dynamics in a natural area of the southern ridge and valley, Tennessee. Natural Areas Journal 28: 275-289.

Matthews, S.N., Iverson, L.R., Prasad, A.M. and Peters, M.P. 2011. Changes in potential habitat of 147 North American breeding bird species in response to redistribution of trees and climate following predicted climate change. Ecography 34: 933-945.

Prasad, A.M., Iverson, L.R., Matthews, S. and Peters, M. 2007. A Climate Change Atlas for 134 Forest Tree Species of the Eastern United States. Northern Research Station, USDA Forest Service, Delaware, Ohio, USA.

Schweitzer, C.J. and Dey, D.C. 2011. Forest structure, composition, and tree diversity response to a gradient of regeneration harvests in the mid-Cumberland Plateau escarpment region, USA. Forest and Ecology Management 262: 1729-1741.

Woodall, C.W., Oswalt, C.M., Westfall, J.A., Perry, C.H., Nelson, M.D. and Finley, A.O. 2009. An indicator of tree migration in forests of the eastern United States. Forest and Ecology Management 257: 1434-1444.