The long-term consequences of climate change remain unresolved. In plants, the consequences of prehistoric climate change were profound, and, because of its projected rapidity, the effects of ongoing change may be even more severe. Indeed, modern change has already influenced plants, including their rate of growth. In regions with harsh climates, growth is tending to accelerate at both high-altitude and high-latitude range limits, and at lower limits, to decline. However, in more benign environments, recent change has been too minor to effect an overall change in growth. Nonetheless, in these regions, observed relationships between growth and climate can aid in projecting future climate-change responses, which is particularly important for foundation species such as Quercus rubra. How will this species respond to ongoing climate change, and how will the response differ with latitude? Will populations near the species’ northern limit fare better than mid-range populations?
We took increment cores from six Q. rubra populations along a latitudinal gradient from central Indiana to northern Michigan. Tree rings were measured, and filtered with a cubic smoothing spline to attenuate the influence of confounding variables. Principal-component regression was conducted on the filtered data to quantify growth responses to monthly temperature and precipitation.
Results/Conclusions
Analyses are complete for four of six populations, which ranged from 39º35’–45º50’ N latitude. From southern Lower Michigan to Upper Michigan, there were two consistent signals among the four populations. The first was a positive response to April temperature in the year preceding the year of ring formation. Although significant only in the first- and third-most southerly sites, the response remained positive across all four. Second, there was a signal of summer moisture stress. In June and July of the year of ring formation, all populations responded negatively to temperature, and except for one population in the middle of the gradient, all responded significantly positively to precipitation. To temperature, only the southern-most site responded significantly, hinting that southerly populations may be more sensitive to moisture stress, however, the summer temperature responses were negative in the other three populations, too.
Thus, responses to climate were similar along the gradient in spite of Q. rubra being near its northern limit at the most northern site, suggesting the species will respond similarly to ongoing climate change throughout the study region. Possible explanations are that each population is locally adapted to its climate, or that phenotypic plasticity allows similar responses to different climates.