Articles by Matthew P. Ayres

How will global warming affect southern populations of boreal trees? In paper birch, Betula papyrifera (Betulaceae), alpine trees with an evolutionary history of relatively cool summers may be more sensitive to climate warming than valley populations. We evaluated this scenario by growing seedlings from different populations in four temperature treatments (mountain field site, valley field site, and two greenhouse rooms).

Populations from low elevations germinated earlier and had higher germination success than population from high elevations (16.8 vs. 22.0 d; 72% vs. 11%). At the valley site, seedlings from native populations grew faster than seedlings from higher elevations (mean ± SE = 0.25 ± 0.02 vs. 0.09 ± 0.04 mm · cm^-1 · d^-1) while at the mountain site, all seedlings grew at similar rates. Seedling grown in cooler environments had higher root : shoot ratios, perhaps to compensate for temperature limitations in nutrient uptake by roots. Leaf area varied among populations but was not affected by environmental differences across the field sites. Net photosynthetic rates at valley temperatures were higher for seedlings grown in the valley than for seedling grown in the mountains or the warm greenhouse (12.0 vs. 10.3 and 5.8 μmoles · m^-2 · s^-1), perhaps due to adaptive phenotypic adjustments. Climatic warming could rapidly produce important phenotypic changes in birch trees (e.g. decreased root : shoot ratio, reduced growth in alpine populations). On a longer time-scale, warming could also result in genetic changes as natural selection favours valley genotypes in alpine sites where they are presently rare.

• Ruel, E-mail: jr@mm.unknown
• Ayres, E-mail: ma@mm.unknown

• Huttunen, Section of Ecology, Department of Biology, University of Turku, FI-20014 Turku, Finland E-mail: liisa.huttunen@utu.fi
• Ayres, Biological Sciences, Dartmouth College, Hanover, NH 03755, USA E-mail: matt.ayres@dartmouth.edu
• Niemelä, Section of Biodiversity and Environmental Science, Department of Biology, University of Turku, FI-20014 Turku, Finland E-mail: pekka.niemela@utu.fi
• Heiska, The Finnish Forest Research Institute, Punkaharju Unit, Finlandiantie 18, FI-58450 Punkaharju, Finland E-mail: susanne.heiska@metla.fi
• Tegelberg, Digitarium - Digitization Centre of the Finnish Museum of Natural History and the University of Eastern Finland, Joensuu Science Park, P.O. Box 111, FI-80101 Joensuu, Finland E-mail: riitta.tegelberg@helsinki.fi
• Rousi, The Finnish Forest Research Institute, Vantaa Unit, P.O. Box 18, FI-01301 Vantaa, Finland E-mail: matti.rousi@metla.fi
• Kellomäki, Faculty of Science and Forestry, School of Forest Sciences, University of Eastern Finland, P.O. Box 111, FI-80101 Joensuu, Finland E-mail: seppo.kellomaki@uef.fi