Annual rings record data throughout a tree’s life, but extracting information from that record is complicated by the interacting multitude of factors that can influence ring widths. Most efforts to analyze tree rings have aimed at reconstructing past climates, particularly from conifers in arid habitats of western North America, where trees grow slowly over centuries, and the influence of rising CO₂ levels has been confounded with changing climate. To determine whether historical increases in atmospheric CO₂ have affected growth of quaking aspens (Populus tremuloides), we took advantage of climate and CO₂ data from throughout the life span of aspen trees in Wisconsin. From a sample of 919 individual trees representing 189 genets, with data from 16 microsatellite loci, we constructed a non-linear, mixed-effects model quantifying the interacting effects of environmental and intrinsic factors on this fast-growing species.
Results/Conclusions

Over the past five decades, aspen growth has increased about 38% as a result of rising CO₂. Growth has also increased with rising moisture levels, and shows a consistent linear effect of individual-level heterozygosity. Thus this dominant species across much of northern North America already shows a dramatic growth increase in response to rising CO₂ levels.