Factors related to tree growth across urban-rural gradients in the Midwest,USA

Several environmental factors influence tree growth at any site. The objective of this study was to examine the relationship between biotic and abiotic factors and tree growth rate (mean ring width averaged over the last 10 years) in settings ranging from urban to rural. Six clusters, each with five communities and two rural parks, were sampled in Illinois, Iowa, Minnesota, Missouri, and Wisconsin, for a total sample of 320 trees. Within each community, trees in parks, and along residential and commercial streets were sampled. Five species were sampled: silver maple (Acer saccharinum L.), honeylocust, (Gleditisia triacanthos L.), hackberry (Celtis occidentalis L.), black maple (Acer nigrum Michx F.), and basswood (Tilia americana L.). Factors were investigated for three scenarios: (i) all trees sampled in all clusters, (ii) a single species, all clusters, and (iii) all species, a single cluster.Baseline variables (cluster, place population, site, species, and age) accounted for 49–71% of observed variation in growth rate. Combined biotic factors accounted for 5 to 6% of observed variation. For all species in a single cluster, combined abiotic factors accounted for 11% of observed variation. Biotic factors related to growth rate detected using multivariate analyses included number of other trees within 9 m, presence of disease and insects, and human-induced mechanical injury. Abiotic factors that were related to tree growth included presence of pavement and core bulk density. For trees in rural parks, number of other trees within 20 m, and for trees in both rural and community parks, number of other trees within 9 m of sample trees were associated with decreased growth rate.