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Abstract

This study assessed the effect of several environmental factors on the timing and relative degree of budding of fruit trees in different locations in an urban setting. Development from immature buds to leaves and flowers was compared across different microclimates. Environmental factors considered included nonporous (impervious) surface area surrounding the tree, tree location, and total number of hours at chilling temperature (32 to 45oF) during the winter-to-spring transition (January to March) as experienced by trees from which branches were clipped weekly and transferred to a warm greenhouse. In the study, thirty-seven Malus “Spring Snow” crabapple trees in different locations within the city of Boulder, Colorado, USA were compared. In the greenhouse, triweekly observations were made of the growth phase of the buds (phenophase). Branches that were clipped from the trees later during the winter-to- spring transition required fewer days for emergence of leaves (leaf-out) and flowers and increased the percentage of buds that leaf out and flower. The impervious surface area within a five-meter radius was not correlated with timing and degree of either leaf emergence or flowering. However, the location of trees in Boulder’s municipal land classification zones affected timing and level of leaf opening. Furthermore, trees located farther from the city center had lower levels of leaf-out and flowering. These findings show that the date of removal of branches impacted the timing and degree of leaf and flower abundance. Future research is needed to ascertain to what extent this effect is mediated by duration of exposure to chilling hours experienced by the tree and other environmental factors (such as increasing daylength) and how other plants functions are affected by warmer temperatures. These present and future results should be useful information for foresters and urban planners in their planting decisions. Potential delays in leaf-out in one area could impact whole ecosystems, e.g., via possible (phenological) mismatches in the timing of food availability and development of leaf- eating primary consumers.