Enhancing Wisconsins Urban Forests PDF Download

Trees in cities can contribute significantly to human health and environmental quality. In 2002, there were an estimated 26.9 million trees (36.9 trees / acre) within non-forested urban areas in Wisconsin. In 2012, the non-forest urban areas were reassessed based on 185 field plots. Urban forest attributes changed between 2002 and 2012 due, in part, to the expansion of urban areas, but also tree planting and natural regeneration, tree growth and tree mortality. Based on the 2012 data, urban forest structure, functions, health, and values in non-forest urban areas in Wisconsin (i.e., hereafter referred to as urban forests) were analyzed using the i-Tree Eco model. In addition, changes in tree populations greater than 5 inches d.b.h. were assessed (2002-2012). Results reveal that urban forests in 2012 have an estimated 42.8 million trees (45.9 trees / acre). Trees are considered as any woody plant with a d.b.h. ≥ 1 inch. Most trees are found in residential areas (69.2 percent). The most common species are common lilac (Syringa vulgaris), Northern white cedar (Thuja occidentalis), and apple species (Malus spp.). Wisconsin's urban forest currently stores about 4.0 million tons of carbon valued at $507 million. In addition, these trees remove about 212 thousand tons of carbon per year ($26.8 million per year) and about 7,030 tons of air pollution per year ($47.7 million per year). Trees in non-forest urban Wisconsin are estimated to decrease annual residential energy costs by $78.9 million per year. The compensatory value is estimated at $19.3 billion. In Wisconsin, 64 percent of the trees were within maintained areas with residential land uses containing the highest proportion of maintained trees. Overall, 1.1 percent of trees were recorded as standing dead. Between 2002 and 2012, one species that had a statistically significant increase in trees greater than 5 inches was silver maple (Acer saccharinum). Species with statistically significant decreases were white ash (Fraxinus americana) and sugar maple (Acer saccharum). Strengths and weaknesses of the national urban forest inventory and analysis protocol were identified and recommendations for intensification are made. Information in this report can be used to advance the understanding and management of urban forests to improve human health and environmental quality in Wisconsin.