Seattle'S ForeSt ecoSyStem ValueS - Forterra

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In Seattle’s Natural Area Parks management unit 29% of the trees are greater than 12 inches in diameter, while 53% have a diameter of 6 inches or less. Of these small diameter trees, 68% are species that are large at maturity (taller than 50 feet). So while they are small today, they have the potential to increase in size over time. Meanwhile, within the Single-family Residential management unit, 18% of the urban forest trees are over 12 inches in diameter and 55% are less than 6 inches diameter. On average, 46% of the tree species that will be large at maturation currently have a trunk diameter less than 12 inches. SIZE COMPOSITION current trunk diameter: < 6 inches 6 - 12 inches > 12 inches expected height at maturity: large medium small large medium small large medium small 10
CITYWIDE GROUND COVER Ground Cover The urban forest softens the impact of impervious surfaces, like roads, buildings, and to a lesser degree maintained grass. Impervious surfaces reduce water infiltration and increase runoff, affecting regional water quality. By measuring ground cover we can assess the distribution of impervious surfaces. Tree cover reduces stormwater impacts by intercepting rainfall, slowing water movement, and increasing infiltration in the ground. Previous research in Seattle suggests that an evergreen conifer canopy that hangs over an impervious surface can reduce runoff by approximately 27%. The field crew measured ground cover type at each plot. The chart to the right represents citywide cover estimates. The amount of each cover type varied by management unit. Downtown plots were dominated by pavement (64%) and buildings (32%), while Single-family Residential plots had similar building cover (31%), but lower pavement cover (17%) and maintained grass (23%). 11
Page 1 and 2: Seattle’s Forest Ecosystem Values
Page 3 and 4: Acknowledgements Authors Lisa Cieck
Page 5 and 6: Executive Summary Across Seattle, i
Page 7 and 8: Urban Forest Assessment Urban fores
Page 9 and 10: The research reported here used the
Page 11 and 12: credit: Lisa Ciecko Urban Forest Di
Page 13: Age and Size The current size of tr
Page 17 and 18: Because canopy cover values are imp
Page 19 and 20: Carbon Storage and Sequestration Ca
Page 21 and 22: Replacement Value Infrastructure sy
Page 23 and 24: Invasive Plant Species Invasive spe
Page 25 and 26: Continued Assessment Scientific dat
Page 27 and 28: Species Native Management % of Tree
Page 29 and 30: References Alliance for Community T

Seattle'S ForeSt ecoSyStem ValueS - Forterra

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