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Regular City Council Meeting Monday,June 13,2011 Page 10 opportunities for urban tree growth and growth along roadways, specifically those being done in Stockholm, Sweden based on their similar cold climates to that of MN. Chair DeBenedet noted that another benefit of that research was having a better understanding that trees planted in boulevards reach a limited maturity as the soil around their root area is compacted and dry and does not provide a supportive en- vironment for their longer maturity and survival. Chair DeBenedet advised that, in initial PWET Commission discussions, they were considering offering a tool kit for developers as an alternative that may help and provide guidance fro the City in some manner as areas of the community are redeveloped, such as Twin Lakes that had used some more innovative stormwater drainage practices based on prompting from the PWET Commission. Councilmember McGehee questioned large parking lots with high curbs around islands draining into the parking lot rather than through the island. Council- member McGehee also questioned the depth of free soil for tree roots in standard parking lots to facilitate their growth. Member Stenlund advised that there was as much need for tree growth below ground as above ground, and when you restrict that root growth, you restrict the tree's longevity considerably. Member Stenlund noted that the proposal of the Stockholm and Helsinki studies was to create a structural roadway that allowed tree roots to expand underground through interaction between water and trees, while still providing roadways that served the various transit modes sufficiently. Member Stenlund advised that the roots usually end up between the bituminous and soil, seeking water and air; with most tree roots located in the top twelve inches, thus creating heaves in roadways and sidewalks. Member Stenlund ad- vised that the original Stockholm study was initiated through the discovery of tree roots finding space to grow under old bunkers in Germany. Mayor Roe suggested that the additional root strength may help trees survive storms as well. Councilmember Pust clarified that it was recommended to have as much space for a tree below ground as above ground. Member Stenlund responded affirmatively, noting that the biomass underground should support a fifty year old tree; but from an engineering perspective, the road and sidewalk amenities needed to also provide structural pavement for vehicle needs and safety concerns. Member Gjerdingen advised that it was good to educate the Commission and res- idents on how close trees should be planted in boulevards in order to allow suffi-