Agenda - Parks and Recreation Commission - 03/14/1996

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Existing trees that/significantly shade ~outh windows at midday d~aSt~g solar midwinter · (November to January~ should be thinned (not . topped) if deciduous o1' removed if evergreen trees. The lower branches ofitall trees within 15 feet of the south-side of a building should be removed so midday, midwinter su~ can shine below the branches. 'Use Solar-FriendlY_Trees. To enhance solar gain during late winter, whi~e still providing summer shade, use "solar-frien~y" trees to the southeast and southwest. For the upl:~r midwest, the most solar-friendly trees are!deciduous species, setting leaves in early May, loifing leaves in late September, and having sparse bra~hes in winter. Where they are fully hardy, the Ket~tuclcy coffeetree, walnut, butternut, and ash are a~. ong the more solar-friendly trees. Moderately sol~,friendly trees include sugar and red maple from noV, hem seed sources. Among the least solar-friendly ~ees are evergreens and trees (such as some oaks) that retain most of their leaves :. in winter. Stiield BuildingS.from Winter Winds Ehant Dens~ Trees U6~vind. Plant shelterbelts on open ru~aI sites and wirld~reaks on moderate-sized lots to reduce winter wi~ds and reduce heating costs: Shelterbelts and windbreaks should be to the west and northmthe directic~a of the prevailing winter winds. Select trees that (and foliage) to the gro~ reasonably fast growin~ and Colorado spruce, E plantings, pine. Specie.~ optimize growth under will retain theft branches md, are fairly stiff, and are' · This can include Norway ~uglas-f[r, and for multi-row ;should be selected to ~articular site conditions. On large, open site~ where winter winds are strong, shelterbelts should be planted more than 50 feet upwind of the stm¢.htres they shelter and should' extend at least 50 feet s~uth and east of lite structures. Shelt6rbelts ~sually feature a shrub row (either upwind or down,rind) to control drifting snow and up to seven rows of trees (primarily evergreens). For long-term cost effectiveness, shelterbelt evergreens sfaould be planted 20 feet apart in staggered rows 20 fe~t apart. Deciduous trees should be spaced further apart. Planted windbreakslof only one or two rows of trees are appropriate wht~re winds are less severe and adequate room is not avidlable for a full shelterbelt. On an open, fairly winder site, a properly planted single row of dense ever green trees can provide measurable wind reduc~ ons and energy savings of up to about 15%. When only one row of trees is used for a windbreak, the trees should ~ tx, spaced more closely together than a shelterbelt. Evergreens, such as spruce, can be spaced at 10 feet apart if the outsides of the row receive full sun. Increase Neighborhood Tree Cover for Wind Reduction. The collective effect of buildings and trees measurably reduces wind from what it would be on a totally open site. The greater the number of trees in the neighborhoodl the greater the overall tree cover and the more effective the trees are in reducing wind Public and private tree planting and preservation of existing trees should be undertaken to aid in wind reduction and to reduce heating . demand. Priority should be given to maximizing the number and height of trees wherever winter solar gain is not compromised. Neighborhood.shelterbelts should also be inco. rporated into development plans to the north and west of clusters of housing, particularly on unvegetoted sites. Increase the Community-wide Urban Forest ..... ' Preserve Existin~ Trce$ in and Near Urban Areas. The pavement and buildings of urban areas and the concentrat0d use of cars and machinery increase s,mmer h~at in cities, creating "urban heat islands." Urban forests reduce summer heat island effects, so tree planting and preservation should be promoted throughout urban areas. Priority should be. given to maximizing the volume of tree foliage by preserving large healthy trees. .. Maximize Tre~ Planting an~' Care. Healthy, actively transpiring trees provide the greatest benefit in moderating the heat island and directly sequestering carboh dioxide (as Well as other pollutants). Trees function most effectively and grow faster when they have sufficient water and urban stresses are minimized. Trees should be planted on sites most suitable for plant growth (parks, undeveloped lands, residential areas, office parks, etc.). Planting of highly urbanized sites like parking · · lots and downtown areas may also be necessary to ".'):-.' provide community-wide climatic benefits. In such cases, more attention is necessary to provide adequate water, soil aeration, drainage, tree protection, and maintenance. ' Prepared by Peggy Sand, landscape amhitect and consultant to the Minnesota ReLeaf Pmgraxn. . For a copy of the report Planting for Energy Conservation in the North and other publlca~iom on energy con:ervatlon plantings, call the MnDNR In/'ormaxi~a Center at (612) 296-6157 or toll free, 1-800-766-6000. 2 1993