Urban Watershed Forestry Concepts

urban watershed forestry concepts

what if… … property tax rates were based in part on your imperviousness and tree cover? … community trees were part of a local public utility based on their water, air and energy benefits … local comprehensive plans focused on maintaining forest cover in addition to planning future development? … trees and forest cover received proper credits in stormwater design and permitting?

“ Watershed forestry is the use of forests and the practice of forestry to protect, restore, and sustain water quality, water flows, and the health and function of watersheds.” (WFAP federal register) “ Urban Watershed Forestry” “ Urban is ….well….urban - developed and developing areas ”

watershed health: how is it measured? ability to intercept and store rainfall and runoff ability to moderate stream flow ability to hold on to and recycle nutrients soils are protected from erosion supports a healthy aquatic systems has the capacity for self-repair

the forest hydrologic cycle Source: Federal Interagency Stream Restoration Working Group, 1998

by the numbers… Rainfall Interception 10 - 40% of annual rainfall (Zinke, 1967) Canopy interception ave. 35-40% (Calder 1990, 2003) Even in winter? Yes! 15% for a deciduous tree (Xiao et al 2000). 27% for an evergreen species (Xiao et al 2000). Infiltration 12.4 in/hr for forest, 4.4 in/hr for lawn 1.9 in/hr for suburban development (Kays, 1982) Disturbed soils show only 35% of the infiltration rate of soils with intact profiles (Kelling et al, 1975)

total amount of forest & tree canopy retention of “critical” forest & tree canopy riparian forests & wetlands steep slopes/erodible soils/headwaters, etc. disconnect or cover impervious features condition of forest (health/age/growth) how well it is managed and maintained? watershed health is tied, in part, to forests…

2000 2030, If we continue along current trends. 130% increase in these counties; loss of 21% of remaining forests. Increase of 30% in stormwater runoff. What will our watersheds and streams look like?

“ It’s like déjà vu all over again.” Source: Barten et al., 2001, J. Forestry 99(3):23-30; Data sources: O’Keefe and Foster 1998, Steele 1999; Alerich 2000 ?

? ? ? Impacts on streams, water supplies, fish, etc. Water yield = f (land use) [%forest] Water quality = f (land use + water yield) %forest (Barten and Watson, unpub. data)

“ with the disappearance of the forest all is changed. “ Man and Nature, George Perkins Marsh, 1864

changes in urban hydrology on a local scale the water balance – Q = P-ET + ^S

Modeling the effects of urban tree canopy on flow and water quality.. Jun Wang, David J. Nowak*, Theodore A. Endreny; SUNY-College of Environmental Science Forestry, *USFS-Northeastern Research Station

If 1 inch of rain in Baltimore produces an average of 500,000,000 gallons of runoff. A loss of 10% tree canopy means 10-20 million gallons more to treat.

primary nps pollution sources agriculture –produces 30-80% of N and P loadings urban –produces 10-20% of N and 15-30% of P for non-point sources; and 10-30% of N&P for point sources forests –produce less than 10% of N (air effect) and less than 2 % of P urban pollution is the fastest growing source

water quality in small watersheds Groffman et al. 2004

Test watershed results: reductions in runoff (total) and pollutants (t/total hours) due to tree canopy Watershed Tree canopy % decline in runoff per % inc. in canopy TSS TP TKN NO2 NO3 Accotink 32 .1 40.3 .19 1.1 0.39 Baisman Run 69 .2 4.5 .02 0.1 0.04 Gwynns Falls 27 .1 44.9 .21 1.2 0.44 Mill Creek 7 .2 12.3 .06 0.3 0.12 Rock Creek 27 .2 136.8 .65 3.7 1.34 Toby Creek 54 .2 41.5 .20 1.1 0.41 14 Mile 29 .6 32.8 .16 0.9 0.32

influence of forests and imperviousness on the health of streams (IBI) Impervious cover Watershed tree cover Riparian buffer tree cover Excellent good fair poor 80- 70- 60- 50- 40- 30- 20- 10- 0 Stream health rating percent (Goetz, et.al, 2003) For 245 watersheds Good <15% impervious >60% Buffered >50% Forested

In summary…. watershed effects of forest loss Less trees – more runoff Impervious cover linked to physical stream degradation (5-15%) Loss of stream biological health – constant drought/flood cycles Turf and impervious generates more pollutants than forest. Air quality declines & pollutant deposition increases Remaining forest cover is fragmented and quality is reduced

stormwater runoff is the number one factor in the decline of urban streams and decreasing urban water quality !

old news The first models for predicting runoff appeared in the 1800s and used runoff coefficients to account for different land use and land covers. The Rational Method (Mulvaney 1851) Peak Discharge = Runoff Coefficient x Rainfall x Basin Area Runoff Coefficients: Forested ground is typically assigned a value of near 0. Pavement is given values approaching 100 percent But why emphasize trees in particular versus other stormwater practices?

save energy improve air quality provide habitat better quality of life neighborhood stability aesthetic values increase property value reduce noise good for business trees are the original “multi-taskers” USDA Forest Service Urban Watershed Forestry Manual, Part 1

?? so if trees and forests provide so many benefits beyond reducing stormwater …shouldn’t they be more of a priority consideration in site design. ?? … yes, but only if trees are given credit for their work…and to give credit, we must be able to provide numbers! (How else can engineers calculate credits?)

don’t trees get some credit already? not in most municipalities not enough to matter to most developers. not enough to equal their true value

why urban watershed forestry? integrate urban and community forestry and watershed planning and management. set watershed goals for the urban forest create more functional urban landscapes in terms of hydrology build tools to assess, protect, and enhance urban green space as a part of storm water mgmt.

objectives: preserve forests and natural vegetation in watersheds enhance urban & suburban tree canopy protect trees at development sites reclaim vacant lands and reduce turf increase the use of trees in stormwater practices

Urban watershed forestry seeks to address issues along the gradient of land use urban foresters as watershed managers watershed planning and forest cover analysis urban tree canopy assessment and stormwater forestry urban reforestation and greening to reduce impacts of impervious

trees & stormwater: some conclusions Watershed health is linked to the amount of forest in the watershed and its distribution. Increases in tree cover and tree size will result in reduced total runoff and peak runoff rates (10% = 2-5%) Tree canopy has a greater effect on small storm events than on large storm events (2 year storm frequency) Effects on runoff are greatest when urban trees are large and well-established (site quality). Trees and stormwater management practices can coexist if planned and designed from the start.

challenges… Urban Foresters Engineers/ Planners Now remember, you have to work together Leftover disturbed areas are not the only place for trees We can retain valuable trees that improve watershed functions We can use trees in SW practices if we design it differently We need wider streets and curbs Keep the trees in the park, we need the tax revenue Don’t worry, we’ll come back and plant trees later.

urban watershed forestry manual series from watershed… to community… to subdivision… to site scale a base of techniques, approaches, and references to build on

urban watershed forestry manual series part 1: Methods for Conserving forest cover in a watershed part 2: Conserving & Planting Trees at Development Sites part 3: Urban Tree Planting Guide Available for download @ www.cwp.org and www.na.fs.fed.us/watershed/

"A town is saved, not more by the righteous citizens within it, than by the woods that surround it..." -Henry David Thoreau, 1862

Urban Watershed Forestry Concepts

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Urban Watershed Forestry Concepts