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How to estimate future forest cover in a watershed
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How to estimate future forest cover in a watershed

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    • 1. How to estimate future forest cover in a watershed
    • 2. future land cover projections
      • GIS-based method to estimate future land cover in a watershed
      • “ Leafout analysis” focuses on forest cover
      • Local governments and watershed groups can use method to:
        • evaluate the effect of different watershed protection scenarios on future land cover
        • predict future stream health
        • set numeric land cover goals
        • develop watershed protection recommendations
    • 3. why land cover is important to watersheds
      • Impervious cover – excellent indicator of stream health
      • More than 200 studies on relationship between IC and various measures of stream quality
      • Forest and wetlands are a beneficial cover type from hydrologic, water quality, and habitat standpoint
      • Other pervious areas – majority is often maintained as turf, may include cropland, pasture or grasslands
    • 4. link between forest cover and stream health
      • Stream health rating of Excellent requires no more than 6% IC and at least 65% riparian forest cover (Goetz et al, 2003)
      • Stream health rating of Good requires no more than 10% IC and at least 60% riparian forest cover (Goetz et al, 2003)
      • Watersheds with at least 65% forest cover usually had a healthy aquatic insect community (Booth, 2000)
    • 5. steps for estimating future land cover
      • Identify developed and undeveloped parcels
      • Calculate the area of each zoning category for undeveloped land
      • Identify and subtract protected land from undeveloped land for each zoning category
      • Multiply the remaining buildable land in each zoning category by the corresponding land cover coefficients
      • Calculate the area of each land cover type for developed land and protected land
      • Sum future land cover on buildable, developed and protected land
    • 6. GIS data needs for future land cover analysis
      • Property boundaries and parcel data
      • Current land cover – impervious, forest, turf, etc
      • Zoning
      • Protected land – conservation easements, conservation zones, parkland, stream buffers, steep slopes, wetlands, erodible soils, floodplains (will vary with local regs)
      • Land cover coefficients (more on this later…)
      • Recent aerial photos may also be helpful
    • 7. assumptions
      • Full buildout of the watershed will occur based on allowable zoning (e.g., no rezoning)
      • Current land cover on developed land will remain the same with the future buildout
      • Protected land will remain the same in future buildout scenario
      • Buildable land will be converted to impervious cover, forest, or other pervious cover, as dictated by land cover coefficients
    • 8. No buildings. Parcels not selected Parcels intersect with buildings so they are selected as “developed” parcels Step 1: identify developed and undeveloped parcels
    • 9. Step 1: results
    • 10. Step 2: calculate the area of each zoning category for undeveloped land
    • 11. Step 3: identify and subtract protected land from undeveloped land for each zoning category
      • Protected land includes specific parcels that are under permanent conservation (e.g., easements, conservation zones, parkland)
      • Also includes types of land that must be preserved during development according to local regulations: stream buffers, wetlands, steep slopes, erodible soils, floodplains…
      • This will vary locally and requires a little research or local knowledge
    • 12. protected lands
    • 13. undeveloped land…
    • 14. … minus protected land…
    • 15. … equals buildable land
    • 16. Step 3: results buildable land by zoning category
    • 17. Step 4: multiply the remaining buildable land in each zoning category by the corresponding land cover coefficients
      • Land cover coefficients represent the fraction of a particular land use that is a certain land cover type
      • Land cover coefficients vary by land use type and intensity
      • Impervious cover coefficients are available from Cappiella and Brown (2001)
      • Forest cover coefficients are an important data gap
    • 18. impervious cover coefficients vary by land use Source: Cappiella and Brown (2001) Land use ICC Agriculture .019 Open urban land .086 2 acre lot residential .106 1 acre lot residential .143 ½ acre lot residential .212 ¼ acre lot residential .278 1/8 acre lot residential .326 Townhomes .409 Multifamily residential .444 Institutional .344 Light industrial .534 Commercial .722
    • 19.  
    • 20.  
    • 21. factors affecting forest cover coefficients
      • Land use type and intensity
      • Age of development
      • Local forest conservation regulations
      • Pre-development land cover (agriculture versus forest)
      • Local clearing and grading practices
      • Reforestation and landscaping requirements
    • 22. forest conservation regulations influence forest cover coefficients Photo courtesy of Harford County DPW Photo courtesy of Randall Arendt Forest cover coefficient = .057 Forest cover coefficient = .40
    • 23. options for deriving forest cover coefficients
      • Assume the worst: 95% of the site (except for protected lands) will be cleared
      • If local forest conservation regulations exist, use the required conservation thresholds
      • Use data from Urban Ecosystems Analyses www.americanforests.org or Urban Forests Effects Model www.ufore.org for your area
      • Do your own detailed calculation using methods described in Cappiella and Brown (2001)
    • 24. Zoning Category Buildable Area (acres) Forest Cover Coefficient Future Forest Cover on Buildable land (acres) Agriculture 765 .168 128.5 Open Urban Land 50 .268 13.4 LDR 732 .321 235.0 MDR 645 .248 160.0 HDR 220 .203 44.7 Institutional 88 .134 11.8 Commercial 130 .067 8.7 Total 2,630 602.1
    • 25. Step 5: calculate the area of each land cover type for developed land and protected land
      • Impervious cover – good indicator of stream health
      • Forest cover – most beneficial type of cover from hydrologic, water quality, and habitat standpoint
      • Other pervious areas – majority is often maintained as turf, may include cropland, pasture or grasslands
    • 26. sources of land cover data
      • Maryland DNR Urban Tree Canopy assessment (includes impervious surfaces from IKONOS data)
      • Chesapeake Bay Program land cover data (includes 2000 impervious surface data and RESAC land cover data http://www.chesapeakebay.net/data/index.htm
      • Local government impervious surfaces (roads, parking lots, etc) and forest cover data
    • 27. common scale issue: Map B contains alot more detail on forest cover while Map A is fairly generalized B A
    • 28. Impervious cover layers
    • 29. Step 5: results
    • 30. Step 6: sum future land cover on buildable, developed and protected land
      • Current land cover on developed and protected land:
      • Impervious: 1,917 acres
      • Forest: 639 acres
      • Turf: 1,278 acres
      • Future land cover on buildable land (estimated using land cover coefficients):
      • Impervious: 680 acres
      • Forest: 600 acres
      • Turf: 1,350 acres
      +
    • 31. Step 6: results Future land cover in the watershed =
    • 32. future land cover spreadsheet
    • 33. you’ve got results: now what?
      • Identify ways to increase future forest cover
      • Repeat Steps 1-6, making adjustments for these measures
      • May need to run several scenarios to find acceptable and realistic future forest cover
      • Set/adopt forest cover goal
      • Implement techniques to maintain or increase forest cover
    • 34. techniques to maintain or increase forest cover
      • Protect priority forests
      • Prevent forest loss during development and redevelopment
      • Maintain existing forest canopy
      • Plant trees during development and redevelopment
      • Reforest public land
      • Reforest private land
    • 35. additional resources
      • Urban Watershed Forestry Manual Part 1: Methods for Increasing Forest Cover in a Watershed. Available for free download from www.cwp.org
      • Impervious Cover and Land Use in the Chesapeake Bay. Available for free download from www.cwp.org
      • USDA Forest Service’s Urban Forests Effects Model (UFORE) www.ufore.org
      • American Forests’ Urban Ecosystem Analysis www.americanforests.org
    • 36. group exercise: estimating future forest cover in the Green River Watershed
      • Identify group reporter
      • Read the Green River Watershed scenario
      • Select a combination of Urban Watershed Forestry techniques to implement in the Green River Watershed
      • Report your results to the entire group
      • Be ready to report out in 30 minutes!