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Analyzing Canopy Loss After Land Development: Insights for Tree Protection

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Analyzing Canopy Loss After Land Development: Insights for Tree Protection

  1. 1. Analyzing Canopy Loss after Land Development: Insights for Tree Protection Laura Grant, MSc Student Susan Day, Professor University of British Columbia, Faculty of Forestry Partners in Community Forestry Conference 11/17/2022
  2. 2. 2 Surrey, BC Canada British Columbia Vancouver Surrey
  3. 3. 3 2004 Katzie Park, Surrey, BC Canada Image from City of Surrey Mapping Online System
  4. 4. 4 2014 Katzie Park, Surrey, BC Canada Image from City of Surrey Mapping Online System
  5. 5. 5 State of Affairs • Populations are increasing • Canopy cover is declining (Nowak and Greenfield 2018) (Nowak and Greenfield 2020) (United Nations, Department of Economic and Social Affairs, & Population Division, 2019)
  6. 6. 6 Scales of Canopy Decline • Global/National • Municipal • Neighborhood & finer (Nowak & Greenfield, 2020) (Hostetler, Rogan, Martin, DeLauer, & O’Neil-Dunne, 2013) (Mincey, Schmitt-Harsh, & Thurau, 2013) (Hilbert, Roman, Koeser, Vogt, & Van Doorn, 2018)
  7. 7. 7 Tree Preservation in Surrey • Tree Protection bylaws since at least 1990s • Follows best management practices standard • Trees are still dying (Surrey; 2006) Image from City of Surrey, 2011
  8. 8. 8 The Urban Forest in the Pacific Northwest • Native species • Douglas-fir • Pacific hemlock • western red- cedar • Exotic species • Summer droughts
  9. 9. 9 Exploring Tree Protection in Surrey, BC
  10. 10. 10 Site Selection • Focus in 2 communities in Surrey • Construction between 2009 and 2017 • No development between 2004 - 2009 • 50 Sites • 131 Tree protection zones Cloverdale South Surrey
  11. 11. 11 Materials • Reports • Planning & development reports • Arborist reports • Google • Earth • StreetView • City of Surrey Mapping Online System (COSMOS) western red-cedar 2007 (google street view) western red-cedar 2019 (google street view)
  12. 12. 12 Patterns in Tree Preservation
  13. 13. 13 Individual Tree Preservation Images from City of Surrey Mapping Online System • Square • Round
  14. 14. 14 Group Tree Preservation: Linear Image from City of Surrey Mapping Online System
  15. 15. 15 Group Tree Preservation: Round Image from City of Surrey Mapping Online System
  16. 16. 16 Group Tree Preservation: Rectangular Image from City of Surrey Mapping Online System
  17. 17. 17 Large Group Tree Preservation: Amorphous Image from City of Surrey Mapping Online System
  18. 18. 18 Edge Influence Index • Ratio • TPZ perimeter : TPZ Area • Preserved tree(s) as the core (Fonseca, 2008) (Harper et al., 2005) (Johnson et al., 2020) Image from Fonseca, 2008
  19. 19. 19 Patterns in Land Development
  20. 20. 20 Previous Land Use: Previously Developed Images from City of Surrey Mapping Online System
  21. 21. 21 Previous Land Use: Agriculture Image from City of Surrey Mapping Online System
  22. 22. 22 Previous Land Use: Agriculture Image from City of Surrey Mapping Online System
  23. 23. 23 Previous Land Use: Forested Image from City of Surrey Mapping Online System
  24. 24. 24 Previous Land Use: Forested Image from City of Surrey Mapping Online System
  25. 25. 25 Previous Land Use: Forested Image from City of Surrey Mapping Online System
  26. 26. 26 Previous Land Use: Forested Images from Google StreetView
  27. 27. 27 Edge Influence and TPZ Shape Edge Influence Index TPZ Shape
  28. 28. 28 Edge Influence and Previous Land Use Previous Land Use Edge Influence Index
  29. 29. 29 100% 80% 60% 40% 20% Previous Land Use & Percent TPZ Exposed % TPZ Exposed to Construction Previous Land Use Previously Developed Forested Agriculture
  30. 30. 30 Exposed TPZ Perimeter vs. Total TPZ Perimeter Image from City of Surrey Mapping Online System
  31. 31. 31 100% 80% 60% 40% 20% Previous Land Use & Percent TPZ Exposed % TPZ Exposed to Construction Previous Land Use Previously Developed Forested Agriculture
  32. 32. 32 Edge Influence and TPZ Area (m2) Area (m2) Edge Influence Index
  33. 33. 33 Next Steps • Analyze gaps in LiDAR • 2009 • 2013 • 2018 • Recommendations for TPZ standards Toccata Townhomes 2013 Toccata Townhomes 2013
  34. 34. 34 Thank you!
  35. 35. 35 References City of Surrey. (2006). Surrey Tree Protection Bylaw. (16100). Surrey, Canda: City of Surrey. Fonseca, M. S. (2008). Edge Effect. In S. E. Jørgensen & B. D. Fath (Eds.), Encyclopedia of Ecology (pp. 1207-1211). Oxford: Academic Press. Harper, K. A., Macdonald, S. E., Burton, P. J., Chen, J., Brosofske, K. D., Saunders, S. C., . . . Esseen, P.-A. (2005). Edge influence on forest structure and composition in fragmented landscapes. Conservation Biology, 19(3), 768-782. doi:https://doi.org/10.1111/j.1523- 1739.2005.00045.x Hilbert, D., Roman, L., Koeser, A., Vogt, J., & Van Doorn, N. (2018). Urban Tree Mortality: A Literature Review. Arboriculture and Urban Forestry, 45(5), 167-200. doi:10.13140/RG.2.2.25953.15204 Hostetler, A. E., Rogan, J., Martin, D., DeLauer, V., & O’Neil-Dunne, J. (2013). Characterizing tree canopy loss using multi-source GIS data in Central Massachusetts, USA. Remote Sensing Letters, 4(12), 1137-1146. doi:10.1080/2150704X.2013.852704 Johnson, L. R., Johnson, M. L., Aronson, M. F. J., Campbell, L. K., Carr, M. E., Clarke, M., . . . Sonti, N. F. (2020). Conceptualizing social- ecological drivers of change in urban forest patches. Urban Ecosystems, 24(4), 633-648. doi:10.1007/s11252-020-00977-5 Mincey, S. K., Schmitt-Harsh, M., & Thurau, R. (2013). Zoning, land use, and urban tree canopy cover: The importance of scale. Urban Forestry & Urban Greening, 12(2), 191-199. doi:10.1016/j.ufug.2012.12.005 Nowak, D. J., & Greenfield, E. J. (2018). Declining urban and community tree cover in the United States. Urban Forestry & Urban Greening, 32, 32-55. doi:10.1016/j.ufug.2018.03.006 Nowak, D. J., & Greenfield, E. J. (2020). The increase of impervious cover and decrease of tree cover within urban areas globally (2012–2017). Urban Forestry & Urban Greening, 49, 126638. doi:10.1016/j.ufug.2020.126638 United Nations, Department of Economic and Social Affairs, & Population Division. (2019). World urbanization prospects 2018: Highlights.
  36. 36. 36 Questions? Laura Grant Laura.grant@ubc.ca

Hinweis der Redaktion

  • Canada, ~80% of population are residing in urban areas
    British Columbia is huge, it’s larger than Texas
    60% of the population of British Columbia resides in LML



    590,000,000 people in Surrey with ~1000 new residents/month
    (City of Surrey, 2020)
    (Invest Surrey & Partners & City of Surrey, 2016)
  • 10 years later the landscape is almost unrecognizable.
    Surrey is marketed to Gen Xers and Milennials as an “affordable” place to purchase a home in the Lower Mainland of BC.
  • Despite urban area being ~3% of global land use, ~55% of globe lives in urban areas

    in some countries, like Canada, ~80% of population are residing in urban areas

    Not a unique situation and not unexpected. Slides 1 & 2 shows they are removing lots of trees, and replanted trees will take years before replacing lost canopy.

    But the loss is beyond what city arborists were anticipating, and so they wanted to do a more in-depth look at where the canopy loss is coming from


  • Broadest scale that loss is viewed, general trends/patterns, changes to the landscape at a large scale. Something like, Climate change. Surrey knows they are losing canopy as a result of climate change, but its beyond the scope of what Surrey can control.

    At the municipal scale, Surrey expects and is experiencing decline. At this scale they know they are losing canopy beyond expected rate, but at this level they cannot tease out reasons why. So they need to look at an even finer scale


    Looking at the neighborhood parcel level. Orange box for scale. Small stands of trees to individual trees. This is the scale where my study is focused. I am asking the question, are the trees Surrey is protecting/preserving really surviving?

  • To answer the question I looked at how they protect trees

    They have tree protection bylaws, there are financial penalties for violating bylaws.

    All development applications have to have an approved tree preservation plan before construction is allowed to begin.

    An ISA certified arborist with a TRAQ qualification has to perform an inventory of the trees on site along with condition rating. City of Surrey has certified arborists that spot check developers. Protection barriers are up to best management practice standards.

    On paper they are doing everything right, but they are still seeing protected trees die.

    This diagram is common appendix feature of many of the Tree Protection bylaws in the Lower Mainland of British Columbia. However, this sketch is not reflective of the urban forest in BC



  • DF- 70m Ar- 18m
    Tp & Th- 60m compared with Pxa- 30m

    Exotic species eastern hardwoods, some evergreen and deciduous species from Eurasia: Chamaecyparis’
     West coast species Calocedrus, Sequoia

    Temperate rainforest, but summer droughts 3-4 months without precip
    East coast & Eurasia species are not fans of the drought, they all have like 70 year old bark while being <30cm in dbh

    So then We (susan and I) started to wonder: how are these trees handling tree protection that aren’t designed for them.

  • Visual identification using orthoimage from Surrey (COSMOS) and GoogleEarth

    Construction window of construction started by April 2009 and completed by 2017. Complete not equal to move-in ready. So grading is done, roof is on the house. No more heavy equipment, or soil disturbance essentially.

    Made sure trees were not exposed to construction within 5 years prior to our window of observation.

    Delineated all the TPZs at the sites, that met above criteria.
  • Reports
    Illustrates decision making, before info zoning,
    Living document of tree decision making, check points/ violations, species lists, preservation maps

    COSMOS & Earth ID areas where construction occurred
    Streetview look at the protected trees

    Find and delineate TPZ areas
  • Square was mostly used on young/small trees this is the exception.
    Larger individuals tended to be in round TPZs, exception of street trees
  • Screen/hedge
    Never wider than a single crown
    Hedges in many of the plans just had 2 feet on construction side as opposed to basing it off of dbh
  • Can be one crown wide, for small groups, otherwise at least 2 crowns wide

    Most frequent protection method
  • Mostly large groups (>1000 m2)
    But sometimes smaller groups, where two small TPZs intersect so build as one
  • edge effect is sometimes used to refer specifically to the phenomenon of increased diversity at edges and so Edge Influence is a broader term
    Index of 1 perimeter = area
    Less than 1 perimeter > area
    Greater than 1 area > perimeter
    Urban forest patches are under a lot of different pressures

    “they act as dispersal barriers or filters, impose mortality, create spatial subsidies (obligate edge crossing), and give rise to novel interactions, especially in the case of invading species.”

    We think of the preserved tree as the core area, are we actually protecting the trees we hope to protect?

  • Small groups, linear groups (hedges/screens)
  • Windbreaks/ hedges to divide fields
    Small groups to individuals closer to buildings
  • Mostly large group to small groups saved, occasionally an individual

    Individuals in this case mostly from the area that had homes
  • No taper on these trees, two trees in the back image have a pretty low Live Crown Ratio
  • Our results similar to the graphic. Amorphous and square differ likely because of size. The majority of our amorphous sites had a large area, and squares tended to be have a small area (young/small individuals)

  • More, small groups preserved in Ag and PD
  • 3 TPZ on right side of image had 100% of perimeter exposed to construction activities

    On the far left of the image, one lot was redeveloped the other wasn’t, When delineated only 52% of the TPZ was exposed to construction

    Hypothesis statement: LULC dictates
  • PD all types of TPZs, with forested & AG less diverse TPZ
  • Each dot represents a TPZ
    Bottom (X) Axis is the area of a TPZ
    Left (Y) Axis is the Edge Influence Index


    We see a steep drop in edge influence around 75m2, then the curve starts flattening out ~150 m2

    This suggests that size of the TPZ is
  • Compare with the land use and TPZ data we extracted

    Have a real answer if what Surrey is doing is successful or not

    Right now we are forcing trees into a landscape they aren’t suited for.
    We need prescriptive TPZs. TPZs that are suited for the trees we are actually protecting, in the climate and location they are actually in.

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