Analyzing Canopy Loss After Land Development: Insights for Tree Protection
Analyzing Canopy Loss
after Land Development:
Insights for Tree
Laura Grant, MSc Student
Susan Day, Professor
University of British Columbia, Faculty of Forestry
Partners in Community Forestry Conference
Surrey, BC Canada
2004 Katzie Park, Surrey, BC Canada
Image from City of Surrey Mapping Online System
2014 Katzie Park, Surrey, BC Canada
Image from City of Surrey Mapping Online System
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)
• Focus in 2 communities in Surrey
• Construction between 2009 and 2017
• No development between 2004 -
• 50 Sites
• 131 Tree protection zones
• Planning & development
• Arborist reports
• City of Surrey Mapping Online
western red-cedar 2007 (google street view)
western red-cedar 2019 (google street view)
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-
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
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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,
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.
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
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.