A Report on the City of Portsmouth s Existing and Possible Urban Tree Canopy

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1 A Report on the City of Portsmouth s Existing and Possible Urban Tree Canopy Key Terms Project Background UTC: Urban tree canopy (UTC) is the layer of leaves, branches, and stems of trees that cover the ground when viewed from above. Land Cover: Physical features on the earth mapped from satellite or aerial imagery such as trees, or water. : The amount of UTC present within parcel boundaries. Possible UTC: The amount of land that is theoretically available for the establishment of tree canopy within parcel boundaries. Possible UTC excludes areas covered by tree canopy, roads, buildings, and water. It is the combination of Possible UTC - Vegetation and Possible UTC - Impervious. Possible UTC - Vegetation: The amount of land that is theoretically available for the establishment of tree canopy in non-tree vegetation areas within parcel boundaries. This excludes areas covered by tree canopy, impervious surfaces, and water. Possible UTC - Impervious: The amount of land that is theoretically available for the establishment of tree canopy in impervious areas within parcel boundaries. This includes impervious areas (roads, parking lots, and sidewalks) except for buildings. The analysis of Portsmouth s urban tree canopy (UTC) was carried out at the request of the Virginia Department of Forestry (VDOF) in collaboration with the City of Portsmouth and the Chesapeake Bay Program. The analysis was performed by the Virginia Geospatial Extension Program (VGEP) at Virginia Tech s Department of Forest Resources and Environmental Conservation in consultation with the Spatial Analysis Laboratory (SAL) of the University of Vermont. The goal of the project was to apply the USDA Forest Service s UTC assessment protocols to the City of Portsmouth. This analysis was conducted based on year 2008 data and excludes all government (state and federal) owned lands. Why is Tree Canopy Important? Urban tree canopy (UTC) is the layer of leaves, branches, and stems of trees that cover the ground when viewed from above. Urban tree canopy provides many benefits to communities including improving water quality, conserving energy, lowering City temperatures, reducing air pollution, enhancing property values, providing wildlife habitat, facilitating social and educational opportunities, and providing aesthetic benefits. How Much Tree Canopy Does Portsmouth Have? Figure 1 shows the UTC analysis for Portsmouth, which is derived from high resolution aerial imagery. 4,620 acres of Portsmouth is covered by tree canopy. This corresponds to 20% of the total land area within the City (Table 1). An additional 7,198 acres of the City could theoretically be improved to support urban tree canopy (termed Possible UTC), Table 2. Land Classes Tree Canopy Non-Tree Vegetation Non-Building Impervious Buildings Impervious Water Total Area Acres % Total Land % Land Area* Area 4, % 29.5% 5, % 32.0% 4, % 27.7% 1, % 10.7% 7, , % 100.0% 0.0% 100.0% Table 1: area and percentages for the City. Figure 1: Land cover for the City of Portsmouth. *% Total Land Area includes area covered by water. 1

2 Using high-resolution (1 meter) National Agriculture Imagery Program (NAIP) imagery acquired in the summer of 2008 (Figure 2a) in combination with remote sensing techniques, land cover data for the City was generated (Figure 2b). A 96.8% accuracy rate was found after conducting an accuracy assessment. Single trees with canopies larger than 9 square meters were detected. 3a Parcels Mapping Portsmouth s Trees Who Owns Portsmouth s Trees? The detailed land cover mapping conducted as part of this assessment allowed the percentage of Existing and Possible UTC to be calculated for each parcel of land (Figure 3). Using this data, ownership patterns for and Possible UTC (Figure 4) can be examined NAIP Imagery (1m) 3b 2b Land Cover Derived from 2008 NAIP Imagery (1m) 3c Possible UTC 2a Figure 2a, 2b: Comparison of 2008 NAIP imagery to the resulting highresolution land cover. Figures 3a, 3b, 3c: UTC metrics summarized at the property parcel level. 2

3 Figure 4: mapped using property parcels provided by Portsmouth. 3

4 Urban Tree Canopy Summarized by Property Parcels Using the parcel data provided by Portsmouth, Existing and Possible UTC were summarized by property parcels. This summary excludes any area outside of property parcel boundaries, areas covered by water, and government owned land. Figure 4 shows through out the City of Portsmouth summarized by property parcels. Portsmouth has 31% (4,098 acres) and 55% (7,198 acres) Possible UTC, table 2. Possible UTC has two components, Possible UTC - Vegetation and Possible UTC - Impervious. 34% (4,477 acres) of parcel land area is associated with Possible UTC - Vegetation. 21% (2,721 acres) of parcel land area is associated with Possible UTC - Impervious (Figure 5). 31% 14% Possible UTC - Impervious 34% 21% Possible UTC - Vegetation Not Suitable for UTC Figure 5: Pie chart showing the City s UTC distribution within parcels. Urban Tree Canopy Summarized by Zoning Categories Using the zoning data provided by Portsmouth, Existing and Possible UTC were summarized by zoning category (pages 4-7). This summary excludes any area outside the analysis boundary, areas covered by water, and government owned land. The zoning category UR has the largest amount of land area with 4,275 acres and the largest amount of, 37% (Table 3). GR and URH are 2nd (30%) and 3rd (11%) in respectively. Figure 6a compares zoning categories by land area for each UTC type for all zones with 200 acres or greater. Figure 6b compares zoning categories by land area for each UTC type for all zones with less than 200 acres. Figure 7 shows Possible UTC by zoning category for the City. Table 2: Acres and percent land area from UTC metrics summarized by property parcels. *Not Suitable for UTC includes all Building Impervious areas within the parcel boundaries. UTC Parcel Metrics Acres % Parcel Land Area Parcel Land Area 13, % 4, % Possible UTC 7, % Possible UTC - Vegetation 4, % Possible UTC - Impervious 2, % Not Suitable for UTC* 1, % GMU GR HR Possible UTC Possible UTC-Vegetation Possible UTC-Impervious Land Area IL IN PRESERVATION/GOVT UR URH Acres Figure 6a: UTC metrics summarized by all zoning categories with an area of 200 acres or greater. 4

5 D2 FBC HLB HLO MX/EMP NMU NR P1 RAC SD T3 T4 T5 T6 WF Possible UTC Possible UTC-Vegetation Possible UTC-Impervious Land Area Acres Urban Tree Canopy Summarized by Zoning Categories Continued Urban Tree Canopy Summarized by Zoning Categories Continued Figure 6b: UTC metrics summarized by all zoning categories with an area of 200 acres or less. 5

6 Zoning Category Urban Tree Canopy Summarized by Zoning Categories Continued Urban Tree Canopy Summarized by Zoning Categories Continued Land Area (Acres) % Land Area Possible UTC Vegetation Possible UTC Impervious % Zoning Category % UTC Type % Land Area % Zoning Category % UTC Type 6 % Land Area % Zoning Category D2 FBC % 9.2% 0.4% 0.3% 25.1% 1.0% 0.6% 43.1% 2.9% % UTC Type GMU % 10.0% 1.6% 1.0% 19.8% 2.8% 2.6% 52.5% 12.4% GR % 41.0% 29.9% 9.0% 39.3% 26.3% 1.9% 8.2% 9.0% HLB % 10.2% 0.0% 0.0% 21.7% 0.1% 0.0% 34.9% 0.1% HLO % 24.2% 0.1% 0.0% 13.0% 0.0% 0.0% 29.2% 0.1% HR % 38.4% 2.7% 0.4% 19.5% 1.3% 0.4% 15.7% 1.7% IL % 14.9% 2.4% 1.2% 24.1% 3.6% 2.3% 45.4% 11.2% IN % 27.9% 8.9% 2.3% 22.5% 6.6% 4.6% 45.9% 22.1% MX/EMP % 29.3% 0.4% 0.2% 54.0% 0.6% 0.1% 16.7% 0.3% NMU % 17.6% 0.5% 0.2% 22.4% 0.6% 0.4% 42.1% 1.7% NR % 62.8% 0.9% 0.1% 25.0% 0.3% 0.0% 5.6% 0.1% P % 0.0% 0.0% 0.0% 0.0% 0.0% 0.0% 0.0% 0.0% PRESERVATION/GOVT % 31.7% 3.0% 1.8% 58.9% 5.1% 0.3% 9.3% 1.3% RAC % 68.4% 0.5% 0.1% 31.1% 0.2% 0.0% 0.6% 0.0% SD % 4.5% 0.1% 0.2% 32.9% 0.6% 0.3% 43.1% 1.2% T % 8.9% 0.1% 0.2% 45.0% 0.5% 0.1% 33.0% 0.6% T % 13.5% 0.2% 0.1% 26.7% 0.3% 0.1% 36.5% 0.7% T % 5.5% 0.1% 0.1% 27.1% 0.3% 0.1% 27.0% 0.5% T % 5.9% 0.1% 0.1% 16.1% 0.2% 0.2% 46.8% 1.0% UR % 35.1% 36.6% 12.3% 37.8% 36.1% 3.6% 11.0% 17.3% URH % 26.7% 11.4% 4.6% 34.3% 13.5% 3.2% 23.8% 15.4% WF 6 0.0% 10.9% 0.0% 0.0% 16.8% 0.0% 0.0% 55.6% 0.1% The % Category value of 3.6% indicates that 3.6% of Portsmouth s land area is tree canopy in areas where the land use is URH. % Land = Area of UTC type for specified land use Area of all land The % Land Use value of 26.7% indicates that 26.7% of URH land is covered by tree canopy. % Category = Area of UTC type for specified land use Area of all land for specified land use The % UTC Type value of 11.4% indicates that 11.4% of all lies in areas of URH land use. % UTC Type = Area of UTC type for specified land use Area of all UTC type Table 3: UTC metrics by type, summarized by zoning categories. For each zone, category UTC metrics were computed as a percent of all zoned land in the City (% Land Area), as a percent of land area by zoning categories (% Zoning Category) and as a percent of the area for the UTC type (% UTC Type).

7 Figure 7: Possible percentage increase of UTC mapped using zoning categories provided by Portsmouth. 7

8 Where to Plant Trees? Decision makers can use GIS to find out specific UTC metrics for a parcel or zoning category. This information can be used to estimate the amount of tree loss in a planned development or set UTC improvement goals for an area. GIS Database Figure 8: Parcel-based UTC metrics can be used to support targeted UTC. Conclusions Portsmouth s urban tree canopy is a vital community asset, reducing stormwater runoff, improving air quality, reducing the City s carbon footprint, enhancing quality of life, contributing to savings on energy bills, and serving as habitat for wildlife. With 30% canopy coverage of all land area within the City, Portsmouth has similar percentages of coverage as Blacksburg, Leesburg, Luray, Manassas, Norfolk and Winchester. Figure 9 shows how Portsmouth compares to other Virginia localities participating in Urban Tree Canopy Assessments. When summarized by property parcels, Portsmouth has 31% with 45% of all parcels with less than 25% canopy coverage. 87% (10,338 acres) of the is located within the following zoning categories: GR, IN, UR, and URH. 60% 50% 53% 52% 47% 44% 39% 41% 40% 30% 30% 44% 48% 44% 41% 42% 38% 33% 27% 27% 27% 30% 40% 39% 36% 27% 20% 22% 20% 10% 0% * Data provided by University of Vermont **Data provided by Fairfax County ^Subset (urban/suburban areas) of locality Figure 9: Comparison of of % land area (excludes water area) with other Virginia localities that have completed UTC assessments. Prepared by: Additional Information Jennifer McKee Geospatial Project Developer Virginia Geospatial Extension Program Department of Forest Resources and Environmental Conservation Virginia Tech , jmckee@vt.edu VA_UTC.html The study was conducted with funding from the Virginia Department of Forestry. More information on the UTC assessment project can be found at the following web sites. utc/ 8