Tree Canopy Assessment: Covington, Kentucky

Transcription

1 Tree Canopy Assessment: Covington, Kentucky Why is Tree Canopy Important? Tree canopy (TC) is the layer of leaves, branches, and stems of trees that cover the ground when viewed from above. Tree canopy provides many benefits to communities, improving water quality, saving energy, lowering summer temperatures, reducing air pollution, enhancing property values, providing wildlife habitat, facilitating social and educational opportunities, and providing aesthetic benefits. Establishing a tree canopy goal is essential for communities seeking to improve their green infrastructure. A tree canopy assessment is the first step in urban forest planning, providing estimates for the amount of tree canopy currently present in an area as well as the amount of new tree canopy that could theoretically be established. How much Tree Canopy Does Covington Have? An analysis of Covington based (Figure 1) on land cover data derived from high-resolution aerial imagery and LiDAR found that 4,161 acres of the area were covered by tree canopy (termed Existing Tree Canopy). Existing Tree Canopy represents 49% of all land in the study area (Figure 2). An additional 36% (3007 acres) of Covington could theoretically be modified to accommodate tree canopy (termed Possible Tree Canopy). In the Possible Tree Canopy category, 28% (2,377 acres) of total land area was grass/shrubs41 (termed Possible Tree Canopy Vegetation) and another 7% (630 acres) was impervious (termed Possible Tree Canopy Impervious). Tree canopy will be easier to establish on the Possible Tree Canopy that is vegetation, but establishing tree canopy on areas classified as Possible Tree Canopy Impervious will have a greater impact on water quality and summer temperatures. Project Background The goal of the project was to apply the USDA Forest Service s Tree Canopy Assessment protocols to City of Covington. The analysis was conducted using imagery acquired in 2012 and LiDAR acquired in 2011 and This project was made possible through funding from the Northern Kentucky Urban and Community Forestry Council (NKUCFC). The assessment was performed by the SavATree Consulting Group in collaboration with the Spatial Analysis Laboratory (SAL) at the University of Vermont. Not Suitable Possible Tree Canopy (Impervious) Possible Tree Canopy (Vegetation) Existing Tree Canopy Figure 1: Study area and example of the land cover derived from high-resolution imagery for this project Figure 2: Tree Canopy metrics for Covington based on % of land area covered by each TC type. Key Terms TC: Tree canopy (TC) 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 aerial or satellite imagery, such as trees, grass, water, and impervious surfaces. Existing TC: The amount of urban tree canopy present when viewed from above using aerial or satellite imagery. Impervious Possible TC: Asphalt or concrete surfaces, excluding roads and buildings, that are theoretically available for the establishment of tree canopy. Vegetated Possible TC: Grass or shrub area that is theoretically available for the establishment of tree canopy. Not Suitable: Areas where it is highly unlikely that new tree canopy could be established (primarily buildings and roads). 9/24/2014 1

2 Mapping Covington s Trees Parcel Summary A previous estimate of tree canopy for the entire study area (including water), derived from the 2011 National Land Cover Database (NLCD 2011) was 42%, much lower than the 49% obtained in this study. This large difference was attributable to the low resolution of NLCD 2011, which only accounted for relatively large patches of tree canopy (Figure 3a). Using high-resolution imagery and LiDAR (Figure 3b), in combination with advanced automated processing techniques, land cover for the study area was mapped with such detail that individual trees were detected (Figure 3c). This new dataset provides the most detailed accounting of tree canopy. After land cover was mapped for the study area, Tree Canopy (TC) metrics were summarized for each property in the study area s parcel database. Existing and Possible Tree Canopy metrics were calculated for each parcel, both in terms of total area (square footage) and as a percentage of the land area within each parcel (TC area divided by land area of the parcel). The resulting data can be used to assess the tree canopy and tree planting opportunities for every property in Covington. Parcels a. NLCD 2011 Percent Tree Canopy (30m) Existing Tree Canopy (TC) b Aerial Imagery (1m) c. Tree Canopy from 2012 Imagery Figure 3: Comparison of NLCD 2011 (a) to high-resolution imagery (b) and tree canopy (c) derived for this study. 9/24/2014 Possible Tree Canopy (TC) Figure 4: Parcel-based TC metrics. TC metrics are generated at the parcel level, allowing each property to be evaluated according to its Existing TC and Possible TC. 2

3 Floodplains Trees are an important in flood plains as they to not only reduce flooding but serve as important habitat. Two floodplain layers were used to summarized tree canopy metrics, the 100 year flood area and the 500 year flood area (Figure 5). The 100 year flood plain has 45% Existing Tree Canopy, same as the study area average of 51%. Expanding out to the 500 year flood plain decreases the relative amount of tree canopy to 41%. There is room to plant trees within both types of flood plains, with Possible Tree Canopy at 49% for the 100 year flood plain and 49% for the 500 year flood plain. Within both flood plain categories most of the room to plant new tree canopy is in agriculture followed by residential, followed by the rights-of-way. 500 Year Flood Plains 100 Year Flood Plains Figure 5: Extents for the 500 year flood plain (left) and 100 year flood plain (right). Figure 6: The height of each bar represents the area in acres of either Existing Tree Canopy, Possible Tree Canopy, and areas the are not suitable for planting trees for the two flood plains. 9/24/2014 3

4 Land Use & Land Cover To examine the relationship between land use and land cover, the total area for each land use class was summarized and then the percent of vegetated cover (trees, grass, and shrubs) in each land use category was computed (Figure 7). This analysis provides an understanding of how green each land use class is. The largest single land use category is Residential, followed by Open Land. Not surprisingly, Agriculture is the most green land use class, with 98% of its land area covered by vegetation. Residential areas are 83% vegetated. At the low end, Commercial land uses have 46% of their land covered by vegetation. Any steps that Covington can take to green up the city will help to reduce storm water runoff and reduce the urban heat island effect. The strategy for greening will likely differ by land use class. Examples include tree giveaway programs for residents, conservation easements along riparian buffers in agricultural areas, and zoning regulations limiting the amount of impervious surfaces in commercial areas. Figure 7: Percent of vegetated cover for each land use class in relation to total land area. The size of the circle represents the total land area, the color gradient represents the percentage of vegetation. Percentages are calculated based on the amount of vegetation relative to land 9/24/2014 4

5 Land Use Tree canopy metrics were also computed for each parcel in the study area. Much like the other metrics that were computed for this study, Residential has a large amount of Existing Tree Canopy and Possible Tree Canopy by area (Figure 8). Agricultural land uses and Institutional land uses contain large proportions of Possible Tree Canopy Vegetation (36% and 34%, respectively). An all lands approach is required for maintaining and increasing tree canopy, with governments, residents, non-profits, and the private sector all playing a role. For all land uses (besides ROW which contains only one feature) there is an inverse relationship between Existing Tree Canopy and Possible Tree Canopy (Figure 9), indicating that land uses with large amounts of tree canopy generally have less room to plant new trees, but this relationship does always hold true in the more urbanized areas where select parcels with low Existing Tree Canopy also have low Possible Tree Canopy. Figure 8: Tree canopy metrics derived from the parcel dataset broken down by Land Use. Figure 9: Relationship between Existing Tree Canopy and Possible Tree Canopy for each parcel in Covington. 9/24/2014 5

6 Zoning An analysis was performed on Covington s zoning classes. In contrast to land use, which indicates the nature and extent of actual landscape features, zoning is a planning tool that indicates where specific land uses are encouraged and/or anticipated to occur. Most of the study area s Existing Tree Canopy occurs in the Open Land and Residential zoning classes, and these classes also contain the largest proportion of Possible Tree Canopy (Figures 10 & 11). Open Land and lawns account for many of the vegetated sites where expanded tree canopy is theoretically possible. The distribution emphasized the vital role that individual citizens play in maintain and expanding tree canopy; any program to maintain or increase tree canopy must include the active support and cooperation of residential landowners. While constituting a smaller portion of the study area s land area, other zoning classes also provide opportunities for expanding tree canopy, including various commercial, and mixed use areas. These urbanized areas are especially important for facilitating runoff retention and other tree canopy benefits. Tree Canopy Existing Percent 0% - 17% 18% - 34% 35% - 53% 54% - 76% 77% - 100% Tree Canopy Possible Percent 0% - 22% 23% - 40% 41% - 56% 57% - 73% 74% - 100% Figure 10: Percent Existing Tree Canopy by zoning in comparison to Percent Possible Tree Canopy by zoning. Figure 11: Tree Canopy metrics summarized by zoning. 9/24/2014 6

7 Urban Heat Island Effect A well-known benefit of trees is their ability to reduce ground surface temperatures, both by direct shading and transpiration. In areas where tree canopy has been removed, surface temperatures can be substantially higher than adjacent forested areas. The effect may be most pronounced in areas with extensive impervious surfaces, which absorb and hold thermal radiation from the sun. Even individual trees can have a noticeable effect, particularly if they shade buildings thereby reducing the need for air conditioning during warmer weather. Analysis of thermal imagery acquired on April 27, 2014 by the Landsat satellite illustrates the urban heat island that exists in Covington (Figure 12). An inverse relationship exists between tree canopy and surface temperature providing clear evidence that trees help to reduce the urban heat island effect (Figure 13). Figure 12: Surface temperature, degrees Fahrenheit on April 27, 2014 (left) in comparison with Existing Tree Canopy (right). Figure 13: Surface temperature in relation to percent tree canopy. Each circle represents a 2000ft grid cell. A 2000ft x 2000ft grid was overlaid on the region and for each grid cell the percent tree canopy, percent impervious, and average surface temperature were summarized. Surface temperature was derived from Landsat satellite imagery acquired on April 27, /24/2014 7

8 Watersheds Existing and Possible Tree Canopy were summarized by watersheds within the study area (Figure 14). DeCoursey Creek-Licking River has the highest percentage of Existing Tree Canopy (55%). This watershed, is moderately forested and has comparatively little urban development. Upper Banklick Creek has the highest percentage of Possible Tree Canopy (57%). Dry Creek-Ohio River contains the second lowest Existing Tree Canopy percentage and has a high percentage of Possible Tree Canopy. The Lower Banklick Creek represents an excellent watershed to focus on for tree planting projects as it contains relatively large amounts of Possible Tree Canopy Vegetation on Residential and Open Lands (Figure15). Tree Canopy Existing Percent 17% - 24% 25% - 44% 45% - 55% 56% - 62% 63% - 67% Tree Canopy Possible Percent 32% - 34% 35% - 38% 39% 40% - 49% 50% - 83% Figure 14: Percent Existing Tree Canopy by watershed in comparison to Percent Possible Tree Canopy by watersheds. Figure 15: Total area (Acres) of Possible Tree Canopy Vegetation for each watershed in Covington and summarized by Land Use. 9/24/2014 8

9 Tree Planting Prioritization To prioritize places to plant trees, Census block groups overlapping the Covington boundaries were selected. Expert stakeholders on the NKUCFC were polled with respect to their management priorities. Because trees provide so many benefits simultaneously, datasets were identified to find where those benefits are lacking. For example, trees make the air cooler by intercepting the sun and casting shadows, which prevents hard impervious surface from receiving, storing, and emitting heat. Trees also evapotranspirate (or 'exhale') water vapor which also has a cooling effect. Therefore areas with high surface temperature are prioritized for tree planting. Below are the six variables corresponding to management objectives, and their corresponding weights derived from stakeholder s responses to the poll. A final UTC Prioritization map was created by standardizing and combining the weighted maps (Figure 16). Prioritization Criteria Figure 16: Prioritization analysis. The stormwater mitigation map was created by deriving the flow direction of water from the digital elevation model and then constraining the flow to impervious features. Next watersheds were derived from that surface and the flow accumulation per watershed was computed, and then summarized within each block group. Greater flow indicates higher planting priority. This is because these are the areas of impervious surface where most stormwater would accumulate. The median household income map uses the data provided by the US Census Bureau. Values are made negative so that lower income areas are higher planting priorities. The air quality map was made by summarizing the Public Right Of Way (PROW) area per block group. The PROW area serves as a proxy measure for air quality and reducing noise pollution from cars. The PROW is also where street trees are planted. Block Groups with more PROW as a percentage of land area are a higher planting priority. The hillside protection map was created by summarizing the amount of contiguous 30 x 30ft area that is 20 degrees or steeper per block group. Higher values indicate higher planting priority because trees stabilize slopes and reduce erosion. The habitat connectivity designed to analyze wildlife habitat by expanding existing large patches of tree canopy by connecting them with smaller patches. Habitat sites are defined as 1)homogeneous patch of grass/shrub, 2) borders an existing large forested patch, 3) does not border a building, and 4) shares at least 60% of its border with tree canopy and/or a habitat planting area (this process is iterative). 9/24/2014 9

10 TREE PLANTING AND CANOPY ENHANCEMENT PLAN Luley and Bond (2002) put forth the following conceptual model for UTC goal attainment. We look at UTC goal attainment in the context of this model. Figure 17: Urban Tree Canopy goal attainment model. PLANTING Tree planting is a common focus of UTC goal plans as planting is charismatic, engages the public, and can be done with volunteers. Select species appropriately outcome If you could only plant one tree to do the most good, where would you plant it? Our prioritization maps are intended to maximize efficiency of your limited resources by providing location-based prioritization based on your desired outcomes. The RFP has framed this planting plan to be focused on public properties, and it has been designed for that purpose. We note that the same spatial prioritization can be used in an all lands, all people approach to a UTC goal. Implementing it on private property is much more complex as landowners with the highest interest in and capacity for tree planting do not always correlate to the areas of greatest priority. However, if you do develop a rebate, giveaway, or other cost-share for private landowners, this same prioritization can also be used for that purpose. Select species appropriately - site Selecting the right tree for the right place is a key to success in planting. Trees are Good via the International Society of Arboriculture (ISA) has some excellent materials to inform the tree selection process: These are suitable for use by professionals or landowners. Urban areas are not a native environment on planet earth. Some non-native species may be preferable for certain urban plantings. However, any species known to be invasive shall not be used. Preferred tree lists are common, but they often consist largely of species unavailable in the nursery trade in a given market and do not provide any filters on use to enhance survival. We rather suggest some approaches to maximize success and resilience of your overall planting scheme. Select for resilience - climate Our Urban Heat Island analysis (pg #, study area report) shows that temperature fluctuations vary across the study area. Anticipated effects of climate change (elevated average and extreme temperatures over the service life of the tree, resilience to severe weather events) should be a factor in species selection. Consider trees that do well in warmer hardiness zones for these areas. While the study area is predominantly Zones 6a and 6b, trees suited to Zones 7a and 7b may be suitable for these hotter areas: Select for resilience - diversity To minimize losses due to pest outbreaks, Dr. Frank Santamour (1990) offered the rule for diversity in urban plantings: they should contain no more than 10% of any single tree species, no more than 20% of any tree genus, and no more than 30% of any tree family. Biodiversity in plantings is one of the best resilience strategies. Try to select plants whose species, genus, and family vary across your planting site to minimize losses to pests that are species-, genus- or family-specific. In 2014, the entire state of Kentucky was placed under quarantine for Emerald Ash Borer (EAB). In the study area, the infestation is particularly high in Boone County. Details on Emerald Ash Borer in Kentucky can be found here: Ash shall be omitted from any planting lists due to EAB. Plant according to standards For organizations such as agencies, NGOs, and companies, trees should be planted according to ANSI A300 Part 6, the national industry consensus standard for tree planting. Organizations may find it easier to follow Best Management Practices: Tree Planting, a how to guide published by ISA and based on ANSI A300 Part 6. For individuals receiving trees through a rebate, giveaway, or other such program, we suggest two excellent free on-line technical resources. The Tree Owner s Manual is a simple and comprehensive guide to tree planting and care developed by the USDA Forest Service: na.fs.fed.us/urban/treeownersmanual/. Planting guidelines in shorter form are available from Trees Are Good via ISA: 9/24/

11 GROWTH Though newly planted trees must be monitored for pest and disease problems, the biggest need for newly planted trees and biggest key to success in establishment is adequate soil moisture. Local precipitation data can be found here: Observed.html#monthly and can be used to alert partners and grant recipients when precipitation falls below norms and trees may need supplemental watering. Planting programs need to be supplemented with mature tree care programs. If citizens are involved in public plantings and do not see a jurisdiction holding up its end of the process with mature tree care, they may be disincentivized regarding participation in future planting efforts. Mature canopies provide much more ecosystem services than smaller canopies. Trees need to reach maximum service life in the landscape to provide maximum return on investment. Ordinances that protect public trees, that protect trees during construction, or that protect all trees on all lands are tools some jurisdictions use to reach tree canopy goals. They may or may not be right for your jurisdiction. If used, they will likely have greatest public acceptance if they are part of a comprehensive program of financial and technical assistance as opposed to a program that relies solely on regulatory approaches, and if they have gone through an open and public process to ensure that opportunities for public comment and weighing of general public values have occurred. LOSSES Mortality comes from landowner preference, pest outbreaks, land use change, and lack of care. Minimizing losses involves strategies to address each of these; some are addressed above. A combination of engagement, enforcement, technical assistance, and a robust and competent private tree care sector are needed to minimize losses and realize UTC goals. 9/24/

12 Conclusions Tree canopy in the region is a vital asset that reduces stormwater runoff, improves air quality, reduces the region s carbon footprint, enhances quality of life, contributes to savings on energy bills, and serves as habitat for wildlife. An urban tree canopy goal could serve as the foundation, not only for increasing the overall tree canopy but for targeted efforts to address environmental issues in the region. Strategies for increasing tree canopy will likely differ by land-use type. The outreach and incentive mechanisms for planting trees on commercial properties will differ greatly from residential properties. Agricultural areas are vital for maintaining tree canopy in the region, but the active use of the land will limit the establishment of new tree canopy except on select areas such as riparian buffers. On the other hand, Residents are not only important for maintaining tree canopy, but they control the most land on which new tree canopy could be most easily established. Activities that educate residents on the importance of maintaining their tree canopy and programs that encourage them to establish new tree canopy will insure a robust urban forest in the region. New developments show a conspicuous lack of tree canopy. New urban development projects in the study area should include in their plans new tree plantings in yards, common areas, and transportation rights-of-way. These new trees will produce a net gain in canopy while mitigating the effects of increased impervious sur- faces. Some land uses will not necessarily be appropriate for planting trees, including the airport along with vegetated lands that are occupied by cemeteries, golf courses, and wetlands. Efforts to increase tree canopy in these areas and other highly-developed zones might be most efficiently focused on extensive impervious surfaces such as parking lots and industrial sites, where tree canopy must be limited in areal extent yet often offer important reductions in stormwater runoff. Strategic tree planting is pertinent to all land-use types that contain vegetated or impervious surfaces; many opportunities exist for expanding tree canopy. For example, other potential sites include road medians, sidewalks, driveways, storage areas, large expanses of lawn, and brushy vegetation. Under the right circumstances, these sites could be modified to support additional trees. Tree canopy has a clear impact on surface temperature. Greening the region will help to reduce summer temperatures, thereby reducing energy use and saving businesses and residents money. Efforts to preserve and expand tree canopy will likely take many forms. Tree canopy prioritization analyses can help managers make strategic decisions to match their objectives, from the property parcel level to the watershed scale. Figure 18: Comparison of Existing and Possible Tree Canopy with other communities in the region. Prepared by: Michael Galvin, SavATree Jarlath O Neil-Dunne, UVM Dexter Locke, UVM Additional Information For more info on the Urban Tree Canopy Assessment please visit Tree Canopy Assessment Team: Noah Ahles, Ernie Buford, James Clark, Maurie Clark, Tayler Engel, Mike Franck, Michael Galvin, Samuel Grubinger, Dexter Locke, Sean MacFaden, Amy Mietkiewicz, Jarlath O Neil-Dunne, Kyle Onofreo, Anna Royar, Benjamin Whitney, Rebecca Zeyzus 9/24/