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Assess canopy cover
Tree canopy cover refers to the proportion of land area covered by tree crowns, as viewed from the air. Canopy cover is tied to many of the benefits provided by the urban forest. Assessing the amount of canopy cover present using aerial imagery is a relatively easy way to get an overall picture of the urban forest.
Measuring canopy cover gives you a starting point. Later, you can reassess canopy cover and see whether practices put into place by the urban forest management plan you are developing have been effective. Canopy cover can be stratified by land use type or geographic area. Historical aerial photographs can be used to look for trends that have developed to the present time. They can be useful in answering questions such as: "Has canopy cover in our city increased over the past X years?"
An analysis of urban forest canopy cover in 21 California cities carried out in 1997 found that among many factors influencing urban tree cover, two factors were most important. These factors were the surrounding natural forest vegetation and land-use type. Among land use types, residential areas supported the highest canopy cover. Cities in areas with few natural trees had the lowest tree canopy covers. Conversely, cities in areas with dense natural tree cover had the highest canopy covers.
Example
An example of the importance of natural forest canopy is seen in an analysis of canopy cover in Rocklin, CA. In the last century, the vegetation in Rocklin was primarily grassland with stringers of oak forest. Over the period from 1952 to 2003 overall canopy cover increased from 11.3% to 18.5%. Analysis showed that the increase in canopy cover was due to both canopy growth of conserved native oak forests in open space lands, conserved individual oaks, and planting of trees in new developments in formerly treeless areas.
Planning for the Future of Rocklin's Urban Forest, Section 3.1
Planning questions
The following questions are designed to help you decide whether you want to measure canopy cover and what you will do with the information you collect.
- Can we define canopy cover targets for the planning area as a whole and/or for segments within the planning area (e.g., residential areas)?
- How does current canopy cover compare to possible canopy cover targets?
- Are canopy cover levels in the parts of the planning area at or near maximum sustainable levels? If so, should these levels be used to set targets?
- What factors (environment/trees/management) are associated with the urban forest in areas that have maximum or optimal canopy cover levels?
- What management actions would be needed to reach target canopy levels?
Work plan
For each category listed below:
- indicate with a check in column 1 those that are of interest to you and will be addressed in the UF management plan
- indicate the methods that will be used to collect the data, who will be responsible for collecting data, and their timeline for supplying the data
- indicate who will the be responsible for summarizing or analyzing the data and their timeline for providing the analysis for the plan
Canopy cover |
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Data collection |
Data analysis |
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Characteristic |
By whom? |
Target date |
By whom? |
Target date |
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Overall canopy cover |
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Canopy cover by land use |
specify land use categories |
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Canopy cover by region |
specify regions |
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Canopy cover changes over time |
specify time frame |
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Other (specify) |
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Outline
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Literature cited
Rowntree, R. and E. Kerkman. 1997. Urban forest canopy cover in California: analysis of 21 cities and towns. Unpublished technical report. USDA Forest Service, Pacific Southwest Research Station. Albany, CA.