Map, Manage, Repeat

by Carrie Asselmeier

 

Our urban forests grow and diminish throughout the years due to varying levels of urban development, natural disasters and local climate trends. The ups and downs of urban forests can be drastic or moderate, making it difficult to measure trends in canopy over short timeframes or during periods of low growth. Natural disasters and periods of rapid development can have dramatic negative impacts on urban tree canopy while periods of low development and high precipitation can contribute to favorable growing conditions. Analyzing changes in the urban forest is an integral part of forest management and assessing overall forest health. 

 

A growing urban forest enhances the myriad of benefits that trees provide for ecosystems and the community including cooling from shade, increasing air quality, and decrease in stormwater runoff. Losses of trees and their canopy have an adverse effect on these benefits. Identifying declining urban forests through change analysis drives changes in forestry management plans and promotion of overall forest health through pest management and increasing tree planting. Canopy change analyses are often included in many of PlanIT Geo’s urban tree canopy assessments in order to identify specific areas of growth or loss. Mercer Island, Washington’s recent tree canopy assessment incorporated data from 2007 and 2017. After analyzing canopy change over a 10 year time period it was found that their canopy had increased substantially by 8%. This was potentially due to a favorable growing climate, growth in newly planted and existing trees, and proactive forest management. Mercer Island is a great example of a change analysis vic-tree!

False color near infrared images showing tree canopy growth In Mercer Island, WA.

Urban tree canopy change analysis creates a visualization of canopy growth or decline from past years using land cover data from previous assessments or creating a new canopy map from historical imagery and comparing that to new data and present imagery. These analyses shed light on the changes in tree canopy and provide insight into the reasons behind growth or decline that can offer recommendations for future planting and forest management. If a baseline assessment does not exist, historical imagery can be used to assess canopy in a previous year. Cities can use 2 or more years of historical data to analyze periods of growth and decline like the City of Colorado Springs did as a part of their first tree canopy assessment in 2019. Canopy change analysis can also spark a continuing evaluation of future growth or decline when analysis is continued every 5-10 years. Continuing to measure the extent of the urban forest over time creates an easier approach to keeping up with the health of your urban forest and updating forestry management plans to stimulate urban tree canopy growth. 

Charlotte, NC - Tree canopy loss due to development

The geospatial services team will presented a webinar:

 

Map. Manage. Repeat. The Value of Updating Your Tree Canopy Assessment

 

 During this webinar, we went ino into further detail on the challenges of using historical imagery, benefits of continued assessment, and examples of change analyses that we have performed.

 

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