In 2015, The Division of Forestry & Wildlife and its Kaulunani Program and Smart Trees Pacific (STP) contracted a study of Honolulu’s urban tree canopy change using high-resolution satellite imagery and LiDAR.
A “tree canopy” is the layer of leaves, branches and tree stems that cover the land surface when viewed from above.
The resulting report is now available to the public for review. Hawai`i is one of the few pioneer States to conduct urban tree canopy change analysis using newly available methods, giving us valuable knowledge to better manage our urban forests. In 2012, Kaulunani and STP conducted an initial analysis of Urban Honolulu’s land cover to give us a baseline of our urban tree canopy. In 2016, we conducted a second Urban Tree Canopy analysis to assess the degree of change from 2010 through 2013. What we found was alarming.
Honolulu is losing tree canopy; in fact, we lost nearly 5% of our total urban tree canopy over four years. The majority of losses were in non-public zoning areas. Net Residential losses alone totaled 355 acres representing 39% of all the tree canopy loss; some land use parcels near Kalaeloa Airport saw unprecedented clear cutting resulting in 100% canopy loss. All land use areas saw decreases; even our conservation areas saw a 1% loss in tree canopy. Close to 98% of the losses were less than a quarter acre each and spread widely across the landscape. These losses equate to at least 76,600 trees. New plantings did occur totaling about 230 acres, which is far short of what is needed to keep pace with the losses, especially considering the time required to grow a canopy.
Honolulu is not alone; urban forests are declining in many cities, and studies show a direct connection to declining human and environmental health because of it.
Why Is Urban Tree Canopy Important?
Current research shows that trees are essential for the livability of our cities. Trees improve physical and mental health; improve environmental quality by reducing CO2 in the atmosphere, improving air quality, slowing and filtering polluted runoff, reducing flooding and soil erosion; Increase property values by 10-20%; Help lower crime rates in communities; Reduce temperatures & the Urban Heat Island Effect; and so much more.
With more than 70% of the world’s population projected to move to cities in the next 30 years, it is more important than ever to protect and increase our green infrastructure to secure a healthy future for our communities and our environment. An important first step in understanding where to start in managing our urban forests is by understanding the condition of our urban tree canopy cover.
What Can Be Done
The 2016 Honolulu Urban Tree Canopy Assessment reported that tree canopy covered 23% (2,892 acres) of the study area, and there is room for an additional 64% (7,924 acres) of the urban land area that could be modified to hold more tree canopy. These opportunities exist in areas currently covered by both vegetated and impervious surfaces. As vegetated areas are converted to impervious areas, planting becomes more challenging.
We need to plant and plan for more urban trees! Policy to support growing and maintaining tree canopy is needed for all of Honolulu’s urban trees. Oahu’s urban tree canopy assessment needs to be continued and expanded to all urban centers in the state of Hawai`i. It is an invaluable tool for Hawai`i to take the next step of setting a Tree Canopy Goal, which allows people to come together and work to manage and grow our urban forest. With losses outpacing new tree plantings and growth it is critical that Honolulu prioritizes urban forest management if we are to ensure a resilient, livable city in years to come.
Older Urban Tree Canopy Assessment Study:
Smart Trees Pacific completed a spatial Urban Tree Canopy Assessment in May 2012 of the major urban centers of Oahu. The assessed area includes more than 250 square miles of Leeward and Windward Oahu, from Kalealoa to Kaneohe. This spatial technology has only been available in recent years and has been applied successfully to other cities, such as New York, Baltimore and Philadelphia. Honolulu is the first tropical island location chosen to participate in an Urban Tree Canopy Assessment.
The Spatial Analysis Lab at the University of Vermont has developed a specialized computer application that uses aerial and satellite photos supplied by the US Geological Survey to extract and map the tree canopy and other ground surface features for analysis. By combining existing land-based maps from the City and State planning offices the analysis identifies the extent of tree canopy, its location, ownership and potential planting sites that can enhance urban tree canopy with its associated benefits. In addition, with the
aid of rainfall, soil and climate zone maps, planners, landscape architects and arborists will be able to make better tree planting decisions.
One goal of the project is to provide government agencies, planners, commercial developers and others with an interest in our urban forest, with an understanding of the current location and ground coverage of our urban tree canopy. The UTC data could be used by environmental groups, non-profit organizations, educators and others to strategically plan how to plant trees to maximize their environmental benefits. This could lead to better management of watershed, storm water control, coastal water quality, urban heat islands and air quality through better use of trees.
This project is part of the long range Hawai`i urban forestry strategy planning initiative in which Smart Trees Pacific has partnered with the USDA Forest Service; State DLNR Division of Forestry and Wildlife, Kaulunani Urban and Community Forestry Program, City and County of Honolulu, Department of Parks and Recreation Urban Forestry Division, and Department of Planning and Permitting, Honolulu Land Information System.
Download a copy of our new STP brochure – Tree Canopy Goals
For more information contact Jolie Wanger.