Tree Mapping Inventory to Enhance Urban Forestry Management

Mapping trees may be an unfamiliar concept to many. However, tracking and mapping trees has become an essential tool in the fight against climate change. In recent years, tree planting and growing have become a global topic, especially with the increasing impacts of climate change through CO2 emissions. Some geographers have mapped potential areas where planting trees can help with climate change mitigation. Implementing strategies like this in an urban setting is a rigorous process that needs a comprehensive understanding of urban forestry at a local level.

In Dar es Salaam, Tanzania —one of the most rapidly urbanizing cities in Africa, with an estimated population of 6 million people—managing trees/urban forest is a challenge, especially with no proper tree inventories.  Full city assessments of tree canopy[1] and tree inventories used by many urban forest managers have become a standard dataset used to set policies, create management plans, sustain, extend and optimize urban forests.

OpenMap Development Tanzania (OMDTZ) and Greenstand, supported by the World Bank, have partnered in a project that aims to enhance urban forestry management—a somewhat new concept in Tanzania—by conducting tree inventories using inexpensive and easily available equipment. Proper urban tree management has proven to increase the quality of life through cleaner air, lower heat stress levels, a healthier environment and improved aesthetics.

In high-income countries, there often exist detailed inventories down to the individual stem! However, the cost of obtaining such inventories in places like Dar es Salaam using the same methods as in Manhattan is simply not feasible. Instead, by using community mapping techniques, it is possible to create standard inventories that are fit for the purpose of management. 

In March, 2020, OMDTZ conducted a pilot survey to test the methodology, which resulted in more than 500 trees mapped. The pre-second phase focused on developing tree mapping guidelines on how to measure tree heights and diameters using cheap open-source tools (i.e. GIMP, QGIS, ODK Collect, Android phone, tape measure, bright-painted stick, and/or a clinometer). We also made a short-instructive tree height measurement methodology video demonstrating the mapping process.

Working with students has always been part of our methodology for effectively imparting knowledge and skills to younger generations. In collaboration with the Tanzania Resilience Academy—a program that aims to equip young people with the tools, knowledge, and skills to address the world’s most pressing urban challenges and ensure resilient urban development—we were able to work with 70 university students from Sokoine University of Agriculture (SUA), The University of Dar es Salaam (UDSM) and Ardhi University (ARU).

In Dar es Salaam, we trained 20 students from ARU and UDSM who collected data in Kinondoni and Ubungo Municipalities along the river Ng’ombe (100-200m on the riparian areas) which will support the Dar es Salaam Metropolitan Development Project (DMDP). The DMDP  aims to improve urban services and institutional capacity in the Dar es Salaam metropolitan area and to facilitate potential emergency response. This undertaking includes upgrading the river to get a baseline tree database, focusing on trees that may be cut down during this process, to later add more trees in order to reduce erosion and maintain urban greening.

In Morogoro, we trained 50 Environmental Science and Management students, equipping them with skills on how tree inventories are conducted. As part of their industrial training, these students conducted ground surveys and mapped tree canopy around the SUA campus. Data collected at SUA is expected to be used for research purposes at the university.

During the industrial placement, the students also learned about a tree inventory approach used in Morelia, Mexico, showing how most of the collected parameters are the same, but cultural differences often determine the type of data that is collected.  

Project Result and Way Forward
The project has helped to create a scalable model that allows us to understand the canopy of the city, enhance urban forestry management and provide the government with quantifiable data to issue cutting permits. We have developed a method using only mobile phones and tape measures that generates data with 0% to 20% error difference from that obtained with clinometers (albeit without calibration using laser rangefinders).

The outcomes of this project were:

• A more targeted management of tree cutting permits
• Identification of tree desert areas
• Mitigation of heat islands
• More effective planting and tending of urban trees
• A greener, more aesthetically pleasing city.
• The ultimate goal of the collaboration between Greenstand and OMDTZ with support from the World Bank is to enhance government and community capacities to establish and manage public green spaces and urban trees with their associated ecosystem.

^{[1] The layer of tree leaves, branches, and stems that provide tree coverage of the ground when viewed from above.}