Benefits and costs of street trees in Lisbon, Portugal

It is well known that urban trees produce various types of benefits and costs. The computer tool i-Tree STRATUM helps quantify tree structure and function, as well as the value of some of these tree services in different municipalities. This study describes one of the first applications of STRATUM outside the U.S. Lisbon's street trees are dominated by Celtis australis L., Tilia spp., and Jacaranda mimosifolia D. Don, which together account for 40% of the 41,247 trees. These trees provide services valued at $8.4 million annually, while $1.9 million is spent in their maintenance. For every $1 invested in tree management, residents receive $4.48 in benefits. The value of energy savings ($6.20/tree), CO2 reduction ($0.33/tree) and air pollutant deposition ($5.40/tree) were comparable to several other U.S. cities. The large values associated with stormwater runoff reduction ($47.80/tree) and increased real estate value ($144.70/tree) were substantially greater than values obtained in U.S. cities. Unique aspects of Lisbon's urban morphology and improvement programs are partially responsible for these differences.