Planning for active management of future invasive pests affecting urban forests: the ecological and economic effects of varying Dutch elm disease management practices for street trees in Milwaukee, WI USA

The effects of Dutch elm disease (DED, Ophiostoma novi-ulmi) on 106,738 American elm (Ulmus americana L.) trees in Milwaukee WI, USA was contrasted through ecologic and economic results of an Actual Outcome to management alternatives of No Control, three sanitation intensities (Best, Good, Fair), and No DED over 40 years. No Control was like the Actual Outcome with over 99% of trees dead. The greatest loss of ecosystem values and lowest net present value (NPV) and benefit to cost ratio (B/C) occurred with the Actual ($8 to $80 million NPV, 0.8 to 1.1 B/C) and No Control ($-7 to $57 million NPV, 0.7 to 0.9 B/C) alternatives. Best Control (1.0% annual mortality) retained the highest tree population (50% survival) and ecosystem value ($161 to $175 million NPV, 1.2 to 2.5 B/C). Good Control (3.5% annual mortality) and Fair Control (5.0% annual mortality) were better alternatives than No Control or the Actual Outcome with 21% and 12% of trees respectively surviving. Not surprising, a No DED scenario retained the highest ecosystem value ($202 to $257 Million NPV, 2.0 to 3.4 BC) with 70% tree survival. The value of stormwater maintained by trees under the Best Control was like the annual cost of this alternative. All other ecosystem values (e.g., air pollution, energy conservation, carbon uptake and storage) were thus retained at no additional cost. This study provides forest pest and disease management strategies for other serious pest problems such as emerald ash borer (Agrilus planipennis) threatening urban tree populations.