Long-term effects and development of a tree preservation program on tree condition, survival, and growth

A long-term research study in Milwaukee, Wisconsin, USA investigated how construction (i.e., repairs to streets, curbs, and sidewalks) affected tree condition, survival, and growth compared to control trees outside construction zones and effects of a tree preservation program on reducing construction impacts. This study is divided into three periods: (1) a limited implementation period (1979-1989) prior to a formal tree preservation program, (2) an intermediate implementation period (1989-2005) during the development and refinement of a tree preservation program, and (3) a full implementation period (2005-2018) after comprehensive execution of the tree preservation program. During the initial limited preservation period, baseline measurements from 1989 showed trees in construction zones died at a higher annual rate (4.1% actual) and had a lower tree condition rating (5.7% actual) in the limited implementation period (1979-1989) as compared to the other two periods. During the intermediate implementation period (i.e. program under development), construction activities resulted in a reduced effect on tree condition (2.4% actual) as measured in 2005. Tree survival and condition in the full implementation period were similar between trees associated with construction zones and non-impacted control trees measured in 2018. Results demonstrate the effect of a tree preservation program on promoting healthy trees in construction zones. Significant findings also show the importance of growing space with trees farther away from curbs and sidewalks having a higher tree condition and survival rate in all three periods. Findings from this study can encourage city-wide-preservation programs elsewhere to protect public street trees from construction.