City Trees

Evaluation of Pollinator Health and IVM Strategies IVM strategies are often drivers for creating bio- diversity as undesirable vegetation is constantly removed and more compatible vegetation either encouraged or in some cases installed. The value of IVM to plant biodiversity and ultimately pollinator health was examined in several ROWs in the eastern U.S. ROWs implementing mechanical methods were also examined along with ROWs that had been con- verted in three recent years from VM to IVM. Plant diversity (number of species/unit area) was higher in recently converted ROWs compared to ROWs that were maintained by VM and by IVM. The higher species diversity in recently converted areas can be described as several opportunistic, invasive, and/or transition species such as weeds and clover, which may have capitalized on the open ground which is created after recent herbi- cide application. The number of plant species is reduced significantly in ROWs maintained by IVM in established areas (but still more diverse com- pared to VM alone) as equilibrium may be achieved by some species eventually out competing the transition species through natural succession. Hymenopteran-specific surveys revealed that VM-managed areas had highest ant populations, which may have occurred as several grassy areas had open spaces, which allowed for ant mounds to be readily built. Ant tracks or pathways were more noticeable in VM-managed areas. Bee populations were higher in recently converted ROWs compared to VM-managed ROWs and those managed by IVM. Higher bee populations likely occurred in the VM/ IVM ROWs as transition plants, including weeds and clover, were in high abundance and probably attracted larger numbers of bees. Bee species compo- sition was, however, skewed between sites with VM sites having the lowest populations of the main bee groups collected, including mining bees (adrenidae), honey bees (apidae) and sweat bees (halicitidae); VM/ IVM sites had highest honey bees (apidae) while IVM sites had the highest bumble bees (megachilidae). >> urban-forestry.com 21 The data indicate that recommended trees in res- toration of underwire areas or compatible in ROW corridors also increase early season nectar sources from 20 percent to 32 percent when compared to traditional or existing trees, with a better distribu- tion of blooms in each season. Recommended trees, while appropriate for the ROW wire zone areas, may thus also enhance pollen and nectar sources available for pollinators, especially if biodiversity of plantings in restoration activities are managed effectively. When bloom availability alignment with most native pollinator bees were examined (using 25 percent as minimum margin for bloom alignment), bloom avail- ability from 32 percent of traditional or currently existing ROW trees did not align with native pollinator life cycles or when they will be most required for pollinator health. ROW-compatible trees, however, provided blooms that were 86 percent of the time in alignment compared to existing ROW trees. The opportunity here, as we examine restoration in ROW, is to utilize trees that are not only ROW- compatible for meeting our enhanced stewardship goals but also provide increased pollinator value.

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