City Trees

large tree biomass after storms or in the aftermath of invasive species such as the emerald ash borer (Agrilus planipennis) and Asian long-horned beetle (Anoplophora glabripennis). Effective planting man- agement hinges on the installation of utility-friendly or compatible trees that are often recommended and are indeed perhaps the most effective way forward for a sustainable ROW tree canopy. The reality of "right trees under wire," however, may wane somewhat as our community partners (private owners) may sometimes shirk the respon- sibility of planting a desirable tree in preference for a species that is more easily available, cheaper to acquire, or one that is deemed to have better color and shape characteristics. One way to re-address the utilization of recommended planting material appropriate for the ROW setting could be to embrace the pollinator plight issue in our planting policies, as wider community acceptance may now be found. What is Pollinator Health? Pollinator health should not be confused with more blooms necessarily. Nectar sources and pollen, to be of value to pollinators, should be available when needed. The presence of adequate overwintering sites along with early-season food sources are also important components needed to support viable pollinator populations. ROW habitats may consist of snags and fallen logs, which provide ideal homes for overwintering bees and other pollinators. These, combined with trees and other planting material that bloom early and provide early-emerging species with sustenance, need also to be a part of this land- scape. Early season bloom trees such as boxelder (Acer negundo), maples (Acer), birch (Betula), etc. all may provide nectar and pollen to "early emergers" until the understory wildflowers begin to bloom. Several bumblebee species, including the rusty patch bumblebee (Bombus affinis) and the yellow banded bumble bee (B. terricola) for example, emerge in early spring and will utilize these early food sources; some researchers attribute the imperiled status of these two species as being due to lack of sufficient diversity and quantity in early season fodder. Compatible ROW Trees: Relevance to the Pollinator Plight In a ROW tree suitability study, floral bloom times and bloom windows of 25 species of trees present in existing ROW service corridors in the Northeast, East, Mid-Atlantic and Midwest of the U.S. were examined in 2015 and 2016. These snapshot bloom times and bloom windows are estimated using Growing Degree Day-based software, Nature Clock (patent pending, Davey Tree Experts). This data demonstrates that floral (insect pollinated) and by extension, pollen (and nectar) sources from existing ROW trees do provide a seasonal source of nectar and pollen that aligns with the life cycles of several pollinator species. The key, however, is the element of biodiversity which helps provide for a larger variety of pollina- tors and may better align with their overwintering and reproductive strategies. Some wind-pollinated trees, although devoid of nectaries, may still attract some insects that benefit from the pollen contained in their flowers, which may be reduced and not very colorful. The bloom windows of trees in the generalized utility ROW that currently exist were compared with that of a recommended planting list of species suitable for the ROW environment. 20 CityTREES The caterpillars of Cecropia moths (Hyalophora cecropia) eat the leaves of many trees, including alder, maple, wild cherry, plum, and willow.

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