EFFECTS OF INVASIVE PLANT SPECIES
ON POLLINATOR SERVICE AND REPRODUCTION
IN NATIVE PLANTS AT ACADIA NATIONAL PARK

Technical Report NPS/NER/NRTR--2007/096

Constance S. Stubbs¹, Francis Drummond¹, and Howard Ginsberg<sup>2

1</sup>University of Maine
Orono, ME 04469

²USGS-Patuxent Wildlife Research Center
Coastal Field Station
University of Rhode Island
Kingston, RI 02881

October 2007

U.S. Department of the Interior
National Park Service
Northeast Region
Boston, Massachusetts

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Executive Summary

Invasive plant species can have profound negative effects on natural communities. Berberis thunbergii (Japanese barberry), Frangula alnus (glossy or alder buckthorn) and Lythrum salicaria (purple loosestrife) are invasive species known to reduce native plant diversity. These invasives are of great concern in Acadia National Park, but are highly attractive resources for pollinators. To determine if these invasive species affect pollinator behavior and thus native plant reproduction, we conducted studies from 2001-2005 testing four major hypotheses: 1) that these invasive species influence pollinator visitation to native plants; 2) that these invasives affect pollen transfer to native plants, 3) that these invasives influence native plant reproduction (fruit set), and 4) that native bee diversity and abundance is influenced by these invasive plant species.

Native bees collected from patches of native and invasive plants were compared with historical records to assess whether invasive plants favor different bee species than those that formerly predominated on Mount Desert Island. This does not appear to be the case. However, several species of bumble bees (Bombus spp.) as well as nine solitary bee species were found that were not documented by the Procter surveys of 1917-1940. Collecting of native bees was limited to the study plants, which, in part explains why some bee species documented in the Procter Surveys were not found. Much more extensive collecting throughout the flowering season and from other regions of the Park would be necessary to determine if any species have been extirpated from Acadia National Park since 1940.

A field guide for identification of native bumble bees has been produced to aid Park Natural Resource personnel in monitoring the status of native bee populations in Acadia. Other educational materials were also developed, including a Power-Point presentation that can be used for educating Park visitors by exposing them to: 1) the role of native plants and their bee pollinators in terrestrial ecosystems; 2) the effects of invasive plants on native plant-pollinator mutualisms; 3) the need for conserving native bees and other pollinators; and 4) conservation strategies for protecting and enhancing native plant-pollinator mutualisms in the Park.

Based on the present findings, Acadia Park Resource Management personnel should continue to closely monitor these invasive species, especially L. salicaria so that their populations do not overrun the native flora of the Park. However, B. thunbergii and F. alnus appear at least in the short time-frame of this research to benefit both the co-flowering native species by attracting, at times more pollinators to them and to benefit native bee populations by providing additional needed food resources. Therefore, until suitable native plant replacements can be found, perhaps their removal need not at present be a high priority, at least from the perspective of pollination patterns. Although native bee populations do fluctuate, the fact that native bee populations were lower in 2005 than 2004 is of some concern. Further monitoring may be warranted to determine if populations are stable or declining.

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