Workshop to Develop Research Priorities for Invasive Aquatic Plants Sea Lodge Hotel, La Jolla, California December 14-15th, 2005 Working Group on Physical & Mechanical Control Chuck Boylen, Vanessa Howard, Mary Pfauth, Robert Doyle & Mark Sytsma

Current and past research activity in the field of physical & mechanical control  What has been the major focus of research?  There hasn’t been much. Most deals with efficacy of removal  Mechanical harvesting  Habitat alteration to deter or minimize growth  Largely operational and mostly focused on harvesting, rototilling and cutting  Most research has been focused on ponds/lake ecosystems & secondarily with estuaries, wetlands or moving water systems  Over half of published papers have focused on North American systems  What were the three (or more) most important findings in the past 10 yrs?  Have there been any?  Chemophobic attitudes are on the rise in many urban areas – new opportunities for mechanical control & science related to it?  How have these findings been incorporated in management, if at all?  These findings are largely gray literature based, not experimental. Research is often done on the periphery of management programs already underway

Critical assessment of research in the field, developing themes & directions for the future that hold promise for better understanding of aquatic plant biology and management.  What areas have been overlooked or under studied?  Role of epilimnetic mixing and macrophyte control through nitrogen limitation  Effects  Temporary modifications to population (harvesting)  Temporary modifications to habitat (shading)  Permanent/long-term alterations to habitat (dredging)  Timing of treatment - when is the best/worst time to harvest? Most harvesting is in response to recreation needs and is limited to the fact that harvesting equipment reaches only so far under the surface.  Long term manipulations of systems previously studied

 Propagule longevity (esp. turions) & viability  Modeling approaches of harvesting impacts. Can we make use of physical/mechanical methods to hone or test modeling accuracy?  How to minimize environmental impacts of mechanical techniques  Making harvesting “fish friendly” by avoiding accidental takes of fish (sound, light, etc. to scare fish off)  How many nuisance exotics are annual? Preventing flowering by mowing/cutting in order to deplete the seed bank. Growth regulators, liquid nitrogen, lasers?  Studies of seed germination – triggers and synchronization of germination. Water fluctuations, temperature, oxidizing the sediment. Not much attention is paid to seed research since many of the worst weeds are clonal. Newly invading species on the horizon could be more effectively controlled with this information  Quantifying non-target impacts (nutrient dynamics, phytoplankton, zooplankton, fish, native plant communities)  Remote sensing technology and early detection efforts

 Mechanical  Aquatic community responses to harvesting – what are they?  Fragments remaining after shredders, do they spark invertebrate population increases?  Plant response to cutting, harvesting? Side branching, wound- response studies in terrestrial plants, long-term responses to disturbance?  Habitat Alterations  Organic matter additions:  Mode of action (irrigation canal work with barley straw)  How to make this effective in a lake or other system where drawdown or other physical controls are not an option? Pelletized additions to the sediment?  Drawdown efficacy – In the south only controls aboveground growth… oxidation of sediment through drawdown may stimulate germination of turions which can then be killed. Nitrate injection to oxidize. In the NE, drawdowns are infrequent because they are inhabited lakes. In the south, repeated drawdowns on reservoirs is feasible, but doesn’t result in eradication… additionally, water is expensive to just let flow downstream. In the NE, late-season drawdowns with subsequent freeze allows partial “donut” ring of control. Drawdown with fire?

 What benefit would additional work in these areas provide to managers? ??  What are the obstacles to accomplishing this work? (e.g., funding, research facilities, interest by students and/or managers?)  Operational issues dissuade publication of certain techniques, responses of species to said species… how to get anecdotal observations into written format for easier access or promote research ideas? Dissemination of observational knowledge (eg – M. Netherland’s dissertation)  Would these things have obvious interest to managers? May be a large obstacle to getting research done?

 What suggestions would help overcome these obstacles?  Controlled explosions of all access points (boat ramps, docks, etc)  Coordination of research facilities – especially long-term experimental sites  LERF ponds - facilities there haven’t been fully utilized due to budgetary constraints  Experimental Lakes District in Canada for long-term research has primarily looked at nutrient additions and not exotic species but such facilities have promise for the next generation of aquatic plant research – particularly for temperate zones  Facilities in different regions  Multidisciplinary centers for targeted research on a world- wide basis  Database for gray literature (APHIS?) Reports to legislatures, summary reports, reconstructing site histories and/or talking to previous employees.  Interest from students – how to increase field components, enticing people into environmental science, education at lower grades

General points/Miscellaneous concepts:  Habitat manipulation tools are often of last-resort or in cases of limited options  Which methodologies/techniques are based on fundamental, well-tested ecological theories?  Literature on disturbance ecology hasn’t been really tapped into  Importance of considering alternate stable states model when considering management options. For example, turbid water limits weed growth, but is high turbidity a desirable option?