The Problem with Purple Loosestrife

Fresh Pond Reservation plays a very important duel role in the life of the citizens of Cambridge.  First, it protects Fresh Pond Reservoir, the terminal drinking water reservoir in the City of Cambridge drinking water system.  Second, the Reservation offers the opportunity for the city’s urban residents to explore a more wild and naturalistic ecosystem within an urban environment.  In order to fulfill its two roles, it is important that the many ecosystems at Fresh Pond Reservation are healthy. 

The threat posed by purple loosestrife, as with all invasive species, is that it upsets the functioning of an ecosystem by altering its components.  Native plant species are adapted for their specific environment and compete against other native species for space and light.  Because of this a native wetland community has greater biodiversity and will be able to support many species of plants and animals.  Invasive plants will often form monocultures, which are more susceptible to disease, and less able to respond to environmental pressures.   One of the most important functions supplied by wetlands are their ability to convert contaminants to more benign forms and recycle nutrients into the environment.  This is especially important for Fresh Pond Reservation, as the wetlands here help to protect the drinking water for the city from contaminants.

A stand of purple loosestrife can change the physical properties of a wetland by shading out smaller plants that would create a wetland understory, and by altering the flow of water and sediments. 

Just as a machine will not function correctly if one takes out all of the different pieces and replaces them with one type, so is an ecosystem unable to function if many of the species are replaced by one.  Purple loosestrife is a threat to the many types of wetland habitats currently found at Fresh Pond Reservation, as well as to the future of water quality from Fresh Pond Reservoir.