FACTORS THAT MAY INFLUENCE INVASIVE SPECIES:
                   Light is the main limiting factor for the growth of  purple loosestrife in a wetland.
 
                                                      Nancy Patterson and Jo Smerdel
                                                          Woodland Hills High School
                                                                Pittsburgh, PA  15221
                                                                           Team 24
 

            * PROBLEM - Background on Alien Species

            * PARTICULAR SPECIES - Purple Loosestrife ( Lythrum salicaria )

            * PROJECT DESCRIPTION - Light is the main limiting factor for the growth of
                                        loosestrife in a wetland.

            * APPLICATION AND VARIATIONS - For any high school biology or ecology class
                                        Questionnaire about your experiences in population studies and/or
                                        alien species

            * PORTFOLIO - Rationale for selection of site and methodology of experimental design
                                        Results and conclusions for this particular research
                                        History of this project's development and application to Science
                                        Standards

            * RESOURCES - Web sites and articles resources for further study
 
 

PROBLEM  

        Exotic or alien species have been introduced to the United States over the years, accidentally or purposefully.  An alien (exotic) species is defined as any organism introduced artificially into a habitat.   These species have been brought into the environment by humans and are carried by animals, vehicles, and even clothing.   Some exotics have found their niches and have even helped a particular ecosystem.   Many popular game fish such as the rainbow and brown trout and the tiger musky are "alien", non-invasive species.  However, some exotics actually harm ecosystems and contribute to the loss of biodiversity.  These species are usually free from predators, pathogens and competition. 

Historically,  some aliens have caused havoc not only to their habitat but also to the economy.  The chestnut blight was accidentally introduced into America in the 1930's on infected elm timber used for veneers.  The blight  managed to wipe out most of the northeastern American chestnut and change the composition of the hardwood forest.  The water hyacinth is native to Central and South America.  In I884 a woman saw it at an international exhibit in New Orleans and brought it back to her home in Florida to plant.  It grew unchecked and now thrives and has displaced native plants.  It clogs waterways and has indirectly lead to the demise of its only predator, the manatee.  Although the manatee eats the water hyacinth, the clogged water ways force the manatee to swim out in the boat lanes.  As a result, manatee are dying from injuries received by boats and the water hyacinth flourishes.  Recent biological controls such as the weevil and grass carp have been imported to check the growth of the hyacinth.  The gypsy moth, imported in the 18th century with the idea of providing silk, infiltrated our northern forest and  caused a serious decline to the forest cover in the late sixties and seventies. 

The unchecked alien population soon overruns its new habitat.  Once established, the aliens are rarely eliminated and may completely dominate the habitat.  This is especially true when the aliens moves into a confined habitat such as an island or a wetland.  Homes for native animals can be destroyed.  Food to maintain any given population can be decreased.  Native plants can not survive the competition for natural resources since most exotics have no natural predators, parasites or susceptibility to diseases. 

Our focus will be on the invasive plant, Lythrum salicaria, commonly called the purple loosestrife.  It is invading the wetlands and taking over this ecosystem causing its destruction. Since they have few natural predators, they quickly establish themselves as the dominant species.  However, as in any organism, there must exist certain limiting factors which control their success. 
 

 

 
 		 PARTICULAR SPECIES  

The purple loosestrife is a tall, perennial herb.  It can grow to heights ranging from 1-12 dm with a distinctly four angled stem.  The leaves are either opposite or whorled with a lance, non-serrated edge.  The showy flower blooms between June-September in a dense purple terminal spike, with each flower having 5-7 petals.  Flowering occurs after a critical day length of 14 hours. 

The plant was introduced to the United States in the 1800, probably on the ballast of ships, in livestock feed or in bedding.   There are also early records for its use as a medicinal herb.  Herbalists still use it today as an eyewash and a remedy for diarrhea.  An infusion of the leaves and flowers are used to gargle for sore throats, to clean wounds and to stop bleeding.  The flowers are used as an extract in hair dye. 

As loosestrife aggressively crowds out native plants, it begins to completely dominate the ecosystem. Economically it can impact by clogging irrigation or drainage ditches on farmlands.   In wetlands, the loosestrife's root systems do not act as a filtering mechanism since they are large and very fleshy.  Over $45 million dollars a year are spent on the control of loosestrife, lost forage from its spread and to regain the natural ecosystems.  Environment Canada provides  $100,000 matching funds with University of Guelph and Grand River Conservation Authority to work on its control. 

Loosestrife tolerates a wide range of environmental conditions and often out competes the natural vegetation.  It thrives on disturbed, moist soils, often invading construction sites.  It has invaded marshes and wetlands, replacing cattails and other wetland plants.  Although it prefers moist, highly organic soils, it can grow in poor calcareous, acidic, or nutrient poor regions.  If the soil is poor, the roots and shoots actually increase in size for a competitive advantage.  In shallow soils it can grow over limestone.  It prospers in ditches on sides of roads, and on sandy dunes from Southern Canada to Guatemala.  Unused pastures and hay fields are also prime areas for growth.  Wetlands connected by waterways are extremely subject to growth and development of purple loosestrife. 
        The seeds of the loosestrife are one of its most remarkable features and greatly contributes to its proliferation.   The seeds are very small, about 0.06 mg.  Each adult plant produces over 2 million seeds which can be dispersed by water, wind and wetland animals.  Because of the seed's ability to be carried in moving water, all areas downstream from a plant are primary regions for development. The seeds can remain viable in the seed bank for several years. They are almost impossible to eradicate.  Even when hand removing the plant, great effort must be taken not to cause the dispersion of seed.  This includes covering the plant with plastic before removing to burn.  Moisture and a temperature ranging from 15-20 degree Centigrade is needed to germinate.  Because of little food storage, once germinated,  the seed needs conditions for photosynthesis very quickly to continue development.  They grow quickly, flowering 8-10 weeks after germination.  They offer little nourishment for birds.  This is one reason for its enormous growth potential.

        Vegetative propagation is another quality which makes purple loosestrife's removal difficult and its presence in an ecosystem so devastating.  Its large roots can easily resort if the entire root is not removed.   Because of their vegetative properties and high seed production, purple loosestrife soon establishes a monoculture.  The plant grows in dense stands which are unsuitable as cover or nesting sites for animals such as ducks, geese, rails, bitterns, muskrats, frogs and turtles.  The stems provide a dense mat which can not be used as brood cover.  The long billed marsh wrens can not nest in them.  Platform nesting waterfowls can not use their stiff stems for nesting materials.  There are some species of birds that have adapted to the loose strife such as the black crowned night heron, the red wing blackbird, and pied billed grebes.  They can use it for nesting materials.  White tail deer and livestock may browse the young stems but the palatability soon decrease in summer.

        Bees do benefit from its presence since loosestrife is a good source of pollen.  The bees return the favor by being the primary mode of pollination.   The plants seems relatively intolerant to shade, perhaps able to exist in 50% shade.

        Control of these plants is extremely difficult.  Its use as an ornamental plant has hindered  control as well as the presence of its seeds in wild flower mixtures.  Many states, such as Idaho, Montana, Illinois, Ohio, Minnesota and Wisconsin  have legislation against the selling and planting of purple loose strife.  Removal is extremely difficult since disturbance and stress promotes infestation.  The opening up of areas actually increase sites for development of the plant.   Moving the plant increases adventitious growth if all root and shoots are not removed.  Extreme care must taken when transporting the plants not to drop any seeds or parts of stem or roots, since all can effectively produce new plants.   Burning areas infested and water level manipulation have been unsuccessful.  Chemical control, such as spraying glyphhosphate, has had limited effect.   Biological control may be the only answer.   Reed canary grass and Japanese millet are it's only natural plant competitors.  Three natural predators which are extremely species specific have been introduced .  The European weevil, H. transversovittatus Goes, attacks the root system of the loose strife and two beetle, G.calmariensis L. and G.pusilla Duftschmid, are leaf feeding beetles.  These have had very favorable results in Canada and are currently approved for use in United States by the USDA-APHIS.

PROJECT DESCRIPTION

HYPOTHESIS: 

        Light is the main limiting factor for the distribution and growth in a population of the purple loosestrife (Lythrum salicaria).
 
MATERIALS:
        Measuring tape
        stakes
        flagging tape
        flexible quadrant ( 6 -one meter slats, 5 small hinges)
        clip boards
        30 quadrant maps
        marking pens

PROCEDURE

        1. Build a collapsible quadrant gauge.
                    a. Using 6 "scrap" lumber flats measuring one meter each, construct a collapsible
                        measuring device. This will be "U" shaped, opened on one side.  A hinge will
                        connect each pair of slats.  Attach the two connected pairs of slats to the ends of
                        the third pair making the corners of the "U" shape.  One side must be open,
                        since .5m of the edges of the quadrant must extend into the water.  Mark .5
                        location from open end on each side of the quadrant.  ( See diagram below)
 
Side "A" folds over "B"on the right side.  Side "F" folds over "G" on the left.  "FG" collapses on "D". "AB" collapses on "C".  "D" and "C" fold together.
      2. For first morning readings, at 9 AM, select ten quadrants, at the site by marking off .5
                        kilometers along the edge of the waterway or wetland land and mark with stake
                        at the beginning and end of the .5K measurement.  Place side of quadrant gauge
                        edge at the end of the end marker and extend open edge into the canal to the .5m
                        mark.

         3. Mark the location of the specific quadrant with two stakes and flagging tape.

         4. Label quadrant map #1.  Note the location, date, time and compass direction of the
                        quadrant.

         5. Using the quadrant map, chart the number and location of:
                        a. loose strife plants of any size in the chosen quadrant using an "X".
                        b. any plant taller than 2 meters using a "0" of approximately the diameter size.
 
         6. Place an "/" through the grid on the map of any shade site in the quadrant at this time.

         7. Repeat steps 2-6 by selecting 9 other quadrants.  To make sure of random selection,
                        place the quadrant gauge at the beginning of the .5k, .2 k, .25k, .3k, .4k, and four
                        arbitrary sites between these stakes for a true random sampling.  Do not forget to
                        mark the edge of the quadrants with stakes.

         8. Repeat procedures 2-7 at 2 other times of the day, preferably at noon and three o'clock.

         9. Calculate the % of shade for each quadrant by counting the total number of shaded
                        squares as compared to 400 squares (total number on quadrant).  Average the
                        total % of shade for each quadrant studied for the three time periods.

         10. Using charts and graphs, compare the total number of loosestrife per quadrant to the
                       average % of amount of shade.

APPLICATION AND VARIATIONS FOR ANY HIGH SCHOOL BIOLOGY OR ECOLOGY CLASS

POPULATION STUDIES FOR ANY HABITAT

    The plan for this project can be used for the study of other populations of invasive species.  Once the species has been chosen, following this plan action of action could be easily implemented.  One could use a hula hoop as a quadrant measuring device.  The collapsible quadrant is effective when part of the area to be studied has trees or goes over water.  This approach takes less time than measuring each individual quadrant.  Time is always a factor when trying to work within the constraints of a class period.  If  the species is an animal, evidence of the animal's presence could be footprints, nests, sounds, or scat.
 

RESEARCH FOR AN  UNKNOWN FACTOR

    When designing a project using this methodology it is important that the process includes only one variable factor.  All other factors must remain constant so that the outcome of the data collecting will be the result of the one variable factor  (which in this project was the abiotic factor - light).  This is perhaps the most difficult feature of experimental design.  Many factors may be hidden or not readily apparent.  Students will have to spend time and discussion among themselves to make sure all factors are controlled except the one tested.

 CONTROLLING FACTORS IN AN EXPERIMENT

     When  we set up this project we tried to make sure that there was only one variable in the project, light.   Other factors  that one might consider for the growth and distribution of purple loosestrife are water, distribution of seeds, temperature, disruption of  land and the amount of bees (pollination).  We felt that these factors were fairly constant for our measure, since all quadrants were in close proximity to each other.  However, all these factors can be a source of further investigation.

TRANSFERRING FIELD INFORMATION INTO GRAPHS AND MAPS

    In depicting our results, we choose Excel, as a simply, readily available tool.  By placing our loosestrife plant numbers and % of shade on adjoining columns in a spread sheet, we were able to generate both the bar graphs for each quadrant and the overall line graph showing the relationships that exist for all quadrants. See RESULTS for examples.

DESIGNING MATERIALS FOR RESEARCH    (A collapsible quadrant gauge and a data collection quadrant map)
 
     At each quadrant location we used our quadrant measuring device to count the number of purple loosestrife and trees (two meters or more in height) and to estimate the amount of shade.  The quadrant measuring device was a three sided apparatus that measured two meters on each side.  Part of it extended over the canal water.  This part measured .5 meters.  It was necessary to measure out into the water since the loose strife grows in the water.  It was also necessary to have one side open so that we could put the device around the trees.

     Our quadrant map was designed for 2 meter square area with 400 squares.  Each square represents a decameter square.

 QUESTIONNAIRES FOR YOUR INPUT TO THE PROJECT

 
PORTFOLIO

 RESULTS (Quadrant maps, Graphs)

        As indicated in our graphs, there are more loosestrife growing in the quadrants that exhibit the least amount of shade.  Quadrant #4 shows the best correlation with 43 plants and only 2.6% shade.  Quadrant #8 has the highest percent of shade, 90.6% with no loose strife.  However, in quadrant #5, with the lowest % of shade, 1.3% there are only 10 plants.  Our line graph shows an inverse relationship between the number of loose strife and % of shade.

 CONCLUSIONS

         These results support our hypothesis: Light is the limiting factor for the distribution and growth in a population of the purple loosestrife (Lythrum salicaria).  Since all of our quadrants are relatively close (within .5K), face the same direction (due East) and have the same soil and water supply (the Delaware and Raritan Canal), most of the limiting factors were negated.  We did not however, measure soil or air temperature.  This could have been a factor since obviously, the temperature would be cooler in the shade.  The air temperature for the day was 96 degree F with a high humidity.  In our literary research, there was evidence that loosestrife could not tolerate more than 50% shade.  We could not substantiate this figure since we did have three loosestrife plants surviving in 89.7% shade in quadrant #10 and  two plants identified in quadrant # 9 with 87.2% shade.  There were probably other factors which we did not control or measure.   For example, quadrant #5 had the least shade (1.3%) but relatively little loosestrife (10). This particular quadrant also had a high amount of black eyed susans.  This was the only quadrant with these plants and they may have an effect on competition, although we could find nothing in the literature to substantiate this effect.  We would suggest further study into the correlation of shade to loosestrife or perhaps the possible connection to black eyed susans to the loose strife.
 
  SELECTION OF SITE

    For this project we chose a wetland found in Princeton, New Jersey.  This wetland is located along the Delaware and Raritan Canal that runs north and south  through  the city of Princeton.  The exact location is a one mile stretch of the canal, near the bridge on Alexander Road that leads into the township of West Windsor to the north of Turning Basin Park.  All of our data collecting took place on the west side of canal with all quadrants facing east..
    We marked a 2.5K section going south along the canal.  We also marked an adjoining 2.5K section going north along the canal.  In each of these sections we selected 5 quadrants that measured 2 meters in length.  There is a tow path that runs along the canal which was once used by the mules to pull boats.  The tow path is now used for recreational purposes.  Going south along the tow path, there are a few small trees.  Going north along the tow path there are more larger trees.  There are other types of vegetation that include crown vetch, poison ivy, black eyed susan and grasses.

PROBLEMS WITH DETERMINING LIGHT

    One problem we anticipated was that the amount of light available in the different quadrants would vary throughout the day.  Therefore, we could not take just estimate the amount of shade at one particular time of day.  We decided to collect data at three different times during the day (9a.m.,12 noon and 3 p.m.).  We averaged the three readings as the amount of shade for a specific quadrant.
 
    Another problem is possibly the way we estimated the amount of shade.  We used a quadrant map which was divided into 400 small units.  As we stood in front of the quadrant, we marked each unit that we perceived to be shaded.  Wind movement of leaves on trees could make it more difficult to make an accurate estimate of shade.

    We assumed that the quadrants with the most shade were the ones having the largest trees found in the quadrant.  However, trees on the other side of the tow path create some shade.  It is possible for a quadrant without any tall trees to have a higher percentage of shade than we expected.  We also found out that the purple loosestrife itself created some shade.

 HISTORY OF THE PROJECT

     During the pre-institute days we researched a project on loss of habitat and fragmentation with respect to the increase of white tailed deer.  We were interested in this species because the overpopulation of the white-tailed deer has become a serious problem in the city of Pittsburgh and its suburbs.  When the Institute commenced, our project's topic dealt with the over-population of deer and its effect on habitats.
      After our first few days at the Institute, we choose another invasive species as the topic of our project, purple loose strife (Lythrum salicaria).  We decided on the study of this species because it is one found in wetlands and it is easily observed along the Delaware and Raritan Canal in Princeton.  Nancy's first introduction to this plant was on a canoe trip in the Geneva Marsh in northwestern Pennsylvania.  She admired the beauty of this plant with its lovely purple flowers and was promptly told that this plant is very bad for the wetlands.
      With topic chosen we began our research with a visit to the biology buildings on campus.  We were able to to speak to two ecology and evolutionary biology professors who were very helpful with their time and information.  The library resources were excellent.  In addition, we retrieved many articles about purple loosestrife from the web.  After researching the topic we learned about the factors that enable the plant to be so successful.  We also learned why it has become a menace to wetlands and why it is so difficult to eradicate.
    Originally we were going to do a population of loosestrife compared to three other species.  This proved to be too vague.  We decided to measure light as a limiting factor.  Again, we had a dilemma: How to measure light without the use of complicated light meters.  We discussed this problem with GLOBE representatives.  They suggested we consider the % of shade by charting the shade on a grid.  After observing our site at various times of the day, we concluded that the only way to get a true reading of the % of shade was to measure shade at 3 different times and get an average.  We choose 9 am, 12 noon, and 3 pm times because of the positions of the quadrants.  At these times, the .5K sections received the most light.
    As mentioned earlier we designed a device that would allow us to count loosestrife and to estimate the percentage of shade in designated quadrants.  We constructed quadrant maps on which to record the data.  Data was collected according to plan and it was tabulated and transferred to a bar graph for each quadrant  and one line graph was made for all the data collected.  The conclusions were then made.
    Our project was written along the guidelines of project based learning.  The basic steps include:

 
  ACADEMIC STANDARDS FOR SCIENCE AND TECHNOLOGY

Our projects fulfills the following standards listed by Pennsylvania Department of Education:

The students will:
                        1. understand species’ dependence on one another and on the environment for
                         survival. (abiotic and biotic factors and their interactions, habitat, population)

SPECIAL NOTE

We would like to thank the Princeton faculty ( Dr. Donald Stratton and Dr. Henry Horn) and the biology library for their cooperation.
 
 

RESOURCES

        Web Links

        General Background on Exotics and Alien Species
           Indigenous, Alien and Invasive, FACT SHEET, World Wildlife Fund
                    General information and terminology.  Good ideas for practical further study
                    and resources

           Impacts of Introduced Species in the United States, Simmmberloff, CONSEQUENCES,
                    Overview of many introduced species in the United States and history of their
                    spread

            The Exotic Species, State of Iowa
                    Short summary of terms with links to specific species

            Exotics, New Jersey Audubon Society
                    Examples of specific invaders such as gypsy moth

      Information on Purple loosestrife and wetlands
             Purple Loose strife and Related Species of Lythrum Banned for Sale in Indiana,
                    Department of Natural Resources, State of Indiana
                    News release announcing the banning of the sale of exotic species and rationale

            Species Abstracts of Highly Disruptive Exotic Plants, Northern Prairie Science Center
                    Detailed description of purple loose strife with possible biological controls

            The Loosestrife Problem,  America's National Wildlife Refuges
                    Describes some control measures

            Missouri Purple Loosestrife Alert, State of Missouri
                    Where, Why and How on the problem of loose strife

            Purple Loose strife, Great Lakes Exotic Plants
                    Short overview, photo and references

            Invasive Exotic Plants of Canada, Fact Sheet No. 4
                    Extensive information with pictures and sketches, distribution map and
                    excellent resources

            Controlling Purple Loosestrife, Kitsap County Parks
                       New methods for control of plant

            Purple Loosestrife, British Columbia
                        Source of our photographs and other species sometimes confused
                        with loose strife

            Purple Loosestrife, State of Iowa
                        General description and  pictures

            Lythrum, Kent
                        Pictures and short background

            New Battle Plan Against Purple Loosestrife, University of Guelph, Ontario
                        Biological control as a means for limiting the growth of purple loose strife

            Value and Use, Federal government
                        Some good uses of  purple loosestrife

            Resource Materials Available, Ducks,
                        Resources materials such as brochures, posters and films
 
        Library Resources:
            Andersson, "Unequal morph frequencies in populations of tristylous Lythrum salicaria from southwest Sweden", Heredity 72 (1994), 81-85

            Eckert, Manicacci and Barrett, "Frequency - dependent selection on morph ratios in tristylous Lythrum salicaria", Heredity 77, 1996, 581-588

            Eckert, Manicacci and Barret, "Genetic Drift and Founder Effect in native versus introduced populations of an invading plant  Lythrum salicaria", Evolution 50 (4), 1996, 512-519

            Gaudet and Keddy, "Competitive performance distribution in shoreline plant communities: A comparative approach", Ecology 76 (1), 1995, 280-291

            Malecki, Blossey, Hight, et. al., "Biological control of purple loosestrife", Bioscience, Vol. 4 (10), 680-686

            Strutt and Kelly, "Above and below ground competition intensity in two contrasting wetland plant communities", Ecology, 77 (1), 1996, 259-270

            Weiher and Keddy, "The assembly of experimental wetland plant communities", OIKOS 73, 1995, 323-335