1. • A non-native annual grass from Eurasia
• Dispersed widely throughout the western U.S., where it is
extremely invasive (Knapp, 1996).
• Few studies have examined the plant’s ability to invade natural
systems in the east
• We are studying the species in Duck Harbor, which is located in
Wellfleet, Cape Cod; more specifically, we are studying B.
tectorum found between the foredune and the bluff at Duck
Harbor
Bromus tectorum
To what extent do B. tectorum seeds tend to disperse?
Are there certain types of vegetation that may contribute to B. tectorum’s survival and thriving?
At what rate can the B. tectorum population grow annually?
The Potential for Invasion of Bromus tectorum In Cape Cod’s Dune System:
• B. tectorum seeds tend to disperse locally (< 1 m.), and there is a greater chance
of establishment if the seeds experience a slight disturbance, such as raking, in
order to settle just below the surface of the sand.
• Between 2012 and 2013, the count of B. tectorum seeds doubled on average
(spikelet lambda ranges from 1.18 to 2.71) and the number of individuals
increased six fold on average (plant lambda ranges from 2.09 to 21.0).
• Bromus Tectorum tends to grow in vegetation communities that lie at the interface
of both dune and heath communities, despite the fact that B. tectorum appears
not to thrive in either system individually.
• B. tectorum is capable of rapid population growth in eastern coastal systems.
• Certain plant communities (interface between dune and heath) may be most
susceptible to invasion and/or serve as indicators of B. tectorum presence.
• A moderate level of disturbance appears to promote B. tectorum populations in
natural systems.
We hope to expand our research sites in order to better understand the Bromus
tectorum invasion as a whole.
• Which additional factors allow the species to thrive?
• Are these conditions present in the species’ habitats in the west?
• Which additional factors determine an area’s invasibility?
Results:
Implications
Future Research
Acknowledgements:
Thank you to Professor Alden Griffith, Tania Ahmed, my
parents, Wellesley College, the Priscilla C. Patton
Endowment Fund, and Cape Cod National Seashore!
At what rate can the B. tectorum population grow
annually?
Mean
Population
Growth (λ)
Between
2012 and
2013
Bromus
Individuals
6.09
(2.09-21.0)
Total
Spikelets
1.97
(1.18-2.71)
Fig. 6: The map to the left pinpoints the exact locations of the four demography
plots within Cape Cod’s Duck Harbor.
Conclusions: Both the number of B. tectorum individuals and spikelets
increased (sometimes substantially) over the course of a year.
Surveying seeds and spikelets over the course of a year allowed us to
measure the doubling on average of B. tectorum seed production and
the average six fold increase of individuals.
Take Home Points:
(Population growth (λ) is the geometric mean with the minimum and maximum values in parentheses.)
Shivani Kuckreja ‘16, Tania Ahmed ‘16, and Professor Alden Griffith, Environmental Studies, Wellesley College
Fig. 1: This figure depicts the number of B. tectorum
seedlings that emerged (out of 100 seeds) in April of
2013. This experiment contains four conditions: a
seedling can either be in a barrier/undisturbed
environment, an open/undisturbed environment, a
barrier/disturbed environment, or an open/disturbed
environment.
Conclusions: As the statistics indicate, the barrier
treatment does not have a significant effect on B.
tectorum’s seedling establishment. However, seedlings
in the disturbed environment have the best
establishment rate of all of the conditions.
To what extent do B. tectorum seeds tend to
disperse?
B. tectorum seeds tend to disperse locally (no effect of barrier), and
there is a greater chance of establishment if the seeds experience a
slight disturbance, such as raking, in order to settle just below the
surface of the sand.
Take Home Points
Fig. 2: This figure depicts the mean total
number of spikelets produced per plot in June of
2013.
Conclusions: As the statistics indicate, the
barrier treatment does not have a significant
effect on B. tectorum’s mean spikelet
production. However, B. tectorum in the
disturbed environment has the greatest spikelet
production of all of the conditions.
Effect of disturbance:
p=0.003
Dispersal barriers: NS
Disturbance and
dispersal barriers: NS
Effect of disturbance:
p=0.021
Dispersal barriers: NS
Disturbance and
dispersal barriers: NS
Fig. 3: The leftmost map depicts the population of
B. tectorum within the plots and along the three
transects that we set up in Cape Cod’s Duck
Harbor. The three panels following the map depict
the % plot cover of Ammophila breviligulata,
Artemisia campestris, and Hudsonia tomentosa,
respectively.
Conclusions: B. tectorum tends to grow in the
same plots as both Ammophila breviligulata and
Artemisia campestris, but tends to remain absent
from plots with Hudsonia tomentosa.
Are there certain types of vegetation that may contribute to B.
tectorum’s survival and thriving?
B. tectorum tends to grow in vegetation communities that lie at the interface of both dune and heath
communities, despite the fact that the species appears not to thrive in either system individually.
Fig. 5: These six graphs depict the % cover of
the six plants that seem to have the most
potential association with B. tectorum, based on
overall patterns we observed within the plots at
Cape Cod’s Duck Harbor. (Fig. 3)
The lines represent logistic regression fits.
Conclusions: The % plot cover of A.
breviligulata positively correlates with the
presence of B. tectorum, as does the % plot
cover of A. campestris. The % plot cover of H.
tomentosa, however, negatively correlates with
the presence of B. tectorum.
Take Home Points
Fig. 4: This figure depicts the similarity and dissimilarity
among plant communities within plots along the three
transects. Circles that are closer to each other are most
similar in both the species they contain and the overall
plot cover. The size of the circle represents the number of
B. tectorum spikelets found within a plot. (The larger the
circle, the more spikelets found in the plot.)
Conclusions: There are many large circles within a close
proximity of each other which indicates that B. tectorum
presence is associated with specific plant communities.
References
A. Knapp, Paul. “Cheatgrass (Bromus tectorum L) dominance in the Great Basin Dessert: History,
persistence, and influences to human activities.” Global Environmental Change 6.1 (1996): 37-52.
Duck Harbor
Research Site
April 2013 Seedlings
AprilLogSeedlings(±1SE)
June 2013 Spikelets
JuneLogSpikelets(±1SE)
Tide-forecast.com
Discoverlife.org