Download Gasik, Novak Groshong. Does Ivy Growth in Riverview Natural Area

Rayna Gasik
Drew Groshong
Fran Novak
12/08/2013
Does Ivy Growth in Riverview Natural Area Affect Soil Nutrients Required for
Miner’s Lettuce to Grow?
Introduction
The effects of non-native species are widely misunderstood and to some extent,
unknown, throughout the globe. Few newly introduced species are able to survive, and
many of those that do survive appear to live innocuously alongside natives. However,
some non-native species become invasive, wreaking havoc on native ecosystems. This
damage to ecosystem function puts native species, and local economies at risk. Humans
have altered ecosystems by both intentionally and unintentionally introducing species.
For example, fire clearing for agricultural purposes can change the way an entire
ecosystem functions by allowing one species (grass) to dominate over others (Mack et al
2000).
English Ivy, once unknown to the Pacific Coast of the United States is now
common in many forested areas. It was originally planted as a decorative climber in
home gardens, however it spread quickly into natural habitats after birds consumed the
berries and spread the seeds. Ivy’s hardiness in gardening also makes it a powerful
adversary for eradication. Many have voiced concerns over ivy’s effect on native plants,
diversity and the surrounding habitat (Bierzychudek 2013).
However, few studies on the effects of ivy in the Pacific Northwest have taken
place. Biggerstaff has studied ivy in the Southeastern US, finding that ivy did have an
effect on germination rate for Coreopsis lanceolata seeds, but only when the ivy was
physically present. No difference between ivy soil or non ivy soil was detected in the
germination rate (Biggerstaff 2007). Dlugosch performed one of the only studies on ivy
in Pacific Northwest, in which areas with English Ivy had a lower percent cover of native
species due to a smaller presence of native bushes (Dlugosch 2005). Though neither
study confirmed that ivy was detrimental to the surrounding environment, both indicated
that ivy could have a larger impact than was previously thought. Further knowledge
concerning this subject will be valuable because complete ivy eradication will be both
labor and cost intensive.
Determining the effect an invader has on primary producers is key to
understanding its impact on the entire ecosystem. Soil nutrients are vital to the growth
and function of primary producers. Plants require a myriad of nutrients, however the ones
that most often limit growth are nitrogen and phosphorous. Ivy differs in many ways
from native plant species, so it makes sense to question whether ivy requires different
concentrations of soil nutrients than species which previously inhabited the area. For
example, due to its nutrient requirements, ivy might deplete nitrogen levels in the soil,
reducing availability to native plants.
In our study, we are measuring the effect of English Ivy on soil nutrients by
comparing the growth of the native plant species, Miner’s Lettuce (Claytonia Perfoliata)
in ivy and non ivy soils. This study will determine if ivy limits Miner’s Lettuce growth
through competition for soil nutrients. We are measuring the biomass and root/shoot ratio
as well as the number of seeds germinated over a six-week study. We have collected soil
samples from ten plots, five of which currently have ivy growth and five of which have
not had ivy present for two years, all in the Riverview Natural Area. With ample sunlight
and water, we hypothesize that there will be a noticeable difference in the growth
between the Miner’s Lettuce in soil from plots containing ivy and from plots without ivy.
Though we do not have the funding necessary to measure the nutrients within the soil, we
believe that the germination, biomass and root/shoot ratio will be sufficient indicators for
our study. High biomass and germinations indicate a healthy plant and a low root/shoot
ratio indicates that nutrients are readily available from the soil. We hope that this study
will accurately depict English Ivy’s effect on native plant species and determine if
English Ivy limits their growth.
Methods
On September 28th 2013, we collected soil samples from ten different plots in
Riverview Natural Area (RVNA), Riverview Cemetery and the Lewis & Clark campus.
There were five plots in RVNA, which is adjacent to the Lewis & Clark campus, in
which the ivy was removed two years prior. The five plots with ivy were on the Lewis &
Clark campus or on the Riverview Cemetery, which is also adjacent to the Lewis & Clark
campus. We used a greenhouse on the Lewis & Clark campus to keep the conditions (ie
temperature, sunlight, water, etc.) for each of the different pots as uniform as possible. In
each of the plots, we collected three samples. We divided each plot in to fifty 1m x 1m
subplots and then we used randomization to select three for each plot. At each subplot we
used a hand shovel to dig about three inches deep to obtain a small amount of dirt and
placed it in a plastic bag. For each plot, we mixed the samples of the three subplots in the
same plastic bag. After collecting all thirty samples, we took all ten plastic bags into the
greenhouse where we removed some soil, sifted it through a sieve to remove plant
material and filled each pot to the same level to make sure each had roughly the same
amount of dirt. We then added enough water to moisten the soil before we planted four
seeds of Miner’s Lettuce (Claytonia perfoliata) in each pot. After that we used
randomization to place the pots in the greenhouse.
Every 3-4 days, one of us would come in, mark all of the newly germinated seeds with
toothpicks, count and record the germination data and then water the plants. The amount
of water added to the plants was different each day but every plant would receive the
same amount of water as the rest on that given day.
After 5 weeks, we removed the plants from the soil in order to weigh them. To do this,
we first had to remove both soil and plant from the pot and wash off all of the dirt.
Finally, we separated the roots and shoots and placed them in separate paper bags labeled
with the sample number and either “root” or “shoot.” All of these bags were then taken
back to the lab and placed in a dryer, which was set at 60°C, for 48 hours, which is
relatively a large amount of time, in order to attempt to remove all of the water content
from the plants so we would only be measuring the biomass of each root and shoot.
When weighing the plants we placed a tray on the balance, zeroed out the balance and
then poured the contents of one of the bags into a tray. This reading was then recorded in
a table with its sample number and identity of either “root” or “shoot.” The contents were
then poured back in the bag, and the bag was placed back in the dryer. This method was
repeated for all of the bags. After leaving the plants in the dryer for another two hours,
we weighed all of the plants again using the same method as before. We did this in order
to ensure that the plants were completely dry and we were only measuring biomass.
Because all of the masses were the same as before, we knew they were completely dry.
Results
Our results did not support our hypothesis. The difference between the total
number of plants that germinated and survived at the end of the study in the two soil
types was only by one plant, so it was insignificant enough that further analysis was not
necessary. The mean biomass per plant per pot (Fig. 1) was 6% higher in ivy absent soil
but differences were not found to be significant (t-test, dif= .0009, t=.184, p=.855). The
mean root/shoot ratio (Fig. 2) was 40% higher for plants grown in soil where ivy was
absent than present; this test was not statistically significant (t-test, dif=.218, t=1.01,
p=.322).
Figure 1. Averages of Biomass per plant per pot in ivy and non ivy soil with two standard
errors (95% confidence)
Figure 2. Averages of root to shoot ratios in ivy and non ivy soil with two standard errors
(95% confidence)
Discussion
Upon analysis of our data, we can conclude that our study did not support our
hypothesis. Though the graph of root/shoot ratio appears to show a large difference of
forty percent higher in ivy present pots, a statistical analysis determined that this
difference is insignificant. Also, the mean biomass per plant per pot was insignificant
upon statistical analysis. We did not feel that it was necessary to include a graph of
plants that had germinated and survived because the difference between the soil types
was only by one plant. Overall, this data would support the null hypothesis that ivy’s
presence does not affect soil quality because a difference in the success of Miner’s
Lettuce was not observed between pots where ivy was present and pots were ivy was
absent. Because our study only measured success of Miner’s Lettuce in soil that ivy had
grown in previously compared to soil that did not have ivy growing in it, we were not
measuring the direct effect of ivy on Miner’s Lettuce but rather its effect on soil
nutrients. However, we feel that we can conclude that ivy’s presence did not have an
effect on soil quality and that Miner’s Lettuce is not competing with ivy for soil
nutrients.
Since we concluded that ivy was not responsible for variation amongst the
different plots, other factors must have been influencing Miner’s Lettuce growth. For
instance, there could be differences in soil quality in the different sampling locations,
unrelated to ivy’s presence or absence. We observed that some of the sites had very
claylike soil while others had more fine soil, so it is likely that this affected plant growth.
Germination also depends largely on the environment inside the individual seed, more
than the surrounding environment, so seed germination is also highly variable. Other
variation, such as varied levels of sun exposure could have contributed to our large
standard error bars, though randomization should have checked for variation causing
differences between the two different categories. A few of our pots did experience some
weed growth, but the amount of weeds was small enough that it was unlikely to have
affected overall biomass and caused much variation.
There were a few factors in our experimental method which could also contribute
to the variation we saw. For example, we kept the soil samples from each of the
individual plots separate instead of mixing together all samples of ivy soil and all of non
ivy soil. If we had mixed the soil, there would have been fewer differences in the soil
between plots within each category and variation would be smaller. Another possible
source of variation was that different people washed the plants in order to obtain the
biomass of roots and shoots. Two different washers could cause an inconsistency in how
much of the soil was washed from the plants and thus cause variation in biomass
measured.
The largest issue with our study was that the time period of six weeks was not
long enough to assert whether or not ivy presence was affecting soil quality. In this time,
our plants did not gain a large enough biomass to really see the differences between plots.
It is also likely that, due to their small biomass, the plants did not have enough time to
run out of nutrients. Given this, a study over 6 months instead of 6 weeks would yield
more comprehensive results. If longer studies produce similar results, we could more
confidently accept the null hypothesis and turn to other possibilities for ivy’s effect on
Miner’s Lettuce. For example, if we know that soil nutrients are not a factor for
competition, we could do a field study to see other ways ivy might compete with Miner’s
Lettuce, such as limiting sunlight. We could also improve the study by sampling more
sites, which would reduce the effect variation had on our results. Growing plants in the
soil is just one way of measuring soil quality. Further studies would benefit from
chemical analysis of the soil and would likely give more definite results since plant
growth is determined many different factors.
Although our study could be improved with more sampling sites and an extended time
period, we have shown that it is unlikely that ivy depletes the soils nutrients enough to
negatively affect Miner’s Lettuce. Similar to the other studies that have been performed
on ivy, we are unable to conclude that ivy’s presence has an effect on the
environment. However, in order to conclude this, further experiments must be
performed. Knowing the ways in which ivy does not affect the environment allows us to
explore other possibilities of ivy’s influence. Ivy has a large presence in the Pacific
Northwest and any impacts, even subtle ones, could significantly alter the surrounding
environment and influence future conservation methods. Ivy is an invasive species and as
such, the possibility that it will outcompete its native counterparts should make it an
important topic for further study.
Acknowledgements
We would like to thank Professor Bierzychudek for assisting us with SPSS difficulties
and for guiding us throughout the study. We would also like to thank our TAs Rebecca
Kidder and Ben Hanson for teaching us procedure in the greenhouse as well as giving us
helpful input on our project. We would like to thank Riverview Natural Area for allowing
us to take soil samples from their property.
Literature Cited
Bierzychudek, G.Binford, W. McLennan, and P. Kennedy. 2013. Laboratory Manual for
Bio 141,
Lewis and Clark College
Biggerstaff, M.S. and C. Beck 2007. Effects of English Ivy (hedera helix) on seed bank
formation and germination. American Midland Naturalist 158 (1): 206-220
Dlugosch, K.M. 2005. Understory community changes associated with English Ivy
invasions in
Seattle’s urban parks. Northwest Science 79 (1): 52-59.
Mack, R.N.,D. Simberloff, W.M Lonsdale, H. Evans, M. Clout, and F. Bazzaz. 200.
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