Climate change and global warming is something we have all
heard of (regardless of whether or not you “believe it”…which we won’t get into
today). It is a reality that we all face, humans and animals and plants alike. We
know that climate change is causing more extreme weather patterns and events, general
global warming at unprecedented rates, and countless stressors on the natural
world.
However, today, as per usual with my blog, I will be focusing on two invasive
plants, kudzu and Japanese honeysuckle, and their relationships to climate
change.
Over the course of this blog, we have discussed numerous
impacts of kudzu and honeysuckle, most of which focused on smaller-scale
issues. But the time has come to dive into the heavy stuff, the issues that are
wide-reaching and, in my opinion, the most important in terms of the future. In
this post, I will be looking into the future at the good, the bad, and the ugly
that climate change may bring out of these invasive plants.
When considering impacts of climate change on invasive
species, I think Hellmann et al. (2008) put it best. Her three final points of impact
were: (1) the effects on the distribution of
invasive species, (2) how climate change may affect the impact of existing
invasive species, and (3) the “altered effectiveness of control strategies”. Here,
we will discuss these three points in relation to our favorite invasive plants,
kudzu and honeysuckle.
The Ugly: Increased invasive distribution
The idea of kudzu being able to expand its distribution
because of climate change goes back to the early 1990s, when the “southern
menace” was seen thriving in northern states such as Maryland, Delaware,
Pennsylvania, New Jersey and New York (Alderman, 1998). Kudzu had been long
established in the American south, so much so that it became somewhat entrenched
in the culture. As Figure 1 shows, there were businesses named after the plant.
This spread in distribution of kudzu is shown in Figure 2, with predicted range
in 2100, only 80 years from now. An article published in 2010 by Bradley et al.,
uses modeling to predict how climate change will increase the range of kudzu.
They concluded that under the most extreme climate change models (that is, what
will happen if nothing is done to slow it down), that kudzu will establish
itself north into Ohio, Pennsylvania, New York, and New England states within the
next 80 years.
Figure 1: Kudzu
Grill in Sandersville, Georgia. Image pulled from Alderman, 1998.
Figure 2: These
images depict current vs future (year 2100) range of kudzu. The future map is
modeled using predictive models of climate change by Bradley et al., 2010.
Similarly
to kudzu, honeysuckle is also expected to increase its reach across the country
because of global warming and the increased area of habitable environments. Both
these species’ ranges are controlled by minimum temperatures, that is how cold
it gets in the winter. But with this temperature rising globally, it stands to
reason the restrictions on these invasives ranges will be lifted. That being said,
honeysuckle will begin colonizing higher elevations than it had previously,
impacting the mountainous forested areas of the Appalachians (Lemke et al.,
2011). Not only will it expand vertically along mountains, but it is also
expected to spread northwest through Mississippi, Tennessee, Kentucky, and Arkansas,
and eastward towards Alabama and Virginia (Wang et al., 2012).
The Bad: Ecological & atmospheric impacts of this increased range
Now that we’ve talked about how these species may spread
into the future due to global warming, let’s talk about how these expansions may
(or may not) impact the ecosystems they are establishing in. A 2013 study by
Hickman and Lerdau showed that kudzu invasions in these “Mid-Atlantic” ecosystems
discusses above, could be briefly put off due to several factors such as length
of growing, soil type, and level of establishment. Invasives species have what
we call and “invasion front”, which is exactly what it sound like; this is the
area at which the species is only just beginning its establishment. Regions at
this invasion front are less susceptible to full establishment and are
therefore at least somewhat protected from full invasion like is what seen in
the south.
While direct impacts maybe withheld for some time in these
frontier regions, impacts of kudzu once fully established, goes far beyond just
killing the things it engulfs. A 2010 study by Hickman et al. showed that the
presence of kudzu drastically increases local nitric oxide emissions and
consequently increases ozone levels in these areas. Without getting too far in
the weeds, kudzu impacts the nitrogen cycle of an area by having incredibly
high rates of use of nitrogen (up to 500% higher than areas without kudzu!).
This increased impact on nitrogen in the soil means that emissions of nitric oxide
from the soil of invaded areas increases by 100%. To put it in perspective, the
authors of this paper, with their findings, suggest that this input of nitrogen
gas and consequent increased ozone should be included when thinking about
overall climate models. That is how big of an impact this one plant species can
have.
The Good: How does all this impact management into the
future?
So, I know the catch phrase in the title of this post is
backwards from the classic western film title. I did that because I like to end
on a positive, or at least as much of a positive as I can with this topic. With
everything that I talked about above, how in the world are we going to manage
something that seems to be the run-away train of plants.
Well, first let’s start with kudzu. There was a recent study
that showed that kudzu in and around New York City didn’t fair so well over
time. This study looked at 20 years of data and saw that on 32% of kudzu population
persisted around this area (Hoffberg & Mauricio, 2016). This suggests that
this plant may not be unstoppable after all. The northern states of invasion
concern that I talked about before, may not be facing as dire a situation as
the south as seen over the decades. It seems that kudzu may be reaching its
northern most limits, and these limits are not as heavily impacted as may have
been feared. With this being said, maybe it is possible to more easily manage
the northern populations and curb the environmental impacts of kudzu for these
areas.
As for honeysuckle, certain
management techniques have been proven successful at curbing the spread of this
species. The most effective way to reduce invasion is to convert land into
public land ownership (Wang et al., 2012). However, this is not a feasible option,
so this study suggest that replanting of native species and repeated fire
disturbance are techniques that reduce the impact and invasiveness of
honeysuckle.
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This
post hit on some very heavy issues that are on the mind of scientists and
civilians around the globe. While this blog focuses on a relatively narrow niche
of topics (literally only two invasive plant species here in the US), the topics
covered here can be generalized and applied to places all over the world in
different ways.
So I urge any readers of this
blog to not just focus on these two plants and how they impact your life, but
to take the issues discussed here and think about how it may impact areas and
peoples you are not connected to. Zooming into the small-scale that I did
during this blog is useful to get your mind around certain issues that seem
overwhelming otherwise. But keeping in mind a larger-scale perspective allows
us to just begin to understand the importance of these issues in terms of our whole
natural world.
Citations:
Alderman, D. H. (1998). The changing south: A vine for
postmodern times: An update on kudzu at the close of the twentieth century.
Southeastern Geographer, 38(2), 167-179.
Bradley, B. A., Wilcove, D. S., & Oppenheimer, M.
(2010). Climate change increases risk of plant invasion in the Eastern United
States. Biological Invasions, 12(6), 1855-1872.
Hellmann, J. J., Byers, J. E., Bierwagen, B. G., &
Dukes, J. S. (2008). Five potential consequences of climate change for invasive
species. Conservation biology, 22(3), 534-543.
Hickman, J. E., Wu, S., Mickley, L. J., & Lerdau, M. T.
(2010). Kudzu (Pueraria montana) invasion doubles emissions of nitric oxide and
increases ozone pollution. Proceedings of the National Academy of Sciences,
107(22), 10115-10119.
Hickman, J. E., & Lerdau, M. T. (2013). Biogeochemical
impacts of the northward expansion of kudzu under climate change: the
importance of ecological context. Ecosphere, 4(10), 1-15.
Hoffberg, S. L., & Mauricio, R. (2016). The persistence
of invasive populations of kudzu near the northern periphery of its range in
New York City determined from historical data1, 2. The Journal of the Torrey
Botanical Society, 143(4), 437-442.
Lemke, D., Hulme, P. E., Brown, J. A., & Tadesse, W.
(2011). Distribution modelling of Japanese honeysuckle (Lonicera japonica)
invasion in the Cumberland Plateau and Mountain Region, USA. Forest
Ecology and Management, 262(2), 139-149
Wang, H. H., Wonkka, C. L., Grant, W. E., &
Rogers, W. E. (2012). Potential range expansion of Japanese honeysuckle
(Lonicera japonica Thunb.) in southern US forestlands. Forests, 3(3), 573-590.
