By Irene Shonle, Gilpin County
Noxious weeds pose a growing threat to
our general ecosystem. These non-native
plants have a competitive advantage over our native plants because of the
lack of insects and diseases that control them in their native countries, and they
are spreading rapidly on both private and public lands.
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| Oxeye daisy monoculture |
The reason this is such a problem is
that these new invaders do not have an evolutionary history with all of the
rest of the plants, insects, birds, and other wildlife that depend on our
ecosystem. The introduction and
establishment of invasive plants into new habitats in which they have not coevolved
with the native organisms have been identified as a major threat to
biodiversity and ecosystem structure and function (Bezemer et al. Annual Review
of Entomology 2013).
Plants are the bottom of the food
chain, with insects and a variety of mammals eating the plants directly, and
then other species such as birds and mountain lions eating the insects and
mammals. Non-native plants such as noxious weeds don’t provide that bottom rung
of the food chain. This is because 90% of herbivorous (plant-eating) insects
are fairly host-specific and may not recognize unfamiliar exotic plants as food. Many mammals also may hesitate at eating new
plants. When weeds crowd out the familiar native plants, the entire food chain
is weakened.
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| This hummingbird moth caterpillar is eating native fireweed |
Examples of our ecosystems collapsing
due to this weakening are coming at an alarming pace. A recent paper (Sánchez-Bayo
et al., Biological Conservation 2019) presented a comprehensive review of 73
historical reports of insect declines from across the globe. More than 40% of
insect species are declining and a third are endangered, the analysis found. The
main drivers of species decline, according to the study, are (in order of
importance): “i) habitat loss, ii) pollution, iii) biological factors,
including pathogens and introduced species; and iv) climate change.” The effect of noxious weeds can be seen twice
here, once in habitat loss, and once in the introduced species bucket.
Additionally, noxious weeds have the
potential to reduce the connectivity of native plant patches by forming large monocultures.
Wide swaths of noxious weeds could isolate suitable habitat patches, thereby
increasing the local extinction risk of native herbivores, pollinators, and
their natural enemies, since many insects fly only short distances and smaller
populations are more vulnerable to getting wiped out by natural disasters or
other events.
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| Large Canada thistle infestation |
Native pollinators are
critical for pollinating native plants (which brings future generations of
plants), and invasive weeds can disrupt their pollination. Several large analyses
have shown that invasive plants, on average, have a negative effect on the
visitation rates of pollinators and reproductive success of the native plants
around them (Morales and Traveset, Ecological Letters, 2009 and Montero-Castano
and Vila, Journal of Ecology, 2012).
So, these are all reasons why it is so
important to keep the populations of noxious weeds to a minimum on both private
and public land. Learn how to recognize
the noxious weeds that are in your area (here is a link to all the Noxious weeds in the State: https://www.colorado.gov/pacific/agconservation/noxious-weed-species
Then, take care of them on your property, and if you see weeds on public property, notify the appropriate land manager. This is an easy way we
can all contribute to the health of our ecosystems.
