For a plant of its low biomass,
mistletoe seemingly has a disproportionate ecosystem effect due to its
parasitic nature (although it has not been classified as a keystone species).
Habitat
Mistletoe often creates
favorable habitats and nesting sites for bird and small mammals due to how it
alters the growth form of its host by making highly branched structures. Some
studies have shown that bird species richness is often higher in areas of
mistletoe infection, partly due to the snags that they cause (Bennetts, 1996).
Furthermore, some bird species show strong preference for mistletoe infected
conifers because nest predation is frequently reduced (Cooney, 2008). Even
Washington’s threatened Western Grey Squirrel shows heavy preference for
mistletoe infected trees for nesting in the absence of oak cavities (Gregory,
2010).
Tree Mortality and Stress
Despite the amount of
high quality habitat that mistletoe creates, many people consider it a pest; it
frequently induces reduced crown height, reduced seed production, and mortality
in its host (Bennetts, 1996). Clearly, this is due to mistletoe’s parasitic
nature. Besides stealing sugars and nutrients from its host, it gains water by
linking its xylem directly to the host xylem, and maintains a higher
evapotranspiration rate to create a difference in water potential between the
mistletoe and the host, even if the host is suffering a moderate water deficit
(Hawksworth, 1996). This is likely to have profound consequences on the mortality of host trees as climate change will likely result in higher levels of water stress on trees around the world (Phillips et al., 2009).
The resulting tree mortality will likely have its own slew of affects on ecosystems. One of the larger implications that one might expect is a change in nutrient cycling; more dead trees might result in higher levels of decomposition when combined with a rising global temperature average, reducing the amount of carbon that a Pacific Northwest forest might be able to sequester. When this happens on such large scales, it can significantly affect other feedback cycles, such as carbon concentrations in the atmosphere (Chaplin III et al., 2008).
The resulting tree mortality will likely have its own slew of affects on ecosystems. One of the larger implications that one might expect is a change in nutrient cycling; more dead trees might result in higher levels of decomposition when combined with a rising global temperature average, reducing the amount of carbon that a Pacific Northwest forest might be able to sequester. When this happens on such large scales, it can significantly affect other feedback cycles, such as carbon concentrations in the atmosphere (Chaplin III et al., 2008).
Example of heavy Mistletoe infection on conifers. Forestryimages.org
I never knew mistletoe was a parasite. Good explanation of how it can impact both producers and consumers within an ecosystem.
ReplyDeleteThough I may be wrong, I'm feeling you've done some pretty detailed research on mistletoe :P Your in depth introduction and explanation of mistletoes are detailed yet well summarized so that its easy to read and understand. One minor suggestions I can give you is to add some labels/explanations on your figure on this page as I believe some people outside of class might get confused on where the Mistletoe infection is at. Keep up with the good work!!
ReplyDeleteReally good and in depth explanations. I am surprised how interesting mistletoe can be and I didn't know that it was a parasite either. Excellent page.
ReplyDelete