Canaries were first used in coal mines in 1896 to warn miners of toxic gases. Their use continued until the 20th century. One little bird was enough to signal what was going on in their environment.
Plants can be canaries too. Researchers have shown that deer browsing can affect the abundance, flowering, and growth of some plant species. Monitoring these species could signal how deer are affecting the environment. Like the canary, they can be ‘indicators.’
One such species, Indian cucumber-root (Medeola virginiana), is a very good candidate as an indicator in Pennsylvania. This species occurs throughout the state and I have found it in every state forest where I have looked for it.
Indian cucumber-root is aptly named as the root (a small bulb) tastes like a cucumber with the crunch of a radish! Most roots are the size of your thumbnail. The photo below is the root of an exceptional plant.
The plant arises from the forest floor in a thin stalk that supports a whorl of leaves. If the plant is particularly healthy – and old! – the stalk will continue up to another whorl of leaves, in which the flowers are centered.
Most plants are maybe 6” tall, but they can grow up to 2 feet.
Their seeds don’t go very far, and the plant probably propagates more via the roots. New plants will arise from the rhizomes of the parent plant the following year.
Indian cucumber-root is a perennial and a preferred food of deer who consume the stem and even the root.
The thinking is that when these plants get eaten by deer:
- They don’t grow as tall
- They are less likely to flower
- And they will be less abundant
It’s like chips in my house. When I am home, their abundance is lower and the bags don’t reproduce as much. Therefore, if you come over and can’t find any chips, then you know I am home.
Monitoring some combination of abundance, flowering, and height might give you insights into the effects of deer on your forest plant community. Sounds promising. But could other factors influence the abundance, flowering, and growth of this species?
Danielle Begley-Miller, a PhD student on the project, set up an experiment to see. She fenced some plots (excluded deer). Some plots were limed (to improve soil conditions – increase Ca and Mg, increase pH, and reduce the cycling of metals like Mn and Al). Some plots were herbicided to remove competing vegetation. There were numerous plots across Bald Eagle and Rothrock state forests that received some, none, or all of these treatments.
It’s called a completely cross-classified design that included controls (nothing was done) and a series of plots that received every possible combination of treatments.
What did she learn? Well, it depends on the canary and the chip.
First, fenced plots ended up with more plants. Deer eat Indian cucumber-root. However, when we began the study, WHERE we found plants depended on the amount of manganese (Mn) in the soil.
Manganese in small amounts is an essential metal needed for cellular processes in all living things. However, at high levels it is toxic. When soils are acidic and manganese is present, it becomes more available to plants at levels that may be toxic.
Second, applying herbicide appeared to have no effect on Indian cucumber-root.
Third, flowering was NOT related to whether a plot was fenced. It was related to two things: soil pH and Mn.
Yeah, it gets more complicated.
- When soil pH was low (acidic) and there was lots of Mn in the soil, adding lime relieved the stress of Mn poisoning and more plants flowered.
- When soil pH was low and there was little Mn available, flowering DECREASED because there was no longer enough Mn available! Remember, Mn is essential but we don’t need much.
What does this all mean? Well, it adds a wrinkle if you want to monitor Indian cucumber-root to assess deer herbivory. The absence of Indian cucumber-root may simply be due to soil chemistry. It’s flowering also may be due to soil chemistry. It’s abundance also may be due to soil chemistry, and Mn-stressed plants may not withstand as much deer browsing.
So this canary may not be a good sentinel and the abundance of chips at my house may have more to do with the number of times my spouse goes to the grocery store or her desire for me to eat fewer cheese puffs.
Danielle’s experiment also shows that applying lime everywhere to address pH may not be wise – because it could cause a problem for some plant species depending on the soil conditions. This isn’t really surprising. It’s recommended farmers do a soil test before they add fertilizer to their fields.
Focusing on one thing without considering the multitude of other possible causes makes things look simple when they are anything but.
-Duane Diefenbach
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Feature Image by Alois Grundner from Pixabay