CalNat Yosemite – Day 4 (Forest Managment & Wildlife)

Our day began with a short lecture from a CalFire representative who spoke to us about the general role of fire in forest management in the Sierra Nevada.  California, as you may or may not know, has always had natural wildfires.  Before the state was urbanized, the fires would start by lighting and burn until they hit bare soil, a water source, or when it rained.  But (for the most part) these wildfires were not the raging waves of flames that we see on the news (or in our neighborhoods) today.

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The main reason many wildfires are so much more intense today is that we began suppressing fires about 150 years ago.  This has caused the forests to become much more dense.  Denser forests mean that there is more fuel to burn.  Wildfires have a way of naturally cleaning out debris and thinning forests over time, so that each fire is relatively mild.  However, the suppression of wildfires has resulted in an increase of fuel to burn.  Thus, today, when a fire starts, it burns hot and long.

This led us into discussions about whether fire is “good” or “bad” and also what makes a “healthy” forest.  For many, seeing a thick forest is what we think of as “healthy” – because it is the type of forest we are used to and the type we aesthetically want to see.  However, in many cases, this density of trees may not actually be what is “healthiest” for a forest.  This inability to see the forest for the dense amount of trees may actually be indicative of a forest that needs to be healed – perhaps healed by fire.

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We continued this discussion outside on a hike along the Chowchilla Mountain Road where we worked a bit more at tree identification and examined areas that had been burned, and the type of pioneer species that come up after a burn.  A seedbed lays dormant in the soils of the Sierra, and these seeds are allowed to bloom after a fire before the competitor species that had been growing above, taking up all the sunlight and nutrients, are now gone.  On the hike, this was seen in a patch of ponderosa pine (Pinus ponderosa) saplings.  Life coming from death.

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We also looked at some evidence of bark beetle destruction.  The drought stresses the pine trees, and when the trees are stressed they produce terpene, which basically says to the beetle “I’m stressed out and weakened, so I’m an easy meal.” So, beetles come along to drill into the tree and lay eggs – LOTS of eggs.  Since the tree’s primary mode of defense against beetles is pitch (i.e. a sap-like substance trees produce to push out intruders like beetles), and pitch is dependent on water, the pines can’t defend themselves very well in a drought.  Once one beetle drills in to lay their eggs, they emit a pheromone that alerts other beetles to come and do the same in this same tree.  The tree slowly dies as the eggs hatch and the beetles eat their way out of the tree.  Again, life coming from death.

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ponderosa pine dying from bark beetle infestation

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bark beetle exit holes

After lunch we had a talk from a representative of the U.S. Geological Survey.  He spoke to us about meadows in Yosemite and the wildlife research he is engaged in regarding the Yosemite Toad (Anaxyrus canorus).  This was pretty exciting for me because I worked on a frog crew all summer, and the frog I was collecting data on (Sierra Nevada Yellow-legged Frog – Rana sierrae) came up a few times in the talk, so I was able to add some comments to the discussion from my own field experience.  It was also interesting to compare the methods of studying the toad and the environmental concerns for the toad to my experience working with the Rana sierrae.  For example, invasive trout are a primary cause of the Rana sierrae‘s status as an endangered species, but trout don’t eat the toad due to a gland that emits a toxin as a mode of defense – the trout spit the toad out but eat the frog who is without this gland.  By the way, the general way to distinguish a toad from a frog is that a toad has bumpy, dry skin and a frog has smooth, wet skin.

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We ended the day with a little field journal time and taking photos to add to our iNaturalist accounts.  More than a little excited for a full day of birding tomorrow!

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