Bio 104

Ecological Succession

May 6, 2010

        Looking at a photograph of the spruce trees behind my parents house taken in 1995 and comparing it to a photograph of the same trees taken only a week ago, it is easy to see the succession that has taken place over only a fifteen year span.  Gazing at the current picture it is obvious that the trees have defoliated, but why?  What could have caused this significant change?

        I believe the trees are in this condition due to parasites, such as gypsy moth caterpillars, using the trees as their host (from here on I will refer to them simply as caterpillars).  In my estimation it was roughly 1995, or possibly a few years prior, when the area encountered an atrocious infestation of these caterpillars.  Although their population has dwindled significantly since then, they are still a predator to our trees.  The spruces have most likely survived as long as they have due to one important abiotic factor: temperature changes.  Northeast Pennsylvania experiences cold winters whose frigid temperatures aid in the destruction of the caterpillar eggs.  Additionally, it is not always warm in May, I can recall many years when it was snowing.  During these sporadic cold spurts, the larvae that have already hatched are killed due to the unusually cold temperatures.  Although the trees are weakened from the caterpillars, the winters allow them to have a small recuperation period.

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        Another abiotic factor having an effect on the spruces is that of sunlight.  During summer the sun is closer to the earth, it is hotter and the amount of sun is greater, as daylight savings allows for more hours of sunshine.  In spite of the fact of defoliation, looking between the two pictures you can see that the trees nevertheless continue to absorb the sunlight and thus grow.  Unfortunately, the sunlight is also that which is allowing the caterpillars to flourish.  The third abiotic factor could possibly be the use of chemical pesticides, especially in 1995 when there was a ...

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