State of the forest, 2016

General ecology (EES-152) students have finished resurveying a portion of the Lehigh Experimental Forest, with the goal of assessing changes in tree growth, mortality, and recruitment since 2013. A total of 690 trees were measured from across the forest, representing more than a 1/4 of all trees. In the three years since 2013, 70 of these 690 trees have died and only three new trees have established in the study area.  Data for the dominant tree species are shown in the plot below.

screen-shot-2016-09-27-at-3-48-51-pm

Tree abundance, mortality, recruitment, and growth rates in the Lehigh University Experimental Forest, 2013-2016. Relative frequency data are from 2013 (M. Spicer, MS thesis 2014) and indicate the percent of each species present (based on a total of 690 trees). Total mortality and recruitment across the time period are shown as percentages. The average increase in basal area of individuals of each species is shown, with the mean value for all species indicated with the vertical dashed line. Total change in basal area for each species, incorporating mortality losses and basal-area gains, is also shown.

We will use these data to discuss the processes controlling forest dynamics as the semester progresses.  However, for now, students should answer the following questions:

  1. The dbh measurements were converted into estimates of area, assuming that each tree was a perfect circle in cross-section. Why do you think basal area was used to compare growth rates among the different species? Why was this expressed as the average change in basal area per tree? What factors might have caused the observed differences in radial growth among species?
  2. What does the pattern of mortality and recruitment suggest about the future of the Lehigh Experimental Forest? What factors might have caused the differences in mortality among species during these two years? What factors might be contributing to the lack of new tree recruitment in the forest?
  3. Assuming the rates of total tree recruitment and mortality are representative of future years, when will there be no trees left in this forest?  In 2013, there were ~2000 trees in the forest. Show your work and describe how you arrived at your estimate.  Do you think it is likely that the trees will really be gone by this time?  Why or why not?
  4. Which species had both very high mortality and very low growth during this time period? Do some research on current threats to this particular species, and summarize your research in a short paragraph.

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Posted on September 27, 2016, in Ecology (EES-152), Teaching and tagged , , , , , . Bookmark the permalink. Leave a comment.

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