Undisturbed Deforested Recovering 90 - Watershed 2 -Watershed 6 60 30 1963–64 1966–67 1969–70 1972–73 Year Annual Net Export (Kg/ha) Compiled by the authors using data from F. H. Bormann and Gene Likens.
Consider the graph to the right that compares the losses
of calcium from the experimental and control sites in the
Hubbard Brook Experimental Forest (Core Case Study).
Note that this figure is very similar to Figure 2.5, which
compares loss of nitrates from the two sites. After studying this graph, answer these questions.
1. In what year did the loss of calcium from the experimental site begin a sharp increase? In what year did
it peak? In what year did it level off?
2. In what year were the calcium losses from the two
sites closest together? In the span of time between
1963 and 1972, did they ever get that close again?
3. Does this graph support the hypothesis that cutting
the trees from a forested area causes the area to lose
nutrients more quickly than leaving the trees in
place? Explain.
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