Introduction Page 15A


More short-term research

Two stoneflies

 

How far can insects fly?

Scientists examining stoneflies, a type of insect that lives part of its life (as a nymph) in streams and part of its life (as an adult) in the forest, have been trying to answer this question.

These scientists drip a harmless chemical called a "label" (containing a rare isotope of nitrogen) into a small section of a stream, which the insects then eat. After the insects leave the stream, or "emerge," scientists can later catch them in the forest.

When they put any insect they catch in a special machine (called a mass spectrometer), they can look look to see if it contains this label. If the insect contains the label, then the scientists know it came from that same small section of stream. If they caught an insect 300 meters from that section of stream, and the insect contains the label, then the insect flew at least 300 meters. As with birds, knowing how far insects can fly in a lifetime is useful information for scientists.

Unusual Weather

So what happens after a big ice storms hits a forest? Beginning in early 1998 we had a chance to answer just that question. In January of that year a storm containing rain and freezing temperatures coated every leaf, twig, needle, branch and trunk of every tree in the HBEF with up to 3 or 4 centimeters of ice. The ice storm was devastating regionally (it affected the entire northeastern US), but only the HBEF had existing long-term plots useful for comparing damage, measuring influences, and following recovery.
After the ice storm

The sheer weight of all of this ice completely bent over small trees and broke off twigs, branches, and in many cases, entire tree crowns. Even three years later evidence of this ice storm - large gaps in the forest canopy, small trees that are still bent over, and large downed limbs - is still visible in many sections of the forest.

The response of the forest ecosystem to the ice storm was dictated mostly by the loss of the forest canopy: in the first two years after the ice storm the forest had only about half as many leaves as it did before the storm. Because the trees needed smaller amounts of nutrients (like nitrogen) from the soil to build their leaves, the extra nutrients in the soil were washed into streams and lost from the ecosystem.

Only because scientists had been carefully measuring the forest before the ice storm were they able to conclude that this response occurred. Natural events like the 1998 ice storm probably have played an important role in shaping the composition of the forest and the fertility of the soil in most of the northeastern US.

Roots & Trees

And how about tree roots? We have all seen large, woody roots running from the base of a tree into the ground. These large roots help the tree stand up and anchor it in place. But did you know that trees produce huge numbers of tiny roots that scientists call "fine roots"? Fine roots are less than 1 mm in diameter. Under any square meter of the ground surface at the HBEF there are over 25 kilometers of these fine roots!

Fine roots perform the critical job of absorbing water and nutrients for the tree, and a large amount of a tree's energy goes into producing these tiny roots. At the HBEF, scientists study fine roots to try to answer questions like:
Click here to watch these roots "grow."

  • How much fine root living matter is present?

  • How long do fine roots live?

  • When do fine roots grow and die?

Can you think of reasons scientists might be interested in these questions?

Researchers need special methods to study fine roots because they are so small and located underground. One popular method uses photography to track root growth.

More fine roots

When using this method, researchers permanently install clear plastic tubes into the ground. These tubes are called "minirhizotrons," are about 7 cm in diameter, and extend about 1 meter into the soil. Eventually fine roots will grow around these tubes, much like they would around other underground obstacles (for example, rocks).

Researchers can then photograph these roots by lowering a tiny camera into the tube. By returning at regular intervals and taking photographs at the same locations in each tube, scientists can record how the roots are growing over time. The advantage of this method is that the roots aren't disturbed very much. Above and to the right is an underground photograph from one of these tubes. Click on the image to see the roots "grow"!

The picture to the left shows how densely fine roots can grow in the forest floor of a northern hardwood forest. Many of these root tips have a symbiotic relationship with fungi, which increases the tree's ability to absorb nutrients and water. This relationship is called a mycorrhiza. Did you know that most plants in the world form similar symbiotic relationships with fungi?


What else? Scientists have also studied:

  • What types of birds are present in the forest, and where they live
  • Where white-tailed deer live and why
  • How many and what kind of snails are present in different parts of the forest
  • How fast trees can grow, and whether or not they're growing slower than we might expect
  • What happens to forest soils that freeze during low-snow years
  • And literally hundreds of other questions

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