Lack of training is a key reason why tree core samples become inaccurate. Differences in controls also might contribute to the accuracy of the sampling. Core sampling only shows the health of the tree that is above ground. The sampling does not show what is in the ground where the tree stands unless the scientist takes samples in the two locations.
Lack of Training
Tree sampling is a specialized part of forestry. It requires special training by the researcher. The scientist uses a unique instrument called an increment borer, which the scientist inserts into the tree trunk at chest level or stump level. The instrument determines the age and health of the tree without cutting it down.
The increment borer
The increment borer can become inaccurate if not given proper maintenance. If not oiled properly, the auger will not go into the tree, so the results will not clearly show the core but something near the core. If the borer is not sharp enough, the same result will occur.
Inaccurate reading of the rings
People who read the rings are dendrochronologists. These folks can make mistakes in reading the rings. Insects, temperature, the falling of a nearby tree all contribute to how the rings grow. One tree can read one way, and a tree that is only a few feet away can read differently because of the amount of light that it receives.
If the tree grew in any area recently exposed to traffic, the results will not show that until years later. Browning or yellowing of the leaves in spring or summer and brittle branches are the first signs of sickness caused by pollution.
Older trees may not show the same signs as a newly planted grove of trees because they have not grown in that area for very long. Trees absorb substances from the air, soil, and the water that they consume.
The depth and the location
To get accurate results, numerous samples of different areas of the tree also contribute. If scientists test just one area, like the upper trunk, then the result may differ from the lower or root sample. The accuracy depends on looking at the entire tree to determine its health.
Accuracy is a matter of education, the quality of the increment borer and the natural conditions of the grove where the tree stands and each individual tree. Not taking as many samples of the area distorts the results, making them inaccurate.