Why do we study tree rings and what do they tell us?

Wednesday 17 January 2018

Besides understanding how climate changed in the past, tree rings can also help us in studying monthly flows of rivers

                    Tree rings hold a wealth of information about not only a tree’s past but also that of the ecosystem in which it lives. Credit: Don DeBold / Flickr
Tree rings hold a wealth of information about not only a tree’s past but also that of the ecosystem in which it lives. Credit: Don DeBold / Flickr

Tree rings are the informers of a tree’s history. They hold a wealth of information about not only a tree’s past but also that of the ecosystem in which it lives. Environmental conditions of the past can be remodeled by studying the tree rings of the species of trees growing in a particular region.

Tree rings are layers of growth that a tree acquires in one year. The colour of old wood is always darker than a comparatively newer wood which creates a contrasting pattern of rings year on year. In the years of good growth, characterised by a healthy supply of resources, the ring is thick. It is thin when the ecosystem has dearth of resources.

How are tree rings studied?

When researchers, who study tree rings, trek to an area of interest, at first they ensure that the area has not been altered by humans through activities like grazing or felling of trees, according to the National Oceanic and Atmospheric Administration (NOAA). After that, they select trees for their studies on the basis of age and location. While old trees are the best for knowing about the climate of the distant past, location is chosen on the basis of sensitivity to environmental conditions. Usually, trees far away from water sources are chosen as they would be most sensitive to the moisture in local atmosphere.

As a first step to studying tree rings, scientists cork the tree to its core without hurting it in anyway. They use a hollow drill bit to core the tree up to its centre which takes a considerable amount of time. Now this core is pulled out to examine patterns of rings and study them in detail under a microscope. The growth history on both living and dead trees can be known by studying these patterns closely.

In a recent development, researchers at the Utah State University have found use for these rings in studying monthly flows of rivers over the past 600 years. Their findings have been published in the journal Journal of Hydrology on January 6, 2018.

"By linking tree rings and flow during the past 100 years when we have recorded observations, we can use trees as a tool for measuring flow long before there were gauges on the rivers," James Stagge, the lead researcher of the project told the website Phys.org.

"Our study takes this one step further and uses different tree species and locations to reconstruct monthly flow, rather than annual flow", he added.

This research can lead the way for formulation of better water management policies in the present and, what could possibly be, a water-scarce future. Based on annual data, the scientists reconstructed a monthly database of stream flow of rivers. This was done for three rivers—Logan, Bear and Weber. For Logan, the monthly data was reconstructed up to 1605, while for Bear and Weber rivers it was done as far as back as 1400. This monthly data informs us about the seasonal changes in the flow of rivers. This, in turn, offers an insight into the impact that rivers can have on local environment, agriculture and life in general. This data can also be projected into the future to know how these rivers would behave and what communities would have to do to use their water wisely.

"It's the seasonality that determines drought, how reservoirs fill, and when there are shortages. Now that we have this method, we can start looking at what major droughts over the past 600 years would mean for today's water supply," Stagge concludes.

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