By Erin Hayes-Pontius
To add to the seemingly never-ending list of proxies paleoecologists use to study the past, here’s another one: trees. If you have been following this blog for a little while, you probably read about what pollen can tell us, but using the trees themselves, rather than their pollen, can tell an entirely different story. Studying the pollen that accumulates in lake sediments has the distinct advantage of providing a record that is as old as the lake itself, which can sometimes be up to millions of years old. However, because of how long it takes lake sediments to accumulate, we cannot always be very confident of the date a particular layer of sediment represents. In contrast, trees generally provide a much shorter record than pollen, but because of their annual rings, give us an annual record to work with.
A device used to extract thin cores from trees (Wikimedia Commons: Beentree 2006).
We are all familiar with the images. The barren landscape. Brown, dead vegetation spanning as far as the eye can see. Lakes and rivers shrinking in size, their relict banks cracked and dry.
These dryspells or droughts can last from days to years and they occur when a region receives below average precipitation. Droughts are generally said to arise from insufficient precipitation amounts over an extended period of time. This shortage in precipitation occurs typically in one season or more, and results in a water shortage for an environmental region. The impact of the drought arises from the interaction between the natural events (less precipitation than expected) and the demand on the water supply (both from the environment and humans), which can exacerbate the impacts of the drought. Because of these factors that can influence the magnitude of the drought, they need to be taken into consideration when working to define a drought (National Drought and Mitigation Center). Frequently the definitions can vary from location to location as certain areas are less adapted to low water conditions than others. But it can also dependent on timing. For example, in the desert a month without rain doesn’t have the same effect as it would in the rainforest. However, if the month without rain in the desert came during the period designated as the rainy season, the impacts would be drastically different.
Depending on how long these dryspells last there can be a huge impact on the ecosystem and economies associated with them. One prime example is the Dust Bowl. Continue reading