Drought and famine occur in our country at least every 10 years. Establishing the trend and/or frequency of such natural environmental disasters is helpful in preparing for future prevention of similar catastrophes. Based on climate data obtained from trees, scientists say that drought has been plaguing our country since at least the 18th century.
"I have studied trees from mountains around Gondar. The study of the tree rings shows that drought has been there since 18th century" says Aster Gebrekristos,(PhD).
She says that the rings on the trees show that drought is not a new phenomenon in the country; what makes it different now is that it has become more frequent. In the near future, too, it is likely to be occurring as frequently as every three years, and all concerned bodies need to prepare for that.
Aster is a Dendrochronologist and a global scientist specializing in the science of forestry. She works for Center for International Forestry Research and World Agroforestry (CIFOR-ICRAF). Dendrochronologists specifically study the formation of rings in the stem of trees and decipher various types of information that the trees store throughout their lifespan. They mainly study the tree rings in the trunks to find out the ages of the tree as well as the climatic or ecological events that occurred at some point during their life span.
Traditionally, people guess the age of the tree by counting the rings. However, Dendrochronologists do not only tell the ages of the tree based on the number, shape, or colour; they analyze what really happened in that particular place in that specific year or period.
"Following those Rings, we should be able to reconstruct climate. If you want to know what has been happening in the past, maybe 100 years. If you don't have the climate data, we can reconstruct from the temperature, we can reconstruct from there and using the reconstructed data, we can also project how the temperature or the rainfall can be projected for some number of years," says Justine Ngoma (PhD) a dendrochronologist from Zambia.
Aster and Justine indicate that studying the number and formation of the rings helps find information that can assist many other disciplines in the field of science.
"The formation of the rings is just marking something. It's marking the end of the growth period. That means, during the rainy season, they might grow. And towards the dry season, they stop. So that's a mark, we call it a ring. That could be different in its formation, species, colour...etc" says Aster.
The analysis of the tree rings gives more insight to the dendrochronologists beyond the climate data in the past. According to Aster and Justine, it is possible to use the knowledge obtained from the tree rings in other disciplines, too.
"There are different branches within dendrochronology. Some people study climate, archaeology, and the dynamics of the forest, earthquakes, volcanism, climate history, and fire frequency. It's just like a book. It's about asking the right question to the tree" elaborates Aster.
At present our planet is highly troubled by climate change. To rehabilitate the climate, people need to have data about the trends of weather, natural disasters... etc. In this regard, trees are found to be the most reliable archives of climate-related data. Based on data that they have been gathering for centuries and even for millennia, trees can tell us about what was happening in that area so that we can figure out what we have to do now and in the future.
"Tree rings are just like the indicators of climate variability; it is actually like climate records. It's like information that trees are recording in their biomass. During favorable climate conditions, the trees grow. And when the conditions become unfavorable, they stop the growth. The stop is marked by a growth ring, what we call growth ring boundaries. When we use it, we can know the growth rate of the species," says Balima Larba Hubert (PhD), a dendrochronologist from Burkina Faso.
In the course of their growth, trees keep a record of their response to the environment or climatic condition of a particular event. As a result, they can serve as natural archives of environmental or ecological data centers.
"We can also extract climate information from the species. We can also extract all the environmental information from the stem. When we combine the rings of different species giving time, we can be able to reconstruct the climate condition and history. So we say that the tree rings are really like dramatic information, environmental information in the broader sense," says Balima.
Trees indeed outlive any living thing. For instance, in the USA there is a tree that is about 4000 years old. In Ethiopia too there is a tree that is as old as 500 years old, Aster recalls based on her study. In addition, naturally, trees are static. As they remain there fixed throughout their life, they remain living and permanent witnesses to the events that took place there over the years. It may be drought, forest fire, insect outbreak, or massive deforestation by humans ..., everything is recorded and documented by the trees that remain in the place.
"The good part of the science is that you're dealing with a tree that does not move, so it keeps the history of that particular place. You can tell the trend of what has been happening in that area because everything that is happening around that area is registered in that tree. For instance, sometime ago people were cutting trees in that area; go and check the trees that are growing there; it is reflected in the growth ring," Justine explains.
Analysis of tree rings helps not only find out the frequency and intensity of climate change, but also enables future climate reconstruction or environmental rehabilitation works by indicating the species of trees that can tolerate specific weather conditions in an area.
Based on data obtained from the tree rings, dendrochronologists are able to conclude what caused the depletion of forest in the specific area, speculate what is going to happen in the future and how to rehabilitate the area.
For instance, Aster indicates that a study in one of the forest areas in North Ethiopia, called Des'a shows that the common trees were forced to migrate uphill as they could not withstand the deteriorating weather at the nearby lowlands. This also suggests that the future rehabilitation of the area should consider what kind of trees that should be planted as part of the reforestation of that place.
"We studied some species from the mountains of Des'a and then we found tree mortality at the lower altitude, so we took samples from the trees and we tried to analyze what happened. It's because of heat stress of lower altitude that the species are migrating up to higher altitudes. So if you want to plant species in that area you don't plant the same species but different one that can tolerate the heat or drought."
In general, the knowledge and information obtained from tree ring analysis data is an indispensable input that can be used by the government or policymakers and other institutions to plan for future national and international programs.
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"Basically, it's a science that if embraced very well, can be used by the government and different stakeholders to plan. So, you understand what is happening now and also in the past and then it helps you to plan for whatever you want depending on the problem that you have noticed through the growth ring pattern," says Justine.
Figuring out the problems of the past becomes mandatory as it avails indispensable data to properly implement interventions for rehabilitating the environment and prevention of climate change or climate reconstruction.
For instance, the government of Ethiopia has been undertaking a large-scale nationwide afforestation campaign entitled "The Green Legacy Initiative" for the last 6 years. The initiative aims, among other things, to reclaim the depleted forest coverage, assist the income generated from fruit trees, and timber production as well as increase the benefit from carbon trade.
Tree planting should make use of information about selecting the most suitable, adaptable species to a certain purpose and a particular planting site based on the data obtained from the tree ring analysis.
"If it is planted for income purposes like timber, then we knows when it's optimal harvesting period by looking at the growth trajectory, for some species, it can be 30 years and for others a hundred years. Then we can determine the rotation period of that forest. And about the carbon payment ... you can also determine if the carbon per species or tree can change to landscape level so you can ask, 'This area sequesters this amount of carbon,' so that can be changed also in terms of payment for ecosystem services," Aster explains.
