Can tree ring analysis reveal if local climate variations have occurred during the past decades?

Transcription

1 Can tree ring analysis reveal if local climate variations have occurred during the past decades? Extended Essay by Anastasia Shikhaleva Senja / Finnfjordbotn videregående skole IB Diploma class Supervisor: Brynjar Nordgård February 2013

2 Abstract: Based on a preparation work, the research question was stated as: Can tree rings analysis reveal if local climate variations have occurred during the past decades? At the beginning were determined and identified a collection of five different Pine trees. From each of them were bored two core samples to get a more accurate final result. After some preparative manipulations with the samples their ring patterns have been closely analyzed and evaluated. To prove the significance of the research question the next step was to determine whether the analysis of the local pine tree samples showed different climate changes that have manifested during the last seventy years. It was also possible to see how this affected the tree growth. Finally, the findings from the tree ring analysis were compared to available meteorological weather data for the actual region. The observations and results from the analyses yielded indicative signs, but no definite conclusions could be drawn within the scope of the actual investigation. 2

3 Table of Contents: 1. Introduction... 4 a. Background... 4 b. Tree rings Methodology Results Analysis and Evaluation a. Tree core samples b. Tree ring analysis versus meteorological data Conclusion Bibliography

4 Introduction Can tree ring analysis reveal (or indicate) if local climate variations have occurred during the past decades? The web site United Nations Framework Convention on Climate Change, prepared for the Doha Climate Change Conference in November 2012, states: Climate change is a complex problem, which, although environmental in nature, has consequences for all spheres of existence on our planet. It either impacts on-- or is impacted by-- global issues, including poverty, economic development, population growth, sustainable development and resource management. It is not surprising, then, that solutions come from all disciplines and fields of research and development. 1 This extended essay aims at analyzing effects of regional climate variations on local tree growth, based on tree ring sample analysis. Background We live in a world rich of nature. Here are nearly nineteen different natural areas, thousands of herb and animal types. Everything around us grows and develops constantly. Nature is full of secrets and mysteries. By learning things around us we can get some more information about past and use it in the presence. It is not a lot of natural objects from the past that we can take a look at. Many of them already disappeared or have changed by the influence of environment. Some of them are very difficult to get and it takes time. But one of such secular plants is a tree, one of the greatest resources that surround us almost everywhere. Trees grow through many hundreds of years and do not change their location. The first and the most important thing that affects their living proses is climate change. It can be a change in average weather conditions or some global processes. But every change reflects on the tree growth. 1 United Nations Framework Convention on Climate Change. Doha Climate Change Conference in November 2012 < [16 November 2012] 4

5 Among the thousands of species that are submitted on the biggest part of terrestrial area is Pinus sylvestris or a Pine Tree 2. Crown is highly raised, conical, and then rounded, broad, with horizontal branches in whorls. Bark at the bottom of the trunk is thick, scaly and gray-brown, with deep cracks. Bark flakes form a plate of irregular shape. At the top of the trunk and the branches of a thin crust in the form of flakes, it is orange-red. Shoots are green at first, then by the end of the first summer they become gray-light brown. This species can be found on large territories. That is why it is considered as a good resource for analysis. The pictures below show a pine tree (left) and the area of Pinus sylvestris habitation 3. There are several different climate zones in the world and each of them has different flora. Climate is the characteristic condition of the atmosphere near the earth's surface at a certain place on earth. It is the long-term weather of that area (at least 30 years). This includes the region's general pattern of weather conditions, seasons and weather extremes like hurricanes, droughts, or rainy periods. Two of the most important factors determining an area's climate are air temperature and precipitation. 4 2 Wikipedia. Scots Pine. < 3 < [ ] 4 World Climates. < [14 November 2012] 5

6 Tree rings All the information of tree s growing process reflects on its tree rings. A tree ring is a wood layer that has been produced during one tree s growing season. A crosssection of a tree often shows a distinct pattern of concentric tree rings. Example of such rings can be found on stumps. It is an interesting fact that by counting of tree ring we can estimate the age of the tree, enough just to collect them from a side to the center, the starting ring. Also, from a tree ring sample, we can get information about the variants of climate variations at that or another summer when that tree have been in a vegetation period. Each of tree rings contains a line between a dark late wood from a previous year and a new formed one that grew in a new year. Such line can be different: narrow or wide. It depends on how much water and light did the tree get during the growth period. The growth condition during the last year, for example: it was relatively warm in the summer with not a big percent of precipitation and some dry periods. Growth of tree rings in tree trunks can be considered as a calendar that goes back thousands of years if we have an opportunity to find very old or dead trunks, for the area that the tree has grown in. There is a scientific method that is called dendrochronology. Part dendro from Greek means a tree limb and chronology or chrono is related to time. Dendrochronology is a scientific method of dating which is based on counting of tree rings. At the same time it is another science that calls Dendroclimatology and determines past climate by analyzing tree ring growth. Clima is weather. Both of sciences are used during my work of tree rings analysis. 6

7 Climate conditions of the northern Norway can be defined as arctic. Here vegetation of trees goes very slowly and only in the summer. Only in a few months trees can get enough sun light and water. Most of them stay and does not grow. That happens in winter, when temperature becomes lower than 15 degrees. Then all processes of vegetation stops. Usually trees can grow in a worm and wet climate however that can t be during the whole year. Most significant for that occurrence months are from May to September incl. (They were used as weather background in the analysis.) These different growth periods form the rings in the tree, each ring marking a growing season. By comparing overlapping tree rings from trees of different ages (that can be obtained from a collection of different tree samples) one can create a natural calendar. That method has been known since the 1700s. Scientists have developed detailed calendars for most of the world by knowledge of dendrochronology. Archaeologists have use of dendrochronology. Within archeology frequently used dendrochronology to date everything from old houses to antique cellos. Dendroclimatology is a science that read tree rings and tries to reconstruct climate in the past by that information. It is a section of science dendrochronology. 5 This essay is based on the analysis of annual growth in local Pine trees. The work presents the analysis of 10 samples from living pine trees, including comparing them and determining some aspects of their growing process. Finally, the tree ring data is compared with official climate data. 5 National Geographic, Norge. Hva er dendrokronologi? < [13 June 2012] 7

8 Methodology Five trees have been investigated; two samples were drawn from each Pine tree. That gave us ten tree samples. Next step is working with samples and analyzing. To make the final statement tables and graphs should be completed. By comparing personal results of the annual and real weather conditions it can be seen some more clear output. Methodology 1. Objectives of study: Five pine trees were found and selected for the analysis. Two samples were taken from each of the tree. The analysis of the tree samples was conducted and tables from the results were created. Results were compared with weather dates for certain years. 2. Materials required Borer Ruler/measuring tape Plastic tablet Map Tree plank Glue Sandpaper 3. Appliances Computer/ GPS Calculator Camera 4. Procedure A. Field section 1 Pine trees were found and determined in the nearest area to school. Each one has been pointed on the map. Later on their GPS coordinates were determined by that information. 2 Two samples were taken from each tree by a next procedure: a The borer was inserted about 1,3 m above ground level, between two lowest branches. b The borer was screwed in in the direction from the chest right to the middle of the tree. c Blade was injected inside the borer to take a sample out. 8

9 d The borer with the blade inside was removed from the tree trunk. e Blade with a tree sample on it was gently taken out. The Pine tree sample was in a plastic table s groove. f Girth of the tree at that point was measured by a measuring tape. g Pictures of trees and a person near them were taken (by a camera), to determine the trees height. B. Laboratory section 3 All samples were glued in a right sequence in a groove of a tree plank. (Two samples from the first tree, then other two samples from another tree etc.) 4 Later they have been left to dry during approximately two days. 5 Then they have been treated with the sandpaper (60 grits and 240 grits). Aligned with the groove, until tree rings on samples were clearly recognized. C. Data collection 6 Tree samples were analyzed and tables were created. (They have considered the information about the tree samples and the Pine trees: site, trees, tree rings, climate dates and other aspects of the research work. All samples were scanned.) 7 Rings were counted once more. Also radiuses were determined. 8 First two samples from the first Pine tree were compared against each other, just like next two and all others. 9 From each pare of the tree samples were chosen the most appropriate one, and compared with others. Pointer years were identified. 10 By using the climate information for last 70 years was created graphs of average temperatures for May, June, July and August during those years. 11 Core data were compared to the meteorological data. Observable tendencies were detected and commented. The analysis of the tree rings from the Pine trees was completed. 9

10 Results Surrounding Area s Analysis The investigation took place in Finnfjordbotn near Finnsnes in Northern Norway, latitude 69 degrees north, 18 degrees east. Maps showing localization of research area Average height of trees in that area is 11 meters. That leads it to a medium tree line. Soil in this area is rich considers many rocks. It is also quiet soft ground. If we will talk about it more specifically, that it is more shady then sunny. Most of trees placed close to each other and sometimes might appear a competition between them. In that case chosen trees were standing as solitary as possible. The forest is close and there are several layers and age classes of trees. It can be found tall or shrub types, for example. 10

11 1. Table showing summative data from field analysis Height, m 9,2 13,3 7,2 8,8 12,3 Stem diameter, cm 30,9 27,4 17,2 21,0 29,9 Trees outlook Looks very young, thin and strong stem. Small amount of dry branches at the base. Stem is wider, compared to the first one here are more thick branches. Dry and dead branches on the lower part of the stem. Few branches on one side of the tree. Strong and wide stem, some branches are fractured. Some of moss on the stem. High and middle-thin stem. Some roots are opened. Coordinates from GPS (degree, minute, second) Table Showing Were On the Tree Samples Have Been Taken Girth (at the point of boring) cm sample 1 sample 2 sample 3 sample 4 sample 5 97,0 86,0 54,0 66,0 94,0 Height from the ground, cm Depth of measurements, cm 120,0 90,0 107,0 103,0 122,0 1-26,0 1-26,8 2-27,0 2-26,7 *n - secondary sample from the same tree 3-26,9 3-27,0 4-27,1 4-26,1 5-27,5 5-26,3 3. Table showing summative data from subsequent laboratory analysis of core samples Number of rings Age (years) Years

12 Analysis of Tree core samples Ten core samples (five pairs, from five trees) have been mounted on core seats and grinded before they were scanned and subsequently analyzed for tree ring patterns. The objectives of the following analyses are: 1. Evaluate the significance of the patterns found in each of the five pairs. 2. Evaluate the difference in patterns between the five trees, by comparing one of the cores from each three. 1. Evaluation of the significance of the patterns found in each of the five pairs. The five pairs are presented below, together with a comparison of the five pairs of core samples; one pair from each tree. Tree number 1. Core samples 1 and 1 : Core 1 has been broken before the borer has reached the center of the tree. Therefore, the scales of the two core scans are different. Below, I show the two cores adjusted to approximately equal magnifications: Evaluation: The sample number 1 is less useful because of the size. The borer was not screwed right until the middle. On the other hand the sample 1 shows us 9 more rings. The first two of them are novices, they are presented as semicircles. Counting from left (2011; sampling year): The sample pair may indicate that the period offered poor growth conditions: the rings were narrow. Similarly, the years may seem to have been favorable for tree growth (wider rings). The period of seems like a good one. Distances between ring stripes are wide and clear. 12

13 Tree number 2. Core samples 2 and 2 : Evaluation: As seen on samples 1 and 1 : The span (a) seem to have been not favorable for tree growth (narrow rings). The seven years ahead ( ; b), on the contrary, may have been better, preceded by the years , which may indicate scarce growth. As in the previous analysis, the sample 2 is more suitable for scan. On the second sample some beginning rings are clearly seen and the first one can be recognized also. Both samples show a pretty similar sequence of tree rings. The tree grew proportionally in all directions. On the both samples the ring from 1991 is shows a good vegetation period of that year. Tree number 3. Core samples 3 and 3 : Evaluation: The sample 3 is considered as a more proper one here is a central ring that is marked by c) (year 1957). Patterns on both samples look similar. Groups of rings from year 1997 to 2005 (a) are very thin; probably there were very cold summers without enough big percentage of sunlight. At the same time the period (b) was also unpleasant. All other tree rings looks enough wide and probably there were better vegetation periods. As it can be recognized from scan pictures, there are several other special years of bad growing periods, for example years 1963 and

14 Tree number 4. Core samples 4 and 4 : Evaluation: As a better one of those two samples was chosen the 4. It is even longer than a radius of the tree. The central and the first ring (c) refer to the year First rings on another sample are wider. Here are many thin rings. There are patterns of (b) and years (a). The first named pattern of bad years was recognized on other samples also. That might indicate climate variations in that area. After the analysis of all rings on both 4 and 4 samples it might be stated that with every year rings had a tendency to become thinner and thinner. It is also refer to the climate changing. Tree number 5. Core samples 5 and 5 : Evaluation: Both samples have a nearly same tree rings pattern. All of the rings are very similar and averagely have the same distance between each other. The sample 5 is more profound. Here are recognized two halve-finished rings. The earliest one we can see belongs to year On the sample 5 indicated a pointer year (a), which is On some other Pine tree samples that year was marked as an unusual one. Climate table can probably explain this. 14

15 2. Evaluation of the difference in patterns between the five trees, by comparing one of the cores from each three. Pine tree samples 1, 2, 3, 4 and 5 were chosen as the most proper for the analysis and comparing. Evaluation: The five core samples were compared relative to each other, to reveal possible common growth trends. Examinations of the core samples indicate the following: Sample 1 : Bad: Good: Bad: Sample 2 : Bad: Good: Bad: Sample 3 : Bad: Good: Bad: Good: Bad: Sample 4 : Bad: Bad: Good: Bad: Sample 5 : Bad: Good:

16 Overall trends, based on tree ring width: 1. The years seem to have a low growth yield. Sample 4 is an exception, showing good yield during the same period 2. The years seem to have an overall high growth yield. Sample 1 starts this good growth at about The years seem to have a low growth yield. This applies to all five samples. 4. Sample 4 may seem to have a low yield in

17 Tree ring analyses versus meteorological data Official climate data are available at the website eklima, run by Norwegian Meteorological Institute, met.no 6 - Data from two nearby met stations Tromsø and Bardufoss (indicated on the maps) - are available. The graphs below show annual mean values for monthly temperatures and precipitation during the years , for Tromsø and Bardufoss, respectively. 6 eklima 17

18 Details of meteorological data. Average Temperatures of May, June, July, August and September. Available temperature data from the neighbouring community Bardufoss and the town Tromsø shows fluctuations on average summer temperatures in the two areas during the period Bardufoss Tromsø The inland town Bardufoss enjoys slightly higher mean temperatures than does Tromsø. which is situated closer to the coast line. The surrounding sea bed tends to cool down the ambient air in the Tromsø area, leading to lower average air temperatures. 18

19 The patterns of temperature fluctuations, however, are highly comparable, indicating that the correlations of the graphs depicts annual climate trends based on registered temperature variations. The overall trends of the meteorological temperature graphs may be described as follows: 1. The largest annual temperature fluctuations occurred during the two decades , with a maximum peak at both stations in 1960 and likewise a minimum in During the period from there has been a general increase in the average temperature. 3. The periods , and seem to expose higher-than-average temperatures. The periods , , and , seem to expose lower-than-average temperatures. Tree ring data versus meteorological data Combining information from the tree ring analyses and the meteorological data, the following can be suggested: 1. Tree ring patterns generally indicated low growth yield during the period One of the five samples showed good yield during the same period, though. This tendency occurred concurrently with a general increase in temperature in the period, from 1983 on. - The general increase in temperature levels continued during the period A positive (increased) growth yield could be observed throughout , but may seem to cease during the next five or six years, despite the increasing mean temperature values during the same period. 3. The years seem to have a low growth yield. This applies to all five samples. In addition, sample 4' may seem to have a low yield in Still, as mentioned above, the general increase in temperature levels continued during the period , without exerting any positive effect on growth. 19

20 Conclusion Tree ring patterns in core samples from five pine trees (Pinus sylvestris) have been examined, in order to detect trends of positive or negative growth periods. The tree ring patterns exposed vague negative growth trends for certain year periods, and similarly vague positive trends for other periods. The findings of the core sample examinations were subsequently compared to temperature fluctuations observed in meteorological temperature data for the region during the relevant time span. As with the tree rings findings above, the meteorological temperature data exposed year spans of temperatures above average, and spans of lower than average temperatures. Positive correlation between the fluctuations of tree ring widths and the temperature data were, however, not easily established. Some of the observations could indicate, though, that periods of high temperature seem to have yielded increased growth (increased tree ring widths), whereas periods of low temperatures similarly lead to narrow rings. However, no definite correlation between temperatures and tree growth has been established. Evaluation The interpretation of the findings in this investigation strongly depends on the amount of data available. With more tree core samples, the growth trends may appear more conclusive. Tree growth is dependent on several factors, among them the abundance of water. It would be highly relevant in future investigations to compare growth trends to available precipitation data, to detect possible correlations. These issues were, however, beyond the scope of this investigation. 20

21 Bibliography Books Fritts H. C. Tree Rings and Climate. London: Academic Press Inc., Websites United Nations Framework Convention on Climate Change. Doha Climate Change Conference in November 2012 < [16 November 2012] Wikipedia. Scots Pine. < < [8 June 2012] World Climates. < [14 November 2012] National Geographic, Norge. Hva er dendrokronologi? < [13 June 2012] J. Zimmerman, Ph. D. Tree Rings What They Are and Why They Vary < [20 September 2012] eklima < 21