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Dendrochronology – a new emerging and Applied Science in Pakistan

xxymena-QlZtqGYwM7c-hdCLIMATE PLAYS an important role in our everyday life and also directly or indirectly influences some of our key economic activities e.g. Agriculture, Forestry, Tourism, Hydropower. It is now widely accepted that the world’s climate is changing (global warming) due to human activities. The urgent question is what does this mean to Pakistan? Developed countries are spending billions of dollars each year to obtain information about the climatic change, supporting professional staff, which are of great practical importance to their Forestry, Agriculture, Hydrology, Glaciology, Earthquakes and Climatological studies.

Every country wants to know what changes might happened to them, so that they may prepare and/or adopt. However, a main limitation to being able to accurately model future scenarios is the lack of long, detailed information on past climate system and their behavior. Records of past climate are too short, lacking or unreliable from mountain system or remote forested areas, and consequently there has been a indespread international effort to find and use other reliable indicator. One of the best “tools” to provide this missing climatic data has been the use of tree-ring (Science of Dendrochronology). The prefix dendro is from the Greek word for tree, dendro, and the word chronology is the name of science that deals with time and the assignment of dates to events. Some authors have restricted the term Dendrochronology to the use of tree rings to date events only. However, the techniques of Dendrochronology are applied to a variety of problems of environment, Climate, Hydrology, Forestry, Glaciology…etc.

[caption id="attachment_26592" align="alignright" width="150"]Prof Dr Moinuddin Ahmed Prof Dr Moinuddin Ahmed[/caption]

Dendrochronology is based on the strong tendency of tree to grow in annual increments on the outer portion of the main stem, just beneath the bark. In regions and some trees where nature permit continuous growth, rings are often indistinct and may not be annual in nature. Only where there is strong genetic tendency and/or periodic dormancy (due to pronounced dry season, or other growth-inhibiting factors) is there likelihood of annual-ring identification.

The anatomical demarcation between rings is readily identifiable in most conifers due to formation of denser, darker latewood at the end of the growing season that contrasts with the lighter earlywood of the following year. In Angiosperms there are two types; Ring-porours and Diffuse-porous. Ring-porous species have well-defined rings with vessels or pores concentrated at the beginning of the each ring. Diffuse-porours trees have less clear ring boundaries and identification of rings can be more difficult. In all trees there may be false, missing or locally absent rings due to unusual growth conditions. Narrow or tiny rings can go undetected unless surface preparation is excellent and proper magnification is used to examine the rings. Therefore simple counting of rings is not a reliable method of determining the tree date of ring. Annual growth rings are formed in the trunk, branches and major roots. Rings in branches and roots are usually discarded since difficult to work with. The trunk rings are the most reliable for analysis and dating.

Annual growth rings of particular tree species are subjected to tree ring dating, cross matching or cross dating, the procedure of matching ring-width variation and other structural characteristics with in a tree and among trees that have grown in a particular area. This allows the identification of the exact calendar year for the formation of each ring.

Dendrochronology is divided into various sub-branches. The prefix dendro is used with the name of particular scientific discipline, so the Dendroclimatology refer to Dendrochronological Investigation of past and future climate, application of tree-ring analysis to the mapping of past and present climatic or in simple words “study of present and past climate from tree-ring is know a Dendroclimatology ”

The northern part of Pakistan is a key area for climatological studies as it is located at the boundary between tropical and continental climatic influences and has quite different climatic controls from the Eastern Greater Himalaya.  Indian monsoon air masses, which bring significant rainfall on the southern margin, penetrate infrequently across the Himalayan Mountain divide to the Trans-Himalayan regions of the Karakoram and Hindukush Mountains.  Precipitation in these northern ranges is concentrated in winter and spring months and carried on westerly disturbances, originating predominantly from Mediterranean and Caspian Sea regions.  Winter precipitation provides the principal source for accumulation on glaciers in the greatest area of perennial ice outside of the polar regions (22,000 km2) (Fowler and Archer 2006).

An often-cited constraint to Dendroclimatic studies in the Himalayas is the paucity of long meteorological records for statistically calibrating to the tree-rings (Cook et al., 2003; Bhattacharyya et al., 1992).  One solution has been to interpolate seasonal data into a 0.5º latitude-longitude grid data set that can then be applied to the tree-ring location (Cook et al. 2003).  Such an approach could also be extended to cover the tree-ring sites in Pakistan.  However, northern Pakistan is fortunate to have at least three stations with around 100 years of temperature and rainfall records (Archer & Fowler, 2004; Fowler & Archer, 2006).

An analysis of instrumental temperature records from seven locations in the Karakoram and Hindukush Mountains has shown that winters have become warmer and summers are cooler (Fowler and Archer, 2006). Another finding has been that the duirnal temperature range (DTR) has consistently increased since the middle of the 20th century.

The author thinks this is a result of changes in large-scale circulation patterns and feedback processes associated with the Indian Monsoon. The downward trend in summer temperatures noted as being consistent with the observed expansion of Karakoram glaciers, which in direct contrast to reported glacial retreats in the Eastern Himalaya (Pearce, 2002). Fowler and Archer (in press) argue that the Western Himalaya is displaying a different response to global warming to that elsewhere reported normally. Such findings highlight the importance of our expended proposed investigation that will enable us to resolve, responding differently to general predictions.

The ITRDB (International Tree-Ring Data Bank) holds over 3,300 tree-ring chronologies from over 100 different species sampled from more than 50 different countries spread around the world.  Pakistan is a notable gap. Our project aims to address this omission and establish a network of linkages/collaborations.

We are collaborating Prof, Dr. Edward Cook, Tree Ring Laboratory, Lamount-Doherty Earth Conservatory, Columbia University, Palisades, New York. Prof. Dr. Connie Woodhouse of Tree Ring Laboratory of University of Arizona, USA and Dr. Jonathan Palmer, Gondwana Tree Ring Laboratory, New Zealand. Our laboratory is providing technical support to the students of various national universities in there research related to this science.

One of our Ph.D student is working on “Drought Reconstruction (Dendroclimatology) of Gilgit and Hunza valley which would be highly beneficial for agriculture, fruit forming and tourism in global warming scenario. Our team is using Dendroecological techniques to explore forest dynamics of many conifer forests of northern Pakistan.

Recently we have successfully explored past 550 years of water flow data of Indus River (Dendrohydrology) while WAPDA has only 50 years of instrumental data on which their water planning is based. It is a proven scientific fact that even 100 years of data is not sufficient for reliable and scientific water planning, therefore these findings would be a milestone in water planning of Pakistan if used by WAPDA. This authority has no choice, their experts have to learn this technique and we will be happy to provide technical support. In future we intend to extend our river flow data up to last 1000 years. Therefore we have submitted another project to Pak/US through Higher Education Commission of Pakistan.

In Pakistan we can also use this science to study glacier movement (Dendroglaciology), Earthquakes (Dendroseismology), forest fires (Dendrophyrology) and dating of archaeological sites or objects (Dendroarchaeology).

The writer is associated with Dendrochronlogy and Plant Ecology, Dept of Botany, Federal Urdu Unversity of Arts Science and Technology, Gulshan-e-Iqbal Campus, Karachi.



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