APPLICATION OF TREE-RING RESEARCH IN PAKISTAN

The study of tree-rings or dendrochronology, is the scientific method of dating based on the analysis of growth-ring patterns from trees (http://en.wikipedia.org/ wiki/). Dendrochronology can date the time at which tree-rings were formed, in many types of wood, to the exact calendar year. This field of research has rapidly expanded over the last 30 years not only in terms of the number of sample locations but also in the analysis methods and the range of applications. A major strength of the research field has been the open sharing of data with the best example of this being the development of the International Tree-Ring Data Bank (ITRDB; http:// www.ngdc.noaa.gov/paleo/treering.html). Currently, the ITRDB contains over 3,200 tree-ring chronologies from over 1,500 sites around the world representing over 100 tree and shrub species. Anybody can visit the website and obtain the data. The rapid growth of research has led to many different applications and a brief over-view of some of them thought to be relevant to Pakistan is presented (Table 1). We will not be providing an introduction to the specific techniques involved since this is another separate exercise (see Fritts 1976; Baillie 1995; Cook & Kairiukstis 1992). Only a limited amount of tree-ring research has so far been conducted in Pakistan and all of it has been based on conifer species. The starting point was an introductory paper by Ahmed (1987). Ahmad (1988) mentioned the problems encountered with tree age estimation. Subsequent papers present initial Abies pindrow tree-ring chronologies from a moist temperate region (Ahmed, 1989) and then switch to a focus on population dynamics of Juniper excelsa and Pinus gerardiana in dry temperate areas (Ahmed et al., 1990a; 1990b; 1991). Ahmed and Sarangzai (1991 a,b) estimated age and growth rates of various conifer species. The first international publication into the climate potential from the tree-rings was published by Esper et al. (1995) based on Juniper excelsa. The same species was subsequently used to determine long-term tree-ring variations (Esper, 2000) and ultimately led to the millennial precipitation reconstruction based on tree-ring oxygen-isotope concentrations (Treydte et al., 2006). Ahmed and Naqvi (2005) have presented four tree-ring chronologies of Picea smithiana from various climatic zones. Recently, Ahmed et al. (2006) investigated the phytosociology and structure of forests from different climatic zones. Recently, Khan et al. (2008) looked at the potential of Picea smithiana from a site in neighbouring Afghanistan and Ahmed et al. (2009 a,b) presented preliminary climatic response functions from the same species in Pakistan. A network of 28 tree-ring sites has recently been compiled for dendroclimatic studies (Figure 1, Table 2; Ahmed et al., 2010). The sites were all from northern Pakistan and consisted of six species from five genera – Abies pindrow (Royle ex D. Don) Royle (West Himalayan fir, ABPI), Cedrus deodara (D. Don) G. Don (Himalayan cedar, CDDE), Juniperus excelsa M. Bieb. (Greek juniper, JUEX), Picea smithiana (Wall.) Boiss. (West Himalayan spruce, PISM), Pinus wallichiana A.B. Jacks (Himalayan blue pine, PIWA) and P. gerardiana Wall. ex D. Don. (Chilgoza pine, PIGE). Species codes follow the general convention listed on the International Tree-Ring Data Bank ITRDB (Grissino-Mayer, 1993).