The current study's findings indicated that the distinctness of 25 tree sampled rings was rated from low to high; and all of them were utilized to estimate their age scenarios and growth rates. Although no cross-dating was not the target of current study, the distinctness of some species rings could encourage us in the future studies of cambial activity of these tree species and then cross-date these species using standard protocols in dendrochronology for accurate dating. Salem (2006) studied the growth rate of several tree species along Wadi Allaqi using tree ring analysis, where he recorded that most tree species are too difficult to core. Acacia species, the species that could be cored, and the tree-ring estimation was less accurate (Shaltout et al., 2010).
The measured tree ring widths depending on the distance between the marginal parenchyma bands indicated that Acacia tortilis subsp. raddiana grows slowly. For individuals of some studied trees in the present study, age scenarios were used to estimate the age of trees at the downstream part. Two scenarios are probable, implying the date of establishment of approximately 1884 or 1886, with a recent growth dated back to 1885. The approximate dates for the midstream part dated back to 1648, while for the upstream part dated back to 1482. The suggested establishment for Balanites aegyptiaca was around 1715 or 1608, while for Acacia ehrenbergiana was either around 1975 or 1945. Tamarix nilotica swiftly established itself, and a new ecosystem replaced the severe arid habitat after the water level in Wadi Allaqi dropped in the 1980s. The long-term trend in tree growth was well captured by these age scenarios (Zeide 1993). The growth rate is depicted by bell-shaped curve, which means that it increases at first and declines after that in the tree's life. On the other hand, trees can live for > 1000 years in some species (Higgins et al., 2000; Abdoun et al., 2005). According to recent research using C14 dating, some Acacia nigrescens and Acacia nilotica individuals are < 100 years old (February et al., 2006). Longevity estimates of > 100 years are depending on mortality rates in the Mojave Desert (> 100 years; Cody, 2000) and repeat photography in Arizona (> 100 years; Bowers et al., 1995) and are expressed as general assertions (150 years; Pellew, 1983). As a result, this figure shouldn't be used for all acacias. In the Negev Desert, Ward and Ward and Rohner (1997) investigated Acacia raddiana estimating its age depending on a Serengeti size-age connection in which large trees are ≥ 200 years old, according to recent statistics (Wiegand et al., 1999). This assumption suggests that long-term environmental influences are stable, resulting in the water-limited circumstances that characterize desert habitats. Short-term growth fluctuation is predictable and does not contradict growth curve model's long-term tendencies. Comparing with the previous results and considering the high aridity of Wadi Allaqi (rainfall < 30 mm/year), our results of most samples were 0.2 to 2.2 mm/year, and lifespan is approximately 200 years, which lie within the ranges previously cited above and agrees with the range of Anderson and Krzywinski (2006).
In the present study, the distances between bands varied among samples, and the width of rings varied considerably between years and among the species (in average maximum ring widths). At midstream part, there is a short distance between bands (ranged between (0.14 to 4.72 mm) compared with the upstream part which ranged from (0.11 to 4.29 mm) and the downstream part (1.85 to 5.63 mm). Some relatively long distances also appear especially near mountains. Narrow, parenchymatic bands like those present in all Acacia tortilis subsp. raddiana wood cores have been successfully used as time markers for dendro-chronological dating and in climatological studies elsewhere (Gourlay, 1995; Eshete and Stahl, 1999). Such methods seem to be applicable to Acacia tortilis subsp raddiana wood from the extremely arid area of Wadi Allaqi. Marginal parenchyma was formed on slightly regular basis, and the band patterns of trees correlated with each other, either between or within sites.
The low correlations within sampled plots and a negatively correlation between samples indicated that local factors are changeable and influence growth condition, and thus the established of marginal parenchyma bands. Within the three-stream parts of Wadi Allaqi, these factors affect the band formation. Annual rainfall in the Wadi Allaqi area rarely exceeds 5 mm and is highly variable in both time and space. Precipitation comes in discontinuous cloudbursts, varying from one to 15 days in the year, and rainless in many years (Abdou et al., 2016). Since the rainfall is very local and there are so few measuring stations, rain occurrences were unable to be correctly recognized. The water amount received by the soil based on the catchment areas of the receiving basin, which are controlled by land topography, and retained based on the texture and depth of the surface deposits (Kassas, 1955). During the previous decades, rainfall was recorded in south Aswan in autumn 1982, October 1987, December 1990, October 1992, May 1993, October 1994, and November 1996, which caused strong torrents in the surrounding wadis (Salem, 2006). Autumn rain events indicate that the Southeastern Desert is a transitional zone where the precipitation pattern gradually changes from predominantly winter rains in the north (i.e., Mediterranean climate) to predominantly summer rains in the south (i.e., Tropical climate) (IDRC, 1997). Generally, the overall amount of rainfall from 1960 to 2013 ranged from 0 to 0.8 mm/month (Carlquist, 2001; Yacoub, 2018). However, the negative correlations could be due to the contrasting conditions in downstream (DAC), midstream (MAC) and upstream (UAC). To clarify this points, a further study needs to carry out.
The growth conditions varied between plots and were shown by the loss of between-plot band correlations. Within plots, however, regional variables are probable to influence all trees by the same way, unless local landscape variability has a large impact. Phenology and temperature, according to (Gourlay and Grime, 1994), are associated with band formation and cambial activity. Seasonal temperature changes exist in Wadi Allaqi (Ayyad and Ghabbour, 1985), therefore one might predict ordinary band formation, especially at the high altitudes among cold winter temperatures (e.g., Eiqat core area in the upstream part). The absence of ordinary band formation shows that the temperature in Wadi Allaqi does not create major regular variations or is insufficiently cold to establish a spell of consistently cold temperatures in the winter (Fahn et al., 1968).
The present results revealed that the outdated scenario for Balanites aegyptiaca and Acacia ehrenbergiana is more in line with the new growth, while asymptotic value indicates that there is more room for expansion in the future because of the high asymptotic value, the greatest tree in the upstream part with a radius of 310 mm for Balanites aegyptiaca, and 60 mm for Acacia ehrenbergiana, hence the outdated scenario for them is the predicted age.
Tamarix has a great resilience to sand erosion and wind. Meanwhile, the Tamarix's internal directional growth (eccentricity) is influenced by wind–sand erosion. Understanding the relationship between eccentric growth, surface cracks, and growth stress is crucial to comprehending the Tamarix's active defense mechanism. This can interpret a function mechanism of the self-adaptive process for Tamarix wind–sand erosion stress. Under external environmental stress, the cambium cell division rate increases in Wadi Allaqi (Han et al., 2013). The structure and appearance of Tamarix trunks were altered by environmental stimulation. Tamarix that was stimulated throughout its growth produced broad rings in rainy years and very thin narrower rings in dry years. Tamarix 's atypical growth was linked to environmental encouragement. The core, or pith, was located on the windward aspect of the building. These findings are consistent with Farahat and Gartner [6], who studied Moringa peregrina species (see also Farahat and Gartner (2019).
Dendrochronology can and must serve as a key bridge toward the formation of a fuller understanding of Egypt and the ancient world around it, even if it is not a panacea for all of the chronological and environmental concerns. This development will not occur quickly or easily; a project of this magnitude will be protracted, hard, and fraught with difficulties (including scientific and logistical). Furthermore, regardless of its importance, dendrochronology must be used in conjunction with other tools, such as historical records (e.g., king lists), archaeological interpretations, C14 dating, Sothic cycles, and synchronisms with other cultures, on which the problematic chronologies currently in use are based. Only by combining dendrochronology with other types of research can we fully fulfil dendrochronology's potential for Egypt and nearby regions, and so provide specific dates for other historians to discuss (Creasman, 2014; Kuniholm, 2014).