The research project addresses two priorities in tree research: dendrochronology, with impact on the age, growth and architecture of large angiosperms (especially baobabs) and dendroclimatology, for obtaining a climate reconstruction over the past 1000-2000 years for areas with scarce climate data (particularly in southern Africa). As model trees we selected individuals belonging to the Adansonia species. Somewhat surprisingly, we found that the African baobab, especially its oldest specimens, are endangered. Thus, over the past 10 years (2007-2016), 9 of the 13 oldest known baobabs, all located in southern Africa, collapsed (Panke, Grootboom, Chapman, Makulu Makete, Dorslandboom, Glencoe, Holboom, Makuri Leboom, Lundu). The first 4 baobabs died definitively, while for the other 3 baobabs some youngest stems survived. This is a result of the increasingly arid climate conditions which have a severe impact on baobabs. The intensification of El Niño has also a significant contribution. It is possible that the next few years would be the last period when monumental baobab trees could be found and investigated in Africa, particularly in southern Africa.
Regarding the dendrochronological component, our main aim is to continue and diversify our research by using the same methodology, which allows to investigate large and live individuals from tropical and temperate areas. The particular objectives are the following: i) to finalize the investigation of the African baobab in ares which have not yet been studied; ii) to extend the research to representative Australian boabs (A. gregorii) and to date them accurately; iii) to investigate the dwarf baobabs from Mannar Island, Sri Lanka; iv) to find new evidence for the presence of the new diploid A. kilima species, which was reported for high altitude areas of Tanzania and Zimbabwe. We intend to identify large and old individuals belonging to this species; v) to diversify our research on Malagasy baobabs, by investigating also other native species and other areas (Morondava, Antsiranana, etc.) which have not been studied; vi) to investigate a second type of closed ring-shaped structure discovered by us in Senegal; vii) to perform an exhaustive research on the ring frequency in baobabs, including super- annual and sub-annual rings. In certain cases, especially in old baobabs, we found that the number of rings between two dated segments is usually significantly lower than the calendar age determined by radiocarbon dating. For such cases, we use the term ”sub-annual rings”. However, in certain cases, the ratio of counted rings vs. calendar years (calculated from radiocarbon dates) was significantly greater than 1. In this case, we use the term ”super-annual rings”; viii) to investigate and date other old trees from Romania and Europe (Moldova, Hungary, Germany, Poland, Portugal, Spain, Greece, etc) belonging to Quercus spp. (oak species), Olea europaea (olive tree), Platanus spp. (plane species), Castanea spp. (chestnut species).
The main objective of the proposed dendroclimatological research is to obtain several 1000-2000- year isotopic tree ring records, which are duplicated in the major climate regimes from southern Africa. The record applies to the entire southern distribution of baobabs to provide a climate transect from Madagascar through Zimbabwe and Botswana to Namibia and Angola. We intend to perform a climate reconstruction for at least 4 areas selected from the following 5 regions: a) Savé Valley, Zimbabwe; b) Makgadikgadi Salt Pans from Central Botswana; c) Eastern Bushmanland, Namibia; d) Namib desert, Namibia; e) South-western Madagascar. The model species are A. digitata for a-c; Vachellia erioloba for d; A. grandidieri and A. za for e. In January 2016, the 6 stems of the iconic Chapman baobab, a landmark of Botswana, collapsed and died. Our research team, together with our collaborators from South Africa, cored the fallen tree and obtained 3 continuous samples with lengths of 1.20-1.40 m. The radiocarbon dating of the deep sample ends indicated ages of over 1000 years. We plan to date by AMS radiocarbon a number of 40 tiny segments extracted from determined distances of each sample, for establishing an accurate length/distance-age scale. Next, a number of ca. 3500 stable isotope analysis for determining δ 13 C values will be performed on individual rings extracted from the samples. The analysis will be done at the iThemba LABS (South Africa) with the participation of one of our research team membres. We expect to obtain a climate reconstruction over the past 1000 years for Central Botswana with an unprecedented resolution and accuracy for Africa. This would represent a very important achievement of our project. The existing tree ring chronologies for Zimbabwe and Namibia extend only over the past 200-500 years. There are no tree ring chronologies for Botswana and Madagascar. We also envisage to extract long samples from the big oaks of Romania for performing a climate reconstruction over the past 500 years.