Otar Abdaladze

Facilitation of Seedling Microsites by Rhododendron caucasicum Extends the Betula litwinowii Alpine Treeline, Caucasus Mountains, Republic of Georgia

ABSTRACT In the Central Greater Caucasus Mountains, Georgia, Betula litwinowii (birch) occurs on north-facing slopes of east-west ridgelines that extend upward to high mountain peaks, forms the alpine timberline at higher elevation, and reaches its highest treeline limit only when associated with the broadleaf evergreen shrub, Rhododendron caucasicum. This association might generate an ecological facilitation of either temperatures or sky exposure, both of which have been related to the altitudes at which timberlines/treelines occur. At the lowest site (2072 m) the greatest abundance of birch seedlings (up to 2.3 seedlings/m2) occurred at shaded microsites beneath the B. litwinowii overstory and along shaded north-facing walls of polyhedral soil depressions just beyond this treeline. These seedling microsites also had substantially colder air and soil temperature regimes than more sun-exposed microsites. Similarly, at the highest elevation site (2512 m) the second greatest seedling abundance (0.73 seedlings/m2) occurred in the shaded understory beneath R. caucasicum. Moreover, these microsites had the coldest minimum air and soil temperatures (−1.3°C at 5 cm depths), along with the greatest number of days (40) with minimum soil temperatures <5°C recorded for the measurement period (11 July to 25 October 2003). In addition to the lowest number of seedlings, the more sun-exposed microsites at all sites also had the greatest percent (28–32%) of red leaves per plant, indicative of high concentrations of photoprotective anthocyanins. Thus, reduced sky exposure, and not cold temperature effects, was associated with greater seedling abundance and fewer red leaves per seedling, despite colder temperature regimes. Thus, facilitation of B. litwinowii seedling establishment by the R. caucasicum overstory appeared to extend the maximum altitude of the Betula treeline via reductions in sunlight exposure, despite lower temperatures.

Characterizing Betula litwinowii seedling microsites at the alpine-treeline ecotone, central Greater Caucasus Mountains, Georgia

Abstract Seedling establishment is an important factor dictating the altitudinal limits of treeline species. Factors which affect seedling mortality and survival, however, have yet to be fully characterized, especially for deciduous treeline species. Here we describe microsite characteristics of successfully established Betula litwinowii seedlings at the alpine-treeline ecotone. Possible harmful effects of sky exposure on seedling physiology (i.e. photoinhibition of photosynthesis) were also examined, as well as possible facilitative effects of co-occurring Rhododendron caucasicum shrubs on northern slopes and microtopographical depressions (mainly watercourses) in ridgetop meadows. On northern slopes, seedling density was highest in newly exposed soils, with 90% of the youngest seedlings (<2 cm) occurring in patches of rocky, bare, or moss-covered soils within the Rhododendron thicket. R. caucasicum was not a significant source of shade for B. litwinowii, as most seedlings were established 0.25–0.5 m away from the nearest shrub, and shade cover generated by R. caucasicum was observed in only 1% of seedlings at midday. On ridgetops, density of B. litwinowii was sixfold higher inside microtopographical depressions compared to outside. Sky exposure of seedlings within depressions was similar to northern slopes, ranging from 50% to 87%. Across all microsites, seedlings were most abundant under 70–87% sky exposure. This preference for open microsites, combined with the observation that sustained photoinhibition of photosynthesis (Fv/Fm < 0.65) was observed only in the most open microsites (i.e. >80% sky exposure), suggests that sky exposure is likely not a significant factor affecting seedling mortality in B. litwinowii, in contrast to results reported for conifer and broadleaf evergreen species at treeline. A higher photosynthetic capacity and a deciduous life history may provide both tolerance and avoidance to the physiological stresses associated with high sky exposure for B. litwinowii seedlings, and other factors, such as soil moisture, more likely account for successful establishment within microtopographical depressions and R. caucasicum thickets.

Reasons and Processes Leading to the Erosion of Crop Genetic Diversity in Mountainous Regions of Georgia

Abstract Agriculture has a long history in Georgia; it has led to a great variety of ancient crops. However, this diversity is under threat for many reasons. First, introduced crops have caused a loss of traditional cultivars, because the introduced crops are preferred due to their higher yield. Moreover, agricultural machines such as forage and grain combine harvesters imported to Georgia are constructed for widely distributed, imported crops and cannot be used to harvest local cultivars. Until recently, genetic erosion of ancient crop varieties was not a problem in the mountain areas of Georgia, which until the 1990s constituted a depository of local crop varieties of wheat, barley, rye, oat, common millet, traditional legumes, vegetables, herbs, and spice plants with specific varieties adapted to mountain conditions. These mountain areas worked as a depository because local mountain communities preserved their traditional ways of life and socioeconomic structures. Their traditional agricultural equipment, used on a large scale until the 1990s, still allows them to maintain areas under cultivation (with grain or other crops) on steep slopes and at high elevations where modern tractors cannot be used. Moreover, some old landraces of wheat and barley are still being used to prepare bread and beer for religious rituals. Currently, many endemic and native representatives of crop plants are in danger of extinction. International nature conservation institutions and Georgian scientific and nongovernmental organizations have developed plans to preserve the genetic resources of local cultivars.

Biotope Types of the Treeline of the Central Greater Caucasus

Some characteristics (habitat, distribution, characteristic species, ecological importance, practical use and danger factors) are given of 17 typical treeline biotopes in the Kazbegi region, situated on the north-facing macro slope of the central part of the Main Watershed Range of the Greater Caucasus. The diversity of species composition is mainly due to peculiar structural properties of the vegetation of these biotopes, rather than ecological (altitude, moist or dry conditions,) and anthropogenic (grazing, haymaking) factors. The majority of the studied biotopes are referred to the II stage of hemeroby, but untouched shrub communities (dominated by Rhododendron caucasicum), elfin crookedstemmed birch forests (dominated by Betula litwinowii) and fragments of tall herbaceous vegetation should be referred to the I stage of hemeroby (natural and close to natural). Current global climate change will cause the most drastic changes in moist (tall herbaceous vegetation), snowline (humid broad-leaved meadows dominated by Trollius ranunculinus), broad-leaved mesophilous meadows (dominated by Anemone fasciculata), elfin crookedstemmed birch forest and scrub biotopes. The numerous biotopes are characterized by high sensitivity, which is caused by the following factors: landscape mainly devoid of forests, high degree of relief and, consequently, bare soil cover, low and unstable snow cover, frequent solifluction, etc. The following biotopes should be regarded as priority habitat types: tall herbaceous vegetation, scrub and elfin crooked-stemmed birch forest.

Plant Diversity in the Central Great Caucasus: A Quantitative Assessment

This book presents the first assessment of the high-elevation flora of the Central Caucasus with a community ecology emphasis. Following a geostatistical-climatological description of the region (in comparison to the European Alps), it describes the montane, alpine and nival plant assemblages on the basis of an ecological approach that combines moisture, soils and local habitat peculiarities. Highlights include the famous giant herb communities in treeless parts of the upper montane belt, the various facets of alpine turf, and the unique assemblages and settings in the nival region. Further chapters address potential niche conservation between the Caucasus and the Alps, as well as a compilation of plant species habitat preferences (indicator values) that applies to a concept developed for the Alps. Richly illustrated and featuring extensive quantitative data on species abundance, the book offers a unique guide to the plant species diversity of this prominent mountain range, and a valuable resource for comparative ecology and biodiversity assessments of warm temperate mountain systems.

Morphological diversity and phylogeography of the Georgian durmast oak (Q. petraea subsp. iberica) and related Caucasian oak species in Georgia (South Caucasus)

The Caucasus region is one of the 25 global biodiversity hotspots and constitutes a shelter area for Neogene relict species as well as a center of ongoing radiation. In order to elucidate the taxonomic identity, divergence patterns, and evolutionary history of the largely widespread Georgian durmast oak (Quercus petraea subsp. iberica), we examined leaf morphology and chloroplast DNA (cpDNA) (trnH-psbA, trnK-matK) sequence variation across its South Caucasian range. Six other oak taxa distributed throughout Georgia were included in the dataset and used for comparison. Evidence for differentiation in both sets of traits was found. Populations represented by different taxa from ecologically equivalent areas showed common morphological features and genetic structures. Molecular analysis clearly indicated the presence of two major haplotype lineages (West Caucasian vs. East Caucasian zonation type) and suggested a maternal lineage diversification of Q. petraea subsp. iberica in the Late Miocene, as a likely result of complex patterns associated with major orogenic and climatic changes. The Quaternary glacial oscillations resulted in a number of less common, derived haplotypes. Based on mismatch distribution analysis and neutrality tests, we found no evidence of demographic expansion for the populations from the West and East Caucasian zonation types. The two Caucasian provinces therefore acted as important shelter/diversification areas and as a lineage crossroad for the Georgian oaks. Close intra- and interspecific cpDNA relationships shared with other oaks from bordering countries support the relevant role played by the Colchis region as a primary refugium for the European temperate forest species.

Plant Diversity of the Central Great Caucasus

The debate on the origin of the alpine flora of the Caucasus began already at the beginning of the last century. Well-known researchers of the flora and vegetation of this region put forward completely different hypotheses about the age and the mode of formation of the alpine flora of the Caucasus.

Vegetation of the Central Great Caucasus Along W-E and N-S Transects

The Great Caucasus covers a significant west to east climatic gradient along its main divide (see Chap. 1). The highlands of the western Caucasus are humid (up to 2200 mm of precipitation per year) and dominated by mesophilic taxa, the highlands of the eastern Caucasus are more continental, with dry summers and an increasing fraction of xerophylic taxa (<800 mm of precipitation per year). Half of the annual amount of precipitation falls on the cold season, therefore large areas of mountains are covered by perpetual snow and glaciers. The annual temperature amplitude is small. One of the features of the Caucasus high mountains, which distinguishes this mountain system from other mountains of Europe are sharp climatic and thus, vegetation changes over relatively small distances. An obvious example is a S-N transect along the ‘Georgian Military Road’. This transect clearly shows how semi-desert vegetation becomes substituted by steppe, open arid woodland, mesophilous beech forest including the beech forest types with Colchic elements, then high mountain meadows, chiono- and kryophilous herbaceous and relict scrub communities even in snow-beds, and near-glacier micro-habitats. Within this transect local shelter by mountains can create is continental oroxerophilous vegetation islands. Interior valleys are protected from both cold and humid air mass penetration from the north explaining many relict xerophilous species of past xerothermic periods (Kharadze 1948).