George Nakhutsrishvili

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.

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.

Drought at erosion edges selects for a 'hidden' keystone species

Background: The presence of plants is crucial in securing steep slopes against soil erosion. Inappropriate land use in mountains often leads to vegetation loss and thus soil degradation. Aims: Here we ask if the edges of large erosion gullies select for specialist plant species that reduce or prevent the progression of soil loss. Methods: We quantified species presence and abundance across micro-transects from intact mountain pastures toward the edge of erosion gullies at ca. 1900 m elevation in the Central Caucasus, Georgia. Results: Out of a large species pool, one particular species, Festuca valesiaca, was the dominant species at the very edge of erosion gullies. Increased δ13C values in Festuca valesiaca leaves by 1.1‰ towards the edge confirmed that this species copes best with the dry conditions at the edge. Conclusion: Our findings illustrate the insurance effect of a highly diverse vegetation. The importance of a single species out of this diverse species suite to sustain key ecosystem functions becomes apparent only under extreme environmental conditions; in this case, at edges of erosion gullies.

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.

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).

A Comparison of Climatic Niches of the Same Alpine Plant Species in the Central Caucasus and the Alps

It has been known for years that the elevational and latitudinal range limits of plant taxa are likely to be correlated (e.g. Humboldt 1817; Pellissier et al. 2013; Randin et al. 2013) and the elevation-for-latitude correspondence model has for long attracted ecologists and biogeographers. However, comparisons of the environmental niche of a common set of native plant species between geographically isolated regions but sharing similar climatic conditions have rarely been achieved (but see Randin et al. 2006 in the Alps). The large number of shared alpine plant species between the Alps and the Caucasus and the increasing availability of georeferenced occurrences and climatic data offer now opportunities to perform such across-mountain range comparisons.

New Indicator Values for Central Caucasus Flora

In this study we have aimed to extend the concept of indicator values of Ellenberg (1974) and Landolt (1977) for vascular plants of the Caucaus (Sakhokia and Khutsishvili 1975a, b, c), taking account those species which also occur in the Alps (more than 400 species). The resulting Nakhutsrishvili Indicator Values for the Caucasus (see Annex) were compared with those of Elias Landolt for the Alps (Landolt 1977). The results show a high overlap of both sets of indicator values, indicating both, a high overlap of the ecological niche of the species of the Alps and the Caucasus, and also an agreement of both experts for many species and indicator value classes (30–50% congruence). The results show that an extension of Landolt indicator values to the Caucasus is possible, and that the Nakhutsrishvili Indicator Value dataset can now be used for vegetation analysis of the Caucasus.

Quantitative Analysis of the Phytosociological Relevés from the Central Greater Caucasus

In the previous chapter, the Flora of the Great Caucasus was described and compared using syntaxonomic, morphological and ecological categories and we reported important or dominant species. Here we exemplify results of very detailed vegetation analysis for the best studied part of the central Caucasus using the Braun Blanquet type of releves of entire species assemblages. The releves were compiled for the Kazbegi region, and for ecosystems along several elevational gradients that is (1) the Mount Kasbek profile from 1700 to 3100 m with a single further releve at 3600 m a.s.l; (2) the Mount Kuro profile from the village of Kazbegi to the upper slopes of Mount Kuro from 1900 to 3050 m a.s.l.; and (3) the Kolteshi range profile from 1850 to 2450 m a.s.l.; and for the Racha region and for ecosystems along several elevational gradients that is the Mamisoni Pass to Chanchakhi glacier from 2800 to 3600 m a.s.l. These releves were made between the early 1960s and the early 2000s.