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The Northern Pocket Gopher ( Richardson) is a small herbivory subterranean rodent. It is known as an eager digger and in areas with intense activity it is suspected of damaging young tree growth. Results from soil analysis and snow measurements are presented to describe the pocket gophers’ summer and winter environment within a ribbon forest in the forest-alpine tundra-ecotone on Niwot Ridge, Colorado Front Range. The distribution of snow and the structure of snow cover are influencing the pocket gopher’s life under cover. Soil analysis showed that pocket gopher activity modified the soil environment. The amount of coarse soil particles in the upper topsoil layers was increased compared to topsoil with no gopher disturbance. The distribution of organic matter within the upper 12 cm was more homogeneous in areas with gopher excavation. None of the damages found on young trees could be attributed to pocket gopher activities without question. The most obvious damages were reduced growth at the windward side (83 %) followed by crippled growth (60 %) and damages caused by snow fungi (32 %). In summary, the pocket gophers in the ribbon forests on Niwot ridge are actively modifying the soil environment by exposing mineral soil and increasing the likelihood of soil erosion by wind and water. There is, however, no evidence that pocket gophers are responsible for the visible prevalent damage on juvenile conifers.

All species have limits to their distribution and individuals that demarcate margins demonstrate an end-point in adaptation to a changing environment. Limits to plant survival arise either from a failure to grow or from an inability to reproduce. Consequently, matching climatic data with geographical distribution has to consider the biological causes for the failure of plants to survive outside any given area. Physical factors, such as thermal time (day-degrees) and growing season length, differentiate between the broadly recognised vegetation zones of High, Low, and Subarctic. However, within these zones the limitations to plant distribution are less readily related to climatic factors. In peripheral areas, relating physical climatic factors to species occurrence requires a knowledge of the many interactions between physiology and genetics of populations as they approach their territorial margins. Examination of the extent of variation found in plants growing in cold habitats reveals large differences both between and within populations and at different seasons in metabolic rates, temperature responsiveness and metabolic efficiency. The High Arctic represents a peripheral zone where conditions are prone to large fluctuations. Consequently, plant distribution will be affected by aspects of the environment that are not permanent, but which occur irregularly with varying frequency and intensity. This paper considers the physiological and genetic properties of polar plant populations that may facilitate persistence in uncertain and heterogeneous adverse environments. Particular attention is given to those species that appear to have maintained a presence at high latitudes since pre-Pleistocene times and have therefore survived many past environmental fluctuations.

In the 20 century, the global climate has warmed about 0.6 K. High-mountain areas as well as areas of high latitudes are experiencing even greater increases in temperature especially in the last half century. With changing climatic conditions, the determinants of global, and in particular, altitudinal distribution of plants and plant communities are likely to change and a subsequent reaction of climate sensitive species and ecosystems is expected. The following paper focuses on observed climate-induced changes in the two uppermost altitudinal vegetational ecotones at the treeline and the upper limit of plant life at the alpine-nival transition zone.

Whitebark pine () is a high elevation stone pine characterized by heavy, wingless seeds that are primarily dispersed by the Clark’s nutcracker (). The relationship between seed dispersal, spatial distribution, and site characteristics of whitebark pine was studied in the timberline ecotone of the Beartooth Plateau, Montana and Wyoming. The study focused on regeneration patterns and prevailing microsite conditions which may limit or promote germination and survival of whitebark pine at its upper elevational limit.

Regeneration of Engelmann spruce ()and subalpine fir () was poor in both study areas. Juvenile whitebark pines were more abundant in areas with moderate to late snow release. Only few young whitebark pine seedlings and germinants were located on Tibbs Butte, whereas in the Wyoming Creek study area, young whitebark pine seedlings clusters (≤ 3 years) were present in all transects. Regeneration densities inside and leeward of the woodland were higher than on the windward side.

Regeneration results were not consistent with reported caching preferences of the Clark’s nutcracker. Sites with moderate to long snow cover, leeward of tree groups or in depressions, appear unfavorable for caching, because of restricted access to stored seeds, but were favorable for germination and survival of whitebark pine. Only nutcracker caches that are not retrieved and that are established in relatively moist and protected microsites contribute to recruitment.

The data of this study show that regeneration of whitebark pine does occur in parts of the timberline ecotone. Recruitment in exposed sites appears unsuccessful. Tree regeneration in timberline ecotones with continental climate character may require the additional moisture found in snowdrifts of small depressions or tree groups.

The subalpine southern Andean timberline is characterized by deciduous forests, which change with increasing altitude to krummholz, built of deciduous and . The current study examines the structure and species composition in timberline ecotones of the southern Andes to assess whether the deciduous timberline in the Andes results as convergent structure of, for example, -timberlines of the Northern Hemisphere.

Through a Braun-Blanquet phytosociological approach, we show how the characteristic structure and combination of timberline vegetation in the southern Andes vary in latitudes from 33°S to 55°S and altitudes between 2000 m and 600 m. Timberline composition was distinct at sites and included a variety of assemblages ranging from northern Azaro-Nothofagetalia communities to assemblages of the Adenocaulo-Nothofagetalia and Violo-Nothofagetalia in the South.

Krummholz generally occurred in a ten to some hundred meter wide ecotone. Four distinctive growth forms were identified; (1) ‘elfin woods’ where trees become more and more stunted as they approach the woodland limit readily observed in previous studies; (2) ‘cornice-like’ growth form characterized by branches close to the ground; (3) restricted to the leeward side, a single-stemmed habit occurred that was characterized by stems aligned downhill before curving up into vertical alignment; and (4) on the wind-exposed side, growth forms were characterized by single-stemmed habit and long branches running uphill. These growth form changes were apparently controlled by changes in abiotic factors and climate rather than genetically determined.

In conclusion, the recognition of the deciduous foliage and deformed habit of timberline trees in the southern Andes is explained by extreme climate. Comparison of same latitudes revealed that maximum altitudes of southern Andean timberline were generally higher than those of evergreen limits in New Zealand but lower than timberlines of Holarctic mountain ranges.

These results serve to emphasize that understanding structure and physiognomy of the southern Andean timberline and its apparent stability may require attention to ecophysiological adaptations and responses of timberline to high-mountain environment.

The Northern Pocket Gopher ( Richardson) is a small herbivory subterranean rodent. It is known as an eager digger and in areas with intense activity it is suspected of damaging young tree growth. Results from soil analysis and snow measurements are presented to describe the pocket gophers’ summer and winter environment within a ribbon forest in the forest-alpine tundra-ecotone on Niwot Ridge, Colorado Front Range. The distribution of snow and the structure of snow cover are influencing the pocket gopher’s life under cover. Soil analysis showed that pocket gopher activity modified the soil environment. The amount of coarse soil particles in the upper topsoil layers was increased compared to topsoil with no gopher disturbance. The distribution of organic matter within the upper 12 cm was more homogeneous in areas with gopher excavation. None of the damages found on young trees could be attributed to pocket gopher activities without question. The most obvious damages were reduced growth at the windward side (83 %) followed by crippled growth (60 %) and damages caused by snow fungi (32 %). In summary, the pocket gophers in the ribbon forests on Niwot ridge are actively modifying the soil environment by exposing mineral soil and increasing the likelihood of soil erosion by wind and water. There is, however, no evidence that pocket gophers are responsible for the visible prevalent damage on juvenile conifers.

The holarctic mutualisms between Pines (, Pinaceae) and nutcrackers (, Corvidae) comprise important textbook examples of interaction and coevolution. However, only recently we have learned to what extent nutcracker seed caching influences the ecology and biology of these pines. The North American mutualism between whitebark pine () and Clark’s nutcracker () demonstrates the greatest array of consequences to the pine, particularly in fire-dependent communities in the northern Rocky Mountains. The impacts of Clark’s nutcracker seed-caching on whitebark pine are evident at multiple spatial and temporal scales, from tree growth form and fine-scale genetic structure and the timing of regeneration and community development to regional and rangewide genetic structure, and post-Pleistocene range expansion.

Humus forms as well as the natural regeneration of European larch ( Mill.) and Swiss stone pine ( L.) were mapped along an altitudinal gradient from the subalpine forest to the alpine zone in the Upper Engadine (Switzerland). The establishment and distribution patterns of larch and stone pine as well as the humus forms are controlled by microtopography which influences other site factors. In the subalpine forest, Mor humus forms are very common, while in the timberline ecotone the humus forms can be described as Mor and Moder humus forms, and in the alpine zone Moder humus forms dominate. The thickness of the organic layers decreases from the subalpine forest to the alpine zone. The density of naturally regenerated European larch and Swiss stone pine has increased since the pastures have been abandoned. The analysis of the density and growth of both tree species lead to the conclusion that conditions above 2300 m a.s.l. are unsuitable for a successful reforestation of the study site.

Tree-ring widths of living and dead Scots pines ( L.) from Dividalen, intra-alpine northern Norway, were combined to two partial chronologies, AD 320–1167 and 1220–1994. Abundant pine remains indicate good growing conditions for Scots pine during the Viking Age and early Medieval times, whereas few logs are preserved from the period 1000–1450. A cold period around 1130 probably triggered massive pine mortality at the forest line and the depression of the pine tree-line by ca. 50 m. The forestline stands recovered first after a second cooling event around 1457. July temperatures were reconstructed for the time windows 587–980 and 1507–1993. Shorter spells of warm summers occurred around 607, 728, 1565, and 1762, and longer warm periods during the Viking Ages (ca. 819–957) and the 20 century since 1915. Cold summers prevailed ca. 749, 769–818, ca. 866, 1573–1624, ca. 1645, 1785–1826, ca. 1842 and 1864–1914.

The principal change in Italy’s rural landscape over the past fifty years has been the spontaneous return of woodlands on land previously used for agriculture and cattle-raising. This secondary succession, together with reafforestation projects carried out by man, is an ongoing process. The spontaneous recolonisation by woodland takes place in many areas, from agricultural land by the sea, in the Mediterranean environment, to the high altitude pastures of the Alps. This colonisation, which involves numerous native and exotic tree species, is sometimes preceded by a more or less long phase of shrub dominance; in other cases, the shrub phase is absent, and trees colonise the land immediately after agricultural use has ceased or when grazing pressure is reduced. The pattern of recolonisation is often influenced by the presence of remnant fodder or fruit trees or pre-existent agricultural artefacts, such as terraces or walls. Already existing woodland types, such as stone pine woods, expand, and new stand types are being formed, like ash-sycamore stands that in the past did not exist in the Italian forest landscape. Many broad-leaved tree species invade old-established sweet chestnut (), cork oak () and umbrella pine () plantations. The ecological and social consequences of this woodland expansion are, so far, virtually unknown. The social perception of this phenomenon is rather complex: some believe that a degradation of the rural territory is taking place and that the spread of woodlands close to villages and along the roads should be halted. Others, for various reasons, consider the ‘renaturation’ of the rural landscape as a positive factor.