Andrea C. Mayer

An Evaluation of Dendroecological Indicators of Snow Avalanches in the Swiss Alps

ABSTRACT Avalanche records are important for land-use planning and risk management in mountainous areas. Written records on dates, disturbed area, and pressure patterns of past snow avalanches are scarce. Tree rings can be used to complement written records on past avalanche activity. We conducted two case studies at documented avalanche tracks in the Swiss Alps to determine the most valuable dendroecological indicators for reconstructing past avalanche events. Both tracks were impacted by avalanche events in 1951 and 1999, the two most exceptional avalanche years in recent Swiss history. The difference in tree age among the track, border, run-out, and control sectors was a valuable indicator of the area impacted by past avalanches, but not a useful tool to establish dates of avalanche occurrences. Comparisons of reaction wood formation, changes in stem eccentricity, and presence of traumatic resin canals among sectors showed significantly larger values of these indicators after the 1999 event in the track areas, and in minor degree in the border areas. Abrupt growth changes following the 1999 event were identified in most disturbed trees. Growth releases were commonly accompanied by the formation of reaction wood. Tree-ring evidences for the 1951 avalanche event were limited mainly due to the removal of debris by local communities. The intensity of avalanche events was difficult to determine using tree-ring indicators. Although dates and areas impacted by documented avalanche events were sometimes assessed using single indicators, more precise reconstructions result from the combined use of several dendroecological indicators.

Influence of colour type and previous cultivation on secondary metabolites in hypocotyls and leaves of maca (Lepidium meyenii Walpers)

BACKGROUND Maca is an Andean crop of the Brassicaceae family which is mainly known for its fertility-enhancing properties following consumption. The hypocotyls display various colours ranging from white to black. Each colour has different biological effects. The aim of this study was to analyse the concentrations of major secondary metabolites in hypocotyls and leaves of maca in a controlled planting experiment in the Peruvian Andes at 4130 m above sea level. The effects of colour type and of previous cultivation of the field were examined. RESULTS In the hypocotyls, the colour type effect was significant for most secondary metabolites; exceptions were beta-sitosterol and campesterol. The lead-coloured, yellow and violet maca hypocotyls were rich in glucosinolates, macaene and macamides, respectively. Previous cultivation affected macaene, campesterol and indole glucosinolate concentrations. Effects on metabolite concentrations in the leaves were minor. Hypocotyls were richer in macaene, macamides and glucosinolates than were leaves, and were poorer in beta-sitosterol and total phenols. CONCLUSION Colour type has to be considered in maca production, as colour associates with variations in concentrations of distinct bioactive metabolites. Leaves may be interesting for animal nutrition purposes as they contain essentially the same secondary metabolites as the hypocotyls but in clearly lower concentrations.

Long-Term Impact of Cattle Grazing on Subalpine Forest Development and Efficiency of Snow Avalanche Protection

Abstract The study presented herein investigated the differences in stand structure of grazed and ungrazed subalpine forests and whether subalpine forests used for grazing satisfactorily protect against avalanches. In subalpine forests of Picea abies L. Karst and Larix decidua Miller, grazed and ungrazed plots of 225 m2 were analyzed through the use of dendroecological methods. The grazed forests were found to be less dense than the ungrazed forests and to have a higher percentage of European larch. However, the density of the forests investigated was high enough to impede the release of avalanches. The young trees grew faster in the grazed forests. There were less dominant trees in grazed forests, and these trees were much older than in ungrazed forests. The main structure types in the grazed and ungrazed forests were multilayered open and uniform dense, respectively. The management of mountain forests as wood pastures seems to enhance the readiness of the forest owners to conduct selective logging operations. Thus, forest grazing can encourage the development of heterogeneously structured forest stands, which can regenerate more easily while fulfilling a function of avalanche protection.

Reconstrucción espacial y temporal de la ocurrencia de avalanchas de nieve en los Andes patagónicos utilizando técnicas dendrocronológicas

Las avalanchas de nieve representan un importante riesgo natural en diversas regiones montanosas alrededor del mundo. Danos a infraestructura y perdidas de vidas humanas son reportados frecuentemente en relacion a eventos catastroficos de avalanchas. En los Andes, numerosas obras de infraestructura se ubican en zonas vecinas a senderos de avalanchas, de las que poco se conoce sobre sus alcances maximos, periodos de retorno y presiones de impacto. A traves de la implementacion de tecnicas dendrocronologicas hemos reconstruido las fechas de ocurrencia y areas de influencia de eventos pasados de avalanchas de nieve. Ejemplares de Nothofagus pumilio con perturbaciones visibles de avalanchas fueron muestreados en sectores del canal, bordes y zonas de frenado de 11 senderos de avalanchas ubicados en Loma de las Pizarras, proximo a El Chalten, Santa Cruz, Argentina. Ademas, areas de control fueron muestreadas para determinar las condiciones de crecimiento en arboles no afectados por avalanchas. Nuestros analisis indican que las cicatrices, las variaciones de excentricidad en el leno, los cambios abruptos de crecimiento y la presencia de leno de tension son los principales indicadores dendrocronologicos en N. pumilio asociados a la ocurrencia de avalanchas. Basados en una ponderacion cuantitativa de los indicadores y en la profundidad de muestreo, calculamos un indice de ocurrencia de eventos, el cual nos permitio determinar para cada sendero los anos con ocurrencia de avalanchas. Considerando de manera integral la actividad de avalanchas en los 11 senderos muestreados, los anos con mayor ocurrencia de eventos fueron 1936, 1966, 1978 y 1995. Complementariamente, registros climaticos fueron analizados con el objetivo de determinar las relaciones entre los anos con ocurrencia de avalanchas y las variaciones mensuales de precipitacion y temperatura. Se observa que los anos con gran frecuencia de avalanchas estan significativamente correlacionados con la ocurrencia de abundantes precipitaciones invernales; no se detectaron relaciones significativas con las variaciones de temperatura. Los resultados alcanzados en esta investigacion prueban el potencial dendrocronologico de N. pumilio para reconstruir patrones espaciales y temporales de avalanchas de nieve en los Andes patagonicos.

Plant species selection by free-ranging cattle in southern Bolivian tropical montane forests

The frequency of selection of functional groups and plant species by free-ranging cattle foraging in a diverse environment and its changes during the dry and the following prehumid seasons were investigated using direct observations and bite counting. The study was conducted at two sites in the Bolivian-Tucuman montane forests in southern Bolivia, by including datasets of a total of 16 animals. Across both study sites and the entire observation period (May to October/November), the cattle were found to select a broad spectrum of plant species from different functional groups. However, just a limited number of species made up a considerable contribution to overall plant selection. The functional group of the graminoids was selected most frequently, but their contribution to plant selection decreased significantly from 63.5% of total bites in May to 15.9% in September/October, in accordance with a decrease in availability. Selection of woody plants (shrubs and tree parts, the latter mainly in the form of leaf litter and fruits) increased with time, reaching its peak at the beginning of the prehumid season, while the herbs showed a curvilinear pattern of selection which was highest in August. Plant species belonging to the functional groups of ferns, climbers and epiphytes were also selected by the cattle, but generally at low relative proportions. Plant selection might be influenced by temporal differences in nutritional quality and availability of the preferred plant species and functional groups. Sampling behaviour seems to be the most likely reason for the inclusion of a broad range of plant species with overall low contribution to plant selection.