Daniel Renison

Combined effects of environment and grazing on vegetation structure in Argentine granite grasslands

Abstract Effects of grazing and environment on vegetation structure have been widely acknowledged, but few studies have related both factors. We made 57 floristic samples in a highly variable landscape of mountain grasslands in central Argentina; 26 sample were in fence-lines with contrasting vegetation. For each sample, we recorded topographic and edaphic parameters, as well as grazing intensity indicators. Floristic gradients were analysed with DCA and relations with abiotic and grazing-related variables were detected with DCCA. Floristic axis 1 was explained by edaphic parameters associated to topography, ranging from communities in well drained soils on upper topographic positions to hydromorphic vegetation in poorly drained soils on lower topographic positions. Species richness decreased as soil moisture increased. Floristic axis 2 was associated with present and long-term grazing indicators, and reflected shifts in vegetation physiognomy and species evenness. Tall tussock grasslands, with low species evenness and evidences of low or null grazing intensity were located at one extreme. Tussocks were gradually replaced by short graminoids and forbs towards the centre of the gradient, as grazing increased, and evenness reached a maximum. In degraded sites with heavy long-term grazing intensities, short perennial species were replaced by an annual species, and evenness decreased. The magnitude of changes in floristic composition produced by grazing decreased with increasing soil moisture, and vegetation-environment relationships were stronger in moderate to highly grazed situations than in lightly or non grazed situations.

Efectos del fuego sobre un bosquecillo de Polylepis australis (Rosaceae) en las montañas de Córdoba, Argentina

El fuego es usado para transformar bosques en pastizales y estimular el rebrote de los pastos para aumentar su valor forrajero. Segun algunos autores, este uso del fuego ha provocado una retraccion de los bosques de Polylepis a sitios rocosos inaccesibles al fuego, mientras que otros autores postulan que su distribucion es debida al ambiente favorable en las rocas y no a la accion del fuego. Aqui evaluamos el efecto relativo del fuego y el ambiente sobre la supervivencia, produccion de semillas y crecimiento de Polylepis australis Bitter (Rosaceae) en un bosquecillo de las montanas de Cordoba. Realizamos un seguimiento de 74 individuos quemados y controles durante 3,5 anos. La presencia de rocas tuvo una fuerte influencia en el porcentaje en que se quemaron los individuos. A su vez, el porcentaje en que se quemaron se relaciono negativamente con la supervivencia, produccion de semillas y el crecimiento en altura. La produccion de biomasa fue mayor cuando se quemaron en un porcentaje intermedio. Exceptuando la proteccion al fuego, la roca no tuvo ningun efecto positivo sobre las variables medidas. Estos resultados sugieren que la distribucion actual de P. australis es al menos en parte debida al fuego. Para su conservacion sugerimos minimizar los fuegos, desarrollar actividades con alto riesgo de incendio en sitios con alta proporcion de roca y, si es posible, proteger los ejemplares expuestos al fuego con piedras.

Factors associated with woody alien species distribution in a newly invaded mountain system of central Argentina

To help determine the major factors associated with alien plant in a newly invaded mountain range; we analyzed the distribution patterns of woody alien species along the altitudinal gradient of the Córdoba mountains, in relation to biotic, abiotic and anthropogenic factors. We selected 303 plots using a Geographic Information System (GIS) covering all the variability of these factors. In the field we registered woody alien occurrence in these 303 and in 303 additional neighbor plots. We used 12 biotic, abiotic and anthropogenic variables from the GIS to predict the probability of presence of alien species through a logistic model. Then, we analyzed if neighbor alien occurrences could explain some additional variance. We created a probability map with 4 categories of alien occurrence which was then validated by new field sampling. Occurrence of woody aliens was highest in the eastern slope (with longer history of species introduction), at low altitudes, near sources of propagule pressure (human settlements, roads and neighbor sites with established alien plants), and associated to sheltered topographies. In the upper belt of the Córdoba Mountains woody invasion is incipient and thus in a transient stage. Accordingly, propagule pressure seems to be the major factor at play, while the relevance of disturbance and biotic interactions is less clear.

Avian responses to tourism in the biogeographically isolated high Córdoba Mountains, Argentina

Species do not respond identically to the presence of humans, and this may have consequences at higher-levels of ecological organization. We established bird transects on and off recreational trails in the high Córdoba Mountains of Argentina, a biogeographic island characterized by high levels of endemism, to examine the effect of human visitation at three different levels: (a) community (avian species richness and diversity), (b) guild (relative density of carnivores, granivores, insectivores, and omnivores), and (c) population (relative density of individual bird species). Human presence in the high Córdoba Mountains decreased avian species richness and diversity, and reduced insectivorous relative density, but we did not detect significant effects on granivores, omnivores, and carnivores. At the population level, 6 of 28 species were negatively affected by human visitation; four of these species are of conservation concern. Our results show negative responses to recreationists at multiple levels (e.g., reductions in density, displacement of species from highly visited areas), which may be related to spatial and temporal access to suitable resources, physical disturbance or species-specific tolerance thresholds. Our study area had lower levels of human visitation relative to other protected areas in the Northern Hemisphere, which raises the issue of whether this kind of biogeographically isolated habitat may be too fragile to sustain increasing levels of tourism.

HIGHLY REDUCED GENETIC DIVERSITY OF ROSA RUBIGINOSA L. POPULATIONS IN THE INVASIVE RANGE

Rosa rubiginosa (Rosaceae) populations introduced to Argentina successfully invade various habitats, forming extensive impenetrable thickets. To investigate the consequences of founder events and to track the native origin of Argentinean populations, the genetic diversity of invasive R. rubiginosa populations was compared with that of native populations in Europe, and genetic similarity was assessed between groups. We sampled 13 Argentinean populations and 20 native populations in Germany and Spain, and we applied two molecular marker techniques (simple sequence repeats and random amplification of polymorphic DNA [RAPD]). Genetic diversity within the invasive range was clearly lower than it was in the native range. Principle coordinate analysis and between‐class analysis did not reveal the exact European origin of the invasive populations, but our data suggest that at least one Argentinean population originated in Germany. Overall, the strong similarity of RAPD and allelic phenotypes throughout Argentina suggests a limited number of introduction events, that the species spread through human transport, and that the few genetic phenotypes present in the species were conserved largely unaltered as a result of mainly asexual reproduction.

The road to sustainability must bridge three great divides.

The worlds large and rapidly growing human population is exhausting Earths natural capital at ever‐faster rates, and yet appears mostly oblivious to the fact that these resources are limited. This is dangerous for our well‐being and perhaps for our survival, as documented by numerous studies over many years. Why are we not moving instead toward sustainable levels of use? We argue here that this disconnection between our knowledge and our actions is largely caused by three “great divides”: an ideological divide between economists and ecologists; an economic development divide between the rich and the poor; and an information divide, which obstructs communications between scientists, public opinion, and policy makers. These divides prevent our economies from responding effectively to urgent signals of environmental and ecological stress. The restoration of natural capital (RNC) can be an important strategy in bridging all of these divides. RNC projects and programs make explicit the multiple and mutually reinforcing linkages between environmental and economic well‐being, while opening up a promising policy road in the search for a sustainable and desirable future for global society. The bridge‐building capacity of RNC derives from its double focus: on the ecological restoration of degraded, overexploited natural ecosystems, and on the full socio‐economic and ecological interface between people and their environments.

Age–size–habitat relationships for Polylepis australis : dealing with endangered forest ecosystems

Assessing tree ages is important for the understanding of forest recruitment patterns and tree growth. However, little experience exists in the subtropics and accurate aging usually involves potentially damaging techniques such as tree coring or even the use of entire cross sections, which is not recommendable in endangered species or ecosystems. We provide an example of how age may be predicted on the basis of tree size and site conditions, using Polylepis australis of Central Argentina. Our study was conducted in two entire river basins where 96 independent trees were successfully cored for age analysis. Site and tree characteristics were registered and tree age determined through standard dendrochronological techniques. The multiple regression procedure selected tree circumference and proportion of rock under the tree canopy as significant variables explaining 48% of the variation in number of growth rings. Trees surrounded by rock clearly grew slower than those surrounded by a higher proportion of soil and vegetation. A comparison with a one site study shows that the ability to predict P. australis age is clearly reduced when geographical range is extended but the explanatory power of our model is still high enough for certain applications and within the range of other one site studies. We suggest that tree size and site characteristics may be used to predict age in other subtropical mountain forests with a well marked growth season.

Latitudinal patterns of bird richness, diversity and abundance in Polylepis australis mountain forest of Argentina

Many South American hotspots of bird endemism are found in Polylepis dominated forests. Although the avifauna of Polylepis forests has been relatively well studied in the tropical Andes, little is known in Argentina. In this study, we characterize the Argentine avifauna of Polylepis australis forests along their entire latitudinal gradient of distribution and provide a first systematic bird list and their conservation status. Fieldwork was carried out from 1,500 to 2,800 m a.s.l. in three study sites: North (Jujuy province), Centre (Tucuman province) and South (Cordoba province); we surveyed 30 point counts per site. We recorded 543 individuals belonging to 50 bird species; two subspecies are endemic to the South site and four species are typical Polylepis forest birds of the North and Centre sites. We identified four species of conservation concern; one globally threatened and three declining at regional level. Bird richness and abundance decreased with latitude; and equitability showed an inverse pattern. Sorensons similarity index ranged from 12% to 40% showing a large latitudinal turnover in avian communities. Disturbance-sensitive species were the most diverse group in the North site. Variations in species richness, evenness and guild composition may be a response to latitude, but also to differences in habitat complexity and food availability, which appear to be a consequence of forest degradation at the South site. We recommend: (1) the enlargement of Calilegua National Park to include the Polylepis australis belt to assure the conservation of many disturbance-sensitive species which could decline or disappear in degraded areas; (2) management of Quebrada del Condorito National Park to increase the forest structure complexity and therefore provide habitat for disturbance-sensitive species.

Range-wide genetic structure and diversity of the endemic tree line species Polylepis australis (Rosaceae) in Argentina

PREMISE OF THE STUDY Knowledge on the range-wide distribution of genetic structure and diversity is required to facilitate the understanding of historical tree migration and for predicting responses to current climate change. With respect to post-glacial migration patterns known from the northern hemisphere, we tested the prediction that the southernmost populations of a subtropical tree line species have lower within-population genetic diversity and higher genetic differentiation than the central and northernmost populations. METHODS We used AFLP to assess the genetic structure of 18 populations of the wind-pollinated Polylepis australis (Rosaceae) sampled over its entire distributional range in three Argentinean high mountain regions. Genetic diversity was calculated as a percentage of polymorphic bands (P) and Neis expected heterozygosity (He); genetic differentiation was assessed using AMOVA, Φ(ST)--statistics, and Bayesian cluster analysis. KEY RESULTS Contrary to our expectations, the northernmost Polylepis australis stands had lower within-population genetic diversity and higher genetic differentiation than the central and southernmost stands. Populations grouped into two major clusters, the first containing the southern populations and four central populations and the second containing the northern and one central population. CONCLUSIONS Patterns of Polylepis australis genetic structure and diversity differ from historical migration scenarios observed for the northern hemisphere. The decline in genetic diversity toward the north may point to an equatorward migration following past climatic changes. Populations within the south and central part appear to be connected by effective long-distance pollination while gene flow in the northern part is probably hampered by geographic isolation.

Short-Term Effects of Pack Animal Grazing Exclusion from Andean Alpine Meadows

Abstract Grazing by livestock can have positive, neutral, and/or negative effects on vegetation depending on the intensity and type of grazing. This includes grazing by pack animals used for tourism in mountain protected areas. We assessed the response of vegetation to the exclusion of grazing by pack animals over one growing season in the highest park in the Southern Hemisphere, Aconcagua Provincial Park, dry Central Andes. Twenty pairs of exclosures and unfenced quadrats were established in three high-altitude Andean alpine meadows that are intensively grazed by horses and mules used by commercial operators to transport equipment for tourists. Vegetation parameters, including height, cover, and composition were measured in late spring when exclosures were established and ~120 days later at the end of the growing season along with above-ground biomass. Data was analyzed using mixed models and ordinations. Vegetation responded rapidly to the removal of grazing. Vegetation in exclosures was more than twice as tall, had 30% more above-ground biomass, a greater cover of grasses including the dominant Deyeuxia eminens, and less litter than grazed quadrats. These changes in the vegetation from short-term exclusion of grazing are likely to increase the habitat quality of the meadows for native wildlife.