Seedling browsing by livestock has been indicated as major threat for forest sustainability use. Nothofagus pumilio forests are part of the livestock raising system in Patagonia, but because of the sparse understory cover, livestock graze mainly on flood meadows within the forest matrix. The complexity of the environment under study (forests and flood meadows) means that an adaptive predictor is needed to evaluate the intensity of resource use by livestock in order to assess its effect on the forest. Distance to flood meadows was evaluated as a predictor of the use intensity of the forest by livestock and its effect on the understory. The study was conducted at three sites in Chubut Province, Patagonia-Argentina. We established transects in the forest 320 m long, starting at the edge flood meadow-forest. In these transects, the livestock presence indicators (soil compaction, density of feces and trails) and composition of the understory were evaluated. Generalized Linear Model for repeated measures for longitudinal data were used. The indicators showed that distance is efficient for estimating forest use intensity by livestock. The understory varied with distance, the cover of exotic herbaceous was higher near the flood meadow. Far from the flood meadow, the cover was entirely composited of native species. The results support the use of distance to flood meadows as a tool for decision making in livestock and forest management in N. pumilio forests, and for further research on livestock effect on the forest.

No abstract

In managed forests, biodiversity conservation is crucial for the sustainable use of ecosystem resources. In the Patagonian-Andes forests of Argentina, lenga (Nothofagus pumilio) is the most important native tree because of its ecological functions and economic importance as a timber provider. In this study, we determined how the shelterwood-cut system impacts understory vegetation attributes in three sites representing typical lenga forests of central Andean-Patagonia. In each site, two 250-m 2 treatment plots (managed and unmanaged) were established, and canopy cover, soil temperature, and moisture were determined. Within plots in 10 randomly placed 0.25-m 2 microplots, we determined plant cover, from which we calculated diversity attributes. Canopy cover and soil moisture were higher in unmanaged treatments, whereas the reverse was true for soil temperature. The Shannon-Wiener index showed similar values (ϳ1), whereas species richness was slightly higher in unmanaged (4.8 Ϯ 0.5) than in managed treatments (3.8 Ϯ 0.3). Generally, native plants dominated the understory (ϳ40%), whereas exotic species were rare (ϳ1%). Shrub cover was higher in managed (24.1 Ϯ 4.2) than in unmanaged (9.5 Ϯ 1.7) treatments, whereas herbaceous species dominated unmanaged forests. These results confirm that the shelterwood-cut system may be used for diversity conservation in Patagonian lenga forests.

In the province of Chubut in Patagonia, Argentina, Nothofagus pumilio forests (locally known as lenga), are managed through selective cuts, which imply the opening of canopy gaps. This management scheme is carried out without taking into consideration the changes of sapling requirements through either a cutting cycle or the precipitation gradient in which these forests thrive. To analyze these changes, we inferred the facilitation-competition balance between the canopy and regeneration, studying the effects of precipitation levels, gap size and gap age on saplings growth in height on 45 canopy gaps artificially created between 1960 and 1993. Results showed that during the first 20 years since gap opening, growth of regeneration is determined by light availability in mesic sites and by water availability in xeric sites. However, differences due to precipitation levels gradually decrease over time. Moreover, in the period between 20 and 35 years after gap opening, in both mesic and xeric sites, growth is limited by light availability. This indicates that in xeric sites, sapling growth requirements shift from a water-dependent situation to a light-dependent situation. The average closing rate of gaps due to lateral growth of bordering trees is high enough so that within the proposed gap size range, gap healing can occur before regeneration reaches the upper stratum. Consequently, in mesic sites gap opening can be done by a single operation that generates gaps with diameters of approximately twice the average height of the canopy (D/H). While in xeric environments, lenga seedling establishment and initial growth require the cover of small gaps, but advanced regeneration requires bigger gaps to reach the canopy. For this reason, gaps should be opened in two stages: the first gaps should be opened with a D/H between 0.8 and 1, and after a cutting cycle of 35 years, these openings should be enlarged to a D/H between 1.5 and 2. The close relationship maintained between the new cohort and the upper strata require special considerations regarding the evolution of the balance between positive and negative interactions during development. Our work highlights the need to adjust management practices to these spatial and temporal variations to achieve an optimal growth along the entire production cycle.Key words: regeneration; group selection; height growth; stem analysis. ResumenCrecimiento de renuevos y expansión de copas en claros del dosel de bosques de Nothofagus pumilio (lenga) en Chubut, Patagonia, ArgentinaEn la provincia del Chubut, Patagonia Argentina, los bosques de Nothofagus pumilio (lenga) son manejados mediante cortas de selección, que implican la apertura de claros en el dosel. Este esquema de manejo es implementado sin tener en cuenta los requerimientos de los renuevos a lo largo de todo el ciclo de cortas ni el gradiente de precipitaciones presente en su distribución. Para analizar estos aspectos estimamos el balance facilitación-competencia entre el dosel y la regeneración, considerando los efectos d...