Question: Is the response of plant traits to environment at the community level similar when considering species abundance and when considering species presence only? Location: Mountain grasslands, central Argentina. Methods: We used data from 57 floristic samples, ordinated through DCCA along moisture and grazing gradients combined with trait values from 85 species (plant height, leaf area, leaf thickness leaf toughness and SLA). For each sample, we calculated the weighted average (considering species abundance) and the simple average (considering only species presence). Through multiple regressions we analysed how each average (dependent variable) responded to moisture and grazing (DCCA scores along Axes 1 and 2, respectively, as independent variables). Results: Weighted averages of all traits were significantly associated to both gradients, while simple averages did not always respond. In some cases the responses followed similar but weaker trends than the responses of weighted averages, but in other cases these responses were qualitatively different. Traits more associated with size (plant height, leaf area, leaf thickness) responded more consistently (similar trends for both averages) to grazing than to moisture, while traits more associated with plant resource acquisition (SLA, leaf toughness) responded more consistently to moisture than to grazing. Conclusion: The trait values and combinations which determine the probability of species presence are not necessary the same as those which determine their probability of becoming abundant. To understand community assembly rules, both species presence and species abundance should be taken into account as the result of different, although closely linked, filtering processes.

No abstract

High mountain forests are often restricted to ravines and much debate has existed on the explanations of this distribution, with arguments ranging from abiotic site conditions being more favorable in ravines to there being reduced herbivory or reduced fire frequency and damage in ravines. We aim at understanding the contribution of fire damage and provide data to help test the hypothesis that fires are less damaging and that trees recover faster in ravines as compared to ridge sites. We evaluated crown damage, post-fire survival, regeneration by resprouts and seeds, and browsed stems in burned and unburned control Polylepis australis trees situated in a ravine and in a ridge forest in the west slope of the mountains of Central Argentina. The proportion of the tree crown scorched by fire was 28 % higher on the ridge than in the ravine (94.3 ± 1.9 % and 66.1 ± 4.5 %, respectively) and was negatively related to tree height which was lower on the ridge. Survival was not differentially affected, but post-fire re-growth and establishment through seeds was lower in the ridge as compared to the ravine. Browsed stems were about twice as frequent in the ridge as in the ravine, more so in the resprouting burned trees. Our study provides evidence that forests are restricted to ravines in part because the effects of fires are less severe at these sites than in ridges, which adds to other possible causes like reduced livestock use of ravines, enhanced regeneration by seed and faster tree growth within ravines all of which are probably mediated by abiotic factors.

Domestic livestock are widespread in seasonally dry forests, likely causing forest degradation and limiting tree seedling establishment. Shrubs can play an important role in facilitating tree regeneration, by protecting trees from livestock damage and ameliorating unfavorable abiotic conditions. We aimed at disentangling the relative contribution of grazing exclusion, long‐term forest conservation, and the potential facilitation effect of shrubs on the performance of saplings of the native tree Kageneckia lanceolata. We planted 400 saplings in grazed and ungrazed areas situated both in a preserved and a degraded forest. In each situation, we established planting plots in three accompanying vegetation treatments: herbs, a nonleguminous spiny shrub and a leguminous spiny shrub. Survival of 3‐year‐old saplings was 10‐fold higher in the preserved than in the degraded forest and 2‐fold higher in the ungrazed than in the grazed site. Differences in survival among accompanying vegetation treatments were much smaller than between grazing treatments. Survival significantly increased with increasing protection by shrubs only in the degraded site. Sapling growth patterns were fairly similar to survival patterns, with no growth in the degraded forest, except for limited growth under both shrubs in the ungrazed site. We conclude that, in selecting plantation sites for the study species, forest condition and grazing exclusion should be prioritized over microsite selection based on neighboring vegetation.

Introducción y objetivos: La restauración de bosques en sitios degradados por actividades antrópicas es una actividad importante en el manejo de sistemas montanos. Aún hace falta investigación tendiente a reducir el efecto de la herbivoría y de las condiciones ambientales hostiles sobre el establecimiento de plantines de árboles. Nos propusimos evaluar la efectividad de una protección física usando tubos de policloruro de vinilo (PVC) en la plantación de dos especies arbóreas nativas de las Sierras de Córdoba (Argentina) en un área con presencia de hormigas cortadoras.  M&M: Las especies de estudio fueron escallonia (Escallonia cordobensis) y maitén (Maytenus boaria). El área de plantación estuvo a 1840 m snm. Usamos 230 plantines por especie, 100 de ellos con y 130 sin protección de PVC. Fueron plantadas durante la estación húmeda en sitios con vegetación baja. Medimos semestralmente y por dos años la altura, la supervivencia y los daños por herbivoría. Resultados: Para escallonia y maitén, respectivamente, la protección aumentó la supervivencia a los dos años en 24 y 26%, aumentó la altura en 7,3 y 12,6 cm, y redujo la herbivoría por hormigas cortadoras en 30 y 51% en comparación con los plantines sin protección.  Conclusiones: El efecto favorable de las protecciones en la supervivencia y crecimiento podría deberse conjuntamente a la disminución de la herbivoría por hormigas cortadoras y al resguardo contra las condiciones abióticas desfavorables. Recomendamos estudios de más años, y tendientes a entender los mecanismos que subyacen a la mejora en el establecimiento de los plantines.