Graciela Rusch

Relationship between Productivity, and Species and Functional Group Diversity in Grazed and Non-Grazed Pampas Grassland

Most hypotheses addressing the effect of diversity on ecosystem function indicate the occurrence of higher process rates with increasing diversity, and only diverge in the shape of the function depending on their assumptions about the role of individual species and functional groups. Contrarily to these predictions, we show that grazing of the Flooding Pampas grasslands increased species richness, but drastically reduced above ground net primary production, even when communities with similar initial biomass were compared. Grazing increased species richness through the addition of a number of exotic forbs, without reducing the richness and cover of the native flora. Since these forbs were essentially cool-season species, and also because their introduction has led to the displacement of warm-season grasses from dominant to subordinate positions in the community, grazing not only decreased productivity, but also shifted its seasonality towards the cool season. These results suggest that species diversity and/or richness alone are poor predictors of above-ground primary production. Therefore, models that relate productivity to diversity should take into account the relative abundance and identity of species that are added or deleted by the specific disturbances that modify diversity.

The influence of spatial heterogeneity on regeneration by seed in a limestone grassland

. The spatial distribution of seedlings in fertilized and non-fertilized grassland patches (1 m x 2 m) was examined in alvar vegetation on the island of Oland, Sweden. We established whether variation in seedling distribution in grassland patches reflects the distribution of conspecific adults. We also established the significance of microsite turf attributes for prediction of seedling distribution at a small scale (10 cm x 10 cm), and the significance of conspecific adults abundance, assemblage of adult species and cover of lichens, mosses, litter and bare ground. Our results indicate that fertilization reduces the importance of regeneration by seed of perennial species and enhances seedling recruitment of winter annuals and biennials. At the patch scale, enrichment does not affect species richness. Community patchiness contributes to the maintenance of diversity by providing a variety of environments with differential regeneration of the component species. Cover of lichens, mosses, litter and bare ground, accounts, in part, for the spatial variation in seedling numbers of certain species. The strong association of seedlings of some species with conspecific adults indicates that limitations in dispersal and/or the occurrence of a more suitable environment for emergence and/or establishment close to conspecific adult plants are likely to constrain the spatial distribution of new individuals in many cases. For other species, the lack of association of seedling densities with the cover of their conspecific adults, suggests that long-distance dispersal or a long-lived seed bank can play a role in counteracting the effect of short-distance dispersal.

Species turnover and seedling recruitment in limestone grasslands

Species turnover and germination were analysed in the Veronica spicata-Avenula pratensis limestone grassland community. Species turnover was estimated on the basis of presence/absence of species in fifty 10×10 cm permanent plots during the period 1986 to 1989. The contribution made by reproduction by seeds to turnover was evaluated by recording newly-germinated seedlings on thirty-five 10×10 cm plots on three occasions during the growing season in each year from 1986 to 1989. Turnover, expressed as the sum of increase and decrease of individual species (when comparing subsequent years), varied much between species and remarkably much between years. Seedling recruitment varied widely amongst and within years, indicating the occurrence of non-synchronized regeneration occasions for different species (...)

Spatial pattern of seedling recruitment at two different scales in a limestone grassland

The effect of community pattern on seedling recruitment was analysed at two different scales, at the community level and at the intra-community level. Results showed that at the community level, the process of seedling recruitment is highly stochastic. The distribution of seeds in the seed-bank is locally clumped at a very small scale and a similar pattern was found for seedling recruitment. This means that at least part of the spatial distribution of seedlings can be explained by the fine-grained differences in the abundance of seeds. At the same time, the processes affecting spatial pattern of seedling recruitment at the community level are constrained by intra-community heterogeneity

Los servicios ecosistémicos como soporte para la toma de decisiones ambiental y socialmente sustentables

The theory of ecosystem services (ES) needs to be operationalized to contribute to practices leading to sustainable use of ecosystems, which includes solving trade-offs between private and public benefits and incorporating monetary and non-monetary values to help inform decisions. We developed a framework to analyse the impacts of farmers’ management alternatives on Nothofagus antarctica (G. Forst.) Oerst. forest in northern Patagonia, and analysed synergies and trade-offs between private and public benefits based on three conceptual and methodological approaches: a) a state-and-transition model of ecosystem dynamics, and b) indicators of values of ecosystem service benefits based on the cascade model, implemented as c) a decision support tool based on a Bayesian network. We optimized a utility function for short (0-10 yr) and long (70-140 yr) term management decisions (levels of grazing, logging and tree planting) based on monetary and non-monetary indicators of benefits that fulfilled “farmer’s satisfaction” objectives. We then assessed the consequences of these decisions on the fulfilment of public benefits as defined by the National Forest Law when projected into short (0-10 yr), intermediate (10-40 yr) and long (70-140 yr) time horizons. We found that when the short-term decisions are projected into a long-time horizon, they lead to high losses of benefits, mainly linked to “regulating and maintenance” ES. On the other hand, long-term decisions improved the level of benefits in degraded systems but resulted in the degradation of well-preserved forests. The decisions that optimize farmer’s satisfaction did not change with different weights of “farm income” in the utility function, indicating the absence of trade-offs between monetary and non-monetary benefits considered in the utility function. The tool developed helps to show long-term impacts of management, and discloses cause-effect relationships between levels of use and multiple benefits. It can therefore support measures aiming to raise awareness about degradation trends, and improve the functional understanding of the system that can lead to identify solutions for socio-economic and environmental sustainability. https://doi.org/10.25260/EA.17.27.1.1.295The theory of ecosystem services (ES) needs to be operationalized to contribute to practices leading to sustainable use of ecosystems, which includes solving trade-offs between private and public benefits and incorporating monetary and non-monetary values to help inform decisions. We developed a framework to analyse the impacts of farmers’ management alternatives on Nothofagus antarctica (G. Forst.) Oerst. forest in northern Patagonia, and analysed synergies and trade-offs between private and public benefits based on three conceptual and methodological approaches: a) a state-and-transition model of ecosystem dynamics, and b) indicators of values of ecosystem service benefits based on the cascade model, implemented as c) a decision support tool based on a Bayesian network. We optimized a utility function for short (0-10 yr) and long (70-140 yr) term management decisions (levels of grazing, logging and tree planting) based on monetary and non-monetary indicators of benefits that fulfilled “farmer’s satisfaction” objectives. We then assessed the consequences of these decisions on the fulfilment of public benefits as defined by the National Forest Law when projected into short (0-10 yr), intermediate (10-40 yr) and long (70-140 yr) time horizons. We found that when the short-term decisions are projected into a long-time horizon, they lead to high losses of benefits, mainly linked to “regulating and maintenance” ES. On the other hand, long-term decisions improved the level of benefits in degraded systems but resulted in the degradation of well-preserved forests. The decisions that optimize farmer’s satisfaction did not change with different weights of “farm income” in the utility function, indicating the absence of trade-offs between monetary and non-monetary benefits considered in the utility function. The tool developed helps to show long-term impacts of management, and discloses cause-effect relationships between levels of use and multiple benefits. It can therefore support measures aiming to raise awareness about degradation trends, and improve the functional understanding of the system that can lead to identify solutions for socio-economic and environmental sustainability. https://doi.org/10.25260/EA.17.27.1.1.295

Community aggregated traits disclose functional responses to seasonal resource fluctuations and spatial heterogeneity

Aim To investigate changes in community-level functional responses to rainfall seasonality in Neotropical grasslands through the analysis of community aggregated traits. Location Semi-natural grasslands in the Rio Grande de Matagalpa watershed, Nicaragua. Methods We measured 14 functional response traits that are indicators of plant resource-use strategies, across 32 herbaceous and four woody species in eight permanent plots: leaf size, specific leaf area, leaf dry matter content, leaf lifespan, foliar concentrations of P, N, Ca, K and Mg, plant height, lateral spread by clonal growth, root depth, start of flowering period and length of the period from flowering to seed shed. We calculated the community-weighted means (CWM) with trait values weighted by species cover for five different paddocks 11 times (between 2 Jul 2007 and 26 May 2008), and grouped them into four periods according to rainfall seasonality: early rainy season, late rainy season, early dry season and late dry season. Results Community aggregated values of specific leaf area, leaf dry matter content, leaf lifespan, foliar concentrations of P, N, Ca, K and Mg, length of the period from flowering to seed shed, and to a lesser extent lateral spread by clonal growth responded to temporal variations in rainfall, and corresponded to a considerable extent to expectations based on plant resource-use strategies along resource supply gradients. Community aggregated values of specific leaf area and foliar nutrient concentration were higher in the rainy season than in the dry season, while we observed an opposite trend with leaf dry matter content and leaf lifespan. Conclusions Semi-natural grasslands of central Nicaragua experience shifts in plant trait dominance that correspond with changes in resource supply given by rainfall seasonality, indicating that the stabilizing function of net primary productivity found in earlier studies can in part be a consequence of temporal differentiation in functional responses.