Species traits weakly involved in plant responses to landscape properties in Mediterranean grasslands

Bagaria G., Pino J., Rodà F., Guardiola M. (2012) Species traits weakly involved in plant responses to landscape properties in Mediterranean grasslands. Journal of Vegetation Science. 23: 432-442.
Enllaç
Doi: 10.1111/j.1654-1103.2011.01363.x

Resum:

Questions: What is the role of landscape structure and dynamics, compared with climatic and geographic factors, in determining species frequencies of grassland plant specialists under habitat loss? Do species traits mediate the relationship between plant community composition and environmental variables? Location: The Mediterranean mountain grasslands of southern Catalonia (NE Iberian Peninsula), over an area of 100 × 20 km. Methods: Using redundancy analysis (RDA), we explored the association between frequency of broad plant specialists and both present and past habitat patterns in the landscape (i.e. habitat amount and reduction over the period 1956-2003), after accounting for the effect of geographical location and climate in 29 grassland patches. Then, we constructed a database of biological and ecological plant traits potentially related to population persistence, in order to assess the role of these traits in explaining the found association between species composition and environmental variables. We used a single, three-table ordination analysis (RLQ) of the species frequencies, environmental variables and species traits to relate species traits to environmental variables, after allowing for phylogenetic dependence of traits. Results: The main environmental gradient explaining species frequencies was climatic and geographic. Habitat amount in the current landscape significantly affected species frequencies, while habitat amount in the past landscape did not. A weak but significant association of species traits with environmental variables was detected. Taking into account the phylogenetic signal in plant traits did not change the results. Conclusions: Plant species in Mediterranean grasslands seem to respond quickly to landscape change, since no effect of past landscape structure was observed on current species frequencies. Moreover, plant traits did not play a major role in mediating species response to environmental variation in these grasslands. Our findings differ from those obtained in northern and central European grasslands, probably due to differences in methodology but also to the smaller contrast in environmental conditions between grasslands and the adjacent forests and scrub in Mediterranean landscapes. © 2011 International Association for Vegetation Science.

Llegeix més

Changes in atmospheric deposition and streamwater chemistry over 25years in undisturbed catchments in a Mediterranean mountain environment

Àvila A., Rodà F. (2012) Changes in atmospheric deposition and streamwater chemistry over 25years in undisturbed catchments in a Mediterranean mountain environment. Science of the Total Environment. 434: 18-27.
Enllaç
Doi: 10.1016/j.scitotenv.2011.11.062

Resum:

Surface water chemistry has changed in response to reduced atmospheric deposition of sulphur and acidity in many regions of Europe and North America. Most of these studies come from acidic or low-alkalinity surface waters under high acidic deposition. Mediterranean climates offer a different biogeochemical context, characterised by streamwaters of higher alkalinity and low acid inputs. In this paper, we use surveys of streamwater chemistry conducted in 1981-1984 and again in 2007 in the Montseny natural park (NE Spain) to test whether streamwaters of these well-buffered catchments respond to changes in atmospheric deposition, which has declined for S during the last decades in NE Spain while remaining about stable for nitrogen. The 23 sampled streams drained heathland, beech forests and evergreen oak forests in relatively undisturbed small catchments underlain by silicate bedrock. Bulk deposition of sulphate at Montseny decreased by 54% while nitrate bulk deposition increased (non-significantly) by 30% in this period. Total N deposition is estimated in the range 15-30kg Nha-1y-1 for NE Spain. This is well above threshold values (e.g. 10kg Nha-1y-1) reported as starting nitrogen saturation symptoms in forest ecosystems in Europe. Baseflow sulphate concentrations decreased on average by 47μeqL-1 or 29% of early 1980s concentrations. Baseflow mean nitrate concentrations increased significantly but only from 5.5 to 8.9μeqL-1. Thus, despite decades of high N deposition, these ecosystems appear to be still far from N saturation. Baseflow alkalinity and base cation concentrations increased substantially, probably a combined result of decreased S deposition, enhanced silicate weathering under current higher temperatures, reduced plant cation uptake as vegetation matures, and slightly drier conditions in the survey of 2007. Overall, these well-buffered catchments have shown sizable changes in baseflow chemistry in response to changed atmospheric deposition and other environmental changes. © 2011 Elsevier B.V.

Llegeix més