Ferran Rodà

Extinction debt: a challenge for biodiversity conservation

Local extinction of species can occur with a substantial delay following habitat loss or degradation. Accumulating evidence suggests that such extinction debts pose a significant but often unrecognized challenge for biodiversity conservation across a wide range of taxa and ecosystems. Species with long generation times and populations near their extinction threshold are most likely to have an extinction debt. However, as long as a species that is predicted to become extinct still persists, there is time for conservation measures such as habitat restoration and landscape management. Standardized long-term monitoring, more high-quality empirical studies on different taxa and ecosystems and further development of analytical methods will help to better quantify extinction debt and protect biodiversity.

Novel Approaches to Study Climate Change Effects on Terrestrial Ecosystems in the Field: Drought and Passive Nighttime Warming

This article describes new approaches for manipulation of temperature and water input in the field. Nighttime warming was created by reflection of infrared radiation. Automatically operated reflective curtains covered the vegetation at night to reduce heat loss to the atmosphere. This approach mimicked the way climate change, caused by increased cloudiness and increased greenhouse gas emissions, alters the heat balance of ecosystems. Drought conditions were created by automatically covering the vegetation with transparent curtains during rain events over a 2–5-month period. The experimental approach has been evaluated at four European sites across a climate gradient. All sites were dominated (more than 50%) by shrubs of the ericaceous family. Within each site, replicated 4-m × 5-m plots were established for control, warming, and drought treatments and the effect on climate variables recorded. Results over a two-year period indicate that the warming treatment was successful in achieving an increase of the minimum temperatures by 0.4–1.2°C in the air and soil. The drought treatment resulted in a soil moisture reduction of 33%–82% at the peak of the drought. The data presented demonstrate that the approach minimizes unintended artifacts with respect to water balance, moisture conditions, and light, while causing a small but significant reduction in wind speed by the curtains. Temperature measurements demonstrated that the edge effects associated with the treatments were small. Our method provides a valuable tool for investigating the effects of climate change in remote locations with minimal artifacts.

Landscape structure and bird species richness: implications for conservation in rural areas between natural parks

Regional planning is bound to play an increasing role in nature conservation policies because much biodiversity is located outside natural parks and other protected areas. Differences in landscape structure between natural parks and surrounding areas may affect their respective species richness and may provide seasonal habitats that enhance total biodiversity. To test these ideas, we analyzed patterns of bird species richness, and its associated conservation value in a largely forested rural area that lies between the natural parks of Sant Llorenc del Munt and Montseny (Catalonia, NE Spain). Relationships of species richness with spatial gradients (X and Y Universal Transversal of Mercator (UTM) coordinates) and with altitude and landscape variables were tested by stepwise multiple regression analysis. Regressions were performed separately for both breeding and wintering species, and considering both all species and only several dominant ecological groups (forest, forest-cropland and cropland species). Bird species richness and its associated conservation value were higher in the study area than in the surrounding borders of natural parks. Cropland and forest-cropland species concentrated outside the natural parks, whereas forest species were uniformly distributed. Total bird species richness was mainly related to landscape diversity and to abundance of open habitats like croplands and shrublands. Cropland species were the most dependent on the abundance of crops and on landscape diversity, whereas forest and forest-cropland species exhibited weak correlations with landscape variables. Most forest species were year-round residents, whereas forest-cropland and cropland species exhibited seasonal shifts in the number of species, mainly because of interchanges with other areas. Results indicate that rural areas play a role complementary to the surrounding natural protected areas in the conservation of bird species richness at different scales. Implications for the design and optimization of ecological networks in the perimetropolitan area of Barcelona are discussed.

Land cover change in Europe between 1950 and 2000 determined employing aerial photography.

BIOPRESS (‘Linking Pan-European Land Cover Change to Pressures on Biodiversity’), a European Commission funded ‘Global Monitoring for Environment and Security’ project, produced land cover change information (1950—2000) for Europe from aerial photographs and tested the suitability of this for monitoring habitats and biodiversity. The methods and results related to the land cover change work are summarized. Changes in land cover were established through 73 window and 59 transect samples distributed across Europe. Although the sample size was too small and biased to fully represent the spatial variability observed in Europe, the work highlighted the importance of method consistency, the choice of nomenclature and spatial scale. The results suggest different processes are taking place in different parts of Europe: the Boreal and Alpine regions are dominated by forest management; abandonment and intensification are mainly encountered in the Mediterranean; urbanization and drainage are more characteristic of the Continental and Atlantic regions.

Saharan dust and the atmospheric inputs of elements and alkalinity to mediterranean ecosystems

Saharan dust delivered by so-called ‘red rains’ strongly influences precipitation chemistry in the Mediterranean region. We show here that at rural sites in eastern Spain, red rains have much higher ion concentrations than non-red rains, and they account for up to 50% of the mean annual input of dissolved elements in bulk precipitation, though they make up only a minor part of the annual rainfall. The mean annual input of alkalinity in red rains is enough to neutralize the input of free acidity in acidic precipitation. Transport of Saharan dust is thus a major ecological force in Mediterranean ecosystems through its effects on the acid neutralizing capacity of the atmosphere and the atmospheric deposition of elements.

Phosphorus limitation and competitive capacities of Pinus halepensis and Quercus ilex subsp. rotundifolia on different soils

Aleppo pine (Pinus halepensis) and the evergreen holm oak (Quercus ilex) dominate forest areas of the Mediterranean Basin. Both species regenerate abundantly after fires: pine through seedlings and holm oak through resprouts. Cumulative nutrient losses caused by frequent fires may have decreased soil nutrient availability in such areas. To assess the role of nitrogen and phosphorus as limiting factors for growth of these species during post-fire recovery, a field fertilisation and competition experiment was conducted in a 5-year post-fire shrubland on calcareous soil, where naturally-regenerated saplings of Aleppo pine and resprouts of interior holm oak (Quercus ilex subsp. rotundifolia) coexist. Three years after fertilisation, relative basal area increment was 56% greater in pines fertilised with 250 kg P ha–1 than in non fertilised ones. N fertilisation had small or no effects. Interactions between N and P fertilisation were not observed. Growth of Aleppo pine only increased with P fertilisation when neighbours were removed. Hence, the negative effect of neighbours on growth was greater when P availability was enhanced by fertilisation. In contrast, holm oak was able to grow more (110%) in response to increased P supply even without neighbour removal. A common garden experiment was then conducted with potted seedlings to investigate whether the suggested higher competitive capacity of holm oak for P held under a range of P amendments on different soils and competitive situations. P fertilisation increased seedling biomass yield of both species. When P availability increased, a negative effect of neighbours on growth was observed for holm oak and in 70 a lesser extent for Aleppo pine. In conclusion, in the field, holm oak resprouts showed higher competitive ability for P uptake compared to Aleppo pine saplings, but in potted seedlings in common garden conditions this trend was not observed. Therefore holm oak is not always competitively superior to Aleppo pine for P. Potted seedlings of both species had a notable plasticity in shoot/root biomass allocation, but only holm oak increased its proportional allocation to roots when neighbours were present. P availability can be a key factor in growth and competitive relations of these two species, but effects differ depending on soil type, individual age, regeneration type (i.e., seedling versus resprouts), and competitive situation.

Nitrogen deposition in Mediterranean forests

Atmospheric deposition of inorganic nitrogen was studied at two forested sites in the Montseny mountains (northeast Spain), peripheral to the Barcelona conurbation, and at a nearby lowland town, using bulk deposition, wet-only deposition, throughfall, and dry deposition inferred from branch-washes and surrogate surfaces (metacrylate plates). Bulk deposition inputs of ammonium and nitrate did not show significant temporal trends over a 16-year period. Bulk inputs of inorganic N were moderate, ranging from 6 to 10 kg N ha(-1) year(-1) depending on the time period considered and the degree of site exposure to polluted air masses from the Barcelona conurbation. Large dry-sedimented particles played a minor role, since wet-only inputs were virtually identical to bulk inputs. On the contrary, branch- and plate-washes indicated substantial dry inputs of N gases and small particles. Total atmospheric deposition was estimated at 15-22 kg N ha(-1) year(-1), most of it being retained within the studied broadleaved evergreen forests. Ecosystem N availability is thus likely to be increasing in these forests.

Effects of a nutrient pulse supply on nutrient status of the Mediterranean trees Quercus ilex subsp. ballota and Pinus halepensis on different soils and under different competitive pressure

Nutrient availability is a key factor in Mediterranean ecosystems that affects the primary productivity and the community structure. The great variability of its natural availability is now increasing due to frequent fires, pollution events and changes in rainfall regime associated to climate change. Quercus ilex ssp. ballota and Pinus halepensis are the most abundant tree species in the NW Mediterranean basin. They frequently compete in the early and middle successional stages. We investigated the effects of N and P pulse supplies on nutrient uptake capacity in these two species in an after-fire field area and in nursery conditions on different soil types and competing conditions. In the field, N fertilisation had weak effects on nutrient concentration and mineralomass likely as a consequence of this nutrient not being limiting in this field site whereas P fertilisation increased the P mineralomass and the Mg, S, Fe, K and Ca concentrations and mineralomass in the different biomass fractions of both species 1 and 3 years after fertilisation application. In the nursery experiments, P fertilisation increased the mineralomass and concentrations of P, Mg, S, Fe, K and Ca in all biomass fractions including the roots in both species and in different soils and competition conditions. The increment of nutrient mineralomass was due to both the increase of growth and of nutrient concentrations. Both species were able to absorb significant amounts of the P applied by fertilisation (between 5 and 20%) in short time (18 months). Competing vegetation decreased the positive effects of P fertilisation, and in many cases the negative effect of competing vegetation on nutrient mineralomass was stronger when P availability was increased by fertilisation. Q. ilex subsp ballota showed a greater competitive ability for P than the more pioneer species Pinus halepensis in the field but not in the nursery conditions. Pinus halepensis had greater nutrient mineralomass in calcareous than in siliceous soils. Q. ilex subsp. ballota had a higher root biomass allocation and root nutrient allocation than P. halepensis, but both species showed a high capacity to increase their nutrient uptake when its availability increased by fertilisation, thus assuring a great nutrient reserve for future growth periods and contributing to retain nutrients in the ecosystem.

The chemistry of precipitation, throughfall and stemflow in two holm oak (Quercus ilex L.) forests under a contrasted pollution environment in NE Spain.

Atmospheric deposition was studied through measurements of bulk deposition, throughfall and stemflow at two sites of contrasted exposure to pollution in the Montseny mountains (Northeastern Spain). To explore the contribution of local or distant sources at both sites, concentration data and precipitation amounts (log transformed) for both bulk deposition and net throughfall were fitted by linear regression. These models indicated the more important contribution of washout scavenging processes and dry deposition at the pollution exposed site. This is relevant in the context of Mediterranean holm oak forests: up to now, most of the studies have been conducted in protected remote sites and were little representative of the fluxes in forests close to industrial activity, traffic, agriculture and residential areas.

Carbon dioxide efflux and pCO2 in soils of threeQuercus ilex montane forests

Soil CO2 efflux and pCO2 in the soil atmosphere were measured during one year at three montane sites of Mediterranean sclerophyllous forests in NE Spain. Two sites were located in the upper and lower slopes of a small catchment in the Prades mountains (mean precipitation 550 mm year−1), and a third site was located on a lower slope in the Montseny mountains (mean precipitation 900 mm year−1). The three sites were similar in bedrock and vegetation, but differed in soil characteristics and water availability. Seasonal variation of CO2 efflux and soil pCO2 were affected by soil temperature and, to a lesser extent, by soil moisture. Annual mean soil CO2 efflux (considered as soil respiration) was similar at Montseny and at the comparably located site at Prades (83 ± 18 S.E. vs. 75 ± 9 mg CO2 m−2 hour−1 , respectively), and was highest at the Prades upper slope site (122 ± 22 mg C02 m−2 hour−1 ). Despite those relatively similar CO2 effluxes, mean soil pCO2 was much higher at both Prades sites than at Montseny. Soil pCO2 always increased with depth at Prades while maxima pCO2 at Montseny were often at 20–30 cm depth. A model based on gas diffusion theory was able to explain why soil pCO2 was much higher at Prades than at Montseny, and to reproduce the shape of the vertical profile of pCO2 at the Prades soils. Nevertheless, the model failed to simulate the soil pCO2 maximum found at 20–30 cm depth at the Montseny site. Model simulations using a time-variable CO2 production rate suggested that pCO2 maxima at intermediate depth could be the result of a transient situation instead of an equilibrium one.