Driving factors of a vegetation shift from Scots pine to pubescent oak in dry Alpine forests

An increasing number of studies have reported on forest declines and vegetation shifts triggered by drought. In the Swiss Rhone valley (Valais), one of the driest inner‐Alpine regions, the species composition in low elevation forests is changing: The sub‐boreal Scots pine (Pinus sylvestris L.) dominating the dry forests is showing high mortality rates. Concurrently the sub‐Mediterranean pubescent oak (Quercus pubescens Willd.) has locally increased in abundance. However, it remains unclear whether this local change in species composition is part of a larger‐scale vegetation shift. To study variability in mortality and regeneration in these dry forests we analysed data from the Swiss national forest inventory (NFI) on a regular grid between 1983 and 2003, and combined it with annual mortality data from a monitoring site. Pine mortality was found to be highest at low elevation (below 1000 m a.s.l.). Annual variation in pine mortality was correlated with a drought index computed for the summer months prior to observed tree death. A generalized linear mixed‐effects model indicated for the NFI data increased pine mortality on dryer sites with high stand competition, particularly for small‐diameter trees. Pine regeneration was low in comparison to its occurrence in the overstorey, whereas oak regeneration was comparably abundant. Although both species regenerated well at dry sites, pine regeneration was favoured at cooler sites at higher altitude and oak regeneration was more frequent at warmer sites, indicating a higher adaptation potential of oaks under future warming. Our results thus suggest that an extended shift in species composition is actually occurring in the pine forests in the Valais. The main driving factors are found to be climatic variability, particularly drought, and variability in stand structure and topography. Thus, pine forests at low elevations are developing into oak forests with unknown consequences for these ecosystems and their goods and services.     

Effects of salicylic acid on post-ischaemic ventricular function and purine efflux in isolated mouse hearts

Abstract

Acetyl salicylic acid (aspirin) is one of the most widely used drugs in the world. Various plasma concentrations of aspirin and its predominant metabolite, salicylic acid, are required for its antiarthritic (1.5–2.5 mM), anti-inflammatory (0.5–5.0 mM) or antiplatelet (0.18–0.36 mM) actions. A recent study demonstrated the inhibitory effects of both aspirin and salicylic acid on oxidative phosphorylation and ATP synthesis in isolated rat cardiac mitochondria in a dose-dependent manner (0–10 mM concentration range). In this context, the present study was conducted to determine the effects of salicylic acid on inosine efflux (a potential biomarker of acute cardiac ischaemia) as well as cardiac contractile function in the isolated mouse heart following 20 min of zero-flow global ischaemia. Inosine efflux was found at significantly higher concentrations in ischaemic hearts perfused with Krebs buffer fortified with 1.0 mM salicylic acid compared with those without salicylic acid (12575±3319 vs. 1437±348 ng ml^?1 min^?1, mean±SEM, n=6 per group, p<0.01). These results indicate that 1.0 mM salicylic acid potentiates 8.8-fold ATP nucleotide purine catabolism into its metabolites (e.g. inosine, hypoxanthine). Salicylic acid (0.1 or 1.0 mM) did not appreciably inhibit purine nucleoside phosphorylase (the enzyme converts inosine to hypoxanthine) suggesting the augmented inosine efflux was due to the salicylic acid effect on upstream elements of cellular respiration. Whereas post-ischaemic cardiac function was further depressed by 1.0 mM salicylic acid, perfusion with 0.1 mM salicylic acid led to a remarkable functional improvement despite moderately increased inosine efflux (2.7-fold). We conclude that inosine is a sensitive biomarker for detecting cardiac ischaemia and salicylic acid-induced effects on cellular respiration. However, the inosine efflux level appears to be a poor predictor of the individual post-ischaemic cardiac functional recovery in this ex vivo model.     

Propagule pressure as a driver of establishment success in deliberately introduced exotic species: fact or artefact?

A central paradigm in invasion biology is that more releases of higher numbers of individuals increase the likelihood that an exotic population successfully establishes and persists. Recently, however, it has been suggested that, in cases where the data are sourced from historical records of purposefully released species, the direction of causality is reversed, and that initial success leads to higher numbers being released. Here, we explore the implications of this alternative hypothesis, and derive six a priori predictions from it. We test these predictions using data on Acclimatization Society introductions of passerine bird species to New Zealand, which have previously been used to support both hypotheses for the direction of causality. All our predictions are falsified. This study reaffirms that the conventional paradigm in invasion biology is indeed the correct one for New Zealand passerine bird introductions, for which numbers released determine establishment success. Our predictions are not restricted to this fauna, however, and we keenly anticipate their application to other suitable datasets.     

Tidal marsh plant responses to elevated CO2, nitrogen fertilization,and sea level rise

Elevated CO₂ and nitrogen (N) addition directly affect plant productivity and the mechanisms that allow tidal marshes to maintain a constant elevation relative to sea level, but it remains unknown how these global change drivers modify marsh plant response to sea level rise. Here we manipulated factorial combinations of CO₂ concentration (two levels), N availability (two levels) and relative sea level (six levels) using in situ mesocosms containing a tidal marsh community composed of a sedge, Schoenoplectus americanus, and a grass, Spartina patens. Our objective is to determine, if elevated CO₂ and N alter the growth and persistence of these plants in coastal ecosystems facing rising sea levels. After two growing seasons, we found that N addition enhanced plant growth particularly at sea levels where plants were most stressed by flooding (114% stimulation in the + 10 cm treatment), and N effects were generally larger in combination with elevated CO₂ (288% stimulation). N fertilization shifted the optimal productivity of S. patens to a higher sea level, but did not confer S. patens an enhanced ability to tolerate sea level rise. S. americanus responded strongly to N only in the higher sea level treatments that excluded S. patens. Interestingly, addition of N, which has been suggested to accelerate marsh loss, may afford some marsh plants, such as the widespread sedge, S. americanus, the enhanced ability to tolerate inundation. However, if chronic N pollution reduces the availability of propagules of S. americanus or other flood‐tolerant species on the landscape scale, this shift in species dominance could render tidal marshes more susceptible to marsh collapse.     

Knowing the way home: strong philopatry of a highly mobile insect species, Brenthis ino

Mobility is crucial for the maintenance of viable metapopulations, but quantitative data to evaluate risks due to insufficient individual mobility of focal insect species are mostly lacking. We selected the butterfly Brenthis ino, a species typically confined to wet fallow grasslands in Central Europe and performed a mark–release–recapture study in a 3.2 ha study area with one big and one small patch of suitable habitat from 22 June to 23 July 2010. The position of each butterfly capture was measured with a GPS and transferred into a GIS. In total, we marked 984 individuals in 1,545 capture events and estimated that the cumulative population size was 2,400 individuals. The initial increase of adult males proceeded much faster than for females, similar to the protandrous population build-up known from other butterflies. Moved distances for both sexes usually did not exceed 80 m, and about 40 % of all individuals used less than 2 % of the available suitable habitat. All individuals switching to the other patch returned later to their patch of origin, confirming that B. ino is highly philopatric. We conclude that low effective mobility in B. ino produces much smaller home ranges than suggested by merely observing flight activities in the field, and that low tendencies towards long-distance movements significantly hamper the maintenance of metapopulations when patch density decreases due to landscape fragmentation.