Publications

The side effects of glyphosate on the soil microflora were monitored by applying a range of glyphosate concentrations (0, 2, 20, and 200 μg g−1

There is an increasing demand for an effective means of post-publication evaluation of ecological work that avoids pitfalls associated with using the impact factor of the journal in which the work was published. One approach that has been gaining momentum is the 'Faculty of 1000' (hereafter F1000) evaluation procedure, in which panel members identify what they believe to be the most 'important' recent publications they have read. Here I focused on 1530 publications from 7 major ecological journals that appeared in 2005, and compared the F1000 rating of each publication with the frequency with which it was subsequently cited. The mean and median citation frequencies of the 103 publications highlighted by F1000 was higher than for all 1530 publications, but not substantially so. Further, the F1000 procedure did not highlight any of the 11 publications that were each cited over 130 (and up to 497) times, while it did highlight 14 publications that were each cited between 4 and 9 times. Further, 46% and 31% of all manuscripts highlighted by F1000 were cited less often than the mean and median respectively of all 1530 publications. Possible reasons for the F1000 process failing to identify high impact publications may include uneven coverage by F1000 of different ecological topics, cronyism, and geographical bias favoring North American publications. As long as the F1000 process cannot identify those publications that subsequently have the greatest impact, it cannot be reliably used as a means of post-publication evaluation of the ecological literature.

The viability of nodding thistle (Carduus nutans) seed buried at three depths in four different soils was evaluated over a 16 year period.Seed viability was affected more by burial depth than by soil type.The amount of viable seed retrieved from the top 2 cm soil layer after 1 year was less than 16% of that buried, while up to 71% and 84% of seed buried at the 5 cm and 20 cm depths respectively remained viable.Sixteen years after burial, up to 20% and 32% viable seed was retrieved from the 5 and 20 cm depths respectively.It is estimated that if left undisturbed, it would take between 14 to 80 years for viable seed numbers to be reduced to 1% of the original seed numbers, depending on soil type.

We observed photoinduced birefringence in elliptical-core optical fibers by using a continuous-wave krypton-ion laser. We induced the birefringence by injecting 20 mW of 647-nm or 50 mW of 676-nm light into the fiber at 45 degrees to the slow axis. The rate of change of the refractive index was found to be proportional to the square of the average power. Polarization mode couplers written into the fibers have been stable for more than 2 years and can be erased by use of light polarized perpendicularly to the original writing beam.

Thanks to a single mode optical fiber, we measure for the first time the dramatic power increase theoretically predicted by Shen and Bloembergen in 1965 for the non-phase-matched anti-Stokes wave in stimulated Raman scattering.

Explaining the variation in communities of soil organisms across plant communities or ecosystems remains a major challenge for ecologists. Several studies have explored how soil communities are affected along ecosystem successional gradients but most of these are based on relatively short term chronosequences. To address the impact of ecosystem age on micro-arthropod communities, we utilized a 5000 year old post-fire chronosequence, which consists of thirty lake islands differing greatly in time since fire in the boreal forested zone of northern Sweden. The Acari community did not change along this chronosequence, indicating that Acari rapidly (<60 yr) reach equilibrium after forest fire and that they are relatively unresponsive to subsequent long term changes in plant community composition and soil quality. The Collembola community composition, however, showed greater responsiveness to the chronosequence and this was best explained through their functional traits. Notably, the youngest (most recently burned) islands, which had the highest ecosystem productivity and fungal mass turnover, were dominated by soil-dwelling (eu-edaphic) Collembola species that are best positioned to take advantage of resource input to the soil. Although plant community characteristics did not emerge as powerful drivers of the Collembola community, we found that Collembola community composition was related to the quality (N and P) of the soil substrate, which reflects a long term legacy of the plant community. Collembola life history characteristics proved to be important for understanding how abundances of different taxa varied relative to one another across the gradients of plant diversity and substrate quality gradients that occur across long-term chronosequences. The causal connection between vertical stratification of Collembola and substrate quality is at present unclear but is likely to be related to their feeding preferences and microhabitat conditions. Because the soil-dwelling Collembola showed a strong decline in abundance with ecosystem retrogression while surface-dwelling Collembola did not these two life history groups may operate as functionally distinct groups within the soil food web across these long-term chronosequences.

In the long-term absence of major disturbances ecosystems enter a state of retrogression, which involves declining soil fertility and consequently a reduction in decomposition rates. Recent studies have looked at how plant traits such as specific leaf mass and amounts of secondary compounds respond to declining soil fertility during retrogression, but there are no comparable studies for lichen traits despite increasing recognition of the role that lichens can play in ecosystem processes. We studied a group of 30 forested islands in northern Sweden differing greatly in fire history, and collectively representing a retrogressive chronosequence, spanning 5000 years. We used this system to explore how specific thallus mass (STM) and carbon based secondary compounds (CBSCs) change in three common epiphytic lichen species (Hypogymnia phsyodes, Melanohalea olivacea and Parmelia sulcata) as soil fertility declines during this retrogression. We found that STMs of lichens increased sharply during retrogression, and for all species soil N to P ratio (which increased during retrogression) was a strong predictor of STM. When expressed per unit area, medullary CBSCs in all species and cortical CBSCs in P. sulcata increased during retrogression. Meanwhile, when expressed per unit mass, only cortical CBSCs in H. physodes responded to retrogression, and in the opposite direction. Given that lichen functional traits are likely to be important in driving ecological processes that drive nutrient and carbon cycling in the way that plant functional traits are, the changes that they undergo during retrogression could potentially be significant for the functioning of the ecosystem.

Seedling emergence of three weeds ( Carduus nutans, Cirsium vulgare and Rumex obtusifolius ) and three clovers ( Trifolium repens, T. subterraneum and T. pratense ) was monitored in gaps of different sizes (0, 2, 6 and 10 cm diameter, plus a 3 m 2 bare plot), which were created in a Loliumperenne/T. repens pasture. Clover emergence was greatest in the bare plots, in contrast with the weeds, whose emergence peaked in small or intermediate‐sized gaps. Relationships between weed emergence and gap size in glasshouse swards were poorly denned. As a result of trampling by cattle, seedling mortality occurred most rapidly for all species in the bare plots. Very few weeds survived in the other gaps, where there was no detectable effect of gap size upon survivorship. Naturally occurring gaps were most abundant during summer, but their size frequency distributions varied little between spring and autumn. The sizes of almost 95% of the natural gaps were within the range of the experimentally‐created gaps. Poor survivorship of weeds within this range, however, suggests that larger gaps are required for regeneration.

Predators often exert multi-trophic cascading effects in terrestrial ecosystems. However, how such predation may indirectly impact interactions between above- and below-ground biota is poorly understood, despite the functional importance of these interactions. Comparison of rat-free and rat-invaded offshore islands in New Zealand revealed that predation of seabirds by introduced rats reduced forest soil fertility by disrupting sea-to-land nutrient transport by seabirds, and that fertility reduction in turn led to wide-ranging cascading effects on belowground organisms and the ecosystem processes they drive. Our data further suggest that some effects on the belowground food web were attributable to changes in aboveground plant nutrients and biomass, which were themselves related to reduced soil disturbance and fertility on invaded islands. These results demonstrate that, by disrupting across-ecosystem nutrient subsidies, predators can indirectly induce strong shifts in both above- and below-ground biota via multiple pathways, and in doing so, act as major ecosystem drivers.

Over time scales of thousands to millions of years, and in the absence of rejuvenating disturbances that initiate primary or early secondary succession, ecosystem properties such as net primary productivity, decomposition, and rates of nutrient cycling undergo substantial declines termed ecosystem retrogression. Retrogression results from the depletion or reduction in the availability of nutrients, and can only be reversed through rejuvenating disturbance that resets the system; this differs from age-related declines in forest productivity that are driven by shorter-term depression of nutrient availability and plant ecophysiological process rates that occur during succession. Here we review and synthesize the findings from studies of long-term chronosequences that include retrogressive stages for systems spanning the boreal, temperate, and subtropical zones. Ecosystem retrogression has been described by ecologists, biogeochemists, geologists, and pedologists, each of which has developed somewhat independent conceptual frameworks; our review seeks to unify this literature in order to better understand the causes and consequences of retrogression. Studies of retrogression have improved our knowledge of how long-term pedogenic changes drive shorter-term biological processes, as well as the consequences of these changes for ecosystem development. Our synthesis also reveals that similar patterns of retrogression (involving reduced soil fertility, predictable shifts in organismic traits, and ecological processes) occur in systems with vastly different climatic regimes, geologic substrates, and vegetation types, even though the timescales and mechanisms driving retrogression may vary greatly among sites. Studies on retrogression also provide evidence that in many regions, high biomass or "climax" forests are often transient, and do not persist indefinitely in the absence of rejuvenating disturbance. Finally, our review highlights that studies on retrogressive chronosequences in contrasting regions provide unparalleled opportunities for developing general principles about the long-term feedbacks between biological communities and pedogenic processes, and how these control ecosystem development.