Does fire severity influence shrub resprouting after spring prescribed burning?

Prescribed burning is commonly used to reduce the risk of severe wildfire. However, further information about the associated environmental effects is required to help forest managers select the most appropriate treatment. To address this question, we evaluated if fire severity during spring prescribed burning significantly affects the resprouting ability of two common shrub species in shrubland under a Mediterranean climate in NW Spain. Fire behaviour and temperatures were recorded in tagged individuals of Erica australis and Pterospartum tridentatum during prescribed burning. The number and length of resprouted shoots were measured three times (6, 12 and 18 months) after the prescribed burning. The influence of a series of fire severity indicators on some plant resprouting vigour parameters was tested by canonical correlation analysis. Six months and one year after prescribed burning, soil burn severity (measured by the absolute reduction in depth of the organic soil layer, maximum temperatures in the organic soil layer and the mineral soil surface during burning and the post-fire depth of the organic soil layer) reduced the resprouting vigour of E. australis and P. tridentatum. In contrast, direct measurements of fire effects on plants (minimum branch diameter, duration of temperatures above 300 °C in the shrub crown and fireline intensity) did not affect the post-fire plant vigour.Soil burn severity during spring prescribed burning significantly affected the short-term resprouting vigour in a mixed heathland in Galicia. The lack of effects eighteen months after prescribed burning indicates the high resilience of these species and illustrates the need to conciliate fire prevention and conservation goals.     

Does functional homogenization accompany taxonomic homogenization of British birds and how do biotic factors and climate affect these processes?

Environmental change has reshuffled communities often causing taxonomic homogenization rather than differentiation. Some studies suggest that this increasing similarity of species composition between communities is accompanied by an increase in similarity of trait composition—functional homogenization—although different methodologies have failed to come to any consistent conclusions. Functional homogenization could have a large effect on ecosystem functioning and stability. Here, we use the general definition of homogenization as “reduced spatial turnover over time” to compare changes in Simpson's beta diversity (taxonomic turnover) with changes in Rao's quadratic entropy beta diversity (functional turnover) in British breeding birds at three spatial scales. Using biotic and climatic variables, we identify which factors may predispose a site to homogenization. The change in turnover measures between two time periods, 20 years apart, was calculated. A null model approach was taken to identify occurrences of functional homogenization and differentiation independent of changes in taxonomic turnover. We used conditional autoregressive models fitted using integrated nested Laplace approximations to determine how environmental drivers and factors relating to species distributions affect changes in spatial turnover of species and functional diversity. The measurement of functional homogenization affects the chance of rejection of the null models, with many sites showing taxonomic homogenization unaccompanied by functional homogenization, although occurrence varies with spatial scale. At the smallest scale, while temperature‐related variables drive changes in taxonomic turnover, changes in functional turnover are associated with variation in growing degree days; however, changes in functional turnover become more difficult to predict at larger spatial scales. Our results highlight the multifactorial processes underlying taxonomic and functional homogenization and that redundancy in species traits may allow ecosystem functioning to be maintained in some areas despite changes in species composition.     

Does taxonomic homogenization imply functional homogenization in temperate forest herb layer communities?

Biotic homogenization, the decrease in beta diversity among formerly distinct species assemblages, has been recognized as an important form of biotic impoverishment for more than a decade. Although researchers have stressed the importance of the functional dimension to understand its potential ecological consequences, biotic homogenization has mostly been studied at a taxonomic level. Here, we explore the relationship between taxonomic and functional homogenization using data on temperate forest herb layer communities in NW Germany, for which taxonomic homogenization has recently been demonstrated. We quantified beta diversity by partitioning Rao’s quadratic entropy. We found a general positive relationship between changes in taxonomic and functional beta diversity. This relationship was stronger if multiple functional traits were taken into account. Averaged across sites, however, taxonomic homogenization was not consistently accompanied by functional homogenization. Depending on the traits considered, taxonomic homogenization occurred also together with functional differentiation or no change in functional beta diversity. The species shifts responsible for changes in beta diversity differed substantially between taxonomic and functional beta diversity measures and also among functional beta diversity measures based on different traits. We discuss likely environmental drivers for species shifts. Our study demonstrates that functional homogenization must be explicitly studied as an independent phenomenon that cannot be inferred from taxonomic homogenization.     

Does follicle excision always result in enlargement of offspring size in lizards?

An experimental reduction of offspring number has been reported to result in enlargement of offspring size in lizards. We applied the “follicle excision” technique to a lacertid lizard (Takydromus septentrionalis) to examine whether this effect is generalisable to lizards. Of the 82 females that produced 3 successive clutches in the laboratory, 23 females underwent follicle excision after they oviposited the first clutch. Follicle excision reduced clutch size, but did not alter egg size. This result indicates that egg size is not altered during vitellogenesis in T. septentrionalis. Females undergoing follicle excision produced a third clutch (a second post-surgical clutch) as normally as did control females. Females switched from producing more but smaller eggs early in the breeding season to fewer but larger eggs later in the season. Our results indicate that female T. septentrionalis maximize reproductive success by diverting an optimal, rather than a higher, fraction of the available energy to individual offspring. This optimized allocation of the available energy to offspring production explains why follicle excision does not result in enlargement of egg size in this species. Our study provides evidence that an experimental reduction of offspring number does not always result in enlargement of offspring size in lizards.     

How general are global trends in biotic homogenization? Floristic tracking in Chile,South America

Aim   To quantify the occurrence of floristic change in the vascular flora of Chile. We test whether continental areas have experienced floristic modification leading to either homogenization, differentiation or tracking.
Location   Continental Chile.
Methods   On the basis of the geographical distribution of native (1806 species) and naturalized plants (552 species) in continental Chile, we quantified change between two floristic stages: (1) pre-European flora, including native extant and extinct species; and (2) current flora, including native and naturalized species, but excluding extinct plants. We compared changes in compositional similarity (calculated by Jaccard's index, Δ J ) between pairs of regions, and similarity decay with respect to geographical distance. Additionally, by means of Whittaker's index, we examined species turnover, distinguishing between native and naturalized plants.
Results   Between floristic stages (pre-European vs. current flora) no significant changes in floristic similarity were noted at national or regional scales. Similarity decay showed no statistical differences between pre-European and current flora. Analysing patterns of geographical turnover, we found that species turnover of naturalized plants over their geographical range is similar to that of native plants.
Conclusions   The composition of the continental flora of Chile does not show significant modifications in similarity patterns after considering naturalized species, thus indicating floristic tracking. The causes of this phenomenon may be related to the current geographical distribution of naturalized plants, which closely parallels that of native plants. Our results differ from those obtained in Northern Hemisphere continents, thus indicating that trends of biotic change may differ between hemispheres.     

Do vascular plants and bryophytes respond differently to coniferous invasion of coastal heathlands?

Invasion by non-native conifers may pose a threat to local biodiversity, but knowledge about introduced conifer effects on Northern Hemisphere ecosystems is scarce. The coastal heathlands of north-west Europe are threatened by invasion of native and introduced tree species. We assess how spread of the introduced conifer Sitka spruce (Picea sitchensis (Bong.) Carr.) into European coastal heathlands affect two major functional groups; vascular plants and bryophytes, and how these effects relate to the environmental changes imposed by the developing tree canopies. We compared the impact of introduced Sitka spruce and native Scots pine (Pinus sylvestris L.) by analysing effects on species richness and turnover of vascular plants and bryophytes along fine-scale transects from individual tree stems into open heathland vegetation. Environmental impacts were assessed by measured environmental variables, and the responses of the two species groups were assessed by calculating changes in their respective mean Ellenberg indicator values. Species richness decreased beneath both conifers, related to decreased light and increased nitrogen and pH. Whereas vascular plants responded negatively to poor light conditions beneath dense and low Sitka spruce canopies, bryophytes were more negatively affected by the warmer and drier microclimates beneath Scots pine. Introduced Sitka spruce impacts the sub-canopy environment differently from the native Scots pine, and the two functional plant groups responded differently to these impacts. This suggests that future forests are likely to differ in species richness and composition, depending on whether succession is based on native or introduced coniferous trees.     

How pervasive is biotic homogenization in human‐modified tropical forest landscapes?

Land‐cover change and ecosystem degradation may lead to biotic homogenization, yet our understanding of this phenomenon over large spatial scales and different biotic groups remains weak. We used a multi‐taxa dataset from 335 sites and 36 heterogeneous landscapes in the Brazilian Amazon to examine the potential for landscape‐scale processes to modulate the cumulative effects of local disturbances. Biotic homogenization was high in production areas but much less in disturbed and regenerating forests, where high levels of among‐site and among‐landscape β‐diversity appeared to attenuate species loss at larger scales. We found consistently high levels of β‐diversity among landscapes for all land cover classes, providing support for landscape‐scale divergence in species composition. Our findings support concerns that β‐diversity has been underestimated as a driver of biodiversity change and underscore the importance of maintaining a distributed network of reserves, including remaining areas of undisturbed primary forest, but also disturbed and regenerating forests, to conserve regional biota.     

Does dust result in mite outbreaks in apple orchards?

The effect of dust on phytophagous mite numbers was examined in five apple orchards situated in the dry, inland apple producing Ceres area, South Africa. The study was conducted over three seasons. The season with the most dust had the least number of mites. There was no relationship between the amount of dust on leaves and mite numbers from different orchards. Of the 15 correlations between the amount of dust on individual trees and the number of mites on these trees, two were marginally not significant and one was highly significant, but negative. Therefore, seasons during which there is a lot of dust did not result in mite outbreaks nor did dusty orchards harbour elevated mite population levels, and trees with a lot of dust did not necessarily harbour more mites than trees with less dust. However, if there is enough dust to cause stress to the trees, phytophagous mite outbreaks could occur.     

Does elevated testosterone result in increased exposure and transmission of parasites?

Male-biased infection is a common phenomenon in vertebrate-parasite systems and male-biased transmission has been experimentally demonstrated. One mechanism that is hypothesized to create male-biased transmission is the immuno-suppressive effect of testosterone because it increases susceptibility to infection. Testosterone also influences host behaviour and, consequently, may increase exposure to parasites. To test how testosterone could increase exposure and transmission, we undertook a longitudinal mark-recapture study where we experimentally elevated testosterone levels in wild male rodents. Individuals in control populations reduced the average number of contacts over the treatment period, while populations with experimentally elevated testosterone levels maintained the number of contacts between hosts. As a result, the transmission potential was higher in testosterone treated populations compared to controls. Our results indicated that males with high-testosterone levels alter the population-level contacts, producing different social networks and increasing transmission potential compared to those where testosterone is at background levels.     

The micro-distribution of aquatic macroinvertebrates in the Wye river system: the result of abiotic or biotic factors?

SUMMARY. 1. Macroinvertebrates were sampled from three habitats at each of forty-five sites in the catchment of the Welsh River Wye. Micro-distribution patterns between three habitat types were assessed for those species which occurred most commonly.
2. Of the fifty-three taxa for which analysis was possible, twenty showed a significant association with habitat type. Eleven occur mostly in margins, eight mostly in riffles, and one in flats (depositing reaches).
3. Twenty-one taxa, including eleven additional to those show significant associations, showed. significant differences between habitats in their relative abundance. Ten were most abundant in margins, eight in riffles and three in flats.
4. Factors possibly responsible for these habitat preferences are discussed.     

Does climate influence assemblages of anurans and lizards in a coastal area of north-eastern Brazil?

Environmental factors influence diverse assemblage features such as species abundances, richness, and nestedness. Amphibians and reptiles play important roles in terrestrial ecosystems, but there is still a lack of information about the assemblages of these animals in many regions. In this study, we aimed to understand how environmental factors influence the anurans and lizards assemblages from São Gonçalo do Amarante, Ceará, Brazil. Herpetofauna samplings were performed monthly in São Gonçalo do Amarante from January 2008 to May 2009, excluding April 2008. We sampled animals (anurans and lizards) using pitfall traps and active searches. The abundance and richness of lizards were positively related to temperature and negatively related to precipitation. Anuran assemblage was not influenced by precipitation, but its abundance was negatively influenced by temperature. Temperature generated a nested pattern in the lizard assemblage, but precipitation did not produce this pattern in anurans. Finally, our results reinforce the importance of environmental factors, mainly temperature, in structuring assemblages of anurans and lizards.     

Does prescribed burning mean a threat to the rare satyrine butterfly Hipparchia fagi? Larval-habitat preferences give the answer

The ecological effects of fire management, especially regarding arthropods are poorly investigated. Burning in winter was assumed to pose a threat to butterfly species hibernating as larvae. To assess the impact of prescribed burning on population viability, we analysed larval-habitat preferences of the highly endangered, xero-thermophilous butterfly Hipparchia fagi in vineyards of the Kaiserstuhl region (southern Germany). Microhabitat preference analyses for mature larvae and egg-laying females revealed a preference of H. fagi for Bromus erectus-dominated communities with sparse vegetation coverage and a distinct tuft growth of the host plant B. erectus on microclimatically benefited slopes. We explain the preference of B. erectus by a preference of vegetation structure. The grass tufts offer a suitable climatically buffered living space for larvae. Egg deposition took place on dry substrate at positions of high solar radiation, thus adapted to hot and dry microclimate. As the larval habitat was sparsely vegetated as well as generally legally protected, fire management was not applicable and therefore not affecting the populations. We think it is conceivable that H. fagi, occurring here at its northern range limit, might expand its larval habitat into denser, combustible B. erectus stands in the course of global warming. A change in habitat preferences would necessitate a re-evaluation of management options.     

Effects of vineyard management on biotic homogenization of insect–flower interaction networks in the Cape Floristic Region biodiversity hotspot

Plant and animal communities, as well as their interaction networks in agricultural landscapes, face threats of biotic homogenization due mostly to intensive management and cropland expansion. It is unclear whether agri-environmental schemes that promote environmentally friendly farming approaches can reduce the effects of these threats which cause reduction in regional (beta) diversity. Here, we examined biotic homogenization of insect–flower interactions in vineyards managed under agri-environmental schemes in the Cape Floristic Region (CFR). The interaction networks studied are of significant conservation value in the fragmented CFR agricultural landscape. Assessment was done using permutational distance-based test for homogeneity of multivariate dispersion to determine whether vineyards contributed to loss of diversity across the landscape through homogenization of their insect–flower interaction networks and flower visitor community. Vineyards did not show significant homogenization of interaction networks and flower-visitor community when compared to natural sites. Organic viticulture, integrated vineyard management and on-going protection of natural vegetation close to vineyards, as practiced in the CFR, are possibly contributing to the reduction in biotic homogenization observed here. Further vineyard expansion must however be prevented to avoid future biotic losses. These measures should be supported by all stakeholders in the conservation sector to achieve wine production while at the same time conserving the natural complement of biodiversity.     

Does helimulching after severe wildfire affect vegetation recovery in a coastal area of Northwest Spain?

Helimulching is commonly applied after high-severity wildfires in North America because of its effectiveness in reducing post-fire runoff and erosion. However, its use in other parts of the world is still very limited and information about its effects in different environments is scarce. In this study, the effects of helimulching on vegetation recovery and species composition were assessed in 70 experimental plots (80 m² each) established in five shrubland areas in Northwest Spain affected by wildfire in summer 2013. The effects on shrub, forb, fern and grass cover, and on total vegetation cover, as well as on species richness, Shannon diversity index and heterogeneity were studied over the 2 years following the fire. The impacts of soil burn severity and mulch depth on these variables were also considered. Overall, the mulching treatment had little effect on the cover variables. Although it had a positive effect on forb cover, these species represented only a small portion of the total vegetation cover. Soil burn severity was not a significant factor in explaining the variation in the variables under study. The treatment had a low impact on species composition. In the mulched plots only three non-native species were recorded and these displayed a limited capacity to act as invasive species as they were absent at the end of the period of study. The results indicate that helimulching is a feasible soil stabilization treatment with neutral effects on vegetation cover and the composition of shrubland in coastal areas of Northwest Spain.

     

Understory response to varying fire frequencies after 20 years of prescribed burning in an upland oak forest

Ecosystems in the eastern United States that were shaped by fire over thousands of years of anthropogenic burning recently have been subjected to fire suppression resulting in significant changes in vegetation composition and structure and encroachment by invasive species. Renewed interest in use of fire to manage such ecosystems will require knowledge of effects of fire regime on vegetation. We studied the effects of one aspect of the fire regime, fire frequency, on biomass, cover and diversity of understory vegetation in upland oak forests prescribe-burned for 20 years at different frequencies ranging from zero to five fires per decade. Overstory canopy closure ranged from 88 to 96% and was not affected by fire frequency indicating high tolerance of large trees for even the most frequent burning. Understory species richness and cover was dominated by woody reproduction followed in descending order by forbs, C3 graminoids, C4 grasses, and legumes. Woody plant understory cover did not change with fire frequency and increased 30% from one to three years after a burn. Both forbs and C3 graminoids showed a linear increase in species richness and cover as fire frequency increased. In contrast, C4 grasses and legumes did not show a response to fire frequency. The reduction of litter by fire may have encouraged regeneration of herbaceous plants and helped explain the positive response of forbs and C3 graminoids to increasing fire frequency. Our results showed that herbaceous biomass, cover, and diversity can be managed with long-term prescribed fire under the closed canopy of upland oak forests.     

Do fish communities function as biotic vectors of organic matter between salt marshes and marine coastal waters?

The contribution of fish communities to organic matter (OM) fluxes, especially between salt marshes and adjacent marine coastal waters are reviewed. For this a data set from the bay of Mont Saint-Michel and literature is examined and discussed. In a range of macro-tidal coasts of Europe, salt marshes are only flooded at spring tides for a short time. Many animals, including fish, then invade the salt marshes through tidal creeks. They forage there for up to a few hours and swim back to sea at ebb. Meanwhile, organic matter is exported as gut content. In the 4000 ha of salt marshes of the bay of Mont Saint-Michel mullets were responsible for the export of about 8 kg of dry weight OM ha^–1 in 1996 and of roughly 12 kg in 1997. Although spatio-temporally variable, the fish communities appear to play a more or less significant role, as biotic vectors in the nutrient fluxes between salt marshes and coastal waters.