Characterizing a tropical deforestation wave: a dynamic spatial analysis of a deforestation hotspot in the Colombian Amazon

Tropical deforestation is the major contemporary threat to global biodiversity, because a diminishing extent of tropical forests supports the majority of the Earth's biodiversity. Forest clearing is often spatially concentrated in regions where human land use pressures, either planned or unplanned, increase the likelihood of deforestation. However, it is not a random process, but often moves in waves originating from settled areas. We investigate the spatial dynamics of land cover change in a tropical deforestation hotspot in the Colombian Amazon. We apply a forest cover zoning approach which permitted: calculation of colonization speed; comparative spatial analysis of patterns of deforestation and regeneration; analysis of spatial patterns of mature and recently regenerated forests; and the identification of local‐level hotspots experiencing the fastest deforestation or regeneration. The colonization frontline moved at an average of 0.84 km yr^?1 from 1989 to 2002, resulting in the clearing of 3400 ha yr^?1 of forests beyond the 90% forest cover line. The dynamics of forest clearing varied across the colonization front according to the amount of forest in the landscape, but was spatially concentrated in well‐defined ‘local hotspots’ of deforestation and forest regeneration. Behind the deforestation front, the transformed landscape mosaic is composed of cropping and grazing lands interspersed with mature forest fragments and patches of recently regenerated forests. We discuss the implications of the patterns of forest loss and fragmentation for biodiversity conservation within a framework of dynamic conservation planning.     

Trypsin Inhibitors during Germination of Vigna sinensis Seeds

The trypsin inhibiting activity of cotyledonary extracts of serido beans (Vigna sinensis) falls continuously during germination to a value which represents 5 % of the value for the dry seed. The specific activity is constant over the first three days and then decreases, reaching a level at the seventh day of germination which represents 20 % of the initial value. It is also shown that the axial parts control the disappearance of the trypsin inhibiting activity of the cotyledons. The results presented here seem to indicate a role for these substances in the process of germination.     

Effects of experimental warming of air,soil and permafrost on carbon balance in Alaskan tundra

The carbon (C) storage capacity of northern latitude ecosystems may diminish as warming air temperatures increase permafrost thaw and stimulate decomposition of previously frozen soil organic C. However, warming may also enhance plant growth so that photosynthetic carbon dioxide (CO₂) uptake may, in part, offset respiratory losses. To determine the effects of air and soil warming on CO₂ exchange in tundra, we established an ecosystem warming experiment – the Carbon in Permafrost Experimental Heating Research (CiPEHR) project – in the northern foothills of the Alaska Range in Interior Alaska. We used snow fences coupled with spring snow removal to increase deep soil temperatures and thaw depth (winter warming) and open‐top chambers to increase growing season air temperatures (summer warming). Winter warming increased soil temperature (integrated 5–40 cm depth) by 1.5 °C, which resulted in a 10% increase in growing season thaw depth. Surprisingly, the additional 2 kg of thawed soil C m^?2 in the winter warming plots did not result in significant changes in cumulative growing season respiration, which may have been inhibited by soil saturation at the base of the active layer. In contrast to the limited effects on growing‐season C dynamics, winter warming caused drastic changes in winter respiration and altered the annual C balance of this ecosystem by doubling the net loss of CO₂ to the atmosphere. While most changes to the abiotic environment at CiPEHR were driven by winter warming, summer warming effects on plant and soil processes resulted in 20% increases in both gross primary productivity and growing season ecosystem respiration and significantly altered the age and sources of CO₂ respired from this ecosystem. These results demonstrate the vulnerability of organic C stored in near surface permafrost to increasing temperatures and the strong potential for warming tundra to serve as a positive feedback to global climate change.     

Comparative response of δ13C, δ18O and δ15N in durum wheat exposed to salinity at the vegetative and reproductive stages

This study compared the performance of the stable isotope composition of carbon (δ¹³C), oxygen (δ¹⁸O) and nitrogen (δ¹⁵N) by tracking plant response and genotypic variability of durum wheat to different salinity conditions. To that end, δ¹³C, δ¹⁸O and δ¹⁵N were analysed in dry matter (dm) and the water‐soluble fraction (wsf) of leaves from plants exposed to salinity, either soon after plant emergence or at anthesis. The δ¹³C and δ¹⁸O of the wsf recorded the recent growing conditions, including changes in evaporative conditions. Regardless of the plant part (dm or wsf), δ¹³C and δ¹⁸O increased and δ¹⁵N decreased in response to stress. When the stress conditions were established just after emergence, δ¹⁵N and δ¹³C correlated positively with genotypic differences in biomass, whereas δ¹⁸O correlated negatively in the most severe treatment. When the stress conditions were imposed at anthesis, relationships between the three isotope signatures and biomass were only significant and positive within the most severe treatments. The results show that nitrogen metabolism, together with stomatal limitation, is involved in the genotypic response to salinity, with the relative importance of each factor depending on the severity and duration of the stress as well as the phenological stage that the stress occurs.     

Population‐genomic approach reveals adaptive floral divergence in discrete populations of a hawk moth‐pollinated violet

Local adaptation to contrasting biotic or abiotic environments is an important evolutionary step that presumably precedes floral diversification at the species level, yet few studies have demonstrated the adaptive nature of intraspecific floral divergence in wild plant populations. We combine a population‐genomic approach with phenotypic information on floral traits to examine whether the differentiation in metric floral traits exhibited by 14 populations of the southern Spanish hawk moth‐pollinated violet Viola cazorlensis reflects adaptive divergence. Screening of many amplified fragment length polymorphism (AFLP) loci using a multiple‐marker‐based neutrality test identified nine outlier loci (2.6% of the total) that departed from neutral expectations and were potentially under selection. Generalized analysis of molecular variance revealed significant relationships between genetic distance and population divergence in three floral traits when genetic distance was based on outlier loci, but not when it was based on neutral ones. Population means of floral traits were closely correlated with population scores on the first principal coordinate axis of the genetic distance matrix using outlier loci, and with the allelic frequencies of four of the outlier loci. Results strongly support the adaptive nature of intraspecific floral divergence exhibited by V. cazorlensis and illustrate the potential of genome scans to identify instances of adaptive divergence when used in combination with phenotypic information.