Accounting for spatial autocorrelation improves the estimation of climate,physical environment and vegetation’s effects on boreal forest’s burn rates

Context

Wildfires play a crucial role in maintaining ecological and societal functions of North American boreal forests. Because of their contagious way of spreading, using statistical methods dealing with spatial autocorrelation has become a major challenge in fire studies analyzing how environmental factors affect their spatial variability.

Objectives

We aimed to demonstrate the performance of a spatially explicit method accounting for spatial autocorrelation in burn rates modelling, and to use this method to determine the relative contribution of climate, physical environment and vegetation to the spatial variability of burn rates between 1972 and 2015.

Methods

Using a 482,000 km² territory located in the coniferous boreal forest of eastern Canada, we built and compared burn rates models with and without accounting for spatial autocorrelation. The relative contribution of climate, physical environment and vegetation to the burn rates variability was identified with variance partitioning.

Results

Accounting for spatial autocorrelation improved the models’ performance by a factor of 1.5. Our method allowed the unadulterated extraction of the contribution of climate, physical environment and vegetation to the spatial variability of burn rates. This contribution was similar for the three groups of factors. The spatial autocorrelation extent was linked to the fire size distribution.

Conclusions

Accounting for spatial autocorrelation can highly improve models and avoids biased results and misinterpretation. Considering climate, physical environment and vegetation altogether is essential, especially when attempting to predict future area burned. In addition to the direct effect of climate, changes in vegetation could have important impacts on future burn rates.

     

Interactions between bovine beta-lactoglobulin and peptides under different physicochemical conditions

The aim of this study was to determine if peptides could interact with beta-lactoglobulin (beta-LG) and what the physicochemical conditions promoting their interaction with the protein are. The binding of negatively charged (beta-LG 125-135 and 130-135), positively charged (beta-LG 69-83 and 146-149), and hydrophobic (alphaS1-CN 23-34 and beta-LG 102-105, both bioactive peptides) peptides to bovine beta-LG was determined using an ultrafiltration method under different physicochemical conditions: pH 3.0, 6.8, and 8.0; buffers of 0.05 and 0.1 M; 4, 25, and 40 degrees C; beta-LG/peptide ratios of 1:5 and 1:10. At pH 3.0, none of the peptides interacted with beta-LG at any temperature, buffer molarity, or beta-LG/peptide ratio probably due to electrostatic repulsions between the highly protonated species. At pH 6.8 and 8.0, charged peptides beta-LG 130-135, 69-83, and 146-149 bound to beta-LG under some physicochemical conditions, possibly by nonspecific binding. However, both hydrophobic peptides probably bind to the inner cavity (beta-barrel) of beta-LG, provoking the release of materials absorbing at 214 nm. Given the known biological activities of the hydrophobic peptides used in this study (opioid and ACE-inhibitory activities), their binding to beta-LG may be relevant to a better understanding of the physiological function of the protein.     

Assessment of N2 fixation by Casuarina equisetifolia inoculated with Frankia ORS021001 using 15N methods

Casuarina equisetifolia seedlings, uninoculated or inoculated with Frankia strain ORS021001 were grown for 4.5 months in pouches, then transplanted into 1 m³ concrete containers forming 1 m² microplots. Trees were harvested 6.5 months later when they were 11 months old. N₂ fixation was measured using three methods of assessment: the direct isotopic method, the A-value method and the difference method. Estimations of N₂ fixation during the 6.5 months following transplantation were respectively 3.27, 2.31 and 3.07g N₂ per tree. From these values it was calculated that about 40–60 kg N₂ would be fixed per hectare in a year at normal densities of 10,000 trees ha^?1. The results of this experiment confirm that Frankia strain ORS021001 can be confidently recommended to inoculate casuarinas in the field. Means to improve nodulation and subsequently N₂ fixation by casuarinas are discussed.     

Dynamics of the free-living populations of gastrointestinal trichostrongyles of cattle in a natural grazing system in Guadeloupe (French West Indies)

The variations in the population size of trichostrongyle infective larvae (L3) in a cow-calf system were recorded for two years in Guadeloupe (humid and hot tropical climate). Calvings were pooled during the dry season for two herds and during the rainy season for two others. Each herd grazed three paddocks of natural pasture according to a rotational system (14 days of grazing per paddock). At the time the animals entered each paddock, the numbers of L3 on pasture were assessed around fecal pats (L3_ap) and within a 1 m radius of pats (L3_1rfp). Seventy-one regressor variables were tested to explain variations in the size of L3 populations: combinations of variables linked to animals (e.g. weight, fecal eggs, stocking rate) and combinations of ecological variables (e.g. rainfall, global radiation, herbage mass). L3_1rfp were highly correlated to L3_ap. However, when the mean global radiation during the third week after the entrance of animals exceeded 20 MJ m⁻² day⁻¹, L3_1rfp was undetectable even with large L3 burdens around pats. Multiple-component analysis and hierarchical classification used on regressor variables led to four classes which were characterized basically by fecal eggs and stocking rate, but not by climatic conditions. Within these classes, there was a limit of global radiation between 8 and 14 days after the entrance of animals; beyond this limit (20 MJ m⁻² day⁻¹), the L3_ap decreased from 1.3 to 27.1 times. The classification factor and global radiation factor explained 50–57% of the variance of L3_ap. From these results, it can be concluded that animal husbandry is just as important as climatic conditions in explaining the number of L3 on pasture in Guadeloupe. Global radiation, fecal eggs and stocking rates appeared to be useful in predicting the level of infectivity of pastures.     

Polycythemia and inappropriate erythropoietin concentrations in two dogs with renal T-cell lymphoma

Two dogs presented with suspected renal disease and polycythemia. Abdominal ultrasound examinations performed on both dogs revealed coalescing masses causing bilateral renomegaly. Serum erythropoietin (EPO) concentrations were physiologically inappropriate. Postmortem examinations revealed renal T-cell lymphoma in both dogs. One of the two dogs also had involvement of the liver and mesentery. EPO-immunohistochemistry on tissue samples demonstrated positive staining in tumor cells and occasional normal renal cells. This report illustrates that paraneoplastic EPO production may induce polycythemia. The pattern of EPO-immunohistochemistry staining suggested that the mechanism of production was due to tumor production of EPO and local hypoxia-induced EPO production from compression of normal renal cells and vasculature.     

First report of the Q biotype of <Emphasis Type="Italic">Bemisia tabaci</Emphasis> in Argentina and Uruguay

Bemisia tabaci adults were collected from pepper and melon at different commercial production greenhouses in Argentina and Uruguay. The biotype status of adults was then established using cytochrome oxidase I gene (mtCOI) as molecular marker. Only the Q biotype was found on all plants sampled. This is the first report of the Q biotype in Argentina and Uruguay.     

Walnut (Juglans spp.) ecophysiology in response to environmental stresses and potential acclimation to climate change

? Context

Walnuts (Juglans spp.) are ecologically and commercially important trees, yet synthesis of past and current research findings on walnut ecophysiology is lacking, especially in terms of potential acclimation to climate change.

? Aims

This study aims to (1) investigate walnut ecophysiology by comparing its attributes to associated deciduous angiosperms, (2) address potential acclimation of walnut to climate change, and (3) identify areas for prioritization in future research.

? Results

There is considerable uncertainty regarding the magnitude of potential effects of climate change on walnut. Some studies tend to indicate walnut could be negatively impacted by climate change, while others do not. Walnut may be at a disadvantage due to its susceptibility to drought and frost injury in current growing regions given the projected increases in temperature and extreme climatic events. Other regions that are currently considered cold for walnut growth may see increased establishment and growth depending upon the rate of temperature increase and the frequency and severity of extreme climatic events.

? Conclusion

Research investigating a combination of environmental factors, such as temperature, carbon dioxide, ozone, water, and nitrogen is needed to (1) better project climate change effects on walnut and (2) develop management strategies for walnut acclimation and adaptation to climate change.     

Stored light in an optical fiber via stimulated Brillouin scattering

We describe a method for storing sequences of optical data pulses by converting them into long-lived acoustic excitations in an optical fiber through the process of stimulated Brillouin scattering. These stored pulses can be retrieved later, after a time interval limited by the lifetime of the acoustic excitation. In the experiment reported here, smooth 2-nanosecond-long pulses are stored for up to 12 nanoseconds with good readout efficiency: 29% at 4-nanosecond storage time and 2% at 12 nanoseconds. This method thus can potentially store data packets that are many bits long. It can be implemented at any wavelength where the fiber is transparent and can be incorporated into existing telecommunication networks because it operates using only commercially available components at room temperature.