Growth and productivity of black spruce in even- and uneven-aged stands at the limit of the closed boreal forest

The increasing commercial interest and advancing exploitation of new remote territories of the boreal forest require deeper knowledge of the productivity of these ecosystems. Canadian boreal forests are commonly assumed to be evenly aged, but recent studies show that frequent small-scale disturbances can lead to uneven-aged class distributions. However, how age distribution affects tree growth and stand productivity at high latitudes remains an unanswered question. Dynamics of tree growth in even- and uneven-aged stands at the limit of the closed black spruce (Picea mariana) forest in Quebec (Canada) were assessed on 18 plots with ages ranging from 77 to 340 years. Height, diameter and age of all trees were measured. Stem analysis was performed on the 10 dominant trees of each plot by measuring tree-ring widths on discs collected each meter from the stem, and the growth dynamics in height, diameter and volume were estimated according to tree age. Although growth followed a sigmoid pattern with similar shapes and asymptotes in even- and uneven-aged stands, trees in the latter showed curves more flattened and with increases delayed in time. Growth rates in even-aged plots were at least twice those of uneven-aged plots. The vigorous growth rates occurred earlier in trees of even-aged plots with a culmination of the mean annual increment in height, diameter and volume estimated at 40–80 years, 90–110 years earlier than in uneven-aged plots. Stand volume ranged between 30 and 238 m³ ha⁻¹ with 75% of stands showing values lower than 120 m³ ha⁻¹ and higher volumes occurring at greater dominant heights and stand densities. Results demonstrated the different growth dynamics of black spruce in single- and multi-cohort stands and suggested the need for information on the stand structure when estimating the effective or potential growth performance for forest management of this species.     

Delineation of vine parcels by segmentation of high resolution remote sensed images

Field delineation is an essential preliminary step for the design of management maps for grape production. In this paper, we propose a new algorithm for the segmentation of vine fields based on high-resolution remote sensed images. This algorithm takes into account the textural properties of vine images. It leads to the computation of a textural attribute on which a simple thresholding operation allows to discriminate between vine field and non-vine field pixels. The feasibility of the automatic delineation is illustrated on a range of vineyard images with various inter-row distances, grass covers, perspective distortions and side perturbations. In most cases it produces precise delineation of field borders while the parcel under consideration remains separate from the rest of the image.     

Identification and pest status of two exotic flea beetle species newly introduced in Portugal: Epitrix similaris Gentner and Epitrix cucumeris (Harris)

Around 2004, a new type of injury was noticed in potato tubers harvested in the north of Portugal. Two North American flea beetles, Epitrix cucumeris and Epitrix similariswere later identified. The second species seems to be responsible for the characteristic type of tuber injury observed. The main morphological characters enabling the two species to be distinguished are presented.     

Dynamic imaging of T cell-dendritic cell interactions in lymph nodes

T cell immune responses begin within organized lymphoid tissues. The pace, topology, and outcomes of the cellular interactions that underlie these responses have, so far, been inferred from static imaging of sectioned tissue or from studies of cultured cells. Here we report dynamic visualization of antigen-specific T cells interacting with dendritic cells within intact explanted lymph nodes. We observed immunological synapse formation and prolonged interactions between these two cell types, followed by the activation, dissociation, and rapid migration of T cells away from the antigenic stimulus. This high-resolution spatiotemporal analysis provides insight into the nature of cell interactions critical to early immune responses within lymphoid structures.     

Depletion of the Outer Asteroid Belt

During the early history of the solar system, it is likely that the outer planets changed their distance from the sun, and hence, their influence on the asteroid belt evolved with time. The gravitational influence of Jupiter and Saturn on the orbital evolution of asteroids in the outer asteroid belt was calculated. The results show that the sweeping of mean motion resonances associated with planetary migration efficiently destabilizes orbits in the outer asteroid belt on a time scale of 10 million years. This mechanism provides an explanation for the observed depletion of asteroids in that region.     

A single amino acid interchange yields reciprocal CTL specificities for HIV-1 gp160

For the IIIB isolate of human immunodeficiency virus type-1 (HIV-1), the immunodominant determinant of the envelope protein gp160 for cytotoxic T lymphocytes (CTLs) of H-2d mice is in a region of high sequence variability among HIV-1 isolates. The general requirements for CTL recognition of peptide antigens and the relation of recognition requirements to the natural variation in sequence of the HIV were investigated. For this purpose, a CTL line specific for the homologous segment of the envelope from the MN isolate of HIV-1 and restricted by the same class I major histocompatibility (MHC) molecule (Dd) as the IIIB-specific CTLs was raised from mice immunized with MN-env-recombinant vaccinia virus. The IIIB-specific and MN-specific CTLs were completely non-cross-reactive. Reciprocal exchange of a single amino acid between the two peptide sequences, which differed in 6 of 15 residues, led to a complete reversal of the specificity of the peptides in sensitizing targets, such that the IIIB-specific CTLs lysed targets exposed to the singly substituted MN peptide and vice versa. These data indicate the importance of single residues in defining peptide epitopic specificity and have implications for both the effect of immune pressure on selection of viral mutants and the design of effective vaccines.     

Peripheral blood lymphocyte subsets in fleece rot-resistant and -susceptible sheep

Objective To compare haematological values and lymphocyte phenotypes in the peripheral blood of fleece rot-resistant and -susceptible sheep.
Procedure Experiments were conducted on 2- and 3-year-old Merino rams, flock 1 (17 rams) and flock 2 (32 rams), respectively. Within each flock, individual rams were classified as fleece rot-resistant or -susceptible, based on established criteria. Total and differential white cell counts, and indirect fluorescent antibody tests specific for B cells and T cells were performed on all sheep. The concentration of various subsets of circulating lymphocytes was then determined in each sheep.
Results There were no significant differences between fleece rot-resistant and -susceptible sheep from either flock in the mean total or differential white cell counts. However, fleece rot-resistant rams in flock 1 did have a significantly higher concentration of circulating SBU-T1⁺ cells than fleece rot-susceptible rams from the same flock. No such difference was noted in the rams from flock 2. While all rams in flock 1 were free of clinical fleece rot, 24 rams in flock 2 (comprising all 17 fleece rot-susceptible and 7 of 15 fleece rot-resistant animals) had clinical signs of the disease. Fleece rot-free rams in this flock (irrespective of their classification as fleece rot-resistant or -susceptible) had significantly higher concentrations of circulating SBU-T1⁺ cells compared with fleece rot-affected animals. They also had significantly higher concentrations of circulating B cells, and total lymphocytes.
Conclusions An examination of peripheral blood lymphocyte subsets in fleece rot-resistant and -susceptible sheep revealed a possible association between resistance to fleece rot and the concentration of circulating SBU-T1⁺ cells.