Recruitment limitation in forests: Lessons from an unprecedented mountain pine beetle epidemic

Since the mid-1990s the forests of central British Columbia have undergone an unprecedented Mountain Pine Beetle (Dendroctonus ponderosae Hopkins) (MPB) epidemic that has resulted in extensive mortality of canopy lodgepole pine (Pinus contorta var. latifolia Engelm.). This study investigated how seed-source availability, seedbed substrate, overstory structure, and time since MPB attack interact to affect post-MPB seedling recruitment of the dominant tree species of these forests. In addition to post-MPB recruitment, these forests may be regenerated by trees established in the understory prior to MPB disturbance. Accordingly, we examined abundance and patterns of all regeneration less than 130 cm tall. We found post-MPB recruitment was sparse. Subalpine fir (Abies laciocarpa (Hook.) Nutt.) comprised the majority of the post-MPB recruitment. It increased with local parent tree basal area and increased strongly with proximity to a major seed source. This resulted in a patchy distribution for subalpine fir post-MPB regeneration. Lodgepole pine post-MPB recruitment was limited by overstory shading. Recruitment of pine decreased as the total overstory basal area increased. Interior spruce (Picea glauca × engelmannii) post-MPB recruitment was similarly limited by total overstory basal area. Seedbed substrates were uniform and dominated by moss. Substrate type distribution did not change as time since MPB disturbance increased. The overall low post-MPB recruitment observed was likely due to a lack of disturbance to the moss-dominated forest floor. Moss is known to be a poor substrate in northern forests. The distribution of all regeneration less than 130 cm tall showed the same trends as the post-MPB regeneration. We believe the post-MPB seedling recruitment dynamics of these forests was not substantially changed from conditions prior to MPB disturbance. There was no pulse of regeneration up to 10 years post-MPB disturbance. Unless this changes, future stand structure will be dominated by the seedling bank established prior to the MPB epidemic. Subalpine fir dominated the seedling bank (68%) and post-MPB recruitment (94%). This suggests that MPB-disturbed forests are undergoing a substantial shift in landscape-level species composition.     

The dust halo of Saturn's largest icy moon, Rhea

Saturn's moon Rhea had been considered massive enough to retain a thin, externally generated atmosphere capable of locally affecting Saturn's magnetosphere. The Cassini spacecraft's in situ observations reveal that energetic electrons are depleted in the moon's vicinity. The absence of a substantial exosphere implies that Rhea's magnetospheric interaction region, rather than being exclusively induced by sputtered gas and its products, likely contains solid material that can absorb magnetospheric particles. Combined observations from several instruments suggest that this material is in the form of grains and boulders up to several decimetres in size and orbits Rhea as an equatorial debris disk. Within this disk may reside denser, discrete rings or arcs of material.     

The sensitivity and specificity of a modified ELISA for the diagnosis of Johne's disease from a field trial in cattle

An enzyme-linked immunosorbent assay (ELISA) for the detection of antibodies against Mycobacterium paratuberculosis in cattle was evaluated in three herds known to have Johne's disease. Prior to testing, the plasma was absorbed with dried Mycobacterium phlei in order to remove cross-reacting antibody specificities. The sensitivity and specificity of the ELISA were calculated after repeatedly testing 327 cattle in the infected herds. Of these, 53 animals had one or more positive faecal cultures or had post-mortem histopathological evidence of infection. The other 274 had three or more negative faecal culture results, and were regarded as non-infected for the purpose of evaluation of the ELISA. Using these criteria for the presence or absence of infection, the M. phlei-absorbed ELISA under field conditions had a 57% sensitivity and a 98.9% specificity. The sensitivity of the absorbed ELISA depended on the stage of disease of the animal under test. In general, it appeared that animals in the more advanced stages of disease were absorbed ELISA positive, whereas those in the early stages of infection were not detected. These results indicate that the M. phlei-absorbed ELISA has an important role as a test for the diagnosis and control of Johne's disease in cattle.     

Morphological and molecular diversity of Colletotrichum spp. causing pepper spot and anthracnose of lychee (Litchi chinensis) in Australia

Since the 1980s a new disease has been affecting Australian lychee. Pepper spot appears as small, black superficial lesions on fruit, leaves, petioles and pedicels and is caused by Colletotrichum gloeosporioides, the same fungus that causes postharvest anthracnose of lychee fruit. The aim of this study was to determine if a new genotype of C. gloeosporioides is responsible for the pepper spot symptom. Morphological assessments, arbitrarily‐primed PCR (ap‐PCR) and DNA sequencing studies did not differentiate isolates of C. gloeosporioides from anthracnose and pepper spot lesions. The ap‐PCR identified 21 different genotypes of C. gloeosporioides, three of which were predominant. A specific genotype identified using ap‐PCR was associated with the production of the teleomorph in culture. Analysis of sequence data of ITS and β‐tubulin regions of representative isolates did not group the lychee isolates into a monophyletic clade; however, given the majority of the isolates were from one of three genotypes found using ap‐PCR, the possibility of a lychee specific group of C. gloeosporioides is discussed.     

Vascular encephalopathy associated with bacterial endocarditis in four dogs

Vascular encephalopathy is a commonly encountered clinical complication of infectious endocarditis in humans, but it has been infrequently reported in dogs. A series of four dogs with bacterial endocarditis that subsequently developed acute onset of neurological deficits is described. Clinical signs, diagnostic test results, and outcomes for each case are presented and compared with the human clinical syndrome.     

Inheritance of resistance to gray leaf spot in crosses involving selected resistant inbred lines of corn

ABSTRACT Three populations derived from crosses of selected resistant inbreds (061, B37HtN, and DS:74:1071) with susceptible inbred FR1141 and a population derived from a cross of B37 x B37HtN were evaluated for gray leaf spot severity in 1992 and 1993 at Urbana, IL, and Andrews, NC. Populations included the susceptible parent (P(1)), the resistant parent (P(2)), F(1) and F(2) generations, backcrosses BCP(1) and BCP(2), and, when space and seed were available, one or more of the F(3), BCP(1)S(1), and BCP(2)S(1) generations. Plants at Urbana were inoculated, and naturally occurring disease was relied upon at Andrews. Individual plants were rated by visually estimating the percent leaf area blighted (necrotic). Generation mean analysis of data combined over years or locations indicated that a simple additive-dominance model was able to explain the inheritance of resistance for all populations. Dominance effects were detected in all population evaluated. For the FR1141 x 061 and FR1141 x B37HtN populations, dominance was significant at early ratings, but not at late ratings. Results from generation mean analysis for individual years, locations, and rating were variable.     

A survey of the Fish Fauna of Sudanese Irrigation Systems with Reference to the Use of Fishes in the Management of Ecological Problems (the Control of Aquatic Weeds, Malaria and Infective Schistosomiasis)

This paper reports on a fundamental study of the fish fauna already present within the irrigation canals. The fauna was investigated with a view to determining its use in the control of nuisance biota. Twenty-seven species of fish were collected, comprising 22 genera and 12 families. This fauna is closely allied to the fauna of the source water, the Blue Nile. Several Blue Nile species are absent and some of those collected are new recordings for the area. Each species of fish collected had neither a suitable feeding habit nor a wide enough distribution to have any significant effect on the levels of nuisance biota. This includes the mosquito fish. Gambusia affinis, which was specifically introduced for mosquito control. Improvement in the ecological conditions within the canals involves both the management of the already-existing fish stocks and the introduction and management of additional species. A reduction in the levels of aquatic weeds using phytophagous fishes should be a high priority with malacopliagous and larvivorous species also being introduced and their stocks managed. Species suitable for introduction, which are generally endemic to the Nile system, are suggested. The fish species diversity falls as the canals become smaller and the water within them subject to much greater variations in flow and quality. The lowest order canals (field canals) are probably unsuitable for permanent fish stocks. The nuisance biota within field canals can be controlled by simple improvements in crop-watering procedures. The widely distributed and diverse fauna found within minor canals suggests that problems due to fish-kills brought about by heavy pesticide and herbicide usage are not so severe as previously thought. The management of the ecological problems is a complex task due to the interrelationships of many factors.