Tree and forest encroachment into fescue grasslands on the Cypress Hills plateau,southeast Alberta,Canada

Tree encroachment into rough fescue (Festuca campestris) grassland has been identified as an ecological concern on the Cypress Hills plateau in southeastern Alberta, Canada. A combination of field sampling (109 transects), a dendrochronological assessment (1361 trees), and a time series analysis of remotely sensed images from five different time periods (1950–2002) were used to determine the extent and rate of tree encroachment and forest development. Tree cover increased by 768 ha (～51%) between 1950 and 2007, representing 10% of the study area, from 1502 ha of pre-1950 forest. Post-1950 tree invasion also created an ingress zone of 750 ha (～10% of study area) based on field transects. Forest cover increased at a consistent rate of 14.3 ha/year. Lodgepole pine (Pinus contorta var. latifolia) was the most common tree species associated with encroachment. Invasion based on the number of established trees occurred at an exponential rate of 3.1%/year after 1890, with density increased by filling spaces adjacent to and between trees within the grassland vegetation. The rate of tree establishment increased to 4.4%/year after 1980, suggesting a change occurred in environmental conditions. Annual atmospheric temperatures increased 0.55 °C from 1929 to 2005 (P < 0.001), with winter (December–February) and spring (March–May) temperatures accounting for most of the increase (P < 0.001), whereas summer (June–August) temperatures slightly decreased (P < 0.050, 0.34 °C) and precipitation increased (P < 0.005, 30 mm). Cattle and elk (Cervus elaphus) grazing was not considered a primary factor for explaining tree encroachment. Based on multidimensional scaling, lodgepole pine establishment was associated with warmer spring temperatures and greater fall (October–November) precipitation. A landscape devoid of wildfires, combined with greater moisture availability, and a longer frost-free season is likely conducive to the sustained establishment of coniferous trees and forest development within the Cypress Hills fescue grassland ecosystem. Long-term conservation of the fescue grasslands could be possible by reintroducing fire.     

Temporal changes of understory plant community in response to pre- and post-harvesting herbicide treatments and partial cutting in aspen-dominated boreal mixedwood stands

In response to concerns about the effects of traditional timber harvesting practices on biodiversity, we examined the effects of alternative silvicultural systems, including partial cutting and modified herbicide use on understory plant communities in an aspen-dominated mixedwood stand. These alternative silvicultural systems match disturbance rates that, based on the intermediate disturbance hypothesis, would support more diverse understory vegetation communities than uncut or clear-cut forests treated with a broadcast spray. Our results indicated that both understory vegetation cover and number of plant species increased at 5 and 10 years after timber harvesting in aspen-dominated boreal mixedwood stands. The highest amount of understory vegetation cover were found in the pre-harvesting herbicide spray treatment areas, likely because understory plants were not directly exposed to the herbicide, whereas the most species occurred in the partial cutting treatment, which represented the most diverse stand structure with both harvested and leave corridors. Understory composition by percent cover of individual species at 10 years post-harvesting was affected by all treatment attributes (i.e., level of harvesting removal, type and time of herbicide application, and mechanical site preparation); however, understory vegetation responded the most to harvesting level. Among treatments, the difference in understory composition was largely attributed to changes in understory species of different shade tolerance.     

Changes in wood properties at the boundary of polyporus amarus decay pockets

Summary Incense cedar heartwood infected by the pocket rot fungus Polyporus amarus was subjected to microtensile testing and miscroscopical examination to determine effects of this fungus upon wood substance adjacent to advanced decay pockets. Although springwood of the annual ring nearest the decay pocket in some samples had a slightly lower tensile strength than springwood from the same ring but a distance from the pocket, the difference was not statistically significant. Microscopical examination revealed the presence of small, sparse bore holes and hyphae in approximately the same number inside and outside the advanced decay pockets, and in discolored regions of incipient decay. A few bore holes and hyphae were found in specimens from what was macroscopically considered to be sound wood. Polarized illumination revealed no evidence of diffusion of cellulolytic enzymes from the hyphae in regions other than within advanced decay pockets, but the small numbers of hyphae and bore holes observed in decay pockets indicated that considerable enzyme diffusion might be necessary for decay to procede. The data suggest that possible alteration of physical, mechanical, and chemical properties in wood substance surrounding decay pockets need not be a significant factor for consideration in utilization of pecky incense cedar.

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Zusammenfassung Kernholz von Zeder (Libocedrus decurrens), das von Polyporus amarus befallen worden war, wurde Mikro-Zugfestigkeitsprüfungen und einer mikroskopischen Durchmusterung unterworfen. Es sollten die Auswirkungen dieses Pilzbefalles auf jene Teile der Holzsubstanz geprüft werden, die unmittelbar an die Befallsstellen angrenzen. Das Frühholz eines Jahrringes, das einer Befallsstelle am nächsten lag, zeigte zwar bei einigen Proben eine geringfügig niedrigere Zugfestigkeit als das Frühholz desselben Jahrringes, das aber von der Befallsstelle weiter entfernt lag. Die Unterschiede waren jedoch statistisch nicht signifikant. Die mikroskopische Durchmusterung deckte das Vorhandensein von kleinen, etwas zerstreut liegenden Bohrlöchern und Hyphen auf, in etwa gleichgroßer Anzahl innerhalb und außerhalb der Stellen fortgeschrittenen Befalls und in den verfärbten Bereichen des beginnenden Befalls. Einige wenige Bohrlöcher und Hyphen wurden ferner in Proben festgetsellt, die bei makroskopischer Betrachtung gesund erschienen. Im polarisierten Licht ließ sich keine Diffusion von aus Hyphen stammenden celluloitischen Enzymen außerhalb der Befallsbereiche beobachten. Die wenigen Hyphen und Bohrlöcher, die in den Befallsstellen beobachtet werden konnten, gaben aber einen Hinweis darauf, daß bei der Ausbreitung eine beträchtliche Enzymdiffusion stattfinden muß. Die ermittelten Werte weisen darauf hin, daß die möglicherweise eintretende Änderung der physikalischen, mechanischen und chemischen Eigenschaften des Holzes in unmittelbarer Umgebung der Befallsstellen als wichtige Faktoren bei der Verarbeitung dieses Holzes beachtet werden müssen.

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Presented at the 1968 Forest Products Research Society Annual Meeting.     

Interaction of sodium dodecyl sulfate with watermelon chromoplasts and examination of the organization of lycopene within the chromoplasts

The properties of plant-derived precipitates of watermelon lycopene were examined in aqueous sodium dodecyl sulfate (SDS) as part of an ongoing effort to develop simpler, more economical ways to quantify carotenoids in melon fruit. Levels of SDS >0.2% were found to increase the water solubility of lycopene in the state in which it was isolated from watermelon. Electron microscopy and chemical analyses suggested that the watermelon lycopene as isolated is packaged inside a membrane to form a chromoplast. Spectral peaks in the visible region of the watermelon chromoplasts in SDS exhibited a bathochromic shift from those in organic solvent. Watermelon chromoplasts in SDS exhibited pronounced circular dichroic activity in the visible region. Binding measurements indicated that about 120 molecules of SDS were bound per molecule of lycopene inside the chromoplast; likely, the detergent molecules are bound to the chromoplast membrane. Around 80% of the chromoplast-SDS complexes were retained on a 0.45 mum membrane filter. Together, these observations are consistent with lycopene in a J-type chiral arrangement inside a membrane to form a chromoplast. The binding of SDS molecules to the chromoplast membrane form a complex that is extensively more water-soluble than the chromoplast alone.     

The influence of storm characteristics on sulfate in precipitation

The effects of storm dynamics on precipitation chemistry were examined using an atmospheric budget for SO₄ ^? . One hundred storms occurring between 1975 and 1978 at Hubbard Brook Experimental Forest in New Hampshire were used as test data. Concentrations of major ions were usually greater in convective storms than in continuous or layer storms. For example the geometric mean concentrations of SO₄ ^? in convective and continuous storms were 4.1 and 1.1 mg L^?1, respectively. Higher SO₄ ^? concentrations also occurred when surface wind directions were south or southwest. The summer maximum in convective activity along with the seasonal dependence of surface wind directions and the seasonal atmospheric chemistry cycle can account for the summer maximum in SO₄ ^? concentrations observed in the northeastern United States.     

Watershed-scale responses to ozone events in a Pinus strobus L. plantation

High O₃ levels during the 1984 growing season in the southern Appalachian Mountains caused extensive damage to a 28 yr old white pine plantation on a 13.4 ha watershed at the Coweeta Hydrologic Laboratory. Ozone stress effects included premature senescence and loss of foliage, stimulation of pine seedling germination, reduced basal area increment, and small but measurable increases in NO₃ ^–-N and K⁺ concentrations in stream water. There were no observable effects of O₃ damage on nutrient concentrations of stemwood and foliage but net nutrient accumulation was reduced due to lower stemwood production. Ozone injury did not predispose trees to root pathogens or bark beetle infestations.     

Assessment of EST- and genomic microsatellite markers for variety discrimination and genetic diversity studies in wheat

It is likely that in the near future sequence information from sequencing programmes and EST libraries will generate an abundance of genic microsatellite markers. This study is focused on the assessment of their likely impact and performance vis-à-vis their genomic counterparts. Microsatellites from two sources were used to assess the genetic diversity in 56 old and new varieties of bread wheat on the UK Recommended List. A set of 12 microsatellite markers generated from genomic libraries and 20 expressed sequence tag (EST)-derived microsatellites were used in the study, and the performance of both marker sets assessed. The EST-derived or genic microsatellites delivered fingerprints of superior quality, amplifying clear products with few stutter bands. Diversity levels as revealed bygenic microsatellites are similar to the few published results. The PIC values for the genic markers were generally lower than those calculated for the genomic microsatellites, though advantages of both marker classes for variety identification applications are discussed. This revised version was published online in July 2006 with corrections to the Cover Date.     

A rapid, seedling-based bioassay for identifying low cadmium-accumulating individuals of Durum wheat (Triticum turgidum L.).

We have developed a seedling-based bioassay that iscapable of identifying low Cd-accumulating phenotypes(homozygous and heterozygous) after 96–120 h ofexposure. Our experiments were conducted using¹⁰⁹Cd as a tracer at subtoxic concentrations tosimulate conditions that might be experienced in thefield. Supply of Cd (10^-11 M) to 4-d oldseedlings for 0–8 h resulted in no differences in rootand leaf Cd content between the low (TL05) and high(TL04) Cd-accumulating isolines. Increasing time ofexposure produced significant differences in leaf Cdaccumulation between isolines, with differencesbecoming most pronounced after the bulk of appliedcadmium ( 95%) was depleted from absorption solutions( 72 h). Similar results were obtained with8-d old seedlings, where differences between genotypeswere more pronounced in young leaves (2nd leaf) orshoot bases. Individuals from five low and highCd-accumulating near isogenic pairs (50individuals/isoline) were screened using Cdconcentration of shoot bases as the screeningcriterion. Mean scores within each isoline pair weresignificantly different, although overlap ofindividual scores was observed at intermediate foliarCd concentrations. The 2^nd leaf to root Cdcontent ratio, which reflects root to shoottranslocation, provided a better parameter todistinguish low from high Cd-accumulating isolines. Plants used for this bioassay could also be rescuedfor subsequent experimental crosses, providing a rapidand cost-effective tool for early detection of the lowCd-accumulating phenotype.     

Gas chromatography for detection of citrus infestation by fruit fly larvae (Diptera: Tephritidae)

Tephritid fruit flies are serious economic pests worldwide. As larvae, they feed and develop within the pulp of host fruits, making infestation difficult to detect by visual inspection. At U.S. ports of entry, incoming produce shipments are checked for infestation by manually cutting open a small sample of fruit and searching for tephritid larvae. Consequently, there is a need for more sensitive, high-throughput screening methods. This study evaluated gas chromatography (GC) as a potential technology for improved detection of hidden infestation. Grapefruits (Citrus × paradisi Macfad.) infested with immature stages of the Caribbean fruit fly Anastrepha suspensa (Loew) (Diptera: Tephritidae) were examined to determine if infested fruit emitted a chemical profile distinct from that of non-infested fruit. Peaks identified by GC analysis were grouped into three classes. Chemicals detected in similar quantities in all samples, or slightly elevated in infested samples, were regarded as non-diagnostic background volatiles. Chemicals highly elevated after oviposition, during the last instar exit stage, and in experimentally-pierced fruit were interpreted to be indicators of citrus peel injury, and included d-limonene and β-ocimene. Chemicals elevated exclusively in the larval infestation stages were considered indicators of feeding damage and potentially diagnostic of infestation, and included hexyl butanoate and an unidentified compound. The peaks associated with injury and feeding were also detectable with a portable ultra-fast GC analyzer that required less than 80 s per sample. Further studies will investigate the potential application of these results for development of a rapid, non-destructive screening method for detection of tephritid infestation.