Home About us Contact
|
Home About us Contact | ||
|
|
||
Fir Trees (fir + tree)
Selected AbstractsSpace allocation in Melanophila knoteki knoteki (Reitt.) var. hellenica (Obenberger) (Col., Buprestidae) in the attack of Greek fir [Abies cephalonica Loud. var. graeca (Fraas) Liu]: a pattern to process approachJOURNAL OF APPLIED ENTOMOLOGY, Issue 1 2004P. V. Petrakis Abstract: The phloeo-cambiophagous buprestid Melanophila knoteki knoteki (Reitt.) var. hellenica (Obenberger.) is not a primary factor of fir decline problem although the beetle substantially contributes to Greek fir Abies cephalonica Loud. var. graeca (Fraas) Liu mortality. By using mapping depiction of the exit holes of the insect on a set of fir trees located on a line transect in a randomized point-centred quarter scheme and employing pattern analysis techniques we were able to reveal various scales of the infestation pattern. Four scales were recognized, two of them corresponding to the pattern of microsite selection on the bark of a fir tree. While the dispersed exit holes exhibited a statistically significant random dispersion on the bark, within each aggregation the pattern was uniform. The area of compartments created by Dirichlet partition approximated very well the sizes of the actual larval galleries. The Dirichlet tessellation of the bark space and the analysis of the parameter of the resulting partitions showed the predominance of the hexagonal conformation of the larval spaces when space was limited. When some exit holes were positioned close together it was found that they were directed away from each other so the resulting galleries were well separated. Several hypotheses are presented as to the mechanisms underpinning the observed patterns. The allocation of space is in accordance with the widely accepted ,central place theory' of W. Christaller, a general theory of pattern generated in the geographical dispersion of human settlements. The revealed pattern was also in accordance with the predictions of the theory of ,central place foraging' of R. H. MacArthur and the theory of ,resource concentration hypothesis' of R. Root. [source] Epidemiology of Heterobasidion abietinum and Viscum album on silver fir (Abies alba) stands of the PyreneesFOREST PATHOLOGY, Issue 1 2010J. Oliva Summary In the last two decades, stand decline and increased mortality has affected silver fir (Abies alba) forests in the Spanish Pyrenees. Simultaneously severe occurrences of the root rot fungus Heterobasidion annosum s.l. and of the mistletoe Viscum album have been reported. We aimed to improve the understanding of the epidemiology of both pathogens in our region. All H. annosum isolates found on silver fir were typed as H. abietinum. H. abietinum was more frequently observed where cuttings had targeted fir trees rather than other species. H. abietinum fruiting bodies were observed in the most recently cut stumps. V. album was more abundant on more dominant fir trees, and in southern aspect stands. The number of V. album colonies in the stand correlated (R2 = 0.40) with silver fir mortality. Stands with a high level of V. album infection tended to have a smaller percentage of basal area in species other than silver fir, and they tended to be located on more south-facing slopes. H. abietinum was widespread in silver fir forests of the Pyrenees. Our data suggest that, in the Pyrenees, the observed H. abietinum incidence may represent a combination of both primary and secondary spread of the pathogen. Favouring mixed forests should be tested as a potential control method for V. album. The correlation between silver fir mortality and V. album infection warrants further study, as the observed tree mortality could have occurred due to other factors than V. album, such as drought damage. [source] Space allocation in Melanophila knoteki knoteki (Reitt.) var. hellenica (Obenberger) (Col., Buprestidae) in the attack of Greek fir [Abies cephalonica Loud. var. graeca (Fraas) Liu]: a pattern to process approachJOURNAL OF APPLIED ENTOMOLOGY, Issue 1 2004P. V. Petrakis Abstract: The phloeo-cambiophagous buprestid Melanophila knoteki knoteki (Reitt.) var. hellenica (Obenberger.) is not a primary factor of fir decline problem although the beetle substantially contributes to Greek fir Abies cephalonica Loud. var. graeca (Fraas) Liu mortality. By using mapping depiction of the exit holes of the insect on a set of fir trees located on a line transect in a randomized point-centred quarter scheme and employing pattern analysis techniques we were able to reveal various scales of the infestation pattern. Four scales were recognized, two of them corresponding to the pattern of microsite selection on the bark of a fir tree. While the dispersed exit holes exhibited a statistically significant random dispersion on the bark, within each aggregation the pattern was uniform. The area of compartments created by Dirichlet partition approximated very well the sizes of the actual larval galleries. The Dirichlet tessellation of the bark space and the analysis of the parameter of the resulting partitions showed the predominance of the hexagonal conformation of the larval spaces when space was limited. When some exit holes were positioned close together it was found that they were directed away from each other so the resulting galleries were well separated. Several hypotheses are presented as to the mechanisms underpinning the observed patterns. The allocation of space is in accordance with the widely accepted ,central place theory' of W. Christaller, a general theory of pattern generated in the geographical dispersion of human settlements. The revealed pattern was also in accordance with the predictions of the theory of ,central place foraging' of R. H. MacArthur and the theory of ,resource concentration hypothesis' of R. Root. [source] Density-dependent effects on tree survival in an old-growth Douglas fir forestJOURNAL OF ECOLOGY, Issue 4 2000Fangliang He Summary 1 ,We mapped the locations of live and dead trees in a large forest plot dominated by pioneer Douglas fir (Pseudotsuga menziesii) with an understorey of the invading late-successional species western hemlock (Tsuga heterophylla) and western red cedar (Thuja plicata) on Vancouver Island, British Columbia, Canada, to test for intra- and interspecific density-dependent effects on tree survival. 2 ,We analysed both the spatial patterning of trees in the plot and the relationships between neighbourhood density and tree survival. We also examined the effects of additional variables (principally elevation) as covariates in our neighbourhood analyses. 3 ,Both the spatial and initial neighbourhood analyses suggested strong intra- and interspecific density-dependent effects on tree survival. Douglas fir survival was significantly higher in less dense patches of conspecifics and non-random tree death led to regularly spaced survivors, as expected from intraspecific competition. The significantly lower survival of western hemlock in denser patches of Douglas fir and the resulting negative spatial association between surviving trees of these two species were consistent with interspecific competition. 4 ,However, having controlled for the influence of elevation on tree survival (probably mediated by variation in soil moisture) in neighbourhood analyses, although the survival of the pioneer Douglas fir trees was still subject to strong density-dependent effects, variation in its density in the overstorey no longer appeared to influence the survival of the invading late-successional species. There was, however, evidence for asymmetric interspecific density dependence between the two late-successional species since western hemlock mortality tended to be higher in denser patches of western red cedar. 5 ,Our results emphasize the importance of considering confounding factors in studies that seek evidence for density dependence. [source] | ||||||||||