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261.
262.
Maggi Kelly Desheng Liu Brice McPherson David Wood Richard Standiford 《Journal of Forest Research》2008,13(5):312-319
Sudden oak death is a disease affecting coastal forests in California and southern Oregon. The spatial pattern of disease
dynamics is important for forest and landscape pathology; in this work we investigated the interaction across landscape scales
of disease symptomology in coast live oaks, Quercus agrifolia, (trunk bleeding, presence of beetles, and presence of the fungus Hypoxylon thouarsianum) and tree mortality through time. We used two-dimensional spatial analysis tools with data gathered in point-centered-quarter
format in 2001 and 2004 to quantify the population density of the disease through time; to examine the spatial pattern of
tree mortality across scales through time; and to examine the spatial co-occurrence of disease symptoms with crown mortality
through time. Early in the study period dead trees were strongly clustered at smaller scales (~300 m) and after three years
this clustering was less pronounced. Bleeding on trees occurred in clusters away from dead trees, particularly in 2004, likely
indicating a new cohort of infected trees. The presence of H. thouarsianum was strongly related to overstory mortality through time. Beetle-infested trees co-occurred with mortality in 2001. By 2004,
they occurred throughout the forest, and were less strongly correlated with overstory tree mortality, suggesting a future
peak of tree mortality. 相似文献
263.
Marco Aurelio Gonzlez-Tagle Luitgard Schwendenmann Javier Jimnez Prez Rainer Schulz 《Forest Ecology and Management》2008,256(1-2):161-167
Although wildfires are occurring frequently in the pine–oak forests in the Sierra Madre Oriental (northeastern Mexico), data on post-fire succession and forest structure are still rare. Our objectives were to (1) assess the changes in woody plant species composition after fire and to (2) to relate successional patterns to environmental variability. Based on their fire history 23 plots were selected in the Parque Ecológico Chipinque (PECH). Changes in forest structure across the chronosequence of burned stands were deduced from density, height and diameter measurements of trees and shrubs (>5 cm in diameter) in all plots of 1000 m2. Differences in woody plant species composition among the plots were evaluated using Shannon evenness measure and the Whittaker's measure and by Hierarchical cluster analysis and Detrended Correspondence Analysis. Hierarchical cluster analysis showed a high similarity among all recently burned plots, independed of the aspect. Multivariate analysis showed that local environmental factors, including time since fire, continue to structure species composition. Oak species (mainly Quercus rysophylla) resprouted successfully after fire and dominated young post-fire stands. Pine species (Pinus pseudotrobus and Pinus teocote) only appeared 18 years after fire and were the dominating species in mature stands (62 years after fire). In contrast, woody plant species composition in older stands tended also to be influenced by factors such as aspect and by the potential solar radiation (PSR) during the growing season. The results demonstrate that in the PECH, natural regeneration is sufficient and woody plant species composition will be similar to pre-fire conditions after 60 years of succession. We conclude that the park managers should consider incorporating natural disturbance regimes into their management practices. 相似文献
264.
A nonlinear mixed-effects modelling approach was used to model the individual tree height–diameter relationship in pyrenean oak (Quercus pyrenaica Willd.). A set of 24,627 pairs of height–diameter measurements were used to fit the model. These were taken at 950 Spanish National Forest Inventory plots embracing six different biogeoclimatic strata. Eleven biparametric nonlinear height–diameter equations were evaluated to find a local model, which only includes the dimensions of the tree as explanatory variables. After selecting the local model, a regional or generalized model was studied. The following stand variables were tested for inclusion in the model as fixed effects: stand density, quadratic mean diameter, arithmetic mean diameter, dominant diameter, arithmetic mean height, dominant height and basal area. Dominant height and basal area of the stand were found to produce the most satisfactory fits in the stand model. Interregional variability was studied by including strata effects as dummy categorical variables and was analysed using the non-linear extra sum of squares method and the Lakkis–Jones test. Height–diameter models were found to be similar for the six biogeoclimatic strata. Finally, a mixed nonlinear model technique was applied to fit the definitive model. By calibrating the model it is possible to predict random components of definitive model from height measurements previously taken from a subsample of trees. The different alternatives tested reveal that only two or three trees are necessary to calibrate the model. 相似文献
265.
The influence of single trees on saturated hydraulic conductivity (Ks) was investigated for six isolated oak trees (Quercus robur) growing on a Dystric Gleysol in an area of parkland in northwest England. The Ks was measured within the A soil horizon over a 0.10–0.25 m depth using a borehole permeameter. 相似文献
266.
Sakina Elshibli Juha Raisio Saila Varis Pekka Vakkari Pertti Pulkkinen 《Scandinavian Journal of Forest Research》2016,31(2):140-147
We present a genetic profile of pedunculate oak (Quercus robur L.) in three woodlands of the Helsinki region. We genotyped all mature trees and samples of seedlings to evaluate patterns of genetic variation and gene flow, and evaluate the long-term stability and natural regeneration of these stands. Although five microsatellite loci showed no significant differences in heterozygosity between generations in most locations, significant (p?.05) pairwise differences were observed between mature trees and seedlings at Seurasaari, with higher diversity within seedlings. Ninety-four percent of the genetic variation occurred within sample sites. Background pollination contributed up to 61% of the diversity among seedlings, and thereby plays an important role in shaping the genetic variation and structure of future generations. Results indicate that pedunculate oak trees in the surveyed parks of Helsinki belong to the same population and that the urban environment per se does not interfere with gene flow over the distances represented here. Based on our findings, a minimal-maintenance program reliant upon natural regeneration of oak in the public parks of Helsinki seems plausible. 相似文献
267.
Effects of dietary Persian oak (Quercus brantii var. persica) fruit extract on survival,growth performance,haematological and immunological parameters in rainbow trout,Oncorhynchus mykiss,fingerlings
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The aim of study was to evaluate the effects of jaft (internal layer of oak fruit) extract on growth, haematological and immunological parameters in rainbow trout fingerlings. A total of 360 fish (average weight 6.25 g, total length 7.75 cm) were randomly distributed in 12 fibreglass tanks (stocking density: 1.04 g L?1) with flow rate of 8 L min?1. The ethanolic extraction of jaft was taken, and, then, a basal diet was supplemented with 0 (control), 0.5, 1 and 2 g kg?1 to formulate four experimental diets. After 8 weeks, blood sampling was performed for haematological and immunological parameters. While immunological parameters such as IgM and lysozyme showed their lowest level in control group, their highest amounts appeared in 2 g kg?1 group. C3, C4 and alternative complement activity increased in fish fed 2 g kg?1 extract compared to control (P ? 0.05). Haematological parameters such as white blood cell, red blood cell, haemoglobin and haematocrit were enhanced in experimental groups (P ? 0.05). Survival and growth indices did not show significant changes in experimental treatments (P ? 0.05). Results indicated feeding rainbow trout with Persian oak extract at 0.5, 1.0 and 2.0 g kg?1 levels significantly enhance the immunological parameters. 相似文献
268.
安康、汉中地区栎林面积91.67万ha,蓄积5102万m~3,占整个有林地面积、蓄积的40~50%。在陕南生态平衡、工农业生产中起着极为重要的作用。现有栎林分布不均,可利用性差,中、幼龄林分比重大,质量不高,生产力低;连续多年超伐,森林蓄积大幅度减少。应采取果断措施,制止当前在栎林资源利用中的失控行为,压缩对栎林的消耗;大力造林和改造次生林,扩大栎林资源面积,提高林分质量;节约资源提高资源利用效益,从根本上缓解栎林供需矛盾。 相似文献
269.
270.
闽北栓皮栎人工林土壤肥力与水源涵养功能的研究 总被引:4,自引:0,他引:4
对福建省浦城县党溪国有林经营所36年生栓皮栎人工林与杉木人工林的土壤肥力与水源涵养功能的比较研究结果表明:栓皮栎人工林具有良好的土壤结构性状和较强的养分供应能力,表层>0.25mm水稳性团聚体含量比杉木人工林高9.99%,土壤有机质比杉木人工林高0.695%;栓皮栎人工林还具有良好的水源涵养功能,林分总持水量比杉木人工林高10%。 相似文献