Results 1 - 10 of 2103
Results 1 - 10 of 2103. Search took: 0.029 seconds
|Sort by: date | relevance|
[en] Accomplishments throughout a 10-year period summarized include: a study of the effects of radiation from a γ source on the ecology of the El Verde rain forest in Puerto Rico, with emphasis on the role of secondary succession in the recovery of forest ecosystems following irradiation; the effects of light and temperature on gaseous exchange in trees using 14CO2 as a tracer in Palcourea; the nature of the sensitivity of pine trees to ionizing radiation and the possible synergistic effects of elevated ozone levels on radiosensitivity; the combined effects of radioactive and thermal effluents on plant communities of a swamp hardwood forest; and the development of a new conceptual approach to the evaluation of environmental quality, with emphasis on ecological perspectives in land use planning
[en] Aim of the study: The effect of physical and chemical conditions at proliferation stage was evaluated in order to elucidate if this stage is the determinant phase to induce a marked effect in Pinus halepensis somatic embryogenesis. Area of study: The study was conducted in research laboratories of Neiker (Arkaute, Spain). Material and methods: Pinus halepensis embryonal masses from ten embryogenic cell lines subjected to nine treatments (tissues cultured at three temperatures on media supplemented with three agar concentrations) at proliferation stage. Main results: Significant differences were observed among different proliferation conditions months later at the end of maturation, germination and acclimatization stages. Research highlights: Aleppo pine embryonal masses are cultured under standard conditions on a culture medium supplemented with 4.5 g/L Gelrite® at 23ºC. However, better results in terms of plantlet production can be obtained proliferating the embryonal masses at 18ºC in a culture media with significantly lower water availability.
[en] To avoid large clear-cut areas in recreation areas, three experiments where group selection was used to transform even-aged stands of Norway spruce (Picea abies (L.) Karst.) into uneven-aged stands were started. Two of these group selection stands were compared with adjacent forests managed by the clear-cut system on the basis of the opinion of seven voluntary groups. The respondents have given their judgement of the forest sites in a semantic differential test. All parties made assessments when visiting the forest sites. In addition, two of the groups made assessments of black and white photographs representing the forest sites. The methods used were found to be both reliable and valid. A very low correlation was obtained between the assessment of whole forest areas and the mean value of the assessments of the stands within the same area. According to this study, the group selection method is preferable to clear-cutting in even-aged stands of Norway spruce if the attitude of the voluntary groups are to be met. 31 refs, 4 figs, 9 tabs
[en] A multi-factor experimental approach and proportional odds model was used to study interactions between five environmental factors significant to Norway spruce seed germination: prechilling (at +4.5 °C), suboptimal temperatures (+12 and +16 °C), osmotically induced water stress (–0.3 Mpa and 0 Mpa), prolonged white light, and short-period far-red light. Temperature and osmotic stress interacted with one another in the germination of seeds: the effect of osmotic stress being stronger at +16 °C than at +12 °C. In natural conditions, this interaction may prevent germination early in the summer when soil dries and temperature increases. Prolonged white light prevented germination at low temperature and low osmotic potential. Inhibitory effect was less at higher temperatures and higher osmotic potential, as well as after prechilling. Short-period far-red light did not prevent germination of unchilled seeds in darkness. Prechilling tended to make seeds sensitive to short pulses of far-red light, an effect which depended on temperature: at +12 °C the effect on germination was promotive, but at +16 °C, inhibitory and partly reversible by white light. It seems that Norway spruce seeds may have adapted to germinate in canopy shade light rich in far-red. The seeds may also have evolved mechanisms to inhibit germination in prolonged light
[en] Remote sensing studies of conifer forests have previously reported that the Thematic Mapper Band 4/Band 3 ratio is positively correlated with regional differences in leaf area index (LAI). Our study was an attempt to determine whether Landsat Thematic Mapper data can be used to detect differences and changes in the LAI of closed canopy pine plantations on a local scale in central Massachusetts. Field measurements of LAI were obtained using locally-derived allometric relationships between leaf area and trunk diameter (DBH). A thinning treatment, which reduced the LAI of one of the larger plantations by more than 25%, resulted in a significant decrease (P < 0.001) in the 4/3 ratio from the prethinned value. No significant change in the 4/3 ratio was found in a nearby broadleaved hardwood forest which served as a radiometric control. However, a decrease in the 4/3 ratio similar to that observed in the thinned plantation was observed in nearby unthinned pine plantations. This change in the reflectance of the unthinned stands may be attributable to a moderate natural reduction in LAI. Such a reduction in LAI would demonstrate the limitations of allometric equations for evaluating LAI under conditions in which the relationship between leaf area and DBH may be changing from year to year. It also would explain why no significant relationship (P > 0.1) was found between the 4/3 ratio and the LAI of the different unthinned plantations which had LAI values ranging from 3.96 to 7.01. We conclude that the TM sensor may be a better guide to moderate changes and differences in the LAI of closed canopy pine plantations at local scales than field measurements involving allometric equations. (author)
[en] Aim of study: Mycorrhizal fungi in Mediterranean forests play a key role in the complex process of recovery after wildfires. A broader understanding of an important pyrophytic species as Pinus pinaster and its fungal symbionts is thus necessary for forest restoration purposes. This study aims to assess the effects of ectomycorrhizal symbiosis on maritime pine seedlings and how fire severity affects fungal colonization ability. Area of study: Central Spain, in a Mediterranean region typically affected by wildfires dominated by Pinus pinaster, a species adapted to fire disturbance. Material and Methods: We studied P. pinaster root apexes from seedlings grown in soils collected one year after fire in undisturbed sites, sites moderately affected by fire and sites highly affected by fire. Natural ectomycorrhization was observed at the whole root system level as well as at two root vertical sections (0-10 cm and 10-20 cm). We also measured several morphometric traits (tap root length, shoot length, dry biomass of shoots and root/shoot ratio), which were used to test the influence of fire severity and soil chemistry upon them. Main results: Ectomycorrhizal colonization in undisturbed soils for total and separated root vertical sections was higher than in soils that had been affected by fire to some degree. Inversely, seedling vegetative size increased according to fire severity. Research highlights: Fire severity affected soil properties and mycorrhizal colonization one year after occurrence, thus affecting plant development. These findings can contribute to a better knowledge of the factors mediating successful establishment of P. pinaster in Mediterranean forests after wildfires. (Author)
[en] Wind damage is one of the major natural disturbances that can occur worldwide in most types of forests. Enhanced management using adequate decision support systems (DSS) can considerably reduce the risk of windthrow. The decision support system 'Forest and Climate Change' (DSS-WuK) which is currently being developed at Goettingen University aims at providing a tool for the quantitative assessment of biotic and abiotic risks for forest ecosystems under the conditions of changing climate. In order to assess the future risks of wind damage the system employs a coupled modelling approach combining the turbulence model SCAlar DIStribution (SCADIS) with the soil-vegetation-atmosphere-transfer (SVAT) model BROOK 90. The present study investigates projections of wind damage in Solling, Germany under climate scenarios A1B and B1, taking into account the windthrow feedbacks-changes of microclimate as a result of tree fall and consequent stabilization or destabilization of a forest stand. The results of the study indicate that in Solling the risk of windthrow for spruce and pine forest stands is likely to increase considerably during the 21st century. The general tendencies indicate that under A1B the probability of damage would be higher than under B1 and that under the same climate and soil conditions the risk for spruce stands would be higher than for pine stands of equal age. The degree of damage and feedback contribution as well as a sign of feedback in each particular case will strongly depend on the particular local or regional combination of climatic and soil factors with tree species, age and structure. For Solling the positive feedback to local climatic forcing is found. The feedback contributes considerably (up to 6% under given conditions) to the projected forest damage and cannot be neglected. Therefore, the adequate projection of future damage probabilities can be performed only with a process-based coupled soil-atmosphere model with corresponding high spatial and temporal resolution.
[en] Aim of the study. Seed production in forest tree species commonly takes a long time due to the length of the juvenile stage. Even though several treatments have been used to induce early flowering in conifer species, experience on their use in subtropical Pinus species is limited. This study aimed to evaluate the effect of GA4/7 dose (0, 1.27 and 2.54 mg cm-2) and application time (July-October), alone or in combination with partial stem girdling, on male and female strobili production in young Pinus patula Schiede ex Schltdl. et Cham. clones. Area of study: Nine clones with different flowering background of high-elevation Pinus patula growing in a six-year old seed orchard established in Central México (Aquixtla, Puebla) at 2,800 m elevation. Material and methods: Two independent flowering trials (FT1 and FT2) were carried out in the seed orchard during the 2009 and 2010 flowering cycles; similar factors were evaluated at both trials but time of application, clones tested, and experimental design used varied for each of them. Partial stem girdling was done at the base of the trunk and the GA4/7 solution was injected into the xylem above the point of girdling. The following spring, the percentage of trees with strobili and the number of strobili per tree were determined for both male and female structures. Main results: Significant differences (p ≤ 0.05) among clones in flowering capacity were found at both trials. None of the treatments applied in FT1 resulted in an increase of strobili formation, most probably because they were applied too late in the growing season. In FT2, however, application of GA4/7 combined with partial stem girdling increased the percentage of trees with strobili and the number of strobili of both sexes, particularly when applied in early July. Partial stem girdling was more effective on promoting male strobili than female ones in gibberellin-treated grafts. Research highlights: Timing of GA4/7 application and stem girdling was important, with a significant interaction with clones tested in FT2 on production of male strobili but not on female strobili. Application of 1.27 mg cm-2 GA4/7 and stem girdling in July promoted the highest percentage of trees with strobili, and increased 25-fold the number of female strobili and 5-fold the number of male strobili per tree as compared to the control treatment. Thus, operational use of this induction treatment would be valuable to increase and accelerate seed production in Pinus patula seed orchards in the region. (Author)