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991.
Resin or pitch pockets cause a significant reduction in timber quality of Norway spruce (Picea abies (L.) Karst). Their occurrence is very variable within the stem and between trees and stands. Researchers have suggested several causes of resin pocket formation with a majority arguing in favour of storms as the main causing factor. 相似文献
992.
Riparian vegetation strongly influences the structure and function of terrestrial and aquatic ecosystems; therefore, harvest of riparian trees can profoundly impact these habitats. Riparian reserves (no harvest zones) are used world-wide to reduce these impacts, including effects on organic matter dynamics. There are, however, few experimental evaluations of their efficacy. Particulate organic matter delivery from riparian vegetation to streams, a critical ecosystem process, was measured over an eight year period after logging in southwestern British Columbia, Canada to quantify the relationship between these litter fluxes and riparian reserves (unlogged controls, 30 and 10-m wide uncut reserves, and clear-cuts). We hypothesized that the timing, composition and quantity of organic matter entering these streams would vary as a function of reserve width, but that these differences would decline with time since logging. We also hypothesized that inter-annual variation in precipitation patterns would partially contribute to litter dynamics. Riparian treatment significantly affected the quantity and composition of litter flux: inputs of needles and twigs were significantly lower and proportion of deciduous litter higher in clear-cut streams compared to other treatments. ANOVA models indicated that treatment differences in litter flux persisted through year 7 for some components of litter, while regression models indicated positive trends between reserve width and litter flux through year 8. This positive slope indicates the clear-cut treatment had yet to recover from logging. Variation in snowfall and plant succession contributed to temporal variation in litter flux; in some cases, litter inputs increased with annual snowfall. Another key finding from this study was that riparian reserves provided total litter inputs to streams that were similar to fully forested controls. 相似文献
993.
Diego Valbuena Peter H. Verburg Arnold K. Bregt Arend Ligtenberg 《Landscape Ecology》2010,25(2):185-199
Land-use/cover change (LUCC) is a complex process that includes actors and factors at different social and spatial levels. A common approach to analyse and simulate LUCC as the result of individual decisions is agent-based modelling (ABM). However, ABM is often applied to simulate processes at local scales, while its application in regional studies is limited. This paper describes first a conceptual framework for ABM to analyse and explore regional LUCC processes. Second, the conceptual framework is represented by combining different concepts including agent typologies, farm trajectories and probabilistic decision-making processes. Finally, the framework is illustrated through a case study in the Netherlands, where processes of farm cessation, farm expansion and farm diversification are shaping the structure of the landscape. The framework is a generic, straightforward approach to analyse and explore regional LUCC with an explicit link to empirical approaches for parameterization of ABM. 相似文献
994.
Robin A Atherton Bennet J McComish Lara D Shepherd Lorraine A Berry Nick W Albert Peter J Lockhart 《Plant methods》2010,6(1):22
Background
Complete chloroplast genome sequences provide a valuable source of molecular markers for studies in molecular ecology and evolution of plants. To obtain complete genome sequences, recent studies have made use of the polymerase chain reaction to amplify overlapping fragments from conserved gene loci. However, this approach is time consuming and can be more difficult to implement where gene organisation differs among plants. An alternative approach is to first isolate chloroplasts and then use the capacity of high-throughput sequencing to obtain complete genome sequences. We report our findings from studies of the latter approach, which used a simple chloroplast isolation procedure, multiply-primed rolling circle amplification of chloroplast DNA, Illumina Genome Analyzer II sequencing, and de novo assembly of paired-end sequence reads. 相似文献995.
996.
The impact of storm water runoff on a small urban stream 总被引:2,自引:0,他引:2
Vilmantė Karlavičienė Sigita Švedienė Danutė Elena Marčiulionienė Peter Randerson Mindaugas Rimeika William Hogland 《Journal of Soils and Sediments》2009,9(1):6-12
Background, aim, and scope In urban areas, storm water runoff often transports various pollutants, some of which settle and form sediments. In order
to have the comprehensive view of the ecological state of storm water runoff recipients, both water and sediments of the stream
must be assessed. In the Baltic Sea Area, the Water Framework Directive & HELCOM Recommendations aim to prevent or minimise
pollution caused by harmful substances arising from storm water runoff, in order to promote the ecological restoration of
the Baltic Sea—one of the most vulnerable seas. The aim of the study was to investigate the toxicity of bottom sediments of
a small storm water runoff recipient focusing on the potential impact of successive discharges of urban storm water. Some
storm water runoff quality parameters and the toxicity of bottom sediments of recipients was studied in this research.
Materials and methods During 9 years, at four discharge points, minimum four grab samples per year at each discharge point were taken for chemical
characterisation. General parameters (pH, SS, BOD7, CODCr and TPH) in liquid phase samples were analysed according to standard methods. Annual limit values were taken from the Lithuanian
EPA requirements for the management of storm water runoff with a focus on prevention and control of contamination. Eleven
composite samples of stream bottom sediments, each consisting of ten sub-samples, were collected in 2006. Toxicity screening
from sediments was performed using the plant Lepidium sativum according to modified I. Magone’s methodology (Magone I, Bioindication of phytotoxicity of transport emission. In: Kachalova
O-L, Zinatne (eds) Bioindication of toxicity of transport emissions in the impact of highway emissions on natural environment. Riga, pp 108–116, 1989). The level of toxic impact of Lepidium sativum (compared to control) was assessed according to the modified method of Wang (Rev Environ Contam Toxicol 126:88–127, 1992).
Results The mean pH of urban storm water runoff does not vary much from neutral, but range values are quite different, from 4.0 up
to 8.7. The highest concentration of SS reached 800 mg L−1, TPH—2.4 mg L−1, BOD7—300 mg O2 L−1 and CODCr—1,400 mg L−1. The SS was above the limit in 64% of total amount of grab samples, TPH—37%, BOD7—41% and CODCr—55%. The toxicity analysis of the bottom sediments showed varying toxicity of bottom sediments along the stream. From nine
analysed samples of bottom sediments, 30% had weak toxicity, 30% medium and 30% strong toxicity on the test organism plant
L. sativum. There was one single sample with no toxic effects, so that the results showed that urban storm water has an unacceptable
environmental impact on recipients. It was also indicated that storm water runoff discharge alone is not the potential source
of toxicity of bottom sediments. The litter demonstrated a weak toxicity of bottom sediments as well.
Discussion Most local authorities do not consider storm water runoff discharges to be a matter of great concern because they believe
that surface runoff arising from rainfall is still relatively clean. The study showed that the current method of monitoring
storm water runoff quality by chemical analyses is not the best tool for environmental impact assessment and must be combined
with toxicity tests of bottom sediments of recipients.
Recommendations and perspectives To avoid the environmental impact of storm water runoff more attention should be paid to the development and implementation
of storm water runoff pollution prevention measures. The study implies that future research concerning the relationships between
storm water runoff deposit characteristics and biological activities must be developed to evaluate the contamination potential
of stream sediment deposits for local aquatic ecosystems. Further studies should be developed to characterise the activities
of the microbial community of storm water runoff sediments, and to monitor bioremediation in situ. 相似文献
997.
Grape phylloxera (Dactulosphaira vitifoliae, FITCH) was a major pest in Vitis vinifera grape production in the late 19th and early 20th century in Europe. Roots of V. vinifera varieties are susceptible to D. vitifoliae attack whereas the leaves are not affected. The pest has been controlled by using American grapevine varieties as rootstocks. However, in recent years, grape producers have reported higher incidences of leaf galls induced by D. vitifoliae on V. vinifera leaves. Research on the occurrence of D. vitifoliae on grapevine leaves and roots has shown that D. vitifoliae is present in all wine-growing regions of Switzerland. In more than 80% of vineyards claiming to be infested, D. vitifoliae was found on leaves of varieties with interspecific crosses in their parentage. Three locations with leaf-galling individuals on V. vinifera were detected. D. vitifoliae individuals were found emerging from soil potentially associated with the commonly used rootstock varieties, which are assumed to be phylloxera tolerant. As climate change may necessitate the relocation of some viticultural areas to new wine-growing regions, there will be a greater need to control D. vitifoliae on leaves of interspecific crosses and the inspected planting material to limit further spread of the pest. 相似文献
998.
This paper attempts to contribute to the forestry valuation literature by providing a template for executing ex ante cost–benefit analyses of large-scale temperate plantation forestry programmes, taking the Irish Government's Forestry Plan as an example. An ex ante assessment of the social efficiency of the Plan is undertaken and, in doing so, a range of externalities is examined using, inter alia, contingent valuation and production function approaches. The appropriate magnitude of subvention of the Plan is also examined. The study demonstrates how large-scale forestry programmes and their external effects, both positive and negative, can be evaluated. In so doing, it provides insights into the methodological difficulties and solutions for assessing the social efficiency of large-scale environmental projects and the appropriate level of their subsidisation. 相似文献
999.
Forest compositional shifts in response to climate change are likely to be initially detectable in the understory tree regeneration layer near species range limits. Because many factors in addition to climate, such as seedbed and soil characteristics, overstory composition, and interactions with other understory biota, drive tree regeneration trends, a thorough understanding of the relative importance of all variables as well as their interrelationships is needed. The range limits of several widespread temperate and boreal tree species overlap in the upper Great Lakes region, USA, thus facilitating an observational study over relatively short regional climate gradients. We used redundancy analysis and variation partitioning to quantify the unique, shared, and total explanatory power of four sets of explanatory variables. The results showed that all four variable sets (climate 9.5 %, understory environment 13.7 %, overstory composition 26.3 %, and understory biota 13.8 %) were significantly associated with tree regeneration compositional variation in mixed temperate–boreal forests. Partitioning also revealed high confounded or shared explanatory power, but also that each set contributed significant unique explanatory power not shared with other sets. Spatial patterning in regeneration composition was strongly related to broad scale environmental patterns, while the large majority of unexplained variation did not have a detectable spatial structure, suggesting factors with local scale variability. Future forest shifts across the landscape will depend not only on the rate and direction of climate change but also on how the strengths and interrelationships among other explanatory variables, such as overstory composition and understory biota, shift with a changing climate. 相似文献
1000.
Solomon I. Shibairo Peter M. A. Toivonen 《The Journal of Horticultural Science and Biotechnology》2013,88(6):862-866
SummaryThe effect of potassium (K) nutrition on the shelf life of carrots (Daucus carota L., cv. Paramount) was studied using a hydroponic system involving rockwool slabs as an inert support. Carrots were grown for 192 d under greenhouse conditions and with 0, 0.1,1.0,10 and 15 mM K supplied in the nutrient medium. Increase in K concentration in the nutrient medium up to 1 mM decreased postharvest moisture loss. Carrot root weight and tissue K concentration increased, and water potential, osmotic potential and relative solute leakage decreased with increasing K concentration up to 1 mM. Concentrations greater than 1 mM had little or no additional effect on postharvest moisture loss, root water and osmotic potentials and relative solute leakage. Root weight did not increase above 10 mM K. The best subset model obtained by backward stepping and the optimum Mallow’s coefficient showed that carrot root weight and relative solute leakage accounted for most of the variation in moisture loss. Root weight correlated negatively and relative solute leakage positively to moisture loss. 相似文献