摘要:

HOLMES, M. G., 1992.Monitoring vegetation in the future: radar.The use of radar for remote sensing of the biosphere has several advantages over conventional methods using the visible and infra‐red wavebands. These advantages include independence from solar energy, an all‐weather capability, and the ability to select an appropriate wavelength to study either the surface layers of vegetation or to penetrate deeper into the canopy to study the properties of undergrowth or the soil substrate. Despite these advantages, radar remote sensing is still in the developmental stage. The mode of operation of the radar instrument, and the physical laws governing the propagation of microwaves in scattering media, introduce some unique aspects for remote sensing of the biosphere.Increased interest in radar has arisen primarily from the need to make multi‐temporal studies of vegetation in areas which are susceptible to cloud cover, such as temperate and equatorial regions. Radar penetrates all but the densest cloud, and therefore overcomes this problem. At the same time, however, many of these wavelengths also penetrate deeply into the crop. As a result, analysis of the principles controlling the interaction of radar wavelengths with vegetation and soil are complex. These principles are discussed in terms of current microwave backscatter models.Vegetation and soil factors influencing radar backscatter are discussed, and the significance of instrument characteristics such as frequency, polarization and incidence angle are considered. The advantages and disadvantages of radar are reviewed, and particular reference is made to the potential of combining optical and radar st

ISSN:0024-4074    

DOI:10.1111/j.1095-8339.1992.tb01634.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

GRITTEN, R. H., 1992.Acid deposition in Snowdonia, North Wales.It has come as something of a surprise that the Snowdonia National Park, one of the least polluted areas in Europe, is suffering from the effects of acid deposition. A high annual rainfall and a hard geology combine to make the area vulnerable to wind‐blown pollutants. The most sensitive ecosystems in the area are lakes and rivers which, showing signs of acid stress, are suffering diminishing salmonid and macroinvertebrate faunas. Upland populations of dippers also appear to be at risk and there is much evidence to show that coniferous afforestation is exacerbating the problems of acidification. There are indications that both broadleaved and coniferous trees are being damaged by acid deposition and certain upland plant communities are at risk. The possible effects on human health are also very worrying. It is the job of the National Park Authority to preserve the landscape of Snowdonia. How do we protect it from acid depositio

ISSN:0024-4074    

DOI:10.1111/j.1095-8339.1992.tb01635.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

ISSN:0024-4074    

DOI:10.1111/j.1095-8339.1992.tb01636.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

PULFORD, I. D., MURPHY, K. J., DICKINSON, G., BRIGGS, J. A.&SPRINGUEL, I., 1992.Ecological resources for conservation and development in Wadi Allaqi, Egypt.The creation of Lake Nasser behind the Aswan High Dam on the River Nile has brought about significant environmental changes in Upper Egypt. A multidisciplinary project was started in 1987 to assess the environmental changes associated with periodic inundation in desert ecosystems. The data presented here provide a baseline for studies aimed at assessing the potential for, and ecological impacts of, sustainable development in the target area, and may act as a blueprint for wider‐scale development. Soil, water, vegetation, animal and human resources are being monitored. There has been a major increase in plant communities dominated by riverain species, at the expense of the original desert wadi vegetation. The water has attracted human settlement, with some 200–250 people now living in the wadi. The inherent high fertility of the soil has allowed them to grow a range of crops in small plots, using a system of shifting cultivation dictated by the lake water level. While this degree of development may be sustainable, larger‐scale development of the fragile wadi ecosystem demands a full assessment of appropriate management techn

ISSN:0024-4074    

DOI:10.1111/j.1095-8339.1992.tb01637.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

SHAHZAD, S., COE, R.&DICK, M. W., 1992.Biometry of oospores and oogonia ofPythium(Oomycetes): the independent taxonomic value of calculated ratios.The oogonia and oospores of 80 isolates, representing 40 species ofPythium, were examined to determine the taxonomic values of direct measurements and derived indices. It was demonstrated that 20 individual oogonia from an isolate provided a suitable data base, with acceptable levels for standard errors of the means. All four measurable and all three calculable variables showed continuous variation between isolates and species, so that no single criterion was able to effect taxonomic separation. The inadequacy of the traditional plerotic/aplerotic concept was revealed. Derived indices were shown to have a significant taxonomic value in addition to the measured parameters from which they were derived. When taken together, using canonical variate analysis, the variables enabled isolates to be grouped into their respective species without recourse to other taxonomic features. The enhanced precision of the assessment of oogonial characteristics has enabled a new approach toPythiumclassification to be developed.

ISSN:0024-4074    

DOI:10.1111/j.1095-8339.1992.tb01638.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

JARVIE, J. K.&BARKWORTH, M. E., 1992.Morphological variation and genome constitution in some perennial Triticeae.A numerical analysis of species of five genomically defined genera of the Triticeae was undertaken, based on 42 morphological characters and 142 operational taxonomic units (OTUs). The primary goal was to determine the degree of congruence between morphological variation and genomic constitution. The second goal was to determine which existing supraspecific classification, if any, best reflected the morphological variation encountered. The five genera investigated wereThinopyrum(J genome),Lophopyrum(E genome),Pseudoroegneria(S genome),Trichopyrum(EES genome) andElytrigia(SJE/SSX genome). Both principal co‐ordinate and cluster analysis of the data placed the OTUs in supraspecific groups that reflected their genomic constitution. Monogenomic taxa were clearly separated. Allotetraploids between the E and S genomes were situated between E and S monogenomic taxa. Allotetraploids between the J and E genomes were situated closest to J genome taxa. The EES taxa ofTrichopyrumwere placed closest toLophopyrum.OTUsof Elytrigiaoverlapped thoseof Pseudoroegneria, but not thoseof LophopyrumorThinopyru

ISSN:0024-4074    

DOI:10.1111/j.1095-8339.1992.tb01639.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

FISHER, J. B.&EWERS, F. W., 1992.Xylem pathways in liana stems with variant secondary growth.The three‐dimensional construction of stem xylem in tropical lianas (woody vines) was studied using several approaches: 1. observations of the xylem surface in stems with bark removed after NaOH treatment or natural retting; 2. reconstructions from serial transverse sections; 3. movement of dye solutions up isolated xylem sectors in intact plants, and 4. flow of dye solutions down branches and xylem sectors in isolated stem segments. Long distance (up to several metres) xylem pathways in unbranched stems and connections between lateral branches and main stems are described for !5 species in eight families which represented seven differnt patterns of secondary growth. The xylem in even the most complex stems is integrated by three‐dimensional interconnections of xylem regions which may appear isolated in transverse section. Interconnections are most common at leaf and branch nodes. Some old stems have peripheral xylem that remains isolated over long distances in unbranched stems, but even these had structural and physiological interconnections between xylem regions at branch no

ISSN:0024-4074    

DOI:10.1111/j.1095-8339.1992.tb01640.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY