The Experts below are selected from a list of 327 Experts worldwide ranked by ideXlab platform
Edith Bermadingerstabentheiner - One of the best experts on this subject based on the ideXlab platform.
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physical injury re crystallization of wax tubes and artefacts identifying some causes of structural alteration to spruce needle wax
New Phytologist, 1995Co-Authors: Edith BermadingerstabentheinerAbstract:summary The study presents investigations of epicuticular wax morphology on spruce needles (Picea abies (L.) Karst.) performed by ambient temperature scanning electron microscopy. To use alterations to epicuticular wax morphology as a successful tool in Forest Damage research, it is necessary to distinguish environmental influences and artefacts from common pollution effects, The present paper summarizes observations of alterations to epicuticular waxes independent of pollution effects, recorded in various field studies. These observations are supplemented by controlled experiments to investigate wax alterations owing to solvents and mechanical injury. Fissures in the antechamber wax were the result of needle shrinkage during drying. Wax alterations, where only the antechamber wax was affected by a continuous loss of the structural integrity of wax tubes, were classified as storage artefacts since they occurred exclusively on needles stored in air-tight glass vials and were unrelated to needle age, sampling site or pollution influence. Such wax alterations were never observed in needles stored in air-permeable paper bags. Mechanical injury also resulted in severe morphological alterations to epicuticular wax structures. The wax tubes on the surface as well as in the antechamber were squashed and flattened. On smoothed and squashed wax layers a significant regrowth of wax tubes was occasionally observed, unrelated to needle age. Though the tubular form of the re-crystallized waxes was similar to those originally present on the surface, the tube diameters were much wider. Since redeveloped wax tubes also occurred on dead needles which had been artificially injured, this process could be classified as re-crystallization analogous to wax re-crystallization out of solvent extracts. The re-crystallization took place within 48 h after the mechanical injury occurred. The implications of the reported wax alterations for a successful use of epicuticular wax morphology as a bioindicator are discussed.
Sam Ekstrand - One of the best experts on this subject based on the ideXlab platform.
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landsat tm based Forest Damage assessment correction for topographic effects
Photogrammetric Engineering and Remote Sensing, 1996Co-Authors: Sam EkstrandAbstract:Detection of Forest Damage is one of the various remote sensing applications complicated by topographic effects. Different vegetation types are known to respond differently to slope and illumination effects. This paper describes the response of Landsat Thematic Mapper data to the topography in Norway spruce Forest, and the possibility to assess Forest Damage in rugged temn. The effect at the examined medium and low solar elevations was non-Lambertian. Minnaert corrections and other empirical functions proposed for different cover types were found to be inadequate. Two new models were developed; one based on Minnaert constants changing with the cosine of the incidence angle, and the other based on an empirical relationship. Both models gave satisfactory results although the empirical model pe$ormed better for nearly shadowed northern slopes. With a model accounting for terrain and canopy inhomogeneity effects using digitized stand data and digital elevation models, healthy to slightly defoliated spruce Forest could be separated from moderately defoliated Forest. The method enables an improvement of the earlier documented Landsat TM capability to detect severely Damaged Forest.
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assessment of Forest Damage with landsat tm correction for varying Forest stand characteristics
Remote Sensing of Environment, 1994Co-Authors: Sam EkstrandAbstract:Abstract The utility of satellite data in Forest decline assessment is influenced by effects associated with variations in stand characteristics such as species composition, age, and density. In this study, the spectral effects of stand variations were determined for Forest dominated by Norway spruce. The usefulness of digitized stand data for potentially reducing these effects were investigated. It is suggested that a Damage estimation algorithm based solely on Landsat TM Band 4 is more appropriate than earlier proposed ratio algorithms in areas with moderate defoliation symptoms but no chlorosis. The two factors with the strongest negative effect on the defoliation assessment were varying hardwood and pine component. A hardwood component of 20% completely neutralized a defoliation of 20%. Age had a clear spectral effect up to 70 years, but above that the response was stable. There was no confusion between defoliation classes in stands with moderate to high density. A spruce defoliation model that used stand data from digitized Forest maps to modify the intensity values of TM Band 4 prior to estimation of defoliation was developed. The resulting assessment of moderate defoliation in Forest areas on level ground was of adequate accuracy when the spruce component was larger than 75%.
Lars Eklundh - One of the best experts on this subject based on the ideXlab platform.
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a new invasive insect in sweden physokermes inopinatus tracing Forest Damage with satellite based remote sensing
Forest Ecology and Management, 2012Co-Authors: Perola Olsson, Anna Maria Jonsson, Lars EklundhAbstract:Forests are important from many perspectives. Forestry delivers products such as timber, fiber and fuel; Forests are also important for recreational activities as well as for the global carbon balance. Consequently, it is important to develop methods that enable efficient monitoring of disturbances, such as insect attacks, over vast Forested areas. These methods can be based on remote sensing, since satellites provide images with frequent spatial coverage. Insect attacks can be detected in these satellite data if the resulting defoliation or discolouration is sufficiently severe. Satellite data also facilitates monitoring of migration patterns of invasive insects since some sensors provide time series that enables tracing of insect attacks back in time. In this study, SPOT and MODIS data were utilized to map Damage in Norway spruce (Picea abies) caused by Physokermes inopinatus, and the associated black encrustation formed by sooty mold during an attack occurring 2010 in Scania, the southernmost province of Sweden. This attack is the first known presence of P. inopinatus in Sweden. The study shows that Damage can be detected with high accuracy in satellite data. In SPOT-data, 78% of the Damage was detected with an overestimation of 46%. The larger Damaged areas could be detected with MODIS 16-days composite NDVI-product with 250 m resolution. In addition, the study indicates that there was Damage already in 2009, the year before any Damage was detected in field. Prior to 2009 no Damage was detected, suggesting that this was the first year of the outbreak. This study documents the outbreak of P. inopinatus in S. Sweden and highlights the potential for remote sensing for monitoring and early detection of Damage of this invasive insect. (C) 2012 Elsevier B.V. All rights reserved. (Less)
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mapping insect defoliation in scots pine with modis time series data
Remote Sensing of Environment, 2009Co-Authors: Lars Eklundh, Thomas Johansson, Svein SolbergAbstract:Insect Damage is a general problem that disturbs the growth of Forests, causing economic losses and affecting carbon sequestration. Coarse-resolution data from satellites are potentially useful for national and regional mapping of Forest Damage, but the accuracy of these methods has not been fully examined. In this study, a method was tested for the mapping of defoliation in Scots pine [Pinus silvestris] Forests in southeast Norway caused by the pine sawfly [Neodiprion sertifer], with the use of multi-temporal MODIS 16-day composite vegetation index data and the TIMESAT processing method. The Damage mapping method used differences in summer mean values and angles of the seasonal profiles, indicating decreasing foliage density, to identify pixels that represent areas containing Forest Damage. In addition to 16-day NDVI the Wide Dynamic Range Vegetation Index (WDRVI) was tested. Damage areas were identified by classifying data into pixels representing Damaged versus unDamaged Forest areas using a boolean combination of thresholded parameters. Classification results were evaluated against the change in LAI estimated from airplane LIDAR measurements, as an indicator of defoliation. The Damage classifications detected 71% to 82% of the pixels with Damage, and had kappa coefficients varying between 0.48 and 0.63, indicating some overestimation. This was due e.g. to failure to include clear-cut areas in the evaluation data. Damage classification with WDRVI only resulted in slight improvement compared to the NDVI. Only weak relationships were found between the LIDAR-estimated defoliation and the change parameters obtained from MODIS. Consequently, mapping of the degree of defoliation from MODIS was abandoned. In conclusion, the Damage detection method based on MODIS data was found to be useful for locating insect Damage, but not for estimating its intensity. Control of the detected Damage areas using high-resolution remote sensing data, aerial survey, or fieldwork is recommended for accurate delineation in operational applications.
Matthias Dobbertin - One of the best experts on this subject based on the ideXlab platform.
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wind speed measurements and Forest Damage in canton zurich central europe from 1891 to winter 2007
International Journal of Climatology, 2010Co-Authors: Tilo Usbeck, Thomas Wohlgemuth, Christian Pfister, Richard Volz, Martin Beniston, Matthias DobbertinAbstract:The most severe Damage to Forests in central Europe occurs during winter storms that are caused by Northern Hemispheric mid-latitude cyclones. These winter storms have caused several catastrophic windthrows during the past four decades. Amounts of Forest storm Damage are believed to be a function of both the size of the Forest and the storm intensity. To test this hypothesis, the Zurich region (city and canton) was chosen because long-term climate observation data is available for the region. The relationships between Forest attributes, wind speed and Forest Damage were explored by comparing data on Forests and wind speed from 107 winters with Forest Damage. Storm Damage was defined as the proportion of Damaged Forests with respect to the growing stock. The variables: daily wind run (91 years), daily maximum hourly average wind speed (107 years) and peak gust wind speed (74 years) were homogenized with respect to high wind speed and related to levels of Forest Damage. High maximum wind speed at the end of the 19th century and at the beginning of the 20th century was followed by low maximum wind speed in the 1940s, 1960s and 1970s. Since then, maximum values have increased. Gusts (extremes of the maximum wind speed) increased from the beginning of the recordings in 1933 and peaked in the early 1990s. Forest Damage due to winter storms is best correlated with peak wind speed. Gusts exceeding 40 m/s and resulting in catastrophic windthrow have increased in recent winters.
John L Koprowski - One of the best experts on this subject based on the ideXlab platform.
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nowhere to run and nowhere to hide response of endemic mt graham red squirrels to catastrophic Forest Damage
Biological Conservation, 2005Co-Authors: John L Koprowski, Marit I Alanen, Ann M LynchAbstract:A consequence of isolation is increased susceptibility to catastrophe. Insect Damage to fragmented and isolated Forests has the potential to serve as a catastrophic force; such Damage has increased worldwide due to climate change and fire suppression policies. We examined the response of endangered endemic Mt. Graham red squirrels to catastrophic insect Damage due to moths, beetles, and introduced aphids. Insects changed the Forest environment significantly for the endemic squirrel by reducing basal area and stem densities of live stems, while increasing number and basal area of standing dead stems. Availability of two major foods, fungi and tree seeds, declined in insect-Damaged Forests relative to trends in unDamaged Forests. Numbers of Mt. Graham red squirrels declined precipitously in insect-Damaged Forests suggesting a catastrophe. Conservation options are limited in such situations. Forest-insect induced catastrophes are likely to become more common in the near future as Forest health declines due to past management tactics and climate change. Prudent conservation measures include the anticipation of insect outbreaks and effective Forest treatments to decrease likelihood of such catastrophes to species of precarious conservation status, while avoiding abrupt changes to critical habitat.
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the response of tree squirrels to fragmentation a review and synthesis
Animal Conservation, 2005Co-Authors: John L KoprowskiAbstract:Habitat fragmentation is often considered a major threat to biodiversity; however, our understanding of how fragmentation impacts populations is poor. Identifying appropriate models for such studies is difficult. Tree squirrels are dependent on mature Forests for food, cover and nests; these are habitats that are being fragmented rapidly and that are easily defined by humans. Squirrels represent excellent models for study of fragmentation. The literature on tree squirrels was reviewed to glean data on density and home-range size in Forest fragments. Sufficient data were available on four species (Sciurus carolinensis, S. niger, S. vulgaris, Tamiasciurus hudsonicus). Density was negatively related to fragment size for S. carolinensis and S. niger and marginally so for T. hudsonicus. Sciurus vulgaris did not exhibit this relationship. Home-range size was analysed for three species of Sciurus and was positively related to Forest fragment size for S. carolinensis and S. niger. Again, only S. vulgaris did not to show this relationship. Sciurus vulgaris is rarely found in small Forest fragments and is believed to be especially sensitive to fragmentation; other tree squirrels appear to be sensitive to fragmentation in more subtle ways. Home range compaction provides a mechanism by which densities may increase in small fragments. The demographic consequences resultant from the high densities of squirrels found in small woodlots are not known but may explain the Forest Damage, avian nest predation and reduced diversity often cited to occur in woodland fragments.