Publications
Found 378 publication(s)
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Bendix, J.; Fries, A.; Zarate, J.; Trachte, K.; Rollenbeck, R.; Pucha-Cofrep, F.; Paladines, R.; Palacios, I.; Orellana Alvear, J.; Oñate-Valdivieso, F.; Naranjo, C.; Mendoza, L.; Mejia, D.; Guallpa, M.; Gordillo, F.; Gonzalez-Jaramillo, V.; Dobbermann, M.; Celleri, R.; Carillo, C.; Araque, A. & Achilles, S. (2017): Radarnet Sur – first weather radar network in tropical high mountains. Bulletin of the American Meteorological Society 98(6), 1235-1254.
Oñate-Valdivieso, F.; Fries, A.; Mendoza, K.; Gonzalez-Jaramillo, V.; Pucha-Cofrep, F.; Rollenbeck, R. & Bendix, J. (2017): Temporal and spatial analysis of precipitation patterns in an Andean region of southern Ecuador using LAWR weather radar. Meteorol. Atmos. Phys. 2017, 1-12.
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DOI: 10.1007/s00703-017-0535-8
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Abstract:
Abstract:
This paper focuses on the analysis of precipita-
tion patterns, using a Local Area Weather Radar to collect
information about the precipitation distribution in an
Andean region of southern Ecuador (cities of Loja, Zamora
and Catamayo). 54 representative events were selected to
develop daily precipitation maps and to obtain their rele-
vant characteristics, which were related to the topography
and the season. The results showed that a strong correlation
between the areas covered by precipitation (RA coef?cient)
and the season exists. In general, humid air masses come
from the east (Amazon Basin), but during the main rainy
season (December to April), humidity also frequently
enters the study region from the west (Paci?c Ocean). The
rainy season is characterized by convective precipitation,
associated with higher evaporation rates during austral
summer. The relatively dry season is formed between May
and November, but considerable precipitation amounts are
registered, too, due to advective moisture transport from
the Amazon Basin, a result of the predominant tropical
easterlies carrying the humidity up the eastern escarpment
of the Andes, generally following the natural course of the
drainage systems.
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Keywords: |
South Ecuador |
rain |
Radar Meteorology |
Wallis, C.I.B.; Brehm, G.; Donoso, D.A.; Fiedler, K.; Homeier, J.; Paulsch, D.; Süßenbach, D.; Tiede, Y.; Brandl, R.; Farwig, N. & Bendix, J. (2017): Remote sensing improves prediction of tropical montane species diversity but performance differs among taxa. Ecological Indicators 1(1), 1-11.
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DOI: 10.1016/j.ecolind.2017.01.022
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Abstract:
Abstract:
Texture information from passive remote sensing images provides surrogates for habitat structure, which is relevant for modeling biodiversity across space and time and for developing effective ecological indicators. However, the applicability of this information might differ among taxa and diversity measures. We compared the ability of indicators developed from texture analysis of remotely sensed images to predict species richness and species turnover of six taxa (trees, pyraloid moths, geometrid moths, arctiinae moths, ants, and birds) in a megadiverse Andean mountain rainforest ecosystem. Partial least-squares regression models were fitted using 12 predictors that characterize the habitat and included three topographical metrics derived from a high-resolution digital elevation model and nine texture metrics derived from very high-resolution multi-spectral orthophotos. We calculated image textures derived from mean, correlation, and entropy statistics within a relatively broad moving window (102 m × 102 m) of the near infra-red band and two vegetation indices. The model performances of species richness were taxon dependent, with the lowest predictive power for arctiinae moths (4%) and the highest for ants (78%). Topographical metrics sufficiently modeled species richness of pyraloid moths and ants, while models for species richness of trees, geometrid moths, and birds benefited from texture metrics. When more complexity was added to the model such as additional texture statistics calculated from a smaller moving window (18 m × 18 m), the predictive power for trees and birds increased significantly from 12% to 22% and 13% to 27%, respectively. Gradients of species turnover, assessed by non-metric two-dimensional scaling (NMDS) of Bray-Curtis dissimilarities, allowed the construction of models with far higher predictability than species richness across all taxonomic groups, with predictability for the first response variable of species turnover ranging from 64% (birds) to 98% (trees) of the explained change in species composition, and predictability for the second response variable of species turnover ranging from 33% (trees) to 74% (pyraloid moths). The two NMDS axes effectively separated compositional change along the elevational gradient, explained by a combination of elevation and texture metrics, from more subtle, local changes in habitat structure surrogated by varying combinations of texture metrics. The application of indicators arising from texture analysis of remote sensing images differed among taxa and diversity measures. However, these habitat indicators improved predictions of species diversity measures of most taxa, and therefore, we highly recommend their use in biodiversity research.
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Keywords: |
Gray level co-occurrence matrix |
Birds |
Image Texture |
Partial least square regression |
Moths |
Orthophotos |
Species turnover |
Trees |
Tropical mountain forest |
Meyer, H.; Lehnert, L.; Wang, Y.; Reudenbach, C.; Nauss, T. & Bendix, J. (2017): From local spectral measurements to maps of vegetation cover and biomass on the Qinghai-Tibet-Plateau: Do we need hyperspectral information?. International Journal of Applied Earth Observation and Geoinformation 55, 21-31.
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DOI: 10.1016/j.jag.2016.10.001
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Abstract:
Abstract:
Though the relevance of pasture degradation on the Qinghai-Tibet Plateau (QTP) is widely postulated, its
extent is still unknown. Due to the enormous spatial extent, remote sensing provides the only possibility
to investigate pasture degradation via frequently used proxies such as vegetation cover and aboveground
biomass (AGB). However, unified remote sensing approaches are still lacking. This study tests the appli-
cability of hyper- and multispectral in situ measurements to map vegetation cover and AGB on regional
scales. Using machine learning techniques, it is tested whether the full hyperspectral information is
needed or if multispectral information is sufficient to accurately estimate pasture degradation prox-
ies. To regionalize pasture degradation proxies, the transferability of the locally derived ML-models to
high resolution multispectral satellite data is assessed. 1183 hyperspectral measurements and vegeta-
tion records were performed at 18 locations on the QTP. Random Forests models with recursive feature
selection were trained to estimate vegetation cover and AGB using narrow-band indices (NBI) as predic-
tors. Separate models were calculated using NBI from hyperspectral data as well as from the same data
resampled to WorldView-2, QuickBird and RapidEye channels. The hyperspectral results were compared
to the multispectral results. Finally, the models were applied to satellite data to map vegetation cover and
AGB on a regional scale. Vegetation cover was accurately predicted by Random Forest if hyperspectral
measurements were used (cross validated R2 = 0.89). In contrast, errors in AGB estimations were consid-
erably higher (cross validated R2 = 0.32). Only small differences in accuracy were observed between the
models based on hyperspectral compared to multispectral data. The application of the models to satellite
images generally resulted in an increase of the estimation error. Though this reflects the challenge of
applying in situ measurements to satellite data, the results still show a high potential to map pasture
degradation proxies on the QTP. Thus, this study presents robust methodology to remotely detect and
monitor pasture degradation at high spatial resolutions.
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Keywords: |
biomass |
Tibetan Plateau |
Pasture degradation |
Hyperspectral measurements |
Random forests |
Qinghai-Tibet Plateau |
Regionalization |
Vegetation cover |
Silva, B.; Alava Nunez, P.; Strobl, S.; Beck, E. & Bendix, J. (2017): Area-wide evapotranspiration monitoring at the crown level of a tropical mountain rain forest. Remote Sensing of Environment 194, 219–229.
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DOI: 10.1016/j.rse.2017.03.023
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Abstract:
Abstract:
Ecosystem water regulation couples energy and water balance, depends on the integrity of the ecosystem, and
responds to changes in climate. Changes in tree-water relationships in the biodiversity hotspot of the tropical
Andes in southern Ecuador might be potentially observed at the level of individual trees, thus providing an efficient
ecosystem monitoring method with applications in forest management and conservation at the tree and
landscape levels. In this study,we combine area-average measurements froma laser scintillometer above the forestwith
optical satellite data at high spatial resolution to obtain area-wide evapotranspiration data. The processing
of field data includes the calculation of energy storage in forest biomass and the partitioning of
evapotranspiration into transpiration and evaporation. Satellite-based estimates are calibrated by using tower
flux measurements and meteorological data within periods of humid and less-humid atmosphere. The annual
evapotranspiration was 1316 mm, of which 1086 mm per year corresponds to the forest transpiration at the
study site. Average values of 4.7 and 4.1 mm d?1 per tree crown are observed under humid and less-humid atmospheric
conditions, respectively, when applying high-resolution area-wide evapotranspiration in individual
crown analysis. Approximately 24% of the observed crowns show a positive monthly change in ET, and 51% of
the crowns show a significant change in the daily ET, which can be considered sensitive individuals concerning
water relationships. The limitations in the area-wide evapotranspiration at the crown level can be explained
by considering the spectral responses of the crown individuals. The presented method can be robustly deployed
in the ecological monitoring of mountain forests.
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Keywords: |
remote sensing |
evapotranspiration |
Schulz, M.; Li, C.; Thies, B.; Chang, S. & Bendix, J. (2017): Mapping the montane cloud forest of Taiwan using 12 year MODIS-derived ground fog frequency data. PLOS ONE 12(2), 1-17.
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DOI: 10.1371/journal.pone.0172663
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Abstract:
Abstract:
Up until now montane cloud forest (MCF) in Taiwan has only been mapped for selected areas of vegetation plots. This paper presents the first comprehensive map of MCF distribution for the entire island. For its creation, a Random Forest model was trained with vegetation plots from the National Vegetation Database of Taiwan that were classified as “MCF” or “non-MCF”. This model predicted the distribution of MCF from a raster data set of parameters derived from a digital elevation model (DEM), Landsat channels and texture measures derived from them as well as ground fog frequency data derived from the Moderate Resolution Imaging Spectroradiometer. While the DEM parameters and Landsat data predicted much of the cloud forest’s location, local deviations in the altitudinal distribution of MCF linked to the monsoonal influence as well as the Massenerhebung effect (causing MCF in atypically low altitudes) were only captured once fog frequency data was included. Therefore, our study suggests that ground fog data are most useful for accurately mapping MCF.
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Keywords: |
Taiwan |
cloud forest |
ground fog |
satellite climatology of fog |
fog remote sensing |
Mountain forest |
vegetation mapping |
vegetation plots |
fog studies |
Random forests |
Vegetation cover |
Obermeier, W.; Lehnert, L.; Kammann, C.; Müller, C.; Grünhage, L.; Luterbacher, J.; Erbs, M.; Moser, G.; Seibert, R.; Yuan, N. & Bendix, J. (2017): Reduced CO2 fertilization effect in temperate C3 grasslands under more extreme weather conditions. Nature Climate Change 7(2), 137-141.
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DOI: 10.1038/nclimate3191
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Abstract:
Abstract:
The increase in atmospheric greenhouse gas concentrations from anthropogenic activities is the major driver of recent global climate change1. The stimulation of plant photosynthesis due to rising atmospheric carbon dioxide concentrations ([CO2]) is widely assumed to increase the net primary productivity (NPP) of C3 plants—the CO2 fertilization effect (CFE). However, the magnitude and persistence of the CFE under future climates, including more frequent weather extremes, are controversial. Here we use data from 16 years of temperate grassland grown under ‘free-air carbon dioxide enrichment’ conditions to show that the CFE on above-ground biomass is strongest under local average environmental conditions. The observed CFE was reduced or disappeared under wetter, drier and/or hotter conditions when the forcing variable exceeded its intermediate regime. This is in contrast to predictions of an increased CO2 fertilization effect under drier and warmer conditions. Such extreme weather conditions are projected to occur more intensely and frequently under future climate scenarios. Consequently, current biogeochemical models might overestimate the future NPP sink capacity of temperate C3 grasslands and hence underestimate future atmospheric [CO2] increase.
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Keywords: |
biomass |
climate change |
Climate-change impacts |
CO2 fertilization |
Grassland ecology |
Ecophysiology |
Schulz, M. (2017): Delineating the montane cloud forest of Taiwan LCRS, phd thesis
Andersen, H. (2017): A quantitative, satellite-based analysis of aerosol effects on liquid-water clouds Ruhr-Universität Bochum, phd thesis
Egli, S.; Thies, B.; Drönner, J.; Cermak, J. & Bendix, J. (2016): A 10 year fog and low stratus climatology for Europe based on Meteosat Second Generation data. Quarterly Journal of the Royal Meteorological Society 143(702), 530-541.
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DOI: 10.1002/qj.2941
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Abstract:
Abstract:
Due to the significant impact of fog and low stratus (FLS) on economy, ecology and traffic systems, there is a growing demand for high-resolution information on FLS occurrence. In this study, a baseline climatology of FLS h day?1 based on data recorded from 2006–2015 by the Spinning Enhanced Visible and Infrared Imager system (SEVIRI) aboard the Meteosat Second Generation satellites is computed for Europe to provide the requested information. It is the first 10 year, spatially explicit climatology for FLS based on data with a temporal resolution of 15 min. The dataset is validated against Meteorological Aviation Routine Weather Reports (METAR) and shows good accordance with an average Heidke Skill Score of 0.45. Temporal and spatial variations in FLS frequency as well as interannual trends are analyzed. Winter shows the highest FLS occurrence, but a general decrease over the investigated period. Spring, summer and autumn show less pronounced trends and lower average FLS frequencies. Possible reasons for these distributions are discussed.
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Keywords: |
remote sensing |
Meteosat Second Generation |
climatology |
fog and low stratus detection |
Obermeier, W.; Lehnert, L.; Kammann, C.; Müller, C.; Grünhage, L.; Luterbacher, J.; Erbs, M.; Moser, G.; Seibert, R.; Yuan, N. & Bendix, J. (2016-09-26). Extreme weather conditions reduce the CO2 fertilization in temperate C3 grasslands. Presented at FACEing the future, Giessen.
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Abstract:
Abstract:
The increase of atmospheric greenhouse gas concentrations resulting from anthropogenic activities is the major driver of global climate change. A net sink effect caused by stimulated plant photosynthesis through rising atmospheric carbon dioxide concentrations ([CO2]) and, consequently, an increased net primary productivity (NPP) of C3 plants (termed the CO2 fertilization effect, CFE) is widely assumed. However, knowledge about the magnitude and persistence of the CFE under future climates including more frequent weather extremes is still lacking. Therefore, we have investigated the CFE in dependence to its accompanying environmental conditions in the long-term time series (16 years) of a temperate grassland grown under “Free Air Carbon dioxide Enrichment” in Gießen, the GiFACE. Our results reveal that the CFE is strongest under local average environmental conditions and reduced or disappeared under wetter, drier and/or hotter conditions. This is in contrast to predictions of an increased CO2 fertilization under drier and warmer conditions. The results are of utmost importance because respective weather and climate conditions are projected in climate scenarios. Consequently, the state-of-art biogeochemical models might overestimate the future NPP sink capacity of temperate C3 grasslands. Since temperate grasslands represent an important portion of the Earth’s terrestrial surface, and therefore the global carbon cycle, atmospheric [CO2] might increase faster than currently expected.
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Keywords: |
climate change |
CO2 fertilization |
global change experiment |
Free Air CO2 Enrichment ( FACE ) |
Grassland ecology |
Gonzalez, V.; Fries, A.; Rollenbeck, R.; Paladines, J.; Oñate-Valdivieso, F. & Bendix, J. (2016): Assessment of deforestation during the last decades in Ecuador using NOAA-AVHRR satellite data. Erdkunde 70(3), 217-235.
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DOI: 10.3112/erdkunde.2016.03.02
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Abstract:
Abstract:
Human activities during the last decades provoked a notable reduction in global forest cover. Knowing that
forest stands act as stock and sinks for carbon and other greenhouse gases, it is important to determine the existing forest
cover at country level and to calculate annual deforestation rates. This work uses NOAA satellite images in a resolution of
1 km x 1 km to classify the surface of continental Ecuador in “forest” – “non-forest” pixels and to estimate the annual
deforestation rate from 1986 to 2001 as well as from 2001 to 2008. The method is based on a decision tree algorithm that
includes different spectral bands of the NOAA-AVHRR sensor and additional topographic and meteorological parameters.
The results show that the total forest cover of continental Ecuador was reduced from 48.1 % in 1986 to 36.8 % in 2008. The
calculated annual deforestation rates indicate that forest reduction increased during the last decade. The most affected area
is the Coastal Lowland, due to the enhanced population pressure, followed by the Amazon Basin, not only caused by the
governmental supported oil and mining industry, but also due to the uncontrolled timber extraction. The Andean Highland
has been less affected, because the major parts of this region were deforested before, during the Pre-Columbian-Era.
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Keywords: |
Ecuador |
NOAA-AVHRR |
deforestation |
Makowski Giannoni, S.; Trachte, K.; Rollenbeck, R.; Lehnert, L.; Fuchs, J. & Bendix, J. (2016): Atmospheric salt deposition in a tropical mountain rainforest at the eastern Andean slopes of south Ecuador – Pacific or Atlantic origin?. Atmospheric chemistry and physics 16, 10241-10261.
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DOI: 10.5194/acp-16-10241-2016
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Abstract:
Abstract:
Sea salt (NaCl) has recently been proven to be of the utmost importance for ecosystem functioning in Amazon lowland forests because of its impact on herbivory, litter decomposition and, thus, carbon cycling. Sea salt deposition should generally decline as distance from its marine source increases. For the Amazon, a negative east–west gradient of sea salt availability is assumed as a consequence of the barrier effect of the Andes Mountains for Pacific air masses. However, this generalized pattern may not hold for the tropical mountain rainforest in the Andes of southern Ecuador. To analyse sea salt availability, we investigated the deposition of sodium (Na+) and chloride (Cl?), which are good proxies of sea spray aerosol. Because of the complexity of the terrain and related cloud and rain formation processes, sea salt deposition was analysed from both, rain and occult precipitation (OP) along an altitudinal gradient over a period between 2004 and 2009. To assess the influence of easterly and westerly air masses on the deposition of sodium and chloride over southern Ecuador, sea salt aerosol concentration data from the Monitoring Atmospheric Composition and Climate (MACC) reanalysis data set and back-trajectory statistical methods were combined. Our results, based on deposition time series, show a clear difference in the temporal variation of sodium and chloride concentration and Na+???Cl? ratio in relation to height and exposure to winds. At higher elevations, sodium and chloride present a higher seasonality and the Na+???Cl? ratio is closer to that of sea salt. Medium- to long-range sea salt transport exhibited a similar seasonality, which shows the link between our measurements at high elevations and the sea salt synoptic transport. Although the influence of the easterlies was predominant regarding the atmospheric circulation, the statistical analysis of trajectories and hybrid receptor models revealed a stronger impact of the north equatorial Atlantic, Caribbean, and Pacific sea salt sources on the atmospheric sea salt concentration in southern Ecuador. The highest concentration in rain and cloud water was found between September and February when air masses originated from the north equatorial Atlantic, the Caribbean Sea and the equatorial Pacific. Together, these sources accounted for around 82.4?% of the sea salt budget over southern Ecuador.
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Keywords: |
atmospheric deposition |
rain |
sodium |
chloride |
occult precipitation |
nutrient transport |
Back trajectories |
Regeling, B.; Thies, B.; Gerstner, A.O.; Westermann, S.; Müller, N.A.; Bendix, J. & Laffers, W. (2016): Hyperspectral Imaging Using Flexible Endoscopy for. Sensors 16, 1-14.
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DOI: 10.3390/s16081288
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Abstract:
Abstract:
Hyperspectral imaging (HSI) is increasingly gaining acceptance in the medical field.
Up until now, HSI has been used in conjunction with rigid endoscopy to detect cancer in vivo.
The logical next step is to pair HSI with flexible endoscopy, since it improves access to hard-to-reach
areas. While the flexible endoscope’s fiber optic cables provide the advantage of flexibility, they
also introduce an interfering honeycomb-like pattern onto images. Due to the substantial impact
this pattern has on locating cancerous tissue, it must be removed before the HS data can be further
processed. Thereby, the loss of information is to minimize avoiding the suppression of small-area
variations of pixel values. We have developed a system that uses flexible endoscopy to record HS
cubes of the larynx and designed a special filtering technique to remove the honeycomb-like pattern
with minimal loss of information. We have confirmed its feasibility by comparing it to conventional
filtering techniques using an objective metric and by applying unsupervised and supervised
classifications to raw and pre-processed HS cubes. Compared to conventional techniques, our
method successfully removes the honeycomb-like pattern and considerably improves classification
performance, while preserving image details.
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Keywords: |
hyperspectral |
oropharyngeal cancer |
Lehnert, L.; Achilles, S.; Schmidt, J.; Büdel, B.; Osses, P.; Thies, B. & Bendix, J., Fog research in the southern Atacama: Measurement setup and first results of the new EarthShape project(2016).
Knoke, T.; Paul, C.; Hildebrandt, P.; Calvas, B.; Castro, L.M.; Härtl, F.; Döllerer, M.; Hamer, U.; Windhorst, D.; Wiersma, Y.F.; Curatola Fernández, G.F.; Obermeier, W.; Adams, J.; Breuer, L.; Mosandl, R.; Beck, E.; Weber, M.; Stimm, B.; Haber, W.; Fürst, C. & Bendix, J. (2016): Compositional diversity of rehabilitated tropical lands supports multiple ecosystem services and buffers uncertainties. Nature Communications 7, 11877.
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DOI: 10.1038/ncomms11877
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Abstract:
Abstract:
High landscape diversity is assumed to increase the number and level of ecosystem services.
However, the interactions between ecosystem service provision, disturbance and landscape
composition are poorly understood. Here we present a novel approach to include uncertainty
in the optimization of land allocation for improving the provision of multiple ecosystem
services. We refer to the rehabilitation of abandoned agricultural lands in Ecuador including
two types of both afforestation and pasture rehabilitation, together with a succession option.
Our results show that high compositional landscape diversity supports multiple ecosystem services (multifunction effect). This implicitly provides a buffer against uncertainty. Our work shows that active integration of uncertainty is only important when optimizing single or highly correlated ecosystem services and that the multifunction effect on landscape diversity is stronger than the uncertainty effect. This is an important insight to support a land-use planning based on ecosystem services.
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Keywords: |
Ecuador |
Community composition |
abandoned pastures |
Ecosystem Services |
compositional diversity |
Uncertainities |
rehabilitation |
Obermeier, W.; Lehnert, L.; Kammann, C.; Müller, C.; Grünhage, L.; Luterbacher, J.; Erbs, M.; Yuan, N. & Bendix, J. (2016-04-18). Extreme weather conditions reduce the CO2 fertilization effect in temperate C3 grasslands. Presented at EGU, Vienna.
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Abstract:
Abstract:
The increase in atmospheric greenhouse gas concentrations from anthropogenic activities is the major driver of global climate change. The rising atmospheric carbon dioxide (CO2 ) concentrations may stimulate plant photosynthesis and, thus, cause a net sink effect in the global carbon cycle. As a consequence of an enhanced photosynthesis, an increase in the net primary productivity (NPP) of C3 plants (termed CO2 fertilization) is widely assumed. This process is associated with a reduced stomatal conductance of leaves as the carbon demand of photosynthesis is met earlier. This causes a higher water-use efficiency and, hence, may reduce water stress in plants exposed to elevated CO2 concentrations ([eCO2 ]). However, the magnitude and persistence of the CO2 fertilization effect under a future climate including more frequent weather extremes are controversial. To test the CO2 fertilization effect for Central European grasslands, a data set comprising 16 years of biomass samples and environmental variables such as local weather and soil conditions was analysed by means of a novel approach. The data set was recorded on a “Free Air Carbon dioxide Enrichment” (FACE) experimental site which allows to quantify the CO2 fertilization effect under naturally occurring climate variations. The results indicate that the CO2 fertilization effect on the aboveground biomass is strongest under local average environmental conditions. Such intermediate regimes were defined by the mean +/- 1 standard deviation of the long-term average in the respective variable three months before harvest. The observed CO2 fertilization effect was reduced or vanished under drier, wetter and hotter conditions when the respective variable exceeded the bounds of the intermediate regimes. Comparable conditions, characterized by a higher frequency of more extreme weather conditions, are predicted for the future by climate projections. Consequently, biogeochemical models may overestimate the future NPP sink capacity of temperate C3 grasslands. Because temperate grasslands represent an important part of the Earth’s terrestrial surface and therefore the global carbon cycle, atmospheric CO2 concentrations [CO2 ] might increase faster than currently expected.
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Keywords: |
CO2 fertilization |
global change experiment |
temperate grassland |
Free Air CO2 Enrichment ( FACE ) |
Lehnert, L.; Wesche, K.; Trachte, K.; Reudenbach, C. & Bendix, J. (2016): Climate variability rather than overstocking causes recent large scale cover changes of Tibetan pastures. Scientific Reports 6, 24367.
Seidel, J.; Ketzler, G.; Bechtel, B.; Thies, B.; Philipp, A.; Böhner, J.; Egli, S.; Eisele, M.; Herma, F.; Langkamp, T.; Petersen, E.; Sachsen, T.; Schlabing, D. & Schneider, C. (2016): Mobile measurement techniques for local and micro-scale studies in urban and topo-climatology. Die Erde 147(1), 259-284.
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DOI: 10.12854/erde-147-2
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Abstract:
Abstract:
Technical development during the last two decades has brought new potential and new applications for
mobile
measurements. In this paper, we present six case studies where mobile measurement devices were
used to acquire data for meteorological and climatological research. Three case studies deal with groundbased
mobile measurements – on buses for urban climate measurements and on a vessel on a lake – and three
with airborne platforms – on a cable car and on an unmanned aerial vehicle for vertical soundings and on a
tethered balloon sonde for cloud physics. For each study, we describe the measurement set-up and address
the potential and drawbacks of these applications. At the end, we discuss general aspects related to mobile
observations especially concerning the time and space dimension of measurements.
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Keywords: |
Mobile measurements |
micro- scale |
atmospheric sounding |
urban climatology |
planetary boundary layer |
Schulz, M.; Thies, B.; Chang, S. & Bendix, J. (2016): Detection of ground fog in mountainous areas from MODIS (Collection 051) daytime data using a statistical approach. Atmospheric Measurement Techniques 9, 1135 - 1152.
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DOI: 10.5194/amt-9-1135-2016
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Abstract:
Abstract:
The mountain cloud forest of Taiwan can be delimited
from other forest types using a map of the ground
fog frequency. In order to create such a frequency map from
remotely sensed data, an algorithm able to detect ground fog
is necessary. Common techniques for ground fog detection
based on weather satellite data cannot be applied to fog occurrences
in Taiwan as they rely on several assumptions regarding
cloud properties. Therefore a new statistical method
for the detection of ground fog in mountainous terrain from
MODIS Collection 051 data is presented. Due to the sharpening
of input data using MODIS bands 1 and 2, the method
provides fog masks in a resolution of 250 m per pixel. The
new technique is based on negative correlations between optical
thickness and terrain height that can be observed if
a cloud that is relatively plane-parallel is truncated by the
terrain. A validation of the new technique using camera data
has shown that the quality of fog detection is comparable to
that of another modern fog detection scheme developed and
validated for the temperate zones. The method is particularly
applicable to optically thinner water clouds. Beyond a cloud
optical thickness of ? 40, classification errors significantly
increase.
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Keywords: |
Fog detection |
Taiwan |
fog |
ground fog |
ground fog detection |
fog remote sensing |