Cette étude porte sur un gisement de seize troncs subfossiles identifiés au sein d’un tronçon de la moyenne vallée du Cher (Région Centre‑Val de Loire, France) dont la géométrie et l’âge des ...formations sédimentaires sont par ailleurs bien connus. Ainsi, en dépit des difficultés posées par les troncs subfossiles en tant qu’objets d’étude, cet article examine les possibilités de reconstitutions des dynamiques fluviales holocènes à partir de ce gisement et interroge les événements hydrologiques dont il peut être la signature. En mettant en perspective l’âge des bois subfossiles (4 individus datés par le radiocarbone) avec celui des sédiments dans lesquels ils sont inclus (7 datations OSL et 1 datation par le radiocarbone) et en nous intéressant à l’orientation des troncs et aux contextes de sédimentation, il apparait que : (1) Les âges des 4 troncs subfossiles datés sont compris entre 8330‑8040 cal BP et 3391‑3235 cal BP, attestant des processus de remaniement et de réenfouissement partiels des macro‑débris ligneux qui composent ce gisement. Le décalage temporel, parfois de plusieurs millénaires, entre l’âge des bois subfossiles et celui des encaissants sédimentaires a permis d’identifier deux hiatus érosifs mis en relation avec le méandrage actif qui caractérise ce cours d’eau durant la seconde moitié de l’Holocène. (2) Les troncs subfossiles ont été observés au sein de deux grands paléochenaux, des bancs sableux et des anciens chenaux de taille plus modeste interprétés comme des bras de chute. Ces environnements de dépôts sont cohérents avec les observations menées sur les bois morts des cours d’eau actuels (chenaux en voie de déconnexion, bancs et îles, pieds de berge). (3) L’examen de l’orientation des troncs traduit un corpus hétérogène. Si des similitudes sont observées, en particulier au sein du banc sableux central, les deux grands paléochenaux contiennent des individus orientés différemment. Ces dispositifs sont mis en relation avec la formation d’embâcles dont il ne resterait que les bois de très grand gabarit. Les facteurs de contrôle, à l’origine de la formation de ce gisement, sont potentiellement multiples. Le retrait de berge ainsi que les paramètres hydro‑climatiques qui le favorisent, sont envisagés comme des facteurs explicatifs pertinents. Cependant, la mort physiologique des végétaux ainsi que les défrichements anthropiques (à l’échelle de la ripisylve et du bassin versant) sont également à prendre en compte. La constitution d’un référentiel régional de troncs subfossiles observés au sein des dépôts fluviatiles et datés pourrait permettre d’améliorer la connaissance de ces facteurs de contrôle.
In streams and rivers, wood from riparian vegetation contributes to habitat complexity and substrates for stream biota, influences channel geomorphology, alters flow, retains sediment and organic ...matter, and enhances nutrient uptake. A few studies have shown that wood amounts in urban streams may be lower than in rural streams or that wood amounts in streams are inversely related to watershed impervious surface cover (ISC). To determine if these patterns occur more broadly, we compared wood amounts in urban and non-urban streams in the South Carolina Piedmont and Blue Ridge Provinces. We measured wood abundance in 20 streams draining urbanized (15–68% ISC) or non-urbanized (≤ 2.5% ISC) watersheds. Our results did not support the hypothesis that urban streams would have less wood than rural streams, and we found no relationship between wood amounts and watershed ISC. Indeed, one urban stream bordered by large riparian trees had the greatest wood volume of all streams in our study. Instead, large wood amounts were best explained by tree canopy cover and length of unobstructed tree-lined channel upstream. These results suggest that the presence of numerous riparian trees influences wood amounts positively even in urban streams where wood amounts might be expected to be low.
Coarse woody debris (CWD) is one of the important components of forest ecosystem, which provides habitat for many species. It is an important consideration for forest and woodland restoration. It ...includes dead standing tree, fallen wood, large branches and tree stumps and other parts. In the forest ecosystem, CWD represents a large amount of orga nic matter, which contributes to the carbon and nitrogen cycling of the forest ecosystem. Globally, forests absorb about 30 % of the world's man-made emissions of CO2 each year, making them an important carbon sink. As an important ecological unit in forest ecosystem, it plays an important role in productivity, nutrient cycling, carbon sequestration, community renewal and biodiversity. It is suggested that the retention of large amounts of CWD in forest ecosystem can improve the intensity of forest carbon sink. Under the background of global climate change, the world's forests are facing the threat of large-scale unnatural death, and a large amount of CWD is formed in the forests. It is found that natural environmental factors (fire and snowstorm, etc.) are the main causes of CWD, and different forest types and different disturbance environments will show different characteristics of CWD. Increasing the research on CWD is of great significance to global sustainable development and management. This review focuses on the research progress of CWD in forest ecosystems from the aspects of the research situation and hot spots, the formation, source, classification basis and characteristics (reserves and decomposition) of CWD at home and abroad. The classification of CWD with the international unified CWD classification standard is conducive to the comparison of research results, can incorporate the research contents into the unified category of data integration, and improve the world CWD database.
According to these short-term results, it is not possible to affirm categorically that the removal of CWD has a negative impact on the nutrient status of soils in gaps created by logging operations. ...Another point to consider is that the canopy closure of gaps in the Amazon Forest generally takes eight years (Hunter et al. 2015). ...canopy closure, the ground cover will mainly be provided by leaves, twigs, bark fragments, and CWD. ...this study aims to evaluate the influences, 1.5 years after the removal of CWD from logging gaps, on soil texture, bulk density, and soil macro- and micronutrient contents up to 150 cm depth. The tree felling occurred in December 2011 and January 2012, in the beginning of the rainy season, with a logging intensity of approximately 4.4 trees ha-1 (diameter at breast height DBH > 50 cm). ...enhanced leaching of nutrients from plant residues to the soil occurred from this and the subsequent rainy season (Ferreira et al., 2006).
Dead wood such as coarse dead wood debris (CWD) is an important component in natural forests since it increases the diversity of plants, fungi, and animals. It serves as habitat, provides nutrients ...and is conducive to forest regeneration, ecosystem stabilization and soil protection. In commercially operated forests, dead wood is often unwanted as it can act as an originator of calamities. Accordingly, efficient CWD monitoring approaches are needed. However, due to the small size of CWD objects satellite data-based approaches cannot be used to gather the needed information and conventional ground-based methods are expensive. Unmanned aerial systems (UAS) are becoming increasingly important in the forestry sector since structural and spectral features of forest stands can be extracted from the high geometric resolution data they produce. As such, they have great potential in supporting regular forest monitoring and inventory. Consequently, the potential of UAS imagery to map CWD is investigated in this study. The study area is located in the center of the Hainich National Park (HNP) in the federal state of Thuringia, Germany. The HNP features natural and unmanaged forest comprising deciduous tree species such as Fagus sylvatica (beech), Fraxinus excelsior (ash), Acer pseudoplatanus (sycamore maple), and Carpinus betulus (hornbeam). The flight campaign was controlled from the Hainich eddy covariance flux tower located at the Eastern edge of the test site. Red-green-blue (RGB) image data were captured in March 2019 during leaf-off conditions using off-the-shelf hardware. Agisoft Metashape Pro was used for the delineation of a three-dimensional (3D) point cloud, which formed the basis for creating a canopy-free RGB orthomosaic and mapping CWD. As heavily decomposed CWD hardly stands out from the ground due to its low height, it might not be detectable by means of 3D geometric information. For this reason, solely RGB data were used for the classification of CWD. The mapping task was accomplished using a line extraction approach developed within the object-based image analysis (OBIA) software eCognition. The achieved CWD detection accuracy can compete with results of studies utilizing high-density airborne light detection and ranging (LiDAR)-based point clouds. Out of 180 CWD objects, 135 objects were successfully delineated while 76 false alarms occurred. Although the developed OBIA approach only utilizes spectral information, it is important to understand that the 3D information extracted from our UAS data is a key requirement for successful CWD mapping as it provides the foundation for the canopy-free orthomosaic created in an earlier step. We conclude that UAS imagery is an alternative to laser data in particular if rapid update and quick response is required. We conclude that UAS imagery is an alternative to laser data for CWD mapping, especially when a rapid response and quick reaction, e.g., after a storm event, is required.
The geomorphic effects of river floods in various climatic settings worldwide have been extensively described, but there is little information on sedimentary processes during and immediately ...following flood peaks. Here we reconstruct sedimentary processes and patterns of the 2012 flood on the Sabie River in Kruger National Park, South Africa, from the preserved geomorphic and sedimentary signature of this event. Based on a combination of geomorphic and sedimentary evidence, the maximal and waning flow stages of the flood event are identified, shown by cut and fill and fining up sequences within aggradational bars, and organic horizons, which may be buried, that correspond to the period of flood peak recession. The presence of organic horizons suggests a strongly seasonal flow regime typical of semi-arid South African rivers. It also provides an exemplar of a flood event stratigraphy that is usually poorly preserved in the geologic record.
•Recent floods on the Sabie River left diagnostic sediment signatures.•Flood sediment stratigraphy is described for the first time.•Both rising and waning flows are captured in the stratigraphy.•An extensive organic layer represents final flood stages.•This flood stratigraphy may be typical of semi-arid rivers.
Data characterizing the temperature dependence of the growth and CO
2
emission of two species of xylotrophic fungi (
D. confragosa
and
D. tricolor
) during their development on wort–agar and wood ...debris in a laboratory experiment are presented. Currently available estimates of the temperature dynamics of CO
2
emission by wood debris do not fully take into account the relationship between temperature, CO
2
emission, growth, and respiratory activity of fungi. In the range of 10–30°C, both linear growth and CO
2
emission activity of fungal mycelium are positively and linearly related to temperature (Spearman’s correlation coefficient, 0.94–0.97) to the same extent (
Q
10
of growth, 2.2;
Q
10
of respiration, 2.1), and CO
2
emission is directly proportional to mycelium area and its specific emission activity. As a result, the temperature effect on CO
2
emission is a derivative of two equally temperature dependent factors: growth and specific emission activity of mycelium. It is equal to the product of the effects of each of the factors separately and is described by an exponential equation, which reflects the non-additive, possibly synergistic nature of the temperature enhancement of CO
2
emission in the range from 20 to 30°C.
Cryptococcus neoformans (San Felice) Vuillemin is an encapsulated yeast of the class Basidiomycetes which produces life-threatening fungal infections on especially immunosuppressed individuals. ...Although flora of Eucalyptus camaldulensis (Dehn.) (Which is considered for natural niche for C. neoformans) exists in various locations in Turkey, the isolation of the yeast is lower than expected.In this study, swabbing technique was used for environmental screening of C. neoformans in Gökova-Akçapınar region where C. neoformans has been isolated in the area in 2011. All of the E. camaldulensis wood debris in this region was involved. C. neoformans colonization was discovered in 11 of 32 trees in Staib and V8 broths. (36,6%). Pure C. neoformans (Aα) ATCC 208821 (10 μl) and C. neoformans (Aa) IUM 96-2828 (10 μl) strains were mixed and inoculated in E. camaldulensis wood debris broth. The mating (sexual reproduction) capability of C. neoformans was investigated and conjugation tube was observed in 59.3% of these broths. Mating capability of C. neoformans increases the risk of life-threatening meningoencephalitis in immunocompromised patients.Moreover, Laetiporus sulphureus (Bull.) Murrill fungous was discovered on all of E. camaldulensis where C. neoformans was isolated.
Cryptococcus neoformans (San Felice) Vuillemin is an encapsulated yeast of the class Basidiomycetes which produces life-threatening fungal infections on especially immunosuppressed individuals. ...Although flora of Eucalyptus camaldulensis (Dehn.) (Which is considered for natural niche for C. neoformans) exists in various locations in Turkey, the isolation of the yeast is lower than expected.In this study, swabbing technique was used for environmental screening of C. neoformans in Gökova-Akçapınar region where C. neoformans has been isolated in the area in 2011. All of the E. camaldulensis wood debris in this region was involved. C. neoformans colonization was discovered in 11 of 32 trees in Staib and V8 broths. (36,6%). Pure C. neoformans (Aα) ATCC 208821 (10 μl) and C. neoformans (Aa) IUM 96-2828 (10 μl) strains were mixed and inoculated in E. camaldulensis wood debris broth. The mating (sexual reproduction) capability of C. neoformans was investigated and conjugation tube was observed in 59.3% of these broths. Mating capability of C. neoformans increases the risk of life-threatening meningoencephalitis in immunocompromised patients. Moreover, Laetiporus sulphureus (Bull.) Murrill fungous was discovered on all of E. camaldulensis where C. neoformans was isolated.
Hurricanes Irma and Maria struck Puerto Rico on the 6th and 20th of September 2017, respectively. These two powerful Cat 5 hurricanes severely defoliated forest canopy and deposited massive amounts ...of litterfall in the forests across the island. We established a 1-ha research plot in each of four forests (Guánica State Forest, Río Abajo State Forest, Guayama Research Area and Luquillo Experiment Forest) before September 2016, and had collected one full year data of litterfall production prior to the arrival of Hurricanes Irma and Maria. Hurricane-induced litterfall was collected within one week after Hurricane Irma, and within two weeks after Hurricane Maria. Each litterfall sample was sorted into leaves, wood (branches and barks), reproductive organs (flowers, fruits and seeds) and miscellaneous materials (mostly dead animal bodies or feces) after oven-drying to constant weight. Annual litterfall production prior to the arrival of Hurricanes Irma and Maria varied from 4.68 to 25.41 Mg/ha/year among the four forests, and annual litterfall consisted of 50–81% leaffall, 16–44% woodfall and 3–6% fallen reproductive organs. Hurricane Irma severely defoliated the Luquillo Experimental Forest, but had little effect on the other three forests, whereas Hurricane Maria defoliated all four forests. Total hurricane-induced litterfall from Hurricanes Irma and Maria amounted to 95–171% of the annual litterfall production, with leaffall and woodfall from hurricanes amounting to 63–88% and 122–763% of their corresponding annual leaffall and woodfall, respectively. Hurricane-induced litterfall consisted of 30–45% leaves and 55–70% wood. Our data showed that Hurricanes Irma and Maria deposited a pulse of litter deposition equivalent to or more than the total annual litterfall input with at least a doubled fraction of woody materials. This pulse of hurricane-induced debris and elevated proportion of woody component may trigger changes in biogeochemical processes and soil communities in these Puerto Rican forests.
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