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11.
12.
Eva van Gorsel Nicolas Delpierre Ray Leuning Andy Black J. William Munger Steven Wofsy Marc Aubinet Christian Feigenwinter Jason Beringer Damien Bonal Baozhang Chen Jiquan Chen Robert Clement Kenneth J. Davis Ankur R. Desai Danilo Dragoni Sophia Etzold Thomas Grünwald Lianhong Gu Bernhard Heinesch Lucy R. Hutyra Wilma W.P. Jans Werner Kutsch B.E. Law Monique Y. Leclerc Ivan Mammarella Leonardo Montagnani Asko Noormets Corinna Rebmann Sonia Wharton 《Agricultural and Forest Meteorology》2009,149(11):1919
Micrometeorological measurements of nighttime ecosystem respiration can be systematically biased when stable atmospheric conditions lead to drainage flows associated with decoupling of air flow above and within plant canopies. The associated horizontal and vertical advective fluxes cannot be measured using instrumentation on the single towers typically used at micrometeorological sites. A common approach to minimize bias is to use a threshold in friction velocity, u*, to exclude periods when advection is assumed to be important, but this is problematic in situations when in-canopy flows are decoupled from the flow above. Using data from 25 flux stations in a wide variety of forest ecosystems globally, we examine the generality of a novel approach to estimating nocturnal respiration developed by van Gorsel et al. (van Gorsel, E., Leuning, R., Cleugh, H.A., Keith, H., Suni, T., 2007. Nocturnal carbon efflux: reconciliation of eddy covariance and chamber measurements using an alternative to the u*-threshold filtering technique. Tellus 59B, 397–403, Tellus, 59B, 307-403). The approach is based on the assumption that advection is small relative to the vertical turbulent flux (FC) and change in storage (FS) of CO2 in the few hours after sundown. The sum of FC and FS reach a maximum during this period which is used to derive a temperature response function for ecosystem respiration. Measured hourly soil temperatures are then used with this function to estimate respiration RRmax. The new approach yielded excellent agreement with (1) independent measurements using respiration chambers, (2) with estimates using ecosystem light-response curves of Fc + Fs extrapolated to zero light, RLRC, and (3) with a detailed process-based forest ecosystem model, Rcast. At most sites respiration rates estimated using the u*-filter, Rust, were smaller than RRmax and RLRC. Agreement of our approach with independent measurements indicates that RRmax provides an excellent estimate of nighttime ecosystem respiration. 相似文献
13.
Tessa Mazor C. Roland Pitcher Wayne Rochester Michel J. Kaiser Jan G. Hiddink Simon Jennings Ricardo Amoroso Robert A. McConnaughey Adriaan D. Rijnsdorp Ana M. Parma Petri Suuronen Jeremy Collie Marija Sciberras Lara Atkinson Deon Durholtz Jim R Ellis Stefan G. Bolam Michaela Schratzberger Elena Couce Jacqueline Eggleton Clement Garcia Paulus Kainge Sarah Paulus Johannes N. Kathena Mayya Gogina P. Daniël van Denderen Aimee A. Keller Beth H. Horness Ray Hilborn 《Fish and Fisheries》2021,22(1):72-86
Bottom trawl fishing is a controversial activity. It yields about a quarter of the world's wild seafood, but also has impacts on the marine environment. Recent advances have quantified and improved understanding of large‐scale impacts of trawling on the seabed. However, such information needs to be coupled with distributions of benthic invertebrates (benthos) to assess whether these populations are being sustained under current trawling regimes. This study collated data from 13 diverse regions of the globe spanning four continents. Within each region, we combined trawl intensity distributions and predicted abundance distributions of benthos groups with impact and recovery parameters for taxonomic classes in a risk assessment model to estimate benthos status. The exposure of 220 predicted benthos‐group distributions to trawling intensity (as swept area ratio) ranged between 0% and 210% (mean = 37%) of abundance. However, benthos status, an indicator of the depleted abundance under chronic trawling pressure as a proportion of untrawled state, ranged between 0.86 and 1 (mean = 0.99), with 78% of benthos groups > 0.95. Mean benthos status was lowest in regions of Europe and Africa, and for taxonomic classes Bivalvia and Gastropoda. Our results demonstrate that while spatial overlap studies can help infer general patterns of potential risk, actual risks cannot be evaluated without using an assessment model that incorporates trawl impact and recovery metrics. These quantitative outputs are essential for sustainability assessments, and together with reference points and thresholds, can help managers ensure use of the marine environment is sustainable under the ecosystem approach to management. 相似文献
14.
Jorge L. Vivan Peter H. May Luís H. H. da Cunha Walter S. de Boef Charles R. Clement 《Agroforestry Systems》2009,76(3):591-604
Evaluation and monitoring are critical to agroforestry (AFS) project management, especially if they aim to contribute to use
and conservation of biodiversity and plant genetic resources. A methodology to analyze information used in decision-making
processes was developed and applied in a biodiversity conservation project in the Brazilian Amazon. Quality of information
gathered at landscape, AFS, species (Bactris gasipaes Kunth, both wild and cultivated varieties) and genetic diversity levels in three dimensions was analyzed. The information
at the landscape level was good, while that in the organizational-institutional and socio-economic dimensions was acceptable;
information gaps were serious in the genetic-ecological dimension. Ecological and economic functionality assessment based
on indicators built upon reported administrative actions suggests that information related to conservation played a greater
role in decision-making and management than information associated with use and development. The application of the methodology
proved instrumental for enhancing efficacy of decision-making within an adaptive management approach to plant genetic resources
use and conservation. 相似文献
15.
Alawa Clement B. I. Etukudo-Joseph I. Alawa Judith N. 《Tropical animal health and production》2011,43(1):127-131
A 6-year retrospective study (2000–2005) of animals slaughtered at the Zango abattoir in Zaria, Kaduna State, Nigeria was
carried out to determine disease conditions encountered in slaughtered animals. Records kept at the abattoir were analysed.
A total of 69,307 cattle, 3,820 goats and 1,763 sheep were slaughtered for the period under study. Of the 69,307 cattle slaughtered
for the period, 22,459 (32.41%) were males and 46,848 (67.59%) were females, while 1,763 sheep were slaughtered comprising
of 506 (28.70%) males and 1,257 (71.30%) females, and 3,820 goats made up of 1,212 (31.73%) males and 2,608 (68.27%) were
females. The major disease and/or pathological conditions were helminthosis (fascioliasis, haemonchosis and paramphistomosis)
16.20%, Streptothricosis 4.15%, Pericarditis 2.20%, liver cirrhosis 2.08%, abscesses 1.04%, pneumonia 0.14%, nephritis 0.05%
and Contagious Bovine Pleuropneumonia, Tuberculosis and Nocardiosis 0.01% each. Out of the 15,075 infected organs, 13,314
(88.38%) were partially salvaged while 1,751 (11.6%) whole organs were condemned. A total of 1,239 pregnant cows, 221 pregnant
ewes and 637 pregnant does were slaughtered, representing a foetal wastage of 2.65% for cattle, 17.58% for sheep and 24.43%
for goats. The result of this study apart from serving as an indicator of field disease condition also demonstrates cases
of serious losses in production due to slaughter of pregnant animals especially for sheep and goats. 相似文献
16.
17.
R.M. Joeckel K.D. Wally B.J. Ang Clement P.R. Hanson J.S. Dillon S.K. Wilson 《CATENA》2011,85(3):253-266
Acidic weathering of the sulfidic Upper Cretaceous Carlile and Pierre Shales in Nebraska has led to the precipitation of the Al sulfate–hydroxide minerals aluminite, alunite, “basaluminite”/felsöbányaite (e.g.,), the aluminum hydroxides gibbsite and bayerite, and the rare Al phosphate hydroxide vashegyite. Kaolinite has also been produced as a result of this acidic weathering. These minerals do not appear as neoformed constituents in any extant soils in the region, and their existence underscores the ability of pyrite oxidation to produce major changes in mineralogy on a Holocene to Recent time scale. Jarosite, hydronium jarosite, gypsum, halotrichite, and melanterite also appear as secondary minerals in the weathered shales. Acidic weathering and the formation of new minerals is extrapedogenic because it occurs well below the limit of modern soil sola. These processes also occur at the edges of major landscape elements and can be considered to have a strong lateral component processes, making them “per latus” processes in our usage. 相似文献
18.
竹节是竹子为适应其生存环境长期择优演化而形成的特殊构造,它对提高细长竹子的刚度与稳定性至关重要。但在竹的利用中,竹节对竹材的力学强度是否会有影响,说法不一。现以毛竹为研究对象,在比较了竹节间材和竹节之间的构造差异的基础上,以竹青、竹黄、竹节未处理和已刨平处理的两种试件形式,分析研究了毛竹的含节材与不含节的节间材在强度上的差异。结果表明,无论是自然状态下的竹材试件,还是刨去刨平青、黄、节的竹材试件,竹节对弯曲强度、顺纹剪切强度、抗压强度等力学性能均未见有降低的作用,相反还有着不同程度的增强作用。但竹节对竹材顺纹抗拉强度有着不可忽视的降低影响。 相似文献
19.
Anthony R Palmer Igshaan Samuels Clement Cupido Andiswa Finca W Fransiska Kangombe Isa AM Yunusa 《African Journal of Range and Forage Science》2016,33(1):43-51
Following a field campaign to determine the species composition, canopy cover, aboveground annual production and leaf area index (LAI) of the semi-arid savanna of north-western Namibia, we present a production model that can be used by graziers to determine the livestock carrying capacity. The model predicts the annual aboveground net primary production (ANPP) from regression equations of canopy cover by annual production fraction for plant functional classes. We tested the output of the model against another fully independent net primary production (NPP) model, namely the MODIS NPP product. The mean MODIS NPP for the 29 sites was 343 ± 22?kg dry matter (DM) ha?1 y?1 as opposed to 285 ± 142?kg DM ha?1 y?1 for the fAP model that used the regression method (p < 0.01). As a proof of concept, these landscape-scale ANPP values are used to calculate a recommended livestock carrying capacity for the Ehirovipuka Communal Conservancy, a 1 980 km2 communal area with both wildlife and livestock populations. In addition, we also provide details of a field method for predicting landscape-scale LAI from line transect data. This approach can be used to ground reference the LAI values generated from the MODIS LAI product. 相似文献
20.
Igshaan Samuels Clement Cupido Melvin B Swarts Anthony R Palmer Jamie W Paulse 《African Journal of Range and Forage Science》2016,33(1):1-9
The Leliefontein communal area in Namaqualand is grazed by mixed species herds that have multiple benefits for pastoralists. This study assessed how the management (herding and free-ranging) of different livestock herds affects their feeding ecology during the wet and dry seasons in a semi-arid shrubland. By using direct observations of livestock grazing in the field, we established their habitat preferences, diet selection and resources overlap. Results indicate that all free-ranging livestock can be considered grazers with cattle being selective. When sheep are herded, they tend to be more generalist feeders and herded goats are browsers. Livestock diet selection and forage preferences are largely linked to the habitats in which they graze and browse. Dietary overlap is highest between free-ranging livestock irrespective of season, whereas herded livestock are able to consume a food source with little potential competition from other livestock. Although the wet-season annual forage resources are able to sustain the livestock population in Leliefontein, this study concludes that the overdependence on annual vegetation would make livestock vulnerable during drought periods when forage production is low. 相似文献