Effects Of Harvesting Research Articles

Rainwater harvesting in Dry Chaco: Regional distribution and local water balance

Rainwater harvesting (RWH) has been essential for the establishment of human settlements in many dry regions of the world that lacked suitable surface or groundwater resources. A vast fraction of the South American Dry Chaco ecoregion still relies on RWH to support, not only livestock production, but domestic and industrial uses as well. As a result, water capture and storage infrastructure is widely disseminated throughout the region. In this paper we characterized the most typical RWH systems in two contrastingly developed sub-regions of Dry Chaco, ranging from extensive ranching to intensive beef and dairy production (central Argentina and western Paraguay, respectively). In each sub-region, we quantified RWH systems density, spatial distribution and associations with landscape features; furthermore, we illustrated how the daily dynamic of water stock in a typical RWH system contributes to assess their capture and storage efficiency. We found that randomly distributed low sophisticated RWH systems prevailed in central Argentina, while clustered distributed high sophisticated ones were more common in western Paraguay. RWH systems density was ten times higher in western Paraguay (0.94 vs. 0.098 units/km2), showing an exponential association with land cleared fraction and proximity to villages. The daily dynamic of water stock of the RWH impoundment showed that water harvest events were exponentially associated with precipitation magnitude events (R2 = 0.86), while annual water losses were explained by infiltration and evaporation fluxes (59 vs. 41%, respectively). Across both sub-regions, RWH accounts for less than 1% of the annual precipitation, playing a minor role on the regional water balance; however at a local level, they can affect several hydrological fluxes including the onset of groundwater recharge and the mitigation of extreme runoff events.

Behavioural response to anthropogenic habitat disturbance: Indirect impact of harvesting on whinchat populations in Switzerland

Harvesting often results in the destruction of both, the nest and the surrounding habitat of ground-nesting farmland birds. While the direct effect of harvesting on nest loss and productivity is well investigated, the behavioural responses of parent birds to harvest events remain ambiguous, though they might have profound consequences for farmland bird populations. The progressive harvest of fields within a pair’s home-range represents a gradual decrease in habitat quality. The response of breeding individuals to anthropogenic nest loss therefore might depend on the extent of remaining suitable habitat. Here, we radio-tracked a cohort of breeding whinchats Saxicola rubetra affected by anthropogenic nest loss due to harvesting. We used the meadow management as a natural experiment, destroying nests at various stages of the mowing process and leaving different relict areas of suitable habitat after nest loss. Divorce and within-season dispersal rates after nest loss were strongly increased in home-ranges with a high proportion of mown area. Re-nesting rates were six times higher in non-dispersing than in dispersing individuals. Thus, dispersing individuals contributed only little to the overall re-nesting rate and to the productivity of the population. This suggests that the habitat-dependent behavioural responses to harvesting can have major effects on farmland birds’ reproductive output. Since harvesting in agricultural landscapes affects many breeding pairs, the resulting changes in the social patterns, the spatial dynamics and the re-nesting rate should be considered in the conservation of farmland bird populations.

Ecological Effects of the Harvest Phase Of Geoduck (Panopea generosaGould, 1850) Aquaculture on Infaunal Communities in Southern Puget Sound, Washington

Intertidal aquaculture for geoducks (Panopea generosa Gould, 1850) is expanding in southern Puget Sound, Washington, where gently sloping sandy beaches are used for field culture. Geoduck aquaculture contributes significantly to the regional economy, but has become controversial because of a range of unresolved questions involving potential biological impacts on marine ecosystems. From 2008 through 2012, the authors used a “before-after-control-impact” experimental design, emphasizing spatial scales comparable with those used by geoduck culturists to evaluate the effects of harvesting market-ready geoducks on associated benthic infaunal communities. Infauna were sampled at three different study locations in southern Puget Sound at monthly intervals before, during, and after harvests of clams, and along extralimital transects extending away from the edges of cultured plots to assess the effects of harvest activities in adjacent uncultured habitat. Using multivariate statistical approaches, strong seasonal and spatial signals in patterns of abundance were found, but there was scant evidence of effects on the community structure associated with geoduck harvest disturbances within cultured plots. Likewise, no indications of significant “spillover” effects of harvest on uncultured habitat adjacent to cultured plots were noted. Complementary univariate approaches revealed little evidence of harvest effects on infaunal biodiversity and indications of modest effects on populations of individual infaunal taxa. Of 10 common taxa analyzed, only three showed evidence of reduced densities, although minor, after harvests whereas the remaining seven taxa indicated either neutral responses to harvest disturbances or increased abundance either during or in the months after harvest events. It is suggested that a relatively active natural disturbance regime, including both small-scale and large-scale events that occur with comparable intensity but more frequently than geoduck harvest events in cultured plots, has facilitated assemblage-level infaunal resistance and resilience to harvest disturbances.

Breeding habitat selection in an obligate beach bird: a test of the food resource hypothesis

The food resource hypothesis of breeding habitat selection in beach-nesting birds suggests that birds breed at sites with more prey to meet the increased energetic requirements associated with breeding. We compare prey resources using pitfall traps and core samples at breeding sites and absence sites of the eastern population of hooded plover, Thinornis rubricollis rubricollis, which, in this part of its range, is a threatened obligate beach bird. Breeding sites had higher abundances, equivalent species richness, and different assemblages of invertebrate prey compared with absence sites. Assemblages at breeding sites were characterised by more isopods, and fewer beetles of the family Phycosecidae. Breeding habitat selection by plovers appears to be associated with selection for sites with more food, and any process that degrades food resources at a site (e.g. kelp harvesting or marine pollution events) may reduce the likelihood of occupancy of that site by breeding birds.

Accumulation and Connectivity of Coarse Woody Debris in Partial Harvest and Unmanaged Relict Forests

When a tree dies, it continues to play an important ecological role within forests. Coarse woody debris (CWD), including standing deadwood (SDW) and downed deadwood (DDW), is an important functional component of forest ecosystems, particularly for many dispersal-limited saproxylic taxa and for metapopulation dynamics across landscapes. Processes, such as natural disturbance or management, modify forest composition and structure, thereby influencing CWD abundance and distribution. Many studies have compared older forests to forests managed with even-aged silvicultural systems and observed a prolonged period of low CWD occurrence after harvesting. With fine-scale spatial data, our study compares the long-term impacts of light partial harvesting on the CWD structure of eastern deciduous hardwood forests. We mapped and inventoried DDW and SDW using variable radius plots based on a 10 m×10 m grid throughout an unmanaged, structurally-complex relict forest and two nearby forests that were partially harvested over 46 years ago. The relict stand had significantly larger individual pieces and higher accumulations of DDW and SDW than both of the partially harvested stands. Connectivity of CWD was much higher in the relict stand, which had fewer, larger patches. Larger pieces and higher proportion of decay-resistant species (e.g. Quercus spp.) in the relict forest resulted in slower decomposition, greater accumulation and increased connectivity of CWD. Partial harvests, such that occur with selection forestry, are generally considered less disruptive of ecosystem services, but this study highlights the long-term impacts of even light partial harvests on CWD stocks and distribution. When planning harvesting events, forest managers should also consider alternative methods to ensure the sustainability of deadwood resources and function.

Multimodel simulations of forest harvesting effects on long‐term productivity and CN cycling in aspen forests.

The effects of forest management on soil carbon (C) and nitrogen (N) dynamics vary by harvest type and species. We simulated long-term effects of bole-only harvesting of aspen (Populus tremuloides) on stand productivity and interaction of CN cycles with a multiple model approach. Five models, Biome-BGC, CENTURY, FORECAST, LANDIS-II with Century-based soil dynamics, and PnET-CN, were run for 350 yr with seven harvesting events on nutrient-poor, sandy soils representing northwestern Wisconsin, United States. Twenty CN state and flux variables were summarized from the models' outputs and statistically analyzed using ordination and variance analysis methods. The multiple models' averages suggest that bole-only harvest would not significantly affect long-term site productivity of aspen, though declines in soil organic matter and soil N were significant. Along with direct N removal by harvesting, extensive leaching after harvesting before canopy closure was another major cause of N depletion. These five models were notably different in output values of the 20 variables examined, although there were some similarities for certain variables. PnET-CN produced unique results for every variable, and CENTURY showed fewer outliers and similar temporal patterns to the mean of all models. In general, we demonstrated that when there are no site-specific data for fine-scale calibration and evaluation of a single model, the multiple model approach may be a more robust approach for long-term simulations. In addition, multimodeling may also improve the calibration and evaluation of an individual model.

Growing season nitrous oxide fluxes across a 125+ year harvested red spruce forest chronosequence

Forest harvesting alters the cycling of nitrogen (N) within temperate forest systems in a manner that may influence atmospheric nitrous oxide (N2O) concentrations. This paper investigates, over a single growing season within the Acadian Forest region of Atlantic Canada, soil N2O fluxes across a clearcut harvest red spruce forest chronosequence that includes an old growth reference site (>125 years). A pulse of soil N2O at ~1–2 years was observed after clearcut harvesting, followed by an exponential decay to a baseline level within one to two decades after the harvesting event. No significant differences between fluxes from the forest sites >20 years of age and the reference old growth site (>125 years) were observed. Soils within the chronosequence acted as both sources and sinks for N2O through the growing season. Low soil N availability was identified as the likely factor limiting soil N2O flux responses to changes in soil temperature and moisture in situ at most sites. This was confirmed by controlled laboratory experiments that measured soil N2O flux responses to moisture, temperature and N amendments. Without N amendments, soils act as an elevated sink for N2O under increased temperature. However, when soil N was not limiting, N2O flux responded primarily to moisture. Overall, the study suggests that moist temperate forest soils that are N-limited can act as a transient source of N2O following clearcut harvesting during the growing season, and that the decrease in the release of N2O from soils following harvesting follows an exponential pattern.

Reply to Kopjar et al.

We thank Kopjar et al. [1] for their comments regarding our recent work published in Eur J Cardiothorac Surg [2]. We reported attenuated vascular smooth muscle cell activation via microRNA-145 as a possible pathogenetic mechanism for the clinical observation of improved vein graft patency using the no-touch (NT) approach. Kopjar et al. [1] focused on a critical aspect of a ‘NT’ vein harvest that has been a major barrier to wide-spread adoption, which being the morbidity of the leg incision. We have read their comments and offer our responses. In this report, our patient numbers were too small to make any definitive conclusions regarding clinical leg wound morbidity. To address this important issue, we direct Kopjar et al. to our ongoing prospective, multicentre randomized controlled clinical trial comparing conventional (CON) saphenous vein graft (SVG) harvest versus the no-touch technique (SUPERIOR SVG Study; http ://clinicaltrials.gov/show/NCT01047449). The primary outcome of the SUPERIOR SVG Study is 1-year graft occlusion; the secondary outcomes include adverse SVG harvesting events at 1 year postcoronary artery bypass graft, which include infection, haematoma, swelling, neuropathy and quality-of-life measures. In this report, we found worse short-term leg assessment scores in NT versus CON at 3 months as well as more incidences of infection (4 vs 0 patients). However, as the authors have pointed out that, at 1 year, such scores were not different between groups. Our data does suggest that, in our patient population, although NT vein harvest was associated with acute morbidity, there may not be associated long-term functional consequences. As for the method of leg closure, all leg incisions were sutured closed with two layers of subcutaneous 2-0 Vicryl (Ethicon, Somerville, NJ, USA) sutures and a single 3-0 monocryl subcuticular layer. Anti-microbial sutures may minimize leg wound harvest-site infections, but were not used in these patients. In this report, all patients were included in the leg assessment study, including the one patient with preoperative peripheral vascular disease, which was not considered severe and without observable chronic skin changes. We do advocate that lower leg harvesting be avoided and thigh saphenous vein segments used for patients with more significant peripheral arterial insufficiency. We also agree that it remains to be seen whether gender will come to be an independent risk factor for infection. The Materials and Methods section points to Supplementary data, which includes the leg wound healing and functional outcomes questionnaire. This can now be accessed on the Eur J Cardiothorac Surg website. Finally, although the representative micrographs of SVG HE 217.76 ± 48.73 vs 202.32 ± 45.53, and 146.19 ± 43.39 vs 132.38 ± 28.34, respectively). Finally, there was a single crossover; a CON SVG was harvested from the leg assigned to NT that developed a leg wound infection and analysed according to intention to treat. We did not perform the as-treated analysis nor would this change the outcome of the analysis. In addition, we thank Kopjar, et al. [1] for their interest in our paper and for raising these important points. Unfortunately, this report was not designed nor able to address many of the issues raised. As Kopjar et al. point out, the SUPERIOR SVG study will address these concerns.

An Automated Approach to Map the History of Forest Disturbance from Insect Mortality and Harvest with Landsat Time-Series Data

Forests contain a majority of the aboveground carbon (C) found in ecosystems, and understanding biomass lost from disturbance is essential to improve our C-cycle knowledge. Our study region in the Wisconsin and Minnesota Laurentian Forest had a strong decline in Normalized Difference Vegetation Index (NDVI) from 1982 to 2007, observed with the National Ocean and Atmospheric Administration’s (NOAA) series of Advanced Very High Resolution Radiometer (AVHRR). To understand the potential role of disturbances in the terrestrial C-cycle, we developed an algorithm to map forest disturbances from either harvest or insect outbreak for Landsat time-series stacks. We merged two image analysis approaches into one algorithm to monitor forest change that included: (1) multiple disturbance index thresholds to capture clear-cut harvest; and (2) a spectral trajectory-based image analysis with multiple confidence interval thresholds to map insect outbreak. We produced 20 maps and evaluated classification accuracy with air-photos and insect air-survey data to understand the performance of our algorithm. We achieved overall accuracies ranging from 65% to 75%, with an average accuracy of 72%. The producer’s and user’s accuracy ranged from a maximum of 32% to 70% for insect disturbance, 60% to 76% for insect mortality and 82% to 88% for harvested forest, which was the dominant disturbance agent. Forest disturbances accounted for 22% of total forested area (7349 km2). Our algorithm provides a basic approach to map disturbance history where large impacts to forest stands have occurred and highlights the limited spectral sensitivity of Landsat time-series to outbreaks of defoliating insects. We found that only harvest and insect mortality events can be mapped with adequate accuracy with a non-annual Landsat time-series. This limited our land cover understanding of NDVI decline drivers. We demonstrate that to capture more subtle disturbances with spectral trajectories, future observations must be temporally dense to distinguish between type and frequency in heterogeneous landscapes.

Growth of Forest Stands and Tree Species Ecological Guilds in Undisturbed and Selectively Logged Amazonian Forests, Northern Brazil

The growth of trees in forest canopy gaps left by the felling of adult commercial trees has been shown to differ for individual ecological guilds of tree species and initial site conditions prior to logging. The objective of this study was to identify patterns in individual tree diameter growth both for the tree population overall and as a function of ecological guild in specific for undisturbed and selectively logged forest and compare between the two. Data came from two areas of non-flooded forest of the Brazilian Amazon in the states of Amazonas and Para for trees with dbh >10 cm. For purposes of statistical analysis tree species were clustered in three ecological guilds based on bole wood specific gravity and successional status. Tree growth irrespective of ecological species guild in the vicinity of logging gaps for the three year period following the harvest event was significantly more elevated in relation to undisturbed forest and this positive difference was proportionately greater for Amazonas in relation to Para. Ecological guilds showed a pattern of increasing growth rate with decreasing bole wood specific gravity and successional status when area and site disturbance status where not taken under account. In response to logging all ecological guilds showed increased growth rates but all were proportional to levels found in the undisturbed forest. Tree species life history characteristics appear to be a more significant factor affecting tree growth than site disturbance status in response to logging at least for the first 3 years after the logging event.

Giant kelp (Macrocystis) fishery in Atacama (Northern Chile): biological basis for management of the integrifolia morph

In Bahia Chasco, Atacama, the integrifolia morph of Macrocystis forms one of the most important kelp forests in northern Chile. In order to determine effects of local harvesting policies, we evaluated the population dynamics of this resource in intact, frequently disturbed, and permanently and completely harvested areas. Recruitment, frond length, reproductive phenology and standing crop were assessed monthly. In intact areas, frond length and ratio of reproductive individuals were higher, but recruitment was poorly stimulated. On the other hand, complete harvest had an important effect on Macrocystis population dynamics. Whereas recruitment and growth were much higher after harvest events, reproductive phenology was lower. The harvest techniques with different frequencies practiced by Bahia Chasco fishermen were less harmful than complete harvest, and we conclude that current exploitation techniques applied in this location are not deleterious for the giant kelp beds. They even have favorable effects by renewing the population through stimulation of sexual reproduction, recruitment and growth of young individuals.

Carbon dynamics in the future forest: the importance of long‐term successional legacy and climate–fire interactions

Understanding how climate change may influence forest carbon (C) budgets requires knowledge of forest growth relationships with regional climate, long-term forest succession, and past and future disturbances, such as wildfires and timber harvesting events. We used a landscape-scale model of forest succession, wildfire, and C dynamics (LANDIS-II) to evaluate the effects of a changing climate (A2 and B1 IPCC emissions; Geophysical Fluid Dynamics Laboratory General Circulation Models) on total forest C, tree species composition, and wildfire dynamics in the Lake Tahoe Basin, California, and Nevada. The independent effects of temperature and precipitation were assessed within and among climate models. Results highlight the importance of modeling forest succession and stand development processes at the landscape scale for understanding the C cycle. Due primarily to landscape legacy effects of historic logging of the Comstock Era in the late 1880s, C sequestration may continue throughout the current century, and the forest will remain a C sink (Net Ecosystem Carbon Balance>0), regardless of climate regime. Climate change caused increases in temperatures limited simulated C sequestration potential because of augmented fire activity and reduced establishment ability of subalpine and upper montane trees. Higher temperatures influenced forest response more than reduced precipitation. As the forest reached its potential steady state, the forest could become C neutral or a C source, and climate change could accelerate this transition. The future of forest ecosystem C cycling in many forested systems worldwide may depend more on major disturbances and landscape legacies related to land use than on projected climate change alone.

Analyzing selective harvest events in three large forest observational studies in North Eastern China

This study presents an analysis of selective harvest events in three 10-ha field plots with mapped trees, representing different forest successional stages in the temperate multi-species forests of North-Eastern China. Non-spatial methods of analyzing the harvest events include species and size selection preference and an assessment of harvest intensities for four species groups (identified using bivariate mixed dbh/height distributions). Spatial aggregation increased very slightly after the harvest event, but in most cases, the change was hardly noticeable. In addition, tree selection preferences involving nearest neighbor structure units are presented, using the attributes “species mingling” and “dominance”. The removals occurred within a broad array of neighborhood constellations, involving suppressed as well as dominant individuals. Previous approaches involving harvest event analysis in multi-species forests were limited to assessing size and species selection preferences. This study uses more advanced methods and presents more detailed interpretations, due to the large and detailed observational datasets and improved analytical tools that have become available recently. Models of tree growth and survival, which represent the overwhelming result of traditional observational studies, only describe a part of forest dynamics. Equally important are the modifications caused by regular human disturbance. There is thus increasing motivation for analyzing selective harvesting activities as presented in this contribution.

Quantifying differences between ecosystems with particular reference to selection forests in Durango/Mexico

Continuous cover forestry (CCF), which is characterized by selective tree removals in uneven-aged forests, is often believed to be superior to single-species planted forests in addressing a wide range of requirements. Sustainability, which is an important component of CCF, implies limiting the harvested timber volume and often also the structural disturbance by harvest events. Structure is central to CCF silviculture because it determines the current output of products and services as well as the resilience and future dynamics of the managed ecosystem. Therefore, measuring deviations from a desired target structure is a fundamental requirement of CCF. Quantitative description of the differences between ecosystems is necessary for classification of forest types and silvicultural targets, as well as for harvest event analysis and nature conservation. The objective of this study is to present such an approach in the context of exploring new methods of measuring structural differences between forest communities. We investigate the dependence of such differences on the scale of resolution. The general approach is based on measuring discrepancies between relative frequencies involving tree species, tree sizes and spatial patterns. Data from selectively managed mixed and uneven-aged pine-oak forests in Mexico provide the empirical basis for the study. The approaches presented in this study can be used to quantify structural differences between forests and between a given structure and some theoretical target structure. A quantitative measure of the difference between two ecosystems can provide foresters with information about the consequences of particular silvicultural activities. The approach presented in this study therefore offers great potential for analysing the impact of human disturbance on forest ecosystems.

Effects of Forest Management on Running Buffalo Clover (TrifoliumstoloniferumMuhl. ex A. Eaton) Distribution and Abundance in the Fernow Experimental Forest

Identifying habitat preferences of species of concern is fundamental to the practice of conservation, but disturbances and other environmental processes can substantially affect suitability. Trifolium stoloniferum, or running buffalo clover, is a federally endangered plant species that occurs on the Fernow Experimental Forest in West Virginia. Previous work and extensive anecdotal evidence suggests that this species is maintained in part by periodic disturbances to its habitat. In the Fernow Experimental Forest, this disturbance is in the form of intermittent logging activities. We investigated the role of forest harvesting practices and environmental variables in fostering T. stoloniferum at the stand level. Censuses have been conducted on T. stoloniferum occurrences in the Fernow since 1994, and occurrences are grouped by subcompartment or watershed, which are the basic management units within this experimental forest. Site characteristics and disturbance history were assessed for their impact upon T. stoloniferum presence and density. Classification tree analysis identified total number of forest harvest events in a subcompartment since 1948 as the most important predictor of T. stoloniferum presence or absence. Regression tree analysis identified aspect as important in determining T. stoloniferum abundance, with west-facing compartments supporting larger populations. This study confirms the importance of disturbance in maintaining T. stoloniferum populations. However, site characteristics independent of disturbance history are also predictors of T. stoloniferum presence and abundance, suggesting that managers attempting to restore or create habitat for T. stoloniferum should account for the interaction between disturbance history and site characters in determining suitability of habitat for T. stoloniferum.

STARS: A New Method for Multitemporal Remote Sensing

There is great potential for the development of remote sensing methods that integrate and exploit both multispectral and multitemporal information. This paper presents a new image processing method: Spectral–Temporal Analysis by Response Surface (STARS), which synthesizes the full information content of a multitemporal–multispectral remote sensing image data set to represent the spectral variation over time of features on the Earth's surface. Depending on the application, STARS can be effectively implemented using a range of different models [e.g., polynomial trend surface (PTS) and collocation surface (CS)], exploiting data from different sensors, with varying spectral wavebands and acquiring data at irregular time intervals. A case study was used to test STARS, evaluating its potential to characterize sugarcane harvest practices in Brazil, specifically with and without preharvest straw burning. Although the CS model presented sharper and more defined spectral–temporal surfaces, abrupt changes related to the sugarcane harvest event were also well characterized with the PTS model when a suitable degree was set. Orthonormal coefficients were tested for both the PTS and CS models and performed more accurately than regular coefficients when used as input for three evaluated classifiers: instance based, decision tree, and neural network. Results show that STARS holds considerable potential for representing the spectral changes over time of features on the Earth's surface, thus becoming an effective image processing method, which is useful not only for classification purposes but also for other applications such as understanding land-cover change. The STARS algorithm can be found at <weblink xlink:href="www.dsr.inpe.br/~mello" xlink:type="simple" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">www.dsr.inpe.br/~mello</weblink> .

Population viability analysis of American mink (Neovison vison) escaped from Danish mink farms

The American mink (Neovison vison) was introduced to Danish fur farms in the 1930s. An unknown number of mink have managed to escape these farms over the years. Today feral mink are found in the wild in most parts of Denmark. A population viability analysis (PVA) was performed using VORTEX, a stochastic population simulation software, to 1) predict the viability and potential population expansion from different sizes of founding populations of farm escapees, 2) investigate which parameters mostly affect the viability, 3) assess the effects of continuous escapes on the feral populations and how the feral populations are affected by management programs, and 4) discuss eradication strategies and their efficiency in management of the feral American mink population in Denmark. The simulations showed that juvenile mortality had the greatest effect on population viability followed by fecundity, adult mortality, and initial population size. Populations supplemented yearly by escapees all reached the carrying capacity and gained genetic variability over the years. Harvesting was modeled as the yearly number of mink caught in Denmark. Most of the simulated harvested populations crashed within few years after the first harvesting event. This indicates that the feral number of mink in Denmark is sustained due to supplements from mink farms and no true feral population exists. To manage the number of feral mink in Denmark it is essential to prevent escapees. The eradication effort would be most effective if focused on late summer and autumn when juvenile mink leave the maternal territory.

On the Stability of Random Multiple Access With Stochastic Energy Harvesting

In this paper, we consider random access by nodes that have energy harvesting capability. Each node is equipped with both a queue for storing the arriving packets and a battery for storing the harvested energy chunks, where the packet arrival and the energy harvesting events are all modeled as discrete-time stochastic processes. In each time slot, each node attempts to transmit the head-of-the-line packet in the queue with some probability if its battery is non-empty, and each transmission consumes one chunk of energy. Therefore, the transmission by one node is not just limited by the availability of packets in the queue but also by the availability of energy chunks in the battery. In most of related previous work, it was implicitly assumed that there exists unlimited energy for transmission, which is impractical in many distributed systems. In this work, we characterize the exact stability region when a pair of bursty nodes, which are harvesting energy from the environment, are randomly accessing a common receiver. The analysis takes into account the compound effects of multi-packet reception capability at the receiver. The contributions in the paper are twofold. First, we accurately assess the effect of limited, but renewable, energy availability due to harvesting on the stability region by comparing against the case of having unlimited energy. Second, the impact of the finite capacity batteries on the achieved stability region is also quantified.

Semidiscrete biomass dynamic modeling: an improved approach for assessing fish stock responses to pulsed harvest events

Continuous harvest over an annual period is a common assumption of continuous biomass dynamics models (CBDMs); however, fish are frequently harvested in a discrete manner. We developed semidiscrete biomass dynamics models (SDBDMs) that allow discrete harvest events and evaluated differences between CBDMs and SDBDMs using an equilibrium yield analysis with varying levels of fishing mortality (F). Equilibrium fishery yields for CBDMs and SDBDMS were similar at low fishing mortalities and diverged as F approached and exceeded maximum sustained yield (FMSY). Discrete harvest resulted in lower equilibrium yields at high levels of F relative to continuous harvest. The effect of applying harvest continuously when it was in fact discrete was evaluated by fitting CBDMs and SDBDMs to time series data generated from a hypothetical fish stock undergoing discrete harvest and evaluating parameter estimates bias. Violating the assumption of continuous harvest resulted in biased parameter estimates for CBDM while SDBDM parameter estimates were unbiased. Biased parameter estimates resulted in biased biological reference points derived from CBDMs. Semidiscrete BDMs outperformed continuous BDMs and should be used when harvest is discrete, when the time and magnitude of harvest are known, and when F is greater than FMSY.

Photophysical Probes for Multiple-Redox and Multiple-Excited-State Interactions in Molecular Aggregates

Photosynthesis takes place through a highly efficient series of energy, electron, and proton transfers initiated by absorption of one or more photons within the visible region of the solar spectrum. Because of the presence of multiple chromophores needed for effective light harvesting, extinction coefficients must be very high. The absorbing multiunit array is held within a rigidly arranged structure that facilitates each electron hop. A fully artificial, yet biomimetic, alternative to photosynthesis that produces fuels directly and efficiently from sunlight and simple low molecular weight molecules would change the world. Achieving this goal requires a detailed understanding of the mechanisms of the key steps of the complex chemical and photochemical processes taking place in natural photosynthesis. One of these mechanisms relies on light harvesting to initiate multiple-step sequences to obtain combustible molecules suitable for burning. In particular, we are devising and testing photophysical models with characteristics that facilitate multiple electron transfers within a single aggregate and are directly relevant to light harvesting. We focus on structural features that promote photoinduced electron transfer at high dye densities, placed for optimal solar utilization and catalysis. The reaction producing oxygen is further complicated by the need for four electrons to complete the sequence, even though the first initiation step is presumably absorption of a single photon. Therefore we explore steps that accumulate charge or have the potential to do so. We also emphasize the synthesis of model systems that probe the complexity of individual steps. This Account examines the factors that influence the efficiency of electron redistribution in multiple-dye, multiple-excited-state, and multiple-redox equivalent arrays. Such knowledge will allow us to optimize the efficiency of electron migration and may contribute to a better understanding of multiple-equivalent light harvesting events by which photosynthetic energy storage takes place.