Long-term forest-floor litter dynamics in Canada's boreal forest: Comparison of two model formulations

Litter decomposition is a key component in ecosystem material cycling that determines (i) forest soil carbon (C) and nutrient content, (ii) release of carbon dioxide to the atmosphere, and (iii) generation and mass transfer of dissolved organic carbon from terrestrial to aquatic ecosystems. In this study, we provide simulations of long term forest-floor litter dynamics generated with both (i) an existing forest nutrient cycling and biomass growth model (ForNBM) with a single-pool formulation of forest-floor litter decomposition (Zhu et al., 2003. Ecol. Model. 169, 347-360), and (ii) a revised version of the model produced by substituting the single-pool formulation with a three-pool version of the formulation tested against data from litterbag experiments (FLDM; Zhang et al., 2010. Ecol. Model. 221, 1944-1953). This is done to determine the importance of subdividing the litter mass into categories of rates of decay (i.e., fast, slow, and very slow) on model accuracy. Forest-forest litter dynamics simulated with the two models are subsequently compared against field measurements collected at several northern jack pine (Pinus banksiana) stands along a southwest-northeast oriented transect (climate gradient) associated with the Boreal Forest Transect Case Study in northwest Canada. Initial comparison shows that the single-pool formulation underpredicts residual litter mass when forests are <65 years old, largely due to the improper treatment of the very slow decomposing litter component. This underprediction is resolved when the three-pool formulation is used. From a ecosystems-response point of view, the revised ForNBM (with the three-pool formulation) demonstrates that (i) forest-floor litter initially increases with forest growth and reaches a plateau once the forest matures; (ii) the forest floor stores more litter and C at the southern and warmer sites than at the northern sites; and (iii) in a similar climate regime, the forest floor stores more litter and C at productive than at nutrient-poor sites.     

Minimizing predation risk in a landscape of multiple predators: effects on the spatial distribution of African ungulates

Studies that focus on single predator-prey interactions can be inadequate for understanding antipredator responses in multi-predator systems. Yet there is still a general lack of information about the strategies of prey to minimize predation risk from multiple predators at the landscape level. Here we examined the distribution of seven African ungulate species in the fenced Karongwe Game Reserve (KGR), South Africa, as a function of predation risk from all large carnivore species (lion, leopard, cheetah, African wild dog, and spotted hyena). Using observed kill data, we generated ungulate-specific predictions of relative predation risk and of riskiness of habitats. To determine how ungulates minimize predation risk at the landscape level, we explicitly tested five hypotheses consisting of strategies that reduce the probability of encountering predators, and the probability of being killed. All ungulate species avoided risky habitats, and most selected safer habitats, thus reducing their probability of being killed. To reduce the probability of encountering predators, most of the smaller prey species (impala, warthog, waterbuck, kudu) avoided the space use of all predators, while the larger species (wildebeest, zebra, giraffe) only avoided areas where lion and leopard space use were high. The strength of avoidance for the space use of predators generally did not correspond to the relative predation threat from those predators. Instead, ungulates used a simpler behavioral rule of avoiding the activity areas of sit-and-pursue predators (lion and leopard), but not those of cursorial predators (cheetah and African wild dog). In general, selection and avoidance of habitats was stronger than avoidance of the predator activity areas. We expect similar decision rules to drive the distribution pattern of ungulates in other African savannas and in other multi-predator systems, especially where predators differ in their hunting modes.     

Mechanisms contributing to the thermal analysis of waste incineration bottom ash and quantification of different carbon species

The focus of this study was to identify the main compounds affecting the weight changes of bottom ash (BA) in conventional loss on ignition (LOI) tests and to obtain a better understanding of the individual processes in heterogeneous (waste) materials such as BA. Evaluations were performed on BA samples from a refuse derived fuel incineration (RDF-I) plant and a hospital waste incineration (HW-I) plant using thermogravimetric analysis and subsequent mass spectrometry (TG–MS) analysis of the gaseous thermal decomposition products. Results of TG–MS analysis on RDF-I BA indicated that the LOI measured at 550 °C was due to moisture evaporation and dehydration of Ca(OH)₂ and hydrocalumite. Results for the HW-I BA showed that LOI at 550 °C was predominantly related to the elemental carbon (EC) content of the sample. Decomposition of CaCO₃ around 700 °C was identified in both materials. In addition, we have identified reaction mechanisms that underestimate the EC and overestimate the CaCO₃ contents of the HW-I BA during TG–MS analyses. These types of artefacts are expected to occur also when conventional LOI methods are adopted, in particular for materials that contain CaO/Ca(OH)₂ in combination with EC and/or organic carbon, such as e.g. municipal solid waste incineration (MSWI) bottom and fly ashes. We suggest that the same mechanisms that we have found (i.e. in situ carbonation) can also occur during combustion of the waste in the incinerator (between 450 and 650 °C) demonstrating that the presence of carbonate in bottom ash is not necessarily indicative for weathering. These results may also give direction to further optimization of waste incineration technologies with regard to stimulating in situ carbonation during incineration and subsequent potential improvement of the leaching behavior of bottom ash.     

The impact of swidden decline on livelihoods and ecosystem services in Southeast Asia: A review of the evidence from 1990 to 2015

Global economic change and policy interventions are driving transitions from long-fallow swidden (LFS) systems to alternative land uses in Southeast Asia’s uplands. This study presents a systematic review of how these transitions impact upon livelihoods and ecosystem services in the region. Over 17 000 studies published between 1950 and 2015 were narrowed, based on relevance and quality, to 93 studies for further analysis. Our analysis of land-use transitions from swidden to intensified cropping systems showed several outcomes: more households had increased overall income, but these benefits came at significant cost such as reductions of customary practice, socio-economic wellbeing, livelihood options, and staple yields. Examining the effects of transitions on soil properties revealed negative impacts on soil organic carbon, cation-exchange capacity, and aboveground carbon. Taken together, the proximate and underlying drivers of the transitions from LFS to alternative land uses, especially intensified perennial and annual cash cropping, led to significant declines in pre-existing livelihood security and the ecosystem services supporting this security. Our results suggest that policies imposing land-use transitions on upland farmers so as to improve livelihoods and environments have been misguided; in the context of varied land uses, swidden agriculture can support livelihoods and ecosystem services that will help buffer the impacts of climate change in Southeast Asia.     

Dealing with double trouble: consequences of single and double herbivory in Brassica juncea

In their natural environment, plants are often attacked simultaneously by many insect species. The specificity of induced plant responses that is reported after single herbivore attacks may be compromised under double herbivory and this may influence later arriving herbivores. The present study focuses on the dynamics of induced plant responses induced by single and double herbivory, and their effects on successive herbivores. Morphological (leaf length, area and trichome density) and chemical changes (leaf alkenyl and indole glucosinolates) in Brassica juncea were evaluated 4, 10, 14 and 20 days after damage by the specialist Plutella xylostella alone, or together with the generalist Spodoptera litura. To assess the biological effect of the plant’s responses, the preference and performance of both herbivores on previously induced plants were measured. We found that alkenyl glucosinolates were induced 20 days after damage by P. xylostella alone, whereas their levels were elevated as early as 4 days after double herbivory. Trichome density was increased in both treatments, but was higher after double herbivory. Interestingly, there was an overall decrease in indole glucosinolates and an increase in leaf size due to damage by P. xylostella, which was not observed during double damage. S. litura preferred and performed better on undamaged plants, whereas P. xylostella preferred damaged plants and performed better on plants damaged 14 and 10 days after single and double herbivory, respectively. Our results suggest that temporal studies involving single versus multiple attacker situations are necessary to comprehend the role of induced plant responses in plant–herbivore interactions.     

Urban Air Quality Assessment Model: UAQAM

The Urban Air Quality Assessment Model (UAQAM) calculates urban concentrations caused by city emissions themselves, the so-called city background concentration. Three versions of the model for describing the dispersion were studied: Box, Gifford Hanna (GH) and a combined form of these two (Box–GH model). Regional background emissions contributing to the urban background concentration were accounted for by using measurements and calculations from a dispersion model on the continental scale. The results of the three UAQAM versions for a number of European cities were compared to measurements of SO₂ and NO _X . The Box–GH model shows better results when compared to the Box model and slightly better results in comparison to the GH model. The Box–GH model has been taken as a starting point for the assessment of urban air quality with UAQAM.