Information Ranking and Power Laws on Trees

We study the situations when the solution to a weighted stochastic recursion has a power law tail. To this end, we develop two complementary approaches, the first one extends Goldie's (1991) implicit renewal theorem to cover recursions on trees; and the second one is based on a direct sample path large deviations analysis of weighted recursive random sums. We believe that these methods may be of independent interest in the analysis of more general weighted branching processes as well as in the analysis of algorithms

Effect of different irrigation volumes during fruit development on quality of virgin olive oil of cv. Frantoio

An experiment was carried out in a high-density olive (Olea europaea L. cv. Frantoio) orchard to determine the effect of different irrigation regimes (full, deficit, complementary) on virgin olive oil (VOO) quality over three consecutive years. Irrigation had negligible effects on free acidity, peroxide value, and fatty acid composition of VOO, but strongly influenced its phenolic concentration. Trees with high water status yielded oils with lower concentrations of total phenols and O-diphenols with respect to oils from severely stressed trees. The concentrations of secoiridoids, like the dialdehydic form of decarboxymethyl elenolic acid linked to (3,4-dihydroxyphenyl)ethanol (3,4-DHPEA-EDA), the isomer of the oleuropein aglycon (3,4-DHPEA-EA) and the dialdehydic form of decarboxymethyl elenolic acid linked to (p-hydroxyphenyl) ethanol (p-HPEA-EDA), were lower in fully-irrigated trees than in trees under deficit irrigation or those that received complementary irrigation only. The concentrations of lignans (+)-1-acetoxipinoresinol and (+)-1-pinoresinol were unaffected by the irrigation regime. Volatile compounds, evaluated on the VOO head space, seemed to be more consistently influenced by the year rather than soil water availability

On-site and off-Site long-term economic impacts of soil fertility management practices: The case of maize-based cropping systems in Kenya

"This article analyzes the on-site and off-site economic impacts of various sustainable land management (SLM) practices in Kenya. Long-term trial data are used to establish the relationship between SLM practices and maize yield. The analysis of on-site effects focuses on the profitability of maize production at the farm level, while the examined off-site effects include carbon sequestration and siltation from maize farms, which increase the cost of potable water production. The major contribution of this study is the use of long-term experimental data to estimate the impacts of land management practices on crop yield and consider their off-site benefits and costs. The results of this study show that soil and water conservation (SWC) structures reinforced with leguminous plants are more profitable when the plants are used as fodder, as opposed to situations in which only SWC structures are used. SWC structures reinforced with vegetation had lower maintenance costs, whereas those that were not reinforced with leguminous trees were not profitable over the long-term period. These results suggest that complementary and multipurpose SWC practices are more likely to be adopted compared to non-complementary and/or single-purpose practices. Thus, SWC practices should be promoted as a package of complementary technologies. If it is not feasible to promote a mix of complementary enterprises, high value crops are likely to make SLM practices more profitable. In areas where SLM practices are not profitable, promotion of alternative livelihoods is necessary. Adoption of SLM also provides global environmental services worth 10% of the net present value of the SLM practices over the 50-year period addressed in the present study Finally, the results of this analysis suggest that farmers who offer significant environmental services should be compensated for their efforts." from Author's AbstractAgroforestry, Land degradation, Soil erosion, Sustainable land management, Land management, Economic impacts, maize,

Sap flow and water transfer in the Garonne river riparian woodland, France : first results on poplar and willow

This work is the first attempt at using Granier sap sensors on Populus nigra, Populus x euramericana cv I45/51 and Salix alba for the monitoring of sap flows in an active floodplain over two consecutive years. The main characteristic of these diffuse porous trees is their capacity to use several tree rings for xylem sap transfer. Results showed that the sap flux densities remained homogeneous on the external 4 cm of the trunk, then decreased with depth. For young trees, the active sapwood can represent half of the trunk. Results indicated that in the same environment and at the same age, daily differences existed between the two major native riparian tree species, the black poplar and the white willow. Their maximal sap flux density (2.6-3.6 dm 3 dm -2 h -1) was similar to other fast growing trees. The influence of age was the third important screened factor. Sap flow measurements over several months indicated that water uptake was variable throughout the season, depending on water availability, and was more pronounced for older trees. The sap flux densities for the planted poplar (I45/51) ranged from 2.2-2.6 dm 3 dm -2 h -1 (about 90 dm 3 day -1) in the wetter spring conditions and dropped to 1.6-1.7 dm 3 dm -2 h -1 (about 60 dm 3 day -1) in less favourable conditions. Under the worst conditions, e.g., the especially long drought in the summer of 1998, these values dropped to 1.0-1.2 (about 40 dm 3 day -1), and even to 0.35 dm 3 dm -2 h -1 (about 12 dm 3 day -1) for a few days. Complementary long-term studies are needed to better understand the complex sap flow changes and to be able to relate them to significant environmental factors. Priority should be given to the long-term monitoring of sap flows at different depths for a correct estimation of actual daily water uptakes by riparian softwood trees

The Application of Chordal Graphs to Inferring Phylogenetic Trees of Languages

Phylogenetic methods are used to build evolutionary trees of languages given character data that may include lexical, phonological, and morphological information. Such data rarely admits a perfect phylogeny. We explore the use of the more permissive conservative Dollo phylogeny as an alternative or complementary approach. We propose a heuristic search algorithm based on the notion of chordal graphs. We test this approach by generating phylogenetic trees from three datasets, and comparing them to those produced by other researchers

Stronger diversity effects with increased environmental stress : a study of multitrophic interactions between oak, powdery mildew and ladybirds

Recent research has suggested that increasing neighbourhood tree species diversity may mitigate the impact of pests or pathogens by supporting the activities of their natural enemies and/or reducing the density of available hosts. In this study, we attempted to assess these mechanisms in a multitrophic study system of young oak (Quercus), oak powdery mildew (PM, caused by Erysiphe spp.) and a mycophagous ladybird (Psyllobora vigintiduo-punctata). We assessed ladybird mycophagy on oak PM in function of different neighbourhood tree species compositions. We also evaluated whether these species interactions were modulated by environmental conditions as suggested by the Stress Gradient Hypothesis. We adopted a complementary approach of a field experiment where we monitored oak saplings subjected to a reduced rainfall gradient in a young planted forest consisting of different tree species mixtures, as well as a lab experiment where we independently evaluated the effect of different watering treatments on PM infections and ladybird mycophagy. In the field experiment, we found effects of neighbourhood tree species richness on ladybird mycophagy becoming more positive as the target trees received less water. This effect was only found as weather conditions grew drier. In the lab experiment, we found a preference of ladybirds to graze on infected leaves from trees that received less water. We discuss potential mechanisms that might explain this preference, such as emissions of volatile leaf chemicals. Our results are in line with the expectations of the Natural Enemies Hypothesis and support the hypothesis that biodiversity effects become stronger with increased environmental stress

Almost all trees have quantum symmetry

From the work of Erdős and Rényi from 1963, it is known that almost all graphs have no symmetry. In 2017, Lupini, Mančinska, and Roberson proved a quantum counterpart: Almost all graphs have no quantum symmetry. Here, the notion of quantum symmetry is phrased in terms of Banica’s definition of quantum automorphism groups of finite graphs from 2005, in the framework of Woronowicz’s compact quantum groups. Now, Erdős and Rényi also proved a complementary result in 1963: Almost all trees do have symmetry. The crucial point is the almost sure existence of a cherry in a tree. But even more is true: We almost surely have two cherries in a tree—and we derive that almost all trees have quantum symmetry. We give an explicit proof of this quantum counterpart of Erdős and Rényi’s result on trees