Living Close to Your Neighbors: The Importance of Both Competition and Facilitation in Plant Communities

Recent work has demonstrated that competition and facilitation likely operate jointly in plant communities, but teasing out the relative role of each has proven difficult. Here we address how competition and facilitation vary with seasonal fluctuations in environmental conditions, and how the effects of these fluctuations change with plant ontogeny. We planted three sizes of pine seedlings (Pinus strobus) into an herbaceous diversity experiment and measured pine growth every two weeks for two growing seasons. Both competition and facilitation occurred at different times of year between pines and their neighbors. Facilitation was important for the smallest pines when environmental conditions were severe. This effect decreased as pines got larger. Competition was stronger than facilitation overall and outweighed facilitative effects at annual time scales. Our data suggest that both competition and the counter‐directional effects of facilitation may be more common and more intense than previously considered

SIMULATING OZONE EFFECTS ON FOREST PRODUCTIVITY: INTERACTIONS AMONG LEAF‐, CANOPY‐, AND STAND‐LEVEL PROCESSES

Ozone pollution in the lower atmosphere is known to have adverse effects on forest vegetation, but the degree to which mature forests are impacted has been very difficult to assess directly. In this study, we combined leaf‐level ozone response data from independent ozone fumigation studies with a forest ecosystem model in order simulate the effects of ambient ozone on mature hardwood forests. Reductions in leaf carbon gain were determined as a linear function of ozone flux to the leaf interior, calculated as the product of ozone concentration and leaf stomatal conductance. This relationship was applied to individual canopy layers within the model in order to allow interaction with stand‐ and canopy‐level factors such as light attenuation, leaf morphology, soil water limitations, and vertical ozone gradients. The resulting model was applied to 64 locations across the northeastern United States using ambient ozone data from 1987 to 1992. Predicted declines in annual net primary production ranged from 3 to 16% with greatest reductions in southern portions of the region where ozone levels were highest, and on soils with high water‐holding capacity where drought stress was absent. Reductions in predicted wood growth were slightly greater (3–22%) because wood is a lower carbon allocation priority in the model than leaf and root growth. Interannual variation in predicted ozone effects was small due to concurrent fluctuations in ozone and climate. Periods of high ozone often coincided with hot, dry weather conditions, causing reduced stomatal conductance and ozone uptake. Within‐canopy ozone concentration gradients had little effect on predicted growth reductions because concentrations remained high through upper canopy layers where net carbon assimilation and ozone uptake were greatest. Sensitivity analyses indicate a trade‐off between model sensitivity to available soil water and foliar nitrogen and demonstrate uncertainties regarding several assumptions used in the model. Uncertainties surrounding ozone effects on stomatal function and plant water use efficiency were found to have important implications on current predictions. Field measurements of ozone effects on mature forests will be needed before the accuracy of model predictions can be fully assessed

Mission Revival Jurisprudence: State Courts and Hispanic Water Law Since 1850

In this Article, the author argues that after the United States\u27 annexation of the Southwest, state judges in California, New Mexico, and Texas knowingly distorted the communal nature of applicable Spanish and Mexican water law. While previous scholars have acknowledged that courts misinterpreted municipal and riparian water rights originating in the Southwest\u27s Hispanic period, most historians have attributed the distortion to ignorance rather than design. Using archival sources, the author demonstrates that American judges created an historical fiction of Spanish absolute water control, and intentionally disregarded actual law and custom dictating water apportionment. The resulting doctrines of pueblo water rights and riparian irrigation rights facilitated water monopoly and accumulation by cities and large landowners. This intentional manipulation of Hispanic law bears implications for legal historical debates and contemporary water allocation problems

Gap Filling in the Plant Kingdom---Trait Prediction Using Hierarchical Probabilistic Matrix Factorization

Plant traits are a key to understanding and predicting the adaptation of ecosystems to environmental changes, which motivates the TRY project aiming at constructing a global database for plant traits and becoming a standard resource for the ecological community. Despite its unprecedented coverage, a large percentage of missing data substantially constrains joint trait analysis. Meanwhile, the trait data is characterized by the hierarchical phylogenetic structure of the plant kingdom. While factorization based matrix completion techniques have been widely used to address the missing data problem, traditional matrix factorization methods are unable to leverage the phylogenetic structure. We propose hierarchical probabilistic matrix factorization (HPMF), which effectively uses hierarchical phylogenetic information for trait prediction. We demonstrate HPMF's high accuracy, effectiveness of incorporating hierarchical structure and ability to capture trait correlation through experiments.Comment: Appears in Proceedings of the 29th International Conference on Machine Learning (ICML 2012

Campus & alumni news

Boston University Medicine was published by the Boston University Medical Campus, and presented stories on events and topics of interest to members of the BU Medical Campus community. It followed the discontinued publication Centerscope as Boston University Medicine from 1991-2005, then continued as Campus and Alumni News from 2006-2013 before returning to the title Boston University Medicine from 2014-present

Unconditional Basic Income : Who gets it? Who pays for it? A social Accounting Approach to Distribution

This paper was prepared for the 35th IARIW General Conference [Copenhagen ‐ Denmark, 20‐25/8/2018]Unconditional basic income is not a new topic in political economy, and it gains new momentum as more and more research is being devoted to it. The discussion focusses on the adequacy and effects such a policy measure may entail for a person and his socio‐economic situation, usually. Object of investigation is the individual, and the corresponding theory is of microeconomic descent. In this paper, in contrast, we develop a method of how to assess feasibility and consequences of an unconditional basic income for a modern, open economy, on the macroeconomic level, using concepts and statistics of a Social Accounting Matrix (SAM) as our main tool. A SAM‐based approach can measure, and perhaps model, the impact on the economic activity of a country, and on its economic institutions of new policy measures such as introducing an unconditional basic income. The economic activity of a country is expressed in monetary flows as registered in the National Accounts. So their underlying principles and definitions are adopted. However, the habitual way of putting an economy into a sequence of institutional accounts connecting each institution’s income to the cost, ‐ similar to business accounting ‐ reveals only one, namely the inner‐institutional half of the economic circuit. The other, outer half, namely, how the costs of one institution generate income for another one is better captured by the format of a Social Accounting Matrix. In the paper, the impact of an unconditional basic income is quantified, for macroeconomic aggregates of institutional sectors and socio‐economic groups of households, taking the German and the Portuguese economies as examples. Purpose of the paper is not to argue for, or against, an unconditional basic income, but to offer a scientific tool with which to calculate and assess possibilities and consequences of the proposal, for a national economy as a whole.info:eu-repo/semantics/publishedVersio

Why GPS makes distances bigger than they are

Global Navigation Satellite Systems (GNSS), such as the Global Positioning System (GPS), are among the most important sensors for movement analysis. GPS is widely used to record the trajectories of vehicles, animals and human beings. However, all GPS movement data are affected by both measurement and interpolation error. In this article we show that measurement error causes a systematic bias in distances recorded with a GPS: the distance between two points recorded with a GPS is -- on average -- bigger than the true distance between these points. This systematic `overestimation of distance' becomes relevant if the influence of interpolation error can be neglected, which is the case for movement sampled at high frequencies. We provide a mathematical explanation of this phenomenon and we illustrate that it functionally depends on the autocorrelation of GPS measurement error ($C$). We argue that $C$ can be interpreted as a quality measure for movement data recorded with a GPS. If there is strong autocorrelation any two consecutive position estimates have very similar error. This error cancels out when average speed, distance or direction are calculated along the trajectory. Based on our theoretical findings we introduce a novel approach to determine $C$ in real-world GPS movement data sampled at high frequencies. We apply our approach to a set of pedestrian and a set of car trajectories. We find that the measurement error in the data is strongly spatially and temporally autocorrelated and give a quality estimate of the data. Finally, we want to emphasize that all our findings are not limited to GPS alone. The systematic bias and all its implications are bound to occur in any movement data collected with absolute positioning if interpolation error can be neglected.Comment: 17 pages, 8 figures, submitted to IJGI