PATTERN-PROCESS LINKAGES IN FORESTED ECOSYSTEMS

Ecological pattern-process linkages have been called the Rosetta’s stone of ecology. The pattern-process linkage is a feedback whereby ecosystem processes drive structural patterns, and vegetation patterns also strongly influence vital ecosystem processes. The role of competition and gap dynamics in creating spatial heterogeneity was assessed in Sitka-spruce western hemlock forests. Results indicated that despite low species richness, these forests are structurally diverse with the spatial imprint of competition obscured by gap dynamics through stand development. The influence of forest structural and spatial heterogeneity on snow accumulation and persistence was examined in a mixed-conifer forest. Tree neighborhood type (open, clump, individual) and winter leaf habit (deciduousness) had a significant effect on snow processes, likely driven by interception and the spatial variation of longwave radiation. Random forest models relied on forest canopy metrics associated with the amount, location, and type of forest vegetation to predicting peak snow water equivalent (SWE) and snow disappearance. Variation of peak snow density was not explained with canopy or terrain metrics. Models parameterized with ground and LiDAR based canopy metrics performed equally well for SWE and snow disappearance. The results of this research provide managers with new tools for objectively quantifying forest heterogeneity, informing treatments that seek to create structural and spatial complexity, and a method for estimating the distribution of snow accumulation and melt in complex forests. These studies provide a clear links between forest spatial patterns and important ecosystem processes including competition, gap dynamics, and snow accumulation and disappearance

SMALL SCALE VARIABILITY IN SNOW ACCUMULATION AND ABLATION UNDER A HETEROGENEOUS MIXED-CONIFER CANOPY

The spatial patterns of snow accumulation and melt in forested watersheds directly control runoff generation processes and the annual quantity and quality of available water to downstream receiving waters. In the western U.S. nearly three quarters of the annual water input into the hydrologic cycle comes from snow accumulation and melt in forested watersheds. This provision of water is one of the most important forest ecosystem services and is necessary for ecological, economic and social health. Despite our understanding of the coupling of forests and watersheds, the relationship between forest spatial patterns and snow hydrology is poorly understood. Forest canopies exhibit heterogeneity manifested as a mosaic of differing species, spatial arrangements, and canopy densities that differentially intercept incoming precipitation, alter wind patterns, and absorb, trap or reflect radiation; controlling the processes of snow accumulation and ablation. Vegetation patterns have been used as surrogates for processes where we expect that spatially recognizable structures give rise to specific ecological processes and vice versa. We investigated how spatial patterns of snow depth, density, snow water equivalent (SWE), and snow disappearance date (SDD) varied within stands of heterogeneous canopy structure. We collected 780 empirical measurements of snow depth, density, and SWE at peak accumulation on two fully georeferenced, mixed-conifer plots at Lubrecht Experimental Forest in western Montana. Throughout the 49 day melt season, we monitored SDD, snow depth, and SWE every third day with 4900 samples per campaign. In 2014, snow depth, density and SWE ranged from 0.0-67.31 cm, 5.43-49.76%, and 0.75-17.90 cm respectively. A canopy competition index ranged from 0.0-86.8 with non-forested areas averaging 11.5 cm SWE, melting around day 41 compared to mature dense canopy with average SWE of 5.1 cm and a SDD around day 9. This preliminary work suggests a strong linkage between canopy structure and accumulation and snowmelt processes. In the future we seek to link canopy patterns and the specific physical mechanisms that lead to differential snow dynamics in forested landscapes. This understanding is essential for improving process-based models and tools for forest managers to optimize forest water resources in a changing climate

Enhanced water loss during the Mars Year 34 C storm

We investigate the evolving water vapour and hydrogen distribution in the martian atmosphere and their associated effect on hydrogen escape during the Mars Year (MY) 34 C storm (a late winter regional dust storm that occurs every Mars year). Improved calculation of the integrated loss of water throughout Mars‘ history (that is currently not well constrained) is possible throughtracking the water loss through time from global simulations constrained by available observations. Through constraining water loss we can provide better insight into planetary evolution. The Open University modelling group global circulation model is combined with retrievals from the ExoMars Trace Gas Orbiter (temperature and water vapour profiles from the Atmospheric Chemistry Suite and water vapour profiles from the Nadir and Occultation for Mars Discovery instrument) and the Mars Climate Sounder (temperature profiles and dust column) on the Mars Reconnaissance Orbiter. This multi-spacecraft assimilation provides the best possible replication of the evolving lower atmosphere. The unusually intense dusty conditions during the MY 34 C storm led to increased amounts of water vapour and hydrogen above 80 km compared to a more typical C storm, which had an important impact on the amount of water escaping Mars’ atmosphere. Modelled hydrogen escape rates during the MY 34 C storm peaked at around 1.4 x 109 cm-2 s-1, three times the escape rate calculated in the MY 30 C storm scenario and equivalent to those found during previous global-scale dust storms. The weak MY 30 C storm and strong MY 34 C storm can be seen as a bracketing pair of events and therefore the calculated escape rates represent the interannual variabiity expected during C storm events. Our results indicate water loss during the C storm event each year is highly variable, and must be considered when calculating the integrated loss of water through Mars’ history

Martian Atmospheric Hydrogen and Deuterium: Seasonal Changes and Paradigm for Escape to Space

Mars\u27 water history is fundamental to understanding Earth-like planet evolution. Water escapes to space as atoms, and hydrogen atoms escape faster than deuterium giving an increase in the residual D/H ratio. The present ratio reflects the total water Mars has lost. Observations with the Mars Atmosphere and Volatile Evolution (MAVEN) and Hubble Space Telescope (HST) spacecraft provide atomic densities and escape rates for H and D. Large increases near perihelion observed each martian year are consistent with a strong upwelling of water vapor. Short-term changes require processes in addition to thermal escape, likely from atmospheric dynamics and superthermal atoms. Including escape from hot atoms, both H and D escape rapidly, and the escape fluxes are limited by resupply from the lower atmosphere. In this paradigm for the escape of water, the D/H ratio of the escaping atoms and the enhancement in water are determined by upwelling water vapor and atmospheric dynamics rather than by the specific details of atomic escape

Genome-wide identification and phenotypic characterization of seizure-associated copy number variations in 741,075 individuals

Copy number variants (CNV) are established risk factors for neurodevelopmental disorders with seizures or epilepsy. With the hypothesis that seizure disorders share genetic risk factors, we pooled CNV data from 10,590 individuals with seizure disorders, 16,109 individuals with clinically validated epilepsy, and 492,324 population controls and identified 25 genome-wide significant loci, 22 of which are novel for seizure disorders, such as deletions at 1p36.33, 1q44, 2p21-p16.3, 3q29, 8p23.3-p23.2, 9p24.3, 10q26.3, 15q11.2, 15q12-q13.1, 16p12.2, 17q21.31, duplications at 2q13, 9q34.3, 16p13.3, 17q12, 19p13.3, 20q13.33, and reciprocal CNVs at 16p11.2, and 22q11.21. Using genetic data from additional 248,751 individuals with 23 neuropsychiatric phenotypes, we explored the pleiotropy of these 25 loci. Finally, in a subset of individuals with epilepsy and detailed clinical data available, we performed phenome-wide association analyses between individual CNVs and clinical annotations categorized through the Human Phenotype Ontology (HPO). For six CNVs, we identified 19 significant associations with specific HPO terms and generated, for all CNVs, phenotype signatures across 17 clinical categories relevant for epileptologists. This is the most comprehensive investigation of CNVs in epilepsy and related seizure disorders, with potential implications for clinical practice

Tree spatial patterns modulate peak snow accumulation and snow disappearance

Forests and snow covered regions frequently co-occur across the northern hemisphere. In these environments, forests are structurally and spatially complex mosaics of tree neighborhoods that are intrinsically linked to ecosystem functions. Tree and canopy structures influence snow accumulation and disappearance processes through interception and radiation attenuation. However, it is unclear to what extent if spatial heterogeneity within the forest canopy induces heterogeneity in snow accumulation and persistence. Using a forest-based approach, we identified and tested the differential effects of within-forest neighborhoods on snow processes. Neighborhood types included individual ponderosa pine (Pinus ponderosa), Douglas-fir (Pseudotsuga menziesii) and western larch (Larix occidentals) trees, tree clumps, openings, and regeneration patches. Neighborhoods were identified within a mixed-conifer forest and paired with intensive measurements of snow accumulation (density and depth) and persistence. Overall, neighborhood type and year had a significant effect on accumulation and snow disappearance. Openings were significantly different from clumps and individuals, always accumulating more snow. Openings retained snow significantly later than clumps but were not significantly different from individuals. Within the individual tree neighborhood, a nested species effect indicated no differences in accumulation but significant differences in disappearance between deciduous and evergreen conifers, with snow persisting longer beneath deciduous western larch. Our results suggest that canopy interception is the primary mechanism driving the accumulation phase, while snow disappearance patterns are a consequence of increased longwave radiation. Reducing canopy interception and longwave radiation by creating widely spaced single trees and small openings will increase snow depth and duration and thus water yield, while maintaining a heterogeneous canopy structure that includes tree clumps can be used to meet multiple objectives including diverse wildlife habitat, timing of green-up, and plant biodiversity

Reference conditions and historical changes in an unharvested ponderosa pine stand: Implications for forest health

Reference conditions are a critical component of ecological restoration and provide a point of comparison for the current degree of deviation from an ecosystem's evolutionary trajectory. In Arizona, the body of knowledge on reference conditions for stand density, age distribution, and spatial patterns is heavily weighted towards moderately productive basalt derived soils on the Coconino National Forest. These conditions may represent the average conditions for frequent fire ponderosa pine forests, but do not adequately capture the full range of variation. With landscape scale restoration treatments proposed across the Southwestern ponderosa pine type, establishing reference conditions that include spatial patterns for a variety of site conditions is a necessary step to assure that treatments are tailored to each site's reference conditions to avoid artificially homogenizing the landscape with a one-size-fits-all approach. Spatial pattern analyses have allowed researchers to link spatially-dependent process such as regeneration, competition, and mortality to structural characteristics; however, the mechanism(s) that control these processes are complex and may never be fully understood. The study of spatial patterns may also allow us to predict stand development following restoration treatments. Using an unharvested, old-growth ponderosa pine stand on a highly productive site with sedimentary derived soils; a forest reconstruction model, univariate and bivariate Ripley's K functions, and regression analysis we determined structural and spatial reference conditions that can be used to guide restoration treatments. We also compared contemporary (2010) and reconstructed (1883) stand structure and spatial patterns to evaluate historical changes. We found a reconstructed (1883) tree density of 88.0 trees ha−1, basal area of 7.97 m2 ha−1, and a quadratic mean diameter of 33.95 cm at breast height. The reference spatial pattern of ponderosa pine was significantly aggregated from 1–2 m and randomly distributed at distances greater than 2 m. Crown radius and interconnectivity projections indicated a few significant "patches" containing 2–3 trees within 1–2 m. A comparison of different sampling scales, 0.5, 1.0, 2.0, and 3.0 ha, indicated that a 0.5 ha plot was adequate to capture stand level spatial patterns. Compared to the reconstructed stand conditions, the contemporary stand had substantially greater tree densities (614 trees ha−1 ) than prior to 1883 and is aggregated up to 50 m. Bivariate spatial analysis indicated early recruitment patterns following fire exclusion were attracted to live presettlement trees from 1–4 m and independent at distances greater than 4 m. We conclude that these results are a product of a variety of factors including soil parent material, climatic variables and decreased dominance of mechanisms that drive aggregation. Using forest health evaluation criteria, we also determined that current stand conditions at Barney Spring are unhealthy and require intervention. To restore a healthy, sustainable, self-regulating system we recommend a complete restoration to include structural manipulations for fuels reduction and to mimic the random reference spatial pattern aided by the reintroduction of frequent, low intensity fire

Spatial aspects of structural complexity in Sitka spruce-western hemlock forests, including evaluation of a new canopy gap delineation method

Structural complexity in long-lived forests where stand-replacing disturbances are rare is thought to emerge from chronic small scale disturbances and competitive interactions between trees. We analyzed tree size distributions, tree spatial patterns, and canopy gap attributes in ten, 1.42 ha stem mapped plots in old-growth Sitka spruce-western hemlock forests in southeast Alaska. Most plots had rotated sigmoid or reverse J-shaped diameter distributions. Overstory tree patterns were uniform at short distance (The accepted manuscript in pdf format is listed with the files at the bottom of this page. The presentation of the authors' names and (or) special characters in the title of the manuscript may differ slightly between what is listed on this page and what is listed in the pdf file of the accepted manuscript; that in the pdf file of the accepted manuscript is what was submitted by the author

Martian atmospheric hydrogen and deuterium: Seasonal changes and paradigm for escape to space

International audienceMars’ water history is fundamental to understanding Earth-like planet evolution. Water escapes to space as atoms, and hydrogen atoms escape faster than deuterium giving an increase in the residual D/H ratio. The present ratio reflects the total water Mars has lost. Observations with the Mars Atmosphere and Volatile Evolution (MAVEN) and Hubble Space Telescope (HST) spacecraft provide atomic densities and escape rates for H and D. Large increases near perihelion observed each martian year are consistent with a strong upwelling of water vapor. Short-term changes require processes in addition to thermal escape, likely from atmospheric dynamics and superthermal atoms. Including escape from hot atoms, both H and D escape rapidly, and the escape fluxes are limited by resupply from the lower atmosphere. In this paradigm for the escape of water, the D/H ratio of the escaping atoms and the enhancement in water are determined by upwelling water vapor and atmospheric dynamics rather than by the specific details of atomic escape