1,361 research outputs found
Light access and leaf trait variation within and among tree species across diverse mixtures within a common garden
No full textLeaf trait measurements alongside estimates of light access for 2615 leaves from 12 common temperate-boreal tree species grown in diverse mixtures within a common garden.This dataset includes trait measurements for 2615 leaves of common temperate-boreal tree species alongside estimates of their light access. Trait values affect how plants function, with consequences that propagate through scales of ecological organization to affect ecosystem function. However, the pathway connecting trait expression to ecosystem function is complicated by feedbacks: trait expression may vary within species in response to community diversity, and trait expression also determines a community’s functional diversity. In this study, we quantify the extent to which light access – which past studies suggest affects trait expression and differs as a result of interactions among plants – differs consistently with community diversity and explains intraspecific trait variation in trees. In a common garden, trees of five angiosperm and seven gymnosperm species were planted to form 37 communities ranging widely in species and functional diversity whereby confounding environmental variation was minimized. We sampled leaves of each species to characterize intraspecific variation within crowns, among trees within communities, and among communities in three traits – leaf size, specific leaf area and nitrogen concentration – and estimated each leaf’s access to light.The University of Minnesota (College of Biological Sciences, College of Food and Natural Resources, Institute on the Environment, and Graduate School), the Canada Research Chair program, and an International Fulbright Science and Technology Award financially supported the collection of the data.Williams, Laura J; Cavender-Bares, Jeannine; Reich, Peter B; Paquette, Alain; Messier, Christian. (2019). Light access and leaf trait variation within and among tree species across diverse mixtures within a common garden. Retrieved from the University Digital Conservancy, https://doi.org/10.13020/jt9r-tf03
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Rotational Velocities in NGC 6475 (Messier 7)
No full textFifty-five spectra at 39 Å/mm are used to determine rotational velocities for 25 stars in the galactic cluster Messier 7 (NGC 675). Compared to field stars, the brighter (-1.4 < Mᵥ < +1.0) cluster stars have very low rotational velocities ( ≈ 91 km /sec), whereas the fainter ( +1.2 < Mᵥ < +2.3) stars have a rather high of about 196 km /sec. The sample is probably incomplete at the fainter magnitude ranges. The frequency of spectroscopic binaries among the earlier type stars is believed to be high, but the of the brighter group remains low even after removal of known binaries. Three Ap or composite stars are found. The rotational velocity characteristics of Messier 7 are compared with those of other clusters. Low for brighter cluster stars is not a unique phenomenon.Digitized from bound copy held at the Parker Library, Steward Observatory
Data and code for remote spectral detection of biodiversity effects on forest biomass
No full textQuantifying how biodiversity affects ecosystem functions through time over large spatial extents is needed to meet global biodiversity goals yet is infeasible with field-based approaches alone. Imaging spectroscopy is a tool with potential to help address this challenge. In this study, we demonstrated a spectral approach to assess biodiversity effects in young forests that provides insight into its underlying drivers and could potentially be applied at large spatial scales. Using airborne imaging (NASA AVIRIS-NG) of a tree diversity experiment (IDENT-Cloquet in Cloquet, MN), spectral differences among plots enabled us to quantify net biodiversity effects on stem biomass and canopy nitrogen. In this repository, we present the spectral data and field data along with spectral model coefficients and example code for fitting and applying spectral models to calculate spectral biodiversity effects.The project was funded by a National Science Foundation and National Aeronautic and Space Administration grant awarded to Jeannine Cavender-Bares (DEB-1342872) and Philip A. Townsend (DEB-1342778) through the Dimensions of Biodiversity program.Williams, Laura J; Cavender-Bares, Jeannine; Townsend, Philip A; Couture, John J; Wang, Zhihui; Stefanski, Artur; Messier, Christian; Reich, Peter B. (2020). Data and code for remote spectral detection of biodiversity effects on forest biomass. Retrieved from the University Digital Conservancy, https://doi.org/10.13020/s7pf-am91
Is Messier 74 a barred spiral galaxy?
No full textWe have obtained ground-based I, J and K
band images of the spiral
galaxy, Messier 74 (NGC 628).
This galaxy has been shown to possess a circumnuclear ring
of star formation from both near-infrared spectroscopy of CO absorption and
sub-millimetre imaging of CO emission. Circumnuclear rings of star formation
are believed to exist only as a result of a bar potential. In this paper we
show evidence for a weak oval distortion in the centre of M 74. We use the
results of Combes & Gerin (1985) to suggest that this weak oval potential
is responsible for the circumnuclear ring of star formation observed in M 74
Cause and effects of the massive star formation in Messier 8 East
No full textContext. Messier 8 (M8), one of the brightest H I
Sugar maple (Acer saccharum Marsh.) growth is influenced by close conspecifics and skid trail proximity following selection harvest
No full textIn this study, we quantified the effects of local neighbourhood competition, light availability, and proximity to skid trails on the growth of sugar maple (Acer saccharum Marsh.) trees following selection harvest. We hypothesized that growth would increase with decreasing competition and increasing light availability, but that proximity to skid trails would negatively affect growth. A total of 300 sugar maples were sampled ∼10 years after selection harvesting in 18 stands in Témiscamingue (Québec, Canada). Detailed tree and skid trail maps were obtained in one 0.4 ha plot per stand. Square-root transformed radial growth data were fitted to a linear mixed model that included tree diameter, crown position, a neighbourhood competition index, light availability (estimated using the SORTIE light model), and distance to the nearest skid trail as explanatory variables. We considered various distance-dependent or -independent indices based on neighbourhood radii ranging from 6 to 12 m. The competition index that provided the best fit to the data was a distance-dependent index computed in a 6 m search radius, but a distance-independent version of the competition index provided an almost equivalent fit to data. Models corresponding to all combinations of main effects were fit to data using maximum likelihood, and weighted averages of parameter estimates were obtained using multimodel inference. All predictors had an influence on growth, with the exception of light. Radial growth decreased with increasing tree diameter, level of competition and proximity to skid trails, and varied among crown positions with trees in suppressed and intermediate positions having lower growth rates than codominants and dominants. Our results indicate that in selection managed stands, the radial growth of sugar maple trees depends on competition from close (≤6 m) conspecific neighbours, and is still affected by proximity to skid trails ∼10 years after harvesting. Such results underscore the importance of minimizing the extent of skid trail networks by careful pre-harvest planning of trail layout. We also conclude that the impact of heterogeneity among individual-tree neighbourhoods, such as those resulting from alternative spatial patterns of harvest, can usefully be integrated into models of post-harvest tree growth
Observational study of hydrocarbons in the bright photodissociation region of Messier 8
No full textAims. Hydrocarbons are ubiquitous in the interstellar medium, but their formation is still not well understood, depending on the physical environment in which they are found. Messier 8 (M8) is host to one of the brightest H I
Reply to comment by Messier et al. on “Present-day expansion of American beech in northeastern hardwood forests: Does soil base status matter?”Appears in Can. J. For. Res. <b>39</b>: 2273–2282 (2009).
No full text We respond to the comment by Messier et al. (2011. Can. J. For. Res. 41: 649–653) on our recent paper questioning the possible influence of the base status of soils in the present-day expansion of American beech ( Fagus grandifolia Ehrh.) in Quebec (2009. Can. J. For. Res. 39: 2273–2282). From our observations, as well as from a large body of scientific evidence reporting on the high sensitivity of sugar maple ( Acer saccharum Marsh.) to the acid–base status of soils, we hypothesized that soil base cation depletion, caused in part by atmospheric deposition, is among the main factors involved in the present-day expansion of American beech over large areas in Quebec. Clearly, we suggested in our paper that acid deposition might act with other factors to explain the expansion of American beech. In this context, our conclusions are far from any oversimplified explanation, as stated by Messier et al., but rather, they point out a level of complexity above the one currently discussed. </jats:p
Continuum model for the growth of interfaces
No full textA continuum model is presented for studying various growth processes. One of the model equations is used to define a growing interface with an arbitrary topology and captures the intrinsic dynamics of the aggregate with surface diffusion incorporated in a natural manner. With an appropriate local growth mechanism, this model represents a continuum version of the Eden growth model. The introduction of another field describing the dynamics of the vapor enables the modeling of phenomena ranging from ballistic deposition to diffusion-limited aggregation (DLA) within the framework of the same equations. Our equations capture nonlocal effects, such as shadowing or screening in a local. way, and permit the monitoring of the interior structure of the growing film. Our results are benchmarked against those of experiments on sputter deposited films. Simple modifications of the model lead to patterns that are different from standard DLA structures but similar to those observed in electrochemical deposition. We also examine models that use the no-overhang approximation in the description of columnar morphology observed in thin films and discuss their validity in comparison with our model
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