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Lisle, IL, United States

Watson G.,Morton Arboretum
Arboriculture and Urban Forestry | Year: 2010

Tree responses to slow-release nitrogen fertilization treatments were limited, but application of fertilizer to the inner half of the root zone improved caliper growth and relative chlorophyll content. Concentrating nitrogen fertilizer applications closer to the base of the tree may be able to take advantage of naturally higher root density, in addition to any further root stimulation resulting from the applied fertilizer treatment. The study site was moderately fertile, as are many urban landscapes where lawn and planting beds surrounding trees are fertilized. The pre-existing level of fertility may have contributed to the limited growth response to the nitrogen applications. © 2010 International Society of Arboriculture.

Stuart-Haentjens E.J.,Virginia Commonwealth University | Curtis P.S.,Ohio State University | Fahey R.T.,Morton Arboretum | Vogel C.S.,University of Michigan | Gough C.M.,Virginia Commonwealth University
Ecology | Year: 2015

The global carbon (C) balance is vulnerable to disturbances that alter terrestrial C storage. Disturbances to forests occur along a continuum of severity, from low-intensity disturbance causing the mortality or defoliation of only a subset of trees to severe stand-replacing disturbance that kills all trees; yet considerable uncertainty remains in how forest production changes across gradients of disturbance intensity. We used a gradient of tree mortality in an upper Great Lakes forest ecosystem to: (1) quantify how aboveground wood net primary production (ANPPw) responds to a range of disturbance severities; and (2) identify mechanisms supporting ANPPw resistance or resilience following moderate disturbance. We found that ANPPw declined nonlinearly with rising disturbance severity, remaining stable until >60% of the total tree basal area senesced. As upper canopy openness increased from disturbance, greater light availability to the subcanopy enhanced the leaf-level photosynthesis and growth of this formerly light-limited canopy stratum, compensating for upper canopy production losses and a reduction in total leaf area index (LAI). As a result, whole-ecosystem production efficiency (ANPPw/LAI) increased with rising disturbance severity, except in plots beyond the disturbance threshold. These findings provide a mechanistic explanation for a nonlinear relationship between ANPPw and disturbance severity, in which the physiological and growth enhancement of undisturbed vegetation is proportional to the level of disturbance until a threshold is exceeded. Our results have important ecological and management implications, demonstrating that in some ecosystems moderate levels of disturbance minimally alter forest production. © 2015 by the Ecological Society of America.

Bowles M.L.,Morton Arboretum | Jones M.D.,Christopher B. Burke Engineering
Ecological Applications | Year: 2013

Understanding temporal effects of fire frequency on plant species diversity and vegetation structure is critical for managing tallgrass prairie (TGP), which occupies a midcontinental longitudinal precipitation and productivity gradient. Eastern TGP has contributed little information toward understanding whether vegetation-fire interactions are uniform or change across this biome. We resampled 34 fire-managed mid- and late-successional ungrazed TGP remnants occurring across a dry to wet-mesic moisture gradient in the Chicago region of Illinois, USA. We compared hypotheses that burning acts either as a stabilizing force or causes change in diversity and structure, depending upon fire frequency and successional stage. Based on western TGP, we expected a unimodal species richness distribution across a cover- productivity gradient, variable functional group responses to fire frequency, and a negative relationship between fire frequency and species richness. Species diversity was unimodal across the cover gradient and was more strongly humpbacked in stands with greater fire frequency. In support of a stabilizing hypothesis, temporal similarity of late-successional vegetation had a logarithmic relationship with increasing fire frequency, while richness and evenness remained stable. Temporal similarity within mid-successional stands was not correlated with fire frequency, while richness increased and evenness decreased over time. Functional group responses to fire frequency were variable. Summer forb richness increased under high fire frequency, while C4 grasses, spring forbs, and nitrogen-fixing species decreased with fire exclusion. On mesic and wet-mesic sites, vegetation structure measured by the ratio of woody to graminoid species was negatively correlated with abundance of forbs and with fire frequency. Our findings that species richness responds unimodally to an environmentalproductivity gradient, and that fire exclusion increases woody vegetation and leads to loss of C4 and N-fixing species, suggest that these processes are uniform across the TGP biome and not affected by its rainfall-productivity gradient. However, increasing fire frequency in eastern TGP appears to increase richness of summer forbs and stabilize late-successional vegetation in the absence of grazing, and these processes may differ across the longitudinal axis of TGP. Managing species diversity in ungrazed eastern TGP may be dependent upon high fire frequency that removes woody vegetation and prevents biomass accumulation. © 2013 by the Ecological Society of America.

Escudero M.,Pablo De Olavide University | Hipp A.L.,Morton Arboretum | Luceno M.,Pablo De Olavide University
Molecular Phylogenetics and Evolution | Year: 2010

Previous work on holocentric chromosomes in the angiosperm genus Carex demonstrates that many of the traditional sections are marked by different ranges of chromosome number, suggesting phylogenetic autocorrelation. It has been hypothesized that shifting constraints on chromosome rearrangements may limit the potential for hybridization among lineages, promoting speciation. In this study, we evaluated alternative evolutionary models to test for such transitions in Carex section Spirostachyae as well as the relative effects of several plausible drivers of intraspecific chromosome diversity. Chromosome number variation in section Spirostachyae shows significant phylogenetic signal, but no evidence of clade-specific shifts in chromosome number distribution. This gradual model of chromosome evolution contrasts with the shifting equilibrium model previously identified in a younger section of the same genus, suggesting that section Spirostachyae may have a more slowly evolving karyotype. Chromosome number variance, on the other hand, exhibits low phylogenetic signal. Average time of coalescence rather than geographic range or chromosome number itself predicts chromosome number variance, demonstrating a previously unreported relationship between population history and cytogenetic variation. © 2010 Elsevier Inc.

Agency: NSF | Branch: Standard Grant | Program: | Phase: MACROSYSTEM BIOLOGY | Award Amount: 59.94K | Year: 2015

Forests of the United States take up and store in plant biomass an enormous amount of carbon emitted from human activities, thereby slowing the accumulation of atmospheric carbon dioxide, a greenhouse gas. Canopy structure, an ecosystem feature that can be broadly characterized using remote sensing technologies, is a well-established determinant of forest carbon storage, with the quantity of canopy leaves a universal predictor of carbon storage that is incorporated into models used to forecast how the Nations dynamic and diverse forested landscape affects climate. Recent work from a limited number of sites shows that the arrangement of leaves within a volume of canopy may be as influential to forest carbon storage as leaf quantity. Results from these studies suggest that leaf quantity and arrangement provide unique, complementary information about the underlying biological controls on forest carbon storage. Thus, coordinated measurements of both leaf quantity and arrangement within the canopies of a diverse array of forests may lead to substantially improved modeled estimates of carbon storage by the Nations forests. In support of this goal, work here uses sites from the National Ecological Observatory Network (NEON) to evaluate whether canopy structural complexity, or the spatial variability in leaf arrangement within a canopy, is a global predictor of forest carbon storage within and across sites varying in physical structure, species composition and diversity, and climate. NEONs standardized methods, systematic sampling design, breadth of data, wide geographic footprint, and built-in gradient of forest physical structure provide an unprecedented opportunity to determine whether carbon storage-canopy structural complexity relationships are broadly generalizable. Enhanced knowledge of the role forest canopy structural complexity plays in carbon storage could transform fundamental understanding of how ecosystem structure affects carbon uptake, leading to more accurate climate models for informing science-based policy. Additionally, the results of this study have broad implications for how forests of the United States are managed in support of greenhouse gas mitigation and will provide new information on how management practices that modify canopy structure broadly affect land carbon sequestration. This project will train undergraduate, graduate, and postdoctoral researchers from a diverse group of academic institutions, and form the basis for a new Biology course at Virginia Commonwealth University taught by the projects postdoctoral associate. The researchers, including students and a postdoctoral associate, will play key roles in an NSF-supported research network that aims to develop broadly applicable remote sensing tools for quantifying forest features relevant to land managers, foresters, policy makers, and ecosystem and climate modelers.

Ecosystem structure-function relationships represent a long-standing research area of ecosystem science; yet, whether relationships between canopy structural complexity (CSC) and net primary production (NPP), characterized at present for only small number of sites, are conserved across eco-climatic boundaries is unknown. Although considerable work has focused on the global importance of leaf area index (LAI) as a predictor or NPP, similar analysis of CSC and NPP spanning eco-climatic domains has not been conducted. As a result, whether CSC is a global predictor of NPP that provides additional mechanistic insight beyond LAI is not known, though site-level analyses, including those conducted by the PIs, suggest CSC may be as important as LAI in explaining variation in NPP. The National Ecological Observatory Network (NEON), with standardized measurements and sampling design, offers an unprecedented platform to transform understanding of forest structure-function relationships on a broad spatial scale. The goals of the project are to use 10 NEON sites containing a total of 176 plots to test whether forest CSC predicts NPP within and across a diverse array of temperate forest types and eco-climatic domains, and to identify underlying mechanisms linking CSC with NPP. Several metrics of CSC will be derived for each NEON site and individual plots within a site using data collected with a portable canopy lidar (PCL). Structural metrics will be related to co-located measurements of wood NPP estimated from the incremental change in woody biomass calculated using tree allometries. An underlying mechanistic basis for global NPP-CSC linkages is hypothesized to include improved resource-use efficiency as CSC increases, which will be examined by correlating CSC with measures of light-use efficiency (wood NPP/fraction of absorbed photosynthetic radiation [fPAR]) and nitrogen-use efficiency (wood NPP/canopy nitrogen mass). Within- and among-site variation in wood NPP as a function of CSC, leaf area index (LAI), and canopy nitrogen mass will be examined using a multi-model inference framework. The PIs hypothesize that model rankings will show variation in wood NPP within and among sites is best explained by multivariate models that include CSC in addition to LAI and canopy nitrogen mass parameters because each canopy feature represents complementary but not redundant mechanistic information. Using NEON sites to advance understanding of how and why CSC affects forest NPP across a broad spatial dimension could transform mechanistic understanding of ecosystem structure-carbon cycling relationships, and greatly improve carbon cycling models and remote sensing applications, while providing a crucial linkage between the two. Broader impacts stem from three separate areas: enhanced participation in a funded NSF Research Coordination Network (RCN), postdoctoral training and career development, and undergraduate research training. The PIs will advise and co/author resulting project publications and presentations with a postdoctoral and student researchers, with the postdoc serving as instructor of record for a 1-credit graduate topics course on ecosystem structure-function relationships at Virginia Commowealth University.

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