Showing papers by "Daniel C. Laughlin published in 2012"

A predictive model of community assembly that incorporates intraspecific trait variation.

Abstract: Community assembly involves two antagonistic processes that select functional traits in opposite directions. Environmental filtering tends to increase the functional similarity of species within communities leading to trait convergence, whereas competition tends to limit the functional similarity of species within communities leading to trait divergence. Here, we introduce a new hierarchical Bayesian model that incorporates intraspecific trait variation into a predictive framework to unify classic coexistence theory and evolutionary biology with recent trait-based approaches. Model predictions exhibited a significant positive correlation (r = 0.66) with observed relative abundances along a 10 °C gradient in mean annual temperature. The model predicted the correct dominant species in half of the plots, and accurately reproduced species' temperature optimums. The framework is generalizable to any ecosystem as it can accommodate any species pool, any set of functional traits and multiple environmental gradients, and it eliminates some of the criticisms associated with recent trait-based community assembly models.

Woody debris and tree regeneration dynamics following severe wildfires in Arizona ponderosa pine forests

Abstract: Severe forest fires worldwide leave behind large quantities of dead woody debris and regenerating trees that can affect future ecosystem trajectories. We studied a chronosequence of severe fires in...

Topical gradients in plant ecology

Abstract: Plant ecology spans multiple levels of biological organization and spatio-temporal scales, and over four dozen plant ecology textbooks have been published since Warming’s (1895) ‘Oecology of Plants.’ With increasing emphasis on specialization, students and teachers can feel paralyzed by the vast literature, and as such may lack an adequate appreciation of the history of the field. The objective of this study was to derive a comprehensive set of topics that are covered in plant ecology textbooks, and to ask (1) what are the most important topical gradients among textbooks, and (2) has the emphasis of topics changed over time? The NMS ordination determined that the first gradient represented a clear contrast in emphasis on physiological ecology versus community ecology. The second gradient represented a contrast in emphasis on abiotic environmental factors versus biotic factors. Negative interactions, growth, demography, gas exchange, mineral nutrition, stress, diversity, disturbance, herbivory, paleoecology, ecosystem ecology, pollution, and global change have increased in emphasis over time. The increasing reliance on data and the number of authors per textbook illustrates how the discipline has matured into a rigorous quantitative science that requires a diversity of specializations. These results can be used to inform the development of curricula within a single course or across several years of study, and to assist the development of new and revised textbooks. Plant ecologists need to be familiar with this core set of topics in addition to becoming an expert in a few of them.

PART OF A HIGHLIGHT ON TRAITS WITH ECOLOGICAL FUNCTIONS Seedlings of temperate rainforest conifer and angiosperm trees differ in leaf area display

Abstract: † Background and Aims The contemporary relegation of conifers mainly to cold or infertile sites has been ascribed to low competitive ability, as a result of the hydraulic inefficiency of tracheids and their seedlings’ initial dependence on small foliage areas. Here it is hypothesized that, in temperate rainforests, the larger leaves of angiosperms also reduce self-shading and thus enable display of larger effective foliage areas than the numerous small leaves of conifers. † Methods This hypothesis was tested using 3-D modelling of plant architecture and structural equation modelling to compare self-shading and light interception potential of seedlings of six conifers and 12 angiosperm trees from temperate rainforests. The ratio of displayed leaf area to plant mass (LARd) was used to indicate plant light interception potential: LARd is the product of specific leaf area, leaf mass fraction, self-shading and leaf angle. † Results Angiosperm seedlings self-shaded less than conifers, mainly because of differences in leaf number (more than leaf size), and on average their LARd was about twice that of conifers. Although specific leaf area was the most pervasive influence on LARd, differences in self-shading also significantly influenced LARd of large seedlings. † Conclusions The ability to deploy foliage in relatively few, large leaves is advantageous in minimizing selfshading and enhancing seedling light interception potential per unit of plant biomass. This study adds significantly to evidence that vegetative traits may be at least as important as reproductive innovations in explaining the success of angiosperms in productive environments where vegetation is structured by light competition.

Ecology of Rusby's Milkvetch ( Astragalus rusbyi), a Rare Endemic of Northern Arizona Ponderosa Pine Forests

Abstract: Rusby's� milkvetch� ( Astragalus rusbyi Greene) is endemic to basaltic soils northwest and west of Flagstaff, Arizona. Recent interest in this species is due in part to its addition to the U.S. Forest Service Region 3 sensitive spe- cies list in 1999 and its occurrence in ecological restoration projects and proposed fuels reduction projects that in- volve tree thinning and prescribed burning. Some of its habitat has been subjected to large wildfires over the last few decades, and other areas have undergone ecological restoration treatments, while much of its range in ponderosa pine forest is slated to undergo such treatments in the near future. In a ponderosa pine restoration study area northwest of Flagstaff, A. rusbyi was an indicator species of remnant grass patches and increased following tree thinning and pre- scribed burning. However, in an area less than 3 km away, there appeared to be no relationship to restoration treat- ments, trees per ha, pine basal area, or canopy cover, but A. rusbyi did appear to be sensitive to an extreme drought event in 2002 and may have remained dormant in that year, a pattern that has been observed in other rare Astragalus species. A. rusbyi has a foliar nitrogen content of 4.4% and a foliar C:N mass ratio of 11. It is classified as a competi- tive ruderal species, meaning it is able to compete well with other understory species, but is not very tolerant of stresses, such as deep shade. We currently do not have a thorough understanding of the ecology of this species, or the effects of ecological restoration or fuels reduction treatments. In this paper we will discuss ecology of other members of the genus Astragalus and explore the relationships of A. rusbyi to moisture, vegetation treatments and overstory mortality.