Strong microsite control of seedling recruitment in tundra

The inclusion of environmental variation in studies of recruitment is a prerequisite for realistic predictions of the responses of vegetation to a changing environment. We investigated how seedling recruitment is affected by seed availability and microsite quality along a steep environmental gradient in dry tundra. A survey of natural seed rain and seedling density in vegetation was combined with observations of the establishment of 14 species after sowing into intact or disturbed vegetation. Although seed rain density was closely correlated with natural seedling establishment, the experimental seed addition showed that the microsite environment was even more important. For all species, seedling emergence peaked at the productive end of the gradient, irrespective of the adult niches realized. Disturbance promoted recruitment at all positions along the environmental gradient, not just at high productivity. Early seedling emergence constituted the main temporal bottleneck in recruitment for all species. Surprisingly, winter mortality was highest at what appeared to be the most benign end of the gradient. The results highlight that seedling recruitment patterns are largely determined by the earliest stages in seedling emergence, which again are closely linked to microsite quality. A fuller understanding of microsite effects on recruitment with implications for plant community assembly and vegetation change is provided

Conifer seedling recruitment across a gradient from forest to alpine tundra: Effects of species, provenance, and site

Background: Seedling germination and survival is a critical control on forest ecosystem boundaries, such as at the alpine-treeline ecotone. In addition, while it is known that species respond individualistically to the same suite of environmental drivers, the potential additional effect of local adaptation on seedling success has not been evaluated. Aims: To determine whether local adaptation may influence the position and movement of forest ecosystem boundaries, we quantified conifer seedling recruitment in common gardens across a subalpine forest to alpine tundra gradient at Niwot Ridge, Colorado, USA. Methods: We studied Pinus flexilis and Picea engelmannii grown from seed collected locally at High (3400 m a.s.l.) and Low (3060 m a.s.l.) elevations. We monitored emergence and survival of seeds sown directly into plots and survival of seedlings germinated indoors and transplanted after snowmelt. Results: Emergence and survival through the first growing season was greater for P. flexilis than P. engelmannii and for Low compared with High provenances. Yet survival through the second growing season was similar for both species and provenances. Seedling emergence and survival tended to be greatest in the subalpine forest and lowest in the alpine tundra. Survival was greater for transplants than for field-germinated seedlings. Conclusions: These results suggest that survival through the first few weeks is critical to the establishment of natural germinants. In addition, even small distances between seed sources can have a significant effect on early demographic performance - a factor that has rarely been considered in previous studies of tree recruitment and species range shifts. © 2013 The work of C. Castanha, M.S. Torn, and L.M. Kueppers was conducted at Lawrence Berkeley National Laboratory under Contract No. DE-AC02-05CH11231 with the U.S. Department of Energy. The U.S. Government retains, and the publisher, by accepting the article for publication, acknowledges, that the U.S. Government retains a non-exclusive, paid-up, irrevocable, worldwide license to publish or reproduce the published form of this manuscript, or allow others to do so, for U.S. Government purposes. The work of M.J. Germino at the U.S. Geological Survey was authored as part of the Contributor's official duties as an Employee of the United States Government and is therefore a work of the United States Government. In accordance with 17 U.S.C. 105, no copyright protection is available for such works under U.S. Law. B. Weibel waives her copyright in the work but not her status as co-author of the work

Mechanismic approaches to explanation in ecology

The search for mechanisms and their description of explanatory and predictive purposes has been, and continues to be, a common practice in scientific research, even after the decline of classical mechanism. However, from the empiricist critique of causality and especially during the second third of the twentieth century, other perspectives came to the forefront of the discussion in the philosophy of scientific explanation. In particular, the deductivist approach of the covering-law model shaped the debate over the nature of explanation in science during some three or four decades, despite the insistent criticisms of authors like Michael Scriven who pointed to the importance of describing the relevant causes for understanding a given fact. The hegemony of the deductivist approach to scientific explanation diminished significantly with the admission of the existence of irreducible random facts, which elicited a wave of failed attempts to construct an inductive model of explanation. The sustained effort of authors such as Mario Bunge and Wesley Salmon contributed to restoring to the causality the respectability that had lost at the hands of the radical wing of empiricism, first due to the Humean critique and later with the general rejection of the metaphysics that professed the logical empiricists. With the decline of logical empiricism, attempts to develop a causal perspective of scientific explanation thrived, and the causal model came to share the hitherto exclusive role of the deductivist perspective in the philosophy of scientific explanation. At present, the field is paying renewed attention to the description of mechanisms, especially causal ones, as a central aspect of explanation and other research practices in several areas of science. This approach offers viable solutions to the various ontological and methodological objections that are opposed to the two traditional approaches (the purely deductive and the purely causal). In this essay we will review the basic characteristics of a bunch of philosophical proposals that highlight the description of mechanisms as a central element to explanation in science and we will briefly discuss its suitability for the field of ecology.Fil: Gonzalez del Solar, Rafael. Universitat Autònoma de Barcelona; EspañaFil: Marone, Luis. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mendoza. Instituto Argentino de Investigaciones de las Zonas Áridas. Provincia de Mendoza. Instituto Argentino de Investigaciones de las Zonas Áridas. Universidad Nacional de Cuyo. Instituto Argentino de Investigaciones de las Zonas Áridas; ArgentinaFil: Lopez de Casenave, Javier Nestor. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Ecología, Genética y Evolución; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentin