Three model communities of trembling aspen (monoculture, and mixed with either paper birch or sugar maple) were grown for seven years in elevated atmospheric CO(2) and O(3) using Free Air CO(2) Enrichment (FACE) technology. We utilized trends in species' importance, calculated as an index of volume growth and survival, as indications of shifting community composition. For the pure aspen communi...

Aim Fire suppression, elk (Cervus elaphus Erxleben) browsing and drought have been suggested as possible explanations for low aspen (Populus tremuloides Michx.) ramet regeneration in elk winter range of the Greater Yellowstone Area (GYA) during the twentieth century. This study analyses the relationship between the rates of aspen regeneration, biophysical factors and human land use since 1830. ...

We report on the recent growth of upland aspen (Populus tremuloides Michx.) thickets in northwestern Yellowstone National Park, USA following wolf (Canis lupus L.) reintroduction in 1995. We compared aspen growth patterns in an area burned by the 1988 fires to aspen growth patterns in an adjacent unburned area. Elk (Cervus elaphus L.) are the principal ungulates that use this area to meet forag...

Using a monograph provided by Warren (1926) and two sets of aspen increment cores collected in 1997 and 1998, we analyzed aspen overstory recruitment in Yellowstone National Park (YNP) over the past 200 years. We found that successful aspen overstory recruitment occurred on the northern range of YNP from the middle to late 1700s until the 1920s, after which it essentially ceased. We hypothesize...

The effect of high temperature on photosynthesis of isoprene-emitting (aspen) and non-isoprene-emitting (birch) trees were measured under elevated CO(2) and ambient conditions. Aspen trees tolerated heat better than birch trees and elevated CO(2) protected photosynthesis of both species against moderate heat stress. Elevated CO(2) increased carboxylation capacity, photosynthetic electron transp...

The aim of this study was to examine the effects of elevated carbon dioxide [CO2] and ozone [O3] and their interaction on wood chemistry and anatomy of five clones of 3-yearold trembling aspen (Populus tremuloides Michx.). Wood chemistry was studied also on paper birch (Betula papyrifera Marsh.) and sugar maple (Acer saccharum Marsh.) seedling-origin saplings of the same age. Material for the s...

The ecological consequences of biodiversity have become a prominent public issue. Little is known on the effect of genetic diversity on ecosystem services. Here, a diversity experiment was established with European and North American aspen (Populus tremula, P. tremuloides) planted in plots representing either a single deme only or combinations of two, four and eight demes. The goals of this stu...

This review summarises the knowledge about the ecology, breeding and management of hybrid aspen (Populus wettsteinii Hämet-Ahti P. tremula L. P. tremuloides Michx.). The review is restricted mainly to Northern Europe, where hybrid aspen has been most intensively studied and cultivated and where it has proved to be one of the fastest-growing hardwoods, suitable for the production of pulpand ener...

Disturbance patterns strongly influence plant community structure. What remains less clear, particularly at a mechanistic level, is how changes in disturbance cycles alter successional outcomes in plant communities. There is evidence that fire suppression is resulting in longer fire return intervals in subalpine forests and that these lengthened intervals increase competitive interactions betwe...

This paper describes the Automated Scheduling and Planning Environment (ASPEN). ASPEN encodes complex spacecraft knowledge of operability constraints, flight rules, spacecraft hardware, science experiments and operations procedures to allow for automated generation of low level spacecraft sequences. Using a technique called iterative repair, ASPEN classifies constraint violations (i.e., conflic...