Suckering response of aspen to traffic-induced-root wounding and the barrier-effect of log storage

In a growth chamber, we tested how the seasonal timing of placing a physical barrier (simulating a possible effect of log storage) and inflicting root damage impacted aspen (Populus tremuloides Michx.) root systems and their suckering capability. Roots from 4-year-old saplings were used, and one half of these root systems had the above-ground portion cut in the winter (dormant) while the other half was cut during the growing season in the summer. Damage was inflicted to the roots by driving a large farm tractor over them, and a covering treatment was applied using a polystyrene board to prevent suckers from emerging from the soil. Soil temperatures for the winter-cut root systems were kept at 5 8C over the growing season, using a water bath, while for the summer-cut root systems soil temperatures were maintained at 17 8C over the growing season. In the winter-cut root systems, both log storage and root wounding caused a 40% reduction in living root mass and carbohydrate reserves, as well as reducing sucker numbers and their growth performance. In the summer-cut root systems log storage and root wounding reduced living root mass by approximately 35% as well as sucker growth, but had less of an impact on the number of suckers produced

N-transfer through aspen litter and feather moss layers after fertilization with ammonium nitrate and urea

When fertilizer is broadcast in boreal forest stands, the applied nutrients must pass through a thick layer of either feather moss or leaf litter which covers the forest floor. In a growth chamber experiment we tested the transfer of N through living feather moss or aspen litter when fertilized with urea ((NH2)2CO) or NH4NO3 at a rate of 100 kg ha−1 and under different watering regimes. When these organic substrates were frequently watered to excess they allowed the highest transfer of nutrients through, although 72% of the applied fertilizer was captured in the substrates. In a field experiment we also fertilized moss and aspen litter with urea ((NH2)2CO) or NH4NO3 at a more operationally relevant rate of 330 kg ha−1. We captured the NO3− or NH4+ by ion exchange resin at the substrate–mineral soil interface. In contrast to the growth chamber experiment, this fertilizer rate killed the moss and there was no detectable increase in nutrient levels in the aspen litter or feather moss layers. Instead, the urea was more likely transferred into the mineral soil; mineral soil of the urea treatment had 1.6 times as much extractable N compared to the NH4NO3 treatment. This difference between the growth chamber and field studies was attributed to observed fertilizer- damage to the living moss and possibly damage to the litter microflora due to the higher rate of fertilization in the field. In addition, the early and substantial rainfall after fertilization in the field experiment produced conditions for rapid leaching of N through the organic layers into the mineral soil. In the field, only 8% of the urea-N that was applied was captured by the ion exchange resin, while 34% was captured in for the NH4NO3 fertilization. Thus, the conditions for rapid leaching in the field moved much of the N in the form of urea through the organic layers and into the mineral soil before it was hydrolyzed

A Functional Framework for Improved Management of Western North American Aspen (Populus tremuloides Michx.)

Quaking or trembling aspen (Populus tremuloides Michx.) forests occur in highly diverse setting across North America. However, management of distinct communities has long relied on a single aspen to-conifer successional model. We examine a variety of aspen dominated stand types in the western portion of its range as ecological systems; avoiding an exclusive focus on seral dynamics or single species management. We build a case for a large-scale functional aspen typology based on existing literature. Aspen functional types are defined as aspen communities that differ markedly in their physical and biological processes. The framework presented here describes two “functional types” and seven embedded “subtypes”: Seral (boreal, montane), Stable (parkland, Colorado Plateau, elevation and aspect limited, terrain isolated), and a Crossover Seral-Stable subtype (riparian). The assessment hinges on a matrix comparing proposed functional types across a suite of environmental characteristics. Differences among functional groups based on physiological and climatic conditions, stand structures and dynamics, and disturbance types and periodicity are described herein. We further examine management implications and challenges, such as human alterations, ungulate herbivory, and climate futures, that impact the functionality of these aspen systems. The functional framework lends itself well to stewardship and research that seeks to understand and emulate ecological processes rather than combat them. We see advantages of applying this approach to other widespread forest communities that engender diverse functional adaptations

Carbon isotope discrimination and water stress in trembling aspen following variable retention harvesting

Variable retention harvesting (VRH) has been proposed as a silvicultural practice to maintain biodiversity and ecosystem integrity. No previous study has examined tree carbon isotope discrimination to provide insights into water stress that could lead to dieback and mortality of trees following VRH. We measured and compared the carbon isotope ratios (δ13C) in stem wood of trembling aspen (Populus tremuloides Michx.) before and after VRH. Eight trees were sampled from isolated residual, edge and control (interior of unharvested stand) positions from each of seven plots in three regions (Calling Lake and Drayton Valley, Alberta and Lac Duparquet, Qu

The handbook for standardized field and laboratory measurements in terrestrial climate change experiments and observational studies (ClimEx)

1. Climate change is a world‐wide threat to biodiversity and ecosystem structure, functioning and services. To understand the underlying drivers and mechanisms, and to predict the consequences for nature and people, we urgently need better understanding of the direction and magnitude of climate change impacts across the soil–plant–atmosphere continuum. An increasing number of climate change studies are creating new opportunities for meaningful and high‐quality generalizations and improved process understanding. However, significant challenges exist related to data availability and/or compatibility across studies, compromising opportunities for data re‐use, synthesis and upscaling. Many of these challenges relate to a lack of an established ‘best practice’ for measuring key impacts and responses. This restrains our current understanding of complex processes and mechanisms in terrestrial ecosystems related to climate change. 2. To overcome these challenges, we collected best‐practice methods emerging from major ecological research networks and experiments, as synthesized by 115 experts from across a wide range of scientific disciplines. Our handbook contains guidance on the selection of response variables for different purposes, protocols for standardized measurements of 66 such response variables and advice on data management. Specifically, we recommend a minimum subset of variables that should be collected in all climate change studies to allow data re‐use and synthesis, and give guidance on additional variables critical for different types of synthesis and upscaling. The goal of this community effort is to facilitate awareness of the importance and broader application of standardized methods to promote data re‐use, availability, compatibility and transparency. We envision improved research practices that will increase returns on investments in individual research projects, facilitate second‐order research outputs and create opportunities for collaboration across scientific communities. Ultimately, this should significantly improve the quality and impact of the science, which is required to fulfil society's needs in a changing world

Using Root Carbohydrates Reserves as an Indicator of Vulnerability to Defoliation in Trembling Aspen

Tent caterpillar (Malacosoma disstria [H¸bner]) and large aspen tortrix (Choristoneura conflictana [Walker]) are native defoliators of trembling aspen (Populus tremuloides Michx.) in the boreal forests of North America. Defoliation events can be sporadic and localized but there can be large scale outbreaks covering hundreds of square kilometers. Large outbreaks are thought to occur in 10-year cycles and can last several years. Generally it is thought that defoliation events have short-term effects on aspen productivity but do not result in significant mortality, as aspen reflushes after these spring defoliation events. However, in combination with other stressors such as drought, it has been observed that aspen clones can be weakened and are more susceptible to stem dieback or even clone mortality. Over a period of 8 years we determined seasonal carbohydrate reserves of different tissues in aspen clones. Non-structural carbohydrate reserves were determined in twig, stem and root samples from 9 different clones. During the collection period some of the aspen clones were defoliated in 2000 and/or 2007. After defoliation, tissue carbohydrate reserves in stems and twigs recovered by the end of the same summer. In contrast, in roots, carbohydrates reserves (particularly starch) were still depressed the second summer after defoliation, relative to clones that were not defoliated. After only one defoliation event starch reserves in the roots were close to zero, suggesting that repeated defoliations could have significant impacts on the survival of aspen clones. The research indicates that root reserves are severely impacted by defoliation and that clones with already low carbohydrate reserves are likely at a higher risk of dieback and mortality and could function as a valuable indicator to assess risks of clonal dieback in aspen