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

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

Research on Aspen Ecology From a Canadian Perspective

Trembling aspen has its core distribution in the boreal mixedwood region of Canada, where it also achieves its highest productivity. As a result there has been significant interest and research activity in Canada focusing on aspen in the past and present. While early on, most aspen research dealt with basic ecology and mostly with the management of aspen as an undesirable species, the direction of aspen research has undergone a significant change since the mid and late eighties. At that time research on aspen gained significant momentum, as technological advances allowed for the processing of aspen fiber for pulp and engineered wood products. In the mid-nineties, the increasing impact of harvesting in the boreal forest and public pressure to develop sustainable forest management practices resulted in a further shift of aspen research to include areas such as aspen regeneration, mixedwood management, and the exploration of the role of aspen in boreal forest biodiversity. In the last 10 years, there has been an increase in research on the use of aspen as a plantation species. Overall, significant advances have been made in a broad range of areas such as aspen ecology and physiology, population ecology, stand dynamics, and genetics in order to address issues applicable to silviculture, mixedwood management, and forest reclamation and restoration in the boreal forest zone. This presentation will give a brief overview over recent research directions in aspen ecology and management and will explore research needs particular to aspen throughout its range in Canada

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

Does the Relationship Between Tree Vigor and Defense Respond to Fertilization and Thinning?

Waring and Pitman suggested that high growth efficiency (GE) (i.e. basal area increment/sapwood area - considered a measure of tree vigor) is related to the ability of lodgepole pine to defend against mountain pine beetles (Dendroctonus ponderosae Hopkins) (MPB). In this study we explore the relationship between GE, and other measures of vigor such as tree size, live crown ratio, growth increment, stem, foliage nutrients and root carbohydrate reserves. We then compare these measures of vigor with characteristics of tree defense such as density of resin ducts, monoterpenes and size of phloem lesions after inoculation with Grossmania clavigera (a blue stain fungus associated with MPB). In a field experiment we tested the suggested relationship between vigor and defense by thinning and fertilization in ten pure lodgepole pine stands in central Alberta. In the third summer after the fertilization and thinning treatment we inoculated trees with the blue stain fungus. The combination of fertilization and thinning increased GE and resin duct density but negatively impacted starch reserves. Lesion size increased with tree size in control plots, however, this relationship was lost when trees were fertilized and thinned. This suggests that treatments to increase growth rate also increased constitutive defenses in larger trees