Seed Release in Lodgepole Pine Forests After Mountain Pine Beetle Outbreak

Serotinous lodgepole pine (Pinus contorta var. latifolia) usually regenerates after fire or harvesting provided conditions that are warm enough to open the cones. There are concerns that large-scale stand mortality due to mountain pine beetle (MPB) outbreak could greatly reduce natural regeneration of lodgepole pine because the closed cones are held in place in the tree canopy without any seed release. We selected 15 stands (five gray-attacked, five red-attacked, and five green) in the Sub-Boreal Spruce biogeoclimatic zone of British Columbia to determine loss of canopy seed via breakage of twig-bearing cones and cone opening (i.e., loss of serotiny) throughout the 2008 growing season. We also quantified seed loss of fallen cones via predation and cone opening. Red-attacked stands lost an estimated 175 000 seed-bearing canopy cones ha-1 yr -1 due to crown friction resulting in twig breakage, representing an over three-fold increase compared to green stands. This result was considered ecologically important since it equated to over 25 % of canopy cones lost to the forest floor. Red- and gray-attacked stands also had 15 % of canopy seed lost due to cone weathering resulting in cone opening. Additional seed losses occurred in the gray-attacked stands due to additional cone opening (58 % yr-1) on the forest floor and predation (12 000 fallen seed-bearing cones ha-1 yr-1). MPB-killed stands released some canopy seed through breakage of twig-bearing cones, partial loss of serotiny, and forest floor cone opening. The implications are: i) seed supply is gradually lost in the first years after attack; ii) if adequate levels of regeneration are to occur, either anthropogenic or fire disturbances must happen shortly after tree mortality. We conclude that lodgepole pine is poorly-adapted to disturbances such as MPB because seed is slowly released onto an unfavorable seed bed

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

Aspen regeneration on log decking areas as influenced by season and duration of log storage

This study assessed aspen regeneration on decking areas as affected by season of log deck building and duration of log storage; as well as root wounding, soil com- paction, and slash depth. On former decking areas that were built after a summer harvest, aspen regeneration was 50% lower and root death 35% greater compared to former decking areas of a fall harvest. Duration of log storage after a fall harvest had little effect on aspen regeneration; short (1.5–3 months) or long (11 months) storage resulted in similar regeneration. Slash load was greatly increased on decking areas while root wounding and soil bulk density were only slightly increased compared to controls. For best management practices, log storage after summer harvest should be avoided especially when logs are kept over the growing period when suckering occurs. Additionally, removing the inter- woven mat of slash covering decking areas and limiting machine traffic to frozen soil will ensure vigorous suckering

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

Regeneration Dynamics of Planted Seedling-Origin Aspen (Populus tremuloides Michx.)

Aspen (Populus tremuloides Michx.) is a foundational tree species of the North American boreal forest. After disturbance, clonal aspen stands quickly achieve canopy closure by sending up numerous clonal shoots (root suckers) from their lateral root system. Controlled aboveground disturbance will commonly induce prolific root suckering and thereby increase stem density in clonal aspen stands, but it is unclear if increases in stem density will be observed in planted seedling-origin aspen stands. The objectives of this study were to determine (1) overall root suckering response of planted aspen to aboveground disturbance; (2) if different cut heights of the stem or infliction of root damage impact the number of root suckers produced. We found that planted aspen regenerated readily after disturbance, averaging five root suckers per cut tree. However, individual response was highly variable, ranging from zero to 29 root suckers per root system. Of the cut trees, 75% produced at least one root sucker and 60% produced at least one stump sprout. Cutting trees close to the soil surface produced more root suckers than leaving a 25 cm stump. While root system size (mass and length) was well correlated with aboveground measures of planted aspen, root suckering was not related to root system size. As a result of increased forest reclamation efforts in the boreal forest region the planting of aspen has become a more common practice, necessitating a better understanding of the regeneration dynamics and root suckering potential of these planted and seedling-origin aspen forests

Propagating trembling aspen from root cuttings: impact of storage length and phenological period of root donor plants

Two experiments were conducted to examine the effects of growing conditions, duration of cold storage, and distinct phenological periods of root donor plants on the propagation success of aspen rootlings. Root donor plants were produced either under greenhouse or open grown conditions. Root cuttings were periodically collected from donor plants that had been stored for various lengths of time in cold storage (up to 180 days), or that were stored dormant in cold storage (up to 150 days) and then grown for another full growing season. Longer storage of donor plants produced only slightly smaller rootlings and resulted in slightly lower establishment success. Rootling establishment success was severely depressed (down to 18% establishment success) when cuttings were collected during the active growth period of donor plants. Carbohydrate reserves did not influence rootling establishment success but did affect root and shoot growth performance. It appears that other factors, such as hormone levels, may be more important in rootling establishment success

Coarse and Fine Root Respiration in Aspen (Populus Tremuloides)

Coarse and fine root respiration rates of aspen (Populus tremuloides Michx.) were measured at 5, 15 and 25 °C. Coarse roots ranged from 0.65 to 4.45 cm in diameter, whereas fine roots were less than 5 mm in diameter. To discrim- inate between maintenance and growth respiration, root respi- ration rates were measured during aboveground growing periods and dormant periods. An additional measurement of coarse root respiration was made during spring leaf flush, to evaluate the effect of mobilization of resources for leaf expan- sion on root respiration. Fine roots respired at much higher rates than coarse roots, with a mean rate at 15 °C of 1290 μmol CO2 m–3 s–1 during the growing period, and 660 μmol CO2 m–3 s–1 during the dormant period. The temperature response of fine root respiration rate was nonlinear: mean Q10 was 3.90 for measurements made at 5–15 °C and 2.19 for measurements made at 15–25 °C. Coarse root respiration rates measured at 15 °C in late fall (dormant season) were higher (370 μmol CO2 m–3 s–1) than rates from roots collected at leaf flush and early summer (200 μmol CO2 m–3 s–1). The higher respiration rates in late fall, which were accompanied by decreased total non- structural carbohydrate (TNC) concentrations, suggest that respiration rates in late fall included growth expenditures, re- flecting recent radial growth. Neither bud flush nor shoot growth of the trees caused an increase in coarse root respiration or a decrease in TNC concentrations, suggesting a limited role of coarse roots as reserve storage organs for spring shoot growth, and a lack of synchronization between above- and be- lowground growth. Pooling the data from the coarse and fine roots showed a positive correlation between nitrogen concen- tration and respiration rate

Forest floor protection during drilling pad construction promotes resprouting of aspen

Drilling pads that are used to explore petroleum reserves in the boreal forest are often only used for a short time. We studied the vegetative regeneration potential of aspen (Populus tremuloides) through root suckers as a means to rapidly recover forest vegetation in these disturbed sites. We compared protecting the original forest floor under a layer of subsoil during the leveling of drilling pads, with the current practice of stripping off the forest floor and topsoil and placing it back on the site (Rollback) in the re-contouring of the reclamation phase. We also tested three techniques of delineating the forest floor so that it can be effectively uncovered during the reclamation phase. After re-contouring and top soil placement on the sites, we assessed the extent of surface disturbance, soil temperature, soil bulk density, and the density and height of aspen regeneration. Aspen suckers were tallest, had the highest density and had better survival when the forest floor was protected compared to the standard Rollback treatment. When protecting the forest floor, delineating the original forest floor from the subsoil cover resulted only in small differences in the aspen regeneration among delineation treatments with little impact on soil compaction and only moderate effects on soil surface disturbance. The study indicates that protection and the careful uncovering of the forest floor with or without using a delineation layer should be a preferred strategy for temporary drilling pad construction and their subsequent reclamation in aspen-dominated boreal forests