North American Forest Ecology Workshop

Management of Whitebark Pine in the GYE

Liz Davy — Mon, 22 Jun 2009 15:40:00 PDT

This presentation will focus on the development and use of a whitebark pine restoration strategy for the Greater Yellowstone Ecosystem.

Forest Histories & Forest Futures

Cathy Whitlock — Mon, 22 Jun 2009 08:30:00 PDT

The climate changes projected for the future will have significant consequences for forest ecosystems and our ability to manage them. It is reasonable to ask: Are there historical precedents that help us understand what might happen in the future or are historical perspectives becoming irrelevant? What synergisms and feedbacks might be expected between rapidly changing climate and land–use in different settings, especially at the wildland–urban interface? What lessons from the past might help us plan for a changing world? Information on forest history comes from a variety of sources, including pollen and charcoal preserved in lake sediments spanning millennia, variations in tree–ring growth indices spanning centuries, and recent forest dynamics. In the last 10 years, considerable paleo–research has focused on the ecological consequences of abrupt climate change, and records of past forest conditions are often detailed enough to describe changes occurring on time scales of years to decades. From this rich and well–resolved database, we can find examples of rapid environmental change in the past, similar to that projected for the future, and examine the ecological consequences that ensued. Studies from the western U.S. and beyond reveal the synergistic effects of past climate and land–use change in shaping present forest composition and dynamics. In addition, networks of paleoecologic sites disclose regional and global patterns of vegetation and disturbance regimes and the widespread responses to large–scale changes in climate. Although the past does not hold an exact analogue for the future, essential lessons can be learned about the sensitivity and resilience of forests to extreme events, the potential rates of ecological change, the role of natural and anthropogenic disturbance as a catalyst of change, and the legacy of human activities on forest environments.

Ecosystem recovery after disturbance: thresholds for biodiversity and resiliency indicators

J. Chandler — Wed, 24 Jun 2009 11:10:00 PDT

This project uses long-term (20 yr) research installations established and maintained by the BC Ministry of Forests and Range and that extend across north-central British Columbia, Canada. Vegetation structure (% cover and height) was measured at regular intervals (1, 2, 3, 5, 10 and 20 yrs) after clearcut or slashburning disturbances. These measurements are being used to develop indicators of biodiversity (composition, richness and biomass) and define response curves for measuring ecological resilience of Sub-boreal Spruce, Engelmann Spruce-Subalpine Fir, and Interior Cedar Hemlock forest ecosystems. We hypothesize that the rate of recovery, as measured by the three biodiversity indicators, varies significantly among ecosystems and across environmental gradients. We also expect that site productivity and the historical fire regime are important in determining vegetation recovery rates after burns of varying severity. To test these hypotheses, we will use post-burn vegetation repeated measures and environmental data collected in the summers of 2007/08 to develop a structural equation model. Our model will be tested using plant community composition first by species and then according to plant functional types. This research will support BC’s Future Forest Ecosystems Initiative, which aims to protect and enhance the resilience of BC’s forests through an adaptive management strategy.

Population Dynamics of the Mexican Beech, an Endangered Tree Species

G. Angeles-Perez et al. — Mon, 22 Jun 2009 00:00:00 PDT

Success in the reproduction of a species depends on the functional responses to biotic and abiotic factors of its developmental stages. With the objective to analyze the population dynamics of Fagus grandifolia subsp. mexicana in relation to site and environmental factors, we conducted a study on the structural changes of the population within a plot of 4,800 m2, during a period of three years. This species, restricted to the Sierra Madre Oriental (East Mountain Range) along the distribution of the mountain cloud forest, is considered an endangered species since only 10 small populations have been reported. We divided the population into small saplings (0.6cm < 2m) which showed a high recruitment rate (4,095 ind. ha-1). The damage rate was consistently low in all developmental stages, only eight individuals died during the three year period. The Absolute Growth Rate (AGR) and Relative Growth Rate (RGR) in height for small saplings was 0.115 m m-1 year-1, and 0.099 m m-1 year-1, respectively. The individuals with dbh 1.0 cm showed a mean AGR and RGR of 0.086 and 0.010 cm cm-1 year-1, respectively. A highly significant positive correlation was detected between small sapling density and percentage of photosynthetic photon flux density. The high recruitment rate of small saplings was strongly correlated with high light availability in the understory, located preferably under the influence of canopy gaps. In spite of the fact that the species is considered to be shade tolerant, its regeneration is favored by the formation of canopy gaps.

Growth Dominance In A Long-Term Red Pine Thinning Experiment

J. Bradford et al. — Mon, 22 Jun 2009 00:00:00 PDT

Forest stand development is driven by individual tree growth, which is a function of resource acquisition and resource-use efficiency. Although larger trees may have a greater opportunity to acquire resources, physiological constraints of larger trees may restrict their ability to convert resources into growth. One approach to understanding the consequences of resource acquisition and utilization on stand growth is to examine growth dominance, defined as positive when larger trees in the stand display proportionally greater growth than smaller trees, and negative when smaller trees have proportionally greater growth than larger trees. Binkley (2004; 2006) developed a method for quantifying stand-level growth dominance and proposed a hypothesis for how dominance progresses through stand development. We applied this approach to long-term red pine silvicultural experiments to characterize how stand age, thinning treatments (thinned from above, below, or both) and stocking levels (residual basal area) influence stand-level growth dominance through time. In stands thinned from below or from both above and below, dominance was not significantly different from zero at any age or stocking level. Growth dominance in stands thinned from above, by contrast, trended from negative at low stocking levels to positive at high stocking levels and was positive in young stands but not significantly different from zero in older stands. Growth dominance in un-thinned stands was consistently positive and increased with age, supporting Binkley’s hypothesis. These results suggest that growth dominance provides a useful tool for assessing the efficacy of thinning treatments designed to reduce competition between trees and promote even growth across a population.

Facilitation of Subalpine Fir and Aspen Regeneration by Overstory Aspen

W. Calder et al. — Mon, 22 Jun 2009 00:00:00 PDT

Forest inventory and analysis data show a 60% decline of aspen in the Interior West relative to historic highs. Succession to conifer is hypothesized to be the major contributor to aspen loss. Fire suppression has likely accelerated conifer displacement of aspen but there are important knowledge gaps in our understanding of how stable aspen communities transition to conifer dominated communities. Regeneration success is a predictor of future overstory composition and structure. The objective of this study was to characterize regeneration dynamics of aspen and subalpine fir as influenced by overstory composition in aspen-subalpine fir transition zones. We measured regeneration density and height classes of aspen ramets and subalpine fir seedlings at seven field sites across the state of Utah that were characterized as having a clearly demarcated overstory transition zone (dominant conifer, aspen-conifer mix, dominant aspen, gap). Subalpine fir establishment was 2-3 fold higher under pure aspen and aspen-fir mixed stands compared to pure subalpine fir stands. Subalpine fir did not establish in canopy gaps adjacent to the transition zones. High density of taller height classes (> 1 meter) were only observed in aspen-conifer mixed stands. Aspen regenerated readily in pure aspen, aspen-conifer mixed stands and in adjacent gaps but did not regenerate under pure subalpine fir stands. The highest density of taller height classes (> 1 meter) for aspen regeneration was achieved in pure aspen stands. The data suggest that a dominant presence of overstory aspen facilitates the establishment of subalpine fir and aspen but that greater height is obtained under different conditions (aspen under pure aspen stands, subalpine fir in mixed stands).

Seedling Regeneration Following Mountain Pine Beetle Infestation And Forest Harvesting

B. Collins et al. — Mon, 22 Jun 2009 00:00:00 PDT

The forests of Colorado and across much of the Mountain West are changing rapidly due to the effects of severe mountain pine beetle infestation. The widespread mortality of many lodgepole pine forests is certain, but the future trajectory of these ecosystems is not. As an initial step in characterizing ecosystem recovery after mountain pine beetle outbreak, this study will compare tree seedling density and herbaceous plant cover between areas that have been harvested to reduce fuel loads and adjacent untreated stands. Our specific objective is to compare various management prescriptions employed by the US Forest Service in response to insect infestations with a no-action alternative. We sampled treated and untreated stands at and near the USFS Fraser Experimental Forest, in central Colorado and compared existing seedling surveys for stands logged during and years prior to the current beetle outbreak. Current treatment units present a range of residual overstory, depth of harvest residue and extent of soil disturbance. Beneath uncut, beetle-killed stands, subalpine fir represented 92% of advanced regeneration below 15cm, and declined in importance with height. Conversely, lodgepole pine represented 44% of seedling above 75cm and the dominance of both lodgepole pine and Engelmann spruce increased in larger seedling classes. In harvested units the density of seedlings established prior to harvest was 18% lower than in untreated stands, the likely result of damage from mechanical operations and burial under harvest residue. On-going work quantifies seedling establishment following overstory mortality and identifies relationships between seedling density and residue depth, soil disturbance and herbaceous cover in post-harvest landscapes.

Productivity Relationships and Developmental Dynamics Over 26 Years Within Mixed Aspen-White Spruce Stands in Minnesota

A. W. D'Amato et al. — Mon, 22 Jun 2009 00:00:00 PDT

The productivity and dynamics of mixed aspen (Populus tremuloides)-white spruce (Picea glauca) forests were examined over a 26-year period across a series of replicated long-term silvicultural trials within northern Minnesota. Long-term growth and biomass production rates were compared between pure aspen, pure white spruce, and mixed aspen-white spruce stands established through planting and/or natural regeneration following clear-cut harvesting in 1982. Interestingly, there were no differences in spruce annual mortality rates between pure and mixed stands, with spruce averaging 1.2 ± 0.26 and 1.4 ± 0.20 % mortality in mixed and pure stands, respectively. In contrast, spruce in pure stands had significantly greater height growth rates than those found in mixtures. Aspen height growth and mortality rates were unaffected by spruce, as there were no differences between aspen grown in pure and mixed stands. Spruce height growth rates were much lower than aspen within mixed stands, resulting in rapid stratification into two-storied stands that contained a lower canopy stratum of white spruce at 4.9 ± 0.3 m and an upper canopy stratum of aspen at 13.8 ± 0.5 m after 26 years of development. Comparisons of productivity rates between pure and mixed stands indicated that there were no significant differences in biomass production rates between pure aspen and mixed aspen-white spruce stands (7.84 ± 0.08 and 6.61 ± 0.97 Mg/ha/yr), whereas pure white spruce stands had much lower levels of productivity (0.98 ± 0.05 Mg/ha/yr). Notably, the highest level of productivity observed across the study was within a stratified, mixed aspen white spruce stand (8.71 Mg/ha/yr); suggesting the potential for higher levels of production within these species mixtures relative to pure populations. In addition, productivity levels associated with spruce within mixtures was largely additive to aspen production, highlighting the potential for increasing productivity in pure aspen systems through spruce underplanting.

An Investigation on the Birds and Their Habitat Requirements in a Tropical Rainforest of Western Ghats, India

A. Das — Mon, 22 Jun 2009 00:00:00 PDT

The study addressed how altitude affected the distribution of birds. Three variants of the evergreen forest at an altitude of 900 to 2200 m two variants of the montane wet temperate (shola) forests between 2000 and 2200 m and the broad-leaved hill forests (BLHF) located between 1500 -1700 m were the habitat types. Study resulted in 5253 birds of 108 species, including 14 endemic species. Bird community structure of various habitats in corresponding altitudes varied significantly in terms of composition, abundance and diversity. The maximum species (59.2%) and individuals (27.2%) were in evergreen forest habitat and minimum in BLHF (22.8 % and 5.73% respectively). Shola habitats located at higher altitudes in the study area possessed higher species richness than mid-elevation broad-leaved hill forest, which occurs within the altitudinal range of 1500- 1700 m. The significant difference in tree species richness of BLHF with adjacent EG and SHOLA habitats partly explain the reduction in number of bird species in this transitional zone. The study showed increased abundance of birds at mid-elevation evergreen habitats and the highest shola habitats with a unique dip at the intermediate broad-leaved hill forests. Apart from the new understanding on the nuances of vegetation-bird community interaction, the study has brought into focus the importance of maintaining and enriching the vegetation complexity as a major objective of the overall Park Management plan.

Classification and Analysis of Tree Hole Occurrence in a Northeast Temperate Forest System

C. Didas et al. — Mon, 22 Jun 2009 00:00:00 PDT

This study examined the types, formation and abundance of tree holes in northeastern US forest stands. Tree holes are water filled depressions on trees that harbor macroinvertebrate communities. They have often been used as microcosms for detrital and population dynamic research, but there have been no published studies on factors that affect tree hole incidence in forest stands. We studied tree holes in stands ranging from CT to northern NH. Distance sampling was used to estimate abundance of tree holes on a per-hectare basis. A mixed-effects logistic regression analysis was used to form model predictors of factors that best predicted tree hole occurrence. Tree species, stand basal area, and diameter at breast height were identified to be the most influential model predictors for determining tree hole occurrence. Tree holes occurred almost exclusively on hardwoods, with maples being most prone to tree holes. Pans and rot holes are the best descriptors for the types of hole formation; however, pans most often give way to a rot lined hole. Rot holes were the most common types of holes discovered and both pans and rot formed holes developed a rot lining. Leaf litter was found in nearly all tree holes, regardless of tree species. Leaf litter has been identified as a dominant nutrient base and composition of leaf litter is most often associated with the tree on which the hole is associated. Tree holes have been recognized to have a role in vector ecology, as they are a breeding site of mosquitoes capable of carrying infectious diseases. Understanding tree hole occurrence and formation is useful for microcosm research and has future applications in patterning vector-borne infectious diseases.

Regional Oak Decline Trends Under Periodic Droughts in the Ozark Highlands of Missouri and Arkansas

X. Fan et al. — Mon, 22 Jun 2009 00:00:00 PDT

The Ozark highlands of Missouri and Arkansas are dominated by highly stocked oak-hickory forests. Oak decline and escalating mortality have become a concern as upland oak-hickory forests mature. Based on annual FIA plot data from 1999 to 2006 we explored oak decline and mortality trends for major oak species (groups) in this region. Oak decline has elevated cumulative mortality of oak species over this seven year period to 11 and 15 percent in terms of relative density and basal area, respectively. This is 2 to 3 times higher than for non-oak species. Oak decline and the associated mortality have occurred primarily within red oak species, while the white oak group has maintained a relatively stable mortality rate comparable to non-oak species. Cross-correlation analyses indicate that mortality was significantly correlated with growing season Palmer Drought Severity Index (PDSI), although mortality typically lagged 2 to 3 years behind individual drought events. Moreover, based on the past 17 years’ PDSI data, it appears that the cumulative impacts of drought may last up to 10 years. The Ozark highlands experienced severe drought extending from 1998 to 2000 and another milder drought from 2005 to 2006. These drought events triggered the escalation of mortality starting around 2000. Spatially, high red oak mortality (proportional basal area mortality >0.15) occurred mainly in the central areas of the Ozarks. Moderate mortality (proportional basal area mortality of 0.10-0.15) was widely dispersed over most of the Ozark highlands, while low mortality was distributed primarily around the outer perimeter of the Ozarks. In contrast, with white oak and non-oak species, high mortality was rare and moderate mortality was sporadic.

Ecosystem Flux Response Due to a Bark Beetle Epidemic at the Glees-Ameriflux Site

J. Frank et al. — Mon, 22 Jun 2009 00:00:00 PDT

GLEES (the Glacier Lakes Ecosystem Experiments Site) is located in the Snowy Range of the Medicine Bow National Forest, WY, and is managed by the Rocky Mountain Research Station of the U.S. Forest Service (Fort Collins, CO). One of the long-term research projects is the GLEES-AmeriFlux site where measurements of energy and trace gas fluxes between the Engelmann spruce-subalpine fir forest and the surrounding atmosphere have been made continuously since 1999. The eddy-covariance technique is used to measure the exchange (fluxes) of carbon-dioxide, water vapor, sensible heat, and momentum between the atmosphere and the subalpine ecosystem. A current epidemic of spruce beetle and western balsam bark beetle is killing the majority of mature trees surrounding the AmeriFlux scaffold. The flux-data are used to follow changes in the net ecosystem production, the water cycle, and the energy balance due to beetle-induced tree mortality.

The Influence of Cutting Cycle and Stocking Level on the Structure and Quality of Managed Old-Growth Northern Hardwoods

C. Gronewold et al. — Mon, 22 Jun 2009 00:00:00 PDT

The effects of 57 years of uneven-aged management on the structure and quality of old-growth northern hardwood forests were examined within a long-term Forest Service study in the Dukes Experimental Forest, Michigan. Treatments within the study included several differing stocking levels (30, 50, 70, and 90 ft2/acre) and cutting cycles (5, 10, 15, and 20 years) replicated across three blocks. Tree growth and quality, as well as stand structural attributes were examined within each treatment and compared to an unmanaged Research Natural Area (RNA). Comparisons of tree grade between treatments indicated that cutting cycle length and stocking level had no effect on tree quality. In contrast, average annual diameter growth was greatest in lower stocking treatments, and regression analyses of tree growth versus residual stocking level indicated that optimum levels of growth were achieved between residual basal areas of 50 and 70 ft2/acre. Comparisons of stand structure between treatment areas and the unmanaged RNA suggested that volumes of CWD in the high residual basal area treatments most closely approximated those found within unmanaged old-growth. Treatments with high residual basal areas and longer cutting cycles had significantly greater snag basal area and volume than other treatments and were closer in this respect to the RNA than other treatments. Analysis of diameter distributions over time indicated that cutting cycle had little effect on distribution shape over the course of this study. In contrast, treatments with lower residual basal areas developed from increasing q to concave or negative exponential distributions over time, while the 90 ft2/acre treatment displayed an increasing q distribution throughout the experiment. The findings of this study suggest that manipulation of stocking levels within northern hardwood stands is of greater importance than cutting cycle in controlling stand growth, as well as influencing the development of structural complexity.

Mapping Mountain Hemlock and Pinpointing Ponderosa Pine: Imputation Mapping Species Distributions in Western Oregon

E. Grossman et al. — Mon, 22 Jun 2009 00:00:00 PDT

Effective forest management and conservation planning depends upon having accurate and detailed vegetation maps. Remote sensing has been an invaluable tool for mapping vegetation, but imagery alone often cannot yield detailed information on individual tree species. Because of this mismatch, there is interest in developing new statistical techniques for integrating ancillary information with remote sensing to produce a map. As part of a nationwide study, we are evaluating several variants of imputation mapping. Here, we compare the ability of two methods (gradient nearest neighbor (GNN) and random forest (RFNN)) to produce maps of tree species distributions at regional scales. These two methods make different assumptions about species-environment relationships and thus have differing strengths and weaknesses. We build the imputation models from 1778 vegetation plots from the US Forest Service’s Forest Inventory and Analysis program (annual plots), and a set of spatial data: a 2006 Landsat image mosaic, modeled climate (PRISM), and topographic variables, for a region that stretches from the Northern Oregon border into California, and encompasses the Cascade Mountains. Preliminary results show that both methods often predict species occurrence at somewhat broader geographic ranges, and a broader range of environmental conditions than they do within our original plot sample. Gradient nearest neighbor is more effective at producing range maps which represent the total area covered by a given species. Random forest predictions track species’ environmental limits more closely with the original data. However, some species are overmapped within their ranges, giving inflated estimates of total area within the mapped region. This tendency also yields different image textures. GNN produces a grainier map with higher edge densities while RFNN produces more compact patches. We conclude that model choice for mapping applications should be based upon intended use of the final map product, because each method has both strengths and weaknesses.

Influence of Age, Diameter, and Location on Compression Wood Formation in White Pine Following Ice Storm Damage

B. Hook et al. — Mon, 22 Jun 2009 00:00:00 PDT

In 1994, two ice storms hit the ridge-and-valley region of southwestern Virginia. Large-diameter trees experienced high levels of branch breakage and many small-diameter trees were bent under the weight of the ice. To right themselves, the conifers formed compression wood. The objective of this study was to quantify the influence of stem diameter, age, crown class, tree location, and influence of nearest neighbor on compression wood formed following the 1994 ice storms in eastern white pine (Pinus strobus, L.). Pinus strobus within a 50 x 100 m plot were destructively sampled at Virginia Techs’ Fishburn Forest in southwestern Virginia and cross-sectional disks were removed at stump height. Disks were sanded, cross-dated, and scanned. Tree locations were spatially mapped with a laser transit, along with distance and attributes of the nearest neighboring trees. The images of the scanned disks were imported into Photoshop and the amount of compression wood formed in the years following 1994 was measured as a percentage of total area in the cross-section. The white pine exhibited a two-age structure with younger trees establishing in 1990s and older trees in the 1960s. Through a comparison of these two age classes, the formation of compression wood appeared to be age independent; however diameter and crown class were related to amount of compression wood formed by the white pines following the 1994 ice storms with smaller diameter and lower crown classes forming relatively more compression wood compared to larger, dominant individuals.

Growth of 10 Tree Species in Relation to Location and Microclimatic Gradients in a Strip Shelterwood

K. Hossain et al. — Mon, 22 Jun 2009 00:00:00 PDT

Strip shelterwood systems are used in some areas to favour establishment of intolerant and moderately tolerant tree species or to facilitate harvesting. There is substantial variation in microclimate within cleared strips, which can influence survival and growth of regeneration. The growth of the established regeneration depends on the microclimate (light, soil moisture, air and soil temperature) at different locations in gaps. This poster presents results from a study being conducted at Nakusp in Southern BC, Canada. The purpose of this study is to improve our understanding of the microclimatic pattern after gap creation and its influence on the growth of planted seedlings of 10 native tree species. Preliminary results, collected 13 to 14 years after planting, show gradual increase of light and air temperature from the south to the north edge of the gaps. Soil moisture stress also increased from the south to the north edge. Species are showing variable growth response to these gradients. Shade intolerant species performed better at the centre and north edge of the gap, while shade tolerant species have survived and established well under the canopy and near the edges. Among the tree species evaluated, Western hemlock and Engelmann spruce were best suited to the south edge and in the intact forest, while Douglas fir performed best at north edge and inside the opening. Regardless of their shade tolerance classification, all the species grow best near the centre of the opening, where light levels are highest.

The Western Aspen Alliance: Promoting Sustainable Aspen Ecosystems in Western North America

P. C. Rogers et al. — Mon, 22 Jun 2009 00:00:00 PDT

A consortium of researchers and managers has formed the Western Aspen Alliance (WAA) to coordinate and facilitate advances in aspen ecology in Western North America. Our prime goal is to disseminate state-of-the-science aspen information to interested managers, scientists, the public, and other users. Recent events, some potentially related to climate change, have spurred interest in aspen ecology. For example, reports of sudden aspen mortality, large-scale seedling establishment following wildfires, and documentation of trophic interactions between wolves, elk, and aspen, have all significantly modified our understanding of aspen ecosystems. We realize, regionally, that an aging aspen cohort will need to successfully regenerate to maintain sustainable populations. Wildlife pressure on aspen regeneration is an issue of concern for managers throughout western North America. The WAA will incorporate these lessons into an ongoing resource bank for managers throughout the region. From a science perspective, we wish to engender a cross-disciplinary network of researchers willing to take on pertinent aspen topics. For example, there is a current need to assess the extent of Sudden Aspen Decline (SAD), seral/stable aspen stands, and historic aspen coverage. Basic research on aspen physiology, disturbance ecology, water yield, genetics, herbivory, and biodiversity/trophic interactions issues are also desired. The social/aesthetic value of aspen is an another up-and-coming research area in need of work. We will form working groups for these issues and pursue additional aspen topics that arise. A central role of the WAA will be to sponsor field visits, workshops, conferences, and collaboration between researchers. We have recently initiated a bibliographic database of aspen research and management topics for use by WAA members. Though sponsored by Utah State University’s College of Natural Resources and the USDA Forest Service, Rocky Mountain Research Station, we are currently working with numerous state and federal agencies, NGO’s, and universities. We welcome your input and participation!

Using Fire to Rehabilitate Oak Stands Degraded by Red Oak Borer: Initial Results

H. Liechtyl et al. — Mon, 22 Jun 2009 00:00:00 PDT

Following a region-wide drought from 1998 to 2000, red oak borer (Enaphalodes rufulus) outbreaks contributed to the decline of several upland red oak species in the Ozark and Ouachita Mountains of Arkansas. Studies following these outbreaks indicated that red oak regeneration potential is poor for many of these stands. A study was initiated to evaluate whether dormant season prescribed fire could enhance oak regeneration and establishment in three degraded stands in Arkansas. Two years following the treatments, seedling density had increased but oak and non-oak composition (as a proportion of total seedling) density was similar to that in the unburned control treatment. A higher proportion of the non-oak than oak understory trees (0.6 in.

Effects of Smoke on Leaf Function of Broadleaf and Conifer Tree Species

G. Lifferth et al. — Mon, 22 Jun 2009 00:00:00 PDT

During summer months, wildfires in western North America can produce large amounts of smoke. Nearly all of the studies that examine the effects of smoke on plants, have been tied to seedling germination, while the effects of smoke on leaf function are nearly uninvestigated. There is emerging evidence suggesting there may be a link between smoke produced from wildfires and patterns of sudden oak disease in California, although smokes’ role in this interaction is unknown. We hypothesize that plants may alter their defense chemistry strategy in response to fire and that smoke is the cue. The objectives of the study were: 1) to compare the effects of smoke exposure on leaf gas exchange and growth of several broadleaf and evergreen species (Populus tremuloides, Acer glabrum, Quercus gambeili, Pinus ponderosa, Pseudotsuga menziesii, and Picea pungens) common in the western North America forests where fires are common; and 2) to examine whether leaf defense chemistry changes in response to smoke exposure. Treated plants were exposed to smoke for 30 minutes in mid May and then again in early June. Following smoke exposure photosynthesis was measured at 30 minute intervals for 6 hours at both ambient and saturating CO2 levels (385 and 1000 ppm) to examine whether smoke affects stomatal or biochemical function. At the end of summer, plant tissues were harvested and weighed and leaves were analyzed for condensed tannins and phenolic glycosides. The results show that smoke negatively affects both stomatal and biochemical function, resulting in significant reductions in photosynthesis and that broadleaf species are more sensitive than conifers. Smoke had no significant affect on growth in any of the tree species, or phenolic glycoside concentrations in Populus tremuloides.

Positive, Negative and Net Effects of Shrub-Tree Seedling Interactions in Red Pine Ecosystems

R. Montromery et al. — Mon, 22 Jun 2009 00:00:00 PDT

In forested ecosystems, young tree seedlings interact with already established vegetation such as adult trees, shrubs, herbs, understory trees, and other juvenile trees. The extent and nature of these interactions can affect growth rates of tree seedlings and their probability of survival. Thick shrub understories are thought to deter regeneration through increased mortality and slow growth of tree seedlings and saplings. After canopy loss or removal, development of dense shrub thickets may decouple tree regeneration responses from those expected based on overstory conditions alone. To explore mechanisms of interaction between tree seedlings and shrubs, we manipulated the magnitude of above- and belowground interactions and monitored survival and growth of 6 tree species (Pinus resinosa, P. banksiana, P. strobus, Acer rubrum, Quercus rubra & Betula papyrifera) common in the Great Lakes region. We found evidence of both competition and facilitation that depended on tree species identity and ecological context (e.g. growing in open or forest interior). Shrubs reduced light availability by 27-28% in closed canopy and gap sites and reduced N availability by >50% in gaps In closed canopy sites, the presence of shade reduced survival of Pinus banksiana, P. resinosa and Betula papyrifera. In gap sites, the presence of roots reduced survival of all species and reduced growth of A. rubrum, P. banksiana and P. strobus. The presence of shade increased survival and growth of Acer rubrum, Betula papyrifera, and Pinus strobus in gap sites but only when roots were not present. For some species (e.g. Acer rubrum, Betula papyrifera), competitive effects of roots appear balanced by facilitative effects of shade leading to no net effect of shrubs on seedling growth or survival.