Disease and Insect Disturbances chaired by Fred Baker

Aspen Mortality in the Intermountain West: What Forest Inventory and Analysis Plots Tell Us

Fred Baker et al. — Tue, 23 Jun 2009 16:00:00 PDT

Reports of a long-term decline in area dominated by aspen forests, coupled with increased mortality attributed to long term drought, have lead to concerns of increased mortality in aspen forests. We examined data collected by USDA Forest Service Inventory and Analysis (FIA) to quantify aspen mortality. Most aspen stands in the Intermountain West are older than 80 years, a recommended rotation age for the best sites. Plot mortality rate was not related to site index or stand age. Many stands, however, have stem density greater than one would expect for self-thinning stands. At a given latitude, aspen plots with mortality were lower in elevation than those without mortality. Mortality of several coniferous species has increased in the past 6-8 years, while the rate of mortality for aspen has remained relatively constant. FIA data provide no evidence of widespread elevated mortality.

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

D. Goodsman et al. — Tue, 23 Jun 2009 16:20:00 PDT

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.

Hydrological Response of Western Subalpine Watersheds Following Mountain Pine Beetle Infestation

R. Hubbard et al. — Tue, 23 Jun 2009 16:40:00 PDT

Mountain pine beetle (Dendroctanous ponderosae) has been infesting large areas of lodgepole pine dominated forests in the western US and Canada over much of the past decade. The US forest service predicts the current epidemic will kill approximately 90% of the lodgepole pine (Pinus contorta) overstory in Colorado. An outbreak of this size and intensity will influence watershed processes for decades to come but the magnitude of these changes is uncertain. Water supply in western North America is controlled primarily by snow accumulation and melt in forested headwater basins. Trees impact runoff through wintertime canopy interception losses of snowfall and summertime transpiration. Management studies suggest that changes in water yield will occur in response to beetle disturbance but there are significant differences between timber harvesting and pine beetle induced mortality. Hydrological responses in beetle killed forests are dependent on local climatology, forest age and species composition, understory response and severity of infestation. Long-term data records at the Fraser Experimental Forest provide an exceptional opportunity to examine the effects and recovery of insect disturbance on subalpine forest ecosystems. Changes in discharge measured at the watershed level are typically quantified using statistical methods applied to time series data. Critical analysis elements are stationarity, and a sufficient data record for statistically significant detection of change. Short-term studies comparing statistical properties of flow often lack these critical elements and should be examined with caution. We show why short-term studies related to pine beetle impact on hydrology are unreliable. During the past five years, approximately 80% of the lodgepole pine overstory has been killed by MPB at Fraser Experimental Forest, yet double mass plots using control basins and analysis of covariance show no significant response to date. A process-based modeling approach offers a realistic alternative to predicting beetle-induced watershed changes.

Cornus florida L. Populations in the Appalachian Ecoregion in Decline

C. Oswalt — Wed, 24 Jun 2009 10:50:00 PDT

Over the last three decades a fungal disease identified as Discula destructiva Redlin has severely impacted Cornus florida L. (flowering dogwood) populations throughout its range. This study presents estimates of historical and current C. florida populations across the Appalachian ecoregion and surrounding area in the eastern United States. Population change is calculated at both the county and regional level. Specific objectives were to 1) quantify current C. florida populations in the Appalachian ecoregion, 2) quantify change in C. florida populations for the period beginning in the mid 1980’s to 2006 and 3) identify regional and spatial trends in C. florida population shifts for the same period. Field sampled data were gathered from the USDA Forest Service Forest Inventory and Analysis (FIA) database. Data were assembled from a total of 41 FIA units in 13 states for county-level estimates of the total number of all live trees for C. florida on timberland within its natural range. Analysis of covariance, comparing historical and current county-level dogwood population estimates with average change in forest density as the covariate, was used to identify significant changes within regional (FIA) units. Results indicate that significant (P < 0.05) regional (FIA unit) declines were observed in 33 of the 41 (80 percent) sampled regional units. Although, declines were widespread throughout all of the regional units surrounding the Appalachians, the largest declines appeared to be centered within the Appalachian Mountains. These results indicate that an important component of the eastern deciduous forest appears to be in serious decline throughout the Appalachians. Furthermore, these results support localized empirical results and landscape scale anecdotal evidence.

Development of Young Lodgepole Pine Leading Stands After Mountain Pine Beetle Attack in the Central BC Interior

K. Runzer et al. — Wed, 24 Jun 2009 11:10:00 PDT

The central interior of British Columbia, Canada is experiencing its largest recorded outbreak of mountain pine beetle (MPB) (Dendroctonus ponderosae Hopkins). Historically MPB only attacked larger (dbh >15cm), mature lodgepole pine (Pinus contorta Dougl. ex loud. var. latifolia Engelm.). However during this outbreak, MPB have attacked trees as young as 15 with dbh ~7.5 cm. Attack in 21 - 40 year old stands has averaged 60% but has been highly variable: ranging from 0 to 95%. Given the success of MPB in young pine stands, their stand dynamics and management will affect future forest composition and structure as well as timber supply. Our objectives were to document species composition, stocking of seedlings, saplings, poles (secondary structure), and level of MPB attack in young pine leading stands and to project their short (40 years) and long term (80 years) growth with and without management intervention in SORTIE-ND. Attack levels below 60% resulted in a small short term productivity losses (< 10%) and no long term loss. When attack rates exceeded 80%, short term productivity losses were between 20 - 35% and dependent on species composition and amount of secondary stand structure. Long term yields were reduced by less than 15%. The species composition of the future stand was a function of attack and species composition of secondary structure. The under planting of attacked stands had little impact on future productivity or species composition. Renewing attacked stands resulted in less productivity than observed in unmanaged stands for the time frames examined. MPB attack in young stands does result in short term yield loss when attack rates exceed 60%; shifts in species composition depending on the makeup of the secondary structure; and small losses in long term productivity. It appears the best management action may be to allow young pine stands to develop without intervention.

Seed Release in Lodgepole Pine Forests After Mountain Pine Beetle Outbreak

Francios Teste et al. — Wed, 24 Jun 2009 11:30:00 PDT

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.