Ann M. Lynch

Multicentury, Regional‐Scale Patterns of Western Spruce Budworm Outbreaks

Tree ring chronologies from 24 mixed—conifer stands were used to reconstruct the long—term history of western spruce budworm (Choristoneura occidentalis) in northern New Mexico. Temporal and spatial patterns of budworm infestations (within—stand occurrences) and outbreaks (more—or—less synchronous infestations across many stands) were investigated to identify local—scale to regional—scale forest disturbance patterns. Nine regional—scale outbreaks were identified from 1690 to 1989. One ancient stand of Douglas—fir trees (Pseudotsuga menziesii) exceeding 700 yr in age revealed that budworms and overstory trees can coexist for extraordinary lengths of time. Using spectral analysis we found that the regional outbreak record contained important cyclical components with periods varying from ≈20 to 33 yr. The statistically significant (P < .05) but variable periodicity of regional outbreaks suggests the forest—budworm dynamic is pseudoperiodic (i.e., a stable limit cycle or damped oscillator perturbed by noise). Duration of infestations within stands was ≈11 yr and has not obviously changed in the 20th century; however, infestations tended to be more synchronous among stands in this century than during earlier centuries. Regional budworm activity was low from the mid—1920s to late 1930s and mid—1960s to late 1970s, and the most recent outbreak, beginning in the late 1970s, was unusually severe. These results, and contrasting infestation patterns in mountain ranges with different land use histories, generally support a hypothesis that human—induced changes in Southwestern forests have led to more widespread and intense budworm outbreaks in the late 20th century. Despite human—induced changes in the 20th century, climate variation also appears to have been important to budworm regimes in this century as well as in earlier times. Regional outbreaks in the 20th century tended to occur during years of increased spring precipitation, and decreased budworm activity coincided with decreased spring precipitation. No clear association with temperature was identified. Comparisons of regional outbreak history since AD 1600 with a reconstruction of spring precipitation from limber pine (Pinus flexilis) ring width chronologies also shows that periods of increased and decreased budworm activity coincided with wetter and drier periods, respectively. This finding contrasts with results from shorter time—scale studies conducted in northwestern U.S. and Canada (western spruce budworm) and eastern Canada (spruce budworm C. fumiferana), where low precipitation and/or warmer temperatures were generally associated with outbreaks. Different patterns of budworm population response to changing moisture regimes might be due to differences in regional forest—budworm systems, or to differences in the spatial and temporal scales of observation. We conclude that changes in forest structure in the southwestern U.S. may have shifted the spatial and temporal pattern of budworm outbreaks. The dynamic behavior and statistically significant association between multicentury, regional budworm and climate time series also suggest that complex budworm dynamics are driven by a combination of internal and external factors.

Relationships between spruce budworm damage and site factors in spruce-fir-dominated ecosystems of Western Upper Michigan

Hix, D.M., Barnes, B.V., Lynch, A.M. and Witter, J.A., 1987. Relationships between spruce budworm damage and site factors in spruce-fir-dominated ecosystems of western Upper Michigan. For. Ecol. Manage., 21:129-140 Damage by the spruce budworm, Choristoneura fumiferana {Clemens), on balsam fir, Abies balsamea (L.) Mill., in local ecosystems (site units) of the Ottawa National Forest {western Upper Peninsula of Michigan, U.S.A.) was studied in relation to site factors. A multi-factor ecological approach was used to distinguish 25 spruce-fir-dominated ecosystems on a variety of different sites, ranging from dry-mesic outwash plains to river floodplains and swamps. Spruce budworm damage on balsam fir appears to be more directly related to site factors (specifically soil type and drainage class) than to stand parameters such as relative dominance or living-plus-dead basal area. Damage on balsam fir was greatest on wetland ecosystems with organic soils and on dryland ecosystems with impeded drainage. The heavy damage on these soils is probably a consequence of shallow rooting habit which predisposes the physiologically mature balsam fir to drought injury, lessened vigor, and a lessened ability to withstand defoliation. Black spruce, Picea mariana (Mill.) B.S.P., also exhibited heavy damage on sites where it is not well adapted, i.e. somewhat excessively drained dryland ecosystems. An understanding of the site factors and the ecosystem classification provide the basis for predicting where the greatest damage can be expected.

Discriminating disturbance from natural variation with LiDAR in semi-arid forests in the southwestern USA

Discriminating amongst spatial configurations and climax size of trees in forests along varying physical gradients from time since last disturbance is a significant component of applied forest management. Understanding what has led to the existing vegetations structure has important implications for monitoring succession and eco-hydrological interactions within the critical zone: the near-surface environment where rock, soil, air, and biota interact and regulate ecosystem services. This research demonstrates the utilities of local indicators of spatial association (LISA) to (1) quantify natural variation in forest structure as derived from aerial Light Detection and Range (LiDAR) across topographically complex landscapes at ecologically relevant scale, i.e., individual trees; (2) map previously recorded but poorly defined forest disturbances; and (3) link scalable topographic indices to observed tree size distributions. We first selected a priori undisturbed and disturbed stands scanned by aerial LiDAR t...

Forest visual resources and pest management: potential applications of visualization technology

Abstract Visualization technology allows us to picture, model and project over several years the effects of pest outbreaks and management activities on visual resources. The capability to visualize different potential future forest conditions can help resource managers plan projects, envision long-term ramifications, and interact with the public, and can facilitate research on human perception and recreational behavior.

Review and recommendations for climate change vulnerability assessment approaches with examples from the Southwest

Climate change creates new challenges for resource managers and decision-makers with broad and often complex effects that make it difficult to accurately predict and design management actions to minimize undesirable impacts. We review pertinent information regarding methods and approaches used to conduct climate change vulnerability assessments to reveal assumptions and appropriate application of results. Secondly, we provide managers with an updated summary of knowledge regarding vulnerability of species and habitats to climate change in the American Southwest. Overall, vulnerability assessments provided valuable information on climate change effects and possible management actions but were far from a comprehensive picture for the future of the Southwest. Scales, targets, and assessment approaches varied widely and focused on only a subset of resources. We recommend land managers critically examine methods when using assessment results; select scale, methods, and targets carefully when planning new assessments; and communicate assessment needs to researchers of climate change response.

Tree Morphologic Plasticity Explains Deviation from Metabolic Scaling Theory in Semi-Arid Conifer Forests, Southwestern USA.

A significant concern about Metabolic Scaling Theory (MST) in real forests relates to consistent differences between the values of power law scaling exponents of tree primary size measures used to estimate mass and those predicted by MST. Here we consider why observed scaling exponents for diameter and height relationships deviate from MST predictions across three semi-arid conifer forests in relation to: (1) tree condition and physical form, (2) the level of inter-tree competition (e.g. open vs closed stand structure), (3) increasing tree age, and (4) differences in site productivity. Scaling exponent values derived from non-linear least-squares regression for trees in excellent condition (n = 381) were above the MST prediction at the 95% confidence level, while the exponent for trees in good condition were no different than MST (n = 926). Trees that were in fair or poor condition, characterized as diseased, leaning, or sparsely crowned had exponent values below MST predictions (n = 2,058), as did recently dead standing trees (n = 375). Exponent value of the mean-tree model that disregarded tree condition (n = 3,740) was consistent with other studies that reject MST scaling. Ostensibly, as stand density and competition increase trees exhibited greater morphological plasticity whereby the majority had characteristically fair or poor growth forms. Fitting by least-squares regression biases the mean-tree model scaling exponent toward values that are below MST idealized predictions. For 368 trees from Arizona with known establishment dates, increasing age had no significant impact on expected scaling. We further suggest height to diameter ratios below MST relate to vertical truncation caused by limitation in plant water availability. Even with environmentally imposed height limitation, proportionality between height and diameter scaling exponents were consistent with the predictions of MST.