Spatio-temporal dynamics of a tree-killing beetle and its predator

by Dr. Molly Darr | Jun 15, 2022 | 2011-2020 Publications

Abstract

Resolving linkages between local-scale processes and regional-scale patterns in abundance of interacting species is important for understanding long-term population stability across spatial scales. Landscape patterning in consumer population dynamics may be largely the result of interactions between consumers and their predators, or driven by spatial variation in basal resources. Empirical testing of these alternatives has been limited by the lack of suitable data. In this study, we analyzed an extensive network of spatially replicated time series to characterize the local and regional processes affecting spatio-temporal dynamics of a tree-killing bark beetle (Dendroctonus frontalis or SPB) and its key predator (Thanasimus dubius) across the southeastern United States. We first used a mechanistic model to evaluate factors affecting the stability of 95 predator–prey time series and then conducted spatial analyses to evaluate scale dependence in the factors affecting the geographical patterning of this system. Across the region, population fluctuations of both species were correlated in space beyond 400 km but there was notable spatial variation in the deterministic and stochastic processes influencing forest-scale (local) fluctuations. Time series analyses indicated that local dynamics of SPB and T. dubius are not cyclical. Instead, the abundance of T. dubius responded almost instantaneously to changes in SPB abundance. Spatial variation in long-term forest-scale abundance of both species was linked most strongly to the abundance of pine habitat indicating a stronger role for resource availability in SPB population dynamics than top-down effects. Our results are consistent with other studies indicating that animal populations tend to be synchronized in space via spatially correlated processes such as weather; yet local dynamics tend to be linked to smaller-scale host patterns. Our study provides a rare empirical assessment of how local processes scale up to produce landscape patterns that influence forest ecology and forest management.

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Cost sharing for pre-commercial thinning in southern pine plantations: Willingness to participate in Virginia’s pine bark beetle prevention program

by Dr. Molly Darr | Jun 15, 2022 | 2011-2020 Publications

Abstract

Forest management that reduces southern pine beetle (SPB) risk benefits not only the landowners, but all who draw benefits from southern pine forests, including other owners whose risk is reduced by landscape-wide efforts. One such practice is pre-commercial thinning (PCT) of pine stands, which may be unattractive to landowners due to substantial upfront costs and delayed or uncertain financial return. Because societal benefits are not fully realized by those who implement PCT, there may be a market externality whereby it is underprovided. Virginia’s Pine Bark Beetle Prevention Program attempts to correct this externality by reimbursing a portion of PCT costs. To examine the efficacy of cost sharing in promoting participation, a survey was sent to 1200 NIPF landowners in Virginia, where southern pine is prevalent and SPB is a concern. Willingness to participate is measured using a referendum-style question for PCT on a hypothetical, qualifying property over a cost-share range of 20% to 90%. Results of discrete choice models indicate that cost sharing has a significant, positive effect on willingness to participate overall, though results indicate that increasing reimbursement above the 50% level is unlikely to increase participation substantively. Education and ownership preferences are also significant predictors of willingness to participate, with potential implications for program targeting and marketing.

Keywords

Pest management, Pre-commercial thinning, Referendum questionnaire, Discrete choice model

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Temperatures experienced by wood-boring beetles in the under-bark microclimate

by Dr. Molly Darr | Jun 15, 2022 | 2011-2020 Publications

Abstract

Most studies of under-bark microclimate have been restricted to observations of a few coniferous trees in wooded locations. The findings of these studies may not generalize to deciduous hardwood trees, or to trees in urban environments. We addressed this limitation with a large data set of under-bark temperatures of ash trees (Fraxinus spp.) in urban and woodlot environments at six different Ontario locations. We observed that daily minimum under-bark temperatures of these deciduous trees are significantly warmer than daily minimum air temperatures in the winter, and that these differences can be important to predictions of overwintering mortality of wood-boring beetles during cold periods. The difference between air and under-bark temperature minima can vary considerably, and we observed that, on 17% of days in the winter of 2008–2009, minimum under-bark temperatures differed by more than 4°C from minimum air temperatures on the north side of woodlot trees (the most conservative value found). With such large differences relatively common, we conclude that assumptions of a constant level of temperature difference between the under-bark microclimate and air temperature are not valid. There were significant differences between under-bark temperature minima in urban and woodlot environments, but the small magnitude of these differences (<0.5 °C) suggests that urban heat island effects will not significantly influence beetle overwintering survival, at least for urban trees bordering a park or yard. Spring maxima under-bark temperatures on the south side of trees were significantly warmer than air temperature maxima, but not for the north side of the trees. This difference leads to significantly faster predicted development times for beetles on the south side of urban trees. However, no difference was found between development times predicted using air temperature and under-bark temperatures for the south side of woodlot trees. Clearly, solar loading leads to faster development rates, and as a result, we suggest urban trees in exposed areas may alter the projected population dynamics of wood-boring insects in wider regions.

Keywords

Agrilus, Deciduous, Microclimate, Phloem, Temperature, Urban

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Vermunt, Bradley, Kim Cuddington, Stephanie Sobek-Swant, Jill C. Crosthwaite, D. Barry Lyons, and Brent J. Sinclair. 2012. “Temperatures Experienced by Wood-Boring Beetles in the under-Bark Microclimate.” Forest Ecology and Management269 (April): 149–57. https://doi.org/10.1016/j.foreco.2011.12.019.

Evaluation of phenological indicators for optimizing spring southern pine beetle (Coleoptera: Curculionidae: Scolytinae) trapping surveys

by Dr. Molly Darr | Jun 15, 2022 | 2011-2020 Publications

Abstract

Since 1987, as many as 16 southeastern US states participate in a 4 wk. annual spring Dendroctonus frontalis (Zimmerman) (Coleoptera: Curculionidae) trapping survey. The purpose of the survey is to assess the current D. frontalis outbreak potential, and anticipate prevention and suppression needs for the coming yr. This prediction system relies on capturing the peak D. frontalis spring dispersal, thus timing of trap deployment is crucial. Forest managers traditionally attempt to deploy traps at the onset of flowering dogwood (Cornus florida L.; Cornaceae) bloom, which is commonly assumed to coincide with peak D. frontalis spring dispersal. The objective of this study is to examine the validity of dogwood bloom as an indicator of peak D. frontalis spring dispersal. Yr-round trapping data in 2014 and 2015 from Mississippi and Florida were used to identify peak D. frontalis and Thanasimus dubius (Fabricius) (Coleoptera: Cleridae) dispersal periods. Peak D. frontalis dispersal then was compared with dogwood blooming dates from the USA National Phenology Network and personal records. Then, both dogwood bloom dates and peak D. frontalis dispersal were compared with timing of actual historic state D. frontalis trapping efforts. We also compared peak D. frontalis dispersal with T. dubius peak dispersal, because T. dubius trap captures are used in the prediction model. Last, we examined the utility of extending the spring survey to 6 wk by comparing the 4 wk peak D. frontalis trap captures with a corresponding 6 wk peak. On average, mean onset of dogwood bloom occurred 3 wk after the peak 4 wk period of D. frontalis flight activity. The average T. dubius peak dispersal occurred 1.5 wk after peak D. frontalis dispersal. The 6 wk extension provided only a 12% overall average increase in D. frontalis trap captures. Eastern redbud (Cercis canadensis L.; Fabaceae) also had been suggested as a replacement trap deployment cue; therefore, eastern redbud and flowering dogwood blooming dates in 2019 were monitored on a Mississippi State University property in Oktibbeha County, Mississippi, USA. On this site eastern redbud trees bloomed on average 2.3 wk before the average bloom date of flowering dogwood trees.

Keywords

bloom; Cercis canadensis; Cornus florida; Dendroctonus frontalis; monitoring

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Thomason, John W., Stephen Clarke, and John J. Riggins. 2020. “Evaluation of Phenological Indicators for Optimizing Spring Southern Pine Beetle (Coleoptera: Curculionidae: Scolytinae) Trapping Surveys.” Florida Entomologist 103 (4): 444–51.

Fuel dynamics and its implication to fire behavior in loblolly pine-dominated stands after southern pine beetle outbreak

by Dr. Molly Darr | Jun 15, 2022 | 2011-2020 Publications

Abstract

Southern pine beetle (SPB) (Dendroctonus frontalis Zimm) outbreaks and wildfire occurrence in recent decades has triggered growing concerns regarding their possible interactions. However, few studies have quantified the fuel characteristics of SPB-killed stands, especially the dynamics of the resulting fuel complex. More importantly, how changes in the fuel complex will affect fire behavior remains unclear. Using field measurements in combination with fire modeling systems, we studied fuel dynamics and its implication to potential fire behaviors by sampling non-outbreak, early post-outbreak (2–3 years), and late post-outbreak (7–8 years) loblolly pine dominated stands in Georgia and South Carolina, USA. We found that the loadings of 1-hr, 10-hr, 100-hr, 1000- hr fuels, and litter depth were significantly greater in post-outbreak stands than in non-outbreak stands. Stand structure was altered in post-outbreak stands, which contained fewer live pines and more hardwoods. We used the Fuel Characteristic Classification System (FCCS) combined with actual data to construct representative fuel beds from the field data. These customized fuel beds were then used to model surface fire behavior that could be altered by the changes in fuel loading and stand structure resulting from SPB outbreaks. Both FCCS and BehavePlus fire modeling systems predicted a faster rate of spread and longer flame lengths in post-outbreak stands than in non-outbreak stands. Late post-outbreak stands under extremely dry conditions were predicted to have the most extreme fire behavior. Our results fill a critical knowledge gap, which will help forest managers make informed decisions on the management of loblolly pine-dominated stands after the southern pine beetle outbreak.

Keywords

Fuel dynamics, Fire behavior, Loblolly-dominated forests, Southern pine beetle outbreaks, Piedmont

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Xie, Hongtao, Jennifer E. Fawcett, and G. Geoff Wang. 2020. “Fuel Dynamics and Its Implication to Fire Behavior in Loblolly Pine-Dominated Stands after Southern Pine Beetle Outbreak.” Forest Ecology and Management 466 (June): 118130. https://doi.org/10.1016/j.foreco.2020.118130.