Evaluation of Multiple Funnel Traps and Stand Characteristics for Estimating Western Pine Beetle-Caused Tree Mortality

Abstract

The western pine beetle, Dendroctonus brevicomis LeConte (Coleoptera: Curculionidae: Scolytinae), is a major cause of ponderosa pine, Pinus ponderosa Dougl. ex Laws., mortality in much of western North America. This study was designed to quantify relationships between western pine beetle trap catches [including those of its primary invertebrate predator Temnochila chlorodia (Mannerheim) (Coleoptera: Trogositidae)], and levels of tree mortality attributed to western pine beetle at 44 trapping sites (stands) and within five general locations (forests) in California. Furthermore, we evaluated relationships between forest stand characteristics and levels of western pine beetle-caused tree mortality. Preliminary analyses were conducted by Pearson's correlation coefficient (r) using tree mortality per hectare and percentage of tree mortality and 10 potential predictor variables. All predictor variables that had significant correlations (western pine beetle per day, western pine beetle: T. chlorodia, percentage of western pine beetle [percentage of total trap catch represented by western pine beetle], trees per hectare, basal area of all tree species, basal area of P. ponderosa, mean diameter at breast height [dbh] and stand density index) were considered for linear and multiple linear regression models for predicting levels of western pine beetle-caused tree mortality. Our results suggest monitoring western pine beetle populations through the use of pheromone-baited multiple funnel traps is not an effective means of predicting levels of western pine beetle-caused tree mortality. However, levels of western pine beetle-caused tree mortality can be efficiently predicted (adjusted R2 >0.90) at large spatial scales (forests; approximately 3,000-14,000 ha of contiguous host) by simply measuring stand density, specifically the basal area of all tree species or stand density index. The implications of these results to forest management are discussed.

Detecting Drought-Induced Tree Mortality in Sierra Nevada Forests with Time Series of Satellite Data

“…Some previous studies found that the density of host tree species has much less predictive power than the overall tree density for western pine beetle-caused tree mortality in California, and areas with highest tree density experienced highest levels of mortality, both absolutely (dead trees per acre) and proportionally (percent of trees that die off) [59,83]. When a tree density map is available for the region, it would also be interesting to derive the relative mortality and test the capability of RF to quantify tree mortality on a proportion basis.…”

“…The majority of these affected areas were subject to infestations of fir engraver beetles (Scolytus ventralis), western pine beetles (Dendroctonus brevicomis), and Jeffrey pine beetles (D. jeffryi) ( Figure S4). Outbreaks of these beetles typically occur in conjunction with weakened trees, and the severe drought likely contributed to the elevated mortality from infestations in 2015 and 2016 [15,18,58,59]. …”

“…Trees need moisture to ward off infestations from insects, thus intensified drought stress makes trees more vulnerable to insect attacks. Bark beetle (Scolytinae) populations, for example, are found to be more successful in denser, drought-stressed forests where they can disperse easily and kill weakened trees [15,[17][18][19]59,83].…”

Pheromones and Other Semiochemicals for Monitoring Rare and Endangered Species

“…In pest management, pheromone-based monitoring is to a great extent focused on indications of abundance in relation to economic injury thresholds. Most of these studies deal with future predictions of abundance and/or damage levels based on host and pest phenology and weather conditions (Anderson et al 2012; Damos and Savopoulou-Soultani 2010; Dömötör et al 2007; Hayes et al 2009; Mori et al 2014). Nevertheless, there are a considerable number of studies that relate trap catches to abiotic conditions, which would constitute a platform for normalizing catches between different occasions (Williams et al 2008).…”

Resiliency of an Interior Ponderosa Pine Forest to Bark Beetle Infestations Following Fuel-Reduction and Forest-Restoration Treatments

“…Factors such as stand density, host density, average tree diameter, and average stand age are consistently identified as primary attributes associated with the severity of bark beetle infestations in the Western United States [21]. For example, Hayes et al [29] showed that levels of D. brevicomis-caused tree mortality in P. ponderosa forests in California can be predicted (Adjusted R 2 > 0.90) at large spatial scales by simply measuring stand density, specifically the basal area of all tree species. In the last decade, numerous studies have examined the effects of fuel-reduction and forest-restoration treatments on the amount, distribution and causes of tree mortality in P. ponderosa (e.g., [24,25,[30][31][32][33][34][35][36][37][38][39][40][41]).…”