Christine G. Niwa

Influence of Prescribed Fire on Carabid Beetle (Carabidae) and Spider (Araneae) Assemblages in Forest Litter in Southwestern Oregon

Abstract The objective of this study was to determine if prescribed fire affects spider (Araneae) and carabid beetle (Carabidae) abundance, and whether the magnitude of this effect varies with time since fire. Within mixed conifer stands, nine understory fuels-reduction burns, ranging from <1 to 15 yr old, were compared with adjacent unburned sites. Pitfall traps were used to compare macroarthropod abundance over 5 mo. In total, 3,441 spiders in 24 families and >120 species, and 14,793 carabid beetles from 17 species, were identified from the samples. Seven spider families and five species of carabid beetles were abundant enough to be analyzed statistically. Four spider families were more abundant in unburned sites (Antrodiaetidae, Cybaeidae, Thomisidae and Linyphiidae) while three families were more numerous in burned sites (Lycosidae, Gnaphosidae and Dictynidae). Four of five carabid beetle species were more abundant in unburned sites [Pterostichus herculaneus Mannerheim, P. setosus Hatch, Scaphinotus rugiceps rugiceps (Horn) and Zacotus matthewsii LeConte]. There was no difference found for Omus cazieri van den Berghe. No differences in species richness or diversity (Simpson, Shannon-Wiener and Berger-Parker indices) were found for spiders or carabid beetles. Overall, the relationship between abundance and time since burning was weak, with marginal significance found only for Dictynidae and Gnaphosidae. We suggest that changes in foraging substrate, prey availability or microclimatic conditions since fire may have interacted with life history characteristics to influence the abundance of these organisms. Differences in fire intensities among years may have masked patterns in arthropod abundance associated with time since burning.

Season and severity of prescribed burn in ponderosa pine forests: Implications for understory native and exotic plants

Abstract We investigated herbaceous richness and cover in relation to fire season and severity, and other variables, five growing seasons following prescribed fires. Data were collected from six stands consisting of three randomly applied treatments: no burn, spring burn, and fall burn. Fall burns had significantly more exotic/native annual/biennial (an/bi) species and greater cover of these species (6.5% exotic; 1.7% native) compared to spring and unburned areas. These patterns are likely related to indirect fire effects associated with fire severity and resource availability, rather than direct fire effects due to burn timing. CART models indicated that high native and exotic an/bi richness and cover were associated with overstory gaps and higher fire severity areas, conditions common to fall burns. Exotics may be more successful at exploiting these environments. No treatment differences were found for native perennials. Location was important for explaining native perennial patterns, but richness and cover were also positively associated with lower fire severity, greater tree cover, and coarse woody debris. Expectations for increased native perennial plant diversity and abundance following prescribed fires may not necessarily be met and exotic species spread may compromise other ecosystem attributes. Restoration in these forests presents a challenge as prescribed fires interact with present environmental conditions that are very different from historical ones.

Kairomonal response of Thanasimus undatulus, Enoclerus sphegeus (Coleoptera: Cleridae), and Temnochila chlorodia (Coleoptera: Trogositidae) to bark beetle semiochemicals in Eastern Oregon

Abstract The kairomonal responses of Thanasimus undatulus (Say), Enoclerus sphegeus F., and Temnochila chlorodia (Mannerheim) to semiochemicals used by Dendroctonus pseudotsugae Hopkins, D. rufipennis Kirby, D. brevicomis LeConte, D. ponderosae Hopkins, and Ips pini (Say) to locate hosts were quantified in the field during the period of D. pseudotsugae dispersal in the spring and early summer. Traps baited with frontalin plus seudenol caught significantly more T. undatulus than traps baited with any other lure. Only a few E. sphegeus were collected during the study, suggesting that it might use semiochemicals other than those tested in this study to locate its prey. All of the traps baited with lures containing exo-brevicomin caught significantly more T. chlorodia than traps baited with other lures. These results suggest that T. undatulus uses seudenol primarily to locate its prey habitat, and T. chlorodia uses exo-brevicomin for the same purpose. These predators likely feed upon bark beetles that produce these compounds or other bark beetles that are found in the same habitats. A secondary pest of ponderosa pine, Pityogenes carinulatus (LeConte), was attracted in significant numbers to the traps baited with I. pini pheromone components. Traps baited with ipsdienol and lanierone caught significantly more P. carinulatus than traps baited with ipsdienol alone.

Longer-Term Effects of Selective Thinning on Microarthropod Communities in a Late-Successional Coniferous Forest

Abstract Microarthropod densities within late-successional coniferous forests thinned 16–41 yr before sampling were compared with adjacent unthinned stands to identify longer term effects of thinning on this community. Soil and forest floor layers were sampled separately on eight paired sites. Within the forest floor oribatid, mesostigmatid, and to a marginal extent, prostigmatid mites, were reduced in thinned stands compared with unthinned stands. No differences were found for Collembola in the forest floor or for any mite suborder within the soil. Family level examination of mesostigmatid and prostigmatid mites revealed significant differences between stand types for both horizons. At the species level, thinning influenced numerous oribatid mites and Collembola. For oribatid mites, significant or marginally significant differences were found for seven of 15 common species in the forest floor and five of 16 common species in soil. Collembola were affected less, with differences found for one of 11 common species in the forest floor and three of 13 common species in soil. Multivariate analysis of variance and ordination indicated that forest thinning had little influence on the composition of oribatid mite and collembolan communities within either the forest floor or soil. Differences in microclimate or in the accumulation of organic matter on the forest floor were likely most responsible for the observed patterns of abundance. Considering the role that microarthropods play in nutrient cycling, determining the functional response of a wide range of taxa to thinning may be important to effective ecosystem management.