Treesearch

In the southwestern U.S., wildland fire frequency and area burned have steadily increased in recent decades, a pattern attributable to multiple ignition sources. To examine contributing landscape factors and patterns related to the occurrence of large (P20 ha in extent) fires in the forested region of northern Arizona, we assembled a database of lightning- and human-caused fires for the period 1 April to 30 September, 1986– 2000. At the landscape scale, we used a weights-of-evidence approach to model and map the probability of occurrence based on all fire types (n = 203), and lightning-caus...

At the request of The Nature Conservancy and the Front Range Fuels Treatment Partnership, we are developing brief summaries of the current state of our scientific understanding of historical fire regimes in the forested landscapes of Colorado's Front Range. The area of interest extends from El Paso and Teller Counties, near Pikes Peak, to Larimer County and the Colorado-Wyoming border. This article focuses on forests in which ponderosa pine is a dominant or co-dominant species. A subsequent article will deal with forests of lodgepole pine, spruce, and fir. M. Kaufmann and T. Veblen have...

We investigated lifetime reproductive success (LRS) of 22 male and 46 female adult Flammulated Owls (Otus flammeolus) in Colorado from 1981-2003. Sexual differences in LRS were at least partially attributable to incomplete breeding histories of females, due to females having a higher estimated emigration rate from the study area than males. The mean number of lifetime breeding attempts for males was 3.4 6 0.6 (SE; range 5 1-12), and for females it was 1.9 6 0.3 (range 5 1-8). Adjusted for emigration beyond the study area, the estimated mean number of lifetime breeding attempts was 3.6 for...

We tested the hypothesis that the response of Paraphidippus aurantius (Lucas 1833) (Salticidae) to a simulated threat of predation would depend on a combination of spider size and reproductive status. In ponderosa pine forests of Colorado we located nests with spiders of varying sizes that were either adult female spiders guarding offspring or juvenile female and male spiders. To simulate a predator threat we applied a disturbance to the sides of spider nests using repeated puffs of air expressed from a rubber bulb or by blowing. We recorded the threat intensity (number of puffs) required...

Intraguild predation occurs when top predators feed upon both intermediate predators and herbivores. Intraguild predators may thus have little net impact on herbivore abundance. Variation among communities in the strength of trophic cascades (the indirect effects of predators on plants) may be due to differing frequencies of intraguild predation. Less is known about the influence of variation within communities in predator-predator interactions upon trophic cascade strength.

Predators affect herbivores directly and indirectly, by consumptive and nonconsumptive effects, and the combined influence of multiple predators is shaped by interactions among predators. I documented the individual and combined effects of birds (chickadees, nuthatches, warblers) and ants (Formica podzolica) on arthropods residing in pine (Pinus ponderosa) canopies in a factorial field experiment. Birds and ants removed herbivores but simultaneously benefited them by removing predatory arthropods. Birds and ants had net negative and positive effects, respectively, on the abundance of...

Seedfall, natural regeneration establishment, and growth of planted seedlings was observed from 1981 to 2001 under shelterwood and seedtree overstories in a replicated study in ponderosa pine in the Manitou Experimental Forest in the Colorado Front Range. Good seed crops were produced only every 4 to 6 years, with almost no viable seed produced in intervening years. With seed predation, only 14% of total seedfall was available for germination. Shelterwood overstories containing between 6 and 14 m2 ha_1 stem basal area over scarified seedbeds provided optimal conditions for natural seedling...

The recent impetus to reduce wildfire risk in urban interface forests of the Colorado Front Range has resulted in the adoption of mechanized thinning to reduce forest density. Lack of suitable markets for the resulting biomass has further prompted the use of in-the-woods chipping and mastication (chunking) to reduce the flammability of the material and scatter it on-site. While these techniques are effective in reducing wildfire risk, little is known about the effect that leaving this biomass has on subsequent understory vegetation recovery and soils. This document describes an area on the...

Disturbances such as fire play a key role in controlling ecosystem structure. In fire-prone forests, organic detritus comprises a large pool of carbon and can control the frequency and intensity of fire. The ponderosa pine forests of the Colorado Front Range, USA, where fire has been suppressed for a century, provide an ideal system for studying the long-term dynamics of detrital pools. Our objectives were (1) to quantify the long-term temporal dynamics of detrital pools; and (2) to determine to what extent present stand structure, topography, and soils constrain these dynamics. We...

The purpose of this study is to assess the long-term ecological effects of mechanical fuel treatments in a mixed Ponderosa pine-Douglas fir forest following two different thinning strategies: (a) chip-harvesting with all biomass retained on-site, and (b) whole-tree harvesting with all thinned material removed from the site. Changes in forest community structure under each of the above treatments are being tracked and compared with unthinned control plots over a 10-year period by monitoring the following parameters: (1) soil chemical properties, including ammonia and nitrate-N pools, net...