Showing papers by "Daniel C. Laughlin published in 2006"

Wildland fire effects on forest structure over an altitudinal gradient, Grand Canyon National Park, USA

Abstract: Summary 1 Restoration of wildland fire to forests is a challenge when historical fire regimes have been altered. We studied four fires that burned over approximately 7865 ha on an altitudinal gradient in Grand Canyon National Park, USA, in 2003. The fires met criteria for the current USA policy allowing the restoration of fire's ecological role in forest landscapes: Wildland Fire Use for Resource Benefits. 2 After the fires burned out, we remeasured 82 permanent pre-established monitoring plots burned by the fires plus 43 additional plots on unburned companion sites. 3 The maximum height of charring of tree boles and basal area mortality increased in mean value and variability with altitude. At a low-altitude Pinus–Quercus site, tree density declined significantly but basal area was unchanged. At a mid-altitude mixed-conifer site and a high-altitude Picea/Abies/Populus site, both density and basal area declined. 4 The thinning effect of fire was concentrated on smaller, shorter, fire-susceptible trees. Small-diameter trees (< 20 cm diameter) made up 79–95% of all tree mortality. Shade-tolerant conifers, particularly true firs and spruce, experienced disproportionate mortality (31–82% basal area decline), while fire-resistant ponderosa pine and Douglas fir tended to survive (2–8% basal area decline). Delayed mortality between the first and second years following the fires accounted for only 4·2% of trees dying at the low-altitude site but 15·6% and 11·2% at the mid- and high-altitude sites, respectively. Regeneration density was highly variable but forest floor and woody debris declined in burned areas. 5 Synthesis and applications. This study shows that, even after an unusually long fire-free period (1880–2003), at the mid- and high-altitude burned sites fire effects were consistent with restoration of historical patterns, moving the ecosystems closer to historical reference conditions. Fires simultaneously reduced the living, dead and ladder fuels that made the forest vulnerable to uncharacteristically severe fire. These effects make the forests more resistant to the expected increases in fire size and severity under future climate conditions. Even at longer-than-historical fire intervals, the wildland fire use policy can benefit Grand Canyon forests.

Assessing Targets for the Restoration of Herbaceous Vegetation in Ponderosa Pine Forests

Abstract: A restoration project is considered a success when the initial target is met, but many targets are plausible. We evaluated the success of a restoration project in its 11th year since treatment in a southwestern ponderosa pine–bunchgrass community and the appropriateness of several targets. We measured the responses of (1) total standing crop; (2) standing crop of five functional groups (C3 and C4 graminoids, leguminous forbs, and nonleguminous perennial and annual forbs); (3) graminoid community composition; and (4) standing crop of five common graminoid species (Festuca arizonica, Muhlenbergia montana, Elymus elymoides, Carex geophila, and Poa fendleriana). Targets were quantified in remnant grass patches, which provided the standards for these targets, and were assessed in three other forest patch types (pre-settlement tree patches, post-settlement tree patches, and patches where all post-settlement trees were removed). Patches where all post-settlement trees were removed reached target levels for total standing crop, C3 and C4 graminoid standing crop, graminoid community composition, and M. montana, E. elymoides, and C. geophila standing crops. Standing crop of legumes and of F. arizonica did not increase over time in any patch type. Targets were not met in pre-settlement patches or in patches where some post-settlement trees were left standing, suggesting that it is unrealistic to expect equal responses across all patch types. If increasing herbaceous standing crop is a major goal, practitioners should create gaps within the pine forest canopy.

A multivariate model of plant species richness in forested systems: old‐growth montane forests with a long history of fire

Abstract: Recently, efforts to develop multivariate models of plant species richness have been extended to include systems where trees play important roles as overstory elements mediating the influences of environment and disturbance on understory richness. We used structural equation modeling to examine the relationship of understory vascular plant species richness to understory abundance, forest structure, topographic slope, and surface fire history in lower montane forests on the North Rim of Grand Canyon National Park, USA based on data from eighty-two 0.1 ha plots. The questions of primary interest in this analysis were: (1) to what degree are influences of trees on understory richness mediated by effects on understory abundance? (2) To what degree are influences of fire history on richness mediated by effects on trees and/or understory abundance? (3) Can the influences of fire history on this system be related simply to time-since-fire or are there unique influences associated with long-term fire frequency? The results we obtained are consistent with the following inferences. First, it appears that pine trees had a strong inhibitory effect on the abundance of understory plants, which in turn led to lower understory species richness. Second, richness declined over time since the last fire. This pattern appears to result from several processes, including (1) a post-fire stimulation of germination, (2) a decline in understory abundance, and (3) an increase over time in pine abundance (which indirectly leads to reduced richness). Finally, once time-since-fire was statistically controlled, it was seen that areas with higher fire frequency have lower richness than expected, which appears to result from negative effects on understory abundance, possibly by depletions of soil nutrients from repeated surface fire. Overall, it appears that at large temporal and spatial scales, surface fire plays an important and complex role in structuring understory plant communities in old-growth montane forests. These results show how multivariate models of herbaceous richness can be expanded to apply to forested systems.

Meeting forest ecosystem objectives with wildland fire use

Abstract: Three 2003 Grand Canyon National Park fires burned 83 plots across the park’s North Rim old-growth forests that range from open ponderosa pine groves to dense spruce–fir–aspen stands at 7,300 to 8,800 feet (2,225 to 2,682 m) elevation. Ignited by lightning, these fires were managed by the U.S. Department of the Interior (USDI) National Park Service as wildland fire use (WFU) to meet resource objectives. As outlined below, they provided an excellent opportunity to evaluate low to mixed-severity fire effects.