Showing papers by "W. Wallace Covington published in 2004"

Comparison of Historical and Contemporary Forest Structure and Composition on Permanent Plots in Southwestern Ponderosa Pine Forests

Abstract: We compared historical (1909-1913) and contemporary (1997-1999) forest struc- ture and composition on 15 permanent plots in ponderosa pine (Pinus ponderosa Dougl. ex Laws.) forests of Arizona and New Mexico. We used the same sampling methods as in the early 1900s and compared stand density, diameter distributions, species composition, and broad age classes from the two periods. Stand density (trees 9.14 cm dbh) significantly (P 0.001) increased on plots from an average of 77.4 trees per plot (s 49.9) at plot establishment in 1909-1913 to 519.1 trees per plot (s 252.3) at remeasurement in 1997-1999. Basal area significantly (P 0.001) increased from 8.0 m 2 per plot (s 3.5) to 28.5 m 2 per plot (s 10.1). Contemporary tree diameter distribution shifted toward smaller size classes as demonstrated by a significant (P 0.001) decrease in quadratic mean diameter from 38.5 cm (s 7.5) in 1909-1913 to 28.6 cm (s 7.1) in 1997-1999. Broad age classes yielded an average of 61.5 (s 49.5) residual live trees classified as "blackjack" ponderosa pine (P. ponderosa 150 years) and 13.3 (s 11.9) "yellow pine" (P. ponderosa 150 years) in 1909-1913. In 1997-1999, 416 live trees (s 229.6) were "blackjack" and 57.2 (s 28.5) trees on average were "yellow pine." Twelve of the 15 plots were not invaded by other tree species (remained pure ponderosa pine type), while composition shifted slightly on three plots toward more shade-tolerant and fire-in- tolerant species. Ninety-one percent of the historically (1909-1913 or older) mapped tree struc- tures (live trees, snags, logs, stumps, etc.) were relocated, which suggested that the forest reconstruction field techniques are reliable within 10%. Dramatic increases in tree densities may represent an increased potential for bark beetle epidemics and stand replacing wildfire over large areas in the Southwest. FOR .S CI. 50(2):162-176.

Slash Pile Burning Effects on Soil Biotic and Chemical Properties and Plant Establishment: Recommendations for Amelioration

Abstract: Ponderosa pine forest restoration consists of thinning trees and reintroducing prescribed fire to reduce unnaturally high tree densities and fuel loads to restore ecosystem structure and function. A current issue in ponderosa pine restoration is what to do with the large quantity of slash that is created from thinning dense forest stands. Slash piling burning is currently the preferred method of slash removal because it allows land managers to burn large quantities of slash in a more controlled environment in comparison with broadcast burning slash. However burning slash piles is known to have adverse effects such as soil sterilization and exotic species establishment. This study investigated the effects of slash pile burning on soil biotic and chemical variables and early herbaceous succession on burned slash pile areas. Slash piles were created following tree thinning in two adjacent approximately 20-ha ponderosa pine (Pinus ponderosa) restoration treatments in the Coconino National Forest near Flagstaff, Arizona. We selected 30 burned slash pile areas and sampled across a gradient of the burned piles for arbuscular mycorrhizal (AM) propagule densities, the soil seed bank, and soil chemical properties. In addition, we established five 1-m 2 plots in each burned pile to quantify the effect of living soil (AM inoculum) and seeding amendments on early herbaceous succession in burned slash pile areas. The five treatments consisted of a control (no treatment), living soil (AM inoculum) amendment, sterilized soil (no AM inoculum) amendment, seed amendment, and a seed/soil (AM inoculum) amendment. Slash pile burning nearly eliminated populations of viable seeds and AM propagules and altered soil chemical properties. Amending scars with native seeds increased the cover of native forbs and grasses. Furthermore adding both seed and living soil more than doubled total native plant cover and decreased ruderal and exotic plant cover. These results indicate that seed/soil amendments that increase native forbs and grasses may enhance the rate of succession in burned slash pile areas by allowing these species to outcompete exotic and ruderal species also establishing at the site through natural regeneration.

Effects of an Intense Prescribed Forest Fire: Is It Ecological Restoration?

Abstract: Relatively intense burning has been suggested as a possible alternative to the restoration of pre-European settlement forest conditions and fire regime in mixed conifer forests, in contrast to thinning of trees and light prescribed burning. In 1993 a management-ignited fire in a dense, never-harvested forest in Grand Canyon National Park escaped prescription and burned with greater intensity and severity than anticipated. We sampled the burned site and an adjacent unburned site (270ha each) 6 years after the fire to assess burn effects on tree structure (species composition, size and age distributions, regeneration, and snags), forest floor fuels, and coarse woody debris. Tree structure before fireregime disruption (1879 CE) was reconstructed with dendroecological techniques. By 6 years after burn the fire reduced average tree density (331 trees/ha) and basal area (28.5m 2 /ha) to levels similar to pre-European reference conditions (approximately 246 trees/ha and 28.5m 2 /ha). Mortality was concentrated in fire-susceptible species, especially white fir, restoring dominance by fire-resistant ponderosa pine. Forest floor fuels were reduced, and regeneration by aspen and understory plants was vigorous. Densities of large snags and logs were high. However the fire also killed a high proportion of old-growth trees, especially aspen. Burning created more spatial variability in forest structure than was present before fire-regime disruption by killing many trees in some areas of the site but few in other areas. The intentional use of severe burning would be challenging to managers because of the increased risk of escaped fires, but the ecological outcome of this particular wildfire was not inconsistent with ecological restoration goals for this ecosystem type.

Ecological Restoration Treatments Increase Butterfly Richness and Abundance: Mechanisms of Response

Abstract: Few ecosystem restoration studies evaluate whether arthropods are important components of ecosystem recovery. We tested the hypothesis that ponderosa pine restoration treatments would increase adult butterfly species richness and abundance as a direct result of increased understory diversity and abundance. To examine mechanisms that potentially affect adult butterfly distribution, we quantified host plant frequency, nectar plant abundance, and insolation (light intensity) in restoration treatment and control forests. This study is unique, because this is the first invertebrate monitoring in ponderosa pine forest restoration treatments in the U.S. Southwest and also because these treatments are the first replicated ponderosa pine restoration treatments at a landscape scale. Three patterns emerged: (1) butterfly species richness and abundance were 2 and 3 times greater, respectively, in restoration treatment units than in paired control forests 1 year after treatment, and 1.5 and 3.5 times greater, respectively, 2 years after treatment, ordination of control and treatment sampling units using butterfly assemblages showed significant separation of control and restoration treatment units after restoration treatment; (2) host plant and nectar plant species richness showed little difference between treated and control forests even 2 years after treatment; and (3) insolation (light intensity) was significantly greater in treated forests after restoration. We suggest that changes in the butterfly assemblage may occur due to light intensity effects before plant community changes occur or can be detected. Butterfly assemblage differences will have additional cascading effects on the ecosystem as prey for higher trophic levels and through plant interactions including herbivory and pollination.

Monitoring an Arizona Ponderosa Pine Restoration: Sampling Efficiency and Multivariate Analysis of Understory Vegetation

Abstract: As monitoring plans for the restoration of Pinus ponderosa forests in the southwestern United States evolve toward examining multifactor ecosystem responses to ecological restoration, designing efficient sampling procedures for understory vegetation will become increasingly important. The objective of this study was to compare understory composition and diversity among thin/burn and control treatments in a P. ponderosa restoration, while simultaneously examining the effects of sampling design and multivariate analyses on which conclusions were based. Using multi-response permutation procedures (MRPP), we tested the null hypothesis of no difference in understory species composition among treatments using different data matrices (e.g., frequency and cover) for two different sampling methods. Treatment differences were subtle and were detected by an intensive 50, 1-m 2 subplot sampling method for all data matrices but were not detected by a less intensive point-intercept sampling method for any matrix. Sampling methods examined in this study controlled results of multivariate analyses more than the data matrices used to summarize data generated by a sampling method. We partitioned data into plant life form and native/exotic species categories for MRPP, and this partitioning isolated plant groups most responsible for treatment differences. We also examined the effects of number of 1-m 2 subplots sampled on mean-speciesrichness/m 2 estimates and found that estimates based on 10subplots and based on 50subplots were highly correlated (r 50.99). Species–area curves indicated that the 50, 1-m 2 subplot sampling method detected the common species of sites but failed to detect the majority of rare species. Additional sampling-design studies are needed to develop single sampling designs that produce multifactor data on plant composition, diversity, and spatial patterns amenable to multivariate analyses as part of monitoring plans of vegetation responses to ecological restoration.

Plant community variability in ponderosa pine forest has implications for reference conditions

Abstract: 1 Corresponding author: pete.fule@nau.edu; 928-523-1463 ABSTRACT: Ponderosa pine plant community and forest structure were compared among three stands in Grand Canyon National Park, Arizona: one stand had 120 years of artificial fire exclusion (NOBURN) and the other two nearby stands had been frequently burned (BURN-E and BURN-W). These forests are valuable places to gauge anthropogenic changes associated with European settlement, due to their land history of limited livestock grazing and no logging. Precipitation varied greatly between sampling years (260 mm in 2000, 505 mm in 2001). Tree density was significantly higher at NOBURN (1424 trees ha-1) with significantly higher rotten coarse woody debris (23.2 Mg ha-1) and duff depth (4.3 cm) than at the burned sites, as expected in the absence of fire. Although species richness was not significantly different among sites (48-89 species), richness differed significantly by year. Shannon’s index of diversity increased by approximately 10% from the dry year to the wet year on all sites. Community composition and plant cover at NOBURN differed significantly from the two burned sites in both years in non-metric multidimensional scaling ordinations. Increasing duff depth was related to decreased plant cover. Two of the three dominant species were different at the fire-excluded site compared to the burned sites. We conclude that although plant community structure was related to fire history, environmental stress and within-stand variability were also important drivers. We suggest selecting reference sites in close proximity to the site to be restored and using a multi-scale, multi-year, multi-site approach to measure reference conditions in ponderosa pine.

Quantifying forest reference conditions for ecological restoration: The Woolsey Plots

Abstract: Sixty-six of the approximately 140 original historical plots (or 47percent) have been relocated on eight National Forests thus far. Of these 66 relocated plots 0 (0/13) are spruce-fir, 13 (13/29) are mixed conifer, and the remainder 53 (53/98) are dominated by ponderosa pine (at least historically pine dominated). This study focused on the ponderosa pine-dominated plots, of which we have relocated over 54 percent. NOTE: This total does NOT include those historical plots located on the Long Valley Experimental Forest near Clints Well, AZ.