Elaine Kennedy Sutherland

Prescribed burning effects on soil enzyme activity in a southern Ohio hardwood forest: a landscape-scale analysis

We assessed the effect of a single, dormant season prescribed fire on soil enzyme activity in oak-hickory (Quercus-Carya) forests in southern Ohio, USA. Four enzymes specific for different C sources were chosen for monitoring: acid phosphatase, β-glucosidase, chitinase and phenol oxidase. Postfire acid phosphatase activity was generally reduced by burning and decreased with increasing longterm soil water potential. Postfire β-glucosidase differed little between control and burned plots. Chitinase activity increased after fire in proportion to fire intensity. Phenol oxidase activity was highly variable and did not correlate well with either fire or soil water potential. Enzyme activities tended to vary more between samples taken upslope vs. downslope of a given tree than as the result of fire or landscape position. Overall enzymes whose activities are controlled by microclimatic or edaphic factors were affected more than those controlled primarily by substrate availability. Single, dormant season fires may consume a large proportion of the forest floor and change the apparent character of the surface organic matter complex without having major effects on soil enzyme activity.

Fire-scar formation and compartmentalization in oak

Fire scars result from the death of the vascular cambium resulting from excessive heating, which exposes sapwood to infection and initiates the wood decay process. In southeastern Ohio, prescribed fires in April 1995 and 1997 scarred Quercus prinus L. and Q. velutina Lam. Low-intensity fires scorched bark and produced scars, primarily on the downslope side of the stem. Eighteen scorched trees (4-23 cm at DBH) were dissected in November 1997, 14 of which had fire scars. The vascular cambium beneath natural bark fissures was most vulnerable to injury. No charred or scorched wood was associated with scars of trees exposed to single fires; wood exposed by scars from the 1995 fire was charred by the 1997 fire. Consistent with the compartmentalization process, discoloration and whiterot occurred within compartment boundaries of wood present at the time of wounding. Scars from the prescribed fires were consistent in size and shape with scars in nearby oak trees previously hypothesized to have been burned prior t...

Characteristics of mixed-oak forest ecosystems in southern Ohio prior to the reintroduction of fire

Contains 12 chapters describing baseline conditions of mixed-oak forest ecosystems in the context of a long-term study of prescribed fire effects.

The chemical characteristics of soil in control and experimentally thinned plots in mesic oak forests along a historical deposition gradient

Abstract This study examined the variations in the chemical parameters of soils of seven forests located along a historical deposition gradient spanning 8.5° longitude from southern Illinois to central West Virginia. Four to six mature control plots were sampled on two of the sites, and two experimentally thinned and two control plots were sampled on the remaining five sites. Most soil properties varied significantly both among experimental forests and between control and thinned plots. Soil pH, Al, PO4 and inorganic N were correlated with longitude, whereas differences in Ca, Mg and Ca:Al ratio among experimental forests were more closely linked to differences in parent materials. Nine of the 12 soil properties measured differed between control and thinned plots, and the variance explained by the proportion of basal area removed in the experimental thinnings was always greater than that explained by longitude or current basal area. Overall, thinned plots had greater soil pH, inorganic N, Ca, Mg, K and Ca:Al ratio, whereas control plots had greater Al and PO4. These patterns of difference were also apparent when the chemical properties of soil of the experimental forests were analyzed individually. We suggest that thinning may have reduced uptake, increased relative nutrient availability, changed leaf and litter quality, and altered decomposition and mineralization rates in such a way as to produce persistent differences in soil properties.

A model of ponderosa pine growth response to prescribed burning

Our objective was to model the radial growth response of individual ponderosa pines to prescribed burning in northern Arizona. We sampled 188 trees from two study areas, which were burned in 1976. Within each study area, control and burned trees were of similar age, vigor, height, and competition index. At Chimney Spring, trees were older, less vigorous, and taller and had a higher competition index than at Brannigan. For each tree, periodic basal area increment (PBA1) was calculated for the years 1974-1984. To determine which variable would best model growth, post-fire growth (19771984 ) was correlated with the 3 year average of previous growth, crown ratio, competition index, and diameter. Post-fire growth response was modeled using stepwise multiple linear regression as a function of previous growth and indicator variables for treatment, treatment-site interaction, climatic variation, and treatment-year interaction. Independent variables of the final model included previous growth, climatic variation, and treatment-year interaction (r2= 0.72). Model coefficients indicated that fire affected growth significantly and negatively for 2 years, and then burned trees grew similarly to control trees. Differences in management history at the two sites did not affect growth after fire. We propose a linear aggregate model of variables controlling radial growth response of southwestern ponderosa pines to fire.

Changes in tracheid and ray traits in fire scars of North American conifers and their ecophysiological implications

BACKGROUND AND AIMS Fire scars have been widely used as proxies for the reconstruction of fire history; however, little is known about the impact of fire injury on wood anatomy. This study investigates changes in tracheid and ray traits in fire scars of Douglas fir (Pseudotsuga menziesii), western larch (Larix occidentalis) and ponderosa pine (Pinus ponderosa), and discusses their ecophysiological implications for tree recovery from fire. METHODS Transverse and tangential microsections were prepared for light microscopy and image analysis. Measurements of tracheids and rays were made in the three spatial dimensions: axially (at different section heights), radially (in different rings) and tangentially (with increasing distance from the wound margin). KEY RESULTS Changes were strongest in the first year after fire injury, with a decrease in tracheid size (by 25-30 %) and an increase in tracheid density (by 21-53 %) for the three species. In addition, an increase in ray size (by 5-27 %) and an increase in ray density (by 19-36 %) were found in P. menziesii and L. occidentalis. Changes were comparable along the fire-injured stem and were often most marked close to the fire scar. CONCLUSIONS The differentiation after fire injury of narrower and more numerous tracheids expresses a trade-off between hydraulic safety and hydraulic efficiency, while that of larger and more numerous rays serves compartmentalization and wound closure, mechanical strength and defence responses. Pinus ponderosa does not generally produce more ray tissue after fire injury and thus appears to be more adapted to fire.

Resin duct size and density as ecophysiological traits in fire scars of Pseudotsuga menziesii and Larix occidentalis

BACKGROUND AND AIMS Resin ducts (RDs) are features present in most conifer species as defence structures against pests and pathogens; however, little is known about RD expression in trees following fire injury. This study investigates changes in RD size and density in fire scars of Douglas fir (Pseudotsuga menziesii) and western larch (Larix occidentalis) as a means to evaluate the ecophysiological significance of traumatic resinosis for tree defence and survival. METHODS Transverse and tangential microsections were prepared for light microscopy and image analysis in order to analyse axial and radial RDs, respectively. Epithelial cells of RDs and fusiform rays associated with radial RDs were also examined. RDs were compared between normal xylem and wound xylem at four different section heights along the fire-injured stem. KEY RESULTS Following fire injury, P. menziesii axial RDs narrowed by 38-43 % in the first year after injury, and the magnitude of this change increased with stem height. Larix occidentalis axial RDs widened by 46-50 % in the second year after injury. Radial RDs were of equivalent size in P. menziesii, but widened by 162-214 % in L. occidentalis. Fusiform rays were larger following fire injury, by 4-14 % in P. menziesii and by 23-38 % in L. occidentalis. Furthermore, axial RD density increased in both species due to the formation of tangential rows of traumatic RDs, especially in the first and second years after injury. However, radial RD density did not change significantly. CONCLUSIONS These results highlight traumatic resinosis as a species-specific response. Pseudotsuga menziesii produce RDs of equivalent or reduced size, whereas L. occidentalis produce wider RDs in both the axial and radial duct system, thereby increasing resin biosynthesis and accumulation within the whole tree. Larix occidentalis thus appears to allocate more energy to defence than P. menziesii.

Forest fuels and potential fire behaviour 12 years after variable-retention harvest in lodgepole pine

Variable-retention harvesting in lodgepole pine offers an alternative to conventional, even-aged management. This harvesting technique promotes structural complexity and age-class diversity in residual stands and promotes resilience to disturbance. We examined fuel loads and potential fire behaviour 12 years after two modes of variable-retention harvesting (dispersed and aggregated retention patterns) crossed by post-harvest prescribed fire (burned or unburned) in central Montana. Results characterise 12-year post-treatment fuel loads. We found greater fuel load reduction in treated than untreated stands, namely in the 10- and 100-h classes (P = 0.002 and 0.049 respectively). Reductions in 1-h (P < 0.001), 10-h (P = 0.008) and 1000-h (P = 0.014) classes were greater in magnitude for unburned than burned treatments. Fire behaviour modelling incorporated the regenerating seedling cohort into the surface fuel complex. Our analysis indicates greater surface fireline intensity in treated than untreated stands (P < 0.001), and in unburned over burned stands (P = 0.001) in dry, windy weather. Although potential fire behaviour in treated stands is predicted to be more erratic, within-stand structural variability reduces probability of crown fire spread. Overall, results illustrate trade-offs between potential fire attributes that should be acknowledged with variable-retention harvesting.