Thinning and burning treatments based on presettlement (prior to Euro- American settlement) stand... more Thinning and burning treatments based on presettlement (prior to Euro- American settlement) stand conditions have been proposed for improving the vigor and growth of Pinus ponderosa. No study has examined effects of different levels of such thinning treatments on tree water, carbon, and nitrogen relations, or compared effects between postsettlement (trees established after Euro-American settlement) and presettlement (estab- lished before
Summary To assess the influence of stream water on leaf gas exchange and water potential in diffe... more Summary To assess the influence of stream water on leaf gas exchange and water potential in different sized boxelder trees (Acer negundo L.), we compared these characteristics in trees growing beside a perennial stream and a nearby ephemeral stream in a montane--riparian forest in northern Arizona. Pat- terns of tree water use were quantified by stable isotope analy- sis (δ
In 2005 faculty in the Northern Arizona University School of Forestry initiated a project to repl... more In 2005 faculty in the Northern Arizona University School of Forestry initiated a project to replace the required sophomore-level writing course taught by the English Department with a new course, “Writing in Forestry,” taught within the School. The goal of the course replacement was to improve students’ experience and competence with the types of writing emphasized in upper division forestry courses and by professional foresters. The School collaborated with PhD students from the Department of English, Applied Linguistics Program to develop and teach the new course. We explain the genesis, development, and curriculum of the course, which has been taught successfully for two years. We also demonstrate the use of corpus analysis to improve student vocabulary.
Background/Question/Methods In the American Southwest, the early 21st century has seen arguably t... more Background/Question/Methods In the American Southwest, the early 21st century has seen arguably the most severe drought in history. The prolonged drought and high temperatures seen in the early 21st century are similar to the future conditions predicted by climate models. The objective of this study was to investigate the patterns in vegetation response to the early 21st century drought across ecosystem types. We hypothesized that current-year above-ground net primary productivity (ANPP) would be explained by both the precipitation in the current year and the productivity in the previous year for all ecosystems. We tested this hypothesis at ten Ameriflux sites in various ecosystem types ranging from desert grasslands to ponderosa pine forests, using Daymet for meteorological information, and using NASA MODIS Enhanced Vegetation Index (EVI) measurements as a surrogate for Aboveground Net Primary Production (ANPP). The EVI was compared to in situ measurements of productivity (Gross Ec...
Conifers have incurred high mortality during recent global-change-type drought(s) in the western ... more Conifers have incurred high mortality during recent global-change-type drought(s) in the western USA. Mechanisms of drought-related tree mortality need to be resolved to support predictions of the impacts of future increases in aridity on vegetation. Hydraulic failure, carbon starvation and lethal biotic agents are three potentially interrelated mechanisms of tree mortality during drought. Our study compared a suite of measurements related to these mechanisms between 49 mature piñon pine (Pinus edulis Engelm.) trees that survived severe drought in 2002 (live trees) and 49 trees that died during the drought (dead trees) over three sites in Arizona and New Mexico. Results were consistent over all sites indicating common mortality mechanisms over a wide region rather than site-specific mechanisms. We found evidence for an interactive role of hydraulic failure, carbon starvation and biotic agents in tree death. For the decade prior to the mortality event, dead trees had twofold greater ...
We review the need for scaling effects of ozone (O3) from juvenile to mature forest trees, identi... more We review the need for scaling effects of ozone (O3) from juvenile to mature forest trees, identify the knowledge presently available, and discuss limitations in scaling efforts. Recent findings on O3/soil nutrient and O3/CO2 interactions from controlled experiments suggest consistent scaling patterns for physiological responses of individual leaves to whole-plant growth, carbon allocation, and water use efficiency of juvenile trees. These findings on juvenile trees are used to develop hypotheses that are relevant to scaling O3 effects to mature trees, and these hypotheses are examined with respect to existing research on differences in response to O3 between juvenile and mature trees. Scaling patterns of leaf-level physiological response to O3 have not been consistent in previous comparisons between juvenile and mature trees. We review and synthesize current understanding of factors that may cause such inconsistent scaling patterns, including tree-size related changes in environmen...
Tree defense against bark beetles (Curculionidae: Scolytinae) and their associated fungi generall... more Tree defense against bark beetles (Curculionidae: Scolytinae) and their associated fungi generally comprises some combination of constitutive (primary) and induced (secondary) defenses. In pines, the primary constitutive defense against bark beetles consists of preformed resin stored in resin ducts. Induced defenses at the wound site (point of beetle entry) in pines may consist of an increase in resin flow and necrotic lesion formation. The quantity and quality of both induced and constitutive defenses can vary by species and season. The inducible defense response in ponderosa pine is not well understood. Our study examined the inducible defense response in ponderosa pine using traumatic mechanical wounding, and wounding with and without fungal inoculations with two different bark beetle-associated fungi (Ophiostoma minus and Grosmannia clavigera). Resin flow did not significantly increase in response to any treatment. In addition, necrotic lesion formation on the bole after fungal ...
Background / Purpose: In semi-arid environments, co-existing plant species may vary in rooting de... more Background / Purpose: In semi-arid environments, co-existing plant species may vary in rooting depth, reflecting niche partitioning and functional differences in water source. In mountains of the southwestern U.S, moisture availability increases with elevation, and winter and summer precipitation inputs differ isotopically. Examining variation in stem water isotopes among plant communities and seasons over elevational gradients is important for understanding how niche partitioning may respond to the predicted warming and drying of the Southwest. Main conclusion: Niche overlap increased as the moisture index (the ratio of precipitation to potential evapotranspiration) increased; the moisture index explained 18.2% of the variation in niche overlap among sites. Our findings support the hypothesis that niche overlap in functional rooting depth is lower at more arid sites, and we present a simple metric for quantifying functional rooting depth and niche overlap based on soil and stem wat...
We compared foliar physiology and several measures of tree resistance to insect attack among pond... more We compared foliar physiology and several measures of tree resistance to insect attack among ponderosa pine (Pinus ponderosa var. scopulorum Engelm.) trees growing in thinned stands. Measurements were made in a second-growth ponderosa pine forest in northern Arizona where the basal area treatments (6.9, 18.4, 27.6, 78.2 m(2) ha(-1)) have been experimentally maintained by frequent thinnings for 32 years before our measurements began in 1994. Most of the physiological characteristics measured were affected by the basal area treatments. As stand basal area increased from 6.9 to 78.2 m(2) ha(-1), predawn water potential, midday water potential, net photosynthetic rate, resin production, phloem thickness, and foliar toughness decreased. Foliar nitrogen concentration was greatest in trees in the intermediate basal area treatments. Our results show that the physiological condition of second-growth ponderosa pine can be manipulated by silvicultural control of stand basal area, and support t...
Thinning and burning treatments based on presettlement (prior to Euro- American settlement) stand... more Thinning and burning treatments based on presettlement (prior to Euro- American settlement) stand conditions have been proposed for improving the vigor and growth of Pinus ponderosa. No study has examined effects of different levels of such thinning treatments on tree water, carbon, and nitrogen relations, or compared effects between postsettlement (trees established after Euro-American settlement) and presettlement (estab- lished before
Summary To assess the influence of stream water on leaf gas exchange and water potential in diffe... more Summary To assess the influence of stream water on leaf gas exchange and water potential in different sized boxelder trees (Acer negundo L.), we compared these characteristics in trees growing beside a perennial stream and a nearby ephemeral stream in a montane--riparian forest in northern Arizona. Pat- terns of tree water use were quantified by stable isotope analy- sis (δ
In 2005 faculty in the Northern Arizona University School of Forestry initiated a project to repl... more In 2005 faculty in the Northern Arizona University School of Forestry initiated a project to replace the required sophomore-level writing course taught by the English Department with a new course, “Writing in Forestry,” taught within the School. The goal of the course replacement was to improve students’ experience and competence with the types of writing emphasized in upper division forestry courses and by professional foresters. The School collaborated with PhD students from the Department of English, Applied Linguistics Program to develop and teach the new course. We explain the genesis, development, and curriculum of the course, which has been taught successfully for two years. We also demonstrate the use of corpus analysis to improve student vocabulary.
Background/Question/Methods In the American Southwest, the early 21st century has seen arguably t... more Background/Question/Methods In the American Southwest, the early 21st century has seen arguably the most severe drought in history. The prolonged drought and high temperatures seen in the early 21st century are similar to the future conditions predicted by climate models. The objective of this study was to investigate the patterns in vegetation response to the early 21st century drought across ecosystem types. We hypothesized that current-year above-ground net primary productivity (ANPP) would be explained by both the precipitation in the current year and the productivity in the previous year for all ecosystems. We tested this hypothesis at ten Ameriflux sites in various ecosystem types ranging from desert grasslands to ponderosa pine forests, using Daymet for meteorological information, and using NASA MODIS Enhanced Vegetation Index (EVI) measurements as a surrogate for Aboveground Net Primary Production (ANPP). The EVI was compared to in situ measurements of productivity (Gross Ec...
Conifers have incurred high mortality during recent global-change-type drought(s) in the western ... more Conifers have incurred high mortality during recent global-change-type drought(s) in the western USA. Mechanisms of drought-related tree mortality need to be resolved to support predictions of the impacts of future increases in aridity on vegetation. Hydraulic failure, carbon starvation and lethal biotic agents are three potentially interrelated mechanisms of tree mortality during drought. Our study compared a suite of measurements related to these mechanisms between 49 mature piñon pine (Pinus edulis Engelm.) trees that survived severe drought in 2002 (live trees) and 49 trees that died during the drought (dead trees) over three sites in Arizona and New Mexico. Results were consistent over all sites indicating common mortality mechanisms over a wide region rather than site-specific mechanisms. We found evidence for an interactive role of hydraulic failure, carbon starvation and biotic agents in tree death. For the decade prior to the mortality event, dead trees had twofold greater ...
We review the need for scaling effects of ozone (O3) from juvenile to mature forest trees, identi... more We review the need for scaling effects of ozone (O3) from juvenile to mature forest trees, identify the knowledge presently available, and discuss limitations in scaling efforts. Recent findings on O3/soil nutrient and O3/CO2 interactions from controlled experiments suggest consistent scaling patterns for physiological responses of individual leaves to whole-plant growth, carbon allocation, and water use efficiency of juvenile trees. These findings on juvenile trees are used to develop hypotheses that are relevant to scaling O3 effects to mature trees, and these hypotheses are examined with respect to existing research on differences in response to O3 between juvenile and mature trees. Scaling patterns of leaf-level physiological response to O3 have not been consistent in previous comparisons between juvenile and mature trees. We review and synthesize current understanding of factors that may cause such inconsistent scaling patterns, including tree-size related changes in environmen...
Tree defense against bark beetles (Curculionidae: Scolytinae) and their associated fungi generall... more Tree defense against bark beetles (Curculionidae: Scolytinae) and their associated fungi generally comprises some combination of constitutive (primary) and induced (secondary) defenses. In pines, the primary constitutive defense against bark beetles consists of preformed resin stored in resin ducts. Induced defenses at the wound site (point of beetle entry) in pines may consist of an increase in resin flow and necrotic lesion formation. The quantity and quality of both induced and constitutive defenses can vary by species and season. The inducible defense response in ponderosa pine is not well understood. Our study examined the inducible defense response in ponderosa pine using traumatic mechanical wounding, and wounding with and without fungal inoculations with two different bark beetle-associated fungi (Ophiostoma minus and Grosmannia clavigera). Resin flow did not significantly increase in response to any treatment. In addition, necrotic lesion formation on the bole after fungal ...
Background / Purpose: In semi-arid environments, co-existing plant species may vary in rooting de... more Background / Purpose: In semi-arid environments, co-existing plant species may vary in rooting depth, reflecting niche partitioning and functional differences in water source. In mountains of the southwestern U.S, moisture availability increases with elevation, and winter and summer precipitation inputs differ isotopically. Examining variation in stem water isotopes among plant communities and seasons over elevational gradients is important for understanding how niche partitioning may respond to the predicted warming and drying of the Southwest. Main conclusion: Niche overlap increased as the moisture index (the ratio of precipitation to potential evapotranspiration) increased; the moisture index explained 18.2% of the variation in niche overlap among sites. Our findings support the hypothesis that niche overlap in functional rooting depth is lower at more arid sites, and we present a simple metric for quantifying functional rooting depth and niche overlap based on soil and stem wat...
We compared foliar physiology and several measures of tree resistance to insect attack among pond... more We compared foliar physiology and several measures of tree resistance to insect attack among ponderosa pine (Pinus ponderosa var. scopulorum Engelm.) trees growing in thinned stands. Measurements were made in a second-growth ponderosa pine forest in northern Arizona where the basal area treatments (6.9, 18.4, 27.6, 78.2 m(2) ha(-1)) have been experimentally maintained by frequent thinnings for 32 years before our measurements began in 1994. Most of the physiological characteristics measured were affected by the basal area treatments. As stand basal area increased from 6.9 to 78.2 m(2) ha(-1), predawn water potential, midday water potential, net photosynthetic rate, resin production, phloem thickness, and foliar toughness decreased. Foliar nitrogen concentration was greatest in trees in the intermediate basal area treatments. Our results show that the physiological condition of second-growth ponderosa pine can be manipulated by silvicultural control of stand basal area, and support t...
Uploads
Papers by Thomas Kolb