Phillip M. Dougherty

Carry-Over Effects of Water and Nutrient Supply on Water Use of Pinus Taeda

A study of the effects of nutrients and water supply (2 × 2 factorial experiment) was conducted in a 12-yr-old stand of loblolly pine (Pinus taeda L.) during a period in which soil moisture was not augmented by irrigation because of frequent rain events. Information on the responses of sapwood-to-leaf area ratio and early-to-late wood ratio, to four years of treatments led to the hypothesis that the combination of increased nutrient and water supply (IF treatment) will increase tree transpiration rate per unit leaf area (EC,1) above EC,1 in the control (C), as well as increasing EC,1 above that when either the supply of water (I) or of nutrients (F) is increased. We further hypothesized that canopy transpiration (EC) will rank IF > F > I = C, based on the ranking of leaf area index (L) and assuming that the ranking of EC,1 is as first hypothesized. We rejected our first hypothesis, because F had lower EC,1 than the other treatments, rather than IF having higher values. We could not reject the second hypothesis; the ranking of average daily EC was 1.8 mm for IF, 1.2 mm for F, and 0.7 mm for both C and I (se < 0.1 mm for all treatments). Thus, it was the lower EC,1 of the F treatment, relative to IF, that resulted in ranking of EC similar to that hypothesized. Lower EC,1 in F trees was found to relate to lower canopy stomatal conductance, even though soil moisture conditions during the time of the study were similar in all treatments. Only trees in the F treatment absorbed a substantial amount of water (25%) below 1 m in the soil. These results indicate a “carry-over” effect of irrigation when combined with fertilization that increases EC in irrigated trees, relative to unirrigated trees, even under conditions when soil moisture is high and similar in all treatments.

Ecophysiological investigations of understory eastern redcedar in central Missouri.

Eastern redcedar (Juniperus virginiana) is a sun—adapted, drought—resistant pioneer species common to pastures, abandoned fields, fence rows, and calcareous rock outcrops throughout the eastern United States. However, it is also a frequent component of the understory in mature oak—hickory forests in central Missouri, where light levels are typically <10% of full sunlight during much of the growing season. This is below eastern redcedars reported optimum for photosynthesis. The competitive survival of understory eastern redcedar under such environmental conditions was apparently due to it being an evergreen conifer in a deciduous forest. Hence, its foliage was able to maintain a positive carbon dioxide balance throughout much of the year, with maximum net photosynthetic rates occurring during periods when the overstory was leafless. The greatest daily average net photosynthetic rates (Phn) occurred during overstory leaf emergence when temperatures were moderate and light levels to the understory trees wer...

Decomposition of roots in loblolly pine: Effects of nutrient and water availability and root size class on mass loss and nutrient dynamics

The decomposition of plant-derived organic matter exerts strong control over the cycling of carbon and nutrients in terrestrial ecosystems and may be significantly altered by increased precipitation and nitrogen deposition associated with global change. It was the goal of this study to quantify the rate of belowground decomposition in an intact loblolly pine forest, and determine how this was affected by increased availability of water and nitrogen. A randomized complete-block factorial of irrigation and fertilization treatments was installed in an 8 yr old loblolly pine plantation in Scotland county, North Carolina. Fresh root samples of three size classes were buried in fiberglass mesh bags in January, 1994 and recovered at two-month intervals for two years. Samples were analyzed for percent mass remaining and contents of macro-nutrients. Roots decomposed in a two stage process: early in the incubation mass loss was correlated to size class and nutrient concentrations, but this correlation disappeared later in the incubation when rates of mass loss converged for all size classes. Decomposition was seldom affected by the irrigation and fertilization treatments, due to the buffering capacity of soil moisture and complex ecosystem-level responses to fertilization. Net mineralization of N, P, K, Ca, and Mg occurred in the smaller size classes of roots providing a source of these nutrients to the aggrading plantation for an estimated 2 to 15 years. The largest size class of roots was a sink for N, Ca, and Mg for the duration of this study, and was a source of P and K for an estimated 20 and 4 years, respectively. It is concluded that in moist temperate ecosystems belowground decomposition will be less affected by the projected increases in moisture and nutrient availability than will decomposition of the forest floor due to the buffering capacity of the soil. Further, small roots provide important sources of macro-nutrients for several decades to aggrading forests after large-scale disturbances such as harvesting of aboveground biomass.

Carbon dioxide efflux from a 550 m3 soil across a range of soil temperatures

Because of scaling problems point measurements of soil CO2 efflux on a small volume of soil may not necessarily reflect an overall community response. The aim of this study was to test this hypothesis in the Biosphere 2 facility and achieve the following broad goals: (1) investigate soil net CO2 exchange‐temperature relationship at the community level; (2) compare soil net CO2 exchange at the community level to the traditional sample point estimates of CO2 efflux scaled up to the community level; (3) evaluate the usefulness of a facility such as Biosphere 2 for conducting community level experiments for studying response to a climatic perturbation under controlled environmental conditions. A 550 m 3 volume of soil with 282, 15 cm tree stumps was enclosed at the Biosphere 2 Center and warmed from 10 to 25 8C over a period of 34 days. Net CO2 exchange from this community was measured at various points on the soil surface with 78.5 cm 2 chambers and for the whole community using each of the three bays at Biosphere 2 Center as a closed system. Soil CO2 efflux rates obtained by point measurements showed tremendous variability from location to location. At the community level and with point measurements, net CO2 exchange increased exponentially with increasing soil temperatures. Q10 values from both the point and community level measurements ranged from 1.7 to 2.5. Scaling of point measurements by soil surface area and time overestimated community rates by 36% revealing some of the limitations of point measurements. This experiment demonstrates how Biosphere 2 facility could be used to study behavior of individual components and measure responses at the community level and test our capacity to scale point in time and space measures of community processes to the community level. # 2002 Elsevier Science B.V. All rights reserved.

Hydrological components of a young loblolly pine plantation on a sandy soil with estimates of water use and loss

Fertilizer and irrigation treatments were applied in a 7- to 10-year-old loblolly pine (Pinus taeda L.) plantation on a sandy soil near Laurinburg, North Carolina. Rainfall, throughfall, stemflow, and soil water content were measured throughout the study period. Monthly interception losses ranged from 4 to 15% of rainfall. Stemflow ranged from 0.2 to 6.5% of rainfall. Rainfall, leaf area index (LAI), basal area (BA), and the interactions of rainfall with LAI or BA influenced prediction models of throughfall, but not stemflow, on a stand level. We found significant differences due to the effects of treatments in the soil water of the top 0.5- and 1-m soil layers by the beginning of the second growing season and throughout the remainder of the study period. Average daily water use and loss from a 1-m soil layer reflected the low water-holding capacity of the sand. Soil water in a 1-m layer was rapidly depleted to within 10% of available water during periods of little or no rainfall. Irrigation did not significantly affect productivity and created a greater potential for loss of water to drainage below 1 m. On the basis of Zahners [1966] method of soil water depletion in a sandy soil under forest cover, total drainage to below l m was 55% of evapotranspiration in unirrigated plots and 150% of evapotranspiration in irrigated plots.

A LINKED MODEL FOR SIMULATING STAND DEVELOPMENT AND GROWTH PROCESSES OF LOBLOLLY PINE

Linking models of different scales (e.g., process, tree-stand-ecosystem) is essential for furthering our understanding of stand, climatic, and edaphic effects on tree growth and forest productivity. Moreover, linking existing models that differ in scale and levels of resolution quickly identifies knowledge gaps in information required to scale from one level to another, indentifies future research needs to fill these information gaps, and provides a test of the present state of modeling sciences for creating model systems for predicting responses to natural and human-based disturbances.

An Investigation of the Impacts of Elevated Carbon Dioxide, Irrigation, and Fertilization on the Physiology and Growth of Loblolly Pine

Southern pine forests that are dominated by loblolly pine (Pinus taeda L.) are the most intensively managed forests in the United States. They provide more than 50% of the total softwood being harvested annually in the United States and represent the first or second most economically important agricultural crops in nine of the twelve southeastern states (U.S. Department Agriculture Forest Service, 1988). Thus, any changes in environmental conditions that will alter productivity of these forests will have important ecological, economical, and sociological consequences. Over the past several decades, the environment of southeastern forests has been changing. Increases in acidic deposition (SO4 and NOx), nitrogen inputs (Husar, 1986), atmospheric CO2 concentration (Conway et al., 1988; Keeling et al., 1989), and tropospheric ozone have all been documented to parallel the increase in population since the beginning of the industrial revolution. Climate change has also been predicted for the southeastern United States for the future. Each of these atmospheric and climatic elements that are being altered by human activities has the potential to affect productivity of southern pine forests. Nutrient availability, water availability, atmospheric CO2 concentration, and temperature are presently the principal factors that are limiting the productivity of southern pine forests. Thus, it is extremely important that we understand how changes in these factors will interact to affect physiological processes of forest stands.

The Influences of Global Change on Tree Physiology and Growth

This chapter is a synthesis of the findings of those projects in the Southern Global Change Program (SGCP) that measured the effects of environment on physiological and growth processes. This synthesis will not attempt to be exhaustive or encyclopedic, instead it will focus on key findings from the program, building conclusions from these results whenever possible. In addition to these conclusions, we will discuss the similarities and differences in results among the projects in the program, as well as with the general body of knowledge of global change effects on trees.