Showing papers by "Paul J. Hanson published in 2003"

Soil Respiration and Litter Decomposition

Abstract: Emissions of CO2 from the organic and mineral soil horizons into the atmosphere are considered a good representation of soil respiration (R soil) when the diffusion-driven losses to the atmosphere are at equilibrium with the biological rates of CO2 production (Hanson et al. 2000). R soil is the net effect of the biological activity of autotrophic roots and associated rhizosphere organisms plus the mineral soil heterotrophic activity of bacteria, fungi, and soil fauna. Whereas the activity of soil heterotrophic organisms is proportionate to the decomposition of soil carbon, CO2 lost from root and rhizosphere activity is a function of the consumption of organic compounds supplied by aboveground organs of plants (Horwath et al. 1994). Notwithstanding the complex nature of the sources of CO2 contributing to it, R soil represents a good measure of the collective response of root and soil biological activity to environmental conditions (Edwards et al. 1970; Hanson et al. 2000). Because soil respiration is a very large fraction of gross primary productivity (Curtis et al., 2002), its quantification must be a high priority in any attempt to establish carbon budgets for ecosystems (see Chapter 22, this volume).

North American temperate deciduous forest responses to changing precipitation regimes

Abstract: Foreword * Preface * Introduction * Carbon Cycle Processes * Water Cycle Processes* Decomposition and Soil Carbon Turnover * Plant Growth and Mortality * Response of Other Organisms * Forest Stand-Level Syntheses * Extrapolations * Appendix: List of Scientific and Common Species Names

Walker Branch Throughfall Displacement Experiment

Abstract: The Walker Branch Watershed (∼100 ha), located at 35°58′ N latitude and 84°17′ W longitude, is a part of the U.S. Department of Energy’s (DOE’s) National Environmental Research Park near Oak Ridge, Tennessee (Johnson and Van Hook 1989). Long-term (50-year) mean annual precipitation is 1352 mm, and mean annual temperature is 14.2°C. The soils are primarily Typic Paleudults derived from dolomitic bedrock. The soils are highly weathered and very deep (> 10 m) on ridge tops and therefore retain little evidence of their carbonate parent material. Plant-extractable water (water held between 0 and − 2.5 MPa) for the upper meter of soil is approximately 183 mm. A large fraction of this water (44%) is held in the upper 0.35 m of the soil profile, where 74% of all fine roots in the upper 0.90 m of the profile are located (Joslin and Wolfe 1998; Chapter 16, this volume). Depth to bedrock at this location is approximately 30 m (McMaster 1967), and deep rooting may be a source of some water.

Estimating the Net Primary and Net Ecosystem Production of a Southeastern Upland Quercus Forest from an 8-Year Biometric Record

Abstract: Although 8 years of manipulated precipitation levels have not produced significant tree-growth responses in an upland Quercus forest in eastern Tennessee (Hanson et al. 2001), interannual differences in physiological processes (Chapters 3, 4, 6–8, and 10, this volume), storage carbohydrates (Chapter 5, this volume), tree and sapling growth rates (Chapter 15, this volume), root growth (Chapter 16, this volume), and foliar-litter production (Chapter 17, this volume) suggest that interannual differences in net primary production (NPP) and net ecosystem production (NEP) are likely. By accepted definition, NPP is the difference between carbon gain from autotrophic organisms (i.e., gross primary production, GPP) minus autotrophic respiration (R auto). NEP is the annual net change in ecosystem carbon storage defined as NPP minus heterotrophic respiration (R hetero). At the local scale, NEP may also be reduced from non-CO2 losses of volatile organic compounds (VOCs) from vegetation (Guenther et al. 1996; Isebrands et al. 1999) and soils (Hanson and Hoffman 1994) and under ambient or flooded conditions from the gain or loss of CH4 from soils, respectively (LeMer and Roger 2000).

Tree and Sapling Growth and Mortality

Abstract: Plant-dry-matter accumulation ultimately depends on the yield of carbon building blocks (i.e., nonstructural carbohydrates) from the difference between carbon assimilation (Chapter 3, this volume) and autotrophic respiration (Chapter 4, this volume). Accumulated sugar and starch reserves in roots and shoots (Chapter 5, this volume) represent the primary compounds, along with stored elements, that must be present to support mass accumulation in the stems of saplings and trees. Waring and Pitman (1985) proposed a hierarchy of photosynthate allocation priorities for trees that considers stem growth to be a relatively low allocation priority, suggesting that changes in stem-growth rates would be a sensitive indicator of water stress response. Sustained low stem-growth rates have also been linked to mortality (Kohyama and Hara 1989; Pedersen 1998; Swaine et al. 1987; Tainter et al. 1984). Because growth and mortality are the integrated result of of physiological responses to environmental stress, they represent key end points for investigations of forest response to changing precipitation regimes. This chapter describes the annual growth and mortality of saplings and large trees during 7 full years of throughfall manipulation (1994–2000) and provides a quantitative description of the response of tree growth to soil-water deficits. The Throughfall Displacement Experiment (TDE) observations are also contrasted with published data for other deciduous hardwood forests, and their application for predicting growth responses to soil-water deficits throughout the eastern deciduous hardwood forest is discussed.

Deciduous Hardwood Photosynthesis: Species Differences, Temporal Patterns, and Responses to Soil-Water Deficits

Abstract: Changes in regional precipitation patterns will directly impact soil and foliage water status, resulting in physiological modifications in trees that can affect carbon assimilation rates (Briggs et al. 1986; Teskey et al. 1986; Ni and Pallardy 1992). Decreasing water potentials in the root and/or foliage can affect the carbon assimilation by adjusting stomatal conductance (Hinckley et al. 1978a; Epron and Dreyer 1993; Lowenstein and Pallardy 1998) or possibly by directly impacting the biochemical potential for carbon assimilation in the leaf (Lawlor 1995; Escalona et al. 1999). Tree species differ in their morphology and use of physiologic adaptations to avoid the negative impacts of drought on carbon assimilation (Hinckley et al. 1978b; Bahari et al. 1985; Briggs et al. 1986; Ni and Pallardy 1992; Abrams and Mostoller 1995; Lowenstein and Pallardy 1998; Tschaplinski et al. 1998). Species-specific differences in gas-exchange response to drought depend on characteristics such as rooting depth, stomatal sensitivity, osmotic adjustment, cavitation avoidance, and increased tolerance of desiccation (Abrams 1990; Lowenstein and Pallardy 1998; Tshaplinski et al. 1998). For example, because of their deep rooting habit, Quercus species are expected to outcompete the more mesic Acer and Cornus species in dry climates (Hinckley et al. 1979; Bahari et al. 1985; Abrams 1990). Species also may differ in their ability to recover predrought photosynthetic rates following a precipitation event (Ni and Pallardy 1992). Because of shallower rooting depths and limited water-storage capacity, photosynthesis of understory species and saplings is expected to be more sensitive to drying when compared to large overstory trees (Donovan and Ehleringer 1991; Flanagan et al. 1992).

Dormant-Season Nonstructural Carbohydrate Storage

Abstract: Like tree growth, dormant-season carbon storage is an important, integrative measure of tree health. Carbon is stored throughout trees in the form of carbohydrates for later use as an energy resource and substrate for synthetic products (Kozlowski et al. 1991). Trees rely on carbon fixed during the latter part of the growing season, and stored through the winter, to produce new organs for gathering light, water, and nutrients (Gholz and Cropper 1991; Kozlowski et al. 1991). Effects of altered throughfall levels leading to changes in carbon-exchange rates should be cumulative over time (Chapin et al. 1990), resulting in either accumulation or degradation of stored nonstructural carbohydrate pools in the wetter or drier environments, respectively. (1987) and (1975) have shown evidence of stress-induced carbohydrate reductions in Quercus. Stored carbohydrate concentrations of stems are typically similar to that of coarse roots, with bothtissues responding similarly to environmental changes. However, given that stems are much more easily accessible, they are most often sampled to assess carbon storage.

Sensitivity of Sapling and Mature-Tree Water Use to Altered Precipitation Regimes

Abstract: Long-term shifts in precipitation caused by changes in regional or global climate could exert a profound influence on the hydrologic regimes of terrestrial ecosystems. Increases and decreases in precipitation could result in altered patterns of runoff, evaporation, and soil-water content, and, in turn, these changes could have serious implications for catchment water yield, hydrologic budgets across broad spatial scales, impacts on terrestrial Vegetation, and consequences for ecosystem goods and Services upon which society depends. Because of their spatial extent, forests are especially important in this regard, and studies have implied that forests may be particularly vulnerable to changes in soil-water content as evidenced by results from manipulative studies on large trees (Cermak et al. 1993; Cienciala et al. 1994; Irvine et al. 1998; Phillips et al. 2001), field investigations on seedlings and saplings (Abrams et al. 1990, Kubiske and Abrams 1994), and Computer simulations (Pastor and Post 1988; Running and Nemani 1991; Ludeke et al. 1995). However, few studies have identified the relative sensitivity of multiple species to altered precipitation regimes and then integrated those sensitivities both for the forest overstory and understory into a picture depicting how species and climatic change may potentially impact forest water use in the future.

Forest Water Use and the Influence of Precipitation Change

Abstract: Altered patterns of precipitation associated with regional or global climatic change can be expected to affect ecosystem water use in a manner that reflects, in the case of drought, the response of individual components of that system to soil-water deficits. For temperate deciduous forests, these components include overstory and understory vegetation, the distribution of size classes among seedlings, saplings, and mature trees, and the differences among the many species that occupy these different canopy strata. In addition, consideration must also be given to leaf area dynamics and potential differences among species in their response to environmental variables, including radiation, vapor pressure deficit, and soil-water content.

Aboveground Autotrophic Respiration

Abstract: Understanding the autotrophic respiratory activity of living tissues in a forest provides useful insights into the responses of the forest to its environment. Respiration measurements also contribute essential data for evaluating and constructing carbon budgets and models. Historically, studies have shown that the primary factors that control autotrophic respiration include temperature, phenology, and species. More recently, studies by (1989), (1995), (1998), (1999), (1999), and (2001) have shown that nitrogen content plays a key role in autotrophic respiration rates. Above-ground autotrophic respiration can be conveniently divided into woody-tissue respiration and foliar respiration. Foliar respiration accounts for from about 30% of aboveground autotrophic respiration in some temperate deciduous forests (Edwards et al. 1981) to as much as 75% in some forests, such as in northern coniferous sites (Lavigne et al. 1997). Woody-tissue respiration is important because the bulk of the biomass in a mature forest stand is in woody tissue, and respiration in the living cells of this tissue occurs continuously, even when trees are “dormant.” Woody-tissue respiration is also a good indicator of growth phenology and can be used to calculate growth rates if the respiration required for maintenance is taken into consideration. Woody-tissues account for from about 25% of the total aboveground autotrophic respiration in some forests, such as in northern coniferous sites (Lavigne et al. 1997), to more than half of the aboveground autotrophic respiration in some temperate deciduous forests (Edwards et al. 1981).

Nutrient Availability and Cycling

Abstract: Precipitation changes can affect forest nutrient cycles in a number of complex ways. Increases or decreases in precipitation may cause changes in productivity and nutrient uptake rates and will surely cause changes in soil-water flux and the hydrologic fluxes of nutrients. To date, most studies have emphasized the effects of temperature or elevated carbon dioxide on these processes, but changes in precipitation may have equal or greater effects (Kirshbaum et al. 1992). Specifically, changes in precipitation could cause changes in (1) the productivity of water-limited ecosystems, (2) water yield, and (3) water quality and soil leaching rates.

Rates of Coarse-Wood Decomposition

Abstract: Although coarse-wood (> 5 cm in diameter) decomposition rates were not evaluated as a part of the Throughfall Displacement Experiment (TDE) effort, a previous dataset from early Walker Branch studies (Todd et al. 1976) was available to address coarse-wood decomposition under ambient conditions. These data are included in this volume because woody decay is important to the ecosystem carbon budget of temperate deciduous forests (Chapter 22, this volume). A multiyear experiment to investigate site and species effects on decay rates and nutrient release or immobilization from decaying wood was established in March of 1972. Trees representing a range of wood characteristics (Carya sp., Liriodendron tulipifera, Pinus echinata, and Quercus prinus) were harvested during the winter of 1971/1972 and cut into sections having a constant length of 30 cm but variable diameters, ranging from 5 to 18 cm. Branch sections were placed on the Walker Branch watershed in valley bottom, midslope, and ridge-top sites. The branches were retrieved from the field twice annually through 1975, at which time the experiment was discontinued because the condition of the branch samples would not support further observations.