- Debbie Maynard, M.S. student
- Brandy Saffell, M.S. student
- Danielle Marias, M.S. student
Post-Docs and Other Research Affiliates
I am comparing the air permeability of refractory vs. treatable Douglas-fir wood. Core samples have been taken from trees on a transect that extends from coastal to interior Oregon. These sites include those west of the Cascade Mountains that have been previously described as containing trees with treatable (permeable) wood, and those east of the Cascade Mountains that have been described as containing trees with refractory (less permeable) wood.
In addition to permeability comparisons, I will be comparing the wood anatomy of samples from different sites to ascertain if any correlations can be drawn between changes in anatomy and corresponding changes in permeability. The project aims to understand the effects of anatomy on permeability in this wood from eastern and western Oregon.
In my previous work, I received an M.S. and Ph.D. in Botany from the University of California at Davis. As a masters student of Thomas Rost, I used wood anatomy to identify the plants used in Native-American basket fragments of unknown composition. As a doctoral student of Ernest Gifford, I described the development of vascular patterns and trichomes at the apex of the fern Scyphularia pentaphylla. From my studies, I developed a life-long interest in wood anatomy and cambial development/differentiation. After several years of undergraduate teaching and advising at colleges and universities in California and Oregon, I returned to graduate school to fulfill my dream of studying wood anatomy.
I am a postdoc in the department of Wood Science and Engineering at OSU. Previous to my current research I received a B.S. in forest management from the University of Wisconsin-Stevens Point and a M.S. in forest ecology from the University of Missouri and a PhD from OSU in both Wood Science and Forest Science.
Below are my current research emphases:
The role of lignin in wood biomechanics, plant hydraulics, tree growth form:
I am working to understand what the physiological consequences are of reducing lignin content in transgenic poplar trees. Low-lignin trees have long been sought for improved pulping efficiency and more recently many low-lignin crops have been touted as improved feedstocks for biofuel production (i.e. less energy and/or harsh chemicals will be needed to remove lignin).
Tree growth rates at a global scale:
To date there has been no formal assessments of historical tree growth rates beyond the regional scale. I have been developing an tree age-specific global database (>10 million tree-ring measurements) and standardization techniques to assess temporal and spatial changes in tree productivity. This will aid in understanding whether tree age and thus shifts in disturbance frequency can interact with increased atmospheric CO2, climate change and nitrogen deposition to influence terrestrial biogeochemical cycling via changes in forest productivity.
Tree-ring stable isotopes:
I am currently establishing how well known physical processes interact with leaf-level physiology to influence hydrogen and oxygen isotopes in water used by plants to fix carbon during photosynthesis. I hope to develop some basic principles of leaf anatomical organization influence these signals within conifers versus hardwoods. This information will help our interpretation of past climates and may also help us better understand the role of plant transpiration in the global hydrological cycle.
Glacial to inter-glacial climate change:
Knowledge of past climate changes can provide us lessons for what we might expect in the future. At present the resolution of Pleistocene to Holocene temperatures and humidities in mid-continental North America is very low. We are combining dendrochronology, radiocarbon dating and stable isotope analyses to long-buried ancient wood to help better infer past mid-continental climates and weather (i.e. determine partitioning in water sources from the Gulf of Mexico versus the Pacific ocean during de-glaciation).
Examples of recent work:
Co-Principle Investigator of a NSF proposal (DEB, Ecosystems Cluster) funded for 2008-2011. "Testing tree carbon capture from paleo to present". Award: $440,000 to Oregon State University and $120,000 to the University of Missouri.
Voelker, SL, RM Muzika and RP Guyette. 2008. Individual tree and stand level influences on the growth, vigor and decline of red oaks in the Ozarks. Forest Science 54(1): 8-20.
Taylor, AM, JR Brooks, B Lachenbruch, JJ Morrell and SL Voelker. 2008. Correlation of carbon isotope ratios in the cellulose and wood extractives of Douglas-fir. Dendrochronologia 26(2): 125-131.
Parke, JL, E Oh, SL Voelker, EM Hansen, G Buckles, and B Lachenbruch. 2007. Phytopthora ramorum colonizes tanoak xylem and is associated with reduced stem water transport. Phytopathology 97(12): 1558-1567.
Guyette, RP, RM Muzika, and SL Voelker. 2007. The historical ecology of fire, climate, and the decline of shortleaf pine in the Ozarks. In JM Kabrick, DC Dey, D Gwaze (eds.). Shortleaf pine restoration and ecology in the Ozarks: proceedings of a symposium, USDA For. Serv. GTR-NRS-P-15, pp. 8-18.
Voelker, SL, RM Muzika, RP Guyette and MC Stambaugh. 2006. Historical CO2 growth enhancement declines with age in Quercus and Pinus. Ecological Monographs 76(4): 549-564.
Manuscripts in preparation:
Mculloh K. JS Sperry, B Lachenbruch, FC Meinzer, PB Reich and SL Voelker. Moving water well: comparing hydraulic efficiency in twigs and trunks of coniferous, ring-porous, and diffuse-porous saplings from temperate and tropical forests.
Voelker, SL, B Lachenbruch, FC Meinzer, NG Lewis, MJ Jourdes, LB Davin, NG Lewis, G Tuskan, L Gunter, SR Decker, MJ Selig, P Kitin and SL Strauss. Strong RNAi-inhibition of 4CL expression alters lignification, saccharification potential and productivity of field-grown poplar.
Voelker, SL, B Lachenbruch, FC Meinzer, P Kitin and SL Strauss. Low-lignin poplar wood: Reduced hydraulic conductivity and resistance to embolism cause shoot dieback and lowered growth efficiency.
Voelker, SL, B Lachenbruch, FC Meinzer and SL Strauss. Altered lignin in poplars affects growth form and mechanical stability.
Kitin, P. and SL Voelker, B Lachenbruch, FC Meinzer and SL Strauss. Microscopy techniques to discern water transport in transgenic low-lignin poplars.
Voelker, SL. Combining global tree-ring and climate data to determine the age dependence of growth responses to major climatic drivers. In Size- and age-related changes in tree structure and function, Spriner. FC Meinzer, T Dawson and B Lachenbruch (eds.).
Voelker, SL, FC Meinzer, B Lachenbruch, RM Muzika and RP Guyette. The contribution of tree age and nitrogen deposition to global increases in tree productivity.
Voelker, SL and B Lachenbruch. Developmental and climatic controls on wood density from six conifer species.
My research interests include whole plant physiology and the long-distance transport of water by plants. In particular, I am interested in how plants with radically different wood anatomy and growth forms coexist in the landscape. What are the tradeoffs associated with coniferous, diffuse-porous and ring-porous wood types? With trees versus vines? Are the wider xylem vessels of ring-porous trees truly more hydraulically efficient on an entire-plant basis than the tracheids in a conifer? And if so, what constraints limit ring-porous trees' ability to out compete conifer species? Pursuing these types of questions has led me to study hydraulic characteristics, plant anatomy, and mechanics.
At Oregon State University, I've worked on two main projects. The first involved using distal: proximal ratios of such characteristics as leaf specific hydraulic conductivity, conduit diameter, sap velocity, and conduit number to assess hydraulic efficiency. By comparing the hydraulic efficiency, which we define as hydraulic conductance per investment in vascular volume, of trees and vines from temperate and tropical areas, we compared tradeoffs between wood types and growth forms.
The second main project is examining tradeoffs in hydraulic safety (vulnerability to embolism) vs. hydraulic efficiency (in this case hydraulic conductivity). While many studies have compared safety and efficiency across species and not observed tradeoffs, we are concentrating on within species comparisons made from the roots to leaves. By comparing within species, we predict this tradeoff will be evident, and we can then compare across species to elucidate how species differ in their optimization of that tradeoff.
For my Ph.D. with Dr. John Sperry (University of Utah), I extended Murray's law, which was derived for cardiovascular systems, to the xylem of plants. Murray's law predicts the conduit taper that maximizes hydraulic conductance per vascular tissue investment. This solution occurs when the sum of the xylem conduit radii cubed (sum r3) is constant at every rank (i.e., the Sr3 in the trunk should equal the sum r3 of all 1yr-old branches combined). Results showed that when the conduits were not providing the structural support of the plant, such as in compound leaves and young ring-porous wood, they complied with Murray's law. However, when conduits provided both mechanical support and water transport, as in conifer and diffuse-porous wood, the conduits deviated from Murray's law.
Woodruff, D, FC Meinzer, and K McCulloh. 2009. Height-related trends in stomatal sensitivity to leaf-to-air vapour pressure deficit in a tall conifer. Journal of Experimental Botany. doi:10.1093/jxb/erp291
McCulloh, K, JS Sperry, F Meinzer, B Lachenbruch, and C Atala. 2009. Murray's law, the "Yarrum" optimum, and the hydraulic architecture of compound leaves. New Phytologist. 184: 234-244.
Meinzer, FC, DM Johnson, B Lachenbruch, KA McCulloh, and DR Woodruff. 2009. Xylem hydraulic safety margins in woody plants: coordination of stomatal control of xylem tension with hydraulic capacitance. Functional Ecology. 23: 922-930.
Johnson D, D Woodruff, K McCulloh, and F Meinzer. 2009. Leaf hydraulic conductance, measured in situ, declines and recovers daily: leaf hydraulics, water potential and gas exchange in four temperate and three tropical tree species. Tree Physiology. 29: 879-887
Johnson, D, F Meinzer, D Woodruff, and K McCulloh. 2009. Leaf xylem embolism, detected acoustically and by cryo-SEM, corresponds to decreases in leaf hydraulic conductance in four evergreen species. Plant, Cell and Environment.
Domec, J-C, B Lachenbruch, F Meinzer, D Woodruff, J Warren, and K McCulloh. 2008. Conflicting requirements for xylem safety and efficiency limit ultimate tree height in a conifer. PNAS. 105:12069-12074
Sperry, J, F Meinzer, K McCulloh. 2008. Safety and efficiency conflicts in hydraulic architecture: scaling from tissues to trees. Plant, Cell and Environment (invited review). 31: 632-645
McCulloh, K. K Winter, F Meinzer, M Garcia, J Aranda, and B Lachenbruch. 2007. A comparison of daily water use estimates using constant heat sap-flow probes and gravimetric measurements in pot grown saplings. Tree Physiology. 27:1355-1360.
Woodruff, D, K McCulloh, J Warren, F Meinzer, and B Lachenbruch. 2007. Impacts of tree height on leaf hydraulic architecture and stomatal control in Douglas-fir. Plant, Cell and Environment. 30(5): 559-569
McCulloh, K, and J Sperry. 2006. Murray's law and the mechanical architecture of plants. In: Ecology and biomechanics. CRC Press Inc., Boca Raton, FL, USA.
McCulloh, K, and J Sperry. 2005. The evaluation of Murray's law in Psilotum nudum (Psilotaceae), an analogue of ancestral vascular plants. American Journal of Botany. 92(6): 985-989.
McCulloh, K, and J Sperry. 2005. Patterns in hydraulic architecture and their implications for transport efficiency. Tree Physiology. 25:257-267.
McCulloh, K, J Sperry, and F Adler. 2004. Murray's law and the hydraulic versus mechanical functioning of wood. Functional Ecology. 18: 931-938.
McCulloh, K. 2004. Do plants obey Murray's law? Ph.D. Dissertation. University of Utah, Salt Lake City, Utah, USA.
McCulloh, K, J Sperry, and F Adler. 2003. Water transport in plants obeys Murray's law. Nature. 421, 939-942.
Hacke, U, V Stiller, J Sperry, J Pittermann, and K McCulloh. 2001. The effect of cavitation and refilling cycles on the cavitation resistance of xylem. Plant Physiology. 125, 779-786.
Hacke, U, J Sperry, W Pockman, S Davis, and K McCulloh. 2001. Trends in wood density and structure are linked to prevention of xylem implosion by negative pressure. Oecologia. 126, 457-461.
Loudon, C and K McCulloh. 1999. Application of the Hagen-Poiseulle equation to fluid feeding through short tubes. Annals of the Entomological Society of America. 92 (1), 153-158.
My current research interests include plant physiology and, the relationship of wood structure and anatomy to plant physiology. To better understand the impacts of tree physiology on wood quality, my research focuses on how changes in wood properties (such as density, anatomical structure, strength) influence wood hydraulic performance. I addressed how such changes affect water transport (and to a limited extent, mechanical properties). Water flowing through the xylem of most plants from the roots to the leaves must pass through junctions where branches have developed from the main stem. These junctions are studied as both flow constrictions and components of a hydraulic segmentation mechanism to protect the main axes of the plant. The hydraulic nature of the branch and growth ring junction also affects the degree to which branches interact and can respond to changes in flow to other branches.
My future research goal is to understand the mechanisms by which species from related vascular plant groups (e.g., conifers vs. flowering plants) may move water under field condition or non-steady stage water transport. Transient mechanisms to be tested in the laboratory include discrepancies between hydraulic conductivity parameters measured under steady and non-steady state flow for roots, trunks, and branches and their effect on the vulnerability to cavitation responses. These data will be combined with measurements of vascular element dimensions, simple pit and bordered pit anatomy, direct corollaries of the water flux predictions. Transient mechanisms to be tested in the field include capacitance phenomena (water storage ability) of the stem, and effect of non-steady driving force on whole tree hydraulics.
I hold a Marie Curie Fellowship for mid-career scientists from the EU, and I am based in Belgium. As part of fellowship, I have worked closely with people in the Lachenbruch and Meinzer labs, as well with other as people in the College of Forestry and the Dept. of Botany and Plant Pathology. I work on the structure/function relationships in plants especially at the nanometer to millimeter scale, and have worked with bark and xylem, elucidating pathways of movement of water, air, and pathogens. Much of my research involves microscopy, and I am involved in developing and using new technologies for techniques such as sample preparation for cryoscanning light microscopy.
Dave Barnard, M.S. in Forest Science. 2010. Stem sapwood water transport and storage strategies in three conifers from contrasting climates.
Steve Voelker, Ph.D. in Wood Science & Engineering and Forest Science. 2009. Functional decreases in hydraulic and mechanical properties of field-grown transgenic poplar trees caused by modification of the lignin synthesis pathway through downregulation of the 4-coumarate:coenzyme A ligase gene.
David Woodruff, Ph.D. in Forest Science. 2008. Height-related trends in structure and function of Douglas-fir foliage.
Sonya Dunham, M.S. in Wood Science & Engineering and Forest Science. 2008. Douglas-fir hydraulic architecture and relationships among xylem properties at multiple scales via a Bayesian analysis.
Heidi Renninger, M.S. in Wood Science & Engineering and Forest Science. 2006. Effects of release from suppresion of hydraulic architecture, photosynthetic capacity, and functional wood characteristics in Douglas-fir and Western hemlock.
Lotties Fallas-Cedeno, M.S. in Wood Science & Engineering and Forest Science. 2005. Water movement in relation to xylem conductivity in four hardwood species.
Hamish Marshall, M.F. in Wood Science & Engineering. 2005. The impact of bark thickness in the forestry supply chain.
Adam Taylor, Ph.D. in Wood Science & Engineering. 2004. Environmental effects on heartwood extractive content and their consequences for natural durability in Douglas-fir and western redcedar.
Jose Antonio Silva Guzman, Ph.D. in Wood Science & Engineering. 2004. Development of an accelerated method for assessing decay of wood plastic composites (WPCs).
Michele Pruyn, Ph.D. in Wood Science & Engineering and Forest Science. 2002. Patterns of stem respiration within tree, with age, and between species in Pacific Northwest trees.
Jean-Christophe Domec, Ph.D. in Wood Science & Engineering and Forest Science. 2002. Structure and hydraulic functions of xylem in two tree species with contrasting amounts of sapwood.
Amy Grotta, M.S. in Wood Science & Engineering and Forest Science. 2002. Competitive interactions in young, coastal Douglas-fir/red alder mixtures: Implications for wood quality.
James Robbins, M.S. in Forest Products and Forest Science. 2000. Influence of spacing and crown recession on wood quality of intensively-managed young-growth Douglas-fir.
David Baker, M.S. in Forest Products and Forest Science. 2000. Wood density patterns of young Costa Rican trees in planted and natural forests.
Jeff DeBell, Ph.D. in Forest Products and Forest Science, 1998. Wood quality studies in second-growth western redcedar (Thuja plicata Donn.)
Rachel Spicer, M.S. in Forest Products and Forest Science. 1997. Hydraulic properties of compression wood in branches and reoriented shoots of Douglas-fir (Pseudotsuga menziesii).
Hua Lei, Ph.D. in Forest Products. 1995. The effects of growth rate and cambial age on wood properties of red alder (Alnus rubra Bong.) and Oregon white oak (Quercus garryana Dougl.).