This report can be found on the Web at

Transcription

1

2 Auburn University is an equal opportunity educational institution/employee. Information contained herein is available to all persons without regard to race, color, sex, or national origin. This report can be found on the Web at

3 Proceedings EMERGING ISSUES ALONG URBAN-RURAL INTERFACES II: LINKING LAND-USE SCIENCE AND SOCIETY April 9-12, 2007 Sheraton Atlanta Atlanta, Georgia Edited by: David N. Laband Conference Co-sponsors: Auburn University Center for Forest Sustainability: A Peak of Excellence at Auburn University USDA Forest Service Southern Center for Wildland-Urban Interface Research & Information National Science Foundation Plum Creek Timber Company Georgia Forestry Commission Auburn University Forest Policy Center Auburn University School of Forestry and Wildlife Sciences Land Policy Institute, Michigan State University September 2007

4 Comparative Wood Anatomy of Ten Selected Urban Trees in the City of Baton Rouge, Louisiana Vanessa A. Ferchaud¹, Yadong Qi², and James I. McNitt² ¹ Urban Forestry Program, Southern University ² Southern University Agricultural Research and Extension Center Abstract Knowledge of tree growth and development is crucial to establishment and management of a healthy urban forest. This paper systematically compared the wood anatomy of ten southern broadleaf tree species grown in the city of Baton Rouge, Louisiana using a new cryostat micro-imaging technique. The species included Magnolia grandiflora L., Ulmus Americana L., Plantanus occidentalis L., Quercus falcata var. pagodifolia, Q. acutissima, Q. shumardii, Q. virginiana Mill., Q. falcata Michx., Q. nigra L., and Q. phellos L. Comparisons were made on wood texture, pith type, vessel arrangement, ray type, annual growth band width, and phloem rays. Southern magnolia and American sycamore had diffuse-porous wood and irregular shaped piths while American elm displayed ring-porous wood and circular-shaped pith. All the oaks species had star-shaped pith and the wood was ring porous. The anatomical characteristics were explored in depth for the ten species. Introduction Urban forests provide enormous environmental benefits by reducing air pollution, slowing stormwater runoff, and helping us conserve energy. Understanding tree structure, growth and development is the key to sound management of urban forests for optimization of their ecological, environmental, and economic functions and benefits. Urban forest professionals should be knowledgeable of native trees and their biological characteristics. Comparative wood anatomy deals with the descriptions of internal wood microstructures. Traditionally, the sliding microtome (sledge) has been the standard instrument for preparation of wood sections, but truly fine sectioning technique with the sliding microtome is difficult (Carlquist, 2001). The most relevant and comprehensive tree anatomy information was published by Shigo (1986 and 1994), containing mostly northern, eastern, and western tree species. In his work, however, the images of the fresh woody cross-sections were taken primarily from hand-sectioned stem stubs. There has been no set of standards available pertinent to sectioning fresh woody stem of different species using cryostat microtome, and there has been no published systematic comparison of wood anatomy of major southern broadleaf trees. Such comparisons should be made using the same anatomical research method for similar aged trees growing in the same environmental conditions. This paper systematically compared the wood anatomy of ten southern broadleaf tree species that are native to the city of Baton Rouge, Louisiana using a new cryostat microimaging technique. The goal was to characterize and compare wood anatomy of the ten southern species in a systematic and comprehensive manner. The specific objectives were 1) to develop a micro-technique suitable for sectioning fresh woody stem using a cryostat and a procedure for wet-mount for light microscopy; 2) to obtain cross-section images of 3-year-old twigs at different magnifications for the ten southern broadleaf tree species, using a state-of-the-art light microscopy imaging system, and 3) to characterize twig anatomical structure for each species including bark, phloem, xylem, pith, earlywood, latewood, annual ring growth and vessel distribution, vascular rays, phloem rays, and phloem fibers, and to identify unique wood anatomical features possessed by the species. Methodology Ten major urban tree speices native to Louisiana were selected for this study including Magnolia grandiflora L., Ulmus Americana L., Plantanus occidentalis L., Quercus falcata var. pagodifolia, Q. acutissima, Q. shumardii, Q. virginiana Mill., Q. falcata Michx., Q. nigra L., and Q. phellos L. Three trees were selected for each species. For each tree, a three-year-old twig facing the north direction was sampled. A total of 30 samples (10 species x 3 randomized sample twigs/species) were collected during the study period from November 2004 to May The twigs ranging from 5-11mm in diameter were cut into individual sections of approximately 1cm in length using a sharp clipper. Each twig section was then embedded on a specimen disc using OTC-compound (Jung tissue freezing medium, Leica Microsystems Nussloch GmbH, Nussloch, Germany) and placed in the chamber of a cryostat (Leica CM-1800 Cryostat Microtome, Nussloch, Germany) for rapid freezing at various low temperatures ranging from -10 to -27. The specimens of each species were then sectioned using the cryostat at the selected temperature. The temperature selection during the sectioning varied with species due to the differences in sample size, wood properties and moisture content. The cross-sections of the twig tissues were sectioned at 60µm thickness, which was found to be the suitable thickness to maintain the integrity of the cross sections and to facilitate the comparative anatomical study. Images of the fresh twig cross-sections were taken using a research stereomicroscope (Olympus SZX12, Olympus America Inc. New York, USA) equipped with a Microfire Digital Firewire Color Camera (Olympus America Inc., New York, USA), and a compound microscope (BX51 by Olympus). For preparation of permanent light microscopy slides, fresh tissue sections of 60µm thickness were preserved in FAA fixation solution (95% ethanol: glacial acetic acid: 37%-40% formaldehyde: water; 50:5:10:35, v/v) for at least 24 hours. Samples were then dehydrated in 40% ethanol for minutes, 70% ethanol for 30 minutes, 80% and 90% ethanol each for 20 minutes and finally 100% ethanol for 20 minutes twice. A couple of drops of fast green dye (Fast Green FCF CAS # , Electron Microscopy Sciences, Fort Washington, PA) solution 190 Emerging Issues Along Urban-Rural Interfaces II Proceedings

5 (1 gram of the fast green power in 20ml of 100% alcohol and 80ml of distilled water) was added during dehydration at 70% ethanol. After dehydration was completed, histochoice clearing agent (Sigma, h-2779, Lot 052K0180) was added to the sample vials to preserve the samples for at least 1 hour. Finally the samples were mounted permanently on clean microscopic glass slides using permount compound (SO-P-15, histological mounting medium, Fisher Scientific Lot 72000, Class IB). Results American elm cross-section (Figures 1 and 2) has a wood texture that is ring porous wood with bands of large, earlywood vessels (pores) in a continuous row. The hardwood annual rings appear like concentric bands of solitary pores and can be counted to age-date the twig. The latewood vessels are smaller and wavy bands (pores arranged in irregular concentric bands), even in the earlywood. American elm has circular shape pith that is made up of cells that are like large balloons or bubbles. The wood rays are seen as thin white narrow stripes or lines (radial parenchyma) that extend across the growth in the radial direction from the bark to the center of the tree. American sycamore cross-section has a wood texture that is diffuse-porous with irregular shape pith. The earlywood and the latewood vessels are relatively same size and solitary. Growth rings are present but not too distinct. Sycamore has large conspicuous broad rays with fine narrow rays running between them. A unique characteristic of sycamore is the ray node (swelling of the ray) that is positioned at the intersection of a new growth ring where the earlywood zone begins (Figures 3 and 4). Southern Magnolia has a diffuse-porous wood texture and the vessels are solitary pores throughout the secondary xylem. The phloem has a large white band that stands out and is called the primary phloem fibers. The phloem also has dilated phloem rays that are shaped like large v-shape fans. The rays are large parenchyma cells that can fill more space so that the phloem region can keep up with the expanding circumference of the stem. The vessels are uniform in size across the entire annual ring (Figure 5). Cherrybark oak is a ring-porous wood with bands of 1-3 large, porous spring vessels and has star-shaped pith. The smaller latewood vessels, arranged in pore chains (an arrangement where pore multiples appear in radial direction only) occupy the wider gaps between the earlywood annual rings. The broad thick rays are very conspicuous and separated by several narrow rays (Figure 6). Sawtooth oak cross-section has star-shaped pith and the annual rings are not distinct. The vessel distribution portrays large and small pores arranged in pore chains parallel to its vascular rays. Broad rays are conspicuous and are separated by numerous narrow rays. Sawtooth oak cross-section appears to have five arms extending radially from the pith to the indented phloem. Between the adjacent arms there is a single broad ray (Figure 7). Figure 1 (left). American Elm Hand-Section Figure 2 (middle). American Elm Cryostat-Section Figure 3 (right). American Sycamore Hand-Section Figure 4 (left). American Sycamore Cryostat-Section Figure 5 (middle). Southern Magnolia Cryostat-Section Figure 6 (right). Cherrybark Oak Cryostat-Section Emerging Issues Along Urban-Rural Interfaces II Proceedings 191

6 Shumard oak wood texture is ring-porous wood, with bands of large, porous spring vessels 1-3 pores in width and star-shaped pith. The annual rings appear like concentric bands and can be counted to age-date the twig. Large earlywood and small latewood pore chains are numerous in a single growth year (Figure 8). Southern live oak annual rings are less distinct. There are large earlywood vessels and small latewood vessels that are aligned in several pore chains arranged parallel to the vascular rays. rays are numerous in the section. The pith is starshaped (sometimes may appear irregular shape in very young stems) with soft, spongy parenchyma tissue (Figure 9). Southern red oak has a wood texture that is ring-porous, with bands of large, porous spring vessels 1-4 or more pores in width. The hardwood annual rings appear like concentric bands and can be counted to age-date the twig. Large earlywood and small latewood pore chains are numerous in a single growth year, and they are surrounded by broad and narrow vascular rays. The pith is star-shaped and has thick balloon-like layers of cells (Figure 10). Water oak has a wood texture that is ring-porous, with bands of large, porous spring vessels 1-2 pores in width. The annual rings appear like concentric bands and can be counted to agedate the twig. Latewood pores are numerous, large and small, and aligned as pore chains. Water oak has a few broad rays that are separated by numerous narrow rays. The pith is star-shaped with soft, spongy parenchyma tissue (Figure11). Figure 7 (left). Sawtooth Oak Cryostat-Section Figure 8 (middle). Shumard Oak Cryostat-Section Figure 9 (right). Southern Live Oak Cryostat-Section Willow oak has a ring-porous wood, with bands of large, porous spring vessels 1-2 pores in width. Latewood vessels are numerous, large and small and aligned as pore chains radially toward the phloem. The annual rings appear like concentric bands and can be counted to age-date the twig. Willow oak has few broad rays that are separated by numerous narrow rays. The pith is star-shaped with soft spongy parenchyma tissue (Figure 12). Discussion The comparative wood anatomy among the ten broadleaf southern tree species is presented in Table 1. The cross sections showed that in the secondary xylems all seven oak species were ring-porous with large vessels in the earlywood and small vessels in the latewood. The earlywood vessels are distinctly visible to the naked eye, forming conspicuous bands 1-4 vessels in width. Latewood vessels are numerous, small and are not sharply defined without a microscope. The vessels are scattered and radially aligned into the secondary xylem, showing the characteristics of flame-shape tracts ranging in different heights. The vessel arrangements are characteristic of pore chains, according to the classification by Bond and Hammer (2002). Sawtooth oak annual rings are indistinct and the vessels are parallel to the vascular rays. Six of the oak tree species have broad (multiseriate) and narrow (uniseriate) rays that extend across the growth rings in the radial direction from the bark to the center of the tree. Southern live oak is the only species that displays only narrow rays at this young age. Among the seven oak species studied, all possessed star-shaped piths, Figure 10 (left). Southern Red Oak Cryostat-Section Figure 11 (middle). Water Oak Cryostat-Section Figure 12 (right). Willow Oak Hand-Section 192 Emerging Issues Along Urban-Rural Interfaces II Proceedings

7 with exception of live oak, which had irregular/star-shaped pith. Southern magnolia and American sycamore have diffuseporous wood and irregular-shaped piths, while American elm displayed ring-porous wood and circular-shaped pith. Conclusion This study presents systematic and comprehensive information on wood anatomy of three-year-old twigs of the ten broadleaf tree species using the cryostat microtechnique. The cryo-sectioning method used in the study provides an easier and better way of sectioning woody stem which will be valuable to facilitate study of wood anatomy. The results obtained from this study will be useful to forestry and urban forestry professionals, arborists, and the public to better understand tree growth and development. The information will also be valuable to teaching of tree anatomy and botany of southern trees. References Bond, B. and P. Hammer Wood Identification for Hardwood and Softwood Species Native to Tennessee. PB1692 of Agriculture Extension Service, University of Tennessee, Knoxville, TN. Carlquist, S Comparative Wood Anatomy. 2nd ed. Revised. Springer Verlag, Berlin Heidelberg, NY. 448 pp. Shigo, A.L Tree Anatomy. Sherwin Dodge, Littleton, NH. 104pp. Shigo, A.L A New Tree Biology. 10th Ed. Sherwin Dodge, Littleton, NH. Table 1. Comparisons of Wood Anatomy Among the Species Species Name Age Wood Texture Pith Type American Elm 3yrs Ring-Porous Circular American Sycamore 3yrs Diffuse-Porous Southern Magnolia 3yrs Diffuse-Porous Cherrybark Oak Irregular shape Irregularoblong Vessel Arrangement Wavy bands/ Solitary Solitary Solitary 3yrs Ring-Porous Star-shape Pore chains Saw Tooth Oak 3yrs Annual ring indistinct Star-shape Pore chains Shumard Oak 3yrs Ring-Porous Star-shape Pore chains Southern Live Oak 3yrs Ring-Porous Irregularstar shape Southern Red Oak 3yrs Ring-Porous Star-shape Pore chains Water Oak 3yrs Ring-porous Star-shape Pore chains Willow Oak 3yrs Ring-Porous Star-shape Pore chains Ray Type Ray Annual Growth Band Width 1-pore Phloem Rays Yes/No Yes Unique Characteristics Solitary pores in 1 st year and nested pores 1-2 pores Yes Ray nodes None Yes Dilated Phloem Rays 1-2 pores Yes Not distinct Yes 1-3 pores Yes Pore chains 1-2 pores No 1-4 or more pores No 1-2 pores No 1-2 pores No Emerging Issues Along Urban-Rural Interfaces II Proceedings 193

8