THE REPRODUCTIVE ECOLOGY OF BROADLEAVED TREES AND SHRUBS: TANOAK

Transcription

1 Research Contribution 9d May 1995 THE REPRODUCTIVE ECOLOGY OF BROADLEAVED TREES AND SHRUBS: TANOAK Lithocarpus densiflorus (Hook. & Arn.) Rehd. by Edward C. Jensen, Debra J. Anderson, and John C. Tappeiner II College of Forestry Forest Research Laboratory Oregon State University

2 The Forest Research Laboratory of Oregon State University was established by the Oregon Legislature to conduct research leading to expanded forest yields, increased use of forest products, and accelerated economic development of the State. Its scientists conduct this research in laboratories and forests administered by the University and cooperating agencies and industries throughout Oregon. Research results are made available to potential users through the University s educational programs and through Laboratory publications such as this, which are directed as appropriate to forest landowners and managers, manufacturers and users of forest products, leaders of government and industry, the scientific community, and the general public. The Authors Edward C. Jensen is an assistant professor and John C. Tappeiner II is a professor in the Department of Forest Resources, College of Forestry, Oregon State University, Corvallis, Oregon. Debra J. Anderson is a forester and natural resource educator for the USDA Forest Service, Umpqua National Forest, Roseburg, Oregon. To Order Copies Copies of this and other Forest Research Laboratory publications are available from: Forestry Publications Office Oregon State University Forest Research Laboratory Corvallis, Oregon Please indicate author(s), title, and publication number if known. Recycled Paper

3 Table of Contents The Reproductive Ecology of Broadleaved Trees and Shrubs: Tanoak, Lithocarpus densiflorus (Hook. & Arn.) Rehd....1 Physical Characteristics...1 Leaves and Stems...1 Flowers and Fruits...1 Growth Habit...2 Habitat and Range...2 Method of Reproduction...2 Sexual Reproduction...2 Vegetative Reproduction...3 Role in Succession...3 Response to Changes in Environment...4 Fisheries and Wildlife...4 Cultural and Historical Values...5 Management Options...5 Literature Cited...6 Associated Literature...6 Additional Notes...7 Educational Package...7 Program Funding Provided by...7 Disclaimer...7

4 THE REPRODUCTIVE ECOLOGY OF BROADLEAVED TREES AND SHRUBS: TANOAK, Lithocarpus densiflorus (Hook. & Arn.) Rehd. Tanoak is a common broadleaved, evergreen tree that grows in mixed conifer hardwood forests of southwestern Oregon and northern California, redwood forests of coastal California, and mixed conifer forests of the Sierra Nevadas. It is adaptable and tenacious, growing on early successional sites following fire and timber harvest and in old-growth forests beneath towering conifers. Contributing to this tenacity is its ability to reproduce from seeds and from sprouts arising from large underground burls. Physical Characteristics Leaves and Stems Tanoak leaves are simple, alternate, and persistent, generally remaining on the tree for three or four growing seasons. Mature leaves are typically 3 5 inches long, stiff and leathery, and dark green above and bluish-white below. Both surfaces on young leaves are covered with dense hairs that rub off with time; these dust-like hairs are very irritating to human eyes and noses. Leaf margins can be either entire or coarsely toothed with a distinct vein running to each tooth. Twigs are stout and round, are covered with dense hairs, and have star-shaped piths. Bark is generally thin (less than 2 inches), grayish- to reddish-brown, and broken into narrow ridges and plates. Flowers and Fruits Tanoak flowers are borne in erect, creamy-white aments (also called catkins) that appear from June to August. Unlike most aments, individual tanoak aments are bisexual, with female flowers borne at the base of the male flowers. Tanoak flowers have an unpleasant odor and bear a large, irritating pollen to which many humans are allergic. Tanoak fruits are acorns that take 2 years to develop; they are borne either singly or in small clusters. They are 3/4 to 1 1/4 inches long, are covered by a shallow, bristly cap, and ripen from September to November, changing from green to light yellow to brown. 1

5 Growth Habit Tanoak has multiple growth forms. Trees commonly reach heights of feet and diameters of 1 3 feet. They may be spire-shaped, rounded, or densely shrubby. They often have multiple trunks that grow from large underground burls. In the mountains of northern California and southwestern Oregon, tanoak also has a shrubby variety (L. densiflorus var. echinoides) that can reach 15 feet tall. While the clumps formed by this variety are often straggly, they respond to disturbance much as the main species does (Tappeiner et al. 1990). Tanoak is difficult to age because its propensity to sprout results in stems of dramatically different ages; thus some stems are much younger than the burl from which they have arisen or than the stems that grow next to them. Habitat and Range WA OR Tanoak Range ID Tanoak grows from southwestern Oregon through the coastal mountains of northern and central California, where it is an important component of redwood forests. It also grows in the northern Sierra Nevadas, although it is less common there and often occurs in isolated groves. It grows from sea level to 5000 feet, most often on sandy, loamy, or gravelly soils that are moist and well drained. Tanoak requires more moisture than many other hardwoods and will often be supplanted by more drought-resistant species on drier sites (Tappeiner et al. 1990). CA Method of Reproduction Tanoak reproduces both from seeds and vegetatively. Sexual Reproduction Tanoak is a heavy and dependable seed producer, producing large acorn crops nearly every other year (Roy 1989). Trees that form from seeds typically become reproductive in their third or fourth decade, but sprouts that arise from burls may bear acorns after only a few years (Tappeiner et al. 1990). Tanoak acorns are large and are commonly 2

6 gathered and eaten by mammals and birds; they also host many insect larvae. Many otherwise viable acorns are lost to predation, especially in clearcuts and open stands (Tappeiner et al. 1990). Because they have an abundance of stored energy, tanoak acorns are able to germinate and survive under a variety of conditions, from dense forests with thick litter layers to exposed clearcuts (Tappeiner et al. 1990). Tanoak seedlings grow slowly and frequently experience die-back and mechanical damage; as a result, they often develop multiple stems. Vegetative Reproduction Tanoaks begin producing underground burls at a very early age, typically in their first or second year (Tappeiner et al. 1990). Each burl contains numerous buds that are capable of sprouting into new, aboveground stems; burls on old trees may contain many thousands of buds. Seedlings commonly sprout within their first several years, resulting in seedling-sprouts with multiple stems. Sprouting typically occurs when the parent plant is damaged or killed, although a change in the plant s environment that increases the amount of light reaching the leaves and stems may be sufficient to induce it. Some maintenance sprouting also occurs, without visible damage to the parent or significant changes to its environment. Unlike many other sprouting tree species, even large tanoaks have the ability to sprout vigorously. Large stumps commonly support tens to hundreds of sprouts, and one gave rise to 1400 (Tappeiner et al. 1990). Multiple sprouts grow rapidly and thin themselves, concentrating growth in relatively few stems. It is common to see four to eight 30-year-old pole-sized sprouts surrounding a larger parent tree or stump (Tappeiner et al. 1990). Role in Succession Because it is tolerant of shade and other understory conditions, tanoak is able to persist, and often flourish, through most stages of forest succession. In the stem initiation stage of a mixed hardwood conifer stand, tanoak can occur as seedlings, as sprouts that arise from seedlings, or, most commonly, as sprout clumps arising from residual trees. New clumps of stems are quite vigorous and will out-compete most other species. As the stand becomes more dense and enters the stem exclusion stage, tanoak is able to sustain itself because it is shadetolerant. However, tanoak in the tree form will sometimes revert to a shrubbier form as large upright stems die and smaller stems arising from the tree s base persist. As the stand enters the stem re-initiation stage, gaps appear in the canopy and light begins to reach the forest floor. During this stage, seedling establishment occurs and established seedlings begin to sprout; large clumps of shrubby tanoak often begin to develop into multi-stemmed trees. In the old-growth stage of mixed hardwood conifer stands, tanoak is especially common in the understory and is likely to appear in all shapes, sizes, and ages. There are 3

7 likely to be many seedlings and saplings and a few larger individuals, forming an uneven-aged diameter distribution. Response to Changes in Environment Tanoak responds favorably to openings that occur in a stand and to many forms of disturbance. Seedlings, trees, and clumps of any size have the ability to sprout. For example, increases in light that result from thinning or patch cutting commonly stimulate increases in tanoak growth and acorn production. Tanoak shrub clumps also sprout vigorously. When tanoak is cut or damaged by fire, the remaining stumps and underground burls typically sprout vigorously. Seedlings are less able to resist the damaging effects of fire, probably because their burls which are smaller, more tender, and nearer the soil surface are more likely to be damaged than are the burls of adult plants. The size of tanoak sprout clumps that may grow when a parent tree or sprout clump is cut can be predicted by examining either the diameter of the tree or the crown area of the original sprout clump (Harrington 1983, Tappeiner and McDonald 1984). Predicting tanoak s size and rate of development can help resource managers understand the competitive effect tanoak may have on other species in a stand (Harrington 1983). Fisheries and Wildlife Tanoak is important for wildlife. Many insects, birds, and mammals eat its acorns, and dense tanoak clumps provide good hiding cover for small and large animals. Bird species positively correlated with tanoak include olive-sided flycatchers, western flycatchers, hermit warblers, and warbling vireos (Raphael 1987). Western gray squirrels, beechy ground squirrels, Townsend s chipmunks, deer mice, dusky-footed woodrats, and black-tailed deer all eat tanoak acorns (Maser et al. 1984). On the other hand, tanoak leaves do not provide good browse for herbivores; in addition, because tanoak is a fierce competitor with other forest plants, it may preclude species that provide better forage. 4

8 Cultural and Historical Values Tanoak acorns were a principal dietary component for several West Coast Indian tribes. Acorns were commonly ground and leached, then used in soups, cooked into mush, or made into bread (Tappeiner et al. 1990). The Costanoan tribe used an infusion of tanoak bark as a wash for face sores. When this infusion was held in the mouth, it was said to help tighten loose teeth (Moerman 1986). The tannins contained in the bark of tanoak are especially good for tanning heavy leather (Tappeiner et al. 1990). Management Options There are a number of reasons that managers might want to encourage the growth of tanoak. On good sites it can be coppiced for hardwood logs, although its growth rate is not likely to equal that of associated conifers such as Douglas-fir, redwood, grand fir, and western hemlock. Its wood is strong and fine grained and can be used like oak wood; it can also be pulped. It is used locally for firewood and is being tested for the generation of electricity. An extract from tanoak bark furnishes excellent tannage for the production of heavy leathers (Roy 1989). Tanoak acorns are an important source of food for many species of wildlife and have been used for feeding hogs and cattle (Roy 1989). Little effort is required to enhance tanoak on sites where it already exists. Cutting aerial stems will stimulate a tremendous sprouting response, and seedlings easily establish themselves even in dense shade and on thick litter layers (Tappeiner et al. 1990). Moving tanoak off-site is more difficult; propagation by cutting and grafting has not been reported, and seedlings, while relatively easy to establish, may grow slowly under cultivation (Tappeiner et al. 1990). Controlling tanoak is difficult but not impossible. Seedlings are apparently susceptible to fire; an intense underburn often provides good control. As plants get older, manual cutting over several consecutive years can provide enough control to get conifers or other species started, but it is an expensive process. Ahrens (1990) found that cutting sprout clumps in their fourth year often resulted in good control because the plant s root reserves were drained before the plant could re-establish its root biomass. Herbicides can also be used selectively and inexpensively to control tanoak shrubs and trees. Triclopyr applied in the early spring will help control tanoak sprouts (M. Newton, personal communication, 1993). In addition, triclopyr can be injected into a cut stem during the fall or winter months, providing good control (Tappeiner et al. 1987). Tanoak trees over 4 inches in diameter can be cut and the stumps sprayed with triclopyr to help reduce sprouting. 5

9 Literature Cited Ahrens, G.R Tanoak (Lithocarpus densiflorus (Hook. & Arn.) Rehd.) root dieback: below- and above-ground site occupancy by stumpsprouts in southwest Oregon. Unpublished Master s thesis. Oregon State University, Corvallis, Oregon. 77 p. Harrington, T.B Prediction of the biomass, leaf area, and crown area of sprout clumps of tanoak (Lithocarpus densiflorus (Hook. & Arn.) Rehd.): a technique for assessing site occupancy by this species. Unpublished Master s thesis. Oregon State University, Corvallis, Oregon. 106 p. Maser, C., B.R. Mate, J.F. Franklin, and C.T. Dyrness Natural History of Oregon Coast Mammals. Museum of Natural History, University of Oregon, Eugene, Oregon. 496 p. Moerman, D.E Medicinal Plants of Native America. University of Michigan Museum of Anthropology, Ann Arbor, Michigan. Technical Reports, Number 19, Volume p. Raphael, M.G Wildlife tanoak associations in Douglas-fir forests in northwest California. P in Multiple-use Management of California s Hardwood Resources. Proceedings of a symposium. T.R. Plumb and H.H. Pillsbury, editors. USDA Forest Service, Pacific Southwest Forest and Range Experiment Station, Berkeley, California. General Technical Report PSW-100. Roy, D.F Lithocarpus densiflorus (Hook. & Arn.) Rehd. Tanoak. P in Seeds of Woody Plants in the United States. C.S. Schopmeyer, editor. USDA Forest Service, Washington, D.C. Agriculture Handbook No Tappeiner, J.C., and P.M. McDonald Development of tanoak understories in conifer stands. Canadian Journal of Forest Research 14: Tappeiner, J.C., P.M. McDonald, and D.F. Roy Lithocarpus densiflorus (Hook. & Arn.) Rehd. Tanoak. P in Silvics of North America. Volume 2. Hardwoods. R.M. Burns and B.H. Honkala, tech. coords. USDA Forest Service, Washington, D.C. Agriculture Handbook 654. Tappeiner, J.C., II, R.J. Pabst, and M. Cloughesy Stem treatments to control tanoak sprouting. Western Journal of Applied Forestry 2: Associated Literature Additional papers on the ecology and management of tanoak are listed in the Associated Literature section that accompanies this educational package. 6

10 Additional Notes Educational Package This leaflet is part of a larger educational program on the reproductive ecology of Pacific Northwest broadleaved trees and shrubs. The complete program consists of two audio-visual components a videotape on the reproductive ecology of broadleaved trees and shrubs and a series of slide-tapes on shrub identification and four printed components: 1) an overview of plant reproduction, 2) a series of leaflets on PNW trees and shrubs, 3) a glossary of relevant terms, and 4) a list of associated literature. To obtain the complete educational package, contact: Forestry Media Center, College of Forestry, Oregon State University, Corvallis, OR 97331, (503) To obtain only the printed documents, contact: Forestry Publications Office, Forest Research Laboratory, Oregon State University, Corvallis, OR Program Funding Provided by Coastal Oregon Productivity Enhancement (COPE) Program, Oregon State University; USDA Forest Service, Pacific Northwest Research Station, Ecological Framework for Management Program; and Silviculture Institute, Oregon State University and the University of Washington. Disclaimer This leaflet contains information on herbicides that may or may not be registered for use in your area. By mentioning these chemicals, we are not recommending their use nor are we implying that other products or treatments may not be equally effective. The persons involved in the preparation and publication of this document assume no responsibility for any results or consequences that arise from the use of treatments or products mentioned in this document. 7

11 Jensen, E.C., D.J. Anderson, and J.C. Tappeiner II THE REPRODUCTIVE ECOL- OGY OF BROADLEAVED TREES AND SHRUBS: TANOAK, LITHOCARPUS DENSIFLORUS (HOOK. & ARN.) REHD. Forest Research Laboratory, Oregon State University, Corvallis. Research Publication 9d. 7 p. Tanoak is an integral part of Pacific Northwest forests. This leaflet describes principal identifying characteristics, habitat and range, methods of reproduction, role in succession and response to disturbance, value to humans and wildlife, and management options. This leaflet supports a complete educational package on the natural history and reproductive ecology of Pacific Northwest broadleaved trees and shrubs; other items in the package include a videotape, three slide-tapes, and a series of printed publications. Jensen, E.C., D.J. Anderson, and J.C. Tappeiner II THE REPRODUCTIVE ECOL- OGY OF BROADLEAVED TREES AND SHRUBS: TANOAK, LITHOCARPUS DENSIFLORUS (HOOK. & ARN.) REHD. Forest Research Laboratory, Oregon State University, Corvallis. Research Publication 9d. 7 p. Tanoak is an integral part of Pacific Northwest forests. This leaflet describes principal identifying characteristics, habitat and range, methods of reproduction, role in succession and response to disturbance, value to humans and wildlife, and management options. This leaflet supports a complete educational package on the natural history and reproductive ecology of Pacific Northwest broadleaved trees and shrubs; other items in the package include a videotape, three slide-tapes, and a series of printed publications.

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