Tilia heterophylla Vent.
Tiliaceae -- Basswood family
White basswood (Tilia heterophylla) is a mediumsized tree of the upper Piedmont region and the Appalachian Mountains where it grows on moist, welldrained soils in coves or along mountain streams with other hardwoods. Its growth is moderately fast and it produces commercially valuable lumber. The soft, lightweight wood is used for cabinetry, woodenware, and pulpwood, among its many uses. The name beetree linden is common because of the extensive use of this tree by bees for honey production. It is also an attractive landscape tree.
The range of white basswood extends from southwestern Pennsylvania west in southern Ohio, Indiana, and Illinois to Missouri; south to northern Arkansas; east to northeastern Mississippi, Alabama, northwestern Florida, and Georgia; and north to Maryland. Outlying populations occur in eastern Pennsylvania and western New York. It reaches its largest growth in the Appalachian Mountains, where it is often dominant. However, it is most common in the mixed mesophytic forests of the Cumberland Plateau, where it is second only to sugar maple (Acer saccharum) in frequency (10,11).
-The native range of white basswood.
Climatic conditions vary widely within the range of white basswood. In its southernmost range in northwest Florida, the mean annual number of days below freezing is 20; at the northernmost extremes in Pennsylvania and western New York, it is 150. These extremes occasionally include temperatures below -18° C (0° F) in the winter and some days in excess of 38° C (100° F) in the summer. Annual precipitation varies widely, ranging from more than 2030 mm (80 in) in some areas in the Southern Appalachians to about 910 mm (36 in) in some northern and western margins of its range (14).
Quite particular in its soil and moisture requirements, white basswood cannot tolerate very wet or very dry conditions, and it almost always grows on moist but well-drained soils. This tree grows best along mountain streams or in mountain coves where the soils have an alluvial or a colluvial origin. These soils are deep, friable, and have considerable humus (11).
White basswood is found on soils of five orders, Inceptisols, Ultisols, Alfisols, Entisols, and Mollisols. Of these, Inceptisols and Ultisols occupy by far the largest areas, and their common property is moisture availability for more than half the year or for more than 3 consecutive months during the warm season. Moisture availability during the warm season is also a property of Alfisols, which are present in the western portions of the range of white basswood, but it is not a property of Entisols and Mollisols. However, the latter orders occupy very small areas in the southern and western margins of the species range (13).
Although rare at very low elevations, basswood is occasionally found on the Coastal Plain but appears with increasing frequency in the upper Piedmont. It is common in the Appalachian Mountains at elevations between 900 m (3,000 ft) and 1500 m (5,000 ft), where it usually grows on north and east exposures and on flood plains or in deep, moist coves (11).
White basswood is a component of five forest cover types (5): White Oak-Black Oak-Northern Red Oak (Society of American Foresters Type 52), Yellowpoplar (Type 57), Yellow-Poplar-Eastern Hemlock (Type 58), Yellow-Poplar-White Oak-Northern Red Oak (Type 59), and Silver Maple-American Elm (Type 62). However, it is not a major species in any of them. In the northern part of its range it grows with northern red oak (Quercus rubra), white ash (Fraxinus americana), black cherry (Prunus serotina), white oak (Q. alba), black oak (Q. velutina), sweet birch (Betula lenta), butternut (Juglans cinerea), American elm (Ulmus americana), American beech (Fagus grandifolia), black walnut (Juglans nigra), eastern hemlock (Tsuga canadensis), and hickories (Carya spp.); farther south in the Appalachians it is more commonly found with yellow buckeye (Aesculus octandra), yellow birch (B. alleghaniensis), sweet birch, sugar maple, black cherry, yellow-polar (Liriodendron tulipifera), cucumbertree (Magnolia acuminata), black locust (Robinia pseudoacacia), loblolly pine (Pinus taeda), and shortleaf pine (P. echinata).
Flowering and Fruiting- White basswood flowers in the latter part of June and early July. Once flowering begins, flowers, pollen, and nectar are abundant. The perfect flowers are protandrous; the anthers usually open in the afternoon and release pollen for 24 hours, after which the stigmas become receptive and nectar production begins. There are 66 insect species known to pollinate basswood; bees and flies are the most common diurnal visitors and moths the principal nocturnal visitors. Nocturnal pollinators produce somewhat less fruit set than diurnal pollinators. Although insect pollination is predominant, wind pollination plays a minor role. White basswood is not self-compatible (1).
The fruits are nutlike, leathery or woody, ellipsoidal, about 13 mm (0.5 in) long, and covered with rust-brown, woolly hairs. The fruits are borne in clusters of six or seven on bracts. The bracts, which are shaped like long, slender leaves, may serve as wings for the purpose of wind dispersal or may function primarily as flags to attract nocturnal pollinators. The light-colored bracts are distinct against the dark foliage at night (1).
Seed Production and Dissemination- White basswood seeds ripen in September and October following pollination and are dispersed in the winter and spring. Little information exists on fruit set and seed dispersal of this species. In general, these events seem to differ little from those of American basswood (Tilia americana) (11).
As with most tree seeds, natural germination is best on mineral soil. No specific information is available for white basswood, but in general, basswood seeds may remain dormant for as long as 2 or 3 years (12).
Seedling Development- Little is known about the early growth of white basswood. Immediate sowing after early collection of American basswood fruits (when they first turn slightly brown) has been found to give good germination success. Germination is epigeal. Basswood seedlings are usually planted as 1-0 or 2-0 stock (12).
Vegetative Reproduction- White basswood sprouts vigorously and commonly grows in clumps of three to six or more stems. Although clump growth is good, the trees are frequently defective and susceptible to sleet and wind damage. Hence, stands of sprouts are less desirable than those of seedling origin (11).
Growth and Yield- Mature white basswood may exceed 27 rn (90 ft) in height and 91 cm (36 in) in d.b.h. Typically, the bole is free of branches, smooth, and cylindrical. The growth rate of basswood is intermediate compared with other southern Appalachian species; it grows faster than most of the oaks and maples, but considerably slower than yellow-poplar and northern red oak. Economic maturity for sawtimber is estimated to be a d.b.h. of between 43 and 61 cm (17 and 24 in), depending on the vigor class of the tree (11).
No volume or yield tables are available for white basswood. A standing inventory of basswood-including net annual growth, removals, and mortality-is available for five Southeastern States (table 1). Although white basswood is not distinguished from American basswood in this survey, the latter species grows only in the northern and westernmost portions of Virginia and North Carolina. White basswood grows in all five States.
|Location||Standing volume||net growth||Removals||Mortality|
¹Volume of stemwood from a 0.3 m (1 ft) stump to a 10 cm (4 in) diameter top, outside bark.
²Personal communication, Herbert A. Knight, resource analyst, Southeastern Forest Experiment Station, Asheville, NC.
Rooting Habit- White basswood roots have been found to have ectotrophic mycorrhizae; a fungus grows on the outside of the short root to form a mantle, and two rows of spherical cells are present in the cortex to form a Hartig net (8).
Reaction to Competition- Basswood is classed as shade tolerant, and variations between American basswood and white basswood are not noted (11).
Damaging Agents- White basswood is relatively free of serious diseases, although it is attacked by cankers, rots, stains, leaf spots, and wilt. Discolorations of the wood are common following wounding of any type, but they are not considered serious defects unless decay enters before the wound heals. Decay fungi attacking white basswood include species of Daedalea, Fomes, Hydnum, Pholiota, Pleurotus, Polyporus, Irpex, and Stereum. Basswoods of stem sprout origin or seedlings that have been wounded are likely to become highly defective; often the main bole of such trees will be almost entirely hollow (6,11).
Cankers caused by Nectria galligena are common on basswood but are not considered serious problems. Other stem diseases of minor importance are Nectria cinnabarina, Botryosphaeria ribis, and Strumella coryneoidea.
Leaf spots are common but do not cause excessive damage. The common leaf spots are caused by species of Cercospora, Phyllosticta, Gnomonia, Phlyctaena, and Asteroma. Wilt caused by species of Verticillium is known to occur in white basswood but so far has been of no consequence in forest stands (6,11).
White basswood is also comparatively free of serious insect enemies, but it is the host of many defoliators, several borers, aphids, and gall midges. Common defoliators include the basswood leafroller (Pantographa limata), elm spanworm (Ennomos subsignaria), linden looper (Erannis tiliaria), whitemarked tussock moth (Orgyia leucostigma), variable oakleaf caterpillar (Heterocampa manteo), basswood leafminer (Baliosus nervosus), bagworm (Thyridopteryx ephemeraeformis), and the Japanese beetle (Popillia japonica).
Important borers include the linden borer (Saperda vestita), Chrysobothris azurea, flatheaded sycamore-heartwood borer (Chalcophorella campestris), which enters the wood at wounds, Dicerca lurida, ambrosia beetles (Platypus compositus), and the twig girdler (Oncideres cingulata) (3).
Like those of yellow-poplar, the tender twigs and smaller branches of basswood are readily browsed by livestock and white-tailed deer.
Because of its thin bark, basswood is very susceptible to fire damage, especially at the seedling and sapling size. Consequently, butt rot is very common and a serious problem in burned stands.
Because of its soft texture, light weight, and dimensional stability, basswood lumber (including that of white basswood) is a choice wood. In addition to lumber uses, it is highly desirable for veneer, slack cooperage, excelsior, drawing boards, and particleboard; other values include bee pasture, yielding a fragrant honey, and shade and ornamental plantings (12).
Currently three species of Tilia in North America are recognized: T. americana, T. heterophylla, and T. caroliniana (9,10), although there are no known races or varieties within them. Recent studies of field specimens, field plots, and nursery plantings indicate that the variation in Tilia is essentially clinal. Pubescence and stellate hairs tend to be absent in the northwest portions of the ranges of basswoods but abundant in South Carolina (2). Flavonoid variation patterns indicate definite differences between northern and southern populations and show an intermediate zone in the southern Appalachians (7). These patterns suggest that there is only one species, Tilia americana L., in the range from Massachusetts to North Carolina. The population occupying the remaining southeastern portion of the range could be named T. americana var. heterophylla.
Hybrid swarms between white basswood and other species have been observed outside the glaciated area in southern Ohio (4). It has also been suggested that the absence of distinct morphological differences between species of basswood leads to inconstancy of insect pollinators and hence to hybridization (1).