BOTANICAL AND ECOLOGICAL CHARACTERISTICS
SPECIES: Tilia americana | Basswood 



GENERAL BOTANICAL CHARACTERISTICS : 
Basswood is a native deciduous tree.  Mature heights range from 75 to
130 feet (23-40 m) with diameter ranges from 36 to 48 inches (91-122 cm)
[16].  The bark of mature trees is up to 1 inch (2.54 cm) thick at the
base of the trunk [2,15].  The bark is furrowed into narrow,
flat-topped, firm ridges with characteristic horizontal cracks; young
trees have smooth, thin bark [15].  The inflorescence is a drooping
axillary cyme.  The fruit is dry, hard, indehiscent, subglobose to
short-oblong, and is usually 0.2 to 0.28 inch (5-7 mm) in diameter, and
bears one or two seeds [29].

The root system of basswood is composed largely of lateral roots; it
does not usually form a taproot [16].  Basswood root depths are usually
shallow relative to associated species root depths.  In prairie soils
bur oak (Quercus macrocarpa), shellbark hickory (Carya lacinosa), and
northern red oak all have deeper roots than does basswood.  Maximum root
depth in basswood averages 1.2 feet (36.5 cm) the first year, and 5 to 6
feet (1.5-1.8 m) by the third year; roots are not well developed below
approximately 2 feet (61 cm) [73].  On prairie soils the deepest roots
of a 28-year-old basswood were 27 feet (8.2 m) but most of the roots
were in the top 4 to 5 feet (1.2-1.5 m) of soil [74].  Adventitious
roots will develop as the stem is buried, as occurs on the sand dunes
near southern Lake Michigan [16].

The tree crown is usually broad and rounded, but in close stands is more
columnar.  The branches are small, weak, and often pendulous [2].

Maximum longevity is approximately 200 years [16].


RAUNKIAER LIFE FORM : 
   Phanerophyte


REGENERATION PROCESSES : 
The youngest recorded age at which basswood first reproduces is 15 years
[48].  Basswood flowers are insect pollinated, mostly by bees and flies
[16].  Basswood produces good quantities of seed at 1- to 3-year
intervals [16,30].  The relatively heavy fruits are not usually carried
long distances by the wind [42,52].  Seeds can remain dormant for up to
3 years [42].  This deep dormancy is thought to be caused by an
impermeable seedcoat, dormant embryo, and tough pericarp.  Acid
scarification and cold stratification enhance seed germination on
mineral soil [16,42,58], but few seeds actually germinate under normal
conditions [16].

Shade enhances establishment and initial survival, but heavy shade
limits subsequent growth and development [16].  Seedlings can establish
in as little as 25 percent of full sunlight [55].  The higher soil
temperatures in forest openings are better suited for good seedling
growth [16], but seedlings are sensitive to soil nutrient deficiencies
which may render them less tolerant to shade than older trees [69].
However, dense reproduction is only obtained under partial canopies [42].

Most basswood reproduction originates as stump sprouts.  Almost all
basswood trees 4 inches (10 cm) or less d.b.h. will sprout from the
stump, and more than 50 percent of sawlog-size trees will sprout as well
[16].  Sprouts have been obtained from basswood trees over 100 years
old; 57 percent of trees 20 inches [50.8 cm] or more in diameter
sprouted [46].


SITE CHARACTERISTICS : 
Basswood is characteristically found in rich uplands on mid-slopes in
mixed deciduous forests.  It is sometimes found in swamps [71].
Basswood is generally confined to sandy loams, loams, or silt loams, and
achieves its best growth on the finer textured soils.  Best growth is on
mesic sites, but basswood will also grow on coarse soils that are well
drained.  In Wisconsin basswood exibits a bimodal distribution with
respect to moisture; it achieves peak importance values on wet-mesic
sites and on dry-mesic sites, but is outcompeted by sugar maple on mesic
sites [17]. In southern Wisconsin, maple-basswood forests are largely
restricted to northern exposures [2].  Basswood is moderately tolerant
of flooding; it occurs on floodplain sites that have probabilities of
annual flooding between 50 and 100 percent [54].  Acceptable soil pH
ranges from 4.5 to 7.5, though basswood occurs most often on less acidic
to slightly basic soils.  Because basswood is nitrogen demanding it
grows poorly on nitrogen deficient soils [16].

At the western limits of its range, basswood usually grows on the
eastern side of lakes and along major drainages where it is naturally
protected from fire.  Basswood is commonly found in ravines and
protected, moist sites at the prairie-woodlands interface in Nebraska
[2].  In North Dakota and Minnesota basswood achieves its highest
densities on intermediate slopes; it is found in lower numbers on both
the drier uplands and the wet bottomlands [72].  According to Crow [16],
basswood's distribution is more closely associated with edaphic and
moisture conditions than with fire.

The maximum elevation at which basswood is found is 4,930 feet (1500 m)
in the southern Appalachian Mountains [22].


SUCCESSIONAL STATUS : 
Facultative Seral Species

Basswood is moderately tolerant of shade.  It achieves its highest
densities in sugar maple-basswood stands that are late successional to
climax forests.  Sugar maple-basswood can eventually replace oak-hickory
on favorable upland sites in the upper Midwest.  Succession of
oak-hickory to sugar maple-basswood can be accelerated where harvesting
or other disturbance releases the tolerant understory species [40].
Braun [9] classified basswood as a member of the regional climax forest
in Ohio that also contains American beech (Fagus grandifolia), ash
(Fraxinus spp.), sugar maple, and yellow-poplar (Liriodendron
tulipifera).  In eastern Nebraska northern red oak and basswood are
described as climax dominants at the western limits of the forest [2].
In New York basswood is a subclimax species, where it may increase in
importance after heavy logging [6].  In Minnesota sugar maple-basswood
communities are climax on fine mineral soils.  In Itasca State Park,
Minnesota, succession from prairie to white pine (Pinus strobus)-bur oak
to sugar maple-basswood is explained by fire exclusion and/or increased
moisture.  The authors concluded available evidence supports the climate
model better than the fire exclusion model [10].

The persistance of the moderately shade tolerant basswood in stands
containing highly shade tolerant sugar maple is dependent on their
differing modes of reproduction.  Sugar maple produces large numbers of
seedlings which are positively correlated with the occurrence of
basswood in the canopy [27].  Stump sprouting allows basswood to
maintain itself in a stand with the more shade-tolerant sugar maple;
basswood stump sprouts can reach canopy size faster than the more
numerous maple seedlings [16,27,71].

Patchy or large scale disturbance may favor basswood because of its
sprouting ability and presence in the understory.  Basswood increased in
relative importance value after a tornado caused severe damage to a
sugar maple-Ohio buckeye (Aesculus glabra) stand in Indiana.  The source
of the increase was not specified by the authors; it may have come from
stump sprouts and/or released individuals, coupled with the loss of
other species [51].


SEASONAL DEVELOPMENT : 
Basswood usually flowers in June, but flowering dates range from late
May to early July [16].  Flowering occurs from 1 to 4 weeks after spring
leaf-out [1,16].  In Minnesota, bud swell occurs in from late April to
early May, and leafing out occurs from early to mid-May.  Seeds are
dispersed in October, and leaf fall occurs from September to October [1].

Related categories for Species: Tilia americana | Basswood