Environmental Engineering Reference
In-Depth Information
are light (1,70,000 seeds/oz). As the capsules break open on the trees throughout the winter and into
the spring, wind dissemination occurs easily (Bonner and Burton 1974). Seed surface architecture
and RAPD markers have been employed to profile and differentiate
P. fortunei
,
P. tomentosa
, and
their hybrid. The surface patterns of winged seeds were examined by scanning electron microscopy.
The patterns of reticulation on the wings and seed coat of
P. fortunei
and the hybrid were found to be
comparable while that on
P. tomentosa
was different (Kumar et al. 1999).
27.3.1.3 seedling development
The seeds of the genus Paulownia germinate quickly and grow rapidly when conditions are favorable
(Figure 27.1j). Seed germination is epigeal. Laboratory studies have found that light is required for
germination (Bonner and Burton 1974). Cold storage (stratification) reduces the light requirement
(Tang et al. 1980).
P
.
tomentosa
needs bare soil, sufficient moisture, and direct sunlight for good
seedling establishment. Seedlings are very intolerant to shade.
27.3.1.4 vegetative reproduction
Paulownia roots sprout easily. In fact, lateral root cuttings of 1-year-old seedlings can be used for
propagation directly in the field (Tang et al. 1980).
27.3.2
p
lant
p
roduction
27.3.2.1 root cuttings
The propagation of Paulownia is simple and easy; for example, the root, stem, shoot or seed can
all be used for propagation with facile methods. Current practice for large-scale production of
Paulownia planting stocks is to use the roots of 1- to 2-year old Paulownia seedlings for rooted
cutting development. With the combination of advanced propagation techniques and the intensive
management in the nursery, a 1-year-old Paulownia tree could have the height of 4 m and root collar
diameter of 6 cm.
27.3.2.2 Propagation by seeds
Seedling and plant development using seed is simple and straightforward. The seeds should be
collected from the selected desired pest-free trees that grow well and have not been damaged by
artificial hybridization of parent trees. Seed treatment for stimulating the germination is needed
by soaking seeds in water until they are fully imbibed. Soaking seeds for 15 min in water (40°C)
results in good germination. Maintaining the moisture of seedlings by watering the beds regularly,
timely weeding, and thinning are needed. When seedlings grow to 5-10 cm high, they should
be transplanted into the nursery field for better development. The related management techniques
for seedling development in the field are similar to those for the plants developed through rooted
cuttings.
27.3.3 p
hySical
p
ropErtiES
of
p
aulownia
w
ood
The wood of Paulownia
is strong but light and does not crack or split when nails or screws are used.
It is very stable dimensionally and is not subjected to warping, cupping, or splitting, even when
exposed to an outdoor environment (http://www.worldpaulownia.com/html/tech.html). Paulownia
wood is lightweight, 17-21 lb/ft
3
as compared with the Appalachian Red Oak of 39-41 lb/ft
3
.
Paulownia wood takes 30-60 days for air-drying, whereas kiln-drying takes 36-60 h depending on
dry kiln configuration, horsepower, and dimension of lumber. The wood is resistant to decay and
rotting if it is not in permanent contact with the ground.
Paulownia
species vary in porosity ranging
from 75 to 88% in comparison to poplar with 70-72%. The density of Paulownia wood, at 10%
moisture content, ranges from 17.8 to 23.2 depending on the species and growing conditions. The
