The rooting ability of branch
cuttings was evaluated for 100 tree species (including 41 families and
78 genera) collected in a tropical rainforest in Sarawak, Malaysia. Leafy
cuttings of natural forest saplings were
planted in a non-mist propagation system with
IBA treatment. During the 6-month experiment, 66 species were rooted with
an overall mean rooting percentage of 37.7% (range 0¯100%). Species
in the families
Dipterocarpaceae and Lauraceae had a low rooting
ability, whereas those in Euphorbiaceae, Rubiaceae, and Annonaceae had
a high rooting ability. Differences in rooting ability were related to
species-specific mature
sizes, diameter growth rates and habitat preferences.
Species of smaller mature sizes and faster diameter growth rates showed
better rooting ability. Species whose forest saplings sprouted more vigorously
after
experimental felling rooted better than those
that showed less vigorous sprouting. Species whose habitats were on lower
elevations, concave slopes, and/or clay-rich soils rooted significantly
better than those that
preferred opposite habitats or habitat generalists
that showed no significant habitat preference. The implications of these
relations are discussed from the viewpoint of saplings' adaptation to physical
damage in their
natural habitats.
Indigenous species are replacing exotic fast-growing
species in the rehabilitation of degraded tropical rainforests. To properly
restore degraded ecosystems, particularly in the moist tropics, a remarkable
number of species
are required. For example, a tropical rainforest
in Sarawak, east Malaysia, contained over 1000 tree species within an area
of approximately 50 ha (Condit et al., 2000). Thus, it is important to
maintain a regular planting
stock of various indigenous tree species to restore
the diversity of tropical rainforests. However, the irregular flowering
and fruiting habits (i.e., "general flowering"; Appanah and Ashton) and
the recalcitrant nature of the
seeds of many species ( Tompsett, 1987) make
seed collection problematic in southeast Asian rainforests. Collection
of wildings have been used to supplement seedling stock, but mortality
is high without proper handling
(e.g., Palmiotto, 1993).
To overcome the unpredictable supply of seeds,
many studies have been conducted investigating the ability of cuttings
to propagate vegetatively, and successful rooting has recently been reported
for a considerable number
of southeast Asian rainforest species (reviewed
by Dick and Aminah, 1994). However, most of the species chosen are economically
important timber trees, including members of the Dipterocarpaceae, which
dominate the
forests. Little information is available regarding
the vegetative propagation of cuttings from species that are economically
less important. In order to successfully rehabilitate the diversity of
degraded forests, we need more
information on the rooting ability of non-timber
tree species, especially since the majority of species in tropical rainforests
are non-timber species.
The study selected 100 study species (41 families
and 78 genera) from the LTER plot. Voucher specimens of the species are
kept at the Forest Research Center of the Forest Department of Sarawak,
Kuching. Branches were collected from saplings of the study species (n=2¯10
per species; height 2¯6 m) under the closed canopy of the forest around
the LTER plot and transferred to the nursery (0.5¯1 km away from the
collecting sites) in sealed .plastic bags containing 0.2 l water. Branches
were collected in June¯July 1997, December 1997, and January 1998.
Ten leafy cuttings of 2¯4 nodes (length~15cm) were prepared for each
species. Two to four leaves
(depending on leaf size) were left attached to
each cutting, and all other leaves were removed. Large leaves were trimmed
to approximately 30 cm2 each. We adopted a non-misting cutting propagation
method: cutting
beds were constructed of cylindrical plastic
containers (50 cm in diameter and 25 cm deep) containing water-saturated
fine river sand and sealed with transparent plastic. The cutting beds were
kept under 50% natural
shade for 6 months. Cuttings of the same species
were planted in the same cutting bed, thus, there was no replication for
each species. Commercial rooting powder (Serbajadi Rooting Powder, Perniagaan
Serbajadi,
Malaysia; active ingredient IBA) was applied
to the base of each cutting. Preparation and planting of cuttings were
completed within 8 h from the time of branch collection. The cutting beds
were watered 1¯3 times during
the experiment when the sand appeared to be dry.
All cuttings were harvested after 6 months. The number and length of all
roots thicker than 1 mm at the base were measured on each cutting.
Of 100 study species, 66 successfully rooted during
the experiment from at least one cutting. Rooting percentage of rooting
species differed from 10 to 100%. Among the six families including >3 study
species,
Dipterocarpaceae and Lauraceae had smaller proportions
of rooting species: 5/16 and 1/4, respectively. In contrast, the majority
of the study species successfully rooted in Euphorbiaceae (16/17), Rubiaceae
(5/5) and
Annonaceae (5/7) (see Appendix A).
Mean root lengths were significantly different
between groups based on mature size (K), growth rate (r) and sprouting
ability (Table 1 and Table 2). Differences between cutting beds were also
significant within each
group, which suggests that between-species variance
was also large within the groups. Species groups with the smallest mature
size (K<20 cm), the fastest growth rate (r>0.02 peryear), and the most
vigorous sprouting
ability showed significantly longer mean root
lengths compared to the other groups, between which there were no significant
differences (Fig. 1 and Fig. 2).
The results suggest that the majority of species
in a mixed dipterocarp forest have the potential for vegetative propagation
from cuttings. We cannot conclude whether the observed proportion of rooting
species (66%) is
high or low compared to other tropical forests,
because no comparable studies have been conducted. However, the observed
rooting abilities are likely underestimates for most of the study species,
because the cuttings
were collected from suppressed forest saplings,
and successful rooting from cuttings is affected by the age and the nutrient
status of donor trees (Kantarli, 1993). Generally, rooting decreases with
the age of donor trees (
Smits et al., 1990). Cuttings collected from
donors in vigorous growing conditions root more successfully than cuttings
from those growing in poor conditions (e.g., under low light), which generally
have lower C:N ratios (
Kantarli and Veierskov). Most of the donor saplings
in this study had been growing in shaded conditions for at least 10 years
(A. Itoh, personal observation). The study results, therefore, should be
considered to be a
conservative estimate of the rooting ability
of these species. It is likely that more species would have rooted successfully
if we had taken cuttings from more vigorous donors. For example, cuttings
from Dryobalanops
aromatica, Shorea parvifolia, and Shorea macroptera
did not root in our experiment, but were reported to produce roots when
collected from young healthy seedlings grown under nursery conditions (e.g.,
Aminah; Smits;
Dick and Aminah). In addition, rooting percentage
could be improved in the species that successfully rooted during this experiment
by choosing more suitable donors. Therefore, vegetative propagation by
cuttings seems
highly viable for many mixed dipterocarp forest
species, especially for those that have small mature sizes.
This study showed that the majority of species
in a mixed dipterocarp forest in Sarawak have significant potential for
vegetative propagation by cuttings. Small and fast growing species showed
especially good rooting
ability. Planting stock for these species can
easily be produced from cuttings for restoration programs, even if seeds
are unavailable. However, many upper canopy and emergent species, including
dipterocarps, showed poor
rooting ability, suggesting that seedling production
from cuttings of these species may be difficult. Variations in rooting
ability were related to both phylogenetic and ecological factors. Thus,
knowledge of the ecological
characteristics of species, especially sprouting
ability, is useful for the preliminary selection of species for cutting
propagation.