Combretum imberbe
Leadwood; Hardekool
This regal Leadwood stands beside the Machayi pan near the Nyandu sandveld, east of Punda Maria.
Note the high-branching growth form and the dull yellowish-green colour of the foliage in the image above.
Note, too, those fallen limbs lying on the ground. Older limbs low down on the tree are no longer major contributors to photosynthesis. They tend to accumulate toxins and slowly rot, staying in place for many years, and finally falling.
'Leadwood' is an excellent name for this tree. The wood of Combretum imberbe is among the heaviest of all Southern African trees, with a specific gravity of 1.2 for air-dried wood. A log thus immediately sinks in water.
The heartwood is exceptionally hard and durable, impervious to borer insects. Trunks of dead Leadwoods can stand for hundreds of years on the landscapes, memorials to lives long gone.
Teenager and grandparent!
The relatively young Leadwood standing on the plains south of Olifants contrasts with the ancient Leadwood on the right, beside the Timbavati river, with its extraordinarily robust trunk and greyish-green foliage. That pale grey bark is characteristic of Leadwoods.
Crocodile skin bark?
Note the distinctive 'blocky' bark of the Leadwood, somewhat reminiscent of crocodile skin. The vertical fissures are roughly parallel and block sizes are similar.
Colour may range from pale ash-grey to mid-grey. In many instances, the pale grey bark, greyish-green leaves and growth form of the tree enable identification from a distance.
New growth on young Leadwoods has a distinctive form. Successive leaf-bearing branchlets are decussate. They taper into sharp ends, and grow at roughly right angles to the branch.
Why does the young tree produce this growth form? These robust and pointed branchlets are designed to deter browsers from devouring young, valuable leaves before the canopy of the tree grows beyond the reach of herbivores. Survival tactics!
Leaves are opposite on the branch, simple, small (to about 60mm), elliptic to obovate and with a characteristically wavy margin. The fresh, pale green colour of the leaves in this image indicates that they are young, but the canopy of mature trees tends toward dull yellow-green to silvery-green.
The leaf apex may be obtuse or rounded, sometimes mucronate or sometime notched. The margin is entire
The term 'lepidote' applies to surfaces of mature leaves. The word refers to a fine coat of dead epidermis scales that may look like separate microscopic dots, but they often are contiguous or overlapping. It is these scales that can give foliage a silvery, grey-green appearance.
Inflorescences are slender spikes up to about 8cm long, normally in the axils of leaves, but also as terminal heads.
Flowers are small, yellowish, sessile and densely packed along the spike. They are sweetly scented. The ovary is inferior and enclosed in the receptacle.
Petals are tiny and the stamens are the prominent feature, being about 1.5 to 2 mm long. The entire inflorescence is shaped like a miniature bottlebrush!
Flowering is somewhat irregular between about November and March.
Same genus . . .
The large fruits at the top of the image are Combretum zeyheri, or the well-named Large-fruited Bushwillow.
On the lower left are the russet-coloured fruits of Combretum hereroense, or the Russet Bushwillow.
Combretum imberbe, or Leadwood, is by far the largest tree of these three species. Notably, its fruits are the smallest, shown at lower right. In the fruiting season, a healthy Leadwood will produce an extraordinarily large crop of fruit.
The curious mind might ask what evolutionary advantage has the Leadwood gained from having the smallest fruits of these three species. That enquiring mind might also ask how samaras, or nuts with wings, are dispersed. Somewhere in all the evidence might lie an answer to the question!
All fruits of the Combretum genus are samaras, mostly with four wings. Leadwood fruits are characteristically pale yellow, and about 1.5x1.5cm in size. These fruits are densely covered in minute silvery scales
The fruits will mature, dry out to light brown and fall to the ground by early winter, probably scattered as they fall by breezes or a passing storm.
A Leadwood in Bangu gorge, east of Olifants
This beautiful tree grows in fertile, moist soils in remote wilderness. The Bangu river does not flow for many months, but the tree will access underlying moisture year-round.
The tree is tall, but the trunk has not yet filled out, indicating rapid growth in a favourable environment.
In Kruger, Leadwoods are fairly common in alluvial soils and mixed woodland, and they occur in almost all soil types across the entire Kruger Park.
Leadwoods are exceptionally slow-growing and long-lived. Radiocarbon dating shows that some trees are over 1,000 years of age. Kruger Park provides a secure environment for these trees, allowing them to grow into full maturity, and many magnificent specimens can be spotted.
Beyond the Park's borders, however, Leadwoods are felled for a wide range of purposes. The heartwood is dark with feint, visible graining, and it takes a polish well. Used to make furniture, salad bowls, table tops, breadboards and a range of household items, this wood delivers a fine product.
The heartwood is dense, heavy and durable. Termites and boring insects cannot penetrate the heartwood. Leadwood fencing posts last for decades. Adding to reasons for Leadwood harvesting is the fact that the wood is superb as a fuel for long-lasting campfires, for cooking and warmth.
Intensity of harvesting tends to correlate with human densities, and increasing human populations across the Lowveld mean that densities of the species, across all trunk diameters, are in decline.
Fewer trees mean lower seed production and a reduced replenishment rate. For seeds that do germinate, and seedlings face additional threats in populated areas from agriculture, grazing animals and fire.
