Pinus patula (PROTA)
|Geographic coverage Africa|
|Geographic coverage World|
Pinus patula Schltdl. & Cham.
- Protologue: Linnaea 6: 354 (1831).
- Family: Pinaceae
- Chromosome number: 2n = 24
- Patula pine, Mexican weeping pine, spreading-leaved pine, jelecote pine (En).
- Pin argenté, pin patula (Fr).
- Pinho patula (Po).
- Msindano (Sw).
Origin and geographic distribution
Pinus patula is native to Mexico. In 1907 it was introduced into South Africa, where it is presently the most widely planted coniferous species and has become invasive in certain areas. Later it was introduced into many other African countries, and it has become the most important pine in East and southern Africa. It is also grown in Australia, New Zealand, Asia and South America.
The wood of young trees is mainly used to manufacture boxes, and that of older trees for light construction, light flooring, joinery, ceilings, panelling, shingles, furniture, cabinet work, fence posts, poles, food containers, pallets, mine props, veneer and plywood. In Madagascar the wood is highly appreciated for glued laminated timber for carpentry and furniture, after the knots have been removed. It is also suitable for hardboard, particle board and wood-wool. Pinus patula is an important source of pulpwood, e.g. for newsprint in South Africa. The wood is excellent fuelwood and is also used for the production of charcoal. Pinus patula is suitable for reclamation of gullies, as the thick mat of fallen branchlets and needles retards surface run-off, limiting the advance of soil erosion. It is also planted in windbreaks, as a shade tree and as an ornamental tree.
Production and international trade
Worldwide, the area planted with Pinus patula is approximately 1 million ha, with plantations in Central, East and southern Africa accounting for 95% of the planted area. Pinus patula is especially important in Kenya, Tanzania, Malawi, Zimbabwe, Madagascar and South Africa. In Kenya it accounts for about 25% of all forest plantations. In South Africa pines are grown on 54% of the total afforested area, with Pinus patula being the most popular species, covering an area of about 375,000 ha. Commercial plantations have also been established in Argentina, Colombia, Ecuador, Peru and Brazil. Exported products include round poles, pulp and paper.
The heartwood is pinkish to creamy white, and not clearly demarcated from the sapwood. The grain is straight, spiral or wavy, texture fine. Growth rings are distinct. The wood contains little resin, although numerous resin canals are present and prominent on the tangential surface. It has a faint odour.
The density of the wood is (330–)430–650 kg/m³ at 12% moisture content. Air-drying properties are good, with only slight twisting of some boards. In Uganda 25 mm thick boards take 2–3 weeks to air dry to 20% moisture content. The rates of shrinkage from green to oven dry are 1.8–4.8(–9.5)% radial and 5.2–11.2% tangential. The dried wood is moderately stable to stable in service.
At 12% moisture content, the modulus of rupture is 47–154 N/mm², modulus of elasticity 5100–12,800 N/mm², compression parallel to grain 25–57 N/mm², shear 4–12 N/mm², cleavage 9–21 N/mm, Janka side hardness 2350–2780 N, Janka end hardness 3360–3420 N and Chalais-Meudon side hardness 1.5–3.8.
The wood saws easily, but if fed too quickly a rough surface will result. It planes easily, but boring, mortising and turning properties are less favourable. It takes and holds nails well and glues easily. The wood is not durable. It is susceptible to attacks by fungi, pinhole, longhorn, Anobium and marine borers, and termites. The sapwood is not susceptible to Lyctus borers. Both heartwood and sapwood are easily impregnated with preservatives in open tank and pressure-vacuum systems.
The wood fibres are 2.0–4.9 mm long and 36–57 μm wide, with a cell wall thickness of 4.0–5.5 μm. The chemical composition of the oven-dry wood is: holocellulose 59–73%, α-cellulose 40–44% and lignin 26–29%. The solubility in cold water is 0.6–3.6%, in hot water 1.5–3.7%, in alcohol-benzene 0.6–3.2% and in 1% NaOH 10.1–14.4%. Pulping with the sulphate (kraft) process yields 43–52% screened pulp, with a kappa number of 21–61. Kraft pulps have moderate to good tensile and bursting strengths and good tearing strength. The tearing strength of the pulp was found to increase with the age of the trees used for pulping, whereas bursting and tensile strengths decreased.
- Evergreen, monoecious, medium-sized tree up to 30(–50) m tall, but in plantations often much smaller; bole branchless for up to 15 m, up to 120(–150) cm in diameter, usually straight and cylindrical; bark surface grey to dark brown, broken into longitudinal, irregular scales in the lower part of the bole, thin, papery and reddish brown higher up; crown pyramidal; branches horizontal or turned upwards at their tips.
- Leaves in bundles of (2–)3–4(–5), needle-shaped, 12–30 cm long, pendulous, bright to yellowish green.
- Male cone axillary, small, yellow-brown.
- Mature female cone in groups of 2–6, short-stalked, ovoid-conic, often curved, 4–12 cm × 2.5–4 cm, oblique at base, pale glossy grey or brown, persistent on the branches, with smooth scales with a minute prickle, 40–80(–125)-seeded.
- Seeds triangular, 3–5 mm long, with a wing 10–20 mm long, grey mottled with black.
- Seedling with hypogeal germination.
Other botanical information
Pinus is a large genus comprising over 110 species, almost all restricted to the northern hemisphere. Many Pinus species are cultivated outside their natural distribution area, in tropical, subtropical and temperate regions. In the tropics 2 species are more important than all others: Pinus caribaea Morelet in the lowland humid tropics and Pinus patula in the cooler highland tropics and subtropics.
Wood-anatomical description (IAWA softwood codes):
- Growth rings: (40: growth ring boundaries distinct); 41: growth ring boundaries indistinct or absent; 43: transition from earlywood to latewood gradual.
- Tracheids: 44: tracheid pitting in radial walls (predominantly) uniseriate (earlywood only); 54: latewood tracheids thin-walled (double wall thickness less than radial lumen diameter); 56: torus present (pits in earlywood tracheids only).
- Ray composition: 79: ray tracheids commonly present; 82: cell walls of ray tracheids dentate; 85: end walls of ray parenchyma cells smooth (unpitted); 87: horizontal walls of ray parenchyma cells smooth (unpitted).
- Cross-field pitting: 91: cross-field pits pinoid; 98: 1–3 pits per cross-field (earlywood only).
- Ray size: 103: average ray height medium (5–15 cells); (104: average ray height high (16–30 cells)); 107: ray width exclusively uniseriate.
- Intercellular canals: 109: axial intercellular (resin) canals present; 110: radial intercellular (resin) canals present; 117: epithelial cells thin-walled.
Growth and development
Pinus patula grows very fast. Under favourable conditions it may attain a height of 15 m after 8 years and 35 m after 30 years. In southern Africa female flowering starts when trees are 2–3 years old, and male flowering 1–2 years later. In southern Africa flowering of both male and female cones is in August–October, with usually a secondary flush of only female cones in January–May. In Kenya usually 2 flushes of both male and female flowering occur in April–May and in October–November, coinciding with the rainy seasons, but female flowering throughout the year has also been recorded. Studies in Zimbabwe showed that synchronization of pollen shedding and female receptivity was good at 1500 m altitude, whereas pollen shedding occurred progressively later at lower altitudes. Outcrossing is predominant, and pollination is mainly by wind. Female cones mature in 22–30 months. The production of viable seeds starts when trees are 5 years old, and is prolific in 8–10-year-old trees. Seed dispersal is usually by wind, but sometimes also by birds, rodents or people.
Pinus patula is grown at 1000–3300 m altitude, in areas with a mean annual temperature of 9–23°C, a mean maximum temperature of the warmest month of 15–29°C, a mean minimum temperature of the coldest month of 6–14°C, an average annual rainfall of (700–)1000–2200 mm, and a dry season of up to 4 months. It grows best at higher altitudes: above 1000 m at 18–30° latitude, and above 2000 m near the equator; several provenances tolerate severe frost. Cone production is best at a mean annual temperature of 13–16°C. Pinus patula has succeeded on a wide range of soils, but prefers well-drained, neutral to acid soils. It is highly susceptible to fire. Pinus patula is strongly light-demanding. It is an aggressive pioneer species that grows readily in forest gaps created by fire. In Zimbabwe, South Africa and Swaziland it is now considered a serious weed, invading forest margins, moist grassland and road cuttings.
Propagation and planting
Pinus patula is mainly propagated by seed. The 1000-seed weight is 6–11 g. Seeds are extracted by air or kiln drying of the cones, which open after 2–7 days. In Zimbabwe cones are sun-dried in open-sided sheds covered with plastic roofs, sometimes supplemented by kiln drying at a maximum temperature of 60°C. Seed can be stored for 5–10 years at 2–8°C and a moisture content of 6–10%. Germination starts 7–10 days after sowing, and germination of fresh or well-stored seed is normally over 85% in Zimbabwe and South Africa. Pre-treatment is not necessary, but germination may be improved by soaking in cold water for 1–8 days or in hydrogen peroxide for 1–4 days. The soil for sowing needs to be inoculated with mycorrhizae by adding some soil collected beneath mature pine trees. Seedlings are planted out when they are 4–12 months old and 10–30 cm tall. Wildlings may also be used as planting material. Normal spacings are 2.4–3 m × 2.4–3 m. Although natural regeneration is often abundant, direct sowing is usually not successful, probably because the root system of seedlings is not deep enough to survive the first dry season. Pinus patula should not be planted near crops because of its shallow root system.
Vegetative propagation by grafting or air-layering is possible, and clonal orchards have been established using these methods. The use of cuttings for clonal propagation is limited by rapid initiation of ontogenetic aging in the plants, typified by the early onset of reproductive maturity and resulting in variation in rooting, growth habit, flowering and leaf morphology. Protocols for in-vitro propagation have been developed.
Natural regeneration is often prolific, e.g. in Malawi, Zimbabwe, South Africa and Madagascar, but is not common in East Africa. Seeds germinate abundantly after a fire.
During the first year after planting out 2–3 weeding operations are required. The response of Pinus patula to fertilizers is site-specific. Pinus patula self-prunes poorly, so trees are pruned when 4–6 year old to a height up to 2.5 m, to reduce fire hazard and improve access (‘low pruning’). In pulpwood plantations no further pruning is done, although pruning up to a height of 6 m height has been recommended to reduce the risk of fire. For the production of sawn timber, dead as well as living branches up to a height of 7(–12) m are removed to produce knot-free timber (‘high pruning’).
Thinning depends on initial spacing, site quality and end product. For the production of sawlogs in Zimbabwe and South Africa, the final aim is a stand of over 400 trees/ha with a bole diameter of about 45 cm, which implies rotations of 25–35 years. In Zimbabwe plantations with a density of 1100 trees/ha (spacing 3 m × 3 m) may be thinned to 650 trees/ha after 6–8 years, and to 400 trees/ha after 12–15 years. In Madagascar heavy thinning is recommended to arrive at a final density of 200–250 trees/ha when the trees are 15 years old. For the production of pulpwood rotations of 15–25 years are normal, resulting in trees with a bole diameter of about 30 cm.
The density of the wood can be increased by planting trees at lower rather than higher altitudes and allowing trees to grow longer before harvest. In Tanzania the density at 12% moisture content was found to increase from 380 kg/m³ for 12-year-old trees to 510 kg/m³ for 30-year-old trees.
Diseases and pests
When planted in hot, humid conditions, Pinus patula is susceptible to infection by Sphaeropsis sapinea (synonym: Diplodia pinea) after hail damage. In South Africa Pinus patula is threatened by pitch canker caused by the fungus Fusarium circinatum, which was first recorded in the country in the 1990s. In nurseries damping off may occur, mainly caused by Fusarium, Pythium and Rhizoctonia spp. In Ethiopia Armillaria root rot is common. Pests include the grasshopper Mecostibus pinivora in Zimbabwe. Pinus patula is attacked by Cinara cronartii (black aphid), Hylastes angustatus (Hylastes beetle) and several defoliating insects.
In Madagascar trees are felled when the bole diameter is 60 cm.
Mean annual increments are 10–40 m³/ha, in southern Africa 18–28 m³/ha. In East Africa yields can be higher than in southern Africa due to the shorter dry season. The total yield (including thinnings) under favourable conditions may be 630–700 m³/ha.
Handling after harvest
To avoid blue stain, log ends must be treated with a preservative immediately after felling, and logs must be extracted and converted as soon as possible. Anti-stain dipping is highly recommended immediately after sawing.
Various provenance collections have been carried out in Mexico since 1947, and provenance and progeny trials have been started in many countries, including Kenya, Malawi and Zimbabwe. Plantations in East and southern Africa are believed to have originated from a very restricted source of germplasm.
Pinus patula is included in the IUCN Red list, but it is classified in the lower risk category, in which it is considered to be of least concern.
Pinus patula responds readily to genetic improvement for increased growth rate, stem form and branching. Advanced genetic improvement programmes have been established in Zimbabwe and South Africa. These programmes have focused on the form and size of stem, branches and crown, and have resulted in substantially increased timber yields. Hybrids of Pinus patula with Pinus oocarpa Schiede ex Schltdl., Pinus radiata D.Don and other Pinus spp. have been developed. Tree improvement programmes are also aimed at increased productivity, increased vigour through modification of root systems and leaf performance, and tolerance to biotic and abiotic stresses. Breeding for tree growth and form has led to lower incidence of reaction wood, wandering pith and knot associated defects. Biotechnological protocols have been developed for somatic embryogenesis, cryopreservation and RAPD molecular markers. More recently protocols for genetic engineering, including the genetic transformation of embryogenic tissue using biolistic and Agrobacterium-mediated systems, have been developed.
Pinus patula is and will remain an important source of timber and pulpwood in tropical Africa, especially in cooler highland regions. On hot, dry sites at lower altitudes Pinus kesiya Royle ex Gordon and Pinus oocarpa are better able to withstand drought stress, and on hot, humid sites Pinus caribaea and Pinus elliottii Engelm. will do better. The main problem associated with Pinus patula is its aggressiveness and weediness. Improvement of yield and quality of the wood is needed to meet growing timber demands. Research is needed to improve timber quality by decreasing lignin content and increasing cellulose content; this would make it easier to process the wood into pulp and paper products, and should improve durability, hardness and stability.
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Correct citation of this article
Nigro, S.A., 2008. Pinus patula Schltdl. & Cham. In: Louppe, D., Oteng-Amoako, A.A. & Brink, M. (Editors). PROTA (Plant Resources of Tropical Africa / Ressources végétales de l’Afrique tropicale), Wageningen, Netherlands. Accessed 8 July 2021.
- See the Prota4U database.