Pinus patula Schiede & Deppe (Pinaceae)

Widely planted timber tree from the Mexican uplands. It is invading montane areas of Malawi and Hawaii. Its spread is facilitated by fire in grasslands and logging in natural forests. The tree's spread threatens some endemic.


Species characteristics

Life form, size and lifespan

Evergreen tree 20 to 30 m tall.

Taxonomy, variation and plasticity

Sometimes difficult to distinguish from forms of related species. Some morphological characters show marked clinal variation in Mexico.

Reproductive biology

Flowering may start when the tree is two years old. Female flowers usually appear a year later than male flowers and are respectively borne in the upper and lower parts of the canopy. In Hawaii and Malawi P. patula starts producing many cones after 6 to 8 years. In Africa seed set varies from 45 to 93 seeds per cone out of a potential 200 to 300, whereas a Mexican collection had only 22 seeds per cone. Cones take 22 months to reach maturity and may remain closed several years until they are scorched by fire. Then the wind-dispersed seeds (4 mm long with a 1 cm long wing, weight = < 0.1 mg) are released and have a high germination capacity (ca 85%). In tropical Africa it appears to set seed freely every year in upland areas between 1000 to 1700 m.

Resilience and resistance

Although easily killed by fire, P. patula is adapted to it as its serotinous cones release seeds after burning and seedling establishment is favoured by bare mineral soil. It possesses mycorrhizal associations and plantations in Malawi failed until they were brought into the country.

Environmental requirements and successional status

The tree requires deep acidic soils with a good moisture supply. In Mexico it often forms monotypic stands or is found in mixtures with other pine species.

Products and uses

Important timber, pulpwood and fuelwood in many parts of the world.


Status in native range

Range and abundance

Native to the highlands of Mexico where it has a restricted distribution (18 N to 24 N). It forms pure dense stands.

Climate

Warm temperate region where the rainfall varies between 1000 and 2000 mm mainly falling during the summer months. Occasional frosts occur.

Site requirements

The species occurs mainly on the eastern side of mountains at an altitude between 1650 and 3000 m. It is found in areas with deep well drained sandy loam.

Weediness

Not reported.

Pests and diseases

Seed set often prevented by rust fungus.


Status in invaded regions

History of introductions and intensity of invasions

It is grown in many parts of the world in large plantations. First introduced to Malawi in 1923 and to Mount Mulanje (16S, 35E) in 1946 when forestry trial plots were established. In the 1950s large-scale forestry plantings were undertaken. Originally P. patula was planted as a nurse crop for the native timber tree Widdringtonia cupressoides (L.) Endl. but the objective was never achieved. In Hawai'i it invades native shrubland in the Haleakala National Park.

Patterns of invasion and time-lag

P. patula is spreading in both grassland and native forest. Regeneration is greatest in the vicinity of plantations but isolated trees became established several km away from the plantations and within 10 years became foci for further spread. In natural forest the pine density tends to increase with logging intensity. The current fire regime is the main factor facilitating the spread of this fire-adapted tree in grasslands. However, it appears that the increased dead matter increases the intensity of fires which has resulted in the death of some pine stands. The impact of variation in fire cycles and intensity on the invasion have yet to be investigated.

Site and climate

The Mulanje Mountain consist of a series of plateau around 1800 m with peaks reaching 3000 m. Mt Mulanje rises abruptly from the surrounding plain (600-700 m) and is isolated from other central African mountains. P. patula is found in a number of plant communities between 1800 and 2400 m. On most of the mountain rainfall is seasonal (mainly summer) and is around 2000-3000 mm per annum on the plateau where night frosts regularly occur. Soils (ferallitic latosols) are acidic (pH ca 4.2)

Floristic region and vegetation types

These mountains are covered by a variety of vegetation types varying with altitude, including forests and grasslands, containing a number of endemic species and invaded by several introduced species. The plateau vegetation is grassland, maintained by fire, and interspersed with forest in sheltered hollows and ravines. Lower elevation vegetation types, but particularly forests, are much destroyed and threatened by human activities.

Pests and diseases

The species is generally considered free of pests and diseases by foresters although lepidoptera do pose a threat in some regions.

Impact on ecosystem

There are indications that P. patula alters the species composition of invaded forest and grasslands and it appears to exclude some uncommon endemic ground flora species. It displaces W. cupressoides, Malawi's national tree, which although not endemic to Mulanje, only reaches its full height (ca 40 m) there. An important component of the shrub layer under P. patula is the invasive Rubus ellipticus.

Impact on humans and related activities

P. patula timber is worth twenty times less than that of W. cupressoides.

Control

Trees are cut near the ground and the slash is stacked in piles. Follow-up operations, preferably burning, are essential within a year or two to eliminate seedlings. The eradication of P. patula from Mt Mulanje has been recommended. Apart from control measures carried out by I. Sakai, a Japanese volunteer, and controlled yearly fires are lighted around the perimeter of the pine plantations killing young seedlings, the recommendations have not been implemented.


Ecological differences

Existence of ecological equivalent species and competitive interactions in invaded regions

There are no native pine species in Malawi. In the absence of P. patula and the native W. cupressoides would spread into the secondary scrub and occasionally into short grassland. Although highly susceptible to fire, W. cupressoides can become dominant if sufficiently fierce periodic fires occur to kill broadleaved trees. However, W. cupressoides is much slower growing than P. patula and in the presence of the latter succession will result in a P. patula dominated canopy. W. cupressoides competitive ability has been further diminished as it has recently suffered from the introduction of the cypress aphid, Cinara cupressi, resulting in the poor health or death of many trees.

Differences in status and ecology between invaded and native ranges

No apparent differences in site requirements or ecology between native and invaded regions exist. In its native range P. patula often compete with other pine species and seed set is affected by fungus.


Selected references

* Bone, R. (1995) The effects of Pinus patula invasion in the indigenous and grasslands of Mount Mulanje, southern Malawi. B.Sc. Thesis, University of Aberdeen.
* Chapman, J.D. (1994) Notes on Mulanje cedar - Malawi's national tree. Commonw. For. Rev. 74, 235-242.
* Chapman, J.D. (1994) Mt. Mulanje, Malawi. In Davis, S.D., Heywood, V.H. & Hamilton, A.C. (Eds) Centres of plant diversity, a guide and strategy for their conservation. Vol. 1. Europe, Africa, south-west Asia and the Middle East, pp. 240-247. IUCN & WWF, Gland.
* Edwards, I. (1982) Plant invaders on Mulanje Mountain. Nyala 8, 89-94.
* Sakai, I. (1989) The problem of Pinus patula on Mulanje Mountain, its threat, and proposed measures for eradication. Forest Res. Inst. Malawi Rep. No. 89006.
* Verboom, G.A. (1992) A report on the invasive status of Pinus patula on Mount Mulanje, Malawi. B.Sc. Thesis, University of Cape Town.
#* Wormald, T.J. (1975) Pinus patula. Tropical Forestry Papers No. 7. Dept of Forestry, Oxford.

Pierre Binggeli

May 1997