Pinus halepensis (Aleppo pine)

P. halepensis is a very drought resistant tree and a prolific producer of serotinous, wind-dispersed seeds that retain their viability over long time periods. Disturbance events associated with fire have promoted the expansion of this species in countries such as Australia, New Zealand and South Africa. In the latter it causes a number of environmental and biodiversity problems, declared a category 2 invader according to the Conservation of Agricultural Resources Act, 1983 (Henderson, 2001). Binggeli (1999) classed P. halepensis as moderately invasive, and Rejmánek (1995) ranked it among the five most invasive pines.

P. halepensis (2n = 24) and P. brutia together form the subsection Halepenses in the section Pinus, subgenus Pinus (diploxylon or hard pines) of Pinus in the family Pinaceae.P. brutia was previously considered a subspecies or variety of P. halepensis by some authors, for example, by Gaussen et al. (1993) in their revision of Pinus in Europe. However, P. brutia is now almost universally accepted as a separate species (Price et al., 1998).

A two- (occasionally three-) needled, monoecious pine species, usually forming a slender single-stemmed tree up to 20 m tall, occasionally reaching 25 m tall, with deep roots. Bark is greyish, smooth at first, but finally fissured and exposing the reddish-brown or orange inner bark. Needles are pale green, usually 6-12 cm long, sometimes up to 15 cm, and less than 1 mm wide, borne on silvery-grey branches, usually abscising after the second year. Resin ducts are marginal with a leaf sheath 8 mm long. Cones are moderately to highly serotinous, conical, 5-12 cm long, turned downwards, grey to reddish-brown, usually opening in the third year. Apophysis on scales flat or raised, with conspicuous umbo, without mucro. Seeds dark brown, mottled, 6-7 mm long; wing 18-28 mm long.

Like most other Mediterranean pines, P. halepensis has been widely planted and its range otherwise manipulated by humans for many centuries, making it difficult or impossible to define precisely the true native range. Forests dominated by P. halepensis comprise about 10% of the shrubland/forest complex in the Mediterranean basin (Houérou, 1974). In conjunction with P. brutia, these two pines cover about 6.8 million ha in this region (Barbéro et al., 1998). There has been considerable debate in the literature on whether P. halepensis is native to Israel or whether occurrence there is entirely anthropogenic; with current consensus being that it has been a component of the vegetation in Israel throughout the Pleistocene, but that it was never a dominant species (Weinstein-Evron and Lev-Yadun, 1999).

It is difficult to separate natural from adventive distribution in many parts of its range and in the western part of the Mediterranean basin, P. halepensis has a large distribution assumed to be naturalized. For example, the area covered by P. halepensis in the Languedoc region of southern France increased three-fold between 1878 and 1904, and an additional 2.6 times between 1908 and 1978 as the species invaded abandoned lands (Acherar et al., 1984; Lepart and Debussche, 1992). This trend is evident in many other parts of its range, especially where large areas of agricultural land have been abandoned following the imposition of set-aside policies in the European Union (Barbéro et al., 1998). As P. halepensis is not a species of major commercial importance, no comprehensive data are available on the global extent of plantings for this species, although there are more details concerning Southern Africa and Australia. Where P. halepensis is planted outside its natural range it can exhibit weedy characteristics and in some areas it has become an important weed, and Richardson and Higgins (1998) review the phenomenon of pines as plant invaders in the southern hemisphere. In other areas, P. halepensis has failed to establish, for example, in the Pescadore Islands in the Taiwan Straits (Kao, 1983). It is also notable that P. halepensis is not widely naturalized or a weed problem in California, USA, despite widespread plantings throughout coastal regions of the state where it grows vigorously without irrigation in areas that receive 400-500 mm of rain per year (DM Richardson, University of Cape Town, South Africa, personal communication, 1999). However, one area of California where it is reported invasive is Catalina Island (Knapp, 2004).P. halepensis has been planted in all countries of southern Africa, where it was first introduced in the mid 1800s. Plantings and trials have been most extensive in South Africa, but the species is also grown in Angola, Botswana, Lesotho, Malawi, Mozambique, Namibia, Zambia and Zimbabwe (Poynton, 1979). P. halepensis is presumed to have been introduced in South Africa before 1830 (Shaughnessy, 1986). The first record of prolific natural regeneration and presumed spread of P. halepensis in the southern hemisphere is from the Caledon district of South Africa in 1855, some 25 years after it arrived in the country. Invasion of fynbos vegetation in South Africa often occurs after a fire (Trabaud, 1991).P. halepensis arrived in Australia in about 1850, and the main phase of planting, mainly in South Australia, was just before 1900. It has been planted fairly widely in the southern part of the continent, mainly in predominantly winter rainfall areas that receiving 450-750 mm per year. In South and Western Australia, it has invaded disturbed eucalypt forest, especially around Adelaide and on the Eyre Peninsula. P. halepensis appears on the noxious weed list for Australian states and territories, its use being controlled in parts of South Australia, and it is presently unassigned prior to assessment in Western Australia (Anon., 1998). In New Zealand, most invaded sites are extensively managed grasslands, but various semi-natural vegetation types are also invaded. In a study of fifteen alien forestry species in Argentina, Zalba (1995) found that P. halepensis showed the greatest expansion.

P. halepensis has shown recent expansion within its naturalized range in France and in several countries with Mediterranean climates where it has been introduced, such as South Africa, Argentina and Australia. Introduced to countries with climatic and environmental similarities to those locations that have recorded problems should be considered with care. However, in many countries P. halepensis is already widely introduced and it would therefore be prudent to monitor such locations for early signs of invasive behaviour.

The seeds of P. halepensis are winged and are wind-dispersed (Lepart and Debussche, 1991). Occasionally seeds may be carried several kilometers from the source but generally the dispersal distance is up to 20 m (Nathan et al., 2000). There is no evidence of biotic seed dispersal (Nathan et al., 2000). Long-distant dispersal is due to P. halepensis having been introduced intentionally to many countries and continents outside its native range.

Within the native range, P. halepensis is an early successional species that colonizes bare and/or disturbed ground, such as following cultivation (Lepart and Debussche, 1991). In Australia, it has invaded disturbed mallee (native eucalypt forest) at many localities in South Australia, especially around Adelaide and on the Eyre Peninsula. In Western Australia, it has spread into clear felled Eucalyptus marginata forest and disturbed ground. In New Zealand, most invaded sites are extensively managed grasslands, but various semi-natural vegetation types are also invaded. P. halepensis is a widespread invader of both fynbos and renosterveld vegetation types in the Cape Floristic Region of South Africa: (e.g. Rouget et al., 2001).

GeneticsP. halepensis is a diploid species with a chrosome number of 2n=24. Genetic variation in P. halepensis is considerable, and can be clearly observed in morphological features, such as trunk straightness, branch thickness and cone shape. Giordano (1960) studied provenances in Italy; differences exist between provenances from Israel, Morocco, Greece and Italy whilst Karschon (1961) established two altitudinal ecotypes in Israel. Morphological and biochemical studies of intraspecific genetic variation within the species have confirmed the existence of two main groups within the natural range of P. halepensis: East Mediterranean and West Mediterranean. The latter is subdivided into four subgroups: Eastern European subgroup (mainly in the Balkan peninsula); West European subgroup (Italy, France and Spain); West North-African subgroup (Morocco and West Algeria) and East North-African subgroup (East Algeria and Tunisia) (Schiller et al., 1986; Schiller and Grunwald, 1987). Different provenances of P. halepensis also display different levels of resistance to pests, and most of the devastating outbreaks of insect pests in Mediterranean Basin pine forests have occurred in planted, rather than natural, pine stands, where inappropriate provenances have been planted, for example, in Morocco (Questienne, 1979). Different provenances of P. halepensis also display different levels of resistance to frost and low water potentials (Schiller and Brunori, 1992) and the importance of careful site-provenance matching is now generally accepted.Physiology and PhenologyIt is a not a very long-lived pine, living for up to 150-200 years, though Lepart and Debussche (1991) report that P. halepensis lives until approximately the age of 100 years, but can bear cones at six years and produce viable seed from age 12.Reproductive BiologyP. halepensis reaches reproductive maturity at a relatively young age enabling it to cope with sites prone to fire. P. halepensis produces seed prolifically (Weber, 2003) and the time interval between seeding events is approximately two years (Moran et al., 2000). According to Moran et al. (2000) the seeds are stored in the canopy and are strongly serotinous. Seeds are able to germinate and establish in the immediate post-fire environment and it would appear that disturbance through fire promotes seedling establishment and invasion (Rouget et al., 2001). There is usually prolific seedling recruitment after fires, leading to dense, even-aged stands. However, seed release is not wholly dependent on fire as dry, hot conditions may also stimulate seed release, as occurs in Israel (Nathan et al., 2000). Lepart and Debussche (1991) note that P. halepensis is not able to recruit seedlings under its own canopy and in natural successions, tends to be replaced by other species such as the oaks Quercus ilex and Q. pubescens. Seeds remain viable for up to ten years (Dean et al., 1986).Environmental RequirementsP. halepensis is one of the most drought-tolerant of all pines and Rouget et al. (2001) consider that this may have contributed to its widespread invasion of semi-arid shrubland in South Africa. It also survives nutrient-poor soils, frost (provenance-specific) and salt spray, but is unable to withstand waterlogging. In warm, humid conditions, P. halepensis is susceptible to damage from hail storms and subsequent infection by Diploidia pinea. In parts of its adventive range, crowns of P. halepensis can be broken by heavy snowfalls.The distribution of P. halepensis in the Mediterranean basin follows the 1.5°C isotherm of mean minimum temperature for the coldest months of the year (Trabaud et al., 1985), with annual precipitation in the 300-900 mm range (Houérou, 1974). In the North African part of its range, Le Houérou (1981) argued that P. halepensis forests extended to the 200-150 mm isohyet at approximately 2500 BC, but that extensive deforestation in the 1800s resulted in the shrinkage of its range to areas with at least 300 mm annual rainfall. It grows from sea level to 1700 m (only in Morocco). Summer temperatures averaging 20-25°C accompanied by 3-month drought are typical in its current natural range. P. halepensis is generally considered to be very frost tolerant, surviving winter temperatures as low as -12°C (Calamassi et al., 1999), but this is dependent on microclimatic conditions.At drier sites within and at the edge of this range, Quercus suber often assumes dominance (Summers, 1939), whereas other pine species (P. pinaster, P. pinea, P. nigra) replace P. halepensis in more humid areas at high elevations. The climatic conditions in the range of P. halepensis are conducive to widespread wildfires; indeed the P. halepensis zone is one of the most flammable of all areas in the Mediterranean Basin. Although P. halepensis is best suited to Mediterranean areas with predominantly winter rainfall, it also grows well when planted outside its natural range in uniform- and summer-rainfall regions.In its natural range in the Mediterranean basin, P. halepensis generally grows on marls, limestone and dolomites, avoiding wet soils and compacted clay soils. In Israel, it grows on luvisols, tolerating terra rossa soils, but preferring brown and pale rendzinas. In South Africa, P. halepensis has proved very accommodating with respect to soils, but it grows best in the presence of lime. It grows well on clay-loams overlying dolerite or shale and, on the highveld, it succeeds on acid, sandy and skeletal soils derived from sandstones. In Australia, it also grows on a wide range of soils, from moderately heavy clays to rather poor sandy podsols, but it does best on sandy loams. For amenity plantings it is generally suitable for most soil types, except for tight clays. Plantations of P. halepensis in southeast Croatia appear to stop the degradation of the limestone soils (karsting) and to improve basic soil properties, resulting in improved regeneration of native trees and shrubs (Tomasevic, 1994) and similar results have been obtained in Bulgaria (Tilev, 1977). In some locations P. halepensis can experience deficiencies in phosphate (Doumas et al., 1983, 1984) and/or potassium (Mandouri, 1981; Doumas et al., 1986).AssociationsP. halepensis is often a dominant component of coniferous forests at lower altitudes in the Mediterranean basin and also occurs in maquis, various other scrub communities and on planted coastal dunes. It typically occurs above a layer of shrubs, such as Arbutus unedo, Erica arborea and Myrtus communis or Cistus species. In Australia, P. halepensis has invaded disturbed native eucalypt forest in South Australia and Eucalyptus marginata forest in Western Australia. Aleppo pine is a widespread invader of two types of vegetation in the Cape Floristic Region of South Africa: fynbos and renosterveld.The most common mycorrhizal fungi found to be associated with P. halepensis in different parts of its range are: Suillus, Rhizopogon and Cenococcum geophilum (Iberia, Spain; Diaz et al., 1996); Amanita spissa, Hebeloma edurum, Lactarius deliciosus, Pisolithus tinctorius, Suillus luteus and S. variegatus (Spain; Torres and Honrubia, 1994); Pisolithus tinctorius, Rhizopogon roseolus, and Suillus collinitus (south-east Spain; Roldan and Albaladejo, 1994); Suillus collinitus, S. granulatus, Rhizopogon roseolus, R. luteolus, Amanita muscaria and Lactarius deliciosus (Spain; Torres and Honrubia, 1991); Tuber melanosporum, T. brumale var. moschatum, T. aestivum, T. albidum and T. maculatum (Italy; Pirazzi and Gregorio, 1987).

Diseases

The foliar rust fungus, Coleosporium inulae, can cause damage in young P. halepensis plantations (Magnani, 1974).

The resin top or blister rust fungus, Cronartium flaccidum, attacks a number of pines in Europe including P. halepensis. This rust has a number of alternate hosts and causes top kill (Raddi and Fagnani, 1978; Moriondo et al., 1980; Luisi, 1983; Karadzic and Vujanovic, 1992).

The fungus Crumenulopsis sororia causes a stem canker on P. halepensis. This disease is favored by abnormally high rainfall. (Abgral and Soutrenon, 1991; Morelet, 1971, 1978).

P. halepensis is attacked by pitch canker, caused by the fungus Gibberella circinata. This fungus initially infects branch tips, causing needle wilt and tip death. Resinous cankers result from infection of the bole (trunk), limbs, cones, and roots (Dallara et al. 1995).

Decay fungi that attack P. halepensis include Phellinus pini, the cause of red ring rot (Sisto and Luis, 1991; Karadzic and Vujanovic, 1992; Arbouche et al., 1993) and
Phellinus torulosus, which causes a white decay (Perlini, 1997).

The fungus Sirococcus strobilinus causes bud death (Morelet, 1972; Munoz López, 1997).

Diplodia needle blight, caused by the fungus Sphaeropsis sapinea, infects P. halepensis. This fungus causes necrosis of top and lateral shoots and cankers characterized by resin exudation (Torres-Juan, 1971; Schiller, 1972; Capretti et al., 1987; Karadzic and Vujanovic, 1992; Diminic et al., 1993; Stiki et al., 1995; Diminic, 1994, 1996; Madar et al., 1996).

Thyriopsis halepensis is a needle infecting fungus of P. halepensis that can occasionally defoliate trees (Glavas, 1983).

Aleppo pine is also known to exhibit knot disease possibly caused by bacteria associated with Pissodes castaneus.

Insects

The scale insect, Leucaspis pusilla (Homoptera Diaspididae), is reported attacking P. halepensis in the Tuscany Region of Italy where it damages trees weakened by abiotic or biotic factors (Raspi and Antonelli, 1987). A related species, L. pini, has caused damage to P. halepensis in Argentina (Mallea et al., 1988).

The Israeli pine bast scale, Matsucoccus josephi (Homoptera: Margarodidae), is the most serious pest of Aleppo pine in Israel (Golan et al., 1983). Damage caused by this introduced insect has dramatically reduced the use of Aleppo pine in plantations in Israel resulting in the replacement of P. halepensis with P. brutia and P. pinea in many areas (O Boneh, Forestry Department KKL, Jewish National Fund, Zefat, Israel, personal communication, 1999).

Several species of bark beetles (Coleoptera: Scolytidae) attack P. halepensis. Hylurgus destruens is considered one of the most destructive pests of Mediterranean pine forests (Monleon et al., 1996). The Mediterranean pine beetle, Orthotomicus erosus, attack trees weakened by drought or other stress factors, throughout most of this tree's geographic range. This insect also attacks logging residues, freshly cut logs and windthrow (Halperin et al., 1982; Mendel and Halperin, 1982; Georgebits, 1974). Pityogenes calcaratus (Coleoptera: Scolytidae) confines its attacks to weakened trees (Halperin et al., 1982; Georgebits, 1974).

P. halepensis is one of a number of pine hosts of the pine processionary caterpillar, Thaumetopoea pityocampa (Lepidoptera: Pityocampidae). This insect is considered to be the most damaging defoliating insect of pines in the Mediterranean Region of Europe, the Near East and North Africa. Larvae construct tents and feed gregariously on the foliage. Heavy populations can strip trees of their foliage, resulting in growth loss and tree mortality. Damage is most severe in young plantations. The urticating hairs of the larvae can cause severe skin irritation in humans (Abgral and Soutrenon, 1991; Buxton, 1983).

Mites

The mite, Cenopalpus wainsteini (Acarina: Tenuipalipadae), is a pest of P. halepensis in northwestern Apulia, Italy, where adverse growing conditions on dry stony ground does not permit sufficient retention of water in the soil when the temperature is most favourable for growth (Macchia et al., 1983).

Mammals

In Israel porcupines, Hystrix indica, cause patchy but sometimes heavy, damage to Aleppo pine, especially on rocky sites with low vegetation cover (Izhaki and Ne'eman, 1996).

Abiotic Factors

P. halepensis is sensitive to elevated levels of ozone (Elvira et al., 1998). Typical ozone injury symptoms of chlorotic mottle and damage to mesophyll cells may lead to the death of young seedlings (Naveh et al., 1980). Ozone exposure (by inducing an increase in diffusive resistance) Anttonen et al., 1998) and moderate water shortage induce similar reductions in gas exchange rates. An antagonistic response modulated by the severity of water stress followed combined exposure to both ozone and water stress (Inclam et al., 1998). In combination, ozone and mild drought decrease the carbon-fixation capacity of P. halepensis, reducing the amount of carbon transferred to the roots, leading to reduced root growth. Thus, high levels of ozone during the summer months may impair the ability of P. halepensis to withstand severe water stress in its natural environment (Gerant et al., 1996).

In many areas within the geographic range of P. halepensis in the Mediterranean Basin, large-scale dieback in stands has been attributed to complex interactions between various factors, and is often the result of planting an inappropriate provenance (Capretti et al., 1987). In Israel, ozone damage predisposes Aleppo pine to attack by Matsucoccus josephi. The combined effect is progressive desiccation from the lower branches and finally death of the tree; this together with the increase of dry matter from bush encroachment increases the intensity of wildfires (Z. Naveh, Faculty of Agriculture Engineering, Technicon, Haifa, Israel, personal communication, 1999).

P. halepensis is a pine considered to have a high intensity fire regime. Forests dominated by this pine are considered one of the most flammable and fire prone vegetation types in the Mediterranean Basin. Average fire interval is about 30-50 years. This species has several adaptations to fire including prolific seed production, ability to produce serotinous cones and large trees develop a thick bark that enables them to tolerate low intensity wildfires or prescribed burns (Agree, 1998).

Among the fungal diseases known to affect P. halepensis, the following are probably the most widespread and damaging: Coleosporium inulae, a heteroecious foliar rust, can seriously damage P. halepensis in young plantations (Magnani, 1974); Cronartium flaccidum (blister rust) (Raddi and Fagnani, 1978; Moriondo et al., 1980; Luisi, 1983; Karadzic and Vujanovic, 1992); Crumenulopsis sororia, a canker, particularly following abnormally high rainfall years (Morelet, 1971, 1978); Gibberella fujikuroi var. subglutinans (conidial state = Fusarium subglutinans) or pitch canker (McCain et al., 1987); Phellinus pini (red ring rot) (Sisto and Luis, 1991; Karadzic and Vujanovic, 1992; Arbouche et al., 1993); Phellinus torulosus (white decay fungus) (Perlini, 1997); Sclerotium bataticola Taub. (Macrophomina phaseolina) (Madar and Reuveni, 1981); Sirococcus strobilinus (S. conigenus) causes bud death (Morelet, 1972; Munoz López, 1997); Sphaeropsis sapinea (Diplodia pinea) or Sphaeropsis canker/crown wilt (Torres-Juan, 1971; Schiller, 1972; Capretti et al., 1987; Karadzic and Vujanovic, 1992; Diminic et al., 1993; Stiki et al., 1995; Diminic, 1994, 1996; Madar et al., 1996); Thyriopsis halepensis (Glavas, 1983).

Among the insect pests of P. halepensis, the following (listed in alphabetical order) are probably the most widespread and/or damaging: Leucaspis pusilla (Homoptera Diaspididae) (Tuscany, Italy; damages trees already weakened by abiotic or biotic factors; Raspi and Antonelli, 1987). Another species, L. pini, has caused damage to P. halepensis in Argentina (Mallea et al., 1988). Matsucoccus josephi (Homoptera: Margarodidae) (Israeli pine bast scale); the most serious pest of P. halepensis in Israel (Golan et al., 1983). Damage caused by this introduced insect has dramatically reduced the use of P. halepensis in plantations in Israel resulting in the replacement of P. halepensis with P. brutia and P. pinea in many areas (O Boneh, Forestry Department KKL, Jewish National Fund, Zefat, Israel, personal communication, 1999); Monochamus galloprovincialis (Cerambycid) (Georgebits, 1974); Orthotomicus erosus (Halperin et al., 1982; Mendel and Halperin, 1982; Georgebits, 1974); Pityogenes calcaratus (Coleoptera: Scolytidae) (Halperin et al., 1982; Georgebits, 1974); Thaumetopoea pityocampa (Thaumetopoeidae; pine processionary caterpillar) (Tsankov et al., 1995; Papitto, 1995); Hylurgus destruens (Coleoptera: Scolytidae) is one of the most destructive pests of pine forests in the Mediterranean region (Monleon et al., 1996); Secondary pests include borers (Pissodes castaneus, Tomicus piniperda, Orthotomicus erosus and Monochamus galloprovincialis) that usually cause problems only after trees have been weakened by environmental stresses (for example, prolonged drought followed by very cold temperatures; Capretti et al., 1987). The mite Cenopalpus wainsteini is an important pest in north-western Apulia, Italy, where adverse growing conditions of the trees on dry stony ground can permit insufficient retention of water in the soil when the temperature was most favourable for growth (Macchia et al., 1983).

In Israel, porcupines (Hystrix indica) cause patchy but sometimes heavy damage to Aleppo pine, especially in rocky sites with low vegetation cover (Izhaki and Ne'eman, 1996).

Current ambient levels of ozone over much of the natural range of Aleppo pine exceed UN-ECE critical level guidelines for the protection of forest trees and this pine is sensitive to ozone (Elvira et al., 1998). Typical ozone injury symptoms of chlorotic mottle and damage to plicate mesophyll cells may lead to the death of young seedlings (Naveh et al., 1980). Ozone exposure (by inducing an increase in diffusive resistance; Anttonen et al., 1998) and moderate water shortage induce similar reductions in gas exchange rates. An antagonistic response modulated by the severity of water stress followed combined exposure to both ozone and water stress (Inclam et al., 1998). In combination, ozone and mild drought decrease the carbon-fixation capacity of P. halepensis, reducing the amount of carbon transferred to the roots, leading to reduced root growth. Thus, high levels of ozone during the summer months may impair the ability of P. halepensis to withstand severe water stress in its natural environment (Gerant et al., 1996).

Declines/Complex disorders

In many areas of the current range of Aleppo pine in the Mediterranean Basin, large-scale dieback in stands has been attributed to complex interactions between various factors, and is often the result of planting an inappropriate provenance (Capretti et al., 1987). In Israel, ozone damage predisposes Aleppo pine to attack by M. josephi. The combined effect is progressive desiccation from the lower branches and finally death of the tree; this together with the increase of dry matter from bush encroachment increases the intensity of wildfires (Z. Naveh, Faculty of Agriculture Engineering, Technicon, Haifa, Israel, personal communication, 1999).

The development of monospecific stands of P. halepensis affects nutrient and water cycling and reduces the level of light reaching the understorey vegetation (Weber, 2003). P. halepensis drops large amounts of leaf litter, presenting a further obstacle to native vegetation which tends to be outcompeted, with a consequent loss of floral diversity (Weber, 2003).

P. halepensis is not a species of major commercial importance, but it is a very important species in its native range, where its main uses are in agroforestry, soil conservation, erosion control, revegetation and land reclamation, and also for Throughout its native and introduced ranges, it has considerable value as an amenity and ornamental tree. It is very widely planted for restoration of degraded sites, especially within its large natural range. Its tolerance of poor, degraded or stony soils makes it very suitable for this purpose. P. pinaster is also used, but P. halepensis is preferred for drier sites, especially on calcareous soils. In parts of the Mediterranean basin, P. halepensis is planted to improve water infiltration rates on hill slopes, for example, on marl limestones near Lorca, south-eastern Spain (de Wit and Brouwer, 1998). P. halepensis is widely grown for a variety of amenity purposes, as windbreaks, shelter belts and shade trees. In the semi-arid parts of South Africa, it is used in community forestry projects (especially in the North Cape Province) to restore degraded areas, and in many temperate regions, P. halepensis is grown as an ornamental tree.It is not used for commercial forestry anywhere in the world, mainly because of its poor stem form and low-quality timber. P. halepensis yields a yellowish-brown, coarse-grained, resinous, moderately dense wood of poor quality which is sometimes used for rough constructional purposes, in low-grade joinery and boxes, as railway sleepers, telephone poles, mine props, also as a firewood and charcoal. Formerly, P. halepensis was often tapped for resin, especially in Portugal and Spain, but this is now only performed in some parts of Greece. The bark has been used in tanning leather.

Weber (2003) lists fire among the control approaches for P. halepensis but notes that this can lead to the release of large numbers of seeds. According to Lepart and Debussche (1991), P. halepensis can be eradicated if consecutive fire events occur within a twelve-year period. However, lack of disturbance also promotes the eventual reduction of P. halepensis as it is outcompeted by other species in such environments (Lepart and Debussche, 1991).Mechanical control methods suitable for P. halepensis include the removal of seedlings and juveniles by pulling and for mature trees, felling or ringbarking (Weber, 2003). Trees do not resprout if they are cut (Lepart and Debussche, 1991) and it is not usually necessary to apply herbicides to the cut stumps of felled P. halepensis (Weber, 2003).Moran et al. (2000) considered that a cone weevil currently being tested in South Africa for release as a biocontrol agent for P. pinaster might also act as an agent for P. halepensis, and the cecidomyid flies Caryphomyia pinicolana and Camistomyi pinicolana may also be potential agents. Research efforts focus on seed and cone feeding species for control of Pinus species in South Africa because of their importance to commercial stakeholders (Moran et al., 2000).

Aleppo pine has poor tree form for sawtimber production, especially when grown in closed stands when it tends to lean, resulting in eccentric piths and a high proportion of compression wood. Consequently, features other than those that determine timber quality are usually considered.Among the most importance features of Aleppo pine that influence where it is planted are its tolerance of drought (it is one of the most drought-tolerant of all pines), nutrient-poor soils, frost (provenance-specific) salt spray, and its inability to tolerate waterlogging. In warm, humid conditions Aleppo pine is susceptible to hail damage and subsequent infection by Diploidia pinea. In parts of its adventive range, crowns of P. halepensis can be broken by heavy snowfalls.Mainly within its natural range, the adaptations of Aleppo pine to deal with fire are a major consideration. Important features of Aleppo pine in this regard are its early attainment of reproductive maturity and the ability of seeds to germinate and establish in the immediate post-fire environment. There is usually prolific seedling recruitment after fires, leading to dense, even-aged stands, although measures to protect seedlings from browsing and grazing mammals are sometimes required. Partly because Aleppo pine shows a low degree of self-pruning compared to other pines, forests of this species are highly flammable. Where the risk of fire damage to forests, other crops and adjoining property is especially high, special measures are needed.

Plants are generally raised from seed in the nursery, though direct sowing is also successful in some areas. In Israel, good results have been obtained with spot sowing under shelter (Heth, 1982). In poor sites, good results are achieved with bare-root seedlings, or containerized 3- to 5-month-old greenhouse-grown seedlings (Heth, 1982). In hot and dry sites, suitable spacings for seedlings are 1.8-2 m, planting 1-3 plants in each hole and thinning after 6-8 years. Planting density has been reduced in some areas (for example, in Israel) as seedling quality and methods of site preparation and weed control have improved.Seed germination is rather protracted, but can be improved by stratifying the seed. Damping off caused by Pythium spp. is problematic in some in nurseries. Early weeding using glyphosate was essential for growing Aleppo pine seedlings in a nursery in Algeria (Chaba et al., 1994).Because of the bushy habitat of Aleppo pine, specimens grown in single-row shelter belts need plenty of growing space (approximately 9-10 m on each side of the row).The most common mycorrhizal fungi found to be associated with P. halepensis in different parts of its range are: Suillus, Rhizopogon and Cenococcum geophilum (Iberia, Spain; Diaz et al., 1996); Amanita spissa, Hebeloma edurum, Lactarius deliciosus, Pisolithus tinctorius, Suillus luteus and S. variegatus (Spain; Torres and Honrubia, 1994); Pisolithus tinctorius, Rhizopogon roseolus, and Suillus collinitus (south-east Spain; Roldan and Albaladejo, 1994); Suillus collinitus, S. granulatus, Rhizopogon roseolus, R. luteolus, Amanita muscaria and Lactarius deliciosus (Spain; Torres and Honrubia, 1991); Tuber melanosporum, T. brumale var. moschatum, T. aestivum, T. albidum and T. maculatum (Italy; Pirazzi and Gregorio, 1987)Mycorrhizal inoculation (together with the application of urban compost) improved survival and growth of P. halepensis seedlings in semiarid conditions in Spain (Seva et al., 1996), but another study in Spain showed that inoculation did not increase plant height and nutrient assimilation in 8 month-old seedlings (Roldan and Albaladejo, 1994). Effects of inoculation are generally more marked on poor soils (for example, sierozems), but weak or non-existent on richer soils (Kadik et al., 1978).There are records of negative impacts from competition with weeds on poor sites. Where woody species, including Quercus coccifera and Pistacia lentiscus, form the undergrowth in natural P. halepensis stands, spring and autumn applications of fenoprop can give moderate success (Seva et al., 1996).When Aleppo pine is planted for shade, it may be desirable to deliberately encourage side branch development by cutting out the leader at a height of 2.4-4.6 m when it is 3.2-5.1 cm in diameter. When single trees are grown in the open for shade, trees are often pruned to 3-4.5 m. In Israel, pruning of lower branches in 3- to 9-yr-old stands and stem injections of systemic insecticides are undertaken to limit damage from Matsucoccus josephi (Golan et al., 1983).A fundamental silvicultural consideration where Aleppo pine is planted in the Mediterranean basin is the selection of the most appropriate provenance for planting at the site.

Fire is the overriding factor in the management of P. halepensis stands in the Mediterranean basin. Fuel management, involving grazing, prescribed burning and chipping of thinning residues to reduce fire hazard, has become a central issue in these forests. In limestone areas, prescribed burning is problematic because of the extreme flammability of P. halepensis, Quercus ilex and Juniperus oxycedrus (Delabraze and Valette, 1983).Growth increments of P. halepensis have been assessed in several parts of the Mediterranean basin, ranging from 2.5 to 3.3 cubic metres/year (Ciancio et al., 1990; Mestrovic, 1997).

Genetic variation in P. halepensis is considerable, and can be clearly observed in morphological features, such as trunk straightness, branch thickness and cone shape. Giordano (1960) studied provenances in Italy; differences exist between provenances from Israel, Morocco, Greece and Italy whilst Karschon (1961) established two altitudinal ecotypes in Israel. Morphological and biochemical studies of intraspecific genetic variation within the species have confirmed the existence of two main groups within the natural range of Aleppo pine: East Mediterranean and West Mediterranean. The latter is subdivided into four subgroups: Eastern European subgroup (mainly in the Balkan peninsula); West European subgroup (Italy, France and Spain); West North-African subgroup (Morocco and West Algeria) and East North-African subgroup (East Algeria and Tunisia) (Schiller et al., 1986; Schiller and Grunwald, 1987).Different provenances of P. halepensis display different levels of resistance to pests, and most of the devastating outbreaks of insect pests in Mediterranean Basin pine forests have occurred in planted, rather than natural, pine stands, where inappropriate provenances have been planted, for example, in Morocco (Questienne, 1979). Different provenances of P. halepensis also display different levels of resistance to frost and low water potentials (Schiller and Brunori, 1992).The importance of careful site-provenance matching is now generally accepted.

The poor stem form and timber of P. halepensis disqualify it from being more widely used.Where P. halepensis is planted outside its natural range it can exhibit weedy characteristics and in some areas it has become an important weed. The first record of prolific natural regeneration and presumed spread of P. halepensis in the southern hemisphere is from the Caledon district of South Africa in 1855, some 25 years after it arrived in the country.P. halepensis is an important weed in Australia, New Zealand and South Africa. In Australia, it has invaded disturbed mallee (native eucalypt forest) at many localities in South Australia, especially around Adelaide and on the Eyre Peninsula. In Western Australia, it has spread into cut-over Eucalyptus marginata forest and disturbed ground. In New Zealand, most invaded sites are extensively managed grasslands, but various semi-natural vegetation types are also invaded. Aleppo pine is a widespread invader of two types of vegetation in the Cape Floristic Region of South Africa: fynbos and renosterveld. Richardson and Higgins (1998) review the phenomenon of pines as plant invaders in the southern hemisphere.It is notable that P. halepensis is not widely naturalized or a weed problem in California, USA, despite widespread plantings throughout coastal regions of the state where it grows vigorously without irrigation in areas that receive 400-500 mm of rain per year (DM Richardson, University of Cape Town, South Africa, personal communication, 1999).