Mycorrhizal fungi of exotic forest plantations Peitsa Mikola Department of Silviculture University of Helsinki Introduction South Africa 0.92 mill. ha, and Chile 0.35 mill. ha. In all these countries the main It is a well-known fact that Suillus grevillei species of plantations are pines (mainly Pinus (Boletus elegans) is to be found growing radiata of California, P. elliottii of Florida, under larch (Larix spp.) and nowhere else. and P. patula of Mexico), although the In late summer, sporophores of Suillus grevil­ indigenous floras of these areas include no lei are almost invariably found in all larch species belonging to the Pinaceae family. forests and plantations, and even under soli­ Australian eucalypts (Eucalyptus spp.) which tary trees. The great mycologist Elias Fries have ectotrophic mycorrhizae are also exten­ already wrote: " Ubi Larix, ibi Boletus sively grown outside their natural range, in elegans". Africa, Asia, and South America. Larch is an exotic tree species in Finland. The aim of this article is to review the Consequently, Suillus grevillei cannot belong fungal flora of exotic forest plantations and to the native Finnish flora but must have to discuss the possible modes of immigration 1 arrived there with or after its hosts, Larix of exotic mycorrhizal fungi. ) spp. The same applies to some other mycor­ rhizal fungi of larch, such as Boletinus asiati­ Mycorrhizal fungi of exotic plantations cus, B. cavipes, and Tricholoma psammopus, Local lists of fungi fruiting in exotic coni­ as well as to all the other areas where Larix ferous plantations have been published by spp. are grown as exotics. Likewise, mycor­ Birch (1937) and Rawlings (1950) for New rhizal fungi of other forest trees have followed Zealand, Purnell ( 195 7) for Victoria ( Aust­ along with their host species when these have ralia), Spegazzini (see references in Singer been cultivated outside their natural range. 1950) for South America, and others. Some Exotic forest trees are today grown exten­ data from these lists, supplemented with sively in many parts of the world, particularly personal communications and my own field in the tropics and subtropics. Systematic observations, are summarized in Table 1. In trials with exotic species have been conducted addition to the fungi listed, a great number since the last century (see Streets 1962) , and of species of Cortinarius, lnocybe, Lactarius, large-scale afforestations were started in some Russula, Tricho.Zoma, and other genera have countries, such as New Zealand and Chile, been described from exotic plantations (Sin­ as long ago as 1920's. According to the FAO ger 1950, and others). The fungal flora of Secretariat (1967 ), there are today some 80 million hectares of forest plantations in the 1) The review is based partly on ~he literature, world, a great many consisting of exotic partly on personal observations .and discussioil!S species. New Zealand, for instance, has 0.46 during a s·tudy tour round tihe world in 1967. mill. ha of plantations, Australia 0.3 mill. ha, The tour was sponsored by FAO.· 169 such plantations may also include indigenous Suillus variegatus is apparently quite a dif­ species. Anderson ( 1966), for instance, found ferent type and is not adaptable to warm numerous European mycorrhizal fungi in climates. Although S. luteus and S. varie­ Eucalyptus plantations in Italy. The majority gatus are equally common in the boreal pine of fungi, however, are usually exotic and, forests, the latter species can hardly be found thus, the fungal population of exotic planta­ anywhere outside its natural range.1 tions differs greatly from that of the indige­ Amanita is another mycorrhizal genus, nous forests in the same area. several species of which have spread with The most conspicuous and widely distrib­ exotic plantations. The most conspicuous uted mycorrhizal fungi of exotic coniferous species, A . muscaria, which forms mycorrhizae plantations are several species of Suillus, S. with both conifers and broad-leaved trees is grevillei being a typical example. Singer today common in New Zealand, Austraha, (1964) lists five species of Suillus for South South Africa, South America and elsewhere. America, and McNabb (1968 ) se en species It seems to avoid the most tropical elimates, for New Zealand, all of which have been however, and is unknown in East Africa introduced with exotic conifers. No species whereas it already grows in Rhodesia (I. A: of Suillus belong to the native flora of the S. Gibson, personal communication). Accord­ southern hemisphere. ing to field observations, it can probably form mycorrhizae with some indigenous trees too Suillus granulatus has been desribed at least with Nothofagus spp. in South almost wherever any species of Pinus has Arne~ rica and New Zealand, just as some indi­ been planted. It seems to be quite an adapt­ genous fungi may be able to form mycorrhi­ able species, growing in both cool boreal zae with introduced trees. forests and subtropical plantations. In regard Several Gasteromycetes (spp. of Rhizopo­ to soil pH, too, it has a wide range; it is gon, Scleroderma, and Pisolithus ) are also indigenous, for instance, in the Pinus hale­ common mycorrhizal associates of exotic pen.~is forests on limestone rocks of the l.Vfediterranean area and grows as an exotic forest plantations. The frequent occurrence under the same species on alkaline soils in of sprorophores of Rhizopogon in pine the La Pampa Province of Argentina. This nurseries was observed quite early (Kessell is somewhat surprising, because, according 1927 ), and in plantations they are often to pure culture experiments (Melin 1925, found as soon as one or two years after plant­ Modess 1941 ), the optimum pH of Suillus ing. Some species of Scleroderma are known granulatus is between 5 and 6 and it does or suspected to be mycorrhizal with eucalypts, not grow at all at a pH above 7.5. Probably sporophores being common under exotic Suillus granulatus is a collective species, eucalypt plantations (Pryor 1956; Levisohn including several subspecies or even separate 1958; Bakshi 1966 ) ; nevertheless, the fungi species with different ecological requirements. may also be indigenous in the area. Pisolithus Reichert ( 1940), for instance, has described tinctorius has been described as an indige­ four closely related species in Israel, none of nous mycorrhizal fungus of eucalypts in which is probably the true Suillus granulatus. Australia (Smith & Pope 1934) and grow­ One of these basophilous Mediterranean ing as an exotic under eucalypt plantations species, S. bellini, grows as an exotic in Cape in both Israel (Reichert & Avizohar-Her­ Province of South Africa (Stephens & Kidd shenzon 1959 ) and South Africa (Stephens 1953a). & Kidd 1953 b ), whereas, according to other Suillus luteus is another widely distributed sources, it is also indigenous in North Ame­ mycorrhizal associate of exotic pine plan­ rica (Schramm 1966), where it forms tations. Although it is the dominant species mycorrhizae with pines and has been intro­ under pine plantations in the East African duced into pine plantations of South Ame­ Highlands (Gibson 1963), for instance, it rica (van Suchtelen 1962 ). seems to avoid very warm climates. Thus, As a whole, exotic tree plantations have according to Singer ( 1963), S. luteus is the greatly enriched the fungal flora of many most common species under pines in south­ 1) According to a recent personal communica­ ern Chile and Argentina, whereas in the tion from Dr. E. Horak, Suillus variegatus is found warmer area of North Argentina it is under pine plantations in the South Island of replaced by S. granulatus. New Zealand. 170 tropical and subtropical countries. Thus, in South Africa, Australia, New Zealand, and South America there are no indigenous South America as long as two or three hun­ species of Amanita, Cantharellus, Hygro­ dred years ago. When, for instance, Dutch phorus or Gomphidius, there is one indige­ settlers planted European oaks around their nous species of Lactarius, and Tricholoma farms in South Africa, they could later ob­ only occurs in the extreme south (Singer serve the deadly poisonous death-cap ( Ama­ 1950). Today all these genera are represent­ nita phalloides) fruiting under these trees. ed by numerous species growing in asso­ Mycorrhizal fungi may also have arrived ciation with introduced trees, Gomphidius, through botanical gardens. The first spe­ for instance, by three North American cimens of many European and North Ame­ species (Singer 1964). rican trees were imported to botanical gar­ Not all the exotic fungi of forest plan­ dens as potted plants. Pinus radiata, for tations are necessarily mycorrhizal. Sapro­ instance, was first introduced into Australia phytic fungi, which in nature grow on such in 1857, when potted seedlings were brought substrates as pine needle litter, may have from Kew Gardens to the botanical gardens found a favourable environment under exot­ of Sydney and Melbourne (Fielding 195 7). ic pine plantations, too, and become natural­ Kew Gardens, in particular, has provided ized. botanical gardens throughout the British Introduced mycorrhizal fungi may some­ Commonwealth with exotic plants. times be of a considerable economic impor­ Likewise commercial nurseries, to which tance, improving the economy of exotic some living plants were also imported, were plantations. Many of the most common intro­ founded quite early, - in South Africa, for duced species, such as Boletus edulis, Suillus instance, in the seventeenth century (Donald