Discussion
Distribution and Hosts
Unlike most species of Arceuthobium, which tend to be relatively host specific (Hawksworth and Wiens 1996), A. oxycedri has a wide host range (Table1 and Table 2). The most commonly reported hosts are various Juniperus species. Seventeen taxa of Juniperus are reported as host plants including several exotic species (e.g., Juniperus virginiana, a North American species reported as a host in the Ukraine). These data suggest that virtually any species of Juniperus is a potential host of A. oxycedri. Other genera of the family Cupressaceae, including species of Chamaecyparis, Cupressus, and Platycladus are also hosts of A. oxycedri. It is interesting to note that the other two known Juniperus infesting species of Arceuthobium, A. azoricum of the Azores Islands (Portugal) and A. juniperi-procerae of Ethiopia and Kenya, each have only a single reported host (Hawksworth and Wiens 1976, 1996).
Arceuthobium oxycedri is confirmed from 31 countries, including 2 in northern Africa, 4 in Mediterranean Europe, 8 in the Balkan Peninsula, 9 from Russia and other former Soviet Republics, 5 in the Near East, and 3 from the Indian subcontinent and western China (Map 13). One country, Afghanistan, is considered questionable. There is also a possibility of the additional occurrences of this dwarf mistletoe in parts of northern Pakistan and the Himalayan Region of India, Nepal, and Bhutan (Map 13). This dwarf mistletoe is found over a wide elevation range, from near sea level along the Mediterranean and Black Seas to elevations from 575 to 1,000 m in Italy, 700 to 900 m in Iraq, 2,600 m in northern India and 3,000 to 3,500 m in western China. Geographically, there appear to be two broad patterns of regional distribution-dispersed or restricted. It appears to be widely dispersed throughout the range of its host plants in northern Africa, Spain, the Balkans, Turkey and adjacent countries, central Asia, and southwestern China. Its distribution is more restricted in France, Italy, Pakistan, and India. Some differences may arise from the intensity of collecting, but mistletoes commonly exist as isolated populations. Interest in the A. oxycedri seems especially keen in Spain, Crimea, and Pakistan. Its broad distribution suggests climate is usually not limiting if a juniper host is present. The range of this dwarf mistletoe appears to generally coincide with its hosts, but the junipers themselves occur in many regions as widely separated populations. Although the ballistic dispersal of dwarf mistletoes assures good local spread, its dioecious habit and rare vectoring by birds makes long distance dispersal very problematic. The distribution of juniper dwarf mistletoe reflects a history of migration with its host and of persistence in some populations and extinction in others.
Management Implications
Juniper forests occur over extensive, regions of northern Africa, Mediterranean Europe, the Near East, central Asia, the Indian subcontinent, and western China. In these arid regions forest growth is slow and regeneration is uncertain. The continued health and even existence of many of these forests is threatened by excessive human use, grazing by domestic livestock, insects, and diseases. One of the major disease agents of Old World junipers and other Cupressaceae is Arceuthobium oxycedri. This dwarf mistletoe has the most extensive natural range of any species in this genus, occurring over a large land area from northern Africa and Mediterranean Europe to western China. Since its original description in 1819, national boundaries within its range have changed significantly, new countries have been established and others have disappeared. The names of many communities and physiographic features of the landscape have also changed. Moreover, there have been significant changes in the nomenclature of some of the host plants of this important parasite. Consequently, existing records require updating to reflect today's geo-political boundaries and taxonomic designations. This will enable research scientists and applied biologists concerned with pest management in juniper forests to readily identify locations where this plant is found, its hosts, where established pest management methods have been developed, and where the socio-economic impacts for this parasitic plant have been studied.
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Title: RMRS-RN-11WWW:
Discussion
Electronic Publish Date: September 2001
Last Update: August
20, 2008