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White Ash

Fraxinus americana

Summary 4

Fraxinus americana (white ash or American ash) is a species of Fraxinus native to eastern North America found in mesophytic hardwood forests from Nova Scotia west to Minnesota, south to northern Florida, and southwest to eastern Texas.

Cover value 5

More info for the term: cover

White ash provides hiding and thermal cover for a variety of mammals and
birds.  The degree to which white ash provides environmental protection
during one or more seasons for wildlife species in several eastern
states has been rated as follows [26,27,28]:

                         ME        PA        WV        MI        KY

White-tailed deer       good      good      good      good      good
Small mammals           good      good      good      good      good
Small nongame birds     good      good      good      good      good
upland game birds       good      good      good      good      good
Waterfowl               good      good      good      good      good

Damaging agents 6

Ash decline (also called ash dieback) is  the most serious problem affecting white ash. Especially  prevalent in the northeastern part of the tree's range, this  disease complex occurs from the Great Plains to the Atlantic  coast between 39 and 45 degrees north latitude (10). The disease,  ash yellows, caused by mycoplasma-like organisms (MLO), has been  found associated with most of the dying trees where ash decline  is conspicuous (9). However, since not all dying trees are  infected with MLO, ash decline is thought to result from multiple  causes. Drought-weakened trees may be invaded by cankercausing,  branch-girdling fungi such as Fusicoccum spp. and Cytophorna  pruinosa. Additional stresses that may be involved in the  etiology of ash decline are air pollution, leaf-spotting fungi,  and viruses. Control recommendations are based primarily on  maintaining good tree vigor (6).

    Air pollution damages white ash. It is rated as sensitive to ozone  and is severely injured by stack gases from soft coal consumption  and from industrial processes, both of which emit sulfur dioxide.

    Two leaf spot fungi, Mycosphaerella effigurata and M.  fraxinicola, are common in nurseries and in the forest  and cause premature defoliation of white ash. Anthracnose (Gloeosporium  aridum) also causes premature defoliation and is most serious  following exceptionally wet springs. An ash strain of tobacco  ringspot virus causes chlorotic areas on the leaves and has been  associated with ash dieback.

    A rust (Puccinia peridermiospora) distorts petioles and  small twigs. Cankers caused by Nectria galligena may cause  branches to break but are rarely found on main stems. Heartwood  rots may be caused by Perenniporia fraxinophilus, Phellinus  igniarius, Pleurotus ostreatus, Tyromyces spraguei,  and Laetiporus sulphureus. These organisms usually enter  through wounds or broken branches, mainly on older trees.

    Of 26 species of nematodes reported from the roots or root zones  of white ash, only one, Meloidogyne ovalis, has been  associated with root injury. However, nematodes can be vectors  for the ringspot virus (5).

    Of the insect pests, the oystershell scale (Lepidosaphes ulmi)  is the most serious. Severe infestations cause yellowing of the  leaves, and if prolonged, may kill some trees. The cottony maple  scale (Pulvinaria innumerabilis) also attacks white ash.

    The brownheaded ash sawfly (Tomostethus multicinctus) and  the blackheaded ash sawfly (Tethida cordigera) are defoliators  that are of concern mainly on ornamental trees. The forest tent  caterpillar (Malacosoma disstria) and the green fruitworm  (Lithophane antennata) feed on forest trees and  occasionally cause complete defoliation within small geographic  areas. The larvae of sphingid moths-Sphinx chersis (the  great ash sphinx), S. kalmiae, and Ceratornia  undulosa-feed on the leaves of white ash, as does the  notched-wing geometer (Ennomos magnaria). The larvae of  two leaf roller moths, Sparganothis dilutocostana and  S. folgidipenna, also feed on ash.

    The ash bark beetle (Leperisinus aculeatus) may cause  slight injury when the adults bore into the bark to hibernate.  The ash borer (Podosesia syringae) may seriously damage  young shade and shelterbelt trees. The ash and privet borer (Tylonotus  bimaculatus) attacks and kills branches, especially on older  trees. Both the red-headed ash borer (Neoclytus acurninatus)  andthe banded ash borer (N. caprea) colonize cut  logs and dead or dying trees (1).

    White ash seedlings are easily damaged or destroyed by deer and  cattle browsing. Rabbits, beaver, and porcupine occasionally use  the bark of young trees for food.

Description 7

General: Olive family (Oleaceae). Native trees growing to 20-30 m tall, maintaining a central leader (strong apical dominance) in youth with an even distribution of branches, developing a dense, conical or rounded crown at maturity. The trunk is long, straight, and free of branches for most of its length (except when open grown). The bark is thick, dark gray, with a uniform, diamond-shaped ridge and furrow pattern. Leaves are deciduous, opposite, pinnately compound, 20-38 cm long, leaflets usually 7(5-9), short-stalked, ovate to ovate-lanceolate or elliptic, acuminate, 6-13 cm long and 3-6 cm wide, sometimes with a few teeth near the tip, dark green and smooth above, whitish below. Flowers are numerous, very small, green to purplish, in small branched clusters near the branch tips, usually either male (staminate) or female (pistillate), a single tree usually bearing only one sex (the species dioecious). Fruits are samaras 2.5-5 cm long, hanging in clusters, with a narrow wing extending about 1/3-1/4 of the way down the cylindrical body. The common name is in reference to the white color of the wood.

This species flowers in April-May, the male first, before appearance of the leaves; fruiting August-October, the seeds dispersed September-November. The pollen is already airborne during the 7-10 days when the female flowers are receptive.

Variation within the species: A number of variants have been described within the species, including F. americana var. biltmoreana (Beadle) J. Wright ex Fern. (= F. biltmoreana Beadle) and F. americana var. microcarpa A. Gray, but the distinctions between these have not been generally confirmed and formal variants are not currently recognized. Diploids (2n=46), tetraploids (2n=92), and hexaploids (2n=138) occur within the species, but it is difficult to associate differences in ploidy level with other patterns of variation.

Environmental concerns 8

Ash decline (or “ash dieback” or “ash yellows”) is the most serious problem affecting white ash. The decline is especially prevalent in New York, Pennsylvania and Vermont but occurs from the Great Plains to the Atlantic coast at 39–45 N latitude. Mycoplasma-like organisms (MLO, the cause of ash yellows) have been found associated with most of the dying trees.Not all dying trees are infected and ash decline is thought to result from multiple causes – MLO plus various fungi and viruses, as well as atmospheric pollution and drought. Maintenance of good tree vigor is the primary control recommendation.

White ash is sensitive to ozone, sulfur dioxide, nitrous oxides, and associated acid deposition, which may cause the appearance of necrotic lesions on the leaves. Most of recent ash decline has occurred in areas with high levels of these gases.

Genetics 9

Population Differences    White ash contains several phenotypic variants of leaf form that  appear to be genetically controlled even though they are randomly  distributed throughout the natural range. Chief among these are  9-leaflet, narrow-leaflet, blunt-leaflet, ascidiate leaflet,  partially pubescent, purple-keyed, and crinkle-leaf forms. A  purple leaf variant is vegetatively propagated and grown as an  ornamental.

    White ash is a polyploid species. Diploids (2n=46) occur  throughout the species range but most tetraploids (2n=92) are  found south of latitude 35° N and hexaploids (2n=138) are  concentrated between latitude 35° and 40° N. Although  three ecotypes were previously recognized on the basis of  seedling morphology and ploidy level (15), recent work has shown  that the variation in several traits is closely related to  latitude. This clonal variation and the strong effects of ploidy  level on several other traits indicate that ecotypes probably do  not exist in white ash (2).

    Hybrids    White ash and Texas ash (Fraxinus texensis (Gray) Sarg.)  intergrade in Texas. The pumpkin ash (Fraxinus profunda (Bush)  Bush) behaves in many respects as if it were a true breeding  hexaploid derivative of a cross between tetraploid white ash and  diploid green ash (Fraxinus pennsylvanica Marsh.).  However, attempts have failed to artificially cross the two  species. It is likely that natural hybridization between white  ash and other species is extremely rare (16).

Sources and Credits

  1. (c) Ross, some rights reserved (CC BY-NC-SA), http://www.flickr.com/photos/13757887@N00/53880594
  2. (c) Gilles Douaire, some rights reserved (CC BY-SA), https://www.flickr.com/photos/douaireg/6337987503/
  3. (c) Virens (Latin for greening), some rights reserved (CC BY), https://www.flickr.com/photos/evelynfitzgerald/3911040871/
  4. Adapted by Jonathan (JC) Carpenter from a work by (c) Wikipedia, some rights reserved (CC BY-SA), http://en.wikipedia.org/wiki/Fraxinus_americana
  5. Public Domain, http://eol.org/data_objects/24641251
  6. (c) Unknown, some rights reserved (CC BY-NC), http://eol.org/data_objects/22778539
  7. Public Domain, http://eol.org/data_objects/1384521
  8. Public Domain, http://eol.org/data_objects/1384525
  9. (c) Unknown, some rights reserved (CC BY-NC), http://eol.org/data_objects/22778540

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