Introductory
SPECIES: Juglans microcarpa | Little Walnut 



ABBREVIATION : 
JUGMIC

SYNONYMS : 
   Juglans rupestris
   Juglans nana


SCS PLANT CODE : 
   JUMI
   JUMIS


COMMON NAMES : 
   little walnut
   Texas walnut
   Texas black walnut
   dwarf walnut
   river walnut
   Mexican walnut
   walnut
   nogal
   nogalillo
   nogalito
   namboca


TAXONOMY : 
The currently accepted scientific name of little walnut is Juglans
microcarpa Berl. [17].  Two varieties are delineated on the basis of
morphological differences such as leaf and fruit size [26].  The
following varieties are commonly recognized [17]:

                  Juglans microcarpa var. microcarpa
                  Juglans microcarpa var. stewartii

Little walnut hybridizes with the closely related Arizona black walnut
(Juglans major) [36], and populations which exhibit various intermediate
characteristics have been reported [26].  At the eastern edge of its
range, little walnut intergrades with black walnut (J. nigra) [3,31].


LIFE FORM : 
Tree, Shrub

FEDERAL LEGAL STATUS : 
No special status

OTHER STATUS : 
NO-ENTRY


COMPILED BY AND DATE : 
D. Tirmenstein  October, 1990.


LAST REVISED BY AND DATE : 
NO-ENTRY


AUTHORSHIP AND CITATION : 
Tirmenstein, D. A. 1990. Juglans microcarpa. In: Remainder of Citation

DISTRIBUTION AND OCCURRENCE
SPECIES: Juglans microcarpa | Little Walnut 



GENERAL DISTRIBUTION : 
Little walnut grows from southwestern Kansas through Oklahoma to central
New Mexico and Texas, south into northeastern Mexico [5,15,31].  In
Texas, little walnut grows from the valley of the Colorado River west to
the mountains of the Trans-Pecos [36].  The variety stewartii grows in
the Chisos Mountains of Texas and extends into Mexico [26].


ECOSYSTEMS : 
   FRES15  Oak - hickory
   FRES21  Ponderosa pine
   FRES28  Western hardwoods
   FRES31  Shinnery
   FRES32  Texas savanna


STATES : 
     AZ  KS  NM  OK  TX  MEXICO


ADMINISTRATIVE UNITS : 
     AMIS  BIBE  CACA  GUMO  LAME


BLM PHYSIOGRAPHIC REGIONS : 
    7  Lower Basin and Range
   13  Rocky Mountain Piedmont
   14  Great Plains


KUCHLER PLANT ASSOCIATIONS : 
   K060  Mesquite savanna
   K061  Mesquite - acacia savanna
   K062  Mesquite - live oak savanna
   K071  Shinnery
   K084  Cross Timbers
   K086  Juniper - oak savanna
   K087  Mesquite - oak savanna


SAF COVER TYPES : 
    66  Ashe juniper - redberry (Pinchot) juniper
    67  Mohrs ("shin") oak
    68  Mesquite
   235  Cottonwood - willow
   240  Arizona cypress


SRM (RANGELAND) COVER TYPES : 
NO-ENTRY


HABITAT TYPES AND PLANT COMMUNITIES : 
Texas walnut occurs abundantly in a number of riparian woodland
communities.  It is included as a dominant or indicator in the following
community type (cts) classifications:

 Area                Classification          Authority

TX: Brewster Co.     general veg. cts        Carignan 1988

NM, TX: Guadalupe    general veg. cts        Gehlbach 1967
   Escarpment

Southwest            riparian cts            Szaro 1990a

Southwest            riparian cts            Szaro 1990b      

TX: Brewster Co.     general veg. cts        Denyes 1956

VALUE AND USE
SPECIES: Juglans microcarpa | Little Walnut 



WOOD PRODUCTS VALUE : 
Wood of little walnut is dark brown, hard and heavy but not strong [36].
Sapwood is white [36].  Annual rings are poorly cemented and the wood
frequently comes apart as it is being worked [20].  This characteristic
limits its use [20].  However, wood is sometimes used to make cabinets,
furniture, paneling, and veneer [36].


IMPORTANCE TO LIVESTOCK AND WILDLIFE : 
Little walnut provides some deer browse in parts of New Mexico [19].
The nuts are a valuable food source for many wildlife species including
squirrels and other rodents [5,30,36].  The rock squirrel readily
consumes nuts when available [30].


PALATABILITY : 
Nuts of little walnut are highly palatable to a wide variety of wildlife
species [5].


NUTRITIONAL VALUE : 
The nut meat of little walnut is described as nutritious and of "high
quality" [30].


COVER VALUE : 
Riparian woodlands dominated by little walnut host a diverse array of
animal life [7].  These areas form particularly good habitat for many
species of birds [7].


VALUE FOR REHABILITATION OF DISTURBED SITES : 
Little walnut has been widely used for shelterbelt plantings [6,38] and
has shown promise for use in some types of rehabilitation projects.
Under certain conditions, it can aid in soil stabilization [33].  Plants
can be easily propagated from seed.  Cleaned seed averages 92 per pound
(203/ kg) [5].  Seed can be planted during the fall in sandy soils at
depths of 1 to 2 inches (3-5 cm) [36].  Methods of propagating by seed
have been examined in detail [5,36].


OTHER USES AND VALUES : 
Little walnut plants are sometimes cultivated for the sweet, edible nuts
[17,30,31].  It is the primary rootstock used in Texas for trials of
nonnative walnuts and has potential value for use in developing walnut
cultivars [29].  It has been cultivated as an ornamental and shade tree
in both the United States and Europe [36].  Plants were first cultivated
in 1868 [5].


MANAGEMENT CONSIDERATIONS : 
Damage:  The walnut husk fly infests ripening fruit of little walnut
after late summer rains [20].  The amount of fruit damaged by this
insect varies annually but generally tends to be less in exposed windy
areas [20].  Mature little walnut appears to be relatively unaffected by
even "devastating" flash floods [14].

Disease:  Little walnut is highly susceptible to root or crown rot when
periodically flooded [24].  It is less susceptible to the fungus-caused
walnut anthracose than black walnut is [3].

BOTANICAL AND ECOLOGICAL CHARACTERISTICS
SPECIES: Juglans microcarpa | Little Walnut 



GENERAL BOTANICAL CHARACTERISTICS : 
Little walnut grows as a large, many-trunked shrub or small, clumped,
spreading, low-branched tree [15].  Plants may grow from 20 to 50 feet
(6-15 m) in height [5,30,31].  The strongly scented trunk is gray to
dark brown and becomes deeply fissured with age [18,36].  Twigs are
slender, orange-reddish, gray-brown, or gray and pubescent [31,36].
Little walnut is a phreatophyte with a long taproot which allows the
plant to obtain water from the water table [30].

Alternate, odd-pinnately compound leaves are 8 to 12 inches (20-30 cm)
long [18,36].  The 7 to 25 narrowly ovate to lanceolate leaflets are
serrate with low teeth [5,36].  The leaf base is cuneate to rounded and
the apex acute [36].  The upper surface is dark yellow to green, dull
and glabrous [31,36]; the lower surface is somewhat paler [31].  Leaves
are glabrous at maturity and aromatic when crushed [5,36].

Little walnut is monoecious [31].  Slender staminate catkins develop on
the wood of the previous year [31].  Yellow-green pistillate flowers are
borne singly or in clusters in short terminal spikes on the current
year's growth [5,31].  Fruit is globose, 0.5 to 0.8 inch (1.2-2.0 cm) in
diameter, brownish, and glabrous with age [5,18].  The fruit is borne
singly or in clusters of two or three [31].  The indehiscent husk or
shell is dark brown, thick, and fibrous [5,18,31].  The hard, dark brown
nut of little walnut [31] is the smallest of all walnuts (Juglans spp.)
[20].  It is globose to ovoid [25], deeply grooved longitudinally, and
0.8 to 0.9 inch (2-2.3 cm) in diameter [31].  The kernel is sweet and
oily [36].

The variety stewartii is characterized by slightly larger fruit (0.8 to
1 inch (21-25 mm) in length) and broader leaflets (0.6 to 0.9 inch
(15-23 mm) wide) [26].  The Arizona walnut is morphologically similar
to little walnut, and identification may be difficult where both species
occur together [30].


RAUNKIAER LIFE FORM : 
   Undisturbed State:  Phanerophyte (microphanerophyte)
   Undisturbed State:  Phanerophyte (mesophanerophyte)
   Burned or Clipped State:  Therophyte


REGENERATION PROCESSES : 
Seed:  Most walnuts bear abundant seed crops at irregular intervals
[12].  Little walnut first bears seed at approximately 20 years of age
[5].  Seed may be dispersed by animals or water.

Germination:  The seeds of most walnuts are characterized by a dormant
embryo [40].  Seed dormancy can be broken by stratification at 34 to 41
degrees F (1-5 degrees C) for 90 to 120 days [1,5].  Light is not
required for germination, and seeds germinate well when deeply buried in
moist soil [1].  Stratified seed generally germinates within 4 weeks,
but much variation has been noted [5].  Under natural conditions, seeds
germinate in the spring [5].  Results of laboratory tests are as follows
[5]:

        germination test conditions    germination energy      
        daily temperature        dur.           amount        days
        days        night       (days)          (percent)

        86           68         30-60            68           14

Germination capacity has averaged 46 percent in greenhouse experiments
[5].  Under natural conditions, seeds may be more likely to germinate on
high terraces than in ephemeral stream channels, which may be subject to
flooding [1].

Seedling establishment:  Seedling recruitment has been examined in
detail [1].  Once established, young plants generally grow rapidly [36].

Vegetative regeneration:  Epicormic branching of walnuts has been
reported [6].  The closely related black walnut reportedly stump-sprouts
after trees are cut or killed by fire [12].


SITE CHARACTERISTICS : 
Little walnut grows along rocky streambottoms, in canyons and arroyos,
and on first terraces of dry river beds [30,36].  It is particularly
common in arroyos of the Chihuahuan Desert [21].  In southeastern New
Mexico, little walnut grows along waterways that extend from the
foothills out onto the plains [20].  This plant commonly dominates
narrow riparian forests, which are often characterized by steep
limestone walls, and various river edge or creek bottom communities
[35,38].  Many sites have relatively high moisture availability.
Moisture is generally obtained from flowing or ephemeral streams and
flash floods [14,30].

Plant associates:  Common overstory associates of the Edwards Plateau of
Texas include pecan (Carya illinoensis), Texas persimmon (Diospyros
texana), netleaf hackberry (Celtis reticulata), and live oak (Quercus
virginiana) [38].  Species such as netleaf hackberry, cedar elm (Ulmus
crassifolia), and littleleaf sumac (Rhus microphylla) are particularly
common on drier sites [37].  Agarito (Mahonia trifoliolata), Ashe
juniper (Juniperus ashei), bald cypress (Taxodium distichum), American
sycamore (Platanus occidentalis), desert willow (Chilopsis linearis),
and Texas persimmon are common components of river edge or riparian
woodland communities [9,37,41].

Soils:  Little walnut commonly grows on shallow calcareous or alluvial
soils [35,37].  On many sites streambottom habitats are characterized
by gravelly soils, coarse sand, or exposed boulders [9,14].

Climate:  Little walnut grows in areas which receive less than 7 to 38
inches (<18 cm-72 cm) of precipitation annually [8,37].

Elevation:  Little walnut grows primarily in valleys at intermediate
elevations [26].  Generalized elevational ranges by geographic location
are as follows:

 Location  Elevation                             Authority

 TX-NM     3,950 to 5,250 feet (1,200-1,600 m)   Legner and Goeden 1987
 NM-TX     <5,200 feet (< 1,585 m)               Cottle 1931



SUCCESSIONAL STATUS : 
Little walnut is largely restricted to drainageways which support
riparian woodland communities.  These woodlands generally represent
climax or "postclimax" communities [8].


SEASONAL DEVELOPMENT : 
Flowering begins with or slightly after leaf emergence [5].  Male and
female flowers, which are borne on the same trees, mature at different
times, thus promoting cross-pollination [5].  Fruit ripens in late
summer or fall [5].  Generalized flowering and fruiting dates for little
walnut by geographic location are as follows:

  Location       Flowering     Fruit ripe      Authority

  SW             March-April     ----          Vines 1960
  Great Plains   March-April     ----          Great Plains Flora Assoc. 1986
 c Great Plains  May            October        Stephens 1973

Seed is typically dispersed in fall [5].  Some fruit falls from the
trees before the last week of August [21], but in many areas, most seed
falls during September and October [1].  Timing of fruit fall depends
largely on weather conditions such as wind and rain [21].

FIRE ECOLOGY
SPECIES: Juglans microcarpa | Little Walnut 



FIRE ECOLOGY OR ADAPTATIONS : 
Little walnut is most commonly associated with riparian woodlands which
burn infrequently.  These narrow canyon forests frequently contrast
strikingly with adjacent desert grassland or shrubland communities [8].
Evidence suggests that recurrent fires in the much drier desert
grassland types may have eliminated invading shrubs and trees [16].

Because of its affinity for moist sites, little walnut exhibits few
specific adaptations to fire.  Reestablishment presumably occurs through
off-site seed.


POSTFIRE REGENERATION STRATEGY : 
   survivor species; surviving root crown or caudex
   off-site colonizer; seed carried by animals or water; postfire yr 1&2

FIRE EFFECTS
SPECIES: Juglans microcarpa | Little Walnut 



IMMEDIATE FIRE EFFECT ON PLANT : 
Little documentation exists on the specific effects of fire on little
walnut.  Mature individuals of the closely related Arizona walnut are
reportedly killed by hot wildfires [4].  Portions of the stumps or root
collars of small black walnuts commonly survive fire [12].


DISCUSSION AND QUALIFICATION OF FIRE EFFECT : 
NO-ENTRY


PLANT RESPONSE TO FIRE : 
The response of little walnut to fire has not been documented.  Small
individuals of the closely related black walnut often sprout freely from
the stump after aboveground vegetation is killed or damaged by fire
[12].  Fowells [12] reports that sprouts which develop high on older
stumps often succumb to rot or decay, but those which develop from the
root collar generally survive.  Larger individuals of the Arizona walnut
apparently did not sprout after a hot wildfire in a Southwestern
riparian woodland [4].


DISCUSSION AND QUALIFICATION OF PLANT RESPONSE : 
NO-ENTRY


FIRE MANAGEMENT CONSIDERATIONS : 
Bock and Bock [4] report that prescribed fire is "difficult to manage
and potentially very destructive in established riparian woodlands of
the Southwest."  These relatively rare and fragile areas provide
important food and cover for desert wildlife [28].  Because browse and
cover are often limited in these areas, burning is not generally
recommended [28].

References for species: Juglans microcarpa

1. Asplund, Kenneth K.; Gooch, Michael T. 1988. Geomorphology and the distributional ecology of Fremont cottonwood (Populus fremontii) in a desert riparian canyon. Desert Plants. 9(1): 17-27. [563]

2. Bernard, Stephen R.; Brown, Kenneth F. 1977. Distribution of mammals, reptiles, and amphibians by BLM physiographic regions and A.W. Kuchler's associations for the eleven western states. Tech. Note 301. Denver, CO: U.S. Department of the Interior, Bureau of Land Management. 169 p. [434]

3. Black, W. M.; Neely, Dan. 1978. Relative resistance of Junglans species and hybrids to walnut anthracnose. Plant Disease Reporter. 62(6): 497-499. [11559]

4. Bock, Carl E.; Bock, Jane H. 1990. Effects of fire on wildlife in southwestern lowland habitats. In: Krammes, J. S., technical coordinator. Effects of fire management of southwestern natural resources: Proceedings of the symposium; 1988 November 15-17; Tucson, AZ. Gen. Tech. Rep. RM-191. Fort Collins, CO: U.S. Department of Agriculture, Forest Service, Rocky Mountain Forest and Range Experiment Station: 50-64. [11273]

5. Brinkman, Kenneth A. 1974. Juglans L. walnut. In: Schopmeyer, C. S., ed. Seeds of woody plants in the United States. Agric. Handb. 450. Washington, DC: U.S. Department of Agriculture, Forest Service: 454-459. [7684]

6. Bryson, J. R.; Fewin, R. J. 1982. Shelterbelt renovation in Knox County, Texas. Great Plains Agricultural Council. 106(J): 69-77. [11740]

7. Carignan, Jeanette M. 1988. Ecological survey and elevational gradient implications of the flora and vertebrate fauna in the northern Del Norte Mountains, Brewster Co., Tx. Alpine, TX: Sul Ross State University. 181 p. Thesis. [12255]

8. Cottle, H. J. 1931. Studies in the vegetation of southwestern Texas. Ecology. 12(1): 105-155. [4556]

9. Denyes, H. Arliss. 1956. Natural terrestrial communities of Brewster County, Texas, with special reference to the distribution of the mammals. The American Midland Naturalist. 55(2): 289-320. [10862]

10. Dick-Peddie, William A.; Alberico, Michael S. 1977. Fire ecology study of the Chisos Mountains, Big Bend National Park, Texas: Phase I. CDRI Contribution No. 35. Alpine, TX: The Chihuahuan Desert Research Institute. 47 p. [5002]

11. Eyre, F. H., ed. 1980. Forest cover types of the United States and Canada. Washington, DC: Society of American Foresters. 148 p. [905]

12. Fowells, H. A., compiler. 1965. Silvics of forest trees of the United States. Agric. Handb. 271. Washington, DC: U.S. Department of Agriculture, Forest Service. 762 p. [12442]

13. Garrison, George A.; Bjugstad, Ardell J.; Duncan, Don A.; [and others]. 1977. Vegetation and environmental features of forest and range ecosystems. Agric. Handb. 475. Washington, DC: U.S. Department of Agriculture, Forest Service. 68 p. [998]

14. Gehlbach, Frederick R. 1967. Vegetation of the Guadalupe Escarpment, New Mexico-Texas. Ecology. 48(3): 404-419. [5149]

15. Great Plains Flora Association. 1986. Flora of the Great Plains. Lawrence, KS: University Press of Kansas. 1392 p. [1603]

16. Hastings, James R.; Turner, Raymond M. 1965. The changing mile: An ecological study of vegetation change with time in the lower mile of an arid and semiarid region. Tuscon, AZ: University of Arizona Press. 317 p. [10533]

17. Kartesz, John T.; Kartesz, Rosemarie. 1980. A synonymized checklist of the vascular flora of the United States, Canada, and Greenland. Volume II: The biota of North America. Chapel Hill, NC: The University of North Carolina Press; in confederation with Anne H. Lindsey and C. Richie Bell, North Carolina Botanical Garden. 500 p. [6954]

18. Krochmal, Arnold; Krochmal, Connie. 1982. Uncultivated nuts of the United States. Agriculture Information Bulletin 450. Washington, DC: U.S. Department of Agriculture, Forest Service. 89 p. [1377]

19. Kuchler, A. W. 1964. Manual to accompany the map of potential vegetation of the conterminous United States. Special Publication No. 36. New York: American Geographical Society. 77 p. [1384]

20. Lamb, S. H. 1971. Woody plants of New Mexico and their value to wildlife. Bull. 14. Albuquerque, NM: New Mexico Department of Game and Fish. 80 p. [9818]

21. Legner, E. F.; Goeden, R. D. 1987. Larval parasitism of Rhagoletis completa (Diptera: Tephritidae) on Juglands microcarpa (Juglandaceae) in western Texas and southeastern NM. Proceedings of the Entomological Society of Washington. 89(4): 739-743. [11546]

22. Little, Elbert L., Jr. 1976. Atlas of United States trees. Volume 3. Minor western hardwoods. Misc. Publ. 1314. Washington, DC: U.S. Department of Agriculture, Forest Service. 13 p. 290 maps. [10430]

23. Little, Elbert L., Jr. 1979. Checklist of United States trees (native and naturalized). Agric. Handb. 541. Washington, DC: U.S. Department of Agriculture, Forest Service. 375 p. [2952]

24. Stickney, Peter F. 1989. Seral origin of species originating in northern Rocky Mountain forests. Unpublished draft on file at: U.S. Department of Agriculture, Forest Service, Intermountain Research Station, Fire Sciences Laboratory, Missoula, MT; RWU 4403 files. 10 p. [20090]

25. Matheron, M. E.; Mircetich, S. M. 1985. Relative resistance of different rootstocks of English walnut to six Phytophthora spp. that cause root and crown rot in orchard trees. Plant Disease. 69(12): 1039-1041. [11544]

26. Powell, A. Michael. 1988. Trees & shrubs of Trans-Pecos Texas including Big Bend and Guadalupe Mountains National Parks. Big Bend National Park, TX: Big Bend Natural History Association. 536 p. [6130]

27. Raunkiaer, C. 1934. The life forms of plants and statistical plant geography. Oxford: Clarendon Press. 632 p. [2843]

28. Severson, Kieth E.; Rinne, John N. 1990. Increasing habitat diversity in Southwestern forests and woodlands via prescribed fire. In: Krammes, J. S., technical coordinator. Effects of fire management of southwestern natural resources: Proceedings of the symposium; 1988 November 15-17; Tucson, AZ. Gen. Tech. Rep. RM-191. Fort Collins, CO: U.S. Department of Agriculture, Forest Service, Rocky Mountain Forest and Range Experiment Station: 94-104. [11277]

29. Shreve, Loy W. 1987. Walnut and persimmon production in China. Annual Report of the Northern Nut Growers Association. 78: 40-45. [11821]

30. Simpson, Benny J. 1988. A field guide to Texas trees. Austin, TX: Texas Monthly Press. 372 p. [11708]

31. Stephens, H. A. 1973. Woody plants of the North Central Plains. Lawrence, KS: The University Press of Kansas. 530 p. [3804]

32. Szaro, Robert C. 1990. Southwestern riparian plant communities: site characteristics, tree species distributions, and size-class structures. Forest Ecology and Management. 33/34: 315-334. [10031]

33. Thornburg, Ashley A. 1982. Plant materials for use on surface-mined lands. SCS-TP-157. Washington, DC: U.S. Department of Agriculture, Soil Conservation Service. 88 p. [3769]

34. U.S. Department of Agriculture, Soil Conservation Service. 1982. National list of scientific plant names. Vol. 1. List of plant names. SCS-TP-159. Washington, DC. 416 p. [11573]

35. Van Auken, O. W.; Ford, A. L.; Stein, A. 1979. A comparison of some woody upland and riparian plant communities of the southern Edwards Plateau. The Southwestern Naturalist. 24(1): 165-180. [10489]

36. Vines, Robert A. 1960. Trees, shrubs, and woody vines of the Southwest. Austin, TX: University of Texas Press. 1104 p. [7707]

37. Wood, Carl E.; Wood, Judith K. 1988. Woody vegetation of the Frio River riparian forest, Texas. Texas Journal of Science. 40(3): 309-322. [11870]

38. Wood, Carl E.; Wood, Judith K. 1989. Riparian forests of the Leona and Sabinal Rivers. Texas Journal of Science. 41(4): 395-412. [11869]

39. Fewin, Robert J.; Helwig, Larry. 1988. Windbreak renovation in the American Great Plains. Agriculture, Ecosystems and Environment. 22/23: 571-582. [9338]

40. Young, James A.; Young, Cheryl G. 1986. Collecting, processing and germinating seeds of wildland plants. Portland, OR: Timber Press. 236 p. [12232]

41. Szaro, Robert C. 1989. Riparian forest and scrubland community types of Arizona and New Mexico. Desert Plants. 9(3-4): 70-138. [604]

Related categories for Species: Juglans microcarpa | Little Walnut