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Wildlife, Animals, and Plants |
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BOTANICAL AND ECOLOGICAL CHARACTERISTICS
GENERAL BOTANICAL CHARACTERISTICS:Arizona pine is a native tree. It reaches 75 to 100 feet (23-30 m) in height and 30 to 50 inches (75-130 cm) in diameter at maturity. The branches are stout, thick, and self pruning. The trunk is usually devoid of branches for half or more of its length. The crown is typically open and varies from short and conical to rounded or flat [81,87,92,106]. Bark of mature trees is about 2 inches (5 cm) thick. Needles are 4 to 9.5 inches (10-24 cm) long. The majority of needles are 4- or 5-fascicled, but some trees are 2- or 3-fascicled [43,48,92]. Average female cone length (2.5 inches (6.3 cm)) is shorter than other varieties of ponderosa pine. However, there is great between-population variation in length of Arizona pine cones [43]: they range from 1.5 to 2.4 inches (5-8 cm) long. Seeds are winged, with the seed body ranging from 3 to 4 mm in length and the wing extending to 15 mm [48,92]. Mature ponderosa pine have deep, extensive root systems [27]. Depending on the substrate, roots may penetrate to depths of 33 to 40 feet (10-12 m). Lateral root development is closely related to crown width and varies with tree density. Lateral roots may extend 100 feet (30 m) in open stands [115]. Arizona pine and interior ponderosa pine can be very similar in appearance. In a study comparing morphological traits used to distinguish Arizona and interior ponderosa pines, Dodge [43] found considerable overlap between the 2 taxa. He concluded that differences between the taxa were "minor," and that between-population morphological differences in Arizona pine were at least as pronounced as between-varietal differences in morphology. Distinguishing the 2 taxa can be further confounded by their tendency to hybridize. Arizona pine is morphologically distinguished from interior ponderosa pine by having shorter needles with a majority of 4- or 5-needled (vs. 2- or 3-needled) fascicles; smaller cones with incurved (vs. reflected) prickles; thinner bark; a rounder, more open crown; and being shorter and less broad at the base at maturity [43,48,77]. The Flora of North America provides botanical descriptions and dichotomous keys for Arizona pine and other varieties of ponderosa pine. RAUNKIAER [109] LIFE FORM:Phanerophyte REGENERATION PROCESSES:Arizona pine reproduces from seed. It is monoecious, with pollen dispersed by wind. Ponderosa pine 1st produces cones at 10 to 20 years of age [81]. Good Arizona pine seed crops are produced every 2 to 3 years [53]. High temperatures during strobili formation have been correlated with good Arizona pine cone crops [38,90]. Ponderosa pine seeds are mostly wind dispersed and do not usually carry more than 120 feet (37 m) from the parent tree [53]. Arizona pine seed (collected in Arizona and germinated in the greenhouse) showed mean viability of 75% [81]. Southwestern ponderosa pine seed germinates with the onset of mid-summer rains; germination continues until onset of fall drought. Mid-summer germinants show best survivorship, probably because they gain the most growth before onset of winter dormancy and succeeding spring drought [84]. Best Arizona pine
seedling establishment occurs in early seral communities, and establishment is somewhat
rare [30,111]. Several conditions are necessary for successful regeneration
of southwestern ponderosa pine: 1) an adequate seed source, 2) mineral soil with
lowing stocking of competing vegetation, 3) open light, 4) adequate moisture at the right time,
and 5) a low rate of herbivory on seedlings. Co-occurrence of these conditions is irregular
and uncommon [12,73,88,111]. A warmer than average spring results in good
cone crops [27,38,90]. A disturbance such as fire is required to
prepare a bare mineral seedbed and create open-light conditions [88]. Twenty-seven months after
cone initiation, a wetter than average summer and fall produces good seed
germination [27]. Seeds appear to require continually moist conditions for at
least 7 days at temperatures above 55 degrees Fahrenheit (13 oC)
[114]. Above-average precipitation the following spring promotes seedling
survival [27]. A pulse of Arizona pine regeneration occurred from 1910-1930,
when these conditions coincided; such a pulse has not occurred since
[111].
SITE CHARACTERISTICS:In the United States, Arizona pine is the least accessible of the 3 varieties of ponderosa pine. It occupies slopes, canyons, rims, and tablelands [48]. Slopes may be steep: Arizona pine sites in the Santa Catalina Mountains of southeastern Arizona ranged from 10 to 36o. In Arizona, Arizona pine soils are mostly derived from limestone, sandstone, and quartzite overlaying schist and granite [43]. Arizona pine is most common between 7,000 and 7,500 feet (2,100-2,300 m), while interior ponderosa pine is more common above 9,000 feet (2,700 m). Elevations between 7,500 and 9,000 feet are occupied by both varieties, and by their hybrids [19,43]. Overall elevational range of Arizona pine by state is: Arizona 6,200 to 9,840 feet (1,900-3,420 m)
[10,16,48,98] Climate is semi-arid to arid with bimodal rainfall. Winter rains occur from December through March and are followed by a dry season extending to June. Monsoonal rains occur from July to September, with greater than 50% of the mean annual rainfall occurring in August [15,19,24]. Total annual rainfall is highly variable, and prolonged drought is common [24]. SUCCESSIONAL STATUS:Ponderosa pine is shade intolerant [12,73], and is often a dominant tree in southwestern sky island plant communities [95,97]. Muldavin and others [97] have identified several Arizona pine habitat types. Successional pathways in Arizona
pine communities are poorly understood, and further research is needed in this
area. Arizona pine is occasionally seral in white fir habitats [95]. Arizona
pine may be
a climax species on dry, mid-elevation (6,800
to 8,500 feet (2,000-2,600 m)) sites [67,95,97,116,119]. Arizona pine types also occur on
high-elevation (<9,300 feet (2,800 m)), relatively moist north- and
east-facing slopes [28,97] that are maintained by
frequent fire [97]. These sites may proceed to mixed-conifer forest in the absence of
fire, with Arizona pine being successionally replaced by
Rocky Mountain Douglas-fir and/or white fir [28,95]. At low elevations (<
6,500 feet (2,000 m)), Arizona pine understories are characterized by Arizona
pine and Rocky Mountain Douglas-fir seedlings and saplings, oaks, and junipers
[85].
SEASONAL DEVELOPMENT:Mean date of pollen spread of Arizona pine in New Mexico was May 22 [44]. In Arizona, pollination occurred in May, 2nd-year cones ripened in September and October, and seed dispersed in October [81]. Southwestern ponderosa pine seed germinates from summer through fall. October drought initiates dormancy. Growth begins with the onset of summer rains [84].
Related categories for SPECIES: Pinus ponderosa var. arizonica | Arizona Pine |
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