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Wildlife, Animals, and Plants |
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BOTANICAL AND ECOLOGICAL CHARACTERISTICS
GENERAL BOTANICAL CHARACTERISTICS:Morphology: Interior ponderosa pine is a native conifer. Young, fast-growing trees have pyramidal crowns that become broader and more rounded as they mature. Height at maturity varies but this variety tends to be shorter than Pacific ponderosa pine. Trees in the Great Basin seldom exceed 100 feet (30 m) [190], while specimens in the southern Rocky Mountains may reach 160 feet (50 m) in height and 50 inches (130 cm) in diameter [259]. Interior ponderosa pine branches are open and self-pruning. Needles are from 3 to 7 inches (7-17 cm) long. The seed cones are 2 to 4 inches (5-10 cm) in length, and bear winged seeds with a body length of 3 to 4 millimeters and wing length of up to 15 millimeters [114]. Bark of mature trees is about 3 inches (8 cm) thick [190]. The root system is deep and spreading; interior ponderosa pine is one of the most wind-firm trees in the inland Northwest [6,7,71]. An 85-year-old tree in Colorado that was 19 feet (5.7 m) in height and 4.5 inches (114.3 cm) dbh had a maximum root depth of 5 feet (1.5 m) and a maximum lateral spread of 10 feet (3 m), with the majority of roots growing down slope. Fine roots were absent [39]. In Nebraska plains grassland clay, a 32-year-old, 25-foot (8 m) tree had lateral roots extending 20 feet (6 m) from the stem. Greatest depth of vertical roots was 12 feet (4 m), with most roots concentrated 3 to 4 feet (0.9-1.2 m) below ground [317]. There are 2 races of interior ponderosa pine: the northern and southwestern types. Northern interior ponderosa pine has a majority of 2-needle fascicles [14,71,307]. The variety's scientific name derives from the stiff, tufted (scopulate) foliage and compact crown characteristic of this race [71]. The southwestern race has a majority of 3-needle fascicles and a relatively open crown [177,307]. Structure: Stands were historically open with varied age class distributions [211,213]. Cooper [73] found that on the Fort Apache Reservation of east-central Arizona, where frequent prescribed burning is practiced, interior ponderosa pine grows in a mosaic of small (about 0.2-acre (0.08 ha)), even-aged groups that are maintained by fire. Trees are widely and randomly spaced. In contrast, structure in an unburned virgin stand on the Fort Valley Experimental Forest was uneven-aged with trees in small, uneven-aged groups. Pole-sized trees predominated, with scattered presettlement trees 14.5 to 41 inches (37-104 cm) dbh, and dense thickets of saplings [75]. (The Fire Ecology section of this report compares of pre- and postsettlement structure of this stand.) Laven and others [196] found presettlement stands on the central Colorado Front Range tended to have widely spaced, uneven-aged trees. Grouping patterns were not evident. Age: Interior ponderosa pine is long lived. Larger trees may attain ages of 700 or more years [190,259], although ponderosa pine between 350 and 425 years of age has a high mortality rate [218]. In a reconstruction of presettlement stand age classes near Flagstaff, Mast and others [211] found that prior to 1876, trees greater than 100 years old made up 68% of the overstory. The oldest interior ponderosa pine on record was a 1,047-year-old tree from Colorado [190]. In the Southwest, Swetnam and Brown [282] recorded a 742-year-old tree from northwestern Arizona. Physiology: The tough, compact foliage of the northern race of interior ponderosa pine probably confers cold tolerance [71]. A deep, extensive root system, high sapwood:heartwood ratio, and sunken stomata make interior ponderosa pine highly drought tolerant throughout its range [34,71]. In the northern and central portions of interior ponderosa pine's distribution, only limber pine and Rocky Mountain bristlecone pine (Pinus aristida) better withstand extended drought [34]. In the Southwest, Barton and Teeri [33] found that interior ponderosa pine seedlings from the Chiricahua Mountains of southeastern Arizona were more drought resistant than southwestern white pine but less so than Mexican pinyon, Chihuahua, and Apache pines. RAUNKIAER [236] LIFE FORM:Phanerophyte REGENERATION PROCESSES:Pollination and seeds: | Interior Ponderosa Pine Mating system is outcrossing of monoecious trees by wind pollination. Interior ponderosa pine 1st produces cones at 10 to 20 years of age [186,191]. Seed production is cyclic: trees in the Black Hills produce good seed crops every 2 to 5 years [50]. The cycle varies with climate and is not reliably periodic [180]. High temperatures during strobili formation have been correlated with good cone crops [84,208]. Jones [170] reported that in the Southwest, cone crops tend to be lighter in mixed-conifer compared to lower-elevation interior ponderosa pine forest. Seed- and cone-feeding insects may greatly reduce the seed crop. On the Kaibab and Coconino national forests of northern Arizona, degree of cone and seed infestation differed significantly (p<0.05) by site. The study did not address how the sites differed [44]. Shrews, rodents, and birds may also greatly reduce the cone crop [180,180,194]. During a 10-year study near Flagstaff, predation by Abert's squirrels varied from 0.3 to 75% of the total cone crop. The number of cones clipped was not related to the size of the total crop [194]. Seeds are mostly wind dispersed and do not usually carry more than 120 feet (37 m) from the parent tree [224]. Seeds cached by rodents may result in some seedling establishment, but rodents are not important dispersal agents of interior ponderosa pine seed. Clark's nutcrackers play a minor but important role in seed dispersal because seeds they cache are more likely to establish than rodent-cached seeds [192]. Seeds require mineral soil and do not germinate until the soil is continuously warm and moist [193]. Schmid and Mitchell [256] found the number of sound seeds collected from trees on the Coconino and Kaibab national forests did not vary significantly (p=0.05) between sites, but did vary significantly among trees. Mean number of sound seeds/cone/tree ranged from 35 to 58. In field trials, germination rate of seed collected and outplanted on the Fort Valley Experimental Forest showed 61 to 90% germination, with germination time varying from 12 to 37 days. First-year survivorship was greatest (13-19%) in seedlings that germinated in early to mid-July, and least (2-7%) in seedlings that germinated in August. Predation of germinants by dark-eyed juncos was responsible for over half of germinant mortality [193]. Seed germination is usually lowest, and seed predation highest, in years when seed crops are low [180]. Ponderosa pine is not a seed banking species, although a minor amount of seed may germinate in its 2nd spring or summer [170]. Seedling establishment: | Interior Ponderosa Pine Seedlings are relatively shade intolerant and require canopy-opening disturbances such as fire, logging, or tree death to establish [32,190,212,268]. Establishment pulses may occur on open sites when wet years follow a fire year, but wet postfire years are not always required for good establishment in the central Rocky Mountains and north. Two major pulses of seedling establishment in Rocky Mountain National Park, Colorado (1870-1890 and 1970-1980), occurred when fire was followed by normal precipitation [213]. Seedlings quickly develop a long taproot that enables them to reach moisture even on hot, burned-over soils [71,190]. Nevertheless, fall drought is a major factor in seedling mortality [169,195] and drought limits seedling establishment at interior ponderosa pine's lower elevational limit [32]. Since interior ponderosa pine in the Southwest has only a 2-month growing season before the onset of fall drought, winter dormancy, and spring drought, seedling mortality is usually highest in regions with bimodal precipitation [193]. Regeneration is further hindered in southwestern ponderosa pine on volcanic soils, which produce smaller seedlings (1 to 2 inches (3-5 cm)) that are more susceptible to frost-heaving compared to seedlings on other soils [153]. Rodent and ungulate browsing may result in considerable seedling loss. Artificial interior ponderosa pine regeneration on the Apache National Forest of east-central Arizona showed 95% mortality, and surviving seedlings showed little height gain, with mule deer and elk browsing. Seedlings in exclosures showed 2 to 3 times the height growth of unprotected seedlings [169]. However, certain gazing regimes favor seedling establishment. Pearson [229] found that in the Southwest, heavy cattle grazing that reduced grass interference with interior ponderosa pine growth, followed by light cattle grazing that allowed tree seedlings to survive, favored ponderosa pine over herbaceous and shrub species. On open sites with favorable moisture conditions, interior ponderosa pine seedlings often establish in large numbers. Dense seedlings often develop into "dog-hair" sapling thickets if stands are not thinned by fire or other means [75]. Boldt and Van Deusen [50] report that high tree densities (> 1 tree/ft2) are common in naturally regenerated interior ponderosa pine stands in the Black Hills. An even-aged, 63-year-old stand that had never experienced fire contained 6,600 trees per acre (16 500/ha), with average d.b.h. of 2.4 inches (6.1 cm). A number of researchers [59,254,281,282] have noted that ponderosa pine establishment in the Southwest tends to occur in pulses, during periods of relatively cooler, wetter climate conditions, but the current rate of establishment appears unprecedented. Mast and others [211] found that rate of interior ponderosa pine seedling establishment varied 8-fold over the 3 centuries prior to fire exclusion; however, presettlement variability in seedling establishment was dwarfed by a 2-orders-of-magnitude increase in seedling establishment in the early 20th century compared to presettlement rates of interior ponderosa pine establishment. Brown and others [59] suggest that these pulses of dense tree establishment and rapid growth result in ladder fuels that increase the severity of the next fire. Growth and mortality: | Interior Ponderosa Pine Biomass allocation shifts as trees mature. As seedlings, ponderosa pine allocates relatively more biomass to roots compared to stems and leaves. Saplings tend to allocate relatively more of their biomass to foliage, and pole-sized trees allocate more biomass to woody tissue [130]. Open-grown interior ponderosa pine generally gain height rapidly in the sapling and pole stages [170], and mortality rates tend to level off at maturity. Knowles and Grant [182] found that interior ponderosa pine on the Colorado Front Range showed a sharp drop in mortality at age 115. The oldest trees sampled were 300+ years old. Minor [217] developed site index curves for interior ponderosa pine in the Southwest. Dendrochronological and basal area analyses of trees in central Colorado showed that interior ponderosa pine growth was positively correlated with presence of Gambel oak and negatively correlated with presence of other interior ponderosa pine (r > 0.93). The authors [40] attributed increased growth of interior ponderosa pine associated with Gambel oak to better soil nutrient status conferred by oak litter and/or increased density of interior ponderosa pine facilitated by Gambel oak nurse trees. Klemmedson [181] also noted the benefit of Gambel oak litter to soil nutrient status and interior ponderosa pine growth. SITE CHARACTERISTICS:Interior ponderosa pine occupies relatively dry, nutrient-poor sites compared to other montane conifers but shows wide ecological amplitude throughout its distribution. Interior ponderosa pine in the Sangre de Cristo Mountains of Colorado is associated with dry sites. Detrended correspondence analysis determined that of 5 co-occurring tree species, only limber pine occurred on sites that were subject to more solar radiation, and had higher soil pH, than interior ponderosa pine [10]. In contrast, interior ponderosa pine in southeastern Arizona occurs on relatively moist sites that are higher in elevation than the habitats of most southwestern pine species [33]. Climate: | Interior Ponderosa Pine Temperature regimens do not vary greatly across ponderosa pine's range: Pearson [230] found only a 2 oFahrenheit difference in mean annual temperature among ponderosa pine sites in Arizona, the Black Hills, Washington, and California. Length of frost-free period in interior ponderosa pine sites depends upon latitude and elevation. In much of its northern range, the frost-free period averages about 120 days. In the extreme Southwest, the frost-free period may lengthen to 240 days [67]. A common climatic factor occurs across interior ponderosa pine's geographical range: Interior ponderosa pine grows on sites too dry to support other timber species. Although the drought season occurs at different times in different regions, periodic prolonged drought is characteristic across interior ponderosa pine's range and limits its expansion into drier types [31,67]. Overall, annual precipitation ranges from 15 to 20 inches (380-510 mm) per year. In low-elevation interior ponderosa pine at desert edges, mean precipitation is as low as 9 inches (230 mm) per year. In mixed-conifer forests at moderate elevations, mean annual precipitation may exceed 25 inches (640 mm) [31]. Climate grades from dry continental interior in the north, to subhumid in south-central Wyoming, to semi-arid in the Southwest and the plains grassland-interior ponderosa pine woodland interface [31,82]. Climate is most favorable for regeneration in the Black Hills, where the wettest months are May and June and summer rains are frequent [31,66]. The Medicine Bow Range of Wyoming, which averages 25 inches (640 mm) annual precipitation, is the wettest portion of interior ponderosa pine's range. Precipitation on the east slope of the Medicine Bow ranges between 12 and 20 inches (300-510 mm), with 2/3rds received from April through September [82]. Transplant studies and abundant natural regeneration under fire exclusion suggest that climate is not limiting for interior ponderosa pine establishment on many plains grassland sites [132]. Climate in the Southwest has a distinct bimodal pattern of winter and summer precipitation. May and June, the wettest months in the northern portion of interior ponderosa pine's range, are the driest months in Arizona and New Mexico [66,82]. Mean annual precipitation in interior ponderosa pine communities in western Texas is 16 to 20 inches (400-510 mm) [264]. Soils: | Interior Ponderosa Pine Interior ponderosa pine occurs widely on igneous and sedimentary parent materials including basalt, volcanic cinder, limestone, and sandstone soils. Textures include clayey and silty loams, sandy loams, gravels, and cobbles [26,66,136,264]. Steep slopes with restricted soil profile development may support at least some interior ponderosa pine [66]. Degree of slope varies and can be steep: sites in the Santa Catalina Mountains of southeastern Arizona ranged from 10 to 36o [95]. Elevation: | Interior Ponderosa Pine Interior ponderosa pine occupies a narrower, often higher elevational range than Pacific ponderosa pine. It is most common from 6,000 to 8,500 feet (1800-2600 m) [31,82]. Elevation by state is:
SUCCESSIONAL STATUS:Interior ponderosa pine is mostly a seral species. It is highly light and drought tolerant, and is usually the 1st conifer to establish on disturbed sites [170]. Lundquist [202] identified fire as the primary force setting back succession in interior ponderosa pine/grassland communities in the Black Hills of South Dakota. Shallow soils that promote tree fall, tree harvest, Armillaria infection, cattle grazing, and storm damage were other major factors setting back succession [213,242]. Catastrophic winds and mountain pine beetle outbreaks have also been identified as stand-initiating events in interior ponderosa pine forests [203]. One or a combination of these events creates growing space for seedlings. Lundquist and Negron [203] predict that interior ponderosa pine seedling establishment stops about 70 years after a stand-replacing event due to canopy closure. Even spacing of mature trees in this "stem exclusion stage" is maintained by frequent, low-severity surface fires. Fine-scale succession occurs in canopy gaps created by death of a group of mature interior ponderosa pine. On most sites, more shade-tolerant trees eventually establish beneath the interior ponderosa pine canopy without fire or other stand-initiating disturbance, although interior ponderosa pine is the climax forest on some harsh, dry sites [213,234,242]. Interior ponderosa pine may be completely replaced by later-successional conifers such as Rocky Mountain Douglas-fir, fir (Abies spp.), and spruce (Picea spp.) after several decades without disturbance. Multistoried stands of interior ponderosa pine have increased as a result of fire exclusion. They are typically structured with seedlings, saplings, and small poles of interior ponderosa pine and later-successional, shade-tolerant conifers, clustered around widely scattered mature interior ponderosa pine. In later stages of succession, the clumps merge to form continuous stands of irregular structure [7]. Interior ponderosa pine is moderately shade tolerant. It tolerates shade better than quaking aspen, whitebark pine, and bur oak but less than western white pine, white spruce, and Rocky Mountain juniper. Unlike the first 4 species, interior ponderosa pine can establish beneath its own canopy [7,29]. On some sites, interior ponderosa pine can be a secondary colonizer in the absence of disturbance. GIS modelling of historic photographs of interior ponderosa pine-plains grassland ecotones on the Colorado Front Range shows a pattern of tree invasion into historic grassland, particularly on north slopes. Interior ponderosa pine invasion began around 1930, when effective fire exclusion began. Two strong pulses of interior ponderosa pine establishment onto grassland occurred in the 1970s and 1980s during years of above-average precipitation. Decreased livestock grazing may have also aided tree invasion into plains grassland in the 1970s and 1980s [212]. Interior ponderosa pine is typically seral to white spruce in the Black Hills of Wyoming and South Dakota. It is climax on sites that are too dry to support white spruce. Quaking aspen may dominate a site following stand-replacing fire, but interior ponderosa pine typically establishes dominance after a few postfire decades. Bur oak may dominate some low-elevation stands in the northern Black Hills and Bearlodge Mountains of eastern Wyoming. Succession to interior ponderosa pine is "very slow" on sites where oak scrub stands develop after fire or other stand-replacing events [7]. East of the Continental Divide in Montana, interior ponderosa pine is a climax species. It forms heavily stocked, uneven-aged stands in the absence of fire [17,234]. In the Missouri Breaks region of Montana, bluebunch wheatgrass-western wheatgrass grasslands succeed to interior ponderosa pine/bluebunch wheatgrass habitats in the absence of fire. Shrubland areas of the region may succeed to interior ponderosa pine/Rocky Mountain juniper without fire [102]. Succession to conifers may be slow in southern New Mexico and Arizona. Aspect strongly influences rate of succession. In the White Mountains of south-central New Mexico, interior ponderosa pine establishment began 15 to 20 years after fire on northern and eastern exposures, while 75 or more years were sometimes required for forest development after fire on southern and western slopes. Once established, however, interior ponderosa pine cover was generally higher on drier slopes than on north-facing slopes [133]. Moir and Dietrich [218] present successional models for interior ponderosa pine in Arizona and New Mexico, both with fire and with fire exclusion. SEASONAL DEVELOPMENT:Timing of cone development, pollination, and seed dispersal events are similar across interior ponderosa pine's range. Germination and seedling establishment differ north to south, with establishment occurring earlier in the year in more northern latitudes. Strobili of interior ponderosa pine in the Great Plains elongate in May and June [271]; late May elongation of cones is reported from northern Arizona [258]. Female cones mature in their 2nd summer [271]. Mean dates of pollination of interior ponderosa pine on the Wyoming-Colorado border were May 24th and 25th [96], while pollination occurred in mid-June in northern Arizona [258]. Seeds are dispersed in fall. They germinate in spring in the Great Basin and the North [190] and after summer rains in July and August in the Southwest [131,169,193]. Phenological development of interior ponderosa pine on the Fort Valley Experimental Forest of northern Arizona was as follows [258]:
Related categories for SPECIES: Pinus ponderosa var. scopulorum | Interior Ponderosa Pine |
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