This description provides characteristics that may be relevant to fire ecology, and is not meant for identification. Keys for identification are available [60,61,62,63,106].
Pacific madrone is a broadleaved, sclerophyllous, evergreen tree [1,29,40,88]. Heights range from 16 to 130 feet (5 to 40 m) [13,62,101,138], with diameters up to 2 to 3 feet (0.6-1 m) [7,63]. Single or multiple curved trunks support a broad, spreading crown composed of heavy, irregularly-shaped limbs [13]. The bark is freely exfoliating, peeling off in large, thin scales. Once the outer bark is shed, the remaining bark has a smooth, polished appearance and a distinctive reddish color [13,101,111,138]. Color of young bark varies widely but darkens to a deep red with age; younger stems may range from green to chartreuse, while young trunks are frequently orange. Older portions of the bark become dark, brownish-red in color and are fissured [13,62,101]. The glossy, leathery leaves are arranged alternately on the stem [63,106].
The urn-shaped flowers are borne in showy, terminal clusters [63,91,106]. The fruit is a pea-sized berry consisting of mealy pulp and numerous seeds [13]. At the base of its stem, Pacific madrone has a woody, globe-shaped, underground regenerative organ known as a burl [65,131]. The massive, wide-spreading root system is associated with ericoid mycorrhizae [97,105]. Once established, Pacific madrone is windfirm, drought enduring, and somewhat tolerant of wet, freezing conditions [40,89].
Fire adaptations: Pacific madrone has low resistance to fire because of its thin bark [11,94]. Pacific madrone depends, however, on periodic fire to eliminate or greatly reduce the conifer overstory [14,141].
Postfire regenerative adaptations include establishment from prolific sprouts and from seed [14]. Following fires that kill aerial stems, Pacific madrone sprouts from dormant buds on the burl [40,59,94,140]. The burl also serves as a source of stored carbohydrates for the sprouts, which rapidly occupy the initial postfire environment [65,86]. Repeated top-kill by fire encourages burl development, enhancing Pacific madrone survival [14,70].
Exposed mineral soil seedbeds and light canopy densities associated with recent burns are conducive to Pacific madrone seedling establishment [14,105,132].
Fire regime: Forests where Pacific madrone occurs were historically characterized by both understory and mixed-severity fires prior to fire exclusion. Oak-Pacific madrone-Douglas-fir and redwood forests, where Pacific madrone occurs, historically experienced understory fires at intervals between 5 and 25 years. Historic fires on some sites were caused mainly by Native American burning [11,12,78]. Remote, steep areas of the redwood type were also likely associated with a mixed fire regime [11]. A redwood-Douglas-fir stand in northern coastal California had fires approximately every 50 years over the past 250 years [142]. Fire typically burned through Douglas-fir-tanoak forests in northern California at 5- to 50-year intervals, killing small saplings and occasional canopy trees. These forests now have very infrequent fires [64]. Douglas-fir-tanoak-Pacific madrone and Douglas-fir-hardwood cover types were characterized by a mixed-severity fire regime, with the former having less than 35-year fire-return intervals [11]. In Douglas-fir/hardwood forests of the Pacific Northwest, the severity of fires varied widely, with many burning at low to moderate severity prior to settlement [5].
Stuart and Stephens [130] review fire regime characteristics for Douglas-fir-tanoak forests that Pacific madrone commonly occurs in. Presettlement fire-return intervals averaged from 10 to 16 years due to the warm, dry climate of inland locations and increased lightning activity at high elevations. In the North Coast Ranges, the primary ignition source was Native Americans. There is little information available on the size and severity of fires in Douglas-fir-tanoak prior to settlement. Areas subject to Native American burning experienced low fire severity. In other areas, fire severity varied spatially and temporally across the landscape, resulting in a complex mosaic of mostly multiaged stands of varying sizes. Fires in interior sites spread more extensively than those closer to redwood forests. Surface fires were common and were intermixed with areas that supported passive and/or active crown fires. In the Six Rivers National Forest, California, surface fires are a normal occurrence in all-aged, all-sized old-growth Douglas-fir-tanoak forests. In old-growth Douglas-fir-tanoak forests, the density of understory trees and shrubs has increased since presettlement times, creating greater vertical fuel continuity and increasing the likelihood that a surface fire could burn into the crowns. In young stands that have been logged or experienced stand-altering wildfire, fire-return intervals are now longer, and greater fire severity is possible because of increased fuel loading [130].
Pacific madrone is common in redwood forests. Fire in redwood forests typically burned in the summer and early fall with variable fire-return intervals. Wetter sites in the northern portion of redwood's range had longer fire-return intervals, ranging from 125 to 500 years. Drier sites in southern locales experienced shorter fire-return intervals, between 6 and 44 years. Some stands had intervals of 1 to 2 years due to regular burning by Native Americans. From 1950 to 2003, fire-return intervals for the northern, central, and southern redwood forests for fires larger than 330 acres (134 ha) were 1,083, 717, and 551 years, respectively. On average, redwood forests experienced moderate-severity surface fires that consumed irregular patches of surface fuel and understory vegetation. Occasional passive crown fires occurred at the southern and eastern edges of its range. Throughout the north-south range of redwood forests, mean fire severities were lowest in the coolest, wettest regions and highest in the warmer, drier areas. The current increase of available fuel and increasing horizontal and vertical fuel continuity may increase the chances for higher severity fires (review by Stuart and Stephens [130]).
White fir (Abies concolor) forests in the Coast Ranges of northwestern California, in which Pacific madrone can occur, had a presettlement average fire-return interval of 27 years, with a range of 12 to 161 years. The average fire-return interval has increased to 74 years since the exclusion of fire [129].
Fire scar, tree age, and basal area distributions were used to assess fire history in 3 Douglas-fir/hardwood stands in the Klamath National Forest, California (see table below). Fire-return intervals changed little from the presettlement era to the settlement era but increased in the fire exclusion era. The upper canopy of was dominated by Douglas-fir with scattered stems of sugar pine (Pinus lambertiana). The lower canopy was dominated by tanoak, Pacific madrone, and canyon live oak [147].
Means and ranges (in years) of fire intervals for 3 Douglas-fir/hardwood sites in the Klamath National Forest, California, for 4 different time periods [147] Site Interval Mean Range Site 1 (n = 11) Complete chronology 1745-1987 22.0 5-50 Presettlement 1745-1849 17.3 5-41 Settlement 1849-1894 15.0 8-26 Exclusion 1894-1987 46.5 43-50 Site 2 (n = 19) Complete chronology 1742-1987 12.9 5-45 Presettlement 1742-1855 10.3 5-18 Settlement 1855-1901 9.2 7-12 Exclusion 1901-1987 28.7 18-45 Site 3 (n = 13) Complete chronology 1752-1987 18.1 3-71 Presettlement 1752-1849 13.9 7-25 Settlement 1849-1913 16.0 5-25 Exclusion 1913-1987 37.0 3-71The following table provides fire regime information on vegetation communities in which Pacific madrone may occur. Find further fire regime information for the plant communities in which this species may occur by entering the species name in the FEIS home page under "Find FIRE REGIMES".
Fire regime information on vegetation communities in which Pacific madrone may occur. For each community, fire regime characteristics are taken from the LANDFIRE Rapid Assessment Vegetation Models [77]. These vegetation models were developed by local experts using available literature, local data, and/or expert opinion as documented in the PDF file linked from each Potential Natural Vegetation Group listed below. Cells are blank where information is not available in the Rapid Assessment Vegetation Model. Pacific Northwest California Pacific Northwest Vegetation Community (Potential Natural Vegetation Group) Fire severity* Fire regime characteristics Percent of fires Mean intervalThe exclusion of fire from some forests may lead to a decline in Pacific madrone populations. The importance of Pacific madrone in both the understory and in the canopy in 2 old-growth Douglas-fir-tanoak forests studied in Mendocino County, California, has been declining in the absence of fire. These forests were subject to frequent fires in the past, and the exclusion of fire has allowed tanoak to become dominant and shade out Pacific madrone. In the absence of major disturbance, there is probably little recruitment of Pacific madrone in most Douglas-fir-tanoak forests [64].
Prescribed burning: Pacific madrone seedlings establish readily following logging and burning of conifer-hardwood stands [132]. Low-severity underburning may minimize Pacific madrone seedling establishment, thereby reducing the density of Pacific madrones capable of sprouting after future disturbances.
Control: McDonald and others [89] suggest that burning should not be used as a method of slash disposal in partially cut hardwood stands where Pacific madrone is managed for timber production. Instead, they recommend that logging debris be either lopped and scattered or piled [89].
Wildlife management: Burning initially increases the palatability of Pacific madrone browse; sprouts are utilized for up to 2 growing seasons after fire [33,140].In its southern range in southwestern Oregon and California, Pacific madrone is often associated with dry foothills, wooded slopes and canyons [101,122]. In California, elevations range from 300 to 4,000 feet (91-1,220 m) [122]. Pacific madrone is common above 3,900 feet (1,200 m) in the San Lucia Range of central California [49]. A common component of coastal redwood and mixed-evergreen forests, Pacific madrone reaches greatest stature and abundance on dry sites at low to moderate elevations along the east slope of the Coast Ranges and in the Siskiyou Mountains [48,108,124]. At the southernmost end of its range in the Transverse and Peninsular ranges, Pacific madrone is found from 2,000 to 3,500 feet (610-1,100 m) elevation [92].
In its northern range, Pacific madrone grows at or near sea level and inhabits mountain slopes up to 3,000 feet (915 m) [92]. Increased regional rainfall apparently allows Pacific madrone to occupy drier habitats than in mixed-evergreen forests [144]. Greatest abundance is usually attained on sites unfavorable to conifer growth [13,42]. Pacific madrone is widespread west of the Cascade Range in Oregon and Washington and is associated with relatively hot, dry lowland sites within coast Douglas-fir and western hemlock forests [43,148]. Pacific madrone communities on Sucia Island, Washington, are located on south-facing ridges where winds are moderate, temperatures somewhat high, and soil moisture low. These sites are protected from extreme wind by windward ridges, but abundant solar radiation strikes the slopes [39]. On the Willamette, Mt Hood, and Siuslaw National Forests of western Oregon, Pacific madrone inhabits dry sites on ridgetops and south-facing slopes up to 5,000 feet (1,500 m) in elevation [138]. Towards the northern edge of its distribution in southern British Columbia and northwestern Washington, Pacific madrone is generally restricted to areas along the immediate coast [43]. The only broadleaved evergreen tree native to Canada [63,74], Pacific madrone rarely extends inland more than 5 miles (8 km) in southern British Columbia [43,63,74]. Sites consist of rocky bluffs along the seacoast; elevations do not exceed 1,000 feet (300 m) [54,63].
Soils: Pacific madrone grows on a variety of soil types, and tree health varies with soil type [2]. Pacific madrone is most abundant on rocky sites, such as bluffs, that are "somewhat excessively" drained [2,13]. Soils supporting Pacific madrone usually exhibit low moisture content throughout most of the summer. Pacific madrone grows on glacial tills or shallow rocky soils in the northern portion of its range. Soils may also be fine textured, ranging from loam to clay loam. Towards the southern end of its distribution, soils are often derived from granite, quartz diorite, sandstone, or shale [40].
Climate: Pacific madrone is restricted to areas having mild oceanic winters; however, temperature and moisture regimes vary considerably throughout its range. Annual precipitation may range from 15 to 166 inches (380-4,220 mm), mostly as rain. Temperature extremes are from -6 to 115 °F (-21 to 46 °>C) [13,40,92,135].
Pacific madrone is drought tolerant [99] and has low tolerance to frost. It can be damaged or even killed if it endures long periods of frost or severe frost (<14 °F (-10 °C)) [74].
Pacific madrone is an important component of cavity-nesting bird habitat in Douglas-fir forests of northwestern California [108,109]. Large Pacific madrone trees are susceptible to heart rot, making them desirable for cavity-nesting birds [36].
Pacific madrone typically grows with mixtures of evergreen and deciduous hardwood species. Mixed stands are highly diverse in structure and composition and provide habitat for numerous wildlife species [89,108].
Palatability/nutritional value: Palatability of Pacific madrone foliage ranks from low to moderately high, depending on conditions. The mature leaves are almost always neglected by browsing animals, whereas the young leafy sprouts are eaten by big game, domestic sheep and goats, deer, and occasionally cattle, when there is a shortage of more palatable vegetation [33,53,113,122]. Pacific madrone leaves provide forage for the dusky-footed woodrat [24]. Cattle and deer browse the seedlings [145]. In California, the Columbian black-tailed and California mule deer browse twigs and foliage [81,116]. Pacific madrone is given a browse rating of fair to useless for mule deer, poor to useless for cattle, domestic sheep and goats, and useless to horses in California [122].
In British Columbia, Pacific madrone is a high-importance winter forage plant for Sitka black-tailed deer, of moderate importance for Roosevelt elk, and of low importance for white-tailed deer, mountain goats, bighorn sheep, Rocky Mountain elk, moose, and caribou [17]. Leaves are eaten by Columbian black-tailed deer on Vancouver Island, British Columbia; on rock-bluff communities where Pacific madrone is abundant, it is a major food species during the winter [30].
Pacific madrone berries are an important food for deer, birds, and other small mammals because they are produced in large quantities and may persist on the tree in winter, when alternative food sources are limited [33,58,122]. The berries are an important food for the dark-eyed junco, fox sparrow, varied thrush, band-tailed pigeon, quail, and long-tailed chat [13,52,81,125].
Cover value: Mixed stands of hardwoods and conifers in which Pacific madrone occurs provide thermal, hiding, and escape cover for big game and small mammals, and perching sites for a variety of bird species [24,89,118]. Both open-nesting and cavity-nesting birds utilize Pacific madrone. Preliminary research on cavity-nesting species within mixed-evergreen forests in northwestern California indicates that Pacific madrone is selected as a nest tree at a higher rate than its availability would suggest. Trees greater than 12 inches (30 cm) in DBH are an important habitat component for primary cavity-nesting species such as the red-breasted sapsucker and hairy woodpecker [108]. Secondary cavity nesters such as the acorn woodpecker, downy woodpecker, mountain chickadee, house wren, and western bluebird also use Pacific madrone.
A review indicates that Pacific madrone is a major component of Douglas-fir-tanoak
(Pseudotsuga menziesii-Lithocarpus densiflorus)-Pacific madrone forests.
These forests are characterized by an
overstory of Douglas-fir with tanoak and Pacific madrone sharing the secondary
canopy in varying proportions. Pacific madrone is a minor component in a variety
of cover types, commonly intermingling with redwood (Sequoia sempervirens),
western hemlock (Tsuga heterophylla), Oregon white oak (Quercus
garryana var. garryana), and Pacific ponderosa pine (Pinus
ponderosa var. ponderosa) throughout its distribution [92].
In British Columbia, Pacific madrone grows with lodgepole pine (Pinus contorta) [73].
The open woodlands of the San Juan Islands are characterized by Douglas-fir and
Pacific madrone in a fescue (Festuca spp.) matrix. Other tree species that may be found on such
sites include Rocky Mountain juniper (Juniperus scopulorum), lodgepole pine, and
Oregon white oak [43].
Pacific madrone is a dominant species in the following vegetation types.
coast live oak (Q. agrifolia)-Pacific madrone/California
hazelnut-blackberry (Corylus cornuta var. californica-Rubus spp.)
interior live oak (Q. wislizenii)-Pacific madrone/poison-oak (Toxicodendron diversilobum)
California black oak (Q. kelloggii)-Pacific madrone-coast live oak [8]
Pacific madrone-Oregon white oak
Pacific madrone-tanoak [104]
Douglas-fir-tanoak-Pacific madrone Society of American Foresters cover type [123]
western hemlock-Douglas-fir-Pacific madrone [137]
Douglas-fir-Pacific madrone/pink honeysuckle (Lonicera hispidula) [25]
Douglas-fir-Pacific madrone/American vetch (Vicia americana)
Douglas-fir-Pacific madrone/salal (Gaultheria shallon)
Pacific madrone-lodgepole pine/salal[39]
Pacific madrone can reduce conifer growth on previously logged or burned sites and is often
considered an undesired competitor [47,48,70,95,107]. The sprouts can reach up to
12 feet (3.7 m) in 3 growing seasons and are capable of creating dense brushfields,
hindering conifer establishment [47,48,70]. Control of Pacific madrone is often
needed to promote growth of more
"valuable" trees such as Douglas-fir [70]. Herbicide
applications are a commonly used method to set back Pacific madrone sprouting.
Young sprouts are susceptible 2,4-D [28,47,48,70]. Cut-surface applications
of herbicides gave acceptable control for 10 years following
application. Ten years after treatment, the
Douglas-fir site not receiving herbicide control had a mean basal area of 7.2 cm². Basal growth
of Douglas-fir receiving the benefit of overstory control increased between 260% and 451%,
depending on the herbicide used [107]. The number of postharvest sprouts
of Pacific madrone can be reduced by choosing what season cutting
is done. More sprouts appeared after April cutting than
February or July cutting. At times, Pacific madrone control may be needed to increase forage production [70].
In the past, leaching from Pacific madrone litter was thought to be allelopathic.
In a study by Rose and others [117], root growth of Douglas-fir seedlings was
not inhibited by Pacific madrone litter [117]. Excellent natural regeneration of
Douglas-fir often occurs under Pacific madrone canopies, as noted by Minore [98],
but the effects of Pacific madrone duff on Douglas-fir regeneration
are not clear. There were no significant differences in conifer regeneration, growth, or cover
of associated species among seedbeds of Pacific madrone duff, conifer
duff, or mineral soil during 10 growing seasons. If Pacific madrone litter does affect Douglas-fir regeneration, it
is because of other influences [98], possibly the reduction in mycorrhizal tips on
Douglas-fir seedling roots [117].
Disease:
Pacific madrone has low resistance to disease and is
host to many pathogens that may lead to tree mortality. Pacific madrone can suffer from
foliar diseases caused by a variety of fungal species
and is susceptible to heart rot, butt rot, and stem cankers [3]. A fungal leaf blister disease caused by
Exobasidium vacinii occurs on
Pacific madrone leaves. This disease is not thought to significantly reduce tree growth, but
it does reduce the aesthetic value of the tree. Phytophthora cactorum is a lethal
canker disease of Pacific madrone that results in root and butt rots [23,136].
All ages and sizes of Pacific madrone are susceptible to dieback and mortality from
Arbutus canker, a disease caused by the fungus Nattrassia mangiferae. The fungus infects the phloem and
vascular cambium and causes shoot blight. Greater
weakening of the trees through defoliation is caused by a secondary opportunistic
pathogen, Fusicoccum aesculi, which
causes dieback and gives the limbs and twigs a burned appearance. The branches and
terminal buds that are killed by fungi are unable to produce more foliage.
The tree does sprout from dormant buds on the burl and grows new shoots,
which are often killed by N. mangiferae [36].
Pacific madrone is affected by Sudden Oak Death (Phytophthora ramorum). Sudden Oak
Death causes a variety of foliar and branch symptoms,
significant dieback, and mortality [41,45,46,102,114,115].
The madrone canker (Botryosphaeria dothidea) greatly reduces seed
production and causes dieback and death of Pacific madrone [91,92].
Annosus root rot can cause mortality to Pacific madrone [22].
For an extensive list on the fungal pathogens that effect Pacific madrone, see
Elliott [35].
Many Pacific madrones were sampled
around the Seattle/Puget Sound area to gauge the effect of urban development and disturbance
and whether they facilitated disease transmission and tree demise. Thinning stands, soil loss
and compaction, and a host of urban impacts increased susceptibility to disease.
Dense stands of Pacific madrone were less infected, and it was predicted that an
increase in the proportion of seriously diseased trees would occur if forest stands
were broken up [3].
Other Threats:
Scotch broom (Cytisus scoparius) and gorse (Ulex europaeus) are invasive, nonnative plant
species that compete with native forest vegetation
for space, nutrients, and water. They are a threat to the sustainability of
Canada's rarest forest ecosystem, the Oregon white oak-Pacific madrone ecosystem on southeastern
Vancouver Island and the southern Gulf Islands [75].
Despite its regular shedding of both bark and leaves, Pacific madrone is a highly ornamental species, prized for its crooked beauty, colorful bark, showy flowers, and brightly colored fruits [33,40]. Trees are cultivated for landscaping in both the United States and Europe [91,140]. Pacific madrone is a well-known bee plant [13,33]. Past commercial uses of Pacific madrone included utilization of the bark for tanning leathers and the wood for making charcoal for gunpowder [91,140].
Historically, West Coast tribes ate Pacific madrone berries and fashioned eating utensils from the bulbous roots [13,56]. The leaves have been reported to possess medicinal properties [33]. Fruit of Pacific madrone can be eaten raw, boiled, or steamed. Berries can be stored for a long time if boiled and dried [53].
Sprout growth from top-killed trees is the primary mode of reproduction following fire [90]. Following fires that kill aerial stems, Pacific madrone initiates rapid postfire recovery by sprouting from adventitious buds located on the burl [1,10,21,25,44,65,90,131]. Seedlings on the forest floor are either killed or put forth a few sprouts from a rudimentary burl. Many seedlings die because the growth rate of sprouts from top-killed trees is much greater, and the sprouts overtop the seedlings.
Fire favors Pacific madrone seedling establishment. Mineral soil provides a favorable seedbed, and lower canopy densities of the initial postfire environment are conducive to the successful establishment and growth of seedlings [105,132]. Availability of seed from crowns depends on fire severity [40]. Any seeds stored in the soil seed bank are likely killed due to their sensitivity to heat [1]. Off-site seed is also dispersed into burns by mammals and birds [40].
Pacific madrone regenerates sexually and asexually [37,69]; however, it primarily reproduces vegetatively by sprouting, not by seed [82].
McDonald and Tappeiner [90] describe 3 reproductive modes relative to Pacific madrone: seedlings, seedling-sprouts, and root-crown sprouts. Seedlings originate from seed and their tops have never died back to the ground. Seedling-sprouts also originate from seed, but their tops are less than 2 inches (5.1 cm) in diameter at the ground line, and they have died back and sprouted at least once. The chances of Pacific madrone becoming a seedling-sprout are low, and seedling-sprouts rarely occur in shade environments. Root-crown sprouts originate from burls on top-killed trees more than 2 inches (5.1 cm) in diameter at ground line [90].
Pollination: Pacific madrone is pollinated by bees [13,18,51]. Hummingbirds have been observed feeding on Pacific madrone blossoms and may also pollinate the flowers [51].
Breeding system: Pacific madrone has low genetic diversity in British Columbia and is known for multilocus outcrossing [18].
Seed production: The age at which Pacific madrone seedlings first produce fruit is not recorded in the literature. The minimum seed-bearing age for root crown sprouts is 4 years, but seed production occurs more commonly at 8 years [91]. On the Challenge Experimental Forest, California, initial flower production occurred at age 4 on a "vigorous sprout", resulting in 62 berries. On another sprout clump, the tallest and most vigorous sprout produced 11 flower clusters at age 8 but produced few berries. Seed count ranged from 2 to 37 seeds/berry, with an average of 20 seeds/berry [82].
A 24-year study estimating seed crops of conifer and hardwood species on a Pacific ponderosa pine site on the Challenge Experimental Forest estimated that the average number of berries on 3 Pacific madrone trees was 49,000/tree, with a range of 13,000 to 108,000/tree during a "very light" seed year. The average number of seeds/berry was 20. Over the 24-year period, Pacific madrone produced 12 seed crops. Two were categorized as "medium-heavy", and 10 were categorized as "very light" [87].
Seed dispersal: Pacific madrone seeds are dispersed largely by birds, but also by mule deer, rodents, and gravity [13,18,71,82,87].
On the Challenge Experimental Forest, berries are disseminated by a host of consumers, particularly the mourning dove and band-tailed pigeon [87].
Seed banking: McDonald [82] states that Pacific madrone has long-term seed dormancy and viability and stays viable for "scores" of years in the soil. When conditions are right (i.e., cool temperatures and adequate moisture), after-ripening is induced and dormancy is broken [82].
Germination: A cold stratification period is critical for germination of Pacific madrone seeds [58,82,91], because the seeds have strong embryo dormancy [91]. McDonald [82] identified optimal stratification requirements for Pacific madrone seeds through a series of tests including cold, light, heat, acid, and stratification. Seeds failed to germinate after stratification at freezing temperatures for 24 days, while a 24-day stratification at above-freezing temperatures (36 ± 2 °F (2.2 ± 1.1 °C)) yielded 43% germination. Light was apparently unnecessary for germination of Pacific madrone seeds. Percent sound Pacific madrone seeds that germinated after heat, acid (sulphuric acid), and stratification treatments is provided in the table below. Stratification alone and acid and stratification significantly enhanced germination over those treatments using heat (P=0.05). No stratification caused poor germination. Mold was a constant problem in all treatments and in most cases became worse with longer stratification and germination periods [82].
Percent of sound Pacific madrone seeds that germinated after 4 stratification treatments and 5 time periods [82]Stratification period (days)
Treatment Stratification Acid & stratification Heat & stratification Heat, acid, & stratification 0 not applicable 1 1 0 30 85 77 19 24 60 94 96 65 64 90 94 94 62 60 120 96 96 2 67In a laboratory study on germination, 2 Pacific madrone populations showed only slight differences in length of time required for stratification. Maleike and Hummel [79] collected seeds from a high-elevation and a sea-level source. The seeds were stratified at 39 °F (4 °C) for 0, 20, 40, 60, and 80 days. Percent germination increased with increasing time in cold stratification up to 60 days. After 60 days there was a decline in percent germination with both seed sources. Maximum germination for the sea-level seeds was reached at both 40 and 60 days. The seeds from the high-elevation seed source reached highest germination at 60 days [79].
Germination of seeds not separated from the berry was found, in a laboratory study, to be poor and intermittent. Berries were stratified in a refrigerator for 45 days and underwent subsequent germination tests. Seedlings did not readily disengage from the berry and seed coat, and there was heavy mortality from fungi. In field trials on the Challenge Experimental Forest, if the berries and seed survived long enough to germinate (i.e., not eaten by birds, rodents, etc.), many seedlings were killed by damping-off and root-rotting fungi [82]. Fungi appear to be a major problem in natural and artificial regeneration of Pacific madrone.
Seed germination is discouraged by low light intensities under a closed canopy; therefore, Pacific madrone may not reproduce satisfactorily under dense forest conditions [26].
Seedling establishment/growth: Disturbance favors seedling establishment of Pacific madrone [82,92,132]. Survival rates of artificial Pacific madrone regeneration were observed on 3 types of Douglas-fir-ponderosa pine stands in the Siskiyou Mountains of southwestern Oregon. The 3 stands were differentiated as: clearcut, 5 to 14 years old; a young conifer-hardwood stand, 50 to 80 years old; and an old conifer-hardwood stand, 150 to 220+ years old. Seeds were sown in December at each location. One lot was sown on bare mineral soil protected by a cage, and 1 lot each on unprotected plots on undisturbed forest floor and bare mineral soil. Germinants began to emerge in early March, with more than 90% of the seedlings appearing within 1 month. Fewer seedlings emerged on unprotected plots than on protected plots due to predation of seed. Seedlings began to die immediately after emergence. Average survival at the end of the 1st summer was significantly lower (P=0.05) in old stands (5%-14%) and young stands (8%-12%) than in clearcuts (32%-34%). On most plots all seedlings had died within 1 year, with 1st-year mortality ranging between 90% and 100%. Causes of seedling mortality, in order of importance, were drought, litterfall covering small seedlings during fall months, damping-off fungi, invertebrate browsers (mainly slugs) in both young and old stands, and spring and fall frost, common in the clearcuts. At the end of the 2nd year, survival ranged from less than 1% to 3% in the young and old stands and after 2 and 3 years in the clearcuts, survival ranged from 5% to 12%. In this study, success of seedlings was dependent on disturbance to the forest floor and reduced litterfall, as indicated by the higher survival in clearcut stands [132]. McDonald [82] stated that the bare mineral soil created by some silvicultural methods is conducive to seedling survival and noted little natural regeneration of Pacific madrone in an undisturbed pure hardwood stand.
Most Pacific madrone seedlings are found in partial shade on bare mineral soil [133]. On recently logged redwood stands in northern California, Pacific madrone established in open environments on relatively hot, dry sites with thin, rocky soil [142]. Seedling establishment is minor in stands with low light, heavy litterfall, damping-off fungi, and browsing invertebrates on the forest floor, all of which kill new seedlings [82,92,105,133,142]. High soil and air temperatures and frost heaving also kill Pacific madrone germinants on exposed microsites in clearcuts. Many Pacific madrone seedlings begin development in heavy organic litter in shade. The heavy organic layer inhibits the moisture-seeking root from penetrating to mineral soil, causing high mortality from fungi and drought [82].
Early growth of Pacific madrone seedlings is slow. In the Santa Cruz Mountains, California, length of 6-month-old seedlings growing in the sun was 1.6 inches (4 cm) for shoots and 4 inches (10 cm) for roots. Seedlings growing in a shady environment had shoots that were 1 inch (3 cm) and roots measuring 1.6 inches (4 cm). Two-year-old seedlings in the Sierra Nevada averaged 3.5 inches (9 cm) tall [82,92].
Vegetative regeneration: Pacific madrone sprouts from the burl after damage by cutting, fire, or disease [36,59,66,89,131]. It is unknown how early the burl develops on seedlings [90].
Pacific madrone has moderate to low shade tolerance [13,16,64,74] and is considered an early-successional hardwood after timber harvest, fire [9,19,55], and other disturbances. Pacific madrone does not generally establish in shade and is usually absent from the understory of mixed-evergreen forests. A study of a Douglas-fir-tanoak forest in Mendocino County, California, revealed no Pacific madrone recruitment in the understory. Most shaded Pacific madrone died [64].
The level of shade tolerance can vary depending on Pacific madrone's north-south range. In the southern portion of its range, Pacific madrone seedlings need partial shade for establishment. As Pacific madrone trees age, the need for light increases, and older trees require top light for survival. In British Columbia Pacific madrone has low shade tolerance [74,92], so Douglas-fir dominates over Pacific madrone in climax stages [74].
Pacific madrone is likely more often subclimax than climax in successional status [92]. Pacific madrone can be eliminated during the stem exclusion stage of succession, but it is possible for it to survive stem exclusion and persist into the old-growth stage [133]. Pacific madrone has been documented in climax forests [15,121] and is classified as a "major climax species" in the western hemlock-Douglas-fir-Pacific madrone association on the Gifford Pinchot National Forest, Washington [137].
Pacific madrone is considered a fire-dependent, seral species in redwood stands of northern coastal California [142].
