Arbutus menziesii Pursh

In western British Columbia, Washington, and Oregon, the climate best suited to Pacific madrone is characterized by mild temperatures with prolonged cloudy periods, narrow diurnal fluctuation, and limited extremes. Average January temperatures range from 2° to 8° C (36° to 46° F) and average July temperatures from 10° to 20° C (50° to 68° F). Winters generally are wet and mild, and summers cool and relatively dry with long frost-free seasons. Average annual precipitation is usually abundant, ranging from 790 to more than 3000 mm (31 to 118 in), 75 to 85 percent of which is received between October 1 and March 1, mostly as rain.

In the interior valleys and hills of the Klamath Mountains and lower west slopes of the southern Cascades, average January temperatures range from 2° to 5° C (36° to 41° F) and average July temperatures from 17° to 25° C (62° to 77° F). Average annual precipitation varies between 760 and 890 mm (30 and 35 in). The average January temperature in the heart of the Pacific madrone range in the Sierra Nevada is 5° C (41° F), and the average July temperature is 22° C (72° F). Average annual precipitation is 1730 mm (68 in).

In the Coast Ranges of California, temperatures where Pacific madrone grows average 2° to 5° C (36° to 41° F) in January and 15° to 20° C (59° to 68° F) in July. Average precipitation varies between 1140 and 1650 mm (45 and 65 in) yearly in the north to 640 to 760 mm (25 to 30 in) in the south. Some fog usually is present throughout this region.

Within the total range of this species, temperature extremes are from -21° to 46° C (-6° to 115° F) and annual rainfall from 460 to 4220 mm (18 to 166 in) (30).

Other than possible horticultural varieties, no natural varieties or hybrids are known.

Young Pacific madrone seedlings need partial shade for establishment, especially in the southern portion of their range. As trees age, the need for light increases and older trees require top light for survival. In British Columbia, the species has a low shade tolerance. An appropriate overall classification for the species is intermediate in tolerance to shade. Pacific madrone probably is more subclimax than climax in successional status.

Two- to 5-year-old madrone seedlings, growing in partial shade, showed large variation in root pattern and length. Some seedlings had a curving, twisting primary root with moderately extensive lateral development, and others had moderately twisted primary roots just below groundline that straightened and grew downward for about 23 cm (9 in).

Trees 50 to 60 years old often have a well-developed root burl from which a spreading root system develops. Some of these roots extend into organic layers near the soil surface and others slant downward. Large trees, 61 to 91 cm (24 to 36 in) in d.b.h., can produce massive root burls 122 to 152 cm (48 to 60 in) in diameter. Uprooted trees indicate a system composed of deep, spreading lateral roots.

Pacific madrone is described as providing abundant fruit almost every year (23). On a good site in the Sierra Nevada from 1958 through 1977, however, bumper seed crops were produced in 2 years, light crops in 8 years, and little or no seed in 10 years. Berry production during a light seed year for three representative trees, 23, 36, and 41 cm (9, 14, and 16 in) in breastheight diameter, ranged from 13,320 to more than 107,000 per tree and seemed to relate best to the amount of living crown (12).

Pacific madrone first produces berries at 3 to 5 years (23). In the northern Sierra Nevada, the dominant sprout in a 4-year-old clump produced 62 berries. Trees 60 to 160 years old produce heavy seed crops if healthy, but the age at which berries no longer are produced is unknown.

Freshly picked red and yellow berries from the northern Sierra Nevada were weighed and numbers of berries and seeds counted. Berries numbered 1,390 to 2,490/kg (630 to 1,130/lb), and seeds 434,310 to 705,470/kg (197,000 to 320,000/lb) (23).

Pacific madrone berries are disseminated by gravity and consumers. Because the berries are heavy, they fall directly beneath tree crowns, generally into a thick layer of tough leathery leaves. They do not bounce or roll far. Animals, however, often carry the berries farther away from tree crowns. Madrone berries are prized as food by birds, rodents, deer, and wood rats. At least five species of birds, especially the mourning dove and band-tailed pigeon, devour berries. More than 17 percent of this pigeon's November diet and 11 percent of its December diet were madrone berries. Stomach analysis of one pigeon indicated that it had eaten 111 berries - so many that it could not fly (25). In the northern Sierra Nevada, snap traps baited with a single red berry caught more white-footed deer mice than those with peanut butter and wheatflakes (12).

Germination of Pacific madrone seed is epigeal and has been described as both moderately high and fair. A test in California gave 55 percent germination after 3 months stratification at 2° to 5° C (36° to 41° F). Two other investigators recommended 3 months of stratification. A laboratory study on seed from the Sierra Nevada, however, indicated that a shorter stratification period might be adequate: seed stratified at 2° C (36° F) for 30 to 40 days with no other treatment produced 94 percent germination. Immersing seed in concentrated sulfuric acid for 1 minute before stratification also gave good results, but applying heat for 1 hour at 95° C (203° F) and then stratifying seriously impaired germination (12).

To evaluate seedling establishment under more natural conditions, germinating seeds in a laboratory were buried in unsterilized sandy loam and no fungicide was applied. Damping-off fungi killed most of the seedlings, and after 11 months, only 6 percent survived. Trials of seedlings from madrone berries in the laboratory and field also indicated high losses from damping-off fungi.

A comprehensive study in the Santa Cruz Mountains of central coastal California (20) showed that fungus attack directly killed 28 percent of madrone seedlings. An additional 22.7 percent mortality, however, was attributed to mild drought preceded by crippling from root decay fungi. Most of the remaining seedling mortality was caused by invertebrates, chiefly slugs. These pests were particularly lethal to seedlings in deep shade. None of the 276 seedlings on shady plots survived.

Losses of seedlings on sunny plots in the semi-open forest were caused mainly by fungi. Only 2 percent of the seedlings on these plots survived to August 2 of the year in which they germinated. In southwestern Oregon, all Pacific madrone seeds germinated the first year after seeds ripened. However, seedlings began to die immediately after emergence and most had died after I year. Cause of death, in descending order, was lack of soil moisture, litterfall, damping off, and invertebrates. First-year mortality was 90 to 100 percent (29).

In general, Pacific madrone seedlings are not abundant. They usually become established in disturbed areas, along road cuts, on bare mineral soil at the base of uprooted trees, or in semi-open forests. In the northern Sierra Nevada, seedlings are established mainly along partially shaded road cuts or in small shaded openings. Occasionally, they become established beneath woody shrubs or small trees in clearcuttings. In southwestern Oregon, percent survival after 3 years, although low, was higher in clearcuttings than in young and old stands (29). The most favorable seedbed for establishment seems to be bare mineral soil free from all, or nearly all, organic material. The notable lack of madrone seedlings beneath madrone trees could be the result of toxic metabolites being formed as an end product of the interaction among fungi, duff moisture content, and invertebrates. Water-soluble leachates from senescent leaves of madrone have been demonstrated to inhibit germination and lower growth of Douglas-fir seedlings in the laboratory (3,31), a finding not substantiated in the field (17,31).

Early growth of Pacific madrone seedlings is slow. In the Santa Cruz Mountains, shoot and root elongation of 6-month-old seedlings in the sunny environment was 4 cm (2 in) for shoots and 10 cm (4 in) for roots; in the shady environment, 3 cm (1 in) for shoots and 4 cm (2 in) for roots. Two-year-old seedlings in the Sierra Nevada averaged 9 cm (3.5 in) tall.

Death of madrone seedlings from transplanting has been described as distressingly high, but ease of propagation from cuttings as fair.

Pacific madrone reproduces mainly by sprouting. Sprouts arise from dormant buds formed at or just above the root collar and tend to be numerous. More than 300 sprouts were counted on a single low 10-inch-diameter Pacific madrone stump in the northern Sierra Nevada.

Low stumps generally produce more sprouts than high stumps. High stumps sometimes support undesirable stool sprouts that form on the edge of the cut surface or, less commonly, on the vertical portion of the stump between the ground and the top. Stool sprouts tend to become infected with heart rot at an early age and are more susceptible, to dieback and death than sprouts from the root crown. Stool sprouts that survive seem to grow well, but their longevity is unknown.

Pacific madrone sprouts grow rapidly. On a site of medium quality in the Klamath Mountains, 3-yearold sprout clumps averaged 13 members per clump, 3.1 in (10 ft) in height, and 2.3 in (7.6 ft) in width (22). In the northern Sierra Nevada on a good site, the annual enlargement of sprout clumps was measured in both a clearcut and a shelterwood. After 10 years, sprouts were taller, 6.7 vs 3.0 in (22 vs 10 ft); wider, 3.1 vs 2.1 in (10.1 vs 7.0 ft); contained more sprouts (15 vs 7); and possessed more volume, 52.1 vs 19.8 cm³ (1,840 vs 700 ft³) (12). In both locations, annual growth of 1.5 in (5 ft) on 2- to 5-year-old sprouts was observed for particularly vigorous members of a clump. Seven years after cutting and burning in southwest Oregon, dense stands of madrone sprout clumps spaced 2.7 by 2.7 in (9 by 9 ft) had a basal area of about 22 m²/ha (96 ft²/acre), 84 percent cover, and an above-ground biomass of 25,000 kg/ha (22,500 lb/acre) (9). This rapid early growth, both in height and crown width, allows Pacific madrone to dominate conifer and shrub associates for many years. It also means that understory species of grasses, forbs, and shrubs are quickly excluded from madrone sprout stands following disturbance (9), in spite of a leaf canopy that is more open than that of tanoak and giant chinkapin (Castanopsis chrysophyl1a) (16).

New information is available for forecasting site occupancy of Pacific madrone for up to 6 years after disturbance. It includes equations that relate width and area of sprout clumps originating from trees greater than 1 inch d.b.h. to size of parent stem and time since cutting (28), and equations that predict potential leaf area and biomass by parent tree diameter class (7).

Ericaceae -- Heath family

Philip M. McDonald and John C. Tappeiner, II

Pacific madrone (Arbutus menziesii) is one of the most widely distributed tree species native to the Pacific coast. Named for its discoverer, Archibald Menzies, a 19th century Scottish physician and naturalist, the species is called arbutus in Canada, and madrone, madroñia, or madroño in the United States. The latter name is ascribed to Father Juan Crespi, chronicler of the 1769 Portola expedition.

Although examples of fine furniture and attractive veneer from madrone are common, utilization is far below potential and management is almost nil.