The MacNab Cypress (Hesperocyparis macnabiana), also known as Shasta Cypress, is a striking evergreen conifer native to northern California, valued for its compact size, aromatic foliage, and ecological role in fire-prone landscapes. With its dense, gray-green sprays and rugged charm, this tree thrives in harsh, rocky soils, often on serpentine substrates, making it a resilient choice for xeriscaping and native plant gardens.
Its cultural and ecological significance, combined with its adaptability, has earned it a place in both natural and cultivated settings. In this detailed guide, we explore the botanical classification, origin, identifying characteristics, habitat, distribution, USDA hardiness zones, uses, and fascinating facts about the MacNab Cypress, offering insights for gardeners, ecologists, and conifer enthusiasts.
Botanical Classification, Origin and Native Area
The MacNab Cypress, scientifically named Hesperocyparis macnabiana, belongs to the Cupressaceae family, which includes cypresses, junipers, and cedars. It is classified within the genus Hesperocyparis, a group of New World cypresses, distinct from the Old World Cupressus genus, following a 2009 taxonomic revision by Jim A. Bartel based on genetic evidence.
The species name macnabiana honors James McNab (1810–1878), a Scottish horticulturist and curator of the Edinburgh Botanic Garden. Synonyms include Cupressus macnabiana, Callitropsis macnabiana, and Neocupressus macnabiana, reflecting past taxonomic debates. As a gymnosperm, it produces cones rather than flowers, and it occasionally hybridizes naturally with Sargent Cypress (Hesperocyparis sargentii), producing unique offspring in overlapping ranges. No infrataxa are recognized, and its distinct flattened sprays set it apart from other California cypresses.
The MacNab Cypress is endemic to northern California, with a history rooted in the region’s rugged landscapes. Described in 1855 by Scottish naturalist Andrew Murray, it was named after James McNab at the suggestion of Murray’s brother, based on specimens collected by A.F. Beardsley. The tree likely evolved in California’s fire-adapted ecosystems, where its serotinous cones rely on heat to release seeds, a trait honed over millennia.
Indigenous peoples of northern California, such as the Pomo and Wintu, may have used its durable wood for tools or fuel, though specific cultural uses are less documented than for other cypresses. Its native range, confined to California’s inner North Coast Ranges and Sierra Nevada foothills, reflects its adaptation to the region’s Mediterranean climate and challenging soils, particularly ultramafic serpentine.
Identifying Characteristics
The MacNab Cypress is a small to medium-sized evergreen shrub or tree, typically growing 3–12 meters (9.8–39.4 feet) tall, rarely reaching 17 meters (56 feet), with a spreading crown often broader than tall. Its foliage is arranged in dense, short, flat sprays—a unique trait among California cypresses—bright glaucous gray-green, with a strong spicy-resinous scent. The scale-like leaves, 1–2 mm long, have an acute tip and a conspicuous white resin gland, while juvenile seedlings produce needle-like leaves up to 10 mm long.
The bark is rough, furrowed, and fibrous, transitioning from reddish-brown to gray with age. The tree produces globose seed cones, 1.5–2.5 cm in diameter, brown or gray, with 3–4 pairs of scales featuring erect, conic umbos (2–4 mm). Pollen cones are small (2–3 mm), with 3–5 pollen sacs, and seeds are 2–5 mm, light to medium brown, sometimes slightly glaucous. Its lacy, flattened branchlets and compact form make it visually distinct.
Habitat
The MacNab Cypress thrives in dry, open slopes and ridges, often on serpentine or volcanic substrates, in chaparral, oak woodlands, and coniferous woodlands at elevations of 300–850 meters (980–2,790 feet). It prefers well-drained, sterile soils derived from basalt, conglomerate, gabbro, greenstone, or serpentine, which are low in nutrients and high in heavy metals, limiting competition.
The tree requires full sun and is adapted to California’s Mediterranean climate, with wet winters and dry summers. It is fire-dependent, with serotinous cones that open after heat exposure, releasing seeds onto bare mineral soil for optimal germination. Seedling mortality is high in shaded, litter-heavy sites due to damping-off fungi, favoring open, post-fire environments. In cultivation, it adapts to xeriscapes and native plant gardens, provided drainage is excellent and summer watering is minimal.
Distribution
The MacNab Cypress is one of the most widely distributed native California cypresses, occurring in over 30 scattered groves across northern California’s inner North Coast Ranges, Sierra Nevada foothills, and Cascade Range. Its range spans counties including Sonoma, Napa, Yolo, Mendocino, Lake, Colusa, Tehama, Shasta, Butte, Nevada, Yuba, and Amador, with two small populations in southwest Oregon.
Notable locations include Aukum in Amador County, Grass Valley in Nevada County, and Hough Springs in Lake County, though some historical sites, like Whiskeytown, are now submerged under reservoirs. It is a component of the northern interior cypress forest, often growing with Sargent Cypress (Hesperocyparis sargentii), knobcone pine (Pinus attenuata), and manzanita (Arctostaphylos viscida). Its distribution is limited by its specific soil and fire regime requirements, and it is not known to naturalize outside its native range.
USDA Hardiness Zones
The MacNab Cypress thrives in USDA Hardiness Zones 7–8, tolerating minimum temperatures between -17.8°C and -6.7°C (0°F to 20°F). It is well-suited to California’s Mediterranean climate, with cool, wet winters and hot, dry summers, but can adapt to similar temperate climates with proper care. In Zone 7, young trees may need protection from extreme cold or drying winds, while in Zone 8, they flourish with minimal intervention.
Its drought tolerance and ability to grow on poor soils make it suitable for low-water landscapes, though it may struggle in regions with high humidity, prolonged frost, or heavy clay soils.
Uses
The MacNab Cypress is primarily valued for its ornamental qualities, with its compact size, lacy gray-green foliage, and spicy scent making it a standout in native plant gardens, xeriscapes, and rock gardens. Its fast growth (15–40 feet) and deer resistance enhance its appeal for landscaping in dry, sunny sites.
Ecologically, it supports wildlife, with rodents and deer consuming seedlings and birds finding shelter in its dense crown. The tree’s soft, close-grained wood is durable and stable, suitable for exterior uses like joinery, shingles, and boats, as well as interior applications like molding and paneling. Its heartwood, which splits well and burns cleanly, is prized for enclosed fires, though its sparking tendency limits open-fire use.
In restoration projects, it stabilizes soils on serpentine slopes and contributes to fire-adapted ecosystems. Historically, its wood was used for fenceposts due to its durability. Its cultural significance is tied to its namesake, James McNab, and its role in California’s native flora, making it a symbol of regional biodiversity.
Fun Facts
The MacNab Cypress is brimming with intriguing facts that highlight its unique character. It is the only North American cypress with flattened branchlets forming a single-plane “spray,” unlike the bristling foliage of other Hesperocyparis species, giving it a lacy, distinctive look. Its serotinous cones, which require fire or desiccation to open, can remain closed on the tree for years, ensuring seed release after wildfires create ideal regeneration conditions.
Western gray squirrels have been observed collecting and partially eating its cones, potentially aiding seed dispersal—a rare behavior for cypresses. The largest known specimen, discovered in Aukum, California, by Frank Callahan, measures 116 cm in diameter and 13.7 meters tall, surpassing earlier records.
The tree’s association with serpentine soils, rich in toxic metals, showcases its resilience in environments where few plants survive. A severe 1943 fire at Rancho Santa Ana Botanic Garden killed all but three MacNab Cypresses, underscoring their vulnerability to crown fires. Finally, its historical presence at Whiskeytown, California, was lost to a reservoir, making surviving groves a precious link to the region’s ecological past.
Cultivation of MacNab Cypress (Hesperocyparis macnabiana)
Cultivating the MacNab Cypress (Hesperocyparis macnabiana), also known as Shasta Cypress, is an enriching endeavor for gardeners and landscapers aiming to incorporate a resilient, native California conifer into xeriscapes, rock gardens, or restoration projects. This compact evergreen, with its lacy gray-green foliage and spicy scent, thrives in harsh, dry conditions, particularly on serpentine soils, making it ideal for low-water landscapes. While relatively low-maintenance, proper care is crucial to ensure healthy growth and prevent issues like fungal diseases or fire-related setbacks.
- Climate Suitability: MacNab Cypress thrives in USDA Hardiness Zones 7–8, tolerating minimum temperatures from 0°F to 20°F (-17.8°C to -6.7°C). It prefers Mediterranean climates with cool, wet winters and hot, dry summers, similar to its northern California origins. In Zone 7, protect young trees from severe frost or drying winds to prevent foliage damage.
- Site Selection: Choose a location with full sun, receiving at least 6–8 hours of direct sunlight daily, to promote dense, vibrant foliage. The tree does not tolerate shade, which can lead to sparse growth. Ensure the site accommodates its mature size (3–12 meters tall, often wider than tall) and mimics its native open, rocky habitat.
- Soil Requirements: Plant in well-drained, sterile, or nutrient-poor soil, ideally serpentine, volcanic, or rocky (pH 6.0–7.5), reflecting its native substrates. The tree excels in low-fertility soils but is intolerant of heavy clay or waterlogged conditions, which cause root rot. Test soil drainage and avoid amending with rich organic matter to maintain its natural preferences.
- Planting Time: The optimal planting seasons are early fall or late winter to early spring, aligning with California’s wet season to aid root establishment before summer drought. Dig a hole twice as wide and as deep as the root ball, positioning the root collar at ground level. Backfill with native soil, tamp gently, and water thoroughly to settle the roots.
- Watering Needs: Water young trees sparingly (once weekly) for the first 1–2 years to establish a strong root system, keeping soil slightly moist but not wet. Once established, MacNab Cypress is highly drought-tolerant and requires minimal to no supplemental watering, except during extreme drought. Avoid overwatering to prevent fungal issues like damping-off.
- Mulching: Apply a thin (1–2 inch) layer of inorganic mulch (e.g., gravel, crushed stone) or minimal organic mulch (e.g., bark) around the base, extending to the drip line but keeping it 2 inches from the trunk. Mulch mimics its native rocky habitat, conserves moisture, and suppresses weeds. Avoid thick mulch layers, which can retain excess moisture and harm roots.
- Fertilization: Fertilize rarely, as MacNab Cypress thrives in low-nutrient soils. If growth is poor, apply a light dose of low-nitrogen, slow-release fertilizer (e.g., 5-10-10) in early spring, using a quarter of the recommended rate to avoid over-fertilization, which can weaken the tree. Mature trees typically require no supplemental feeding.
- Pruning: Prune minimally to remove dead, damaged, or crossing branches, ideally in late winter before new growth begins. Use clean, sharp shears for precise cuts. The tree’s natural spreading form requires little shaping, but light trimming can enhance structure for ornamental use. Avoid heavy pruning, as it may stress the tree and disrupt its fire-adapted growth.
- Pest and Disease Management: Monitor for pests like spider mites or cypress bark beetles, treating infestations with insecticidal soap or neem oil. The tree is susceptible to damping-off fungi in seedlings and root rot in poorly drained soils. Ensure excellent drainage, avoid overhead watering, and plant in open, sunny sites to reduce fungal risks. Fire management is critical, as crown fires can be lethal.
- Spacing: Space trees 5–10 meters apart to accommodate their mature spread (often wider than tall), ensuring adequate sunlight and air circulation to prevent fungal issues. For group plantings or restoration projects, mimic natural groves by planting 3–5 meters apart. Consider their height (3–12 meters) when planting near structures or pathways.
- Wind Protection: Young MacNab Cypresses, with shallow roots, are moderately wind-tolerant but may need support in exposed, dry sites. Stake newly planted trees for the first 1–2 years using flexible ties to allow slight trunk movement, which strengthens roots. Remove stakes once established to promote independent growth and stability.
- Winter Care: In Zone 7, protect young trees from winter burn by applying an anti-desiccant spray to foliage and ensuring soil is moist before freeze-up, as evergreens lose moisture in cold, dry conditions. Mulch lightly around the base to insulate roots. Mature trees are cold-hardy within their range and require minimal winter care, even in Mediterranean winters.
- Long-Term Growth: MacNab Cypresses grow moderately fast (0.5–1 meter per year), reaching 3–12 meters at maturity with lifespans of 100–200 years in optimal conditions. Their lacy foliage, compact form, and fire-adapted traits make them ideal for xeriscaping, native plant gardens, or ecological restoration. Regular monitoring, especially for fire and fungal risks, ensures health and ecological contributions.