Калифорниялық батыс кипарисінің Санта-Круз түрі

Californian species of western cypress

The Santa Cruz cypress (Hesperocyparis abramsiana; formerly classified as Cupressus abramsiana) is a species of North American tree within the cypress family. The species is endemic to the Santa Cruz Mountains within the Santa Cruz and San Mateo counties of west central California. In 2016, the conservation status of the Santa Cruz cypress changed to Threatened. The cited reasoning was a decrease in threats against their habitat.

Individuals can grow 10 to 25 meters tall with branches 5–10 cm in diameter covering the trunk to nearly the ground. The shape of the tree is pyramidal, with branches longer toward the base. The tree’s leaves are light green and scale like and can grow up to 15mm in length, persisting on branches for many years. The bark of the trunk is fibrous with thin grey vertical stripes. Individuals begin to produce cones at 11 years in age. Pollen cones can grow up to 4mm long and produce large amounts of pollen that spread in the wind. Female seed cones are produced annually on the tree and grow up to 20 to 30mm in diameter. They remain on the tree until the supporting branches die, typically as a result of natural fires. Individuals can live beyond 100 years, with one of the oldest individuals identified as being between 127 and 162 years old.

The reproductive age of the Santa Cruz cypress is on average 11 years of age. Seed viability falls to 10 percent by the time a tree is 30 years old. and the Gymnosperm Database.

The species was named by Wolf to honor Dr LeRoy Abrams, a botanist at Stanford University. Abrams had also studied the trees with Wolf in 1937.

The habitat of the Santa Cruz cypress consists of the chaparral and closed cone pine forest communities in the Santa Cruz Mountains. The habitat ranges from 300 to 750m in elevation, consisting of poorly developed sandstone or granitic soils. The climate of this area produces cool, wet winters and hot, dry summers, and natural fire regimes periodically destroy the vegetation in the area. The Santa Cruz cypress have evolved to be dependent on these fires for reproduction. The trees are obligate seeders, meaning they do not regenerate after burning up in a fire. Instead, the seeds germinate after the fire to minimal competition. They are then able to regenerate and grow the population. If fires are too frequent, seedlings will not be able to reach reproductive age. If fires are too infrequent, the trees do not reproduce often enough to maintain population size. One exceedingly rare type, the Butano cypress, exists in only one grove, of about 10 acres. This grove was described by William Dudley in the early 1900s. However, a lengthy section of the 2016 federal report titled "Genetic introgression" (also known as introgressive hybridization) explains how the integrity of this species is also threatened by nearby horticultural plantings of a sister species, Monterey cypress, whose historically native range is nearby: on the opposite side of Monterey Bay. Hybridization is known to occur between the two endemics — as well as with a widely planted sister species native to Arizona: Arizona cypress. The ease of hybridization of cypress species in the American southwest has fostered a parallel history of taxonomic disagreements of where genus and species distinctions should apply. It thus provides a case study of neoendemism in conifers. As well, it illustrates an element of ongoing human impact — wind dispersed pollen contamination from horticultural plantings — that cannot easily be corrected to meet conservation goals.

Another major human derived threat to the species is climate change. Rising temperatures may push populations northwards, as well as further alter the fire regime. The species is also damaged by vandalism and unauthorized recreational activities. Actions like carving into bark damage the trees, encouraging infections and disease.