Cypress – A Rare Natural Community

By the CNPS Vegetation Science team

For the past year, the CNPS Vegetation Program has been working with volunteers to produce a fine-scale map of cypress stands throughout the state. Why the interest and focus on cypress? There are 11 species of cypress (Hesperocyparis spp.) that occur in California, seven of which have been assigned a California Rare Plant Rank of 1B (rare, threatened, or endangered in California and elsewhere). These include Santa Cruz cypress (H. abramsiana), Tecate cypress (H. forbesii), Gowen cypress (H. goveniana), Monterey cypress (H. macrocarpa), Piute cypress (H. nevadensis), pygmy cypress (H. pygmaea), and Cuyamaca cypress (H. stephensonii). Baker cypress (H. bakeri), is currently on a watch list because it is broadly but infrequently distributed throughout the state.

The rarest cypress species in the state is the Cuyamaca cypress. It is known from just four locations in San Diego County, on the southwestern slopes of Cuyamaca Peak between 1,035 and 1,705 meters in elevation. Cuyamaca cypress is restricted to gabbroic soils, a difficult place in which to grow due to high levels of iron and magnesium, as well as low levels of phosphorus and calcium.

Threats to cypress species in California include changes to the natural fire regime. Cypress are serotinous, which means that their cones do not open on their own when the seeds reach maturity. Instead, the cones remain attached to the parent tree for a year or more, and open rapidly when exposed to temperatures higher than normal. This means that seeds are stored in the tree canopy rather than in the soil, as is typical for most plant species. Because cypress are serotinous, wildfire is an important natural disturbance. The heat produced by fire opens cones, resulting in a massive release of fertile cypress seeds. Although cypress trees have thin bark and typically do not survive fire, the seeds released by fire ensure the continuation of the stand.

Human-induced changes to the natural fire regime have led to the disappearance of many cypress stands. If the interval between fires is too short, trees are unable to reach reproductive age before the next fire, often causing cypress to be replaced by adjacent vegetation types. Unfortunately, climate change is expected to increase extreme fire weather as temperatures increase and droughts become more common.

CNPS has recently recruited a new volunteer to continue a statewide mapping effort. Tiffany Edwards began volunteering with CNPS in July 2012, spending one day a week working alongside our Vegetation Program staff. Tiffany recently received her M.S. in Environmental Management from Duke University, where she studied long-term changes in plant community composition and exotic species invasion in a restored wetland. We are fortunate to have her on board!

Thanks to the hard work of our volunteers, mapping of four cypress species is nearly complete. Our next steps include verifying and finalizing our work to date, and prioritizing the next cypress species for mapping.