Floristic diversity in New Mexico is the fourth highest in the nation, with 4,204 documented plant taxa (Allred, 2012). Unfortunately, over 12% of vascular plants in the state are considered at risk (Stein & Gravuer, 2008). These species face additional challenges caused by expected associated ecological changes, which are especially significant for small populations with restricted ranges, including many of the species endemic to New Mexico.
New Mexico lists 235 plant species as rare and imperiled, with 103 species that are considered globally imperiled, and 109 species that occur only in New Mexico and nowhere else in the world. New Mexico’s rare and imperiled species include 13 federally listed species, 37 plant species listed as endangered in the State of New Mexico, 35 species listed as sensitive by the Bureau of Land Management, and 75 species listed as sensitive by the Forest Service (EMNRD – Forestry Division, 2017). Due to the many documented threats to native plants in New Mexico, we are directing our attention towards proactive and effective conservation of rare and endangered plants.
Why do plant species become rare and what anthropogenic (human-caused) factors contribute to this outcome? Rare plants often face restrictions due to environmental factors such as specific substrate requirements and climatic conditions. Gypsum Townsend’s aster (Townsendia gypsophila) is an example of a narrowly distributed endemic species that only occurs on gypsum outcrops in the White Mesa area near San Ysidro, NM. Direct human induced threats to Townsendia gypsophila include gypsum mining and recreational mountain biking (Roth and Sivinski, 2015).
Some rare plants are subject to population decline due to habitat destruction caused by anthropogenic disturbances like recreation and energy development projects. Aztec gilia (Aliciella formosa), which occurs in northwestern New Mexico in San Juan County, is an example of a species with a very limited population that faces intense disturbances from off-road vehicle use and oil and gas exploration and development (New Mexico Rare Plant Technical Council, 1999).
When the unique habitats of endemic plant species are altered, sensitive species disappear more quickly because they are not adapted to survive in disturbed sites. Disturbances affect the viability of already small populations by lowering reproduction rates, decreasing pollination success, increasing competition with invasive species, and increasing predation. In some unique habitat types, you might find more than one rare plant species. Tharp’s blue-star (Amsonia tharpii), Allred’s flax (Linum allredii), Gypsum wild buckwheat (Eriogonum gypsophilum), and Gypsum milkvetch (Astragalus gypsodes), all occur in the same geographic region and habitat in Eddy County, New Mexico, south of Carlsbad. Active oil and gas development, gypsum mining, off-road vehicle use, and road and pipeline development in the gypsum hills of the Chihuahuan desert have collectively damaged the already limited habitat for these rare plant species (New Mexico Rare Plant Technical Council, 1999). The gypsum hills of southeastern New Mexico host an impressive diversity of endemic species, which we would like to protect from further habitat destruction, alteration, and fragmentation to prevent population declines.
Sometimes our knowledge of a species is limited due to the lack of funding for trend monitoring programs and baseline surveys to document abundance, distribution, status, and threats. This is demonstrated by the example of the Chihuahua scurfpea (Pediomelum pentaphyllum), which is endemic to southwestern New Mexico and southeastern Arizona. When this species was petitioned for federal listing in 2007 only two populations were known, but since then the BLM has conducted intensive status surveys and documented four additional populations, some of which include thousands of individuals. Although still rare, Chihuahua scurfpea is evidently more widespread than we previously thought. We are starting to better understand its ecology and distribution, and are instituting safeguards to minimize our impacts on scurfpeas. With a greater understanding of rare plants and their associated threats, we can be more effective conservationists and potentially prevent federal listings under the Endangered Species Act. The BLM is launching a seasonal field crew in summer 2017 to set up long term population trend monitoring sites for a select group of rare plants in New Mexico to better understand population dynamics through time and the potential impacts of threats. This information can then be utilized to make informed management decisions and provide protection for these rare species.
These examples of rare and endangered plants shed light on the tentative existence of imperiled species in New Mexico, and highlight the need for more information regarding the status of all rare plants within the State. With small populations restricted to specific habitat types and intense anthropogenic threats ranging from recreation and energy development to more widespread threats rare plants need our attention and help more than ever!