Pinus nelsonii Shaw

Pinaceae

Occurs in the southern part of the Sierra Madre Oriental of Mexico, its main threats are cattle grazing and fire

Associated Names:

Distribution

Esatern Mexico in the States of: Coahuila (Mont. del Carmen), Nuevo León, San Luis Potosí and Tamaulipas.

Subpopulations are localised and severely fragmented.

Habitat and Ecology

Pinus nelsonii occurs in the semi-arid foothills and on mesas of the Sierra Madre Oriental; the most extensive populations are found around the Sierra Peña Nevada in Nuevo León-Tamaulipas. It is restricted to sites on rocky limestone with shallow soils. Its altitudinal range is 1600–2300(–2450) metres above sea-level. Annual precipitation ranges from 300–600 mm, falling mostly in the summer during brief thunderstorms. Associated conifers are P. cembroides, P. remota and Juniperus spp. It occurs in a scrubland zone with deciduous woody taxa, e.g. Quercus, Mahonia, Comarostaphylis, Brahea, and Sophora, and arborescent monocots, such as Yucca and Dasylirion. At higher altitudes it may grade into Pinyon-Juniper woodland, while lower down it is bounded by a hotter and drier semi-desert scrubland often dominated by Cactaceae and Yucca spp. Like several other narrow endemic conifers, P. nelsonii is probably an edaphic relict on limestone.

Human Uses

There is no commercial exploitation of this species due to its low stature and its rarity in remote and inaccessible locations. Its seeds resemble those of the true pinyon pines (Pinus subsect. Cembroides) and are edible like these, but the seed crop is usually low compared with these species. Apart from a few specimens in botanic gardens and other dendrological collections, this interesting pine is not known in horticulture.

Conservation Status

Global status

Endangered B2ab(ii,iii,iv,v)

Global rationale

Most localities / subpopulations do not cover more than 1km², so the area of occupancy (84km²) calculated here, based on 57 herbarium collections from 21 localities and using a grid of 2km wide for each locality is probably optimistic and is in reality probably smaller. With continuing decline this species meets the B-criteria for Endangered.

Global threats

Pinus nelsonii has a scattered occurrence largely limited to limestone outcrops. Its total population almost certainly numbers fewer than 10,000 mature trees, mostly in (sub)populations of a few hundred individuals. It is thought to be in decline due to habitat disturbance and loss associated with increased cattle ranging and incidence of destructive fires associated with this type of land use. Several localities with this little tree reported in the literature or with older herbarium collections have not been retraced in recent years and the subpopulations may have disappeared.

Conservation Actions

This species is in urgent need of protective measures, probably best achieved by the creation of reserves containing substantial subpopulations, and by excluding activities related to “range improvement” for cattle in such areas.