Mexico: Nuevo Leon: Restoration of Dwarf Pine (Pinus culminicola) in the Cerro El Potosi

Project Stage:
Completed

Start Date:
1997-11-01

End Date:
2001-11-01

Primary Causes of Degradation

Degradation Description

Dwarf pine (P. culminicola) was described by Andresen and Beaman (1961) as a new species endemic to Cerro El Potosı. Later the same authors described the distribution of the species as a total of 106 ha (Beaman & Andresen 1966). In 1975 the species was also found in three other sites of the same Sierra (Sierra La Marta and Sierra La Viga in the state of Coahuila, and Cerro Pena Nevada in Nuevo Leon) with similar spatial patterns and altitudinal distribution ranges to those determined for Cerro El Potosı. In 1978 wildfires at Cerro El Potosı burned 34% of the dwarf pine population. During the past four decades, a reduction of the area formerly covered by dwarf pine has been observed, due to human impact involving timber extraction, road building, and land use change for the development of telecommunication and aerial navigation infrastructure. A manganese mine was opened and later abandoned in the region. Recently (1998), several wildfires drastically reduced the area formerly covered by dwarf pine at Cerro El Potosı. Currently, only 30 ha of fragmented dwarf pine area exist at Cerro El Potosı, and these include many old trees with low seed production that are subject to cattle grazing. The species is now considered endemic and is subject to special protection. There are no studies of P. culminicola populations in the other mountains where it occurs; unfortunately these areas are not protected and are also subjected to grazing and wildfires.

Reference Ecosystem Description

Dwarf pine was first found in the summit area of Cerro Potosí in Nuevo León in 1959. This is the most extensive known population. Three or four small populations are also recorded on the high ridges about 50 km northwest of there on the Nuevo León-Coahuila border. Soils are rocky and calcareous. It grows at 2965-3700 m, the highest mean elevaton of any pine. Since its current distribution includes only the highest elevations on summits within its range, it must be regarded as severely at risk of extinction due to global warming. Existing climate parameters are not well-known due to a lack of weather stations at these summits. On Cerro Potosí the species is at its lower elevational limits as an understory shrub with Agave and grasses in an open P. hartwegii-P. ayacahuite forest. With increasing elevation and site exposure, the erect pines yield dominance to P. culminicola, and at the summit it forms extensive mats interspersed with occasional gnarled and stunted P. hartwegii. The pine mats carry fire well; with areas of up to several dozen hectares have burned in recent years on various sides of the mountain, an overall pattern apparently consistent with an hypothesis of stand replacing fire at timescales of 50 to 200 years, although this would obviously be responsive to anthropogenic ignitions, which are quite possible at this easily accessible site. Farjon and Styles (1997) report that at lower elevations, in the Sierra La Marta, Coahuila, P. culminicola grows in a scrub community with Quercus spp., Arctostaphylos, Ceanothus, Agave, and grasses; on the Cerro La Viega and the Sierra de Arteaga, Coahuila, they grow in a similar community that also includes Abies and Pseudotsuga (species not specified).

Project Goals

Fragmentation and habitat loss are the main threats to the survival of most endangered species; hence, the inclusion of dynamic processes of plant communities in restoration plans would result in lower habitat loss and fragmentation. Lesica and Allendorf (1999) argue that a primary goal of restoration is the establishment of long-term viable populations that will restore ecosystem functions and processes, prevent erosion, and protect biological diversity. In spite of the uniqueness of the species, there are few published studies of the ecology of dwarf pine. Garza et al. (2002) described a high fungal diversity (51 species of macromycetes from 19 families and 42 genera) associated with P. culminicola. Aguirre et al. (2001) described the vegetation types of the area and examined the stem density pattern of P. culminicola and P. hartwegii and found the former to be more abundant at higher elevations. In this study we tested restoration techniques for P. culminicola, through replanting and the use of herbivore exclosures in the protected natural area Cerro El Potosı, within its natural distribution range.

Monitoring

The project does not have a monitoring plan.

Stakeholders

Given the protected status of the Cerro El Potosi the habitat of Dwarf pine is protected by Mexican law. The researchers in this case were evaluating the effects of grazing on the reproduction of the species, and the limited range of the species and the continuation of grazing in these high altitude prairie habitats make the involvement of local ranchers critical to the species’ continued survival. The researchers found that free range grazing decimated the endemic reproduction as well as the restoration efforts, indicating that restoration efforts required management plans to address grazing in these habitats.

Description of Project Activities:
The experiment was laid out in December 1997 at three elevations and vegetation types: (1) high elevation at 3,500 m in Pinus culminicola matorral, (2) intermediate elevation at 3,400 m in P. culminicola - P. hartwegii forest, and (3) lower elevation at 3,300 m in P. hartwegii - P. culminicola forest. At each elevation three square plots of 625 m2 were established for planting 2-year-old dwarf pine seedlings that had been grown in a seedling nursery. Three treatments were made for each plot: (1) small mammal plus cattle exclusion (chicken wire), (2) cattle exclusion (barbed wire), and (3) free range. For each treatment at each elevation, 110 seedlings were planted at a density of approximately 2 seedlings in each 10 square meters. At the time of planting, seedlings were approximately 100 mm tall and 5 mm in stem diameter.

Ecological Outcomes Achieved

Eliminate existing threats to the ecosystem:
Both elevation and exclosure were found to have an effect on seedling survival for the duration of the experiment. Seedling mortality was high in all treatments, with only about 50% of seedlings surviving 4 years after planting in the areas excluded for cattle and small mammals. Seedling survival was significantly higher in areas excluded from both cattle and small vertebrates than in areas with cattle exclosures only. Survival was much lower where no exclosure was used. Many seedlings in the free-range treatment were grazed and trampled, although this did not happen uniformly to all seedlings. This implies that grazing is low and erratic in the area. However, 2 years after planting, more than 80% of seedlings had died at the highest elevation. By the fourth year after planting, no free-range seedlings had survived at any elevation. Where small mammals were not excluded, seedlings were found to be nibbled and occasionally had broken stems. This damage was also present, although rarely, in the area excluded for cattle plus small mammals, where it was attributed to the parrots that are common in the area or to small mammals that may have climbed over or burrowed under the chicken wire fence. In general, elevation did not account for differences in seedling survival; the patterns found for exclosures were consistent at all elevations. The fact that seedling survival was constant between environments suggests that seedling mortality during these first years is the result of seedling vigor rather than competition. However, in 1999 seedling mortality was consistently greater at the highest elevation where the surrounding vegetation is Pinus culminicola matorral, perhaps as a result of a very harsh winter. Mean stem diameter for all seedlings was low during 1998 (5.09 mm), 1999 (5.15 mm), and 2000 (5.66 mm), perhaps at the expense of root growth. In 2001 stem diameter increased to 8.07 mm. There were no differences in stem diameter that could be attributed to elevation or access to cattle and small mammals. Seedlings doubled their height since planting in 1997 and 2001. The increase in height was smaller during 1998 - 2000 than in 2001, perhaps as a result of early root growth. The final mean seedling height was approximately 120 mm. After 4 years in the field, plants were still very short and hence in the layer where trampling and grazing by cattle and small mammals may occur. There was a tendency for seedlings to be taller at the lowest elevation (3,300 m). Whether this is a result of better growing conditions or heavier shade remains to be tested. Seedlings excluded from small mammals also had a tendency to be taller, perhaps as a result of occasional nibbling of shoots of unprotected seedlings.

Factors limiting recovery of the ecosystem:
In addition to low density of Pinus culminicola due to habitat loss and wildfire, the study found low levels of natural and planted seedling recruitment to be a further threat to this endemic species. Naturally emerging seedlings were not detected during the 4 years of the study. It is possible that seeds were consumed by rodents, as found for other habitats, or that conditions for seedling establishment occurred in events that do not happen annually, such as masting or above-average spring rainfall. Elevation in general did not account for variations in survival, which is in agreement with distribution of the species within Cerro El Potosı as described by Aguirre et al. (2001). Seedling growth was poor during the 4 years, which implies that seedlings remained susceptible to grazing and trampling by cattle and small mammals. In this study we have shown that free-range cattle severely limit seedling recruitment; hence, its special protection status (Diario Oficial de la Federacion 2000) should be followed by management plans that exclude free-range cattle, and perhaps seed-consuming parrots and rodents, from restoration areas. Seedling planting is a must given that natural germination was not observed during the study. Reforestation programs in Mexico do not traditionally evaluate survival of planted seedlings or saplings. However, because the omnipresent cattle are typically not excluded, it is believed that plant mortality must be very high, and thus further studies dealing with the impact of herbivory and trampling after reforestation should be encouraged throughout Mexico. Seedling survival was poor after 4 years for seedlings protected from cattle and small mammals, and no seedlings survived after being exposed to grazing and trampling for 3 - 4 years. Mortality was similar at all sites in spite of differences in environments and plant communities present at different elevations. After 4 years, surviving seedlings were still very small and thus susceptible to trampling and grazing by both cattle and small mammals.

Socio-Economic & Community Outcomes Achieved

Key Lessons Learned

There were no naturally occurring seedlings found in this study; hence, it appears that replanting will be necessary to ensure the continued survival of this endemic species. In addition to protection of natural populations of dwarf pine from wildfires, reforestation programs that include protection for seedlings from cattle and small mammals should be implemented.

Long-Term Management

All planted seedlings were labeled so they could distinguished from any naturally established seedlings. The study monitored seedlings annually from November 1998 to November 2001. Plant survival was determined by checking the position of each planted seedling. Stem diameter and total height were measured for all surviving seedlings. To test whether grazing and elevation affected seedling survival, we used a two-way analysis of variance (ANOVA). To test whether elevation affected seedling growth in diameter and height, we used one-way ANOVA.

Sources and Amounts of Funding

unspecified The research project was supported by Fondo Mexicano para la Conservacion de la Naturaleza and Programa de Apoyo a la Investigacion Cientifica y Tecnologica from the Universidad Autonoma de Nuevo Leon.

Other Resources

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