Sabina Lara-Cabrera

VEGETATION OF TEPHRA DEPOSITS 50 YEARS AFTER THE END OF THE ERUPTION OF THE PARICUTÍN VOLCANO, MEXICO

Abstract Volcanic eruptions offer unique opportunities for the study of successional processes. The Paricutín Volcano eruption that started in 1943 and lasted for 9 years created different conditions for primary and secondary succession. Bare areas at the time of the eruption (mainly agricultural fields) offer an opportunity to study the effect of major natural disturbances in sites previously affected by human activities. One representative area, the Mesa de Cutzato, was surveyed to determine vegetation species composition and structure 50 years after the volcanic eruption ceased. Our results showed that few species have established and that total plant cover remained low (< 10%) and is patchy. Four species dominated these patches: Eupatorium glabratum (23% relative cover), Senecio stoechadiformis (14%), Senecio salignus (12%) and Muhlenbergia minutissima (6%). These species are either early successional or disturbance-tolerant species. No late successional species, particularly tree species, were found. Our results suggested that in old agricultural fields covered by tephra, known as arenales, succession is proceeding slowly.

Salvia tonaticensis (Lamiaceae), a rare new species from Mexico

Salvia tonaticensis is described and illustrated as a new species to science. It is known from the extreme southern portion of the Estado de Mexico and northern Guerrero, Mexico. It belongs to section Polystachyae; however, unlike the species of the section hitherto known, it possesses simple, bifurcate and trifurcate multicellular hairs on the stems, abaxial leaf surface, petioles, and inflorescence rachis. The flowers are also larger than those of other species of the section, and the calyces are densely tomentose with purple or white multicellular hairs that vary from simple to dendriform. Within the section this species shows some morphological similarities to S. connivens.ResumenSe describe e ilustra como especie nueva para la ciencia a Salvia tonaticensis, conocida del extremo sur del Estado de México y norte de Guerrero. Se ubica en la sección Polystachyae; pero, se diferencia de las especies hasta ahora conocidas de esta sección por presentar pelos multicelulares simples, bifurcados y trifurcados en tallo, envés de las hojas, pecíolos y raquis de la inflorescencia, por las flores más grandes, los cálices densamente tomentosos con pelos multicelulares que varían de simples a dendríticos, de color morado o blanco. Dentro de esta sección muestra varias similitudes morfológicas con S. connivens.

Effects of organic matter added to sand deposits of volcanic origin on recruitment of seedlings.

Abstract Vegetational development in areas covered by volcanic ash from the Paricutin Volcano shows striking differences among types of plant cover at the time of the eruption. Forests affected by deposition of ash recovered soon after the eruption (1943–1952), but areas lacking vegetation at the time of the eruption today lack a closed canopy. We tested the effect of adding organic matter, straw, and a combination of organic matter and straw on recruitment of seedlings in a sand deposit formed in agricultural fields covered by ash from the Paricutin Volcano in Michoacán, Mexico. Number of seedlings varied significantly among treatments. At the end of the rainy season, plots with organic matter showed the highest number of seedlings (154 ± 20 seedlings/m2) followed by plots with organic matter and straw (82 ± 7 seedlings/m2), plots with straw (68 ± 14 seedlings/m2), and control plots (21 ± 13 seedlings/m2). In contrast, plots with organic matter and straw accumulated significantly more biomass (61.7 ± 10.8 g/m2) than organic-matter plots (14.5 ± 3.1 g/m2) or mulched plots (9.9 ± 3.1 g/m2). Clustering of experimental plots indicated that species composition of seedlings differed between plots with organic matter and straw, and plots with straw or organic matter. Our results suggest that the nature of organic matter that accumulates in soil can have a significant effect on composition of the seedling community, and support Egglers hypothesis that lack of organic matter prevents development of vegetation in sandy substrates of volcanic origin.

Altitudinal genetic variation among native Pinus patula provenances: performance in two locations, seed zone delineation and adaptation to climate change

Abstract To select the genetic source of Pinus patula Shiede and Deppe seed best adapted to different native zones for reforestation, seedlings of 12 provenances native to a selected altitudinal gradient in Oaxaca, southern Mexico, were planted on two sites at contrasting altitudes (high 3000 m above sea level (masl) and low, 2500 masl) within the species natural distribution, and tested for growth in height at age 18, 24 and 36 months. Differences among provenances and between sites showed significance (p<0.05). Seedling growth showed a climatic and altitudinal pattern, in which seedlings from populations originating in low-middle altitudes had higher growth than populations originating in high altitudes, and from the extreme low altitude limit. Results were used to delineate climatic and altitudinal seed zones for contemporary and future climate zones in the decade centered in year 2030, using the average results of six climate-emissions scenarios. The results indicate that splitting the region into four seed zones is appropriate under contemporary climate scenarios with the following altitude limits: Zone 1, from 2300 to 2500 masl; Zone 2, 2500 to 2700 masl; Zone 3, 2700 to 2900 masl and Zone 4 from 2900 to 3100 masl. The equivalence on climatic intervals was also defined for mean annual temperature, precipitation and an annual aridity index (AAI). Values of contemporary AAI occurring at a given altitude by year 2030 were determined, with results suggesting that populations should be shifted 200 to 250 m attitudinally upward, through a program of assisted migration, to realign them to the future climate for which they are adapted.