Dinámica estacional del banco de frutos del teocintle Zea diploperennis (Gramineae)

[No abstract available

Dinámica estacional del banco de frutos del teocintle Zea diploperennis (Gramineae)

[No abstract available

Seedling biomass allocation and vital rates of cloud forest tree species: Responses to light in shade house conditions

Patterns of above- and below-ground biomass allocation in seedlings of nine common cloud forest (CF) tree species of western Mexico were examined under varying controlled light conditions using artificial shade houses. We analysed the relationships between vital rates (growth and survival) and four morphological traits (SLA, biomass allocation to stems, leaves and roots). We hypothesised that these traits represent differentiation axes in the way seedlings face the heterogeneous light regime typical of the CF understorey. For all species, traits between the different light levels, i.e. allocation to leaves, roots and stems differed among light levels. Five species had the largest SLA in the lowest light levels at the end of the experiment (Citharexylum, Dendropanax, Fraxinus, Quercus and Magnolia). Juglans was the only species with a large SLA at the highest light level (377.47 cm2 g-1). In contrast, light levels did not cause any significant variation in SLA of Persea and Simplococarpon at the end of the experiment. The relative height growth rates (RHGR) of the seedlings of five species were significantly different between light levels (P < 0.05). Overall, all species grew better in the highest light levels. The RHGR of three species were correlated positively with SLA. In turn, allocation to stem, leaves and root biomass were strongly correlated with the RHGR of five species (e.g. Citharexylum, Dendropanax and Fraxinus). Survival did not vary significantly between treatments in any species, only in the case of Simplococarpon (P < 0.05) and was correlated with all morphological variables. For this species, Peto and Peto's test showed a significantly larger survival of seedlings in the highest light level. The mean responses of these species based on all traits to the controlled light variation did not differed significantly. Our results show that these species display a wide range of resource allocation patterns when exposed to the varying light conditions that may be found in the forest understorey and highlight the role of morphological traits in this variation. � 2009 Elsevier B.V. All rights reserved

Population structure and ecology of a tropical rare rhizomatous species of teosinte Zea diploperennis (Gramineae)

One of the objectives of the Sierra de Manantlán Biosphere Reserve (Jalisco, México) is the conservation in situ of the teosinte Zea diploperennis Iltis, Doebley, Guzman & Pazzi. Zea diploperennis is perennial, shade intolerant and its 1-3 m shoots are architecturally similar to maize. Clonal growth is of the phalanx type. Genets are iteroparous (modules semelparous). The demography of seven module and genet populations was studied in seven sites representing three stages of old-field succession. Seven permanent one-meter-square plots were randomly established in each site. All genets initially present and those that became established during our study were mapped and labeled according to year of establishment The magnitude of demographic fluctuations was greater in module populations. Genet population dynamics followed a seasonal rhythm with a maximum population size obtained at the onset of the rainy season. A relation was documented between percent annual mortality of a cohort and its age: the younger the cohort, the greater the mortality. This was a statistically significant relationship, Y = [sin(-0.288x + 1.657)]2 (r = 0.92, p < 0.01), where is proportion annual mortality of genets and is the age of the cohort. The maximum rates of genet mortality occurred during the rainy season when population densities were greatest. As a consequence, we postulate that competition occurs principally during the rainy season. Linear relationships were observed between rate of population increase of genets versus old-field successional stage and soil type. Those areas with poor soil (Ultisol), degraded soil or soils with similar physical characteristics could be rehabilitated by introducing Z. diploperennis. Such rehabilitation would achieve two distinct objectives, promote propagation of this rare endemic and reclaim areas that are susceptible to erosion and further degradation

Population structure and ecology of a tropical rare rhizomatous species of teosinte Zea diploperennis (Gramineae)

One of the objectives of the Sierra de Manantl�n Biosphere Reserve (Jalisco, M�xico) is the conservation in situ of the teosinte Zea diploperennis Iltis, Doebley, Guzman & Pazzi. Zea diploperennis is perennial, shade intolerant and its 1-3 m shoots are architecturally similar to maize. Clonal growth is of the phalanx type. Genets are iteroparous (modules semelparous). The demography of seven module and genet populations was studied in seven sites representing three stages of old-field succession. Seven permanent one-meter-square plots were randomly established in each site. All genets initially present and those that became established during our study were mapped and labeled according to year of establishment The magnitude of demographic fluctuations was greater in module populations. Genet population dynamics followed a seasonal rhythm with a maximum population size obtained at the onset of the rainy season. A relation was documented between percent annual mortality of a cohort and its age: the younger the cohort, the greater the mortality. This was a statistically significant relationship, Y = [sin(-0.288x + 1.657)]2 (r = 0.92, p < 0.01), where is proportion annual mortality of genets and is the age of the cohort. The maximum rates of genet mortality occurred during the rainy season when population densities were greatest. As a consequence, we postulate that competition occurs principally during the rainy season. Linear relationships were observed between rate of population increase of genets versus old-field successional stage and soil type. Those areas with poor soil (Ultisol), degraded soil or soils with similar physical characteristics could be rehabilitated by introducing Z. diploperennis. Such rehabilitation would achieve two distinct objectives, promote propagation of this rare endemic and reclaim areas that are susceptible to erosion and further degradation

Nurses for Brosimum alicastrum reintroduction in secondary tropical dry forest

Brosimum alicastrum Sw. is a multi-purpose species and it is dominant in some American tropical forests. In Western Mexico, forests dominated by B. alicastrum, called mojoteras, have been dramatically altered. The present work aims to supply basic elements for the reintroduction of mojoteras in the Sierra de Manantlán Biosphere Reserve. The question we posed was: Are there nursing species for the reintroduction of B. alicastrum seedlings in secondary tropical dry forest? A hundred randomly chosen 2-year-old B. alicastrum seedlings were planted in five treatments: under the covering of 80 individuals belonging to four species (Tabebuia chrysantha (Jacq.) G. Nicolson, Thouinia serrata Radlk., Acacia macilenta Rose and Acalypha cincta Muell. Arg.) and 20 on open ground. After 1 year, the survival of Brosimum alicastrum seedlings was significantly different among the treatments (G2=12.11, P<0.05). The treatments with the highest significant B. alicastrum seedling survival rate were under the covering of Acalypha cincta and Thouinia serrata (55 and 40%, respectively), whereas under the covering of Acacia macilenta, Tabebuia chrysantha and on open ground, the survival rate was the lowest (<5%). © 2004 Published by Elsevier B.V

Livestock impact on dynamic and structure of tropical dry forest of the Sierra de Manantlán, Mexico

Cattle foraging within tropical dry forest (TDF) is a common practice in West of Mexico. Effect of cattle exclosure on structure and dynamics of tropical dry forest was analyzed using four years' record in the Sierra de Manantlán Biosphere Reserve, Mexico. Sixteen permanent plots were randomly established at four sites of TDF (eight plots with livestock exclosure and eight plots without livestock exclosure). During four years, all plant individuals ? 1.30 m height were recorded. Sixty species were registered, 41 in cattle exclusion treatments and 38 in treatment without exclusion; 20 species were shared among treatments during the four years study. Species richness was not significantly different (P>0.05) between treatments (plots with exclosure vs. plots without exclosure). Only until the fourth year, Shannon-Wiener index was significantly different between treatments (P < 0.05). For all species, except for three, higher population growth rates (?) were observed at the exclosure treatment