Search

Cloud forests are highly diverse mountain ecosystems, but habitat loss and fragmentation threaten many species with extinction. Demographic parameters are essential to implement effective conservation actions and to understand the mechanisms of species coexistence, but there are very few population models with transition matrices for fern species. We evaluated the demographic dynamics of three coexisting fern species of different growth form in a cloud forest in eastern central Mexico for six years. The matrix analyses showed that the populations of a trunk‐forming fern (Cyathea divergens) and a short caulescent fern (Marattia laxa) were stable while the population of a trunkless, herbaceous fern (Parablechnum schiedeanum) was decreasing. Survival was the demographic process of the life cycle that contributed the most to the population growth of the three species. As expected, with shorter longevity and high precocity, P. schiedeanum exhibited the demographic pattern of herbaceous species. In contrast, with greater longevity and a longer maturation period, the demography of C. divergens and M. laxa was more comparable with that of tree species. Our results support the hypothesis that the demography of the tropical fern species can be compared with life‐history strategies of angiosperms and gymnosperms. [ABSTRACT FROM AUTHOR]

Premise: Mistletoes parasitize many hardwood and softwood tree species; however, they play key roles in forest ecosystems. Adult individuals of Psittacanthus schiedeanus take up water and xylem nutrients from both deciduous and evergreen host trees, suggesting the ability to modify its physiology according to the availability of host resources. Yet, there is little information regarding the effects of mistletoes on their host trees from the eophyll stage to reproductive phases of the parasite. Methods: Taking advantage of the fact that P. schiedeanus can reach sexual maturity in 1 year, we investigated its physiological performance during development on deciduous (Liquidambar styraciflua) and evergreen (Quercus germana) host trees in a cloud forest in eastern Mexico. Variables related to chlorophyll fluorescence, carbon assimilation, photosynthetic pigments, and nitrogen, phosphorus, and carbon contents of the parasite and non‐infected and infected hosts were analyzed in a nursery experiment. Results: Mistletoe had lower water‐use efficiency and higher transpiration rates than the host species did. Despite the fact that P. schiedeanus obtained resources from species with differing phenology and resource availability, the parasite steadily improved its CO2 assimilation, electron transport rate, and nutrient content from seedling establishment to adult life stages. Mistletoe decreased the photosynthetic reactions of carbon metabolism in the deciduous host, photosynthetic light reactions in the evergreen host, and nutritional status of both host species, mostly in the evergreen host. Conclusions: The hypothesis that mistletoes adjust their physiology according to the availability of host resources could extend to the early growth of the parasite. [ABSTRACT FROM AUTHOR]

Climate change is expected to increase the frequency of extreme climatic events, yet few studies have addressed the capacity of plant species to deal with such events. Species that are widespread are predicted to be highly plastic and able to acclimate to highly changing conditions. To study the plasticity in physiological responses of the widely distributed epiphyte Tillandsia utriculata, we transplanted individuals from a coastal scrub and broadleaf evergreen forest to a similar coastal scrub site and forest. After a 45‐day acclimation, the plants were moved to a semi‐controlled greenhouse at each site, and then subjected to a 20‐day drought. Physiological variables were measured during the acclimation and the drought. The individuals of scrub and forest populations had similar relative water content and carbon assimilation in the contrasting conditions of the two transplantation sites despite the high discrepancy between the environments at their original site. Electron transport rates were higher in individuals from the scrub population. Electron transport rates were also higher than estimated from carbon assimilation, suggesting that photorespiration was present. The individuals of the coastal scrub population had a higher capacity to dissipate excess energy this way. The relative distance index of plasticity was high overall, indicating that some traits are highly plastic (titratable acidity, carbon assimilation) in order to maintain the stability of others (maximum quantum yield Fv/Fm and relative water content). We conclude that T. utriculata is a highly plastic species with a high capacity to tolerate extreme environmental changes over a short time. [ABSTRACT FROM AUTHOR]

Prescribed burning is a management instrument applied to reduce the risk of fire and favour revegetation. Our objective was to generate information about the dynamics of post-fire regeneration via the soil seed bank (SSB), for fire management in subtropical forests. Samples taken at soil depths of 0-3cm, 3-6 cm and 6-10 cm before and 5 h after a prescribed burn showed that the fire immediately increased the number of germinable seeds and species in a Mexican pine-oak forest. Most of the germinable seeds were from species in genera with small seeds exhibiting physical or physiological dormancy, and that are tolerant or require fire for germination. Fire increased the number of germinable seeds during the wet season and the number of species was greater in the area control at 0-6-cm soil depth after 1 year; so that the fire modified the SSB seasonal pattern. Species diversity was not altered and was dominated by perennial herbaceous and shrub species both before and 2 years after the fire. Although fire completely eliminated the aboveground biomass of the understorey vegetation, the SSB can promote regeneration and persistence of understorey vegetation following a prescribed surface fire of low severity for the ecosystem studied. [ABSTRACT FROM AUTHOR]

We determined the effect of heat shock on seed germination of 23 species growing in fire-prone areas covered by pine-oak and montane cloud forests. Seeds of each species were exposed to 60, 80, 100 or 120°C for 5 or 60 min in dry and moist sand. Seeds of nine species were incubated for 15 h in moist sand and exposed to the temperature that best promoted germination. Eighteen species required heat shock for germination, and five tolerated it. Dry heat shock for 5 min promoted germination of these species; heat shock in moist sand at 100°C induced germination of 10 species. Exposure for 60 min to heat shock in dry and moist sand improved germination of 14 and 5 species respectively. Logistic models indicate that germination probabilities of most species are increased by temperatures of 70-120°C. Depending on substrate and seed hydration, heat shock increased or left unchanged the germination of most pine-oak and montane cloud forest species. Thus, montane cloud forest seeds can survive low-intensity surface fires. Most species with seeds hydrated before heat shock showed little or no germination. Prescribed burns at the end of the rainy season may therefore be harmful to pine-oak and montane cloud forest species. [ABSTRACT FROM AUTHOR]

We determined the effect of heat shock on seed germination of 23 species growing in fire-prone areas covered by pine-oak and montane cloud forests. Seeds of each species were exposed to 60, 80, 100 or 12°8C for 5 or 60 min in dry and moist sand. Seeds of nine species were incubated for 15 h in moist sand and exposed to the temperature that best promoted germination. Eighteen species required heat shock for germination, and five tolerated it. Dry heat shock for 5 min promoted germination of these species; heat shock in moist sand at 100°C induced germination of 10 species. Exposure for 60 min to heat shock in dry and moist sand improved germination of 14 and 5 species respectively. Logistic models indicate that germination probabilities of most species are increased by temperatures of 70-120°C. Depending on substrate and seed hydration, heat shock increased or left unchanged the germination of most pine-oak and montane cloud forest species. Thus, montane cloud forest seeds can survive low-intensity surface fires. Most species with seeds hydrated before heat shock showed little or no germination. Prescribed burns at the end of the rainy season may therefore be harmful to pine-oak and montane cloud forest species. [ABSTRACT FROM AUTHOR]

The vegetation and the vascular plants of an ecotonal zone between the floristic provinces of the Desert Plateau (Chihuahuan Desert) and Gulf Coastal Plain in northeastern México were studied. The study zone has a surface of 2,526.25 km² and it is located in the northern part of the state of Nuevo León. On the basis of physiognomy, ecological characteristics and dominant species, seven types of vegetation were recognized. With the aid of 50 sampling plots, aerial photographs and floristic composition, the units of vegetation were delimited and mapped. 405 species (varieties and subspecies included) were identified. The study zone showed geographical affinity with the vegetation of the Chihuahuan Desert in the Desert Plateau of México (Hilaria mutica grassland, low thornless scrub of Flourensia cernua and medium size mixed scrub of Acacia-Prosopis-Flourensia-Larrea) and with the Gulf Coastal Plain (medium size mixed scrub of Leucophyllum frutescens and Acacia rigidula and high mixed scrub of Helietta parvifolia). The medium size and high thorny scrubs of Prosopis-Acacia showed no clear relationships with any of the floristic provinces. The coexistence of shrubby vegetation characteristic of the lowlands in the Gulf Coastal Plain and the vegetation usually present in the Chihuahuan Desert, can be explained in view of the increment of aridity and gentle raising of the continental surface in east-west direction, and of the absence of notable topographic accidents in the northeastern region of México. [ABSTRACT FROM AUTHOR]

After assimilation, plants often fractionate stable carbon and nitrogen isotopes among different organs depending on synthesis and transport of metabolites. We investigated stable carbon and nitrogen isotope compositions among leaves of different age (0 to 6 months) in two mangrove fern species ( Acrostichum danaeifolium Langsd. & Fisch. and Acrostichum aureum L.) from Mexico. Leaves of all ages were analysed for δ 13 C, δ 15 N, carbon and nitrogen concentrations and gas exchange parameters. In both species, δ 13 C slightly decreased with leaf age. Leaf salt concentration increased with leaf age, and thus did not decrease 13 C discrimination markedly. Enrichment in 13 C in younger versus older leaves can be explained by stage of development: Carbon is assimilated and incorporated into autotrophic leaves, but also transported as 13 C-enriched carbohydrates into still expanding and more heterotrophic younger leaves—indicated by lower rates of photosynthesis. Depletion in 13 C in old autotrophic leaves, which export photosynthetic assimilates, could mainly be explained by respiratory fractionation releasing 13 C-enriched CO 2 . In contrast, δ 15 N values in A. danaeifolium increased with leaf age. This pattern could be related to the transport of 15 N-depleted amino acids into younger leaves, and leaf construction with these compounds. In conclusion, 13 C depletion and 15 N enrichment with leaf age were described for other plant species earlier and were explained by different mechanisms of carbon and nitrogen assimilation and the export of these assimilates from older to younger leaves. These stable isotope patterns were approved for two mangrove fern species in this study. [ABSTRACT FROM AUTHOR]