Ferns and lycophytes in amazonia: diversity patterns and usefulness as habitat indicators

Siirretty Doriast

Species richness and diversity along edaphic and climatic gradients in Amazonia

The number of species is known to decrease from the humid tropics towards drier and colder climates, but how species richness varies along environmental and spatial gradients within the tropical rain forests is not clear. We inventoried 214 transects of 0.25 ha to document species diversity patterns in an example plant group (ferns and lycophytes) across non-inundated rain forests of western and central Amazonia, and assessed how well these conformed with proposed hypotheses about species richness. The observed number of species varied between 6 and 71 per transect. The effective number of species (emphasising the degree of unevenness in species abundances) varied between 1.02 and 8.60, and diversity profiles revealed considerable differences among transects in community structure. Although the density of individuals varied over almost two orders of magnitude, species diversity was better explained by other variables. In particular, within-transect species diversity increased substantially with increasing soil cation concentration. It also increased with soil aluminium concentration, heterogeneity in soil chemistry, annual rainfall and dry season rainfall, and was higher in western than in central Amazonia. Multiple regression models explained up to 70% of the variance in species diversity, but the relationships between species diversity and the environmental gradients became progressively weaker as species abundances were given more weight in the calculation of diversity. Our results conformed to the proposal that site productivity promotes species diversity. This seemed to arise from larger species pools on more fertile soils and in wetter climates, even when it could be expected that the older and more widespread infertile soils would have provided more opportunities for speciation. © 2014 The Authors.</p

The role of soils on pteridophyte distribution in tropical American forests

The distributions of plant species are affected by characteristics of their environment, most importantly climate and soils. Ferns and lycophytes (hereafter pteridophytes) are no exception to this general ecological principle. However, until relatively recently, little information has been available about pteridophyte-soil relationships in the tropics. Here we review literature that sheds light on the impact of soil conditions on pteridophyte distribution in the lowland forests of tropical America. We provide examples of both soil-related community-level patterns in species turnover and distributions of individual species and genera along soil gradients. We then discuss the relevance of these patterns for the evolution and diversification of pteridophyte lineages and for practical applications, such as the use of pteridophytes as indicators in classification and mapping of soil-related habitats. Finally, we discuss challenges in filling the gaps of knowledge in pteridophyte-soil relationships and suggest possible solutions for them.</p

Redução de esforço amostral vs. Retenção de informação em inventários de pteridófitas na Amazônia Central

The large area covered by the Amazonian domain and the limited financial support for biodiversity studies demand efficient research programs. Aiming to evaluate the consequences of reduced sampling effort on the retention of ecological information, we tested how differences in plot width affect the perceived relationship between environmental variation and the composition of the pteridophyte community in Central Amazonia. Measures of slope, canopy openness and soil clay content were taken in 37 terra-firme forest plots. All pteridophyte individuals were identified and mapped according to three sample strips. We tested the effects of environmental variables on pteridophyte composition of 250 × 2.5 meters-plots and on sub-samples of reduced width. The reduction of plot width from 2.5 to 1 m (60% reduction in sampling effort) corresponded to a reduction of 24% of the project’s costs concerning field work expenses. This would reduce the number of sampled species from 52 to 44. The reduction of 20% plot width (from 2.5 to 2 m) would cause a reduction of two (4%) sampled species and a reduction of 8% of the costs. For all tested plot widths, community composition was associated with soil clay content and was not associated with the terrain slope. The effect of canopy openness on pteridophyte species composition was not consistent among sample sizes. These may be related to the relatively lower importance of light availability in determining community structure at the studied spatial scale. We concluded that the smallest plots were informative enough to detect the main gradients of composition and their association to environmental factors. This would allow a reduction in total costs, or the allocation of available budget to more plots, which could increase the power of the statistical analyses, reduce the confidence intervals and increase probability of detecting more species. © 2007, Universidade Estadual de Campinas UNICAMP. All rights reserved

Redução de esforço amostral vs. retenção de informação em inventários de pteridófitas na Amazônia Central

The large area covered by the Amazonian domain and the limited financial support for biodiversity studies demand efficient research programs. Aiming to evaluate the consequences of reduced sampling effort on the retention of ecological information, we tested how differences in plot width affect the perceived relationship between environmental variation and the composition of the pteridophyte community in Central Amazonia. Measures of slope, canopy openness and soil clay content were taken in 37 terra-firme forest plots. All pteridophyte individuals were identified and mapped according to three sample strips. We tested the effects of environmental variables on pteridophyte composition of 250 × 2.5 meters-plots and on sub-samples of reduced width. The reduction of plot width from 2.5 to 1 m (60% reduction in sampling effort) corresponded to a reduction of 24% of the project’s costs concerning field work expenses. This would reduce the number of sampled species from 52 to 44. The reduction of 20% plot width (from 2.5 to 2 m) would cause a reduction of two (4%) sampled species and a reduction of 8% of the costs. For all tested plot widths, community composition was associated with soil clay content and was not associated with the terrain slope. The effect of canopy openness on pteridophyte species composition was not consistent among sample sizes. These may be related to the relatively lower importance of light availability in determining community structure at the studied spatial scale. We concluded that the smallest plots were informative enough to detect the main gradients of composition and their association to environmental factors. This would allow a reduction in total costs, or the allocation of available budget to more plots, which could increase the power of the statistical analyses, reduce the confidence intervals and increase probability of detecting more species. © 2007, Universidade Estadual de Campinas UNICAMP. All rights reserved

Beware my spines: a new spiny fern (Dennstaedtia, Dennstaedtiaceae) from central and western Amazonia

A new spiny fern belonging to the genus Dennstaedtia is described from Brazilian and Peruvian Amazonia. Dennstaedtia aculeata (sp. nov.) is the third spiny species known for the genus, and the first in South America. It is compared with another Neotropical spiny Dennstaedtia, D. spinosa. We also present images, illustrations and a distribution map of the specimens, and discuss the habitat preference of the species towards nutrient-richer soils and spinescence in the family

Geologically recent rearrangements in central Amazonian river network and their importance for the riverine barrier hypothesis

The riverine barrier hypothesis is a central concept in Amazonian biogeography. It states that large rivers limit species distributions and trigger vicariant speciation. Although the hypothesis has explanatory power, many recent biogeographical observations addressing it have produced conflicting results. We propose that the controversies arise because tributary arrangements in the Amazon river system have changed in geologically recent times, such that large tracts of forest that were on the same side of a river at one time got separated to different sides at another. Based on topographical data and sediment dating, we map about 20 major avulsion and river capture events that have rearranged the river network in central Amazonia during the late Pleistocene and Holocene. We identify areas where past riverine barrier effects might still linger in the absence of a major river, as well as areas where such effects may not yet have accumulated across an existing river. These results call for a reinterpretation of previous biogeographical studies and a reorientation of future works to take into account the idiosyncratic histories of individual rivers.</p

Effects of forest degradation on Amazonian ferns in a land-bridge island system as revealed by non-specialist inventories

Tropical forests have been rapidly deforested and degradation worldwide has outpaced biodiversity field sampling. No study to date has assessed the effects of insular habitats induced by hydroelectric dams on Amazonian understory plants. Fern community responses to anthropogenic effects on tropical forest islands can be revealed at a faster pace by using simple and cheap, yet informative, protocols that could be applied by non-specialists. This study seeks to both understand the drivers of fern and lycophytes assemblages on forest islands and investigate the relative costs and effectiveness of a simplified sampling protocol that can be applied by non-specialists. Fern species were sampled by a non-specialist who photographed all ferns and lycophytes within seventeen 0.25-ha plots on 10 forest islands at the lake of Balbina Hydroelectric dam, central Amazonia. Sampling was carried out opportunistically during a field expedition planned to conduct tree inventories. As predictors, we used locally measured or GIS-derived descriptors of plot and landscape conditions. We used multivariate and linear models to further assess the influence of predictors on patterns of species richness and composition of ferns assemblages. A total of 286 photographed individual ferns or lycophytes represented at least 23 species and 14 genera. The average number of taxa per plot was 6.1 in the islands and 14.3 in the mainland. The species pool found on islands was a nested subset of the mainland fern community. Species richness was positively related to island size and negatively related to isolation and fire severity. Area, isolation and fire severity also significantly explained variation in community composition. The relative cost of the picture-based fern protocol applied was very modest (only 4% of the total expedition budget), even compared to the typically low cost of alternative field campaigns. We conclude that fern community structure in this forest archipelago was primarily driven by island size, isolation and fire disturbance. Moreover, we show that a simple sampling protocol carried out by a non-specialist can lead to inexpensive and highly reliable ecological data. This opens an avenue for crowdsourcing ecological fern data collections using a citizen science approach.</p

Shifts in structural diversity of Amazonian forest edges detected using terrestrial laser scanning

Forest edges are an increasingly common feature of Amazonian landscapes due to human-induced forest fragmentation. Substantial evidence shows that edge effects cause profound changes in forest biodiversity and productivity. However, the broader impacts of edge effects on ecosystem functioning remain unclear. Assessing the three-dimensional arrangement of forest elements has the potential to unveil structural traits that are scalable and closely linked to important functional characteristics of the forest. Using over 600 high-resolution terrestrial laser scanning measurements, we present a detailed assessment of forest structural metrics linked to ecosystem processes such as energy harvesting and light use efficiency. Our results show a persistent change in forest structural characteristics along the edges of forest fragments, which resulted in a significantly lower structural diversity, in comparison with the interior of the forest fragments. These structural changes could be observed up to 35 m from the forest edges and are likely to reflect even deeper impacts on other ecosystem variables such as microclimate and biodiversity. Traits related to vertical plant material allocation were more affected than traits related to canopy height. We demonstrate a divergent response from the forest understory (higher vegetation density close to the edge) and the upper canopy (lower vegetation density close to the edge), indicating that assessing forest disturbances using vertically integrated metrics, such as total plant area index, can lead to an erroneous interpretation of no change. Our results demonstrate the strong potential of terrestrial laser scanning for benchmarking broader-scale (e.g. airborne and space-borne) remote sensing assessments of forest disturbances, as well as to provide a more robust interpretation of biophysical changes detected at coarser resolutions