Habitat association of tree seedlings and herbivory in lowland evergreen rainforest on white-sand and terra-firme in the upper Rio Negro

Stropp, J.et al. Plant Ecology and Diversity 7, 255-265. doi: 10.1080/17550874.2013.773103

It has been proposed that the interaction between herbivory and soil nutrient availability drives habitat association of tree species in Peruvian Amazonia. Nevertheless, there is no empirical evidence that this interaction holds across other Amazonian regions. We address this knowledge gap by testing whether the interaction between herbivory and soil nutrient contributes to habitat association of tree species in white-sand and terra-firme forests in the upper Rio Negro, Brazil. We conducted a reciprocal transplanting field experiment in which we controlled for the presence of herbivores. We tested for differences in tree-seedling growth and herbivory among seven white-sand and seven terra-firme habitat-specialist species. Additionally, we assessed whether tree seedlings differed in their functional traits. We found no empirical evidence that an interaction between herbivory and soil nutrients shapes habitat association

in white-sand and terra-firme forests of the upper Rio Negro. Tree seedlings showed higher mortality when growing in their non-typical habitat. Growth and herbivory were similar regardless of the presence or absence of herbivore protection and type of soil. Conclusions: We suggest that the overall differences in soil nutrient status between white-sand and terra-firme forests in the upper Rio Negro are insufficient to trigger an interaction between herbivory and soil nutrient availability.

Are all species necessary to reveal ecologically important patterns? 

Pos, E.T. et al. Ecology and Evolution. doi: 10.1002/ece3.1246.

While studying ecological patterns at large scales, ecologists are often unable to identify all collections, forcing them to either omit these unidentified records entirely, without knowing the effect of this, or pursue very costly and time-consuming efforts for identifying them. These “indets” may be of critical importance, but as yet, their impact on the reliability of ecological analyses is poorly known. We investigated the consequence of omitting the unidentified records and provide an explanation for the results. We used three large-scale independent datasets, (Guyana/ Suriname, French Guiana, Ecuador) each consisting of records having been identified to a valid species name (identified morpho-species – IMS) and a number of unidentified records (unidentified morpho-species – UMS). A subset was created for each dataset containing only the IMS, which was compared with the complete dataset containing all morpho-species (AMS: = IMS + UMS) for the following analyses: species diversity (Fisher’s alpha), similarity of species composition, Mantel test and ordination (NMDS). In addition, we also simulated an even larger number of unidentified records for all three datasets and analyzed the agreement between similarities again with these simulated datasets. For all analyses, results were extremely similar when using the complete datasets or the truncated subsets. IMS predicted ≥91% of the variation in AMS in all tests/analyses. Even when simulating a larger fraction of UMS, IMS predicted the results for AMS rather well. Using only IMS also out-performed using higher taxon data (genus-level identification) for similarity analyses. Finding a high congruence for all analyses when using IMS rather than AMS suggests that patterns of similarity and composition are very robust. In other words, having a large number of unidentified species in a dataset may not affect our conclusions as much as is often thought.

Soil physical constraints as a limiting factor of palm and tree basal area in Amazonian forests.

Emilio, T, et al. Plant Ecology & Diversity 7, 215-229. doi:10.1080/17550874.2013.772257

Trees and arborescent palms adopt different rooting strategies and responses to physical limitations imposed by soil structure, depth and anoxia. However, the implications of these differences for understanding variation in the relative abundance of these groups have not been explored.
We analysed the relationship between soil physical constraints and tree and palm basal area to understand how the physical properties of soil are directly or indirectly related to the structure and physiognomy of lowland Amazonian forests.

We analysed inventory data from 74 forest plots across Amazonia, from the RAINFOR and PPBio networks for which basal area, stand turnover rates and soil data were available.We related patterns of basal area to environmental variables n ordinary least squares and quantile regression models.

Soil physical properties predicted the upper limit for basal area of both trees and palms. This relationship was direct for palms but mediated by forest turnover rates for trees. Soil physical constraints alone explained up to 24% of palm basal area and, together with rainfall, up to 18% of tree basal area. Tree basal area was greatest in forests with lower turnover rates on well-structured soils, while palm basal area was high in weakly structured soils.

Our results show that palms and trees are associated with different soil physical conditions. We suggest that adaptations of these life-forms drive their responses to soil structure, and thus shape the overall forest physiognomy of Amazonian forest vegetation.

Fast demographic traits promote high diversification of Amazonian trees

Baker, T.R., et al. Ecology Letters 17: 527-536. doi: 10.1111/ele.12252

The Amazon rain forest sustains the world’s highest tree diversity, but it remains unclear why some clades of trees are hyperdiverse, whereas others are not. Using dated phylogenies, estimates of current species richness and trait and demographic data from a large network of forest plots, we show that fast demographic traits – short turnover times – are associated with high diversification rates across 51 clades of canopy trees. This relationship is robust to assuming that diversification rates are either constant or decline over time, and occurs in a wide range of Neotropical tree lineages. This finding reveals the crucial role of intrinsic, ecological variation among clades for understanding the origin of the remarkable diversity of Amazonian trees and forests.

ATDN were also used in:

Mitchard, E.T.A. et al. Strongly divergent estimates of Amazon forest carbon density from ground plots and satellites. Global Ecology and Biogeography: 23: 935–946. doi: 10.1111/geb.12168

Scratchpads developed and conceived by (alphabetical): Ed Baker, Katherine Bouton Alice Heaton Dimitris Koureas, Laurence Livermore, Dave Roberts, Simon Rycroft, Ben Scott, Vince Smith