. Forest structure and dynamics vary across the Amazon Basin in an east-west gradient coincident with variations in soil fertility and geology. This has resulted in the hypothesis that soil fertility may play an important role in explaining Basin-wide variations in forest biomass, growth and stem turnover rates. Soil samples were collected in a total of 59 different forest plots across the Amazon Basin and analysed for exchangeable cations, carbon, nitrogen and pH, with several phosphorus fractions of likely different plant availability also quantified. Physical properties were additionally examined and an index of soil physical quality developed. Bivariate relationships of soil and climatic properties with above-ground wood productivity, stand-level tree turnover rates, above-ground wood biomass and wood density were first examined with multivariate regression models then applied. Both forms of analysis were undertaken with and without considerations regarding the underlying spatial structure of the dataset. Despite the presence of autocorrelated spatial structures complicating many analyses, forest structure and dynamics were found to be strongly and quantitatively related to edaphic as well as climatic conditions. Basin-wide differences in stand-level turnover rates are mostly influenced by soil physical properties with variations in rates of coarse wood production mostly related to soil phosphorus status. Total soil P was a better predictor of wood production rates than any of the fractionated organic- or inorganic-P pools. This suggests that it is not only the immediately available P forms, but probably the entire soil phosphorus pool that is interacting with forest growth on longer timescales. A role for soil potassium in modulating Amazon forest dynamics through its effects on stand-level wood density was also detected. Taking this into account, otherwise enigmatic variations in stand-level biomass across the Basin were then accounted for through the interacting effects of soil physical and chemical properties with climate. A hypothesis of self-maintaining forest dynamic feedback mechanisms initiated by edaphic conditions is proposed. It is further suggested that this is a major factor determining endogenous disturbance levels, species composition, and forest productivity across the Amazon Basin.

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Basin-wide variations in Amazon forest structure and function are mediated by both soils and climate

Aim Conservation and land‐use planning require accurate maps of patterns in species composition and an understanding of the factors that control them Substantial doubt exists, however, about the existence and determinants of large‐area floristic divisions in Amazonia Here we ask whether Amazonian forests are partitioned into broad‐scale floristic units on the basis of geological formations and their edaphic properties



Location Western and central Amazonia



Methods We used Landsat imagery and Shuttle Radar Topography Mission (SRTM) digital elevation data to identify a possible floristic and geological discontinuity of over 300 km in northern Peru We then used plant inventories and soil sampling to document changes in species composition and soil properties across this boundary Data were obtained from 138 sites distributed along more than 450 km of road and river On the basis of our findings, we used broad‐scale Landsat and SRTM mosaics to identify similar patterns across western and central Amazonia



Results The discontinuity identified in Landsat and SRTM data corresponded to a 15‐fold change in soil cation concentrations and an almost total change in plant species composition This discontinuity appears to be caused by the widespread removal of cation‐poor surface sediments by river incision to expose cation‐rich sediments beneath Examination of broad‐scale Landsat and SRTM mosaics indicated that equivalent processes have generated a north–south discontinuity of over 1500 km in western Brazil Due to similarities with our study area, we suggest that this discontinuity represents a chemical and ecological limit between western and central Amazonia



Main conclusions Our findings suggest that Amazonian forests are partitioned into large‐area units on the basis of geological formations and their edaphic properties The evolution of these units through geological time may provide a general mechanism for biotic diversification in Amazonia These compositional units, moreover, may correspond to broad‐scale functional units The existence of large‐area compositional and functional units would suggest that protected‐area, carbon sequestration, and other land‐use strategies in Amazonia be implemented on a region‐by‐region basis The methods described here can be used to map these patterns, and thus enable effective conservation and management of Amazonian forests

https://onlinelibrary.wiley.com/doi/pdf/10.1111/j.1365-2699.2011.02585.x

Geological control of floristic composition in Amazonian forests.

Forest structure and dynamics have been noted to vary across the Amazon Basin in an east-west gradient in a pattern which coincides with variations in soil fertility and geology. This has resulted in the hypothesis that soil fertility may play an important role in explaining Basin-wide variations in forest biomass, growth and stem turnover rates.

To test this hypothesis and assess the importance of edaphic properties in affect forest structure and dynamics, soil and plant samples were collected in a total of 59 different forest plots across the Amazon Basin. Samples were analysed for exchangeable cations, C, N, pH with various P fractions also determined. Physical properties were also examined and an index of soil physical quality developed.

Overall, forest structure and dynamics were found to be strongly and quantitatively related to edaphic conditions. Tree turnover rates emerged to be mostly influenced by soil physical properties whereas forest growth rates were mainly related to a measure of available soil phosphorus, although also dependent on rainfall amount and distribution. On the other hand, large scale variations in forest biomass could not be explained by any of the edaphic properties measured, nor by variation in climate.

A new hypothesis of self-maintaining forest dynamic feedback mechanisms initiated by edaphic conditions is proposed. It is further suggested that this is a major factor determining forest disturbance levels, species composition and forest productivity on a Basin wide scale.

/pdf/regional-and-large-scale-patterns-in-amazon-forest-structure-bsi6itvcdu.pdf

Regional and large-scale patterns in Amazon forest structure and function are mediated by variations in soil physical and chemical properties

https://www.locus.ufv.br/bitstream/123456789/21369/1/artigo.pdf

Biodiversity consequences of land-use change and forest disturbance in the Amazon:a multi-scale assessment using ant communities

Background: There is no generally agreed classification scheme for the many different vegetation formation types occurring in the tropics. This hinders cross-continental comparisons and causes confusion as words such as ‘forest’ and ‘savanna’ have different meanings to different people. Tropical vegetation formations are therefore usually imprecisely and/or ambiguously defined in modelling, remote sensing and ecological studies. Aims: To integrate observed variations in tropical vegetation structure and floristic composition into a single classification scheme. Methods: Using structural and floristic measurements made on three continents, discrete tropical vegetation groupings were defined on the basis of overstorey and understorey structure and species compositions by using clustering techniques. Results: Twelve structural groupings were identified based on height and canopy cover of the dominant upper stratum and the extent of lower-strata woody shrub cover and grass cover. Structural classifications di...

On the delineation of tropical vegetation types with an emphasis on forest/savanna transitions

. We explored the floristic composition of terra firme forests across Amazonia using 55 plots. Firstly, we examined the floristic patterns using both genus- and species-level data and found that the species-level analysis more clearly distinguishes among forests. Next, we compared the variation in plot floristic composition at regional- and continental-scales, and found that average among-pair floristic similarity and its decay with distance behave similarly at regional- and continental-scales. Nevertheless, geographical distance had different effects on floristic similarity within regions at distances

/pdf/multi-scale-comparisons-of-tree-composition-in-amazonian-10oq8842lj.pdf

Multi-scale comparisons of tree composition in Amazonian terra firme forests

Peru is one of the richest peatland countries in the tropics. Its peatlands extend over all three of its regions, with a significant area in the Amazon. These peatlands provide key ecosystem services – storing immense amounts of carbon, uptaking carbon dioxide, nurturing unique biodiversity, regulating water at local and regional levels, and providing both livelihoods and cultural values for local people.
The country’s peatlands have deteriorated through anthropogenic activities, including infrastructure construction and resource extraction (e.g. oil, minerals), and unsustainable uses or practices of varying intensity (e.g. overgrazing, peat extraction, palm felling, overhunting); such practices both threaten them and increase their vulnerability. Climate changes also compromise their stability.
The Peruvian regulatory framework includes norms and instruments for the sustainable management of wetlands, but peatland-specific regulations are yet to be developed. Recent advances include the elaboration of a national definition for peatlands; however, peatlands are yet to be explicitly included in climate change strategies like REDD+ and NDCs.
There is a critical lack of scientific research on Peruvian peatlands; they need to be mapped and inventoried, and their ecological properties and economic and social values characterized. If they are to be sustainably managed, it is also essential to identify and value the knowledges and practices of indigenous communities.
The opportunities for the conservation and good management of these key ecosystems are many, including consolidation of mechanisms of payment for ecosystem services, implementation of sustainable resource management plans by the local population, expansion of protected natural areas, and recognition of communities’ tenure rights.

/pdf/what-do-we-know-about-peruvian-peatlands-5ggtc78ibg.pdf

What do we know about Peruvian peatlands

Integrating regional and continental scale comparisons of tree composition in Amazonian terra firme forests E. N. Honorio Coronado, T. R. Baker, O. L. Phillips, N. C. A. Pitman, R. T. Pennington, R. Vásquez Martı́nez, A. Monteagudo, H. Mogollón, N. Dávila Cardozo, M. Rı́os, R. Garcı́a-Villacorta, E. Valderrama, M. Ahuite, I. Huamantupa, D. A. Neill, W. F. Laurance, H. E. M. Nascimento, S. Soares de Almeida, T. J. Killeen, L. Arroyo, P. Núñez, and L. Freitas Alvarado Instituto de Investigaciones de la Amazonı́a Peruana, Av. A. José Quiñones km 2.5, Iquitos, Peru Ecology and Global Change, School of Geography, University of Leeds, Leeds, UK Center for Tropical Conservation, Duke University, Durham, USA Royal Botanic Garden Edinburgh, 20a Inverleith Row, Edinburgh EH3 5LR, UK Proyecto Flora del Perú, Jardı́n Botánico de Missouri, Oxapampa, Peru Finding Species, 6930 Carroll Ave., Suite 600, P.O. Box 5289, Takoma Park, Maryland 20912, USA

/pdf/integrating-regional-and-continental-scale-comparisons-of-42jrto1wal.pdf

L. Freitas Alvarado

Papers

Multi-scale comparisons of tree composition in Amazonian terra firme forests

What do we know about Peruvian peatlands

Integrating regional and continental scale comparisons of tree composition in Amazonian terra firme forests