Wednesday, August 5, 2020: 3:30 PM
Marielle Smith1, Scott C Stark2, Juliana Schietti3,4, Nathan Gonçalves5, David M. Minor6, Danilo RA Almeida Sr.7, Daniel Gomes Rocha8,9, Susan Aragón10,11, Mendell S. Souza12, Daniel Almeida12, Nicolas Zaslavsky de Lima12, Kelly Torralvo13, Albertina Lima13, Ricard Scoles14, Marcelo Menin15, Marcelino Carneiro Guedes16, Hélio Tonini17, Kátia Emídio da Silva18, Diogo Martins Rosa19, Bruce Nelson20, Carlos Leandro Cordeiro21, Raimundo Cosme de Oliveira22, Gang Shao1, Joost van Haren23,24, Veronika Leitold1, Sean M McMahon25, Luiz Aragao26, Gabriel de Oliveira27, Rafael Leandro de Assis28,29, José Luís C. Camargo29, Rita Mesquita30, David Breshears31, Flávia R. C. Costa32 and Scott R. Saleska33, (1)Department of Forestry, Michigan State University, East Lansing, MI, (2)Department of Forestry, Michigan State University, east lansing, MI, (3)Universidade Federal do Amazonas (UFAM), Manaus, Brazil, (4)Coordenação de Pesquisas em Ecologia, Instituto Nacional de Pesquisas da Amazônia (INPA), Manaus, Brazil, (5)Forestry, Michigan State University, East Lansing, MI, (6)Department of Geographical Sciences, University of Maryland, College Park, MD, (7)Department of Forest Sciences, University of São Paulo, Piracicaba, Brazil, (8)Department of Wildlife, Fish, and Conservation Biology, University of California, Davis, Davis, CA, (9)Grupo de Ecologia e Conservação de Felinos na Amazônia, Instituto de Desenvolvimento Sustentável Mamirauá, Tefé, Brazil, (10)Programa de Pós-Graduação em Recursos Naturais da Amazônia, Universidade Federal do Oeste do Pará, Santarém, Santarém, Brazil, (11)Instituto de Ciencias de la Naturaleza, Territorio y Energías Renovables, Pontificia Universidad Católica del Perú, Lima, Peru, (12)Universidade Federal do Oeste do Pará, Santarém, Brazil, (13)Instituto Nacional de Pesquisas da Amazônia, Manaus, Brazil, (14)Universidade Federal do Oeste do Pará, Santarém, Santarém, Brazil, (15)Departamento de Biologia, Instituto de Ciências Biológicas, Universidade Federal do Amazonas, Manaus, Brazil, (16)Embrapa Amapá, Brazil, (17)Embrapa Pecuária Sul, Rio Grande do Sul, Brazil, (18)Embrapa Amazônia Ocidental, Manaus, Brazil, (19)Secretaria de Estado do Desenvolvimento Ambiental de Rondônia (SEDAM/RO), Brazil, (20)Environmental Dynamics, Brazil's National Institute for Amazon Research (INPA), Manaus, Brazil, (21)Instituto Internacional para Sustentabilidade (IIS), Rio de Janeiro, Brazil, (22)Embrapa Amazônia Oriental, Santarém, Brazil, (23)Biosphere 2, University of Arizona, Tucson, AZ, (24)Honors College, University of Arizona, Tucson, AZ, (25)Forest Global Earth Observatory, Smithsonian Environmental Research Center, Edgewater, MD, (26)Instituto Nacional de Pesquisas Espaciais, Brazil, (27)Department of Geography and Atmospheric Science, University of Kansas, Lawrence, KS, (28)University of Oslo, Oslo, Norway, (29)National Institute of Amazonian Research, Manaus, Brazil, (30)Biological Dynamics of Forest Fragments Project, Institute Nacional de Pesquisas da Amazônia, Manaus, Brazil, (31)School of Natural Resources and the Environment, University of Arizona, Tucson, AZ, (32)Instituto Nacional de Pesquisas da Amazônia (INPA), Manaus, Brazil, (33)Department of Ecology and Evolutionary Biology, University of Arizona, Tucson, AZ
Background/Question/Methods Forest canopy structure is the physical manifestation of tree demographic processes and has been mechanistically linked to key ecosystem functions. Therefore, understanding the patterns and drivers of forest structural variation through seasons and across environmental gradients may provide valuable insights into the mechanisms of forest responses to climatic changes. These relationships are particularly important to understand, and yet have been poorly characterised, in the climatically critical forests of the Amazon basin. Here, we present the findings of two studies that illustrate the importance of vertical forest structure and light environments to the (1) seasonal and (2) spatial structuring of mature Amazonian forests. For the first study, we made monthly ground-based lidar measurements over 4 years, including a strong El Niño drought event, at an evergreen Amazonian site (K67). For the second, we compiled a large database of ground-based lidar collected from 285 forest plots, which span large-scale gradients of mean annual precipitation, seasonality, and soil fertility across the Amazon basin.
Results/Conclusions
Vertical forest structure and light environments shifted significantly between seasons (at K67) and across Amazonian forest plots. Seasonally, LAI (leaf area index) of lower and upper canopy levels at K67 exhibited significantly higher seasonal variation than total LAI (lower LAI: 7.02%, CI 3.85-9.89; upper LAI: 11.19%, 95% CI 6.56-16.56; total LAI: 2.58%, CI 1.57-3.48). Low seasonal variation in total LAI resulted from opposing seasonal patterns of the within canopy layers, which were highly anticorrelated (R2 = 0.57-0.61, p < 0.01). We separated lower canopy leaf area into highly illuminated and shaded understory regions, which were also anti-correlated (R2 = 0.73-0.96, p < 0.0001), reflecting opposing responses of leaves to seasonal water deficits. Seasonal patterns were similar, but accentuated during the drought year. Within the spatial dataset, variation in the distributions of separate (high to low) photic environments among forest plots was greater than variation in total vertical canopy structure. Together, our results highlight the importance of spatial and temporal variation in vertical forest structure, and in particular, photic environments—a hidden aspect of structural variation that likely drives differences in tree functional composition—on the form and function of Amazon forests. Understanding how forest canopies and microenvironments change seasonally and across broad environmental gradients, and are related to hydraulic, phenological, and other functional strategies, is critical to developing a mechanistic understanding of Amazon forest responses to changing climate.
