Dear Colleagues,

The Neotropics include the largest rainforest on Earth, along with many other forest types that vary from dry to wet, lowland to high-elevation cloud forests, and flooded to terra firme forests. These forests harbor astonishing diversities of plants and provide many important ecosystem services, including the regulation of regional to global climates. However, our understanding of the evolutionary and ecological drivers that shape both the diversity and function of these Neotropical forest ecosystems, as well as their capacity—or incapacity—to respond to ongoing anthropogenic global change, are still part of an active debate. In this Special Issue of Plants, we aim to compile a collection of outstanding and groundbreaking studies that use state-of-the-art methods to help us understand the diversity and functioning of Neotropical forests. We include a variety of scientific viewpoints to enhance our knowledge on the many valuable environmental services provided by diverse neotropical forests, as well as the many threats that these forests face in a changing world.

Dr. Alvaro Duque
Dr. Flávia Regina Capellotto Costa
Dr. Kenneth J. Feeley
Guest Editors

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• Amazon
• Andes
• carbon cycle
• climate change diversity
• hotspots of diversity
• lianas
• remote sensing

Title: Seedling Growth in Primary and Secondary Forests: Contrasting Above-Ground and Below-Ground Resource Strategies
Authors: Nohemi Huanca-Nuñez; Robin L. Chazdon; Sabrina E. Russo
Affiliation: School of Biological Sciences, University of Nebraska–Lincoln, 1101 T Street, 402 Manter Hall, Lincoln, NE 68588-0118, USA

Title: Long-Term Palm Increases in Northwestern Amazonia
Authors: Crystal H. McMichael
Affiliation: Department of Ecosystem and Landscape Dynamics, Institute for Biodiversity and Ecosystem Dynamics, University of Amsterdam, Amsterdam, Netherlands

Title: Ecotones as indicators of the state of Neotropical forests
Authors: Catherine M. Hulshof De La Peña
Affiliation: Department of Biology, Virginia Commonwealth University, Richmond, VA, 23284
Abstract: Tropical forests are incredibly diverse, ranging from dry to wet forests, cloud forests, and flooded to terra firme forests. Despite, or perhaps because of, this diversity, tropical biologists often conduct research exclusively in one or perhaps a few forest types. Rarely do we study the ecotone – that interstitial region between forest types. Ecotones are hyper-diverse, dynamic systems that control the flow of energy and organisms between adjacent ecosystems. In this review, I describe how studying ecotones can provide key indicators for monitoring the state of neotropical forests. I, first, describe how ecotones have been studied in the past and summarize our current understanding of tropical ecotones. Next, I outline methods and tools for studying ecotones that combine remote sensing, new statistical techniques, and field-based forest dynamics plot data. Lastly, I provide three example lines of research focusing on the ecological and evolutionary dynamics of the ecotone between tropical dry and rain forests; between tropical dry forests and the Sonoran Desert; and the ecotone between Cerrado and Amazonian forests, a particularly well-studied tropical ecotone.

Title: Tropical Dry Forest Trees And Lianas Are Anatomically And Demographically Similar At The Seedling Stage
Authors: María Natalia Umaña
Affiliation: Department of Ecology and Evolutionary Biology, University of Michigan, Ann Arbor, Michigan, USA
Abstract: A long-standing notion in plant ecology is that lianas differ substantially from trees both anatomically and demographically. In general, lianas climbing on tree trunks tend to have wider vessels, higher vessel dimorphism, larger parenchyma fractions and lighter wood in comparison to trees. Lianas are also thought to grow faster than trees, particularly during seasonal droughts. However, whether these anatomical and demographic differences hold true at the seedling stage, when most lianas are self-supporting, remains unclear. Here we compared seedling wood anatomy and relative growth rates (RGR) of ten tree species and ten liana species from three tropical dry forests. To further understand the possible differences in RGR between lianas and trees, we also examined the links between wood traits and RGR, considering the effects of seedling height and light availability. We measured thirteen wood anatomical traits related to hydraulics, storage and mechanical support, and calculated individual RGR for a one-year period. Seedlings of trees and lianas had similar storage (i.e., axial and radial parenchyma fractions) and mechanical-related (i.e., wood density, fiber fraction and wall thickness) traits. Similarly, traits commonly associated with efficiency (i.e., vessel lumen size and fraction) and safety (i.e., intervessel pit diameter aperture, dimorphism) in water transport were similar between lianas and trees. Yet, liana seedlings had more vessels per unit area, and a higher variation in vessel lumen size, than tree seedlings. We did not find significant differences in RGR between the two groups. Taller seedlings with higher variation in vessel lumen size, and larger fractions of vessels and axial parenchyma cells grew faster; but taller seedlings with more vessels per unit area grew slower. Taken together, these results suggest that lianas and trees are both anatomically and demographically similar at the seedling stage; and that vessel and parenchyma traits can predict seedling RGR, but the effects of these traits on RGR depend on seedling height. Overall, this study provides evidence that the well-known anatomical and demographic differences between trees and lianas may not necessarily occur during the seedling phase, and that the effects of wood anatomical traits on seedling growth are size-dependent.