We synthesize findings from the world’s largest and longest-running experimental study of habitat fragmentation, in central Amazonia. Over the past 36 years, 11 forest fragments ranging from 1 ha to 100 ha in size have experienced a wide array of ecological changes. Edge effects have been a dominant driver of fragment dynamics, strongly affecting forest microclimate, tree mortality, carbon storage and fauna. The matrix of vegetation surrounding fragments has changed markedly over time (evolving from large cattle pastures to mosaics of abandoned pasture and secondary regrowth forest), and this, in turn, has strongly influenced the dynamics of fragments and faunal communities. Both rare weather events and apparent global-change drivers have significantly influenced forest structure and dynamics across the entire study area, both in forest fragments and in nearby intact forest. Such large-scale drivers are likely to interact synergistically with habitat fragmentation.

An Amazonian rainforest and its fragments as a laboratory of global change

Land-use change is a key driver of the global biodiversity crisis and a particularly serious threat to tropical biodiversity. Throughout the tropics, the staggering pace of deforestation, logging, and conversion of forested habitat to other land uses has created highly fragmented landscapes that are increasingly dominated by human-modified habitats and degraded forests. In this chapter, we review the responses of tropical bats to a range of land-use change scenarios, focusing on the effects of habitat fragmentation, logging, and conversion of tropical forest to various forms of agricultural production. Recent landscape-scale studies have considerably advanced our understanding of how tropical bats respond to habitat fragmentation and disturbance at the population, ensemble, and assemblage level. This research emphasizes that responses of bats are often species and ensemble specific, sensitive to spatial scale, and strongly molded by the characteristics of the prevailing landscape matrix. Nonetheless, substantial knowledge gaps exist concerning other types of response by bats. Few studies have assessed responses at the genetic, behavioral, or physiological level, with regard to disease prevalence, or the extent to which human disturbance erodes the capacity of tropical bats to provide key ecosystem services. A strong geographic bias, with Asia and, most notably, Africa, being strongly understudied, precludes a comprehensive understanding of the effects of fragmentation and disturbance on tropical bats. We strongly encourage increased research in the Paleotropics and emphasize the need for long-term studies, approaches designed to integrate multiple scales, and answering questions that are key to conserving tropical bats in an era of environmental change and dominance of modified habitats (i.e., the Anthropocene).

/pdf/responses-of-tropical-bats-to-habitat-fragmentation-logging-3gb9sod5mi.pdf

Responses of Tropical Bats to Habitat Fragmentation, Logging, and Deforestation

Land-use practices can dramatically shift the trajectories of rain forest recovery. In a 25-year study, Amazon rain forest regenerated following deforestation as long as seed availability and seedling recruitment were not interrupted. In contrast, rain forest converted to cattle pastures via cutting and burning prior to abandonment diverted succession, leading to highly simplified stands dominated by a single genus. Annual fires eliminated seedlings, saplings, coppice, and seeds in the soil, except for several Vismia species. Once established, Vismia regenerated by continual resprouting and resisted the establishment of other rain forest species, especially the normal suite of pioneers. Through time, succession both in abandoned clearcuts and pastures increased in stem density and biomass; however, species accumulation and ecosystem services were limited in pastures when compared with those in abandoned clearcuts. Therefore, prescribed burning to maintain pastureland leaves a legacy that is not readily extinguished, whereas abandoning clearcuts engenders an accelerated rain forest regeneration.

Amazon Rain Forest Succession: Stochasticity or Land-Use Legacy?

Phenology has established its status as an integrative environmental science and as a key component for climate change research. We aim to present a review of phenological research in South and Central America. We describe the flowering and fruiting patterns of the main vegetation types studied to date, and highlight areas where phenological information is lacking. Phenological research is still required even though the number of papers published has increased, especially in the twenty-first century. The distribution of phenological studies on South American vegetation was very uneven over the different vegetation types and life forms. Tropical moist forest continues to be, by far, the most widely studied ecosystem while trees were the life-form observed in almost all papers surveyed. Currently, long-term phenological datasets are rare and few long-term monitoring systems are known for South and Central America. Few papers reviewed were concerned with the effects of climatic change and its evaluation using plant phenology, which differed greatly from Northern Hemisphere research which had a strong focus on phenology and climate change. Among new developments we mention phenology and edge effects and fragmentation, and remote monitoring of phenology with digital cameras. Finally, building phenology networks is the greatest challenge for South and Central American phenologists, demanding an effort from and cooperation among universities, research institutions, governmental, and non-governmental agencies.

A Review of Plant Phenology in South and Central America

Deforestation is the primary driver of carbon losses in tropical forests, but it does not operate alone. Forest fragmentation, a resulting feature of the deforestation process, promotes indirect carbon losses induced by edge effect. This process is not implicitly considered by policies for reducing carbon emissions in the tropics. Here, we used a remote sensing approach to estimate carbon losses driven by edge effect in Amazonia over the 2001 to 2015 period. We found that carbon losses associated with edge effect (947 Tg C) corresponded to one-third of losses from deforestation (2592 Tg C). Despite a notable negative trend of 7 Tg C year-1 in carbon losses from deforestation, the carbon losses from edge effect remained unchanged, with an average of 63 ± 8 Tg C year-1 Carbon losses caused by edge effect is thus an additional unquantified flux that can counteract carbon emissions avoided by reducing deforestation, compromising the Paris Agreement's bold targets.

https://advances.sciencemag.org/content/advances/6/40/eaaz8360.full.pdf

Persistent collapse of biomass in Amazonian forest edges following deforestation leads to unaccounted carbon losses

Assessing the persistent impacts of fragmentation on aboveground structure of tropical forests is essential to understanding the consequences of land use change for carbon storage and other ecosystem functions. We investigated the influence of edge distance and fragment size on canopy structure, aboveground woody biomass (AGB), and AGB turnover in the Biological Dynamics of Forest Fragments Project (BDFFP) in central Amazon, Brazil, after 22+ yr of fragment isolation, by combining canopy variables collected with portable canopy profiling lidar and airborne laser scanning surveys with long-term forest inventories. Forest height decreased by 30% at edges of large fragments (>10 ha) and interiors of small fragments (<3 ha). In larger fragments, canopy height was reduced up to 40 m from edges. Leaf area density profiles differed near edges: the density of understory vegetation was higher and midstory vegetation lower, consistent with canopy reorganization via increased regeneration of pioneers following post-fragmentation mortality of large trees. However, canopy openness and leaf area index remained similar to control plots throughout fragments, while canopy spatial heterogeneity was generally lower at edges. AGB stocks and fluxes were positively related to canopy height and negatively related to spatial heterogeneity. Other forest structure variables typically used to assess the ecological impacts of fragmentation (basal area, density of individuals, and density of pioneer trees) were also related to lidar-derived canopy surface variables. Canopy reorganization through the replacement of edge-sensitive species by disturbance-tolerant ones may have mitigated the biomass loss effects due to fragmentation observed in the earlier years of BDFFP. Lidar technology offered novel insights and observational scales for analysis of the ecological impacts of fragmentation on forest structure and function, specifically aboveground biomass storage.

Persistent effects of fragmentation on tropical rainforest canopy structure after 20 yr of isolation.

This study characterizes the flowering and fruiting phenology of the 13 most common pioneer tree species in early successional forests of the Central Amazon. For each species, 30 individuals, 10 each in three secondary forests, were monitored monthly for four years at the Biological Dynamics of Forest Fragments Project, north of Manaus. Five species showed nearly continuous flowering and fruiting throughout the study, indicating that resources were available to pollinators and dispersers on a regular basis. The other eight species showed stronger seasonality in reproduction, seven of them annually, and one supra-annually. Overall, flowering was concentrated in the transition from the dry to the rainy season and fruiting was concentrated in the rainy season. There was no relationship between reproductive phenology and tree pollinator type or dispersal mode. Reproductive phenology was remarkably consistent year to year. The pioneer community showed a variety of phenological patterns but as a whole tended to be characterized by annual flowering and fruiting, either continuously or seasonally, thereby fitting generalizations of pioneer species relative to mature forest species.

/pdf/reproductive-phenology-of-central-amazon-pioneer-trees-3j8dmlxemc.pdf

Reproductive Phenology of Central Amazon Pioneer Trees

Succession in the Brazilian Amazon depends on prior land-use history. Abandoned clearcuts become dominated by Cecropia trees and exhibit species replacements characteristic of natural succession in forest lightgaps. In contrast, abandoned pastures are dominated by Vismia trees that inhibit natural succession for a decade or more. Here we explore how advance regeneration and limited seed dispersal may contribute to the arrested succession in Vismia-dominated stands. Vegetation surveys showed that every Vismia stem in 3–8 year old Vismia stands originated as a re-sprout. In Cecropia stands, all tree species, including Vismia, originated mostly from seeds, after deforestation and abandonment. The 100% re-sprouts of Vismia in the abandoned pastures confirms that Vismia dominance results from re-sprouting following pasture fires. Seed rain in both Vismia and Cecropia dominated stands was limited almost exclusively to second growth species already reproducing in those stands, suggesting that the bats and birds ...

/pdf/seed-rain-and-advance-regeneration-in-secondary-succession-1qevbixb3b.pdf

Rita de Cássia Guimarães Mesquita

Papers

Persistent effects of fragmentation on tropical rainforest canopy structure after 20 yr of isolation.

Reproductive Phenology of Central Amazon Pioneer Trees

Seed Rain and Advance Regeneration in Secondary Succession in the Brazilian Amazon