Warming, drought, and disturbances lead to shifts in functional composition: a millennial‐scale analysis for Amazonian and Andean sites

Tropical forests are changing in composition and productivity, probably in response to changes in climate and disturbances. The responses to these multiple environmental drivers, and the mechanisms underlying the changes, remain largely unknown. Here, we use a functional trait approach on timescales of 10,000 years to assess how climate and disturbances influence the community-mean adult height, leaf area, seed mass, and wood density for eight lowland and highland forest landscapes. To do so, we combine data of eight fossil pollen records with functional traits and proxies for climate (temperature, precipitation, and El Niño frequency) and disturbances (fire and general disturbances). We found that temperature and disturbances were the most important drivers of changes in functional composition. Increased water availability (high precipitation and low El Niño frequency) generally led to more acquisitive trait composition (large leaves and soft wood). In lowland forests, warmer climates decreased community-mean height probably because of increased water stress, whereas in highland forests warmer climates increased height probably because of upslope migration of taller species. Disturbance increased the abundance of acquisitive, disturbance-adapted taxa with small seeds for quick colonization of disturbed sites, large leaves for light capture, and soft wood to attain fast height growth. Fire had weak effects on lowland forests but led to more stress-adapted taxa that are tall with fast life cycles and small seeds that can quickly colonize burned sites. Site-specific analyses were largely in line with cross-site analyses, except for varying site-level effects of El Niño frequency and fire activity, possibly because regional patterns in El Niño are not a good predictor of local changes, and charcoal abundances do not reflect fire intensity or severity. With future global changes, tropical Amazonian and Andean forests may transition toward shorter, drought- and disturbance-adapted forests in the lowlands but taller forests in the highlands

Human practices behind the aquatic and terrestrial ecological decoupling to climate change in the tropical Andes

Anthropogenic climate change and landscape alteration are two of the most important threats to the terrestrial and aquatic ecosystems of the tropical Americas, thus jeopardizing water and soil resources for millions of people in the Andean nations. Understanding how aquatic ecosystems will respond to anthropogenic stressors and accelerated warming requires shifting from short-term and static to long-term, dynamic characterizations of human-terrestrial-aquatic relationships. Here we use sediment records from Lake Llaviucu, a tropical mountain Andean lake long accessed by Indigenous and post-European societies, and hypothesize that under natural historical conditions (i.e., low human pressure) vegetation and aquatic ecosystems' responses to change are coupled through indirect climate influences—that is, past climate-driven vegetation changes dictated limnological trajectories. We used a multi-proxy paleoecological approach including drivers of terrestrial vegetation change (pollen), soil erosion (Titanium), human activity (agropastoralism indicators), and aquatic responses (diatoms) to estimate assemblage-wide rates of change and model their synchronous and asynchronous (lagged) relationships using Generalized Additive Models. Assemblage-wide rate of change results showed that between ca. 3000 and 400 calibrated years before present (cal years BP) terrestrial vegetation, agropastoralism and diatoms fluctuated along their mean regimes of rate of change without consistent periods of synchronous rapid change. In contrast, positive lagged relationships (i.e., asynchrony) between climate-driven terrestrial pollen changes and diatom responses (i.e., asynchrony) were in operation until ca. 750 cal years BP. Thereafter, positive lagged relationships between agropastoralism and diatom rates of changes dictated the lake trajectory, reflecting the primary control of human practices over the aquatic ecosystem prior European occupation. We interpret that shifts in Indigenous practices (e.g., valley terracing) curtailed nutrient inputs into the lake decoupling the links between climate-driven vegetation changes and the aquatic community. Our results demonstrate how rates of change of anthropogenic and climatic influences can guide dynamic ecological baselines for managing water ecosystem services in the Andes.info:eu-repo/semantics/acceptedVersio

Human practices behind the aquatic and terrestrial ecological decoupling to climate change in the tropical Andes

Anthropogenic climate change and landscape alteration are two of the most important threats to the terrestrial and aquatic ecosystems of the tropical Americas, thus jeopardizing water and soil resources for millions of people in the Andean nations. Understanding how aquatic ecosystems will respond to anthropogenic stressors and accelerated warming requires shifting from short-term and static to long-term, dynamic characterizations of human-terrestrial-aquatic relationships. Here we use sediment records from Lake Llaviucu, a tropical mountain Andean lake long accessed by Indigenous and post-European societies, and hypothesize that under natural historical conditions (i.e., low human pressure) vegetation and aquatic ecosystems' responses to change are coupled through indirect climate influences—that is, past climate-driven vegetation changes dictated limnological trajectories. We used a multi-proxy paleoecological approach including drivers of terrestrial vegetation change (pollen), soil erosion (Titanium), human activity (agropastoralism indicators), and aquatic responses (diatoms) to estimate assemblage-wide rates of change and model their synchronous and asynchronous (lagged) relationships using Generalized Additive Models. Assemblage-wide rate of change results showed that between ca. 3000 and 400 calibrated years before present (cal years BP) terrestrial vegetation, agropastoralism and diatoms fluctuated along their mean regimes of rate of change without consistent periods of synchronous rapid change. In contrast, positive lagged relationships (i.e., asynchrony) between climate-driven terrestrial pollen changes and diatom responses (i.e., asynchrony) were in operation until ca. 750 cal years BP. Thereafter, positive lagged relationships between agropastoralism and diatom rates of changes dictated the lake trajectory, reflecting the primary control of human practices over the aquatic ecosystem prior European occupation. We interpret that shifts in Indigenous practices (e.g., valley terracing) curtailed nutrient inputs into the lake decoupling the links between climate-driven vegetation changes and the aquatic community. Our results demonstrate how rates of change of anthropogenic and climatic influences can guide dynamic ecological baselines for managing water ecosystem services in the Andes.This work was supported by the National Science Foundation (NSF) - DEB 1260983 and EAR 1338694 and 1624207. XB has received funding from the postdoctoral fellowships programme Beatriu de Pinós, funded by the Secretary of Universities and Research (Government of Catalonia) and by the Horizon 2020 programme of research and innovation of the European Union under the Marie Sklodoska-Curie grant agreement No 801370

Limnological response to climatic changes in western Amazonia over the last millennium

The Little Ice Age (LIA - A.D. 1400 to 1820, 550 to 130 cal yr BP) was a significant worldwide climatic fluctuation, yet little is known about its impact on the ecology of Amazonia or its human inhabitants. Using organic geochemistry and diatoms, we investigate the limnological impact of this event in an Amazonian record spanning the last 760 years. The sedimentary record is from Lake Pata (Lagoa da Pata), which lies on the Hill of Six Lakes (Morro dos Seis Lagos), in the wettest section of the western Brazilian Amazonia. We found that many of the diatom taxa recovered from this remote site are either morphotypes of known species or species new to science. Eunotia and Frustulia dominated our fossil diatom assemblage over time, indicating oligotrophic waters of low pH. The limnological characteristics of this pristine system changed very little over the last millennium, except for a slight intensification of precipitation indicated by the increase in Aulacoseira granulata abundances, in C/N ratios, and in sedimentation rates. This phase lasted from 1190 to 1400 A.D. (760 to 550 cal yr BP). Although occurring before the onset of LIA, the observed change matched increases in precipitation observed in Venezuelan glaciers and Peruvian speleothems. We conclude that although the changes in precipitation detected in our lake match the timing of precipitation increase in some South American records, the event was shorter and its effects in this region of Amazonia were mild compared with other regional records. Our paleolimnological data provide additional insights into the interpretation of a remarkably stable fossil pollen record, in that the highest variance in vegetation occurred over the last millennium. Because Lake Pata has no human influence, part of its value is in providing a reference, with which variability in other settings that do have a human history, can be compared

Limnological response to climatic changes in western Amazonia over the last millennium

The Little Ice Age (LIA - A.D. 1400 to 1820, 550 to 130 cal yr BP) was a significant worldwide climatic fluctuation, yet little is known about its impact on the ecology of Amazonia or its human inhabitants. Using organic geochemistry and diatoms, we investigate the limnological impact of this event in an Amazonian record spanning the last 760 years. The sedimentary record is from Lake Pata (Lagoa da Pata), which lies on the Hill of Six Lakes (Morro dos Seis Lagos), in the wettest section of the western Brazilian Amazonia. We found that many of the diatom taxa recovered from this remote site are either morphotypes of known species or species new to science. Eunotia and Frustulia dominated our fossil diatom assemblage over time, indicating oligotrophic waters of low pH. The limnological characteristics of this pristine system changed very little over the last millennium, except for a slight intensification of precipitation indicated by the increase in Aulacoseira granulata abundances, in C/N ratios, and in sedimentation rates. This phase lasted from 1190 to 1400 A.D. (760 to 550 cal yr BP). Although occurring before the onset of LIA, the observed change matched increases in precipitation observed in Venezuelan glaciers and Peruvian speleothems. We conclude that although the changes in precipitation detected in our lake match the timing of precipitation increase in some South American records, the event was shorter and its effects in this region of Amazonia were mild compared with other regional records. Our paleolimnological data provide additional insights into the interpretation of a remarkably stable fossil pollen record, in that the highest variance in vegetation occurred over the last millennium. Because Lake Pata has no human influence, part of its value is in providing a reference, with which variability in other settings that do have a human history, can be compared

Data from: Scarce fire activity in the north and north-western Amazonian forests during the last 10,000 years

Data related to:William D. Gosling, S. Yoshi Maezumi, Britte M. Heijink, Majoi N. Nascimento, Marco F. Raczka, Masha T. van der Sande, Mark B. Bush, Crystal N.H. McMichaelScarce fire activity in the north and north-western Amazonian forests during the last 10,000 yearsPlant Ecology & DiversityDOI: https://doi.org/10.1080/17550874.2021.200804

Quantifying local-scale changes in Amazonian forest cover using phytoliths

The ecosystem services and immense biodiversity of Amazon rainforests are threatened by deforestation and forest degradation. A key goal of modern archaeology and paleoecology in Amazonia is to establish the extent and duration of past forest disturbance by humans. Fossil phytoliths are an established proxy to identify the duration of disturbance in lake sedimentary and soil archives. What is not known, is the spatial scale of such forest disturbances when identified by phytoliths. Here we use phytolith assemblages to detect local-scale forest openings, provide an estimate of extent, and consider long-term forest recovery. We use modern phytolith assemblages of 50 Amazonian lakes to i) assess how phytolith assemblages vary across forest cover at 5 spatial scales (100 m, 200 m, 500 m, 1 km, 2 km), ii) model which phytolith morphotypes can accurately predict forest cover at 5 spatial scales, and iii) compare phytoliths with pollen to quantify their relative ability to detect forest cover changes. DCA results show phytolith assemblages could be used to differentiate low, intermediate, and high forest cover values, but not to distinguish between biogeographical gradients across Amazonia. Beta regression models show Poaceae phytoliths can accurately predict forest cover within 200 m of Amazonian lakes. This modern calibration dataset can be used to make quantitative reconstructions of forest cover changes in Amazonia, to generate novel insights into long-term forest recovery. Combining phytoliths and pollen provides a unique opportunity to make qualitative and quantitative reconstructions of past vegetation changes, to better understand how human activities, environmental and climatic changes have shaped modern Amazonian forests