Fine root dynamics across pantropical rainforest ecosystems

Fine roots constitute a significant component of the net primary productivity (NPP) of forest ecosystems but are much less studied than aboveground NPP. Comparisons across sites and regions are also hampered by inconsistent methodologies, especially in tropical areas. Here, we present a novel dataset of fine root biomass, productivity, residence time, and allocation in tropical old-growth rainforest sites worldwide, measured using consistent methods, and examine how these variables are related to consistently determined soil and climatic characteristics. Our pantropical dataset spans intensive monitoring plots in lowland (wet, semi-deciduous, and deciduous) and montane tropical forests in South America, Africa, and Southeast Asia (n = 47). Large spatial variation in fine root dynamics was observed across montane and lowland forest types. In lowland forests, we found a strong positive linear relationship between fine root productivity and sand content, this relationship was even stronger when we considered the fractional allocation of total NPP to fine roots, demonstrating that understanding allocation adds explanatory power to understanding fine root productivity and total NPP. Fine root residence time was a function of multiple factors: soil sand content, soil pH, and maximum water deficit, with longest residence times in acidic, sandy, and water-stressed soils. In tropical montane forests, on the other hand, a different set of relationships prevailed, highlighting the very different nature of montane and lowland forest biomes. Root productivity was a strong positive linear function of mean annual temperature, root residence time was a strong positive function of soil nitrogen content in montane forests, and lastly decreasing soil P content increased allocation of productivity to fine roots. In contrast to the lowlands, environmental conditions were a better predictor for fine root productivity than for fractional allocation of total NPP to fine roots, suggesting that root productivity is a particularly strong driver of NPP allocation in tropical mountain regions.WHH was funded by Peruvian FONDECYT/CONCYTEC (grant contract number 213-2015-FONDECYT). The GEM network was supported by a European Research Council Advanced Investigator Grant to YM (GEM-TRAITS: 321131) under the European Union's Seventh Framework Programme (FP7/2007-2013). The field data collection was funded NERC Grants NE/D014174/1 and NE/J022616/1 for in Peru, BALI (NE/K016369/1) for work in Malaysia, the Royal Society-Leverhulme Africa Capacity Building Programme for work in Ghana and Gabon and ESPA-ECOLIMITS (NE/1014705/1) in Ghana and Ethiopia. Plot inventories in South America were supported by funding from the US National Science Foundation Long-Term Research in Environmental Biology program (LTREB; DEB 1754647) and the Gordon and Betty Moore Foundation Andes-Amazon Program. GEM data in Gabon were collected under authorization to YM and supported by the Gabon National Parks Agency. Y.M. is supported by the Jackson Foundation. We would like to acknowledge the GEM team across the tropical regions and countries of Bolivia, Brazil, Ghana, Gabon, Ethiopia, Malaysia, and Peru

Seasonal trends of Amazonian rainforest phenology, net primary productivity, and carbon allocation.:Seasonal trends of Amazonian forests.

The seasonality of solar irradiance and precipitation may regulate seasonal variations in tropical forests carbon cycling. Controversy remains over their importance as drivers of seasonal dynamics of net primary productivity in tropical forests. We use ground data from nine lowland Amazonian forest plots collected over 3 years to quantify the monthly primary productivity (NPP) of leaves, reproductive material, woody material, and fine roots over an annual cycle. We distinguish between forests that do not experience substantial seasonal moisture stress (“humid sites”) and forests that experience a stronger dry season (“dry sites”). We find that forests from both precipitation regimes maximize leaf NPP over the drier season, with a peak in production in August at both humid (mean 0.39 ± 0.03 Mg C ha−1 month−1 in July, n = 4) and dry sites (mean 0.49 ± 0.03 Mg C ha−1 month−1 in September, n = 8). We identify two distinct seasonal carbon allocation patterns (the allocation of NPP to a specific organ such as wood leaves or fine roots divided by total NPP). The forests monitored in the present study show evidence of either (i) constant allocation to roots and a seasonal trade-off between leaf and woody material or (ii) constant allocation to wood and a seasonal trade-off between roots and leaves. Finally, we find strong evidence of synchronized flowering at the end of the dry season in both precipitation regimes. Flower production reaches a maximum of 0.047 ± 0.013 and 0.031 ± 0.004 Mg C ha−1 month−1 in November, in humid and dry sites, respectively. Fruitfall production was staggered throughout the year, probably reflecting the high variation in varying times to development and loss of fruit among species

Pantropical modelling of canopy functional traits using Sentinel-2 remote sensing data

Funding Information: This work is a product of the Global Ecosystems Monitoring (GEM) network (gem.tropicalforests.ox.ac.uk). J.A.G. was funded by the Natural Environment Research Council (NERC; NE/T011084/1 and NE/S011811/1) and the Netherlands Organisation for Scientific Research (NWO) under the Rubicon programme with project number 019.162LW.010. The traits field campaign was funded by a grant to Y.M. from the European Research Council (Advanced Grant GEM-TRAIT: 321131) under the European Union‘s Seventh Framework Programme (FP7/2007-2013), with additional support from NERC Grant NE/D014174/1 and NE/J022616/1 for traits work in Peru, NERC Grant ECOFOR (NE/K016385/1) for traits work in Santarem, NERC Grant BALI (NE/K016369/1) for plot and traits work in Malaysia and ERC Advanced Grant T-FORCES (291585) to Phillips for traits work in Australia. Plot setup in Ghana and Gabon were funded by a NERC Grant NE/I014705/1 and by the Royal Society-Leverhulme Africa Capacity Building Programme. The Malaysia campaign was also funded by NERC GrantNE/K016253/1. Plot inventories in Peru were supported by funding from the US National Science Foundation Long-Term Research in Environmental Biology program (LTREB; DEB 1754647) and the Gordon and Betty Moore Foundation Andes-Amazon Program. Plots inventories in Nova Xavantina (Brazil) were supported by the National Council for Scientific and Technological Development (CNPq), Long Term Ecological Research Program (PELD), Proc. 441244/2016-5, and the Foundation of Research Support of Mato Grosso (FAPEMAT), Project ReFlor, Proc. 589267/2016. During data collection, I.O. was supported by a Marie Curie Fellowship (FP7-PEOPLE-2012-IEF-327990). GEM trait data in Gabon was collected under authorisation to Y.M. and supported by the Gabon National Parks Agency. D.B. was funded by the Fondation Wiener-Anspach. W.D.K. acknowledges support from the Faculty Research Cluster ‘Global Ecology’ of the University of Amsterdam. M.S. was funded by a grant from the Ministry of Education, Youth and Sports of the Czech Republic (INTER-TRANSFER LTT19018). Y.M. is supported by the Jackson Foundation. We thank the two anonymous reviewers and Associate Editor G. Henebry for their insightful comments that helped improved this manuscript.Peer reviewedPostprin

The productivity, metabolism and carbon cycle of two lowland tropical forest plots in south-western Amazonia

Background: The forests of western Amazonia are known to be more dynamic that the better-studied forests of eastern Amazonia, but there has been no comprehensive description of the carbon cycle of a western Amazonian forest. Aims: We present the carbon budget of two forest plots in Tambopata in south-eastern Peru, western Amazonia. In particular, we present, for the first time, the seasonal variation in the detailed carbon budget of a tropical forest. Methods: We measured the major components of net primary production (NPP) and total autotrophic respiration over 3-6 years. Results: The NPP for the two plots was 15.1 ± 0.8 and 14.2 ± 1.0 Mg C ha −1 year −1 , the gross primary productivity (GPP) was 35.5 ± 3.6 and 34.5 ± 3.5 Mg C ha −1 year −1 , and the carbon use efficiency (CUE) was 0.42 ± 0.05 and 0.41 ± 0.05. NPP and CUE showed a large degree of seasonality. Conclusions: The two plots were similar in carbon cycling characteristics despite the different soils, the most notable difference being high allocation of NPP to canopy and low allocation to fine roots in the Holocene floodplain plot. The timing of the minima in the wet-dry transition suggests they are driven by phenological rhythms rather than being driven directly by water stress. When compared with results from forests on infertile forests in humid lowland eastern Amazonia, the plots have slightly higher GPP, but similar patterns of CUE and carbon allocation

Ecosystem carbon dynamics from Andes to Amazon : investigating the effects of environmental parameters on productivity and carbon cycling of an Andean tropical montane forest

The productivity and carbon cycling of tropical forests are an important aspect of the global carbon cycle. These variables have been investigated in lowland tropical forests, but they have rarely been studied in tropical montane forests. This thesis examines spatial and temporal patterns of above- and below-ground forest ecosystem carbon cycling along a transect of study sites ranging from lowland Amazonia (194 m) to the high Andes in S.B. Peru (3025 m), with a mean annual temperature ranging from 26.4 QC (194 m) to 11.8 QC (3020 m) and an annual rainfall ranging from 3086 mm yr" (1000 m) to 1706 mm yr" (3025 m). Measurements of above-ground (stem, canopy litterfall) and below-ground (fine roots, soil respiration, soil organic matter) carbon stocks and CO2 fluxes were made at nine one-hectare forest plots along the elevational gradient extending from lowland forest, through pre-montane, lower montane and upper montane forest, with relatively homogeneous stand structure, geological substrate and topography. I began by documenting the spatial and temporal patterns of above-ground carbon allocation along the elevational gradient. In particular, I analysed net primary productivity allocation to canopy components (leaf, twigs, flowers, fruit, bromeliads, epiphytes) along the elevational gradient in detail and observe the effects of seasonal variation on each component of above-ground production. Consistently lower values of mean annual above-ground productivity were observed in the cloud immersion zone of the montane forest. Then, the below-ground components of the ecosystem were recorded through spatial and temporal measurements of soil CO2 efflux and fine root dynamics (carbon stocks, net primary productivity and residence time). CO2 efflux did not show a significant trend along the elevation gradient, with the range of soil C02 efflux values similar to that observed in lowland tropical forest sites, despite the large variation in mean annual temperatures. Below-ground, a step change in fine root productivity was recorded at the base of the mountain (~1 000 m) between most lowland plots and tropical montane forest plots, although there was no significant change in fine root productivity with elevation above 1000 m. These measurements allowed for a comparison of the allocation of net primary productivity above- and below-ground along the elevational gradient. I combined the data obtained in this D.Phil thesis with data from recent lowland studies to examine the spatial patterns of above- and below-ground carbon dynamics along the elevational transect. The ratio of fine root biomass to stem biomass increased significantly with increasing elevation, whereas the allocation of net primary productivity above- and below-ground remained approximately constant at all elevations. Although net primary productivity declined in the tropical montane forest, the partitioning of productivity between the ecosystem sub-components remained the same in lowland, pre-montane and montane forests. Further, most processes driving the internal carbon cycle (net primary productivity, carbon stocks, autotrophic respiration) showed evidence of a step change at the base of the cloud immersion zone (1500 - 1855 m), and no significant change within the cloud immersion zone. These patterns imply that cloud forest characteristics (such as increased and year-long moisture resulting from frequent cloud cover immersion, a decrease in PAR incidence and slower soil nutrient uptake rates) combine with cooler temperatures to drive the internal carbon cycle.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

The Global Ecosystems Monitoring network: Monitoring ecosystem productivity and carbon cycling across the tropics

A rich understanding of the productivity, carbon and nutrient cycling of terrestrial ecosystems is essential in the context of understanding, modelling and managing the future response of the biosphere to global change. This need is particularly acute in tropical ecosystems, home to over 60% of global terrestrial productivity, over half of planetary biodiversity, and hotspots of anthropogenic pressure. In recent years there has been a surge of activity in collecting data on the carbon cycle, productivity, and plant functional traits of tropical ecosystems, most intensively through the Global Ecosystems Monitoring network (GEM). The GEM approach provides valuable insights by linking field-based ecosystem ecology with the needs of Earth system science. In this paper, we review and synthesize the context, history and recent scientific output from the GEM network. Key insights have emerged on the spatial and temporal variability of ecosystem productivity and on the role of temperature and drought stress on ecosystem function and resilience. New work across the network is now linking carbon cycling to nutrient cycling and plant functional traits, and subsequently to airborne remote sensing. We discuss some of the novel emerging patterns and practical and methodological challenges of this approach, and examine current and possible future directions, both within this network and as lessons for a more general terrestrial ecosystem observation scheme.The core establishment of the GEM network has been supported by the Gordon and Betty Moore Foundation, and European Research Council Advanced Investigator Grant GEM-TRAIT (321131). Site development in individual locations have been supported by multiple grants from the UK Natural Environment Research Council, in particular NE/D014174/1, NE/J023418/1, NE/I014705/1, NE/K016369/1, NE/K016385/1, NE/F005776/1, NE/N012453/1, NE/P001092/1 and NE/S01084X/1. Activities in Africa have been additionally supported by Royal Society-Leverhulme and Royal Society-DFID Africa Capacity Building Awards. Work in Malaysia has been greatly supported by the Sime Darby Foundation. YM is supported by the Jackson Foundation

Spatial patterns of above-ground structure, biomass and composition in a network of six Andean elevation transects

Background: The Amazon to Andes transition zone provides large expanses of relatively pristine forest wilderness across environmental gradients. Such elevational gradients are an excellent natural laboratory for establishing long-term interactions between forest ecosystems and environmental parameters, which is valuable for understanding ecosystem responses to environmental change. Aims: This study presents data on elevational trends of forest structure (biomass, basal area, height, stem density), species richness, and composition from six elevational transects in the Andes. Methods: We analysed the spatial patterns of forest structure, above-ground biomass and composition from 76 permanent plots, ranging from lowland Amazonian rain forest to high-elevation cloud forests in Ecuador, Peru, and Bolivia. Results: Forest above-ground woody biomass stocks ranged from 247 Mg ha −1 (Peru, 210 m) to 86 Mg ha −1 (Peru, 3450 m), with significantly decreasing trends of tree height and biomass and an increasing trend of stem density with increasing elevation. We observed an increase in forest richness at three taxonomic levels at mid-elevation, followed by a decrease in richness within the cloud immersion zone. Conclusions: The transects show an increase in stem density, a decline in tree height and above-ground coarse wood biomass and a hump-shaped trend in species richness with increasing elevation. These results suggest that environmental change could lead to significant shifts in the properties of these ecosystems over time