Understanding different dominance patterns in western Amazonian forests.

Dominance of neotropical tree communities by a few species is widely documented, but dominant trees show a variety of distributional patterns still poorly understood. Here, we used 503 forest inventory plots (93,719 individuals ≥2.5 cm diameter, 2609 species) to explore the relationships between local abundance, regional frequency and spatial aggregation of dominant species in four main habitat types in western Amazonia. Although the abundance-occupancy relationship is positive for the full dataset, we found that among dominant Amazonian tree species, there is a strong negative relationship between local abundance and regional frequency and/or spatial aggregation across habitat types. Our findings suggest an ecological trade-off whereby dominant species can be locally abundant (local dominants) or regionally widespread (widespread dominants), but rarely both (oligarchs). Given the importance of dominant species as drivers of diversity and ecosystem functioning, unravelling different dominance patterns is a research priority to direct conservation efforts in Amazonian forests.

Una nueva especie de Chrysochlamys (Clusiaceae, Clusioideae, Clusieae) del Parque Nacional Cordillera Azul, Loreto, Perú

Se describe e ilustra Chrysochlamys montieliae, nueva especie de la familia Clusiaceae, subfamilia Clusioideae, tribu Clusieae, procedente del Parque Nacional Cordillera Azul, del Departamento de Loreto. Siguiendo los criterios de la UICN, proponemos categorizarla como Datos Insuficientes (DD), debido a que solo es conocida de la localidad tipo. Igualmente, se discute sus relaciones con las especies afines.

Chrysochlamys montieliae, a new species of the Clusiaceae family, Clusioideae subfamily, Clusieae tribe, from the Cordillera Azul National Park, Department of Loreto, is described and illustrated. Following the IUCN criteria, we propose to categorize it as Data Deficient (DD), since it is only known from the type locality. In addition, their relationships with related species are discussed.

Occurrence and characterization of insect galls in two reserves of the Peruvian Amazon / Ocorrência e caracterização de galhas de insetos em duas reservas da Amazônia peruana

Abstract An insect gall inventory was carried out in two reserves of the Peruvian Amazon, Allpahuayo-Mishana National Reserve and Quistococha Regional Reserve, both situated in Iquitos, northeastern Peru. Four vegetation types were surveyed between December, 2021 and December, 2022: terra firme forest, white-sand wet forest, and white-sand dry forest in Allpahuayo-Mishana National Reserve, and palm swamp forest in Quistococha Regional Reserve. Overall, we found 262 gall morphotypes, distributed across 75 host species representing 66 plant genera and 30 families. Fabaceae was the plant family with the greatest number of gall morphotypes (n = 48), followed by Calophyllaceae (n = 21) and Euphorbiaceae (n = 20). The plant genera that supported the highest diversity of galls were Caraipa (n = 17), Eschweilera (n = 16), Tapirira (n = 16), Micrandra (n = 14), and Iryanthera (n = 10). The plant species Tapirira guianensis (n = 16), Caraipa utilis (n = 14), Micrandra elata (n = 14), Eschweilera coriacea (n = 11), and Sloanea parvifructa (n = 10) exhibited the highest richness of galls. Among the host plants, C. utilis stands alone as the only species noted as both endemic to the Amazonian region and bearing a Vulnerable (VU) conservation status. The leaves were the most attacked organs (90% of all galls). Most morphotypes are glabrous (89%), green (67%), globoid (53%), and one-chambered (91%). We found galling insects belonging to the orders Diptera, Thysanoptera, Lepidoptera, and Hemiptera. The galling insects of Cecidomyiidae (Diptera) were the most common, inducing 22% of the gall morphotypes. In addition to the gallers, we also observed the presence of successors, cecidophages, and parasitoids. Among the sampled vegetation types, the terra firme forest presented the highest richness of gall morphotypes and host plant species. This is the first systematic inventory of insect galls in this part of the Peruvian Amazon.

Resumo Um inventário de galhas de insetos foi realizado em duas reservas da Amazônia peruana, Reserva Nacional Allpahuayo-Mishana e Reserva Regional Quistococha, ambas situadas em Iquitos, nordeste do Peru. Quatro tipos de vegetação foram pesquisados entre dezembro de 2021 e dezembro de 2022: floresta de terra firme, floresta úmida de areia branca e floresta seca de areia branca na Reserva Nacional Allpahuayo-Mishana, e floresta de pântano de palmeiras na Reserva Regional Quistococha. No total, encontramos 262 morfotipos de galhas, distribuídos em 75 espécies hospedeiras representando 66 gêneros de plantas e 30 famílias. Fabaceae foi a família de plantas com o maior número de morfotipos de galhas (n = 48), seguida por Calophyllaceae (n = 21) e Euphorbiaceae (n = 20). Os gêneros de plantas que apresentaram a maior diversidade de galhas foram Caraipa (n = 17), Eschweilera (n = 16), Tapirira (n = 16), Micrandra (n = 14) e Iryanthera (n = 10). As espécies de plantas Tapirira guianensis (n = 16), Caraipa utilis (n = 14), Micrandra elata (n = 14), Eschweilera coriacea (n = 11) e Sloanea parvifructa (n = 10) apresentaram a maior riqueza de galhas. Dentre as plantas hospedeiras, C. utilis destaca-se como a única espécie listada como endêmica da região amazônica e com um status de conservação Vulnerável (VU). As folhas foram os órgãos mais atacados (90% de todas as galhas). A maioria dos morfotipos é glabra (89%), verde (67%), globoide (53%) e possui apenas uma câmara interna (91%). Encontramos insetos galhadores pertencentes às ordens Diptera, Thysanoptera, Lepidoptera e Hemiptera. Os insetos galhadores da família Cecidomyiidae (Diptera) foram os mais comuns, induzindo 22% dos morfotipos de galhas. Além dos galhadores, também observamos a presença de sucessores, cecidófagos e parasitoides. Entre os tipos de vegetação amostrados, a floresta de terra firme apresentou a maior riqueza de morfotipos de galhas e espécies de plantas hospedeiras. Este é o primeiro inventário sistemático de galhas de insetos nesta região da Amazônia peruana.

Amazon tree dominance across forest strata.

The forests of Amazonia are among the most biodiverse plant communities on Earth. Given the immediate threats posed by climate and land-use change, an improved understanding of how this extraordinary biodiversity is spatially organized is urgently required to develop effective conservation strategies. Most Amazonian tree species are extremely rare but a few are common across the region. Indeed, just 227 'hyperdominant' species account for >50% of all individuals >10 cm diameter at 1.3 m in height. Yet, the degree to which the phenomenon of hyperdominance is sensitive to tree size, the extent to which the composition of dominant species changes with size class and how evolutionary history constrains tree hyperdominance, all remain unknown. Here, we use a large floristic dataset to show that, while hyperdominance is a universal phenomenon across forest strata, different species dominate the forest understory, midstory and canopy. We further find that, although species belonging to a range of phylogenetically dispersed lineages have become hyperdominant in small size classes, hyperdominants in large size classes are restricted to a few lineages. Our results demonstrate that it is essential to consider all forest strata to understand regional patterns of dominance and composition in Amazonia. More generally, through the lens of 654 hyperdominant species, we outline a tractable pathway for understanding the functioning of half of Amazonian forests across vertical strata and geographical locations.

Long-term thermal sensitivity of Earth's tropical forests.

The sensitivity of tropical forest carbon to climate is a key uncertainty in predicting global climate change. Although short-term drying and warming are known to affect forests, it is unknown if such effects translate into long-term responses. Here, we analyze 590 permanent plots measured across the tropics to derive the equilibrium climate controls on forest carbon. Maximum temperature is the most important predictor of aboveground biomass (-9.1 megagrams of carbon per hectare per degree Celsius), primarily by reducing woody productivity, and has a greater impact per °C in the hottest forests (>32.2°C). Our results nevertheless reveal greater thermal resilience than observations of short-term variation imply. To realize the long-term climate adaptation potential of tropical forests requires both protecting them and stabilizing Earth's climate.

Field methods for sampling tree height for tropical forest biomass estimation.

Quantifying the relationship between tree diameter and height is a key component of efforts to estimate biomass and carbon stocks in tropical forests. Although substantial site-to-site variation in height-diameter allometries has been documented, the time consuming nature of measuring all tree heights in an inventory plot means that most studies do not include height, or else use generic pan-tropical or regional allometric equations to estimate height.Using a pan-tropical dataset of 73 plots where at least 150 trees had in-field ground-based height measurements, we examined how the number of trees sampled affects the performance of locally derived height-diameter allometries, and evaluated the performance of different methods for sampling trees for height measurement.Using cross-validation, we found that allometries constructed with just 20 locally measured values could often predict tree height with lower error than regional or climate-based allometries (mean reduction in prediction error = 0.46 m). The predictive performance of locally derived allometries improved with sample size, but with diminishing returns in performance gains when more than 40 trees were sampled. Estimates of stand-level biomass produced using local allometries to estimate tree height show no over- or under-estimation bias when compared with biomass estimates using field measured heights. We evaluated five strategies to sample trees for height measurement, and found that sampling strategies that included measuring the heights of the ten largest diameter trees in a plot outperformed (in terms of resulting in local height-diameter models with low height prediction error) entirely random or diameter size-class stratified approaches.Our results indicate that even limited sampling of heights can be used to refine height-diameter allometries. We recommend aiming for a conservative threshold of sampling 50 trees per location for height measurement, and including the ten trees with the largest diameter in this sample.

Contrasting patterns of diameter and biomass increment across tree functional groups in Amazonian forests.

Species' functional traits may help determine rates of carbon gain, with physiological and morphological trade-offs relating to shade tolerance affecting photosynthetic capacity and carbon allocation strategies. However, few studies have examined these trade-offs from the perspective of whole-plant biomass gain of adult trees. We compared tree-level annual diameter increments and annual above-ground biomass (AGB) increments in eight long-term plots in hyper-diverse northwest Amazonia to wood density (rho; a proxy for shade tolerance), whilst also controlling for resource supply (light and soil fertility). rho and annual diameter increment were negatively related, confirming expected differences in allocation associated with shade tolerance, such that light-demanding species allocate a greater proportion of carbon to diameter gain at the expense of woody tissue density. However, contrary to expectations, we found a positive relationship between rho and annual AGB increment in more fertile sites, although AGB gain did not differ significantly with rho class on low-fertility sites. Whole-plant carbon gain may be greater in shade-tolerant species due to higher total leaf area, despite lower leaf-level carbon assimilation rates. Alternatively, rates of carbon loss may be higher in more light-demanding species: higher rates of litterfall, respiration or allocation to roots, are all plausible mechanisms. However, the relationships between rho and AGB and diameter increments were weak; resource availability always exerted a stronger influence on tree growth rates.

Increasing biomass in Amazonian forest plots.

A previous study by Phillips et al. of changes in the biomass of permanent sample plots in Amazonian forests was used to infer the presence of a regional carbon sink. However, these results generated a vigorous debate about sampling and methodological issues. Therefore we present a new analysis of biomass change in old-growth Amazonian forest plots using updated inventory data. We find that across 59 sites, the above-ground dry biomass in trees that are more than 10 cm in diameter (AGB) has increased since plot establishment by 1.22 +/- 0.43 Mg per hectare per year (ha(-1) yr(-1), where 1 ha = 10(4) m2), or 0.98 +/- 0.38 Mg ha(-1) yr(-1) if individual plot values are weighted by the number of hectare years of monitoring. This significant increase is neither confounded by spatial or temporal variation in wood specific gravity, nor dependent on the allometric equation used to estimate AGB. The conclusion is also robust to uncertainty about diameter measurements for problematic trees: for 34 plots in western Amazon forests a significant increase in AGB is found even with a conservative assumption of zero growth for all trees where diameter measurements were made using optical methods and/or growth rates needed to be estimated following fieldwork. Overall, our results suggest a slightly greater rate of net stand-level change than was reported by Phillips et al. Considering the spatial and temporal scale of sampling and associated studies showing increases in forest growth and stem turnover, the results presented here suggest that the total biomass of these plots has on average increased and that there has been a regional-scale carbon sink in old-growth Amazonian forests during the previous two decades.