Revelando as causas e a distribuição temporal da mortalidade arbórea em uma floresta de terra-firme na Amazônia Central

We analyzed the causes and temporal distribution of tree mortality in 10 ha of an old growth forest located in E.E.S.T / INPA, Manaus, Amazonas. The study aimed to 1) reveal the main causes of tree death and 2) describe the variation in mortality over the year and also correlates it with climatic variables. The study was conducted in two transects of 20 x 2,500 m (5 ha each) and all individuals with DBH ≥ 10 cm were sampled, totaling 5,808 trees. The transects were monitored every month, alternately, for a year. The sanitary condition of living trees was observed in each monitoring. The dead individuals were classified according to their mode of death (standing, broken or uprooted). The pre and post-death of the trees were analyzed in order to identify the cause of the death. During one year of monitoring, 67 individuals died or 6.7 trees / ha and the mortality rate was 1.15%. year-1. Of the 67 dead trees, 24 died uprooted, 23 broken and 20 standing dead. Mortality was highly correlated with the rates of monthly rainfall (r = 0.85). Therefore, the events of death are more frequent in the rainy season. The correlation between mortality and wind speed was not as strong as expected (r = - 0.29) and the direction of the individuals fall was random. Altogether were distinguished six categories of cause of tree death. Storms (rain + wind) was the main cause, accounting for 45% of deaths. Close behind was stress and biotic factors, killing 20 of the 67 dead individuals. Of these 20 trees, at least one was killed by liana Apuí and 3 died from infestation by pathogenic fungi. The results indicate that from the small intervals between monitoring is possible to determine the cause of trees death in tropical forests and elucidate the effect of seasonal variations on mortality. The work has generated new information to the Amazon and it is suggested that these studies are included in the projects of forest dynamics.Foi analisado as causas e a distribuição temporal da mortalidade arbórea em 10 ha de floresta não perturbada localizada na E.E.S.T/INPA, Manaus, Amazonas. O estudo teve como objetivo 1) revelar as principais causas da morte arbórea e 2) descrever a variação da mortalidade ao longo do ano além de correlaciona-la com variáveis climáticas. O trabalho foi conduzido em dois transectos de 20 x 2.500m (5 ha cada) e todos os indivíduos arbóreos com DAP ≥ 10cm foram amostrados, somando 5.808 árvores. Os transectos foram monitorados todos os meses durante um ano de forma alternada. O estado fitossanitário das árvores vivas foi observado em cada uma das medições. Os indivíduos mortos foram classificados de acordo com seu modo de morte (em pé, quebrado ou desenraizado). As condições pré e pós-morte das árvores foram analisadas com a finalidade de se identificar a causa da sua morte. Durante um ano de monitoramento, morreram 67 indivíduos ou 6,7 árvores/ha e a taxa de mortalidade calculada foi de 1,15%.ano-1. Das 67 árvores mortas, 24 morreram desenraizadas, 23 mortas em pé e 20 mortas quebradas. A mortalidade foi altamente correlacionada com as taxas de precipitação mensal (r = 0,85). Portanto, os eventos de morte são mais frequentes na estação chuvosa. A correlação entre mortalidade e velocidade máxima mensal do vento foi fraca e negativa (r = -0,3) e a direção de queda dos indivíduos foi aleatória. Ao todo se determinou seis categorias de causa de morte arbórea. As tempestades (chuva + vento) foram a principal causa, responsável por 45% das mortes. Logo atrás das tempestades veio a causa estresse e fatores bióticos, matando 20 dos 67 indivíduos mortos. Dessas 20 árvores, pelo menos uma foi morta por cipó Apuí e 3 morreram por infestação de fungos patogênicos. Os resultados indicam que a partir dos pequenos intervalos entre as remedições é possível determinar as causas de morte arbórea nas florestas tropicais, além de elucidar o efeito das variações sazonais sobre a mortalidade. O trabalho gerou informações inéditas para a Amazônia e sugerese que esses estudos sejam inseridos nos projetos de monitoramento da dinâmica florestal

Dinâmica do componente arbóreo de uma mata de galeria inundável (Brasília, Distrito Federal) em um período de oito anos

(Dinâmica do componente arbóreo de uma mata de galeria inundável (Brasília, Distrito Federal) em um período de oito anos). As matas de galeria são importantes na manutenção dos recursos hídricos e da biodiversidade do Planalto Central, mas estão submetidas a fortes impactos antrópicos. Aquelas que ocorrem em solos mal drenados são pouquíssimo estudadas, com consequências negativas sobre sua conservação. Este trabalho objetivou avaliar a dinâmica florística e estrutural de um trecho de mata de galeria inundável na Fazenda Sucupira (15°54'22" S; 48°00'34" W), Brasília, Distrito Federal, em um período de oito anos (2000 a 2008). Nas duas medições realizadas, em 40 parcelas (0,8 ha) de 20 × 10 m, foram amostrados todos os indivíduos arbóreos com DAP ³ 3,0 cm. A primeira medição registrou 3.048 indivíduos, distribuídos em 50 espécies e 41 gêneros (32 famílias). Na segunda medição foram encontrados 2.728 indivíduos, pertencentes a 59 espécies e 48 gêneros (36 famílias). Em 2008 verificou-se diminuição de 320 indivíduos, mas acréscimo de 9 espécies, 7 gêneros e 4 famílias. O período monitorado revelou altas taxas de mortalidade (4,25% ano-1) e recrutamento (3,67% ano-1), mudanças consideráveis na importância de muitas espécies, sem alterações significativas na diversidade: H' = 2,84 nats indivíduo-1, J' = 0,73 em 2000; H' = 3,02 nats indivíduo-1, J' = 0,74 em 2008. Esses ambientes diferenciados parecem ser muito dinâmicos em sua florística, sem que a estrutura comunitária e a diversidade sejam afetadas. Mais estudos de dinâmica, por períodos mais longos, ainda são necessários para que se possa compreender o ambiente florestal inundável do Brasil Central com mais segurança, gerando informações que subsidiem ações prementes de conservação.(Dynamics of the arboreal component in a swamp gallery forest (Brasília, Federal District) over an eight year period). Gallery forests play an important role in supporting the water resources and biodiversity of the Brazilian Central Plateau, but they have been under strong anthropic impact. Those that occur in poorly drained soils are little studied, with negative consequences for their conservation. The aim of this work was to evaluate the floristic and structural dynamics of a swamp gallery forest fragment at Fazenda Sucupira (15°54'22" S; 48°00'34" W), Brasília, Federal District, over an eight year period (2000 to 2008). Two measurements were carried out in 40 plots (0.8 ha) of 20 × 10 m. All individuals with DAP ³ 3.0 cm were recorded. The first measurement registered 3,048 individuals, distributed in 50 species, 41 genera (32 families). In the second measurement 2,728 individuals were found, belonging to 59 species, 48 genera (36 families). In 2008 there was a reduction of 320 individuals but an addition of 9 species, 7 genera and 4 families. The monitoring period showed high rates of mortality (4.25% year-1) and recruitment (3.67% year-1), changes in the importance of many species, without significant modification of the diversity index: H' = 2.84 nats ind.-1, J' = 0.73 in 2000 and H' = 3.02 nats ind.-1, J' = 0.74 in 2008. This unique type of gallery forest seems to be dynamic in its floristic community, without detectable effects on structure and diversity. More studies focused on community dynamic, for longer periods are still needed for a better understanding of the swamp forest environment in Central Brazil, and to generate information for conservation action plans

Green leaf volatile emissions during high temperature and drought stress in a central Amazon rainforest

Prolonged drought stress combined with high leaf temperatures can induce programmed leaf senescence involving lipid peroxidation, and the loss of net carbon assimilation during early stages of tree mortality. Periodic droughts are known to induce widespread tree mortality in the Amazon rainforest, but little is known about the role of lipid peroxidation during drought-induced leaf senescence. In this study, we present observations of green leaf volatile (GLV) emissions during membrane peroxidation processes associated with the combined effects of high leaf temperatures and drought-induced leaf senescence from individual detached leaves and a rainforest ecosystem in the central Amazon. Temperature-dependent leaf emissions of volatile terpenoids were observed during the morning, and together with transpiration and net photosynthesis, showed a post-midday depression. This post-midday depression was associated with a stimulation of C5 and C6 GLV emissions, which continued to increase throughout the late afternoon in a temperature-independent fashion. During the 2010 drought in the Amazon Basin, which resulted in widespread tree mortality, green leaf volatile emissions (C6 GLVs) were observed to build up within the forest canopy atmosphere, likely associated with high leaf temperatures and enhanced drought-induced leaf senescence processes. The results suggest that observations of GLVs in the tropical boundary layer could be used as a chemical sensor of reduced ecosystem productivity associated with drought stress. © 2015 by the authors; licensee MDPI, Basel, Switzerland

Revealing the causes and temporal distribution of tree mortality in Central Amazonia

Tree mortality is a critical process in forest ecosystems, as it influences floristic composition, structure, dynamics, carbon storage, and forest nutrient cycling. However, the mechanisms behind tree death in tropical regions are still poorly characterized. This lack of information is mainly because tree mortality data come from long-interval inventories and studies that measured tree death seasonally are scarce. Here we offer novel insights into the power of fine temporal scale observations and we use a natural history approach to understand the processes and mechanism of tree mortality. We monitored tree mortality every month during one year, in 10 ha of terra-firme forest. To determine the pathways of mortality, we considered the state of the tree at the start of the investigation and the pre and post-mortem characteristics. From November 2010 to October 2011, 67 out of 5808 trees died. Despite the 2010 drought, mortality was highly correlated with monthly rainfall (r = 0.85). In total, six pathways of mortality were assessed. Storms were the main cause of mortality, killing 45% of all dead trees, followed by Biotic/abiotic factors accounting for 30% of tree mortality. The high mortality registered in the rainy season was mostly (78%) due to healthy trees dying uprooted or snapped. Finally, we would benefit from studies that assess mortality on a monthly basis and in combination with quantitative long-term data, we can substantially improve our understanding of the mechanisms behind tree death in the tropics. © 2018 Elsevier B.V

Convergent evolution of tree hydraulic traits in Amazonian habitats: implications for community assemblage and vulnerability to drought

Amazonian droughts are increasing in frequency and severity. However, little is known about how this may influence species-specific vulnerability to drought across different ecosystem types. We measured 16 functional traits for 16 congeneric species from six families and eight genera restricted to floodplain, swamp, white-sand or plateau forests of Central Amazonia. We investigated whether habitat distributions can be explained by species hydraulic strategies, and if habitat specialists differ in their vulnerability to embolism that would make water transport difficult during drought periods. We found strong functional differences among species. Nonflooded species had higher wood specific gravity and lower stomatal density, whereas flooded species had wider vessels, and higher leaf and xylem hydraulic conductivity. The P50 values (water potential at 50% loss of hydraulic conductivity) of nonflooded species were significantly more negative than flooded species. However, we found no differences in hydraulic safety margin among species, suggesting that all trees may be equally likely to experience hydraulic failure during severe droughts. Water availability imposes a strong selection leading to differentiation of plant hydraulic strategies among species and may underlie patterns of adaptive radiation in many tropical tree genera. Our results have important implications for modeling species distribution and resilience under future climate scenarios

Leaf isoprene and monoterpene emission distribution across hyperdominant tree genera in the Amazon basin

Tropical forests are acknowledged to be the largest global source of isoprene (C5H8) and monoterpenes (C10H16) emissions, with current synthesis studies suggesting few tropical species emit isoprenoids (20–38%) and do so with highly variable emission capacities, including within the same genera. This apparent lack of a clear phylogenetic thread has created difficulties both in linking isoprenoid function with evolution and for the development of accurate biosphere-atmosphere models. Here, we present a systematic emission study of “hyperdominant” tree species in the Amazon Basin. Across 162 individuals, distributed among 25 botanical families and 113 species, isoprenoid emissions were widespread among both early and late successional species (isoprene: 61.9% of the species; monoterpenes: 15.0%; both isoprene and monoterpenes: 9.7%). The hyperdominant species (69) across the top five most abundant genera, which make up about 50% of all individuals in the Basin, had a similar abundance of isoprenoid emitters (isoprene: 63.8%; monoterpenes: 17.4%; both 11.6%). Among the abundant genera, only Pouteria had a low frequency of isoprene emitting species (15.8% of 19 species). In contrast, Protium, Licania, Inga, and Eschweilera were rich in isoprene emitting species (83.3% of 12 species, 61.1% of 18 species, 100% of 8 species, and 100% of 12 species, respectively). Light response curves of individuals in each of the five genera showed light-dependent, photosynthesis-linked emission rates of isoprene and monoterpenes. Importantly, in every genus, we observed species with light-dependent isoprene emissions together with monoterpenes including β-ocimene. These observations support the emerging view of the evolution of isoprene synthases from β-ocimene synthases. Our results have important implications for understanding isoprenoid function-evolution relationships and the development of more accurate Earth System Models. © 2020 Elsevier Lt

Species-specific shifts in diurnal sap velocity dynamics and hysteretic behavior of ecophysiological variables during the 2015–2016 el niño event in the amazon forest

Current climate change scenarios indicate warmer temperatures and the potential for more extreme droughts in the tropics, such that a mechanistic understanding of the water cycle from individual trees to landscapes is needed to adequately predict future changes in forest structure and function. In this study, we contrasted physiological responses of tropical trees during a normal dry season with the extreme dry season due to the 2015–2016 El Niño-Southern Oscillation (ENSO) event. We quantified high resolution temporal dynamics of sap velocity (Vs), stomatal conductance (gs) and leaf water potential (ΨL) of multiple canopy trees, and their correlations with leaf temperature (Tleaf) and environmental conditions [direct solar radiation, air temperature (Tair) and vapor pressure deficit (VPD)]. The experiment leveraged canopy access towers to measure adjacent trees at the ZF2 and Tapajós tropical forest research (near the cities of Manaus and Santarém). The temporal difference between the peak of gs (late morning) and the peak of VPD (early afternoon) is one of the major regulators of sap velocity hysteresis patterns. Sap velocity displayed species-specific diurnal hysteresis patterns reflected by changes in Tleaf. In the morning, Tleaf and sap velocity displayed a sigmoidal relationship. In the afternoon, stomatal conductance declined as Tleaf approached a daily peak, allowing ΨL to begin recovery, while sap velocity declined with an exponential relationship with Tleaf. In Manaus, hysteresis indices of the variables Tleaf-Tair and ΨL-Tleaf were calculated for different species and a significant difference (p < 0.01, α = 0.05) was observed when the 2015 dry season (ENSO period) was compared with the 2017 dry season (“control scenario”). In some days during the 2015 ENSO event, Tleaf approached 40°C for all studied species and the differences between Tleaf and Tair reached as high at 8°C (average difference: 1.65 ± 1.07°C). Generally, Tleaf was higher than Tair during the middle morning to early afternoon, and lower than Tair during the early morning, late afternoon and night. Our results support the hypothesis that partial stomatal closure allows for a recovery in ΨL during the afternoon period giving an observed counterclockwise hysteresis pattern between ΨL and Tleaf. © 2019 Gimenez, Jardine, Higuchi, Negrón-Juárez, Sampaio-Filho, Cobello, Fontes, Dawson, Varadharajan, Christianson, Spanner, Araújo, Warren, Newman, Holm, Koven, McDowell and Chambers

Precipitation mediates sap flux sensitivity to evaporative demand in the neotropics

Transpiration in humid tropical forests modulates the global water cycle and is a key driver of climate regulation. Yet, our understanding of how tropical trees regulate sap flux in response to climate variability remains elusive. With a progressively warming climate, atmospheric evaporative demand [i.e., vapor pressure deficit (VPD)] will be increasingly important for plant functioning, becoming the major control of plant water use in the twenty-first century. Using measurements in 34 tree species at seven sites across a precipitation gradient in the neotropics, we determined how the maximum sap flux velocity (vmax) and the VPD threshold at which vmax is reached (VPDmax) vary with precipitation regime [mean annual precipitation (MAP); seasonal drought intensity (PDRY)] and two functional traits related to foliar and wood economics spectra [leaf mass per area (LMA); wood specific gravity (WSG)]. We show that, even though vmax is highly variable within sites, it follows a negative trend in response to increasing MAP and PDRY across sites. LMA and WSG exerted little effect on vmax and VPDmax, suggesting that these widely used functional traits provide limited explanatory power of dynamic plant responses to environmental variation within hyper-diverse forests. This study demonstrates that long-term precipitation plays an important role in the sap flux response of humid tropical forests to VPD. Our findings suggest that under higher evaporative demand, trees growing in wetter environments in humid tropical regions may be subjected to reduced water exchange with the atmosphere relative to trees growing in drier climates. © 2019, Springer-Verlag GmbH Germany, part of Springer Nature