Mortalidad y reclutamiento de árboles en un bosque nublado de la cordillera de Los Andes, Venezuela

Tree mortality and recruitment was studied in a Tropical lower montane moist forest (sensu Holdridge) located in the Venezuelan Andes (8o39’N; 71o24’O). Data from six 0,25 ha permanent plots, with 23 successive measurements (1968 – 2000) were used to analyze tree mortality in individuals with a breast height diameter (dbh) = 10 cm. Fifty five tree species were recorded, including palms, with 622 individuals ha -1 , and a mean basimetric of 46 m 2 ha -1 . Among the most abundant species are found Myrcia fallax, Graffenrieda latifolia and Beilschmeidia sulcata, with more than 100 trees ha -1 . Annual tree recruitment and mortality rates averaged 1.64 and 1,59%, respectively. Significant differences among periods were found for both rates. Tree density increased in 12”%. Similarly, estimation of average tree half life varied among plots and averaged 43.1 years. Apparently forest dynamics is not affected by human pressure. However, some forest conservation actions are suggestedSe estudió la mortalidad y el reclutamiento de los árboles con un diámetro a la altura de pecho (dap) = 10 cm, en un bosque húmedo montano bajo (sensu Holdridge) situado en la Cordillera de los Andes (8o39’N; 71o24’O), entre 2200 y 2500 m.s.n.m. El análisis se realizó con datos provenientes de seis parcelas permanentes de 0,25 ha, con 23 mediciones sucesivas (1968 – 2000). Se registraron 55 especies arbóreas incluyendo palmas, con 622 individuos ha -1 y un área basal promedio de 46 m 2 ha -1 . Entre las especies más abundantes se encuentran Myrcia fallax, Graffenrieda latifolia y Beilschmeidia sulcata, con más de 100 ind ha -1 . Las tasas anuales de reclutamiento y mortalidad de los árboles fueron de 1,64 y 1,59%, respectivamente, con diferencias estadísticas entre parcelas solo para el reclutamiento. En cuanto a la variación entre periodos, se encontraron diferencias significativas para ambas tasas. Se observó un incremento en la densidad arbórea de un 12%. Así mismo, las estimaciones de vida media proyectadas varían entre parcelas para un promedio de 43,21 años. Se concluye que aparentemente el bosque no está siendo afectado en su dinámica; sin embargo, se sugieren algunas acciones que podrían contribuir a su conservación

Diametric tree growth in functional groups species in a seasonal forest of the venezuelan western plains

Se estudiaron las tasas de crecimiento de especies arbóreas que pertenecen a diferentes grupos funcionales y que ocupan distintas posiciones fisiográficas en un bosque estacional de la Reserva Forestal Caparo, Venezuela. Los grupos fueron conformados de acuerdo con sus requerimientos de luz y la altura máxima que pueden alcanzar los individuos. Se utilizaron datos de parcelas permanentes, con mediciones continuas durante 18 años del diámetro a la altura del pecho (DAP) a partir de 10 cm de DAP. Los mayores diámetros corresponden a los grupos de tolerantes intermedias grandes (>30 m de altura) y de tolerantes grandes. En general, los valores de crecimiento diamétrico encontrados están en el intervalo reportado en la zona tropical. La densidad total difirió significativamente entre grupos funcionales, pero no entre posiciones fisiográficas. Las mayores tasas anuales de crecimiento por categoría diamétrica correspondieron a las categorías intermedias. Se hallaron diferencias significativas de las tasas de crecimiento para los grupos, mas no entre posiciones fisiográficas. Las palmas son las especies que presentaron la mayor tasa de crecimiento, seguidas por las intolerantes medianas y las intolerantes pequeñas; las tolerantes intermedias y las tolerantes pequeñas presentaron las tasas menores. Estos resultados coinciden con lo esperado, considerando las características propias de cada uno de esos grupos.Tree species diametric growth rates were studied for different functional groups and in several physiographic positions in theExperimental Area of Caparo Forest Reserve, Venezuela. Functional groups were defined according to light requirements and maximum tree heights. We used a data set from permanent plots where diameter at breast height (DBH) was measured during a period of 18 years for all trees with DBH ≥ 10 cm. The largest DBH values were found for large (>30 m in height) intermediate tolerant species and large tolerant species. In general, growth rates estimated in this study are within the range reported for the tropical zone. Regarding tree total density significant differences were found among functional groups, but not between physiographic positions. The highest values of tree growth rate per diametric category were recorded for the intermediate categories. Moreover, highly significant differences were found between tree growth rates of functional group species, but not between physiographical positions. The group of palms showed the highest growth rates followed by small intermediate tolerant species. Intermediate tolerant species and small tolerant species showed the lowest tree growth rates. These results are in agreement with expected patterns regarding the traits of these functional groups

Water table depth modulates productivity and biomass across Amazonian forests

Water availability is the major driver of tropical forest structure and dynamics. Most research has focused on the impacts of climatic water availability, whereas remarkably little is known about the influence of water table depth and excess soil water on forest processes. Nevertheless, given that plants take up water from the soil, the impacts of climatic water supply on plants are likely to be modulated by soil water conditions. Lowland Amazonian forests. 1971–2019. We used 344 long‐term inventory plots distributed across Amazonia to analyse the effects of long‐term climatic and edaphic water supply on forest functioning. We modelled forest structure and dynamics as a function of climatic, soil‐water and edaphic properties. Water supplied by both precipitation and groundwater affects forest structure and dynamics, but in different ways. Forests with a shallow water table (depth <5 m) had 18% less above‐ground woody productivity and 23% less biomass stock than forests with a deep water table. Forests in drier climates (maximum cumulative water deficit < −160 mm) had 21% less productivity and 24% less biomass than those in wetter climates. Productivity was affected by the interaction between climatic water deficit and water table depth. On average, in drier climates the forests with a shallow water table had lower productivity than those with a deep water table, with this difference decreasing within wet climates, where lower productivity was confined to a very shallow water table. We show that the two extremes of water availability (excess and deficit) both reduce productivity in Amazon upland (terra‐firme) forests. Biomass and productivity across Amazonia respond not simply to regional climate, but rather to its interaction with water table conditions, exhibiting high local differentiation. Our study disentangles the relative contribution of those factors, helping to improve understanding of the functioning of tropical ecosystems and how they are likely to respond to climate change

Variation in stem mortality rates determines patterns of above-ground biomass in Amazonian forests: implications for dynamic global vegetation models

Understanding the processes that determine above-ground biomass (AGB) in Amazonian forests is important for predicting the sensitivity of these ecosystems to environmental change and for designing and evaluating dynamic global vegetation models (DGVMs). AGB is determined by inputs from woody productivity [woody net primary productivity (NPP)] and the rate at which carbon is lost through tree mortality. Here, we test whether two direct metrics of tree mortality (the absolute rate of woody biomass loss and the rate of stem mortality) and/or woody NPP, control variation in AGB among 167 plots in intact forest across Amazonia. We then compare these relationships and the observed variation in AGB and woody NPP with the predictions of four DGVMs. The observations show that stem mortality rates, rather than absolute rates of woody biomass loss, are the most important predictor of AGB, which is consistent with the importance of stand size structure for determining spatial variation in AGB. The relationship between stem mortality rates and AGB varies among different regions of Amazonia, indicating that variation in wood density and height/diameter relationships also influences AGB. In contrast to previous findings, we find that woody NPP is not correlated with stem mortality rates and is weakly positively correlated with AGB. Across the four models, basin-wide average AGB is similar to the mean of the observations. However, the models consistently overestimate woody NPP and poorly represent the spatial patterns of both AGB and woody NPP estimated using plot data. In marked contrast to the observations, DGVMs typically show strong positive relationships between woody NPP and AGB. Resolving these differences will require incorporating forest size structure, mechanistic models of stem mortality and variation in functional composition in DGVMs

Variation in stem mortality rates determines patterns of above-ground biomass in Amazonian forests: implications for dynamic global vegetation models

Understanding the processes that determine above-ground biomass (AGB) in Amazonian forests is important for predicting the sensitivity of these ecosystems to environmental change and for designing and evaluating dynamic global vegetation models (DGVMs). AGB is determined by inputs from woody productivity [woody net primary productivity (NPP)] and the rate at which carbon is lost through tree mortality. Here, we test whether two direct metrics of tree mortality (the absolute rate of woody biomass loss and the rate of stem mortality) and/or woody NPP, control variation in AGB among 167 plots in intact forest across Amazonia. We then compare these relationships and the observed variation in AGB and woody NPP with the predictions of four DGVMs. The observations show that stem mortality rates, rather than absolute rates of woody biomass loss, are the most important predictor of AGB, which is consistent with the importance of stand size structure for determining spatial variation in AGB. The relationship between stem mortality rates and AGB varies among different regions of Amazonia, indicating that variation in wood density and height/diameter relationships also influences AGB. In contrast to previous findings, we find that woody NPP is not correlated with stem mortality rates and is weakly positively correlated with AGB. Across the four models, basin-wide average AGB is similar to the mean of the observations. However, the models consistently overestimate woody NPP and poorly represent the spatial patterns of both AGB and woody NPP estimated using plot data. In marked contrast to the observations, DGVMs typically show strong positive relationships between woody NPP and AGB. Resolving these differences will require incorporating forest size structure, mechanistic models of stem mortality and variation in functional composition in DGVMs

Estimating the global conservation status of more than 15,000 Amazonian tree species

Estimates of extinction risk for Amazonian plant and animal species are rare and not often incorporated into land-use policy and conservation planning. We overlay spatial distribution models with historical and projected deforestation to show that at least 36% and up to 57% of all Amazonian tree species are likely to qualify as globally threatened under International Union for Conservation of Nature (IUCN) Red List criteria. If confirmed, these results would increase the number of threatened plant species on Earth by 22%. We show that the trends observed in Amazonia apply to trees throughout the tropics, and we predict thatmost of the world’s >40,000 tropical tree species now qualify as globally threatened. A gap analysis suggests that existing Amazonian protected areas and indigenous territories will protect viable populations of most threatened species if these areas suffer no further degradation, highlighting the key roles that protected areas, indigenous peoples, and improved governance can play in preventing large-scale extinctions in the tropics in this century

Hyperdominance in Amazonian Forest Carbon Cycling

While Amazonian forests are extraordinarily diverse, the abundance of trees is skewed strongly towards relatively few ‘hyperdominant’ species. In addition to their diversity, Amazonian trees are a key component of the global carbon cycle, assimilating and storing more carbon than any other ecosystem on Earth. Here we ask, using a unique data set of 530 forest plots, if the functions of storing and producing woody carbon are concentrated in a small number of tree species, whether the most abundant species also dominate carbon cycling, and whether dominant species are characterized by specific functional traits. We find that dominance of forest function is even more concentrated in a few species than is dominance of tree abundance, with only ≈1% of Amazon tree species responsible for 50% of carbon storage and productivity. Although those species that contribute most to biomass and productivity are often abundant, species maximum size is also influential, while the identity and ranking of dominant species varies by function and by region

Water table depth modulates productivity and biomass across Amazonian forests

Funding: This work was part of the PhD thesis of the first author, developed at the Graduate Program in Ecology of the National Institute of Amazonian Research (INPA), with a fellowship funded by Coordenação de Aperfeiçoamento de Pessoal de Nível Superior – Brasil (CAPES), Finance Code 001, (88887.141433/2017-00). The authors are also grateful for the financial and research support of the Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq), Amazonas State Research Foundation (FAPEAM), the Newton Fund via the Natural Environment Research Council (NE/M022021/1 to O.L.P. and F.R.C.C.), PPBio Manaus, Centro de Estudos Integrados da Biodiversidade Amazônica and RAINFOR. We also thank Karina Melgaço, Aurora Levesley and Gabriela Lopez-Gonzalez for curating and managing ForestPlots.net. This was ForestPlots.net Project 26 led by Thaiane Sousa. This is publication number 832 of the Technical Series of the Biological Dynamics of Forest Fragments Project (BDFFP, INPA/STRI).Aim : Water availability is the major driver of tropical forest structure and dynamics. Most research has focused on the impacts of climatic water availability, whereas remarkably little is known about the influence of water table depth and excess soil water on forest processes. Nevertheless, given that plants take up water from the soil, the impacts of climatic water supply on plants are likely to be modulated by soil water conditions. Location : Lowland Amazonian forests. Time period : 1971–2019. Methods : We used 344 long-term inventory plots distributed across Amazonia to analyse the effects of long-term climatic and edaphic water supply on forest functioning. We modelled forest structure and dynamics as a function of climatic, soil-water and edaphic properties. Results : Water supplied by both precipitation and groundwater affects forest structure and dynamics, but in different ways. Forests with a shallow water table (depth <5 m) had 18% less above-ground woody productivity and 23% less biomass stock than forests with a deep water table. Forests in drier climates (maximum cumulative water deficit < −160 mm) had 21% less productivity and 24% less biomass than those in wetter climates. Productivity was affected by the interaction between climatic water deficit and water table depth. On average, in drier climates the forests with a shallow water table had lower productivity than those with a deep water table, with this difference decreasing within wet climates, where lower productivity was confined to a very shallow water table. Main conclusions : We show that the two extremes of water availability (excess and deficit) both reduce productivity in Amazon upland (terra-firme) forests. Biomass and productivity across Amazonia respond not simply to regional climate, but rather to its interaction with water table conditions, exhibiting high local differentiation. Our study disentangles the relative contribution of those factors, helping to improve understanding of the functioning of tropical ecosystems and how they are likely to respond to climate change.Peer reviewe

The number of tree species on Earth

One of the most fundamental questions in ecology is how many species inhabit the Earth. However, due to massive logistical and financial challenges and taxonomic difficulties connected to the species concept definition, the global numbers of species, including those of important and well-studied life forms such as trees, still remain largely unknown. Here, based on global groundsourced data, we estimate the total tree species richness at global, continental, and biome levels. Our results indicate that there are 73,000 tree species globally, among which ∼9,000 tree species are yet to be discovered. Roughly 40% of undiscovered tree species are in South America. Moreover, almost one-third of all tree species to be discovered may be rare, with very low populations and limited spatial distribution (likely in remote tropical lowlands and mountains). These findings highlight the vulnerability of global forest biodiversity to anthropogenic changes in land use and climate, which disproportionately threaten rare species and thus, global tree richness

The number of tree species on Earth.

One of the most fundamental questions in ecology is how many species inhabit the Earth. However, due to massive logistical and financial challenges and taxonomic difficulties connected to the species concept definition, the global numbers of species, including those of important and well-studied life forms such as trees, still remain largely unknown. Here, based on global ground-sourced data, we estimate the total tree species richness at global, continental, and biome levels. Our results indicate that there are ∼73,000 tree species globally, among which ∼9,000 tree species are yet to be discovered. Roughly 40% of undiscovered tree species are in South America. Moreover, almost one-third of all tree species to be discovered may be rare, with very low populations and limited spatial distribution (likely in remote tropical lowlands and mountains). These findings highlight the vulnerability of global forest biodiversity to anthropogenic changes in land use and climate, which disproportionately threaten rare species and thus, global tree richness