176 research outputs found
Forest disturbance and recovery: A general review in the context of spaceborne remote sensing of impacts on aboveground biomass and canopy structure
Abrupt forest disturbances generating gaps \u3e0.001 km2 impact roughly 0.4–0.7 million km2a−1. Fire, windstorms, logging, and shifting cultivation are dominant disturbances; minor contributors are land conversion, flooding, landslides, and avalanches. All can have substantial impacts on canopy biomass and structure. Quantifying disturbance location, extent, severity, and the fate of disturbed biomass will improve carbon budget estimates and lead to better initialization, parameterization, and/or testing of forest carbon cycle models. Spaceborne remote sensing maps large-scale forest disturbance occurrence, location, and extent, particularly with moderate- and fine-scale resolution passive optical/near-infrared (NIR) instruments. High-resolution remote sensing (e.g., ∼1 m passive optical/NIR, or small footprint lidar) can map crown geometry and gaps, but has rarely been systematically applied to study small-scale disturbance and natural mortality gap dynamics over large regions. Reducing uncertainty in disturbance and recovery impacts on global forest carbon balance requires quantification of (1) predisturbance forest biomass; (2) disturbance impact on standing biomass and its fate; and (3) rate of biomass accumulation during recovery. Active remote sensing data (e.g., lidar, radar) are more directly indicative of canopy biomass and many structural properties than passive instrument data; a new generation of instruments designed to generate global coverage/sampling of canopy biomass and structure can improve our ability to quantify the carbon balance of Earth\u27s forests. Generating a high-quality quantitative assessment of disturbance impacts on canopy biomass and structure with spaceborne remote sensing requires comprehensive, well designed, and well coordinated field programs collecting high-quality ground-based data and linkages to dynamical models that can use this information
Forest response to increased disturbance in the central Amazon and comparison to western Amazonian forests
Uncertainties surrounding vegetation response to increased disturbance rates
associated with climate change remains a major global change issue for Amazonian
forests. Additionally, turnover rates computed as the average of mortality
and recruitment rates in the western Amazon basin are doubled when compared
to the central Amazon, and notable gradients currently exist in specific wood
density and aboveground biomass (AGB) between these two regions. This study
investigates the extent to which the variation in disturbance regimes
contributes to these regional gradients. To address this issue, we evaluated
disturbance–recovery processes in a central Amazonian forest under two scenarios
of increased disturbance rates using first ZELIG-TROP, a dynamic vegetation
gap model which we calibrated using long-term inventory data, and second
using the Community Land Model (CLM), a global land surface model that is
part of the Community Earth System Model (CESM). Upon doubling the mortality
rate in the central Amazon to mirror the natural disturbance regime in the
western Amazon of ∼2% mortality, the two regions continued to
differ in multiple forest processes. With the inclusion of elevated natural
disturbances, at steady state, AGB significantly decreased by 41.9% with
no significant difference between modeled AGB and empirical AGB from the
western Amazon data sets (104 vs. 107 Mg C ha−1, respectively).
However, different processes were responsible for the reductions in AGB
between the models and empirical data set. The empirical data set suggests that
a decrease in wood density is a driver leading to the reduction in AGB. While
decreased stand basal area was the driver of AGB loss in ZELIG-TROP, a forest
attribute that does not significantly vary across the Amazon Basin. Further
comparisons found that stem density, specific wood density, and basal area
growth rates differed between the two Amazonian regions. Last, to help
quantify the impacts of increased disturbances on the climate and earth
system, we evaluated the fidelity of tree mortality and disturbance in CLM.
Similar to ZELIG-TROP, CLM predicted a net carbon loss of 49.9%, with an
insignificant effect on aboveground net primary productivity (ANPP).
Decreased leaf area index (LAI) was the driver of AGB loss in CLM, another
forest attribute that does not significantly vary across the Amazon Basin,
and the temporal variability in carbon stock and fluxes was not replicated in
CLM. Our results suggest that (1) the variability between regions cannot be
entirely explained by the variability in disturbance regime, but rather
potentially sensitive to intrinsic environmental factors; or (2) the models
are not accurately simulating all tropical forest characteristics in response
to increased disturbances
Benchmarking and parameter sensitivity of physiological and vegetation dynamics using the Functionally Assembled Terrestrial Ecosystem Simulator (FATES) at Barro Colorado Island, Panama
Plant functional traits determine vegetation responses to environmental variation, but variation in trait values is large, even within a single site. Likewise, uncertainty in how these traits map to Earth system feedbacks is large. We use a vegetation demographic model (VDM), the Functionally Assembled Terrestrial Ecosystem Simulator (FATES), to explore parameter sensitivity of model predictions, and comparison to observations, at a tropical forest site: Barro Colorado Island in Panama. We define a single 12-dimensional distribution of plant trait variation, derived primarily from observations in Panama, and define plant functional types (PFTs) as random draws from this distribution. We compare several model ensembles, where individual ensemble members vary only in the plant traits that define PFTs, and separate ensembles differ from each other based on either model structural assumptions or non-trait, ecosystem-level parameters, which include (a) the number of competing PFTs present in any simulation and (b) parameters that govern disturbance and height-based light competition. While single-PFT simulations are roughly consistent with observations of productivity at Barro Colorado Island, increasing the number of competing PFTs strongly shifts model predictions towards higher productivity and biomass forests. Different ecosystem variables show greater sensitivity than others to the number of competing PFTs, with the predictions that are most dominated by large trees, such as biomass, being the most sensitive. Changing disturbance and height-sorting parameters, i.e., the rules of competitive trait filtering, shifts regimes of dominance or coexistence between early- and late-successional PFTs in the model. Increases to the extent or severity of disturbance, or to the degree of determinism in height-based light competition, all act to shift the community towards early-successional PFTs. In turn, these shifts in competitive outcomes alter predictions of ecosystem states and fluxes, with more early-successional-dominated forests having lower biomass. It is thus crucial to differentiate between plant traits, which are under competitive pressure in VDMs, from those model parameters that are not and to better understand the relationships between these two types of model parameters to quantify sources of uncertainty in VDMs
Volatile monoterpene \u27fingerprints\u27 of resinous Protium tree species in the Amazon rainforest
Dynamics of the Terra-firme primary forest in Manaus-AM region using the Markov probabilistic transition matrix
To combine protection and utilization of forest resources in the tropics, the understanding of forest dynamics is essential. It is also important in the definition of strategies for rehabilitation of degraded areas. In Forestry, forest dynamics could be translated as the understanding of recruitment, mortality and biomass increment rates over time. For this study, these rates were estimated based on measurements carried out in 2000 and 2004 over two transects measuring 20 by 2500 m (5 hectares) each, in Manaus region. This paper deals with forest dynamics of a pristine forest based on the probabilistic transition matrix (the first-order Markov Chain) approach. The main objective is to report 4-year (2000 to 2004) changes in the forest structure. Diameter distribution and tree mortality will be projected ahead to 2008 (t+2), based upon a 4-year period of observations completed in 2004 (t+1) and its immediate past in 2000 (t). In terms of fresh aboveground biomass, this site accumulated 8.34 t.ha-1.ano-1. The chi ² test has shown no statistical difference (p = 0.01) between observed diameter frequency and the expected projected by Markov Chain. This result indicates that the Markov Chain approach is a reliable tool to project the forest dynamics on a short-term basis. In 2008, the total number of individuals will have a decrease of 2.7%, and the mortality rate will 15% higher than in 2004.Os fatores que envolvem os processos da dinâmica da floresta influenciam a sua biodiversidade e, portanto, a qualidade da floresta. A definição de estratégias que envolve a proteção e o uso adequado da floresta manejada e a recuperação de áreas já degradadas tornam-se possÃvel com o estudo da estrutura e dinâmica da floresta primária por meio de informações como a mortalidade, o recrutamento e a permanência das árvores no sistema florestal. Este trabalho teve como objetivo avaliar a dinâmica de uma floresta não perturbada e fazer projeções da dinâmica florestal usando a matriz de transição probabilÃstica (Cadeia de Markov). As taxas de recrutamento, mortalidade e incremento foram determinadas a partir de inventários florestais realizados em dois transectos, nos sentidos Norte-Sul e Leste-Oeste (20 x 2500 m cada, totalizando 10 ha), localizados no km 50 da BR 174, na estrada vicinal ZF-2, Manaus/AM, nos anos de 2000 e 2004. A floresta acumulou 8,34 t.ha-1.ano-1 de biomassa fresca acima do solo. De acordo com projeção para 2008, o número total de árvores diminuirá em 2,67% (de 5987 indivÃduos (2004) para 5827 (2008)) e a mortalidade será 15% maior (de 264 (2004) para 311 (2008)). O teste Qui-quadrado mostrou que não há diferença significativa (1% de probabilidade) entre as informações coletadas e projetadas. Esses resultados permitem concluir que a Cadeia de Markov é um eficiente instrumento para projetar a dinâmica da floresta natural, contribuindo para o planejamento em curto prazo das atividades que utilizam os recursos florestais
Evolution of opinions on social networks in the presence of competing committed groups
Public opinion is often affected by the presence of committed groups of
individuals dedicated to competing points of view. Using a model of pairwise
social influence, we study how the presence of such groups within social
networks affects the outcome and the speed of evolution of the overall opinion
on the network. Earlier work indicated that a single committed group within a
dense social network can cause the entire network to quickly adopt the group's
opinion (in times scaling logarithmically with the network size), so long as
the committed group constitutes more than about 10% of the population (with the
findings being qualitatively similar for sparse networks as well). Here we
study the more general case of opinion evolution when two groups committed to
distinct, competing opinions and , and constituting fractions and
of the total population respectively, are present in the network. We show
for stylized social networks (including Erd\H{o}s-R\'enyi random graphs and
Barab\'asi-Albert scale-free networks) that the phase diagram of this system in
parameter space consists of two regions, one where two stable
steady-states coexist, and the remaining where only a single stable
steady-state exists. These two regions are separated by two fold-bifurcation
(spinodal) lines which meet tangentially and terminate at a cusp (critical
point). We provide further insights to the phase diagram and to the nature of
the underlying phase transitions by investigating the model on infinite
(mean-field limit), finite complete graphs and finite sparse networks. For the
latter case, we also derive the scaling exponent associated with the
exponential growth of switching times as a function of the distance from the
critical point.Comment: 23 pages: 15 pages + 7 figures (main text), 8 pages + 1 figure + 1
table (supplementary info
Use of metallic dendrometers for individual diameter growth patterns of trees at Cuieiras River basin
This study dealt with the analysis of individual growth pattern for about 300 trees distributed over two transects (East-West and North-South) measuring 20 by 2500 m, which were stratified by plateau, slope and "baixio", and three diameter at breast height (dbh) classes (10≤dbh<30 cm; 30≤dbh<50 cm e dbh≥50 cm). In each tree a metal "dendrometer" band was fixed to the trunk and growth in circumference was measured with a digital caliper. Measurements were carried out for 19 months, from June/1999 to December/2000; for this study only 12 months of year 2000 were considered. Individual growth pattern varied significantly over time (p = 0,00), and slightly (p = 0,08) when the interaction months and dbh classes was included; on the other hand, the signal is very weak (p = 0,25) when topographical classes were added to the later interaction, and no signal at all (p = 0,89) when the interaction between months and topographical classes were analyzed. Mean annual increment in diameter considering all 272 monitored trees was 1,64 ± 0,21 mm yr-1 (p = 0,05), falling within the interval estimated for BIONTE and Tapajós National Forest which are 1,5 and 2 mm per year, respectively.Este trabalho tem como objetivo analisar padrões de crescimento individual de diversas árvores que ocorrem em duas topossequências (direções Norte-Sul e Leste-Oeste), de uma amostra representativa da floresta de terra-firme na Amazônia Central. Foram selecionados de forma aleatória, aproximadamente, 300 indivÃduos, sendo 150 em cada topossequência, distribuÃdos em mesmas proporções nas três classes topográficas (platô, encosta e baixio) e nas três classes de diâmetro (10≤ DAP < 30 cm; 30≤ DAP< 50 cm e DAP≥ 50 cm). Em cada uma dessas árvores foi instalada uma fita metálica, com extremidades parcialmente sobrepostas e ligadas por uma mola; o avanço de uma das pontas, dentro de uma abertura, representa o crescimento em circunferência, que foi medido com um paquÃmetro digital. As medições foram realizadas mensalmente ao longo de 19 meses, de junho/1999 a dezembro/2000; neste estudo foram considerados apenas os 12 meses do ano 2000. O padrão individual de crescimento em diâmetro varia muito com o passar dos meses (p = 0,00) e apenas razoavelmente quando os meses são interagidos com as classes de diâmetro (p 0,08); por outro lado, há fraca uma evidência (p = 0,25) quando as classes topográficas são acrescentadas na interação anterior e praticamente nenhuma evidência (p = 0,89) quando é analisada a interação meses e classes topográficas. Dentre todas as árvores selecionadas (300 indivÃduos), foram mantidas na análise 272 indivÃduos. A média do incremento anual em diâmetro, considerando as 272 árvores monitoradas, foi de 1,64 ± 0,21 mm (p = 0,05), ficando dentro do intervalo dos incrementos obtidos no BIONTE e FLONA Tapajós, que é de 1,5 a 2 mm por ano
Methanol and isoprene emissions from the fast growing tropical pioneer species Vismia guianensis (Aubl.) Pers. (Hypericaceae) in the central Amazon forest
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