Article

Fragmentation increases wind disturbance impacts on forest structure and carbon stocks in a western Amazonian landscape

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Abstract

Tropical second-growth forests could help mitigate climate change, but the degree to which their carbon potential is achieved will depend on exposure to disturbance. Wind disturbance is common in tropical forests, shaping structure, composition, and function, and influencing successional trajectories. However, little is known about the impacts of extreme winds on second-growth forests in fragmented landscapes, though these ecosystems are often located in mosaics of forest, pasture, cropland, and other land cover types. Indirect evidence suggests that fragmentation increases risk of wind damage in tropical forests, but no studies have found such impacts following severe storms. In this study, we ask whether fragmentation and forest type (old vs. second growth) were associated with variation in wind damage after a severe convective storm in a fragmented production landscape in western Amazonia. We applied linear spectral unmixing to Landsat 8 imagery from before and after the storm, and combined it with field observations of damage to map wind effects on forest structure and biomass. We also used Landsat 8 imagery to map land cover with the goals of identifying old- and second-growth forest and characterizing fragmentation. We used these data to assess variation in wind disturbance across 95,596 hectares of forest, distributed over 6,110 patches. We find that fragmentation is significantly associated with wind damage, with damage severity higher at forest edges and in edgier, more isolated patches. Damage was also more severe in old-growth than in second-growth forests, but this effect was weaker than that of fragmentation. These results illustrate the importance of considering landscape context in planning tropical forest restoration and natural regeneration projects. Assessments of long-term carbon sequestration potential need to consider spatial variation in disturbance exposure. Where risk of extreme winds is high, minimizing fragmentation and isolation could increase carbon sequestration potential. This article is protected by copyright. All rights reserved.

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... We explored two potential causes of this spatial heterogeneity. First, we found no evidence that ACD loss was greater along trails ( Supplementary Fig. 3), which is inconsistent with expectations that tree damage and mortality are greatest along forest edges 21 . This discrepancy is possible because local trails are likely not wide enough to increase wind exposure. ...
... We expect this is true because our study area contains secondary forests, and because field measurements indicate that old-growth forests in this area steadily increased in ACD between 1997 and 2017 20 . We are also likely to underestimate ACD losses from the blowdown because post-blowdown lidar data were collected a year after the disturbance, and initial recovery can be rapid 11,21,27 . Consequently, we consider our conclusion regarding carbon loss and increased gap area to be conservative. ...
... DF = 206, P < 0.001). However, the mean and maximum ΔNPV in our data (0.02 and 0.09, respectively) were smaller than ΔNPV values reported in other studies-in fact, these values are approximately one order of magnitude smaller than those reported for large blowdowns 9 , and the mean value is within the 95% confidence interval for no mortality in one previous study 21 . Further, although we observed a statistically significant relationship between ΔNPV and ACD loss, the explanatory power of this relationship was very low (r 2 = 0.03) ( Supplementary Fig. 9). ...
Article
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Field measurements demonstrate a carbon sink in the Amazon and Congo basins, but the cause of this sink is uncertain. One possibility is that forest landscapes are experiencing transient recovery from previous disturbance. Attributing the carbon sink to transient recovery or other processes is challenging because we do not understand the sensitivity of conventional remote sensing methods to changes in aboveground carbon density (ACD) caused by disturbance events. Here we use ultra-high-density drone lidar to quantify the impact of a blowdown disturbance on ACD in a lowland rain forest in Costa Rica. We show that the blowdown decreased ACD by at least 17.6%, increased the number of canopy gaps, and altered the gap size-frequency distribution. Analyses of a canopy-height transition matrix indicate departure from steady-state conditions. This event will initiate a transient sink requiring an estimated 24–49 years to recover pre-disturbance ACD. Our results suggest that blowdowns of this magnitude and extent can remain undetected by conventional satellite optical imagery but are likely to alter ACD decades after they occur.
... The woody debris created may quickly decompose (e.g., after 2-46 years) (Chambers, Higuchi, Schimel, Ferreira, & Melack, 2000;Hérault et al., 2010) releasing mineralized nutrients (Vitousek & Denslow, 1986) while adding residual organic matter to the soil (dos Santos et al., 2016). Mortality of the pre-disturbance tree cohort often continues into the recovery phase, when for example, isolated survivors and resprouters suffer from mechanical and/or physiological stress induced by successive wind disturbances or changes in environmental conditions (Everham & Brokaw, 1996;Lugo, 2008;Putz & Brokaw, 1989;Schwartz et al., 2017). Mortality also occurs during recovery when the new cohort rapidly fills growing space and self-thinning commences (Scalley, Scatena, Lugo, Moya, & Estrada Ruiz, 2010;Vandermeer & Cerda, 2004). ...
... Higher recovery rates and lower loss rates suggest that these forests have a higher resilience to windthrow than to logging. Biomass loss due to postwindthrow mortality was predominantly stochastic and may have a range of causes such as delayed mortality of damaged/disease-prone trees, competition with newly incoming regeneration, physiological stress after exposure to altered environmental conditions, and increased susceptibility to recurrent smaller scale wind disturbances (Laurance & Curran, 2008;Laurance et al., 2006;Schwartz et al., 2017). We showed that delayed mortality is particularly important in windthrows with low to moderate severity. ...
... Unless they are replaced by late-successional species over the course of succession, the total ecosystem volume captured by the forest remains low, as do carbon stocks. Importantly, forests with smaller and lower wood density pioneer trees can have slower rates of biomass accumulation (Hérault & Piponiot, 2018) and be more vulnerable to new windthrows (Ribeiro et al., 2016;Rifai et al., 2016) and other disturbances such as pathogen attack, drought, fire, and land use/fragmentation (Hérault & Piponiot, 2018;Laurance & Curran, 2008;Schwartz et al., 2017;Silvério et al., accepted). ...
Article
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Amazon forests account for ~25% of global land biomass and tropical tree species. In these forests, windthrows (i.e. snapped and uprooted trees) are a major natural disturbance, but the rates and mechanisms of recovery are not known. To provide a predictive framework for understanding the effects of windthrows on forest structure and functional composition (DBH ≥10 cm), we quantified biomass recovery as a function of windthrow severity (i.e. fraction of windthrow tree‐mortality on Landsat pixels, ranging from 0‐70%) and time since disturbance for terra‐firme forests in the Central Amazon. Forest monitoring allowed insights into the processes and mechanisms driving the net biomass change (i.e. increment minus loss) and shifts in functional composition. Windthrown areas recovering for between 4‐27 yrs had biomass stocks as low as 65.2‐91.7 Mg ha⁻¹ or 23‐38% of those in nearby undisturbed forests (~255.6 Mg ha⁻¹, all sites). Even low windthrow‐severities (4‐20% tree mortality) caused decadal changes in biomass stocks and structure. While rates of biomass increment in recovering vegetation were nearly double (6.3±1.4 Mg ha⁻¹ yr⁻¹) those of undisturbed forests (~3.7 Mg ha⁻¹ yr⁻¹), biomass loss due to post‐windthrow mortality was high (up to ‐7.5±8.7 Mg ha⁻¹ yr⁻¹, 8.5 yrs since disturbance) and unpredictable. Consequently, recovery to 90% of ‘pre‐disturbance’ biomass takes up to 40 yrs. Resprouting trees contributed little to biomass recovery. Instead, light‐demanding, low‐density genera (e.g. Cecropia, Inga, Miconia, Pourouma, Tachigali and Tapirira) were favored, resulting in substantial post‐windthrow species turnover. Shifts in functional composition demonstrate that windthrows affect the resilience of live tree biomass by favoring soft‐wooded species with shorter lifespans that are more vulnerable to future disturbances. As the time required for forests to recover biomass is likely similar to the recurrence interval of windthrows triggering succession, windthrows have the potential to control landscape biomass/carbon dynamics and functional composition in Amazon forests. This article is protected by copyright. All rights reserved.
... wind-induced tree mortality based on empirical studies: these studies rely on observations of forest damage after individual cyclone events, which are both limited in their temporal extent, and driven by contingent factors such as cyclone trajectory and force (Lugo, 2008) and human land use legacy (Kulakowski et al., 2011;Schwartz et al., 2017). In various studies, a higher probability and level of damage has been found to be correlated to tree characteristics such as larger diameter (Halder et al., 2021;Ostertag et al., 2005), larger height (Dunham and Cameron, 2000;Vandecar et al., 2011), or lower wood density Webb et al., 2014). ...
... The current model could be further refined by including other aspects of wind impact on trees, such as successive damages that do not immediately cause death but increases delayed mortality (Tanner et al., 2014;Walker, 1995), coping mechanisms such as defoliation (reduction of wind drag at the cost of temporary lower productivity) and re-sprouting (allowing survival even after stem breakage). Other factors influencing tree mortality, such as preexisting stem rotting or deformities, interactions with other forms of disturbance such as insect attacks, fire and drought (Newman, 2019;Reichstein et al., 2013;Seidl et al., 2011a), as well as human land use legacy and fragmentation (Laurance and Curran, 2008;Schwartz et al., 2017;Uriarte et al., 2009), could also be considered conjointly with the wind disturbance model. Parameter calibration and model validation could also be improved with the help of high-resolution satellite data that monitor wind gap formation and dynamics (Ballère et al., 2021;Hayashi et al., 2015;Kislov and Korznikov, 2020). ...
... Finally, the work in this thesis could serve as a general framework, based on which individual-based models could be further developed to include other natural disturbance processes such as fire, drought, insect or pathogen outbreaks (Brazhnik et al., 2017;Lucas et al., 2017;Seidl et al., 2011a;Shugart et al., 2018), as well as how anthropogenic land use change such as fragmentation or selective logging interact with natural disturbances and influence their effects (Laurance and Curran, 2008;McGroddy et al., 2013;Schwartz et al., 2017;Uriarte et al., 2009), in the hope of constructing a comprehensive view of how disturbance is expected to shape forests in the present and in the future. ...
Thesis
Natural disturbances have an important influence on the structure, composition and functioning of tropical forests and a role in the regulation of biogeochemical cycles. The frequency and intensity of natural disturbances are modified by climate change: a better knowledge of their mechanism of action is necessary to predict the consequences of this modification. Modeling allows us to evaluate the role of each of the ecological processes and their link with environmental factors. Remote sensing tools inform us about the structure and functioning of forests at large scales, and can be useful for the calibration and validation of vegetation models. In this thesis, I employed both approaches to examine how tropical forests are shaped by natural disturbances, particularly wind, which is a major disturbance factor in many tropical regions. First, I evaluated the transferability of a spatially explicit, individual-based model via sensitivity testing and calibration of global parameters. The model correctly predicts forest structure at two contrasting sites, and its response is consistent with variations in climate forcing. Calibration of a small number of key parameters was required, including the parameter controlling mortality and crown allometry. To investigate the sensitivity of the model to mortality, I implemented a wind damage module based on biophysical principles and coupled with wind speed to model forest responses to extreme wind events. With increasing disturbance level, canopy height decreased steadily but biomass showed a non-linear response. Wind intensity had a strong impact on canopy height and biomass, but not the frequency of extreme wind events. Finally, I tested whether radar data from Sentinel-1 satellites could be used to detect gaps due to natural disturbances in French Guiana. The Sentinel-1 data detected more natural gaps above 0.2 ha than the optical satellite data, and they showed a spatial pattern consistent with the optical images. The level of disturbance did not vary with altitude. We found more disturbance during dry seasons, which could be due to the delayed response of precipitation rather than the direct response of drought. In conclusion, this thesis demonstrates that the integration between modeling and remote sensing sheds light on the effects of natural disturbances on tropical forests. The resulting results can be used to study other types of disturbances and their interactions on a large scale.
... This was based on other studies which have highlighted how altered patterns of forest cover associated with forest clearing and logging operations alter climatic conditions such as air flow and windiness (e.g. [25][26][27]) leading to accelerated rates of tree fall [28][29][30][31] including the collapse of large old trees [32]. We also postulated that the probability of collapse of large old trees on sites would be positively associated with the amount of the surrounding landscape that was burned. ...
... Altered wind speeds and wind fetch associated with logging operations have been documented in numerous forest ecosystems around the world (e.g. [25,[27][28][29][30]43], including in the Mountain Ash forests that were the focus of this investigation [36]. ...
Article
Full-text available
Large old trees are critically important keystone structures in forest ecosystems globally. Populations of these trees are also in rapid decline in many forest ecosystems, making it important to quantify the factors that influence their dynamics at different spatial scales. Large old trees often occur in forest landscapes also subject to fire and logging. However, the effects on the risk of collapse of large old trees of the amount of logging and fire in the surrounding landscape are not well understood. Using an 18-year study in the Mountain Ash (Eucalyptus regnans) forests of the Central Highlands of Victoria, we quantify relationships between the probability of collapse of large old hollow-bearing trees at a site and the amount of logging and the amount of fire in the surrounding landscape. We found the probability of collapse increased with an increasing amount of logged forest in the surrounding landscape. It also increased with a greater amount of burned area in the surrounding landscape, particularly for trees in highly advanced stages of decay. The most likely explanation for elevated tree fall with an increasing amount of logged or burned areas in the surrounding landscape is change in wind movement patterns associated with cutblocks or burned areas. Previous studies show that large old hollow-bearing trees are already at high risk of collapse in our study area. New analyses presented here indicate that additional logging operations in the surrounding landscape will further elevate that risk. Current logging prescriptions require the protection of large old hollow-bearing trees on cutblocks. We suggest that efforts to reduce the probability of collapse of large old hollow-bearing trees on unlogged sites will demand careful landscape planning to limit the amount of timber harvesting in the surrounding landscape.
... However, it remains intrinsically difficult to reach general conclusions on factors driving wind-induced tree mortality based on empirical studies: these studies rely on observations of forest damage after individual cyclone events, which are both limited in their temporal extent, and driven by contingent factors such as cyclone trajectory and force (Lugo, 2008) and human land use legacy (Kulakowski et al., 2011;Schwartz et al., 2017). In various studies, a higher probability and level of damage has been found to be correlated to tree characteristics such as larger stem diameter (Ostertag et al., 2005;Halder et al., 2021), larger height (Dunham and Cameron, 2000;Vandecar et al., 2011), or lower wood density Webb et al., 2014). ...
... Other factors influencing tree mortality, such as preexisting stem rot or deformities, interactions with other forms of disturbance such as insect attacks, fire and drought (Seidl et al., 2011;Reichstein et al., 2013;Newman, 2019). Human land use legacy and fragmentation (Laurance and Curran, 2008;Uriarte et al., 2009;McGroddy et al., 2013;Schwartz et al., 2017) could also be considered conjointly with the wind disturbance model: this could potentially be useful for forest conservation and management, by evaluating how forest response to disturbance is modulated by different resource use and management strategies . Parameter calibration and model validation could also be improved with the help of high-resolution satellite data that monitor wind gap formation and dynamics (Hayashi et al., 2015;Kislov and Korznikov, 2020;Ballère et al., 2021). ...
Article
Full-text available
Extreme wind blowdown events can significantly modify the structure and composition of forests, and the predicted shift in tropical cyclone regimes due to climate change could strongly impact forests across the tropics. In this study, we coupled an individual-based and spatially-explicit forest dynamics model (TROLL) with a mechanistic model estimating wind damage as a function of tree size, traits, and allometry (ForestGALES). We assimilated floristic trait data and climate data from a subtropical forest site in Taiwan to explore the effect of wind regimes on forest properties. We found that the average canopy height and biomass stocks decreased as wind disturbance strength increased, but biomass stocks showed a nonlinear response. Above a wind intensity threshold, both canopy height and biomass drastically decreased to near-zero, exhibiting a transition to a non-forest state. Wind intensity strongly regulated wind impact, but varying wind frequency did not cause discernible effects. The implementation of within-stand topographic heterogeneity led to weak effects on within-stand forest structure heterogeneity at the study site. In conclusion, the intensity of wind disturbances can potentially greatly impact forest structure by modifying mortality. Individual-based modeling provides a framework in which to investigate the impact of wind regimes on mortality, other factors influencing wind-induced tree mortality, as well as interaction between wind and other forms of forest disturbance and human land use legacy.
... An important process affecting the differential volume and structure of wood resources near the edge in forest patches is higher tree mortality [23,40,70]. Wind damage is most commonly cited as the main cause of higher tree mortality near the edge [24,57,75,76]. Stands consisting of light-demanding species such as pine are particularly affected, as are other types of stands in which species with higher light requirements are relatively common at the forest edges [77]. ...
... Stands consisting of light-demanding species such as pine are particularly affected, as are other types of stands in which species with higher light requirements are relatively common at the forest edges [77]. Some studies show that, despite the weak relationship between the size of a forest patch and the extent of wind damage, usually more damage is noted in patches with higher edginess [75]. In some countries, fires are an important factor influencing the reduction of wood resources at forest edges [54]. ...
Article
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Forest fragmentation is a widespread phenomenon that directly or indirectly affects the processes that take place both in forest ecosystems and in their immediate surroundings. So far, many studies confirm its negative effects, especially on biodiversity. On the other hand, there are few studies that address the effects of forest fragmentation on the amount of accumulated biomass or carbon, as well as on the characteristics of wood resources in managed forests. Therefore, issues related to timber production, which are important from the point of view of multifunctional forest management, are omitted. The aim of our research was to add to the knowledge in this area. In particular, we focused on assessing the impact of forest fragmentation on wood resources based on an analysis of edge effects in forest patches (units formed by combining forest fragments characterized by structural connectivity). Vector data describing the topography of forest fragments in Poland and the results of the National Forest Inventory (NFI) from 2015–2019 were used as material for solving this problem. The results of our research showed that the effects of fragmentation on managed pine stands depend on the age of the stand and the fertility of the habitat. In young stands growing on barren or strongly barren habitats, growing stock volume turned out to be significantly higher in the edge zone. In older stands, especially on moderately fertile habitats, significantly higher resources were found in the interior zone of forest patches. Habitat quality also had a significant effect on the amount of carbon accumulated. In strongly barren habitats, higher carbon mass was found in edge zones, while in moderately fertile habitats, stands had higher carbon volume in the interior zone. Our results illustrate that forest fragmentation is a very complex process that can increase or reduce wood resources, depending on the age of the stand and the quality of the habitat. From the standpoint of measurable benefits, it was concluded that protection from the negative effects of fragmentation should focus primarily on older stands and more fertile habitats.
... As deforestation increases the fragmentation of intact forests over increasingly large areas (Hansen et al., 2013;INPE, 2016), wind-related disturbances can be expected to increase. For example, Schwartz et al. (2017) showed that forest degradation by fragmentation and windstorms has already degraded large tracts of forests. ...
... Amazonia, biomass loss, fire scar, forest degradation, forest dynamics, tree mortality, windstorms spatial extent of blowdown events using remote sensing imagery (Chambers et al., 2013;Espírito-Santo et al., 2014;Negrón-Juárez et al., 2010) or from postdisturbance field inventories, which often lag the windstorm event by many months or years (Marra et al., 2014;Schwartz et al., 2017). While these studies have shown that wind disturbance exerts strong influences on the structure and diversity of tropical forests, they often lack mechanistic approaches to understand how forests respond to synergistic interactions between windstorms and other forest disturbances. ...
Article
1.Widespread degradation of tropical forests is caused by a variety of disturbances that interact in ways that are not well understood. 2.To explore potential synergies between edge effects, fire and windstorm damage as causes of Amazonian forest degradation, we quantified vegetation responses to a 30‐minute high‐intensity windstorm that in 2012, swept through a large‐scale fire experiment that borders an agricultural field. Our pre‐ and post‐windstorm measurements include tree mortality rates and modes of death, aboveground biomass, and airborne LiDAR‐based estimates of tree heights and canopy disturbance (i.e., number and size of gaps). The experimental area in the southeastern Amazonia includes three 50‐ha plots established in 2004 that were unburned (Control), burned annually (B1yr), or burned at three‐year intervals (B3yr). 3.The windstorm caused greater damage to trees (>10 cm DBH) in the burned plots (B1yr: 13 ± 9% of 785 trees; B3yr: 17 ± 13% of 433) than in the Control plot (8 ± 4% of 2300; ± CI). It substantially reduced vegetation height by 14% in B1yr, 20% in B3yr and 12% in the Control plots, while it reduced aboveground biomass by 18% of 77.7 Mg ha−1 (B1yr), 31% of 56.6 (B3yr) and 15% of 120 (Control). Tree damage was greatest near the agricultural field edge in all three plots, especially among large trees and in B3yr. Trunk snapping (70%) and uprooting (20%) were the most common modes of tree damage and mortality, with the height of trunk failure on the burned plots often corresponding with the height of historical fire scars. Of the windstorm‐damaged trees, 80% (B1yr), 90% (B3yr), and 57% (Control) were dead four years later. Trees that had crown damage experienced the least mortality (22–60%), followed by those that were snapped (55–94%) and uprooted (88–94%). 4.Synthesis. We demonstrate the synergistic effects of three kinds of disturbance on a tropical forest. Our results show that the effects of windstorms are exacerbated by prior degradation by fire and fragmentation. We highlight that understory fires can produce long‐lasting effects on tropical forests not only by directly killing trees but also by increasing tree vulnerability to wind damage due to fire‐scars and a more‐open canopy. This article is protected by copyright. All rights reserved.
... Recently, availability of satellite data has made these landscape-wide studies effects more quantifiable, illuminating patterns to assess cause and effect of hurricane disturbance [6]. There are landscape-scale studies on forest susceptibility to hurricane (or large storm) wind forces causing vegetation loss. ...
Article
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The impact of Hurricane Maria on the U.S. Caribbean was used to study the causes of remotely-sensed spatial variation in the effects of (1) vegetation index loss and (2) landslide occurrence. The vegetation index is a measure of canopy 'greenness', a combination of leaf chlorophyll, leaf area, canopy cover and structure. A generalized linear model was made for each kind of effect, using idealized maps of the hurricane forces, along with three landscape characteristics that were significantly associated. In each model, one of these characteristics was forest fragmentation, and another was a measure of disturbance-propensity. For the greenness loss model, the hurricane force was wind, the disturbance-propensity measure was initial greenness, and the third landscape characteristic was fraction forest cover. For the landslide occurrence model, the hurricane force was rain, the disturbance-propensity measure was amount of land slope, and the third landscape characteristic was soil clay content. The model of greenness loss had a pseudo R 2 of 0.73 and showed the U.S. Caribbean lost 31% of its initial greenness from the hurricane, with 51% lost from the initial in the Luquillo Experimental Forest (LEF) from Hurricane Maria along with Hurricane Irma. More greenness disturbance was seen in areas with less wind sheltering, higher elevation and topographic sides. The model of landslide occurrence had a pseudo R 2 of 0.53 and showed the U.S. Caribbean had 34% of its area and 52% of the LEF area with a landslide density of at least one in 1 km 2 from Hurricane Maria. Four experiments with parameters from previous storms of wind speed, storm duration, rainfall, and forest structure over the same storm path and topographic landscape were run as examples of possible future scenarios. While intensity of the storm makes by far the largest scenario difference, forest fragmentation makes a sizable difference especially in vulnerable areas of high clay content or high wind susceptibility. This study showed the utility of simple hurricane force calculations connected with landscape characteristics and remote-sensing data to determine forest susceptibility to hurricane effects.
... Specific wind characteristics influence various processes: average wind speed could gradually reduce soil moisture [34], while maximum wind speed may affect dispersal of plant and animal species, as well as animal behavior and species interactions [19,35]. Notably, extreme maximum wind speeds can reduce canopy cover and increase tree mortality [36], particularly in fragmented forests with more edges [37]. Gap width was important in explaining wind conditions regardless of forest structure (i.e., canopy height). ...
Article
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Forest fragmentation threatens forest biodiversity and ecosystem function. One of the concerns relates to increases in edge effects, which among other things affects the forest microclimate that influences the distribution and behavior of species. In Alberta, Canada, boreal anthropogenic disturbances from in situ oil exploration are increasing forest fragmentation, especially in the form of exploratory well pads and seismic lines (i.e., linear forest clearings created during the exploration phase of oil extraction). Dissection of these forests by seismic lines has the potential to change local patterns in wind and light, and thus may alter forest communities. Although alterations of these abiotic conditions are likely, the magnitude of these changes is unknown, particularly the effects of changes in the width and orientation of linear disturbances. Here we investigated changes in light and wind on seismic lines compared to that of adjacent undisturbed forests and nearby cleared openings. Specifically, we examined how seismic line characteristics (i.e., line direction, line width, and adjacent canopy height) altered local responses in these abiotic conditions. Generalized Linear Mixed Effect models predicted a 2-fold increase in average light intensity and maximum wind speeds, and a 4-fold increase in average wind speeds on seismic lines compared to adjacent forests. These changes did not approach the conditions in large openings, which compared to forests had a 3-fold increase in average light intensity, a 16-fold increase in average wind speeds, and a 4-fold increase in maximum wind speeds. Line width and orientation interacted with adjacent forest height altering the abiotic environment with wider lines having a 3-fold increase on maximum wind speed. We conclude that even localized, narrow (<10-m wide) forest disturbances associated with oil sands exploration alter forest microclimatic conditions. Recent changes in practices that reduce line width as well as promoting tree regeneration, will minimize the environmental effects of these anthropogenic disturbances.
... Similar to the risks of pests and pathogens, within a given stand there is evidence that older and taller trees are more susceptible to windthrow due to the physics of taller trees and root rot (Lohmander and Helles, 1987;Ruel, 1995). Nevertheless, fragmented or thinned forests experience elevated mortality and collapse of trees from windthrow because of increased exposure (Laurance and Curran, 2008;Reinhardt et al., 2008;Schwartz et al., 2017). ...
Article
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Several key international policy frameworks involve forests, including the Paris Agreement on Climate Change and the Convention on Biological Diversity (CBD). However, rules and guidelines that treat forest types equally regardless of their ecosystem integrity and risk profiles in terms of forest and carbon loss limit policy effectiveness and can facilitate forest degradation. Here we assess the potential for using a framework of ecosystem integrity to guide policy goals. We review the theory and present a conceptual framework, compare elements of integrity between primary and human-modified forests, and discuss the policy and management implications. We find that primary forests consistently have higher levels of ecosystem integrity and lower risk profiles than human-modified forests. This underscores the need to protect primary forests, develop consistent large-scale data products to identify high-integrity forests, and operationalize a framework of ecosystem integrity. Doing so will optimize long-term carbon storage and the provision of other ecosystem services, and can help guide evolving forest policy at the nexus of the biodiversity and climate crises.
... Between 1999 and 2010, fires burned more than 85,000 km² of forests in the southern portion of the Amazon (Morton, Le Page, DeFries, Collatz, & Hurtt, 2013). Additionally, windstorms can interact with forest fragmentation and fires by increasing the mortality of large trees, particularly at forest edges (Silvério et al., 2018), thus increasing fuel loads and consequently forest flammability (Schwartz et al., 2017). ...
Article
The forests of southeastern Amazonia are highly threatened by disturbances such as fragmentation, understory fires, and extreme climatic events. Large-bodied frugivores such as the lowland tapir (Tapirus terrestris) have the potential to offset this process, supporting natural forest regeneration by dispersing a variety of seeds over long distances to disturbed forests. However, we know little about their effectiveness as seed dispersers in degraded forest landscapes. Here, we investigate the seed dispersal function of lowland tapirs in Amazonian forests subject to a range of human (fire and fragmentation) and natural (extreme droughts and windstorms) disturbances, using a combination of field observations, camera traps, and light detection and ranging (LiDAR) data. Tapirs travel and defecate more often in degraded forests, dispersing much more seeds in these areas [9,822 seeds per ha/year (CI 95% = 9,106; 11,838)] than in undisturbed forests [2,950 seeds per ha/year (CI 95% = 2,961; 3,771)]. By effectively dispersing seeds across disturbed forests, tapirs may contribute to natural forest regeneration—the cheapest and usually the most feasible way to achieve large-scale restoration of tropical forests. Through the dispersal of large-seeded species that eventually become large trees, such frugivores also contribute indirectly to maintaining forest carbon stocks. These functions may be critical in helping tropical countries to achieve their goals to maintain and restore biodiversity and its ecosystem services. Ultimately, preserving these animals along with their habitats may help in the process of natural recovery of degraded forests throughout the tropics. Abstract in Portuguese is available with online material.
... Over 70% of all remaining tropical forests in the world are second-growth forests growing on former agricultural or logged lands (Food and Agriculture Organization of the United Nations [FAO] 2010). These regenerating forests differ from old growth in composition, size structure, and spatial configuration in the landscape and thus are expected to respond differently to climate extremes (FAO 2010, Anderson-Teixeira et al. 2013, Uriarte et al. 2016a, Schwartz et al. 2017. Differences in species composition between old-and second-growth forests suggest that second-growth forests are likely to suffer stronger drought impacts. ...
Article
Climate models predict increases in drought conditions in many parts of the tropics. Yet the response of tropical forests to drought remains highly uncertain, especially with regards to the factors that generate spatial heterogeneity in drought response across landscapes. In this study, we used Landsat imagery to assess the impacts of a severe drought in 2015 across a ~80,000 ha landscape in northeast Puerto Rico. Specifically, we asked whether drought effects varied systematically with topography and with forest age, height, and fragmentation. We quantified drought impacts using anomalies of two vegetation indices, the enhanced vegetation index (EVI) and normalized difference water index (NDWI), and fit random forest models of these metrics including slope, aspect, forest age, canopy height, and two indices of fragmentation as predictors. Drought effects were more severe on drier topographic positions, i.e. steeper slopes and southwest facing aspects, and in second-growth forests. Shorter and more fragmented forests were also more strongly affected by drought. We also assessed which factors were associated with stronger recovery from drought. Factors associated with more negative drought anomalies were also associated with more positive post-drought anomalies, suggesting that increased light availability as a result of drought led to high rates of recovery in forests more severely affected by drought. In general, recovery from drought was rapid across the landscape, with post-drought anomalies at or above average across the study area. This suggests that forests in Puerto Rico might be resilient to a single year drought, though vulnerability to drought varies depending on forest characteristics and landscape position. This article is protected by copyright. All rights reserved.
... Previous work has also demonstrated significant correlations between wind speed estimates using models (e.g. H*wind, Powell et al. 1998), and forest damage determined by spectral shifts before and after the storm (Chambers et al. 2007, Zeng et al. 2009, Negron-Juarez et al. 2014, Rifai et al. 2016, Schwartz et al. 2017). ...
Article
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Hurricane Maria made landfall as a strong Category 4 storm in southeast Puerto Rico on September 20th, 2018. The powerful storm traversed the island in a northwesterly direction causing widespread destruction. This study focused on a rapid assessment of Hurricane Maria’s impact to Puerto Rico’s forests. Calibrated and corrected Landsat 8 image composites for the entire island were generated using Google Earth Engine for a comparable pre-Maria and post-Maria time period that accounted for phenology. Spectral mixture analysis (SMA) using image-derived endmembers was carried out on both composites to calculate the change in the non-photosynthetic vegetation (ΔNPV) spectral response, a metric that quantifies the increased fraction of exposed wood and surface litter associated with tree mortality and crown damage from the storm. Hurricane simulations were also conducted using the Weather Research and Forecasting (WRF) regional climate model to estimate wind speeds associated with forest disturbance. Dramatic changes in forest structure across the entire island were evident from pre- and post-Maria composited Landsat 8 images. A ΔNPV map for only the forested pixels illustrated significant spatial variability in disturbance, with patterns that associated with factors such as slope, aspect and elevation. An initial order-of-magnitude impact estimate based on previous work indicated that Hurricane Maria may have caused mortality and severe damage to 23-31 million trees. Additional field work and image analyses are required to further detail the impact of Hurricane Maria to Puerto Rico forests.
... The distribution of these species is influenced by the heterogeneity of the forest architecture. For example, the microclimate differs at the edge in comparison to the forest interior, on certain elements as sunlight penetrance, temperature, humidity and wind disturbance (Laurance 2004;Schwartz et al. 2017). This leads to differences in the forest structure, composition, and biomass (Laurance et al. 2011(Laurance et al. , 2016, that subsequently influence species, especially those that rely principally on plant resources. ...
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From the forest edge to the forest interior, a small-scale gradient in the microclimate exists. Little is known about its influence on the abundance, diversity and morphological traits of insects in Amazonian forests, a major component of global terrestrial diversity. Our study investigates these traits in Arctiinae and Geometridae moths at the interior and the edge of a Peruvian lowland rainforest (Panguana field station, Puerto Inca Province). A total of 1286 Arctiinae and 2012 Geometridae specimens were collected, sorted according to DNA barcodes and identified using relevant type material. Moths’ assemblages at the forest edge differed significantly in their composition. At the forest edge, small-sized taxa (Lithosiini, Sterrhinae, Geometrinae) were less abundant whereas larger-sized Arctiini were more abundant. Moths were significantly larger at the forest edge than inside the forest, and these differences hold at subfamily and tribal level, possibly reflecting moth mobility, and abiotic conditions of habitats: larger moths might better tolerate desiccating conditions than smaller moths. A larger proportion of females was found at the forest edge, probably due to differences in the dispersal activity among sexes and/or in the tolerance to desiccation due to size. Our results revealed the edge effect on two rich herbivorous taxa in the Amazon basin. We provide a fully illustrated catalogue of all species as a baseline for further study and conservation purposes.
... greater area of forest being closer to forest edges, which are more susceptible to damage from high winds ( Schwartz et al. 2017). Second, landscape context could influence the short-and long-term response of forest communities to natural disturbances by affecting the mechanisms by which communities respond to disturbance -specifically, by affecting regeneration ( Catterall et al. 2008). ...
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1. When deforestation results in small forest fragments surrounded by a non‐forest matrix, forest stands within these fragments experience changes in structure and community composition. They also continue to experience natural disturbances like hurricanes and ice storms. It is unclear whether the landscape context of forest stands influences plant community response to natural disturbances. 2. Using data from surveys of forested plots in the years immediately following and 19 years after a severe ice storm, we measured changes in woody stem density, species richness, and beta diversity. 3. Plots with greater storm damage had greater gains in stems and species, and greater shifts in community composition. In addition, there were interactions between the degree of storm damage and landscape context. The short‐term effects of storm damage were magnified in plots with less forest on the surrounding landscape and farther from the forest edge. In plots with high damage, a return towards pre‐storm conditions over the long‐term occurred more often in plots farther from the forest edge compared to those close to the edge. 4. Synthesis: Future climate scenarios predict increases in severe weather and accompanying ecosystem disturbance. Our results show that it is important to consider landscape context when assessing the response of forest communities to such disturbances.
... For example, warming and drying conditions increased levels of regeneration failure among Lodgepole Pine (Pinus contorta) and Douglas-Fir seedlings following fire . Major disturbances like large, severe wildfires that remove extensive areas of canopy can open up forests to greater wind speeds (Gratkowski, 1956;Schwartz et al., 2017), altering microclimatic conditions in early successional forests (Rosenberg et al., 1983), and influencing the persistence and survival of legacies (McKenzie et al., 2011;Lindenmayer et al., 2018a). ...
Article
In forests subject to stand-replacing disturbances, early successional stands can provide important habitats for a range of species not typically present in long-undisturbed areas. Compared to old-growth forests, the habitat values of – and key ecological processes in – early successional forests have been less studied, perhaps due to a perception that early successional forests revert to a homogenous “clean slate” following stand-replacing disturbances. In this paper, we draw on 36 years of long-term research in the Mountain Ash (Eucalyptus regnans) and Alpine Ash (Eucalyptus delegatensis) forests of south-eastern Australia, together with examples from elsewhere around the world, to show that not all kinds of early successional forests are created equal. We argue that the ecological values of early successional forests can be profoundly affected by six inter-related factors: (1) The evolutionary context and environmental domain of a given ecosystem. (2) Successional stage and condition of a forest stand prior to disturbance. (3) Disturbance intensity, severity and type (e.g. wildfire versus clearcutting). (4) Post-disturbance conditions including climate and weather. (5) Post-disturbance management (e.g. salvage logging) which can have significant impacts on biological legacies. And, (6) The relative spatial extent and spatial arrangement of early and late successional forest across a landscape. These factors can influence ecological values directly, or through effects on the types, amount and spatial patterns of biological legacies present in early successional forest. We present a conceptual model highlighting the inter-relationships between these factors and illustrate its use through a detailed case study. Strategies to improve the management of early successional forests include: (1) Identifying the species associated with post-disturbance environments and the reasons why they occur in such environments. (2) Understanding the types, numbers, and spatial patterns of biological legacies that remain after natural disturbance. (3) Identifying critical areas that should be excluded from logging or other human disturbance. (4) Limiting the extent of post-disturbance activities like salvage logging that undermine the ecological values of, and ecosystem processes in, early successional forests. And, (5) Balancing the relative amounts of early successional versus late successional forest in a given landscape or region to ensure that a variety of forest types are present at any given time, and that critical biological legacies are retained. Paradoxically, ensuring that landscapes support extensive areas of late successional forest is critical so that future early successional forests are not devoid of the biological legacies necessary for ecosystem function and recovery.
... green vegetation, shade, and NPV), and quantifies the per-pixel fraction of each endmember 75 . As storm damage increases the amount of woody and dead vegetation exposed to the sensor, the increase in NPV fraction (ΔNPV) after Hurricane María reflects the magnitude of storm damage [29][30][31][32] . ...
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Projected increases in cyclonic storm intensity under a warming climate will have profound effects on forests, potentially changing these ecosystems from carbon sinks to sources. Forecasting storm impacts on these ecosystems requires consideration of risk factors associated with storm meteorology, landscape structure, and forest attributes. Here we evaluate risk factors associated with damage severity caused by Hurricanes María and Irma across Puerto Rican forests. Using field and remote sensing data, total forest aboveground biomass (AGB) lost to the storms was estimated at 10.44 (±2.33) Tg, ca. 23% of island-wide pre-hurricane forest AGB. Storm-related rainfall was a stronger predictor of forest damage than maximum wind speeds. Soil water storage capacity was also an important risk factor, corroborating the influence of rainfall on forest damage. Expected increases of 20% in hurricane-associated rainfall in the North Atlantic highlight the need to consider how such shifts, together with high speed winds, will affect terrestrial ecosystems.
... There has not been an adequate study directly linking road density to forest destruction during the windstorms. However, the creation of linear edges, increasing forest fragmentation and gust speeds by channeling inside the forest areas, has been reported as problematic for forests (Dupont et al. 2018;Schwartz et al. 2017). The road pattern is related to logging and transportation resulting from the need for timber extraction. ...
Article
Key message Windstorms have recently caused noteworthy destruction across the Northern forests of Turkey. The intensive forest management practices applied for more than 60+ years may unknowingly have resulted in wind-sensitive forests in the region. After a storm, the forest service salvages the losses, but no further precaution is taken against future storms. To our knowledge, there has not been any research looking into the cumulative effects of environmental factors on storm damage in Turkish forests. Maxent, which is an ecological niche model, might help decision-makers in developing forest management strategies against storms given its ease of use, known successful performance, and flexible variable evaluation approach. This study revealed that management preferences were mainly responsible for forest storm damage in Kastamonu Province, Turkey. ContextExcessive wind cause serious damages to individual trees and forest stands. When unintentionally coupled with the forest management preferences, catastrophic levels of damage might be unavoidable.AimsThe main objective was to assess the environmental factors contributing to the impact of a strong windstorm that occurred between March 14 and 15, 2013 and resulted in 1.5-million m3 timber losses in the Kastamonu Regional Directorate of Forestry.Methods Maximum entropy modeling (Maxent) and geographic information systems (GIS) were used to evaluate the factors contributing to the forest damage.ResultsStand type, diameter class, and elevation were the most important variables affecting the level of wind damage. The pure and mixed coniferous stands were the hardest hit when compared with the deciduous stands. The damage increased as the density of forest roads grew.Conclusion It was concluded that windstorms pose serious threats to Turkish forests. Storm damage risks must therefore be integrated into forest management. In order to better understand the environmental factors contributing to the destructive effects of windstorms in forests, it would be best to focus on the telltale signs pointing the wrong-doing in forest management preferences at larger environmental scale rather than looking for reasons behind the occurrences of scattered small-scale damage.
... However, valleys may also amplify disturbances, as the wind can be constricted and accelerated (Everham and Brokaw 1996). At the regional scale, significant correlations have been found between wind speed and forest structural losses (Chambers et al. 2007, Zeng et al. 2009, Negrón Juárez et al. 2014a, Schwartz et al. 2017). Wind speed decreases as a hurricane moves inland, and it decreases at larger radii from the eyewall of the storm (Boose, Serrano, andFoster 2004, Negrón Juárez et al. 2014). ...
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Widely recognized as one of the worst natural disaster in Puerto Rico's history, hurricane María made landfall on September 20, 2017 in southeast Puerto Rico as a high-end category 4 hurricane on the Saffir-Simpson scale causing widespread destruction, fatalities and forest disturbance. This study focused on hurricane María's effect on Puerto Rico's forests as well as the effect of landform and forest characteristics on observed disturbance patterns. We used Google Earth Engine (GEE) to assess the severity of forest disturbance using a disturbance metric based on Landsat 8 satellite data composites with pre and post-hurricane María. Forest structure, tree phenology characteristics, and landforms were obtained from satellite data products, including digital elevation model and global forest canopy height. Our analyses showed that forest structure, and characteristics such as forest age and forest type affected patterns of forest disturbance. Among forest types, highest disturbance values were found in sierra palm, transitional, and tall cloud forests; seasonal evergreen forests with coconut palm; and mangrove forests. For landforms, greatest disturbance metrics was found at high elevations, steeper slopes, and windward surfaces. As expected, high levels of disturbance were also found close to the hurricane track, with disturbance less severe as hurricane María moved inland. Results demonstrated that forest and landform characteristics accounted for 34% of the variation in spatial forest spectral disturbance patterns. This study demonstrated an informative regional approach, combining remote sensing with statistical analyses to investigate factors that result in variability in hurricane effects on forest ecosystems.
... Tropical forests are in a cycle of nonequilibrium, a cycle driven by the response to the large step changes of hurricanes (Burslem et al., 2000). Recently, new tools for understanding the nature and duration of the forest hurricane response have become available for use; satellite data can provide landscape-wide qualities of the historical response (Schwartz et al., 2017), and earth system models can provide the long-term forest response given the projections of the increased frequency of hurricanes (Lee et al., 2018). While these tools can provide a large amount of spatially complete, cost-effective, and consistently recorded data, the data need to be placed in context of what is actually happening at the ecosystem level. ...
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With projected increasing intensity of hurricanes and large uncertainty in the path of forest recovery from hurricanes, studies are needed to understand the fundamental response of forests to canopy opening and debris deposition: the response of the abiotic factors underneath the canopy. Through two manipulative experiments and instrumenting prior to Hurricane Maria (2017) in the Luquillo Experimental Forest (LEF) of Puerto Rico, this study found a long recovery time of primary abiotic factors (beneath canopy light, throughfall, and temperature) influenced by the disturbance of canopy opening, as well as complex responses by the secondary abiotic factors (relative humidity, soil moisture, and leaf saturation) influenced by the disturbance of the primary factors. Recovery took 4–5 years for beneath canopy light, while throughfall recovery took 4–9 years and neither had recovered when Hurricane Maria passed 3 years after the second experiment. Air and soil temperature seemingly recovered quickly from each disturbance (
... Moreover, the analysis without T. pusillus indicated that the amount of cropland and landscape diversity negatively affected scorpion abundance and composition, respectively. Surrounding croplands may affect the vegetation dynamics inside the fragment by increasing the edge effect, thereby altering microclimate conditions, and thus, increasing landscape heterogeneity (Schwartz et al. 2017;Ng et al. 2018; Ahuatzin et al. 2019). Atlantic forest fragments from northeastern Brazil are commonly surrounded by sugarcane matrix . ...
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The effects of land use conversion on the maintenance of biodiversity remains a major issue in conservation biology. With this as context, recent studies have successfully evaluated the potential of scorpions as bio-indicators of human disturbance. Here, we explored this assumption to identify the effects of landscape structure on scorpion assemblages distributed in two tropical environments in Brazil, with different levels of human disturbance. Scorpions were collected from 28 sampling localities across the Atlantic Forest (n = 12) and Caatinga dry forest (n = 16), resulting in 3,781 specimens from 13 species, 5 genera, and 2 families. We found that scorpion species composition and abundance were more sensitive to changes in landscape configuration than was species richness. Additionally, scorpion assemblage responses were quite different between the two environments. From this observation we highlighted three main findings: (i) the Atlantic Forest assemblage possesses an abundance-dependent response to landscape; (ii) variation in species composition of Atlantic Forest and Caatinga were affected by landscape diversity and presence of croplands, respectively; (iii) the Atlantic Forest is inhabited by assemblages that are more sensitive to landscape changes than that is Caatinga. Implications for insect conservation We argue that a site-dependent process may explain the effects of human activities on scorpion assemblages at local and regional scale. Moreover, we provide substantial information for decision-makers to support their conservation strategies for neglected ecosystems, such as those present in Caatinga and the Atlantic Forest.
... Forest edges adjacent to cleared fields are subject to prolonged forest degradation. These edges and forest patches are exposed to hotter, dryer, and windier conditions (Didham and Lawton 1999, Schwartz et al. 2017). These edge effects degrade forests over time and have important implications for forest structure, especially because they tend to disproportionately increase mortality of canopy dominant trees over the short-term (Laurance et al. 2000). ...
Chapter
This Report provides a comprehensive, objective, open, transparent, systematic, and rigorous scientific assessment of the state of the Amazon’s ecosystems, current trends, and their implications for the long-term well-being of the region, as well as opportunities and policy relevant options for conservation and sustainable development.
... Nonetheless, altered functional composition indicates that blowdowns may affect the resilience of biomass stocks by favoring soft-wooded species with shorter life spans, which are also more vulnerable to future disturbances (Magnabosco Trumbore et al. 2015). The impacts of blowdowns can be more pronounced in secondary and fragmented forests with altered composition and structure, and a relatively higher proportion of exposed edges (Silvério et al. 2019;Schwartz et al. 2017). That aspect is critical since these account for large areas of the remnant forests in highly deforested regions of the Amazon (Brando et al. 2014;Hansen et al. 2013). ...
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This Report provides a comprehensive, objective, open, transparent, systematic, and rigorous scientific assessment of the state of the Amazon’s ecosystems, current trends, and their implications for the long-term well-being of the region, as well as opportunities and policy relevant options for conservation and sustainable development.
... C flux measurements are affected by wind speed and direction because these measurements affect how much air passes through the instruments in the flux tower, which are subsequently measured and recorded (Vander Zanden and Gratton, 2011;Turner et al., 2019). Being a sub-tropical forest with well-established vegetation, the Dinghushan Biosphere Reserve is somewhat sheltered from the wind (Zeng et al., 2010;Schwartz et al., 2017). Additionally, this study also measured slow wind speeds even though our measuring equipment was mounted on a mast that rises above the forest canopy. ...
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Subtropical forests are a major carbon (C) storage pool and are therefore rich in biomass energy reservoirs. However, there have been no studies that quantify the C storage economic value, especially in the region of the Dinghushan Biosphere Reserve. This study is the first attempt to apply the eddy covariance technique to measure biomass energy storage and the associated economic value and demonstrates that CO2 flux measurement is a viable method for quantifying the ecosystem biomass energy storage. CO2 flux and micro-meteorological data were collected and analyzed to calculate the daily C sequestration and establish their inter-relationship. In addition, we used the C price estimates of Guangdong Province in China to determine the capital value of the C sequestered. The measured average annual precipitation was 1459.4 mm, the average temperature was 22.9 °C and the highest photosynthetic photon flux density (PPFD) was 334.92 μmol m⁻²s⁻¹. CO2 flux and biomass energy storage varied seasonally. Photosynthetic photon flux density (PPFD) was highly correlated with gross primary production (GPP) (r² = 0.99, p < 0.0001). Soil temperature was correlated with net ecosystem exchange (NEE) (r² = 0.84, p < 0.0001). There was a positive correlation (r² = 0.49, p < 0.0001) between soil moisture and NEE. The Dinghushan Biosphere Reserve sequestered an average of 5300 tCy⁻¹ equivalent to RMB 3.3 million (USD 530,000). We conclude that economically, the Dinghushan Biosphere Reserve is highly significant to China's Guangdong Province because of its rich biomass energy reserves via C sequestration and our findings will stimulate the formulation of more aggressive conservation policies that will inevitably lead to better management of the reserve.
... C flux measurements are affected by wind speed and direction because these measurements affect how much air passes through the instruments in the flux tower, which are subsequently measured and recorded (Vander Zanden and Gratton, 2011;Turner et al., 2019). Being a sub-tropical forest with well-established vegetation, the Dinghushan Biosphere Reserve is somewhat sheltered from the wind (Zeng et al., 2010;Schwartz et al., 2017). Additionally, this study also measured slow wind speeds even though our measuring equipment was mounted on a mast that rises above the forest canopy. ...
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The study aimed to show that droughts are increasing in frequency and intensity in the Dinghushan Biosphere Reserve and to illustrate the effects of seasonal droughts on carbon gain in a sub-tropical forest. This is in response to the threat posed by increased droughts due to global climate change. We used four drought indices to accurately determine periods of drought and periods of increased precipitation. Thereafter, the measured eddy flux and soil moisture content data collected from 2003 to 2014 were compared between the droughts and wet periods to determine drought impacts on the ecosystem carbon gain. Drought accounted for about 20% of the 12-year study period, with the highest drought events and severity occurring between 2012 and 2013. The average annual precipitation and air temperature during the study period were 1404.57 ±43.2 mm and 22.65 ±0.1 ℃, respectively, showing a decrease of 523 mm in precipitation and an increase of 2.55 ℃ in temperature, compared to the 30-year records (1990-2020). Contrary to most published data for most forest ecosystems globally, Dinghushan Biosphere Reserve recorded significant carbon gain during 60% of the drought period.
... The PR reduction in Pr in the Arc region is more pronounced in monmean and monmax than for the Cerrado and the PR increase in WIND is a lot higher than in the Cerrado. This is in line with previous evidence that fires could induce fragmentation in the Amazon forests and extreme wind disturbances (Schwartz et al 2017, Silvério et al 2019, although the synergistic effects of fire, fragmentation and windstorms on a tropical forest are much more complex (Silvério et al 2019) than discussed in this study. ...
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2015 saw the strongest El Niño event in the historical record, resulting in extreme drought conditions in Brazil. As drought conditions may also lead to greater fire danger, this study uses the 2015 fire in Brazil as a case study to examine whether and to what extent human-induced climate change has contributed to the fire weather conditions in the Cerrado and the southern Amazonia transitional forests known as the Arc of deforestation. Our results show that anthropogenic climate change is indeed a driver of meteorological conditions conducive to strong fire weather in these two regions, measured by fire weather index (FWI), especially on shorter timescales of daily and weekly. The anthropogenic climate change signal of FWI on short timescales corresponds to a similar order of increase in the FWI sub-indices (initial spread index and fine fuel moisture code) that can rapidly change due to the influence of the instantaneous weather conditions. For both regions the changes in fire weather in response to anthropogenic climate change are dominated by the combination of temperature and relative humidity responses. High FWI is more likely to occur under El Niño conditions, less likely under La Niña conditions, although the impacts of El Niño vs La Niña conditions are not symmetric when compared with El Niño Southern Oscillation neutral states. To summarize, both human-induced climate change and the presence of El Niño increased the likelihood of occurrence for the strong fire weather condition in 2015. Our results suggest that local and regional adaptation measures, such as improved drought monitoring and warning systems, could help with effective planning of fire prevention, firefighting actions, and disaster preparedness.
... forest degradation (Silverio et al., 2018;Schwartz et al., 2017). Under natural conditions, disturbed forests recover to their pre-disturbance conditions through complex interactions that vary across spatial and temporal scales (Chazdon, 2014). ...
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Forest disturbance and regrowth are key processes in forest dynamics, but detailed information on these processes is difficult to obtain in remote forests such as the Amazon. We used chronosequences of Landsat satellite imagery (Landsat 5 Thematic Mapper and Landsat 7 Enhanced Thematic Mapper Plus) to determine the sensitivity of surface reflectance from all spectral bands to windthrow, clear-cut, and clear-cut and burned (cut + burn) and their successional pathways of forest regrowth in the Central Amazon. We also assessed whether the forest demography model Functionally Assembled Terrestrial Ecosystem Simulator (FATES) implemented in the Energy Exascale Earth System Model (E3SM) Land Model (ELM), ELM-FATES, accurately represents the changes for windthrow and clear-cut. The results show that all spectral bands from the Landsat satellites were sensitive to the disturbances but after 3 to 6 years only the near-infrared (NIR) band had significant changes associated with the successional pathways of forest regrowth for all the disturbances considered. In general, the NIR values decreased immediately after disturbance, increased to maximum values with the establishment of pioneers and early successional tree species, and then decreased slowly and almost linearly to pre-disturbance conditions with the dynamics of forest succession. Statistical methods predict that NIR values will return to pre-disturbance values in about 39, 36, and 56 years for windthrow, clear-cut, and cut + burn disturbances, respectively. The NIR band captured the observed, and different, successional pathways of forest regrowth after windthrow, clear-cut, and cut + burn. Consistent with inferences from the NIR observations, ELM-FATES predicted higher peaks of biomass and stem density after clear-cuts than after windthrows. ELM-FATES also predicted recovery of forest structure and canopy coverage back to pre-disturbance conditions in 38 years after windthrows and 41 years after clear-cut. The similarity of ELM-FATES predictions of regrowth patterns after windthrow and clear-cut to those of the NIR results suggests the NIR band can be used to benchmark forest regrowth in ecosystem models. Our results show the potential of Landsat imagery data for mapping forest regrowth from different types of disturbances, benchmarking, and the improvement of forest regrowth models.
... First, we used land cover data derived from MODIS imagery (6.25 hectare pixels). This relatively large pixel size may result in omission of some second-growth forests from our dataset, as many second-growth forest patches are quite small (less than one hectare; Schwartz et al., 2017a). These small patches comprising mixed pixels with other land cover types might not be detected by the classification, especially during early stages of growth when canopies are open and short. ...
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Carbon sequestration through tropical reforestation and natural regeneration could make an important contribution to climate change mitigation, given that forest cover in many tropical regions increased during the early part of the 21st century. The size of this carbon sink will depend on the degree to which second-growth forests are permanent and protected from re-clearing. Yet few studies have assessed permanence of reforestation, especially not at a large spatial scale. Here, we analyzed a 14-year time series (2001–2014) of remotely sensed land-cover data, covering all tropical Latin America and the Caribbean, to quantify the extent of second-growth forest permanence. Our results show that in many cases, reforestation in Latin America and the Caribbean during the early 21st century reversed by 2014, limiting carbon sequestration. In fact, reversals of reforestation, in which some or all gains in forest cover in the early 2000s were subsequently lost, were ten times more common than sustained increases in forest cover. Had reversals of reforestation been avoided, forests could have sequestered 0.58 Pg C, over four times more carbon than we estimate was sequestered after accounting for impermanence (0.14 Pg), representing a loss of 75% of carbon sequestration potential. Differences in the prevalence of reforestation reversals across countries suggest an important role for socio-economic, political, and ecological context, with political transitions and instability increasing the likelihood of reversals. These findings suggest that national commitments to reforestation may fall short of their carbon sequestration goals without provisions to ensure long-term permanence of new forests.
... Further studies could determine whether OF patches are the exclusive long-term consequences of old selective logging in the area that probably triggered forest degradation (Tabarelli and Mantovani, 2000;Montti et al., 2014). They may also determine if OF patches are just consequences of natural disturbances, such as extreme winds or droughts that can affect successional trajectories in regenerating forests, or if they result from both human and natural disturbances (Schwartz et al., 2017). At the same time, detecting the general degradation degree in the natural forest is relevant even when the lack of knowledge results from heterogeneity occurring at such a small spatial scale that cannot be captured by remote sensing (Luyssaert et al., 2014). ...
Article
FULL TEXT DOWNLOAD LINK UNTIL SEPT 30 https://authors.elsevier.com/c/1bYnRB8ccoJOV Recent studies have shown the importance of subtropical forests as terrestrial carbon sinks and also their vulnerability to human disturbances and climate change. The Semi-deciduous Atlantic Forest presents large extensions replaced by productive uses, such as tree plantations, and forest remnants showing high levels of structural heterogeneity. No studies have performed carbon stock densities estimations in different pools in the region. We wonder how changes in forest structure and forest replacement by pine plantations affect ecosystem carbon stock densities in different pools and fluxes. We performed carbon estimates based on field data and compared closed (CF) and open (OF) canopy natural forest patches and Pinus taeda plantations at harvest age (PP). Structural changes in the natural forest had a profound effect on the ecosystem by halving the forest carbon stock while pulp-intended pine plantations reached the carbon stock of closed forest at harvest age. Main changes from CF to OF were a 55% decrease in the carbon of biomass and a 42% decrease in SOC. Instead, carbon stock density in biomass of PP was similar to CF but the carbon in fallen deadwood was 78% lower while in the litter layer was double; the SOC at 0–5 cm depth was 31% lower in PP than CF. Our study shows that structural changes in the natural forest halve the forest carbon stock while pulp-intended pine plantations can reach the closed forest carbon stock at harvest age. However, PP do not seem to be effective for carbon storage in the long term because of regular harvesting and clearing and their short-life products. Therefore, to effectively store the forest carbon, arresting deforestation, replacement and degradation of the original forest is crucial.
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With projected increasing intensity of hurricanes and large uncertainty in the path of forest recovery from hurricanes, studies are needed to understand the fundamental response of forests to canopy opening and debris deposition: the response of the abiotic factors underneath the canopy. Through manipulative experiments and instrumenting hurricane María in the Luquillo Experimental Forest of Puerto Rico, this study found a long recovery time of the primary abiotic factors (light, throughfall, and temperature) influenced by the disturbance of canopy opening, and complex responses by the secondary abiotic factors (humidity, soil moisture, and leaf saturation) influenced by the disturbance of the primary factors. Recovery took up to 9 years for beneath canopy light, while throughfall recovery took 6 years. Air and soil temperature seemingly recovered fairly quickly from each disturbance, however temperature was the most important modulator of secondary factors, which followed the long-term patterns of the throughfall. While the soil remained wetter and humidity stayed lower until recovery, leaves in the litter and canopy were wetter and drier, with evidence that leaves dry out faster in low rainfall and saturate faster in high rainfall after disturbance. Comparison of satellite and field data before and after the 2017 hurricane showed the utility of satellites in expanding the data coverage, but the muted response of the satellite data suggest they measure dense forest as well as thin forest that is not as disturbed by hurricanes. Thus, quick recovery times recorded by satellites should not be assumed representative of all of the forest.
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Tropical cyclones play an increasingly important role in shaping ecosystems. Understanding and generalizing their responses is challenging because of meteorological variability among storms and its interaction with ecosystems. We present a research framework designed to compare tropical cyclone effects within and across ecosystems that: a) uses a disaggregating approach that measures the responses of individual ecosystem components, b) links the response of ecosystem components at fine temporal scales to meteorology and antecedent conditions, and c) examines responses of ecosystem using a resistance–resilience perspective by quantifying the magnitude of change and recovery time. We demonstrate the utility of the framework using three examples of ecosystem response: gross primary productivity, stream biogeochemical export, and organismal abundances. Finally, we present the case for a network of sentinel sites with consistent monitoring to measure and compare ecosystem responses to cyclones across the United States, which could help improve coastal ecosystem resilience.
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Governance is essential to the structure of incentives and the accounting necessary for large-scale deployment of methods for carbon dioxide removal from the atmosphere, particularly in light of the urgency to upscale carbon removal to stay below the 2°C global climate change target. A key governance challenge is operationalizing standards for the permanence of carbon sequestered in terrestrial and coastal ecosystems. There are multiple risks of reversal of carbon storage in these ecosystems and release of carbon back to the atmosphere. This paper reviews issues of permanence in four approaches for carbon removal focusing on carbon uptake and potential side-effects of long-term land commitments. Recognizing that permanence is a considerable barrier to large-scale application of land-based carbon removal, we argue that temporary carbon storage can still provide climate benefits in the short run. A multilateral governance framework should redefine permanence requirements and reflect principles of sustainability, polycentricity, and land stewardship.
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Andean tropical montane forests (TMF) are hotspots of biodiversity that provide fundamental hydrological services as well as carbon sequestration and storage. Agroforestry systems occupy large areas in the Andes but climatic pressures, market volatility and diseases may lead to agroforest abandonment, promoting secondary succession. Secondary forests are well-adapted and efficient carbon sinks whose conservation is vital to mitigate and adapt to climate change and to support biodiversity. Little is known, however, about how secondary TMF recover their aboveground biomass (AGB) and composition after abandonment. We established a 1.5 ha plot at 1,780 masl on a 30-year old abandoned agroforest and compared it against two control forest plots at similar elevations. Agroforestry legacies influenced AGB leading to far lower stocks (42.3 ± 5.4 to 59.6 ± 7.9 Mg.ha⁻¹ using allometric equations) than those expected after 30 years (106 ± 33 Mg.ha⁻¹) based on IPCC standard growth rates for secondary montane forests. This suggests a regional overestimation of mitigation potentials when using IPCC standards. Satellite-derived AGB largely overestimated our plot values (179 ± 27.3 Mg.ha⁻¹). Secondary growth rates (1.41- 2.0 Mg.ha⁻¹.yr⁻¹ for DBH≥ 10 cm) indicate recovery times of ca. 69 to 97 years to reach average control AGB values (137 ± 12.3 Mg.ha⁻¹). This is 26 years above the average residence time of montane forests at our elevation (71 ± 1.91 years) suggesting a non-recovery or far slower recovery to control AGB values. Compared to the control plots, three variables differed strongly: lower DBH (15.8 ± 5.9 cm vs 19.8 ± 11.0 cm), lower basal area (12.67 ± 0.7 vs 28.03± 1.5 m².ha⁻¹) and higher abundance of lighter-wood tree genera (0.46 ± 0.10 vs 0.57 ± 0.11 gr.cm³) such as Inga, a common shade-tree in Andean agroforests. With 3.2 million hectares committed to restoration, Peru needs to target currently neglected TMF recovery schemes to support biodiversity, water and carbon storage and fulfill its international commitments.
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Abstract. Forest disturbance and regrowth are key processes in forest dynamics but detailed information of these processes is difficult to obtain in remote forests as the Amazon. We used chronosequences of Landsat satellite imagery to determine the sensitivity of surface reflectance from all spectral bands to windthrow, clearcutting, and burning and their successional pathways of forest regrowth in the Central Amazon. We also assess whether the forest demography model Functionally Assembled Terrestrial Ecosystem Simulator (FATES) implemented in the Energy Exascale Earth System Model (E3SM) Land Model (ELM), ELM-FATES, accurately represents the changes for windthrow and clearcut. The results show that all spectral bands from Landsat satellite were sensitive to the disturbances but after 3 to 6 years only the Near Infrared (NIR) band had significant changes associated with the successional pathways of forest regrowth for all the disturbances considered. In general, the NIR decreased immediately after disturbance, increased to maximum values with the establishment of pioneers and early-successional tree species, and then decreased slowly and almost linearly to pre-disturbance conditions with the dynamics of forest succession. Statistical methods predict that NIR will return to pre-disturbance values in about 39 years (consistent with observational data of biomass regrowth following windthrows), and 36 and 56 years for clearcut and burning. The NIR captured the observed successional pathways of forest regrowth after clearcut and burning that diverge through time. ELM-FATES predicted higher peaks of initial forest responses (e.g., biomass, stem density) after clearcuts than after windthrows, similar to the changes in NIR. However, ELM-FATES predicted a faster recovery of forest structure and canopy-coverage back to pre-disturbance conditions for windthrows compared to clearcuts. The similarity of ELM-FATES predictions of regrowth patterns after windthrow and clearcut to those of the NIR results suggest that the dynamics of forest regrowth for these disturbances are represented with appropriate fidelity within ELM-FATES and useful as a benchmarking tool.
Article
Tropical cyclones play an increasingly important role in shaping ecosystems. Understanding and generalizing their responses is challenging because of meteorological variability among storms and its interaction with ecosystems. We present a research framework designed to compare tropical cyclone effects within and across ecosystems that: a) uses a disaggregating approach that measures the responses of individual ecosystem components, b) links the response of ecosystem components at fine temporal scales to meteorology and antecedent conditions, and c) examines responses of ecosystem using a resistance–resilience perspective by quantifying the magnitude of change and recovery time. We demonstrate the utility of the framework using three examples of ecosystem response: gross primary productivity, stream biogeochemical export, and organismal abundances. Finally, we present the case for a network of sentinel sites with consistent monitoring to measure and compare ecosystem responses to cyclones across the United States, which could help improve coastal ecosystem resilience.
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Large quantities of dead wood can be generated by disturbances such as wildfires. Dead trees created by disturbances play many critical ecological roles in forest ecosystems globally. The ability of deadwood to serve its ecological roles is contingent, in part, on the length of time trees remain standing following disturbance. Here, we briefly outline the results of a 10‐year study that aimed to quantify the rate of collapse of trees killed in a major wildfire in the wet ash forests of mainland south‐eastern Australia. We also quantified the factors associated with dead tree collapse. Our analyses revealed that 23% of 417 measured trees collapsed between 2011 and 2021. The most parsimonious model of the factors influencing tree collapse revealed a strong effect of diameter; smaller diameter trees were more likely to collapse over the 10 years of our study than larger diameter trees. In addition, trees in small and large patches were more likely to collapse than trees in contiguous forest (where there had been no logging in the surrounding area). If current rates of tree fall are maintained, then many of trees initially measured will have collapsed by 2030. Such losses of dead trees will have major negative effects on key values of ash‐type forests such as biodiversity conservation.
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Many countries have made major commitments to carbon sequestration through reforestation under the Paris Climate Agreement, and recent studies have illustrated the potential for large amounts of carbon sequestration in tropical second-growth forests. However, carbon gains in second-growth forests are threatened by non-permanence, i.e. release of carbon into the atmosphere from clearing or disturbance. The benefits of second-growth forests require long-term persistence on the landscape, but estimates of carbon potential rarely consider the spatio-temporal landscape dynamics of second-growth forests. In this study, we used remotely sensed imagery from a landscape in the Peruvian Amazon to examine patterns of second-growth forest regrowth and permanence over 28 years (1985-2013). By 2013, 44% of all forest cover in the study area was second growth and more than 50% of second-growth forest pixels were less than 5 years old. We modeled probabilities of forest regrowth and clearing as a function of landscape factors. The amount of neighboring forest and variables related to pixel position (i.e. distance to edge) were important for predicting both clearing and regrowth. Forest age was the strongest predictor of clearing probability and suggests a threshold response of clearing probability to age. Finally, we simulated future trajectories of carbon sequestration using the parameters from our models. We compared this with the amount of biomass that would accumulate under the assumption of second-growth permanence. Estimates differed by 900 000 tonnes, equivalent to over 80% of Peru's commitment to carbon sequestration through 'community reforestation' under the Paris Agreement. Though the study area has more than 40 000 hectares of second-growth forest, only a small proportion is likely to accumulate significant carbon. Instead, cycles between forest and non-forest are common. Our results illustrate the importance of considering landscape dynamics when assessing the carbon sequestration potential of second-growth forests.
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Deforestation in the tropics is not only responsible for direct carbon emissions but also extends the forest edge wherein trees suffer increased mortality. Here we combine high-resolution (30 m) satellite maps of forest cover with estimates of the edge effect and show that 19% of the remaining area of tropical forests lies within 100 m of a forest edge. The tropics house around 50 million forest fragments and the length of the world’s tropical forest edges sums to nearly 50 million km. Edge effects in tropical forests have caused an additional 10.3 Gt (2.1–14.4 Gt) of carbon emissions, which translates into 0.34 Gt per year and represents 31% of the currently estimated annual carbon releases due to tropical deforestation. Fragmentation substantially augments carbon emissions from tropical forests and must be taken into account when analysing the role of vegetation in the global carbon cycle.
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Secondary succession in the tropics can follow alternative pathways. Land-use history is known to engender alternative successional communities, but the underlying mechanisms driving and sustaining divergence remain unclear. In this study we aim to answer the following questions: (1) does previous land use act as a filter for species composition in secondary forests; and (2) what are the relative roles of management practices, soil properties and landscape composition in determining species composition?
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Deep convective updrafts often penetrate through the surrounding cirrus anvil and into the lower stratosphere. Cross-tropopause ice, water vapor, and chemical transport occurs within these “overshooting tops” (OTs) as well as a variety of hazardous weather conditions. OTs are readily apparent in satellite imagery and, given their importance for weather and climate, a number of automated satellite-based detection methods have been developed. Some of these methods have proven to be relatively reliable and their products are used in diverse Earth science applications. Nevertheless, analysis of these methods and feedback from product users indicates that use of fixed infrared temperature-based detection criteria often induces biases that can limit their utility for weather and climate analysis. This paper describes a new multispectral OT detection approach that improves upon those previously developed by minimizing use of fixed criteria and incorporating pattern recognition analyses to arrive at an OT Probability product. The product is developed and validated using OT and non-OT anvil regions identified by a human within MODIS imagery. The product offered high skill for discriminating between OT and anvil and identified 69% of human OT identifications for a particular Probability threshold with a false detection rate of 18%, outperforming previously existing methods. The false detection rate drops to 1% when OT-induced texture detected within visible imagery is used to constrain the IR-based OT Probability product. The OT Probability product is also shown to improve severe storm detection over the U.S. by 20% relative to the best existing method.
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Multinomial logistic models of land use/land cover in montane Costa Rica and landscape pattern analysis showed that relative to agriculture, secondary forest occurred closer to old-growth forest, further from roads, in forest reserves, and at higher elevations. Collinearity between explanatory variables yielded simple multivariate models; proportion of surrounding old growth predicted secondary forest most accurately. An old-growth matrix [mean patch size (MPS) 24.5 ha], located mainly within protected areas, dominated elevations greater than 2500 m. A matrix of agriculture (MPS 23.5 ha), with smaller patches (approximately 9 ha) of secondary forest and old growth, dominated elevations from 1500 to 2500 m. Combining secondary forest with old growth decreased forest patch number and increased MPS from 7.3 to 37.1 ha. I concluded that: (a) secondary forest pattern is nonrandom, so ancillary data will aid its mapping with satellite imagery. The variables elevation, agriculture distance, road distance, and population density distinguished secondary forest from old growth with 74% accuracy; (b) socioeconomic and biological forces probably interact to create these secondary forest patterns; and (c) the strong association between secondary forest and old growth supports the concept that tropical forest recovery depends on the landscape structure of remnant forest.
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Regrowth of tropical secondary forests following complete or nearly complete removal of forest vegetation actively stores carbon in aboveground biomass, partially counterbalancing carbon emissions from deforestation, forest degradation, burning of fossil fuels, and other anthropogenic sources. We estimate the age and spatial extent of lowland second-growth forests in the Latin American tropics and model their potential aboveground carbon accumulation over four decades. Our model shows that, in 2008, second-growth forests (1 to 60 years old) covered 2.4 million km2 of land (28.1% of the total study area). Over 40 years, these lands can potentially accumulate a total aboveground carbon stock of 8.48 Pg C (petagrams of carbon) in aboveground biomass via low-cost natural regeneration or assisted regeneration, corresponding to a total CO2 sequestration of 31.09 Pg CO2. This total is equivalent to carbon emissions from fossil fuel use and industrial processes in all of Latin America and the Caribbean from 1993 to 2014. Ten countries account for 95% of this carbon storage potential, led by Brazil, Colombia, Mexico, and Venezuela. We model future land-use scenarios to guide national carbon mitigation policies. Permitting natural regeneration on 40% of lowland pastures potentially stores an additional 2.0 Pg C over 40 years. Our study provides information and maps to guide national-level forest-based carbon mitigation plans on the basis of estimated rates of natural regeneration and pasture abandonment. Coupled with avoided deforestation and sustainable forest management, natural regeneration of second-growth forests provides a low-cost mechanism that yields a high carbon sequestration potential with multiple benefits for biodiversity and ecosystem services.
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Old-growth forests are subject to substantial changes in structure and species composition due to the intensification of human activities, gradual climate change and extreme weather events. Trees store ca. 90 % of the total aboveground biomass (AGB) in tropical forests and precise tree biomass estimation models are crucial for management and conservation. In the central Amazon, predicting AGB at large spatial scales is a challenging task due to the heterogeneity of successional stages, high tree species diversity and inherent variations in tree allometry and architecture. We parameterized generic AGB estimation models applicable across species and a wide range of structural and compositional variation related to species sorting into height layers as well as frequent natural disturbances. We used 727 trees (diameter at breast height ≥ 5 cm) from 101 genera and at least 135 species harvested in a contiguous forest near Manaus, Brazil. Sampling from this data set we assembled six scenarios designed to span existing gradients in floristic composition and size distribution in order to select models that best predict AGB at the landscape level across successional gradients. We found that good individual tree model fits do not necessarily translate into reliable predictions of AGB at the landscape level. When predicting AGB (dry mass) over scenarios using our different models and an available pantropical model, we observed systematic biases ranging from −31 % (pantropical) to +39 %, with root-mean-square error (RMSE) values of up to 130 Mg ha−1 (pantropical). Our first and second best models had both low mean biases (0.8 and 3.9 %, respectively) and RMSE (9.4 and 18.6 Mg ha−1) when applied over scenarios. Predicting biomass correctly at the landscape level in hyperdiverse and structurally complex tropical forests, especially allowing good performance at the margins of data availability for model construction/calibration, requires the inclusion of predictors that express inherent variations in species architecture. The model of interest should comprise the floristic composition and size-distribution variability of the target forest, implying that even generic global or pantropical biomass estimation models can lead to strong biases. Reliable biomass assessments for the Amazon basin (i.e., secondary forests) still depend on the collection of allometric data at the local/regional scale and forest inventories including species-specific attributes, which are often unavailable or estimated imprecisely in most regions.
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Land-use change occurs nowhere more rapidly than in the tropics, where the imbalance between deforestation and forest regrowth has large consequences for the global carbon cycle. However, considerable uncertainty remains about the rate of biomass recovery in secondary forests, and how these rates are influenced by climate, landscape, and prior land use. Here we analyse aboveground biomass recovery during secondary succession in 45 forest sites and about 1,500 forest plots covering the major environmental gradients in the Neotropics. The studied secondary forests are highly productive and resilient. Aboveground biomass recovery after 20 years was on average 122 megagrams per hectare (Mg ha(-1)), corresponding to a net carbon uptake of 3.05 Mg C ha(-1) yr(-1), 11 times the uptake rate of old-growth forests. Aboveground biomass stocks took a median time of 66 years to recover to 90% of old-growth values. Aboveground biomass recovery after 20 years varied 11.3-fold (from 20 to 225 Mg ha(-1)) across sites, and this recovery increased with water availability (higher local rainfall and lower climatic water deficit). We present a biomass recovery map of Latin America, which illustrates geographical and climatic variation in carbon sequestration potential during forest regrowth. The map will support policies to minimize forest loss in areas where biomass resilience is naturally low (such as seasonally dry forest regions) and promote forest regeneration and restoration in humid tropical lowland areas with high biomass resilience.
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We conducted an analysis of global forest cover to reveal that 70% of remaining forest is within 1 km of the forest’s edge, subject to the degrading effects of fragmentation. A synthesis of fragmentation experiments spanning multiple biomes and scales, five continents, and 35 years demonstrates that habitat fragmentation reduces biodiversity by 13 to 75% and impairs key ecosystem functions by decreasing biomass and altering nutrient cycles. Effects are greatest in the smallest and most isolated fragments, and they magnify with the passage of time. These findings indicate an urgent need for conservation and restoration measures to improve landscape connectivity, which will reduce extinction rates and help maintain ecosystem services.
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Debate continues over the adequacy of existing field plots to sufficiently capture Amazon forest dynamics to estimate regional forest carbon balance. Tree mortality dynamics are particularly uncertain due to the difficulty of observing large, infrequent disturbances. A recent paper (Chambers et al 2013 Proc. Natl Acad. Sci. 110 3949─54) reported that Central Amazon plots missed 9─17% of tree mortality, and here we address ‘why’ by elucidating two distinct mortality components: (1) variation in annual landscape-scale average mortality and (2) the frequency distribution of the size of clustered mortality events. Using a stochastic-empirical tree growth model we show that a power law distribution of event size (based on merged plot and satellite data) is required to generate spatial clustering of mortality that is consistent with forest gap observations. We conclude that existing plots do not sufficiently capture losses because their placement, size, and longevity assume spatially random mortality, while mortality is actually distributed among differently sized events (clusters of dead trees) that determine the spatial structure of forest canopies.
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Forest inventory studies in the Amazon indicate a large terrestrial carbon sink. However, field plots may fail to represent forest mortality processes at landscape-scales of tropical forests. Here we characterize the frequency distribution of disturbance events in natural forests from 0.01 ha to 2,651 ha size throughout Amazonia using a novel combination of forest inventory, airborne lidar and satellite remote sensing data. We find that small-scale mortality events are responsible for aboveground biomass losses of ~1.7 Pg C y(-1) over the entire Amazon region. We also find that intermediate-scale disturbances account for losses of ~0.2 Pg C y(-1), and that the largest-scale disturbances as a result of blow-downs only account for losses of ~0.004 Pg C y(-1). Simulation of growth and mortality indicates that even when all carbon losses from intermediate and large-scale disturbances are considered, these are outweighed by the net biomass accumulation by tree growth, supporting the inference of an Amazon carbon sink.
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Studies have found that convective storms with overshooting-top (OT) signatures in weather satellite imagery are often associated with hazardous weather, such as heavy rainfall, tornadoes, damaging winds, and large hail. An objective satellite-based OT detection product has been developed using 11-mm infrared window (IRW) channel brightness temperatures (BTs) for the upcoming R series of the Geostationary Operational Environmental Satellite (GOES-R) Advanced Baseline Imager. In this study, this method is applied to GOES-12 IRW data and the OT detections are compared with radar data, severe storm reports, and severe weather warnings over the eastern United States. The goals of this study are to 1) improve forecaster understanding of satellite OT signatures relative to commonly available radar products, 2) assess OT detection product accuracy, and 3) evaluate the utility of an OT detection product for diagnosing hazardous convective storms. The coevolution of radar-derived products and satellite OT signatures indicates that an OT often corresponds with the highest radar echo top and reflectivity maximum aloft. Validation of OT detections relative to composite reflectivity indicates an algorithm false-alarm ratio of 16%, with OTs within the coldest IRW BT range (,200 K) being the most accurate. A significant IRW BT minimum typically present with an OT is more often associated with heavy precipitation than a region with a spatially uniform BT. Severe weather was often associated with OT detections during the warm season (April–September) and over the southern United States. The severe weather to OT relationship increased by 15% when GOES operated in rapid-scan mode, showing the importance of high temporal resolution for observing and detecting rapidly evolving cloud-top features. Comparison of the earliest OT detection associated with a severe weather report showed that 75% of the cases occur before severe weather and that 42% of collocated severe weather reports had either anOTdetected before a severe weather warning or no warning issued at all. The relationships between satellite OT signatures, severe weather, and heavy rainfall shown in this paper suggest that 1) when an OT is detected, the particular storm is likely producing heavy rainfall and/or possibly severe weather; 2) an objective OT detection product can be used to increase situational awareness and forecaster confidence that a given storm is severe; and 3) this product may be particularly useful in regions with insufficient radar coverage.
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A new method called Fmask (Function of mask) for cloud and cloud shadow detection in Landsat imagery is provided. Landsat Top of Atmosphere (TOA) reflectance and Brightness Temperature (BT) are used as inputs. Fmask first uses rules based on cloud physical properties to separate Potential Cloud Pixels (PCPs) and clear-sky pixels. Next, a normalized temperature probability, spectral variability probability, and brightness probability are combined to produce a probability mask for clouds over land and water separately. Then, the PCPs and the cloud probability mask are used together to derive the potential cloud layer. The darkening effect of the cloud shadows in the Near Infrared (NIR) Band is used to generate a potential shadow layer by applying the flood-fill transformation. Subsequently, 3D cloud objects are determined via segmentation of the potential cloud layer and assumption of a constant temperature lapse rate within each cloud object. The view angle of the satellite sensor and the illuminating angle are used to predict possible cloud shadow locations and select the one that has the maximum similarity with the potential cloud shadow mask. If the scene has snow, a snow mask is also produced. For a globally distributed set of reference data, the average Fmask overall cloud accuracy is as high as 96.4%. The goal is development of a cloud and cloud shadow detection algorithm suitable for routine usage with Landsat images.
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State-of-the-art socioeconomic scenarios of land-cover change in the Amazon basin for the years 2030 and 2050 are used together with the Regional Atmospheric Modeling System (RAMS) to simulate the hydrometeorological changes caused by deforestation in that region under diverse climatological conditions that include both El Niño and La Niña events. The basin-averaged rainfall progressively decreases with the increase of deforestation from 2000 to 2030, 2050, and so on, to total deforestation by the end of the twenty-first century. Furthermore, the spatial distribution of rainfall is significantly affected by both the land-cover type and topography. While the massively deforested region experiences an important decrease of precipitation, the areas at the edge of that region and at elevated regions receive more rainfall. Propa- gating squall lines over the massively deforested region dissipate before reaching the western part of the basin, causing a significant decrease of rainfall that could result in a catastrophic collapse of the ecosystem in that region. The basin experiences much stronger precipitation changes during El Niño events as defor- estation increases. During these periods, deforestation in the western part of the basin induces a very significant decrease of precipitation. During wet years, however, deforestation has a minor overall impact on the basin climatology.
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Despite the importance of forest edges in ecology, only one study has previously been carried out in New Zealand on the modification of climate across forest edges. We measured light exposure, wind speed, air and soil temperature, and vapour pressure deficit (VPD) perpendicular to a north-south aligned, mature, edge of native broadleaf rainforest adjoining grazed pasture. At a point 80 m into the forest from the edge, light was only c. 0.7% and wind speed c. 20% of that in the open, and there was much less diurnal fluctuation in soil temperature, air temperature and VPD. The gradient of microclimate near the edge, as measured with a third (mobile) weather station, was abrupt for soil temperature and similar to the pattern of light exposure, with almost complete change over about 10 m. The gradient was less steep for wind speed, air temperature and VPD, with at least 40 m being required to stabilise these variables when wind was directed into the forest. These findings suggest that forest buffers of at least 40 m may be needed to protect forest reserves and streams from climatic exposure.
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The ACSL are discontinuous lines of organized mesoscale cloud clusters that propagate across the central Amazon Basin at speeds of 50-60 km h-1. The ACSL undergo six possible life cycle stages: coastal genesis, intensification, maturity, weakening, reintensification, and dissipation. Analysis also indicates that mesoscale clusters within the ACSL are composed of three distinct cloud components: a prestorm region that often contains towering cumulus, leading edge convection (LEC), and multiple, precipitating cloud layers in the trailing stratiform region (TSR). Divergence and vertical velocity calculations indicate deep vertical ascent in the LEC and a region of midlevel convergence (~500 mb) in the TSR. The latter midlevel convergence is associated with a weak updraft above 500 mb and an unsaturated downdraft below. Vertical motions in the TSR are an order of magnitude smaller than in the LEC. -from Authors
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We tested whether and how functional composition changes with succession in dry deciduous and wet evergreen forests of Mexico. We hypothesized that compositional changes during succession in dry forest were mainly determined by increasing water availability leading to community functional changes from conservative to acquisitive strategies, and in wet forest by decreasing light availability leading to changes from acquisitive to conservative strategies. Research was carried out in 15 dry secondary forest plots (5-63 years after abandonment) and 17 wet secondary forest plots (< 1-25 years after abandonment). Community-level functional traits were represented by community-weighted means based on 11 functional traits measured on 132 species. Successional changes in functional composition are more marked in dry forest than in wet forest and largely characterized by different traits. During dry forest succession, conservative traits related to drought tolerance and drought avoidance decreased, as predicted. Unexpectedly acquisitive leaf traits also decreased, whereas seed size and dependence on biotic dispersal increased. In wet forest succession functional composition changed from acquisitive to conservative leaf traits, suggesting light availability as the main driver of changes. Distinct suites of traits shape functional composition changes in dry and wet forest succession, responding to different environmental filters.
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We analyzed the pattern of large forest disturbances or blow-downs apparently caused by severe storms in a mostly unmanaged portion of the Brazilian Amazon using 27 Landsat images and daily precipitation estimates from NOAA satellite data. For each Landsat a spectral mixture analysis (SMA) was applied. Based on SMA, we detected and mapped 279 patches (from 5 ha to 2,223 ha) characteristic of blow-downs. A total of 21,931 ha of forest were disturbed. We found a strong correlation between occurrence of blow-downs and frequency of heavy rainfall (Spearman's rank, r2 = 0.84, p < 0.0003). The recurrence intervals of large disturbances were estimated to be 90,000 yr for the eastern Amazon and 27,000 yr for the western Amazon. This suggests that weather patterns affect the frequency of large forest disturbances that may produce different rates of forest turnover in the eastern and western Amazon basin.
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Forest regeneration following disturbance is a key ecological process, influencing forest structure and function, species assemblages, and ecosystem-climate interactions. Climate change may alter forest recovery dynamics or even prevent recovery, triggering feedbacks to the climate system, altering regional biodiversity, and affecting the ecosystem services provided by forests. Multiple lines of evidence-including global-scale patterns in forest recovery dynamics; forest responses to experimental manipulation of CO2 , temperature, and precipitation; forest responses to the climate change that has already occurred; ecological theory; and ecosystem and earth system models-all indicate that the dynamics of forest recovery are sensitive to climate. However, synthetic understanding of how atmospheric CO2 and climate shape trajectories of forest recovery is lacking. Here, we review these separate lines of evidence, which together demonstrate that the dynamics of forest recovery are being impacted by increasing atmospheric CO2 and changing climate. Rates of forest recovery rates generally increase with CO2 , temperature, and water availability. Drought reduces growth and live biomass in forests of all ages, having a particularly strong effect on seedling recruitment and survival. Responses of individual trees and whole-forest ecosystems to CO2 and climate manipulations often vary by age, implying that forests of different ages will respond differently to climate change. Furthermore, species within a community typically exhibit differential responses to CO2 and climate, and altered community dynamics can have important consequences for ecosystem function. Age- and species-dependent responses provide a mechanism by which climate change may push some forests past critical thresholds such that they fail to recover to their previous state following disturbance. Altered dynamics of forest recovery will result in positive and negative feedbacks to climate change. Future research on this topic and corresponding improvements to earth system models will be key to understanding the future of forests and their feedbacks to the climate system. © 2013 Blackwell Publishing Ltd.
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Old-growth forest ecosystems comprise a mosaic of patches in different successional stages, with the fraction of the landscape in any particular state relatively constant over large temporal and spatial scales. The size distribution and return frequency of disturbance events, and subsequent recovery processes, determine to a large extent the spatial scale over which this old-growth steady state develops. Here, we characterize this mosaic for a Central Amazon forest by integrating field plot data, remote sensing disturbance probability distribution functions, and individual-based simulation modeling. Results demonstrate that a steady state of patches of varying successional age occurs over a relatively large spatial scale, with important implications for detecting temporal trends on plots that sample a small fraction of the landscape. Long highly significant stochastic runs averaging 1.0 Mg biomass⋅ha(-1)⋅y(-1) were often punctuated by episodic disturbance events, resulting in a sawtooth time series of hectare-scale tree biomass. To maximize the detection of temporal trends for this Central Amazon site (e.g., driven by CO(2) fertilization), plots larger than 10 ha would provide the greatest sensitivity. A model-based analysis of fractional mortality across all gap sizes demonstrated that 9.1-16.9% of tree mortality was missing from plot-based approaches, underscoring the need to combine plot and remote-sensing methods for estimating net landscape carbon balance. Old-growth tropical forests can exhibit complex large-scale structure driven by disturbance and recovery cycles, with ecosystem and community attributes of hectare-scale plots exhibiting continuous dynamic departures from a steady-state condition.
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Rain forest fragments in central Amazonia were found to experience a dramatic loss of above-ground tree biomass that is not offset by recruitment of new trees. These losses were largest within 100 meters of fragment edges, where tree mortality is sharply increased by microclimatic changes and elevated wind turbulence. Permanent study plots within 100 meters of edges lost up to 36 percent of their biomass in the first 10 to 17 years after fragmentation. Lianas (climbing woody vines) increased near edges but usually compensated for only a small fraction of the biomass lost as a result of increased tree mortality.
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Tropical Cyclone ‘Rona’ crossed the coast of the Daintree lowlands of northeastern Australia in 1999. This study reports on its impact on forest canopy openness at six lowland rain forest sites with contrasting management histories (old-growth, selectively logged and regrowth). Percentage canopy openness was calculated from individual hemispherical photographs taken from marked points below the forest canopy at nine plots per site 3–4 mo before the cyclone, and at the same points a month afterwards. Before the cyclone, when nine sites were visited, canopy openness in old-growth and logged sites was similar, but significantly higher in regrowth forest. After the cyclone, all six revisited sites showed an increase in canopy openness, but the increase was very patchy amongst plots and sites and varied from insignificant to severe. The most severely impacted site was an old-growth one, the least impacted a logged one. Although proneness to impact was apparently related to forest management history (old-growth being the most impacted), underlying local topography may have had an equally strong influence in this case. It was concluded that the likelihood of severe impact may be determined at the landscape-scale by the interaction of anthropogenic with meteorological, physiographic and biotic factors. In the long term, such interactions may caution against pursuing forest management in cyclone-prone areas.
Book
This volume describes how to process and interpret spectral images using physical models to bridge the gap between the engineering and theoretical sides of remote-sensing and the outdoors world. Examples are drawn from a variety of landscapes and interpretations are tested against the reality seen on the ground. The reader is led through analysis of real images (using figures and explanations) and examples are chosen to illustrate important aspects of the analytic framework. The book is supplemented by a web-site hosting digital color versions of figures in the book as well as ancillary images (www.cambridge.org/9780521662214).
Article
Naturally regenerating and restored second growth forests account for over 70% of tropical forest cover and provide key ecosystem services. Understanding climate change impacts on successional trajectories of these ecosystems is critical for developing effective large-scale forest landscape restoration (FLR) programs. Differences in environmental conditions, species composition, dynamics, and landscape context from old growth forests may exacerbate climate impacts on second growth stands. We compile data from 112 studies on the effects of natural climate variability, including warming, droughts, fires, and cyclonic storms, on demography and dynamics of second growth forest trees and identify variation in forest responses across biomes, regions, and landscapes. Across studies, drought decreases tree growth, survival , and recruitment, particularly during early succession, but the effects of temperature remain unexplored. Shifts in the frequency and severity of disturbance alter successional trajectories and increase the extent of second growth forests. Vulnerability to climate extremes is generally inversely related to long-term exposure, which varies with historical climate and biogeography. The majority of studies, however, have been conducted in the Neotropics hindering generalization. Effects of fire and cyclonic storms often lead to positive feedbacks, increasing vulnerability to climate extremes and subsequent disturbance. Fragmentation increases forests' vulnerability to fires, wind, and drought, while land use and other human activities influence the frequency and intensity of fire, potentially retarding succession. Comparative studies of climate effects on tropical forest succession across biogeographic regions are required to forecast the response of tropical forest landscapes to future climates and to implement effective FLR policies and programs in these landscapes. Abstract in Spanish is available with online material.
Article
High descending winds generated by convective storms are a frequent and a major source of tree mortality disturbance events in the Amazon, affecting forest structure and diversity across a variety of scales, and more frequently observed in western and central portions of the basin. Soil texture in the Central Amazon also varies significantly with elevation along a topographic gradient, with decreasing clay content on plateaus, slopes and valleys respectively. In this study we investigated the critical turning moments (Mcrit - rotational force at the moment of tree failure, an indicator of tree stability or wind resistance) of 60 trees, ranging from 19.0 to 41.1 cm in diameter at breast height (DBH) and located in different topographic positions, and for different species, using a cable-winch load-cell system. Our approach used torque as a measure of tree failure to the point of snapping or uprooting. This approach provides a better understanding of the mechanical forces required to topple trees in tropical forests, and will inform models of wind throw disturbance. Across the topographic positions, size controlled variation in Mcrit was quantified for cardeiro (Scleronema mincranthum (Ducke) Ducke), mata-matá (Eschweilera spp.), and a random selection of trees from 19 other species. Our analysis of Mcrit revealed that tree resistance to failure increased with size (DBH and ABG) and differed among species. No effects of topography or failure mode were found for the species either separately or pooled. For the random species, total variance in Mcrit explained by tree size metrics increased from an R2 of 0.49 for DBH alone, to 0.68 when both DBH and stem fresh wood density (SWD) were included in a multiple regression model. This mechanistic approach allows the comparison of tree vulnerability induced by wind damage across ecosystems, and facilitates the use of forest structural information in ecosystem models that include variable resistance of trees to mortality inducing factors. Our results indicate that observed topographic differences in windthrow vulnerability are likely due to elevational differences in wind velocities, rather than by differences in soil-related factors that might effect Mcrit.
Article
Forest inventory studies in the Amazon indicate a large terrestrial carbon sink. However, field plots may fail to represent forest mortality processes at landscape-scales of tropical forests. Here we characterize the frequency distribution of disturbance events in natural forests from 0.01 ha to 2,651 ha size throughout Amazonia using a novel combination of forest inventory, airborne lidar and satellite remote sensing data. We find that small-scale mortality events are responsible for aboveground biomass losses of ~1.7 Pg C y(-1) over the entire Amazon region. We also find that intermediate-scale disturbances account for losses of ~0.2 Pg C y(-1), and that the largest-scale disturbances as a result of blow-downs only account for losses of ~0.004 Pg C y(-1). Simulation of growth and mortality indicates that even when all carbon losses from intermediate and large-scale disturbances are considered, these are outweighed by the net biomass accumulation by tree growth, supporting the inference of an Amazon carbon sink.
Article
Wind disturbance can create large forest blowdowns, which greatly reduces live biomass and adds uncertainty to the strength of the Amazon carbon sink. Observational studies from within the central Amazon have quantified blowdown size and estimated total mortality but have not determined which trees are most likely to die from a catastrophic wind disturbance. Also, the impact of spatial dependence upon tree mortality from wind disturbance has seldom been quantified, which is important because wind disturbance often kills clusters of trees due to large treefalls killing surrounding neighbors. We examine (1) the causes of differential mortality between adult trees from a 300-ha blowdown event in the Peruvian region of the northwestern Amazon, (2) how accounting for spatial dependence affects mortality predictions, and (3) how incorporating both differential mortality and spatial dependence affect the landscape level estimation of necromass produced from the blowdown. Standard regression and spatial regression models were used to estimate how stem diameter, wood density, elevation, and a satellite-derived disturbance metric influenced the probability of tree death from the blowdown event. The model parameters regarding tree characteristics, topography, and spatial autocorrelation of the field data were then used to determine the consequences of non-random mortality for landscape production of necromass through a simulation model. Tree mortality was highly non-random within the blowdown, where tree mortality rates were highest for trees that were large, had low wood density, and were located at high elevation. Of the differential mortality models, the non-spatial models overpredicted necromass, whereas the spatial model slightly underpredicted necromass. When parameterized from the same field data, the spatial regression model with differential mortality estimated only 7.5% more dead trees across the entire blowdown than the random mortality model, yet it estimated 51% greater necromass. We suggest that predictions of forest carbon loss from wind disturbance are sensitive to not only the underlying spatial dependence of observations, but also the biological differences between individuals that promote differential levels of mortality.
Chapter
Problems of air and water pollution have become sufficiently acute and extensive that piecemeal solution of the problems is no longer adequate. It has become clear that even if each city meets clean air and water standards for human health the regional ecosystems may be degraded. It is thus necessary to monitor and manage the environment on a regional or even global basis. At this scale, however, heterogeneity of all types becomes almost overwhelming. Spatial heterogeneity, multilevel phenomena, multiple management activities, and multiple time scales interfere with the abilities of managers and regulatory agencies to detect and prevent environmental deterioration. This chapter addresses strategies for dealing with complexity and heterogeneity, largely in the context of environmental protection.
Article
The interaction of wind and trees can result in substantial changes to forest structure and is of interest to many forest ecologists, but the complexity of the relationship has confounded many studies. The result of the interaction can take many forms across a range of scales, may have chronic and acute components, and can be exacerbated by other conditions, such as wet snowfall and salt deposition. Leaves may be abraded, causing subsequent desiccation; young trees may socket (that is, become loosened around the root collar by swaying) and in extreme cases topple because of inadequate rooting; leaders, branches, and crowns may break; older trees may be windthrown when stem and root plate overturn or may experience windsnap when the stem fails above ground level. However, many studies commence after the interaction is complete. Such post event investigation frequently seeks simple relationships and frequently yields disappointing results. There is no escaping the fact that the interaction is complex, and an understanding of the process and response requires the integration of multiple disciplines, such as soil science, physiology, ecology, mechanics, meteorology, and climatology. This chapter seeks to demonstrate that such integration, although difficult, is possible. The chapter also attempts to outline the processes and mechanisms of wind and tree interaction that can be used to understand the likelihood of wind disturbance.
Article
Context Tropical forest regeneration is increasingly prominent as agro-pastoral lands are abandoned. Regeneration is characterised as favouring ‘marginal’ lands; however, observations of its drivers are often coarse or simple, leaving doubt as to spatial dynamics and causation. Objectives We quantified the spatial dynamics of forest regeneration relative to marginality and remnant forest cover in a 3000 km2 pastoral region in northern tropical Australia. Methods Classification and regression trees related the extent and distribution of regeneration to soil agricultural potential, land-cover history, terrain slope, distance to primary forest, and primary forest fragment size, as defined by aerial photography. Results Secondary forest extent and distribution overwhelmingly reflect the proximity and size of primary forest fragments. Some 85 % of secondary forest area occurs <1 km of primary forest, and 86 % of secondary forest patches >50 ha are <400 m from primary forest and coincident with historic primary forest fragments. Where primary forest fragments are >8.5 ha, secondary forest area declines less rapidly with increasing distance from primary forest up to 1.5 km. Marginality inferred by soil potential and slope had no bearing on regeneration, except at the coarsest of spatial scales where regeneration is a proxy for primary forest cover. Conclusion Findings underline the need to conserve even modest rainforest patches as propagule reservoirs enabling regeneration. Marginality per se may have a limited role in regeneration. As most secondary forest was an extension of primary forest, its unique conservation value relative to that of primary forest may likewise merit reconsideration.
Article
Windthrow is all too often looked at as an exceptional, catastrophic phenomenon rather than a recurrent natural disturbance that falls within the spectrum of chronic and acute effects of wind on forests, and that drives ecosystem patterns and processes. This paper provides an integrative overview of the nature, contributing factors and impacts of wind-caused disturbance in forests, including its effects on trees, stands, landscapes and soils. Windthrow is examined through the integrating concepts of: the capacity of trees for acclimative growth, the limitation of acclimative growth under inter-tree competition, the recurrent nature of severe weather, how terrain and soil conditions affect local stand vulnerability and the effect of recurrent windthrow on stand dynamics and soils. Windthrow management should take place within a framework of general risk management, with evaluation of the likelihood, severity and potential impacts of wind damage considered with reference to the broad and specific aims of management. There is much to be gained from interdisciplinary communication about the nature and consequences of recurrent wind damage. There are opportunities for climatologists, engineers, ecologists, geomorphologists and others to develop integrative process models at the tree, stand and landscape scales that will improve our collective understanding, and inform management decision-making.
Article
The effect of a category 4 hurricane (Hurricane Hugo, 18 September 1989) on subtropical wet forest in Puerto Rico was examined at stand and species levels with respect to the frequency of tree damage, mortality, and resprouting. Roughly a quarter of the trees suffered some type of damage involving the main stem, and mortality due to the hurricane was 9%. Mortality among trees was primarily due to uprooting and broken stems. Many surviving trees sprouted new branches following the hurricane, indicating that this was an important component of stand recovery following hurricane damage. Patterns of species-specific damage and recovery formed two distinct groups. One group ("pioneers'), represented by three species, suffered a high frequency of stem breakage and mortality during the hurricane and had a low capacity to sprout new branches after being damaged. The remaining species ("nonpioneers') lost many branches during the hurricane, thereby suffering low to moderate stem damage and mortality, and sprouted many new branches following the hurricane. Stem breakage and related species-specific characteristics were significantly correlated with wood density and shade tolerance. Species exhibited few significant size-specific relationships with respect to hurricane damage, mortality, or resprouting, with the exception of branch damage, which often increased as a function of tree size. Nonpioneers dominate early in recovery because of the ability to survive a storm and sprout new branches following the storm, while the immediate impact of a hurricane on the abundance of pioneer species is strongly negative. -from Authors
Article
Oil palm expansion is a major threat to forest conservation in the tropics. Oil palm can also be a sustainable economic alternative if incentives for expansion outside forests are set in place. Consistent methods to monitor the time and location of oil palm expansion and the area converted from different land covers are essential for the success of such incentives. We developed methods to detect and quantify annual land cover changes associated with oil palm expansion in the Peruvian Amazon between 2001 and 2010 at two spatial scales and for two production modes. At the coarse scale, comprising the whole Peruvian Amazon, we used MODIS data to detect forest conversion to large-scale, industrial oil palm plantations based on metrics characterizing temporal changes in vegetation greenness associated with the conversion. At the fine scale, we used data from the satellite sensors Landsat TM/ETM + and ALOS-PALSAR to map and quantify the area from different land covers converted into large and small-scale oil palm plantations annually, in a focus area near the city of Pucallpa. Estimates were obtained from the elaboration and further combination of maps representing oil palm plantations by ages in 2010 and non-oil palm land covers in each year between 2001 and 2010. Validation data were obtained in the field and from geospatial information from previous studies. At the coarse scale, MODIS