scholarly journals Testing the Amazon savannization hypothesis: fire effects on invasion of a neotropical forest by native cerrado and exotic pasture grasses

2013 ◽  
Vol 368 (1619) ◽  
pp. 20120427 ◽  
Author(s):  
Divino V. Silvério ◽  
Paulo M. Brando ◽  
Jennifer K. Balch ◽  
Francis E. Putz ◽  
Daniel C. Nepstad ◽  
...  
Keyword(s):  
Canopy Cover ◽  
Fire Effects ◽  
Forest Edge ◽  
Fire Frequency ◽  
Fire Intensity ◽  
Stable States ◽  
Area Index ◽  
Tropical Regions ◽  
Pasture Grasses ◽  
Transitional Forest

Changes in climate and land use that interact synergistically to increase fire frequencies and intensities in tropical regions are predicted to drive forests to new grass-dominated stable states. To reveal the mechanisms for such a transition, we established 50 ha plots in a transitional forest in the southwestern Brazilian Amazon to different fire treatments (unburned, burned annually (B1 yr ) or at 3-year intervals (B3 yr )). Over an 8-year period since the commencement of these treatments, we documented: (i) the annual rate of pasture and native grass invasion in response to increasing fire frequency; (ii) the establishment of Brachiaria decumbens (an African C 4 grass) as a function of decreasing canopy cover and (iii) the effects of grass fine fuel on fire intensity. Grasses invaded approximately 200 m from the edge into the interiors of burned plots (B1 yr : 4.31 ha; B3 yr : 4.96 ha) but invaded less than 10 m into the unburned plot (0.33 ha). The probability of B. decumbens establishment increased with seed availability and decreased with leaf area index. Fine fuel loads along the forest edge were more than three times higher in grass-dominated areas, which resulted in especially intense fires. Our results indicate that synergies between fires and invasive C 4 grasses jeopardize the future of tropical forests.

scholarly journals Measuring Woody Encroachment along a Forest–Savanna Boundary in Central Africa

2009 ◽  
Vol 13 (8) ◽  
pp. 1-29 ◽  
Author(s):  
E. T. A. Mitchard ◽  
S. S. Saatchi ◽  
F. F. Gerard ◽  
S. L. Lewis ◽  
P. Meir
Keyword(s):  
Vegetation Change ◽  
Vegetation Index ◽  
Alternative Hypothesis ◽  
Canopy Cover ◽  
Fire Frequency ◽  
Weight Of Evidence ◽  
Competitive Balance ◽  
Area Index ◽  
Boundary Area ◽  
Canopy Area

Abstract Changes in net area of tropical forest are the sum of several processes: deforestation, regeneration of previously deforested areas, and the changing spatial location of the forest–savanna boundary. The authors conducted a long-term (1986–2006) quantification of vegetation change in a 5400 km2 forest–savanna boundary area in central Cameroon. A cross-calibrated normalized difference vegetation index (NDVI) change detection method was used to compare three high-resolution images from 1986, 2000, and 2006. The canopy dimensions and locations of over 1000 trees in the study area were measured, and a very strong relationship between canopy area index (CAI) and NDVI was found. Across 5400 km2 12.6% of the area showed significant positive change in canopy cover from 1986 to 2000 (0.9% yr−1) and 7.8% from 2000 to 2006 (1.29% yr−1), whereas <0.4% of the image showed a significant decrease in either period. The largest changes were in the lower canopy cover classes: the area with <0.2 m2 m−2 CAI decreased by 43% in 20 years. One cause may be a recent reduction in fire frequency, as documented by Along Track Scanning Radiometer-2/Advanced ATSR (ATSR-2/AATSR) data on fire frequency over the study area from 1996 to 2006. The authors suggest this is due to a reduction in human pressure caused by urbanization, as rainfall did not alter significantly over the study period. An alternative hypothesis is that increasing atmospheric CO2 concentrations are altering the competitive balance between grasses and trees. These data add to a growing weight of evidence that forest encroachment into savanna is an important process, occurring in forest–savanna boundary regions across tropical Africa.

scholarly journals Automated computation of leaf area index from fruit trees using improved image processing algorithms applied to canopy cover digital photograpies

2016 ◽  
Vol 123 ◽  
pp. 195-202 ◽  
Author(s):  
Marco Mora ◽  
Felipe Avila ◽  
Marcos Carrasco-Benavides ◽  
Gonzalo Maldonado ◽  
Jeissy Olguín-Cáceres ◽  
...  
Keyword(s):  
Image Processing ◽  
Leaf Area Index ◽  
Leaf Area ◽  
Canopy Cover ◽  
Fruit Trees ◽  
Area Index ◽  
Image Processing Algorithms ◽  
Processing Algorithms

scholarly journals Tropical Dry Forest Resilience to Fire Depends on Fire Frequency and Climate

2021 ◽  
Vol 4 ◽  
Author(s):  
Maximilian Hartung ◽  
Geovana Carreño-Rocabado ◽  
Marielos Peña-Claros ◽  
Masha T. van der Sande
Keyword(s):  
Tropical Forests ◽  
Tropical Dry Forest ◽  
Remote Sensing Data ◽  
Fire Frequency ◽  
Dry Forest ◽  
Fire Disturbance ◽  
Fire Intensity ◽  
Forest Resilience ◽  
Landsat Satellite ◽  
In Fire

Wildfires are becoming increasingly frequent and devastating in many tropical forests. Although seasonally dry tropical forests (SDTF) are among the most fire-threatened ecosystems, their long-term response to frequent wildfires remains largely unknown. This study is among the first to investigate the resilience in response to fire of the Chiquitano SDTF in Bolivia, a large ecoregion that has seen an unprecedented increase in fire intensity and frequency in recent years. We used remote sensing data to assess at a large regional and temporal scale (two decades) how fire frequency and environmental factors determine the resilience of the vegetation to fire disturbance. Resilience was measured as the resistance to fire damage and post-fire recovery. Both parameters were monitored for forested areas that burned once (F1), twice (F2), and three times (F3) between 2000 and 2010 and compared to unburned forests. Resistance and recovery were analyzed using time series of the Normalized Burn Ratio (NBR) index derived from Landsat satellite imagery, and climatic, topographic, and a human development-related variable used to evaluate their influence on resilience. The overall resilience was lowest in forests that burned twice and was higher in forests that burned three times, indicating a possible transition state in fire resilience, probably because forests become increasingly adapted during recurrent fires. Climatic variables, particularly rainfall, were most influential in determining resilience. Our results indicate that the Chiquitano dry forest is relatively resilient to recurring fires, has the capacity to recover and adapt, and that climatic differences are the main determinants of the spatial variation observed in resilience. Nevertheless, further research is needed to understand the effect of the higher frequency and intensity of fires expected in the future due to climate change and land use change, which may pose a greater threat to forest resilience.

scholarly journals Structural, physiognomic and aboveground biomass variation in savanna-forest transition zones on three continents. How different are co-occurring savanna and forest formations?

2014 ◽  
Vol 11 (3) ◽  
pp. 4591-4636 ◽  
Author(s):  
E. M. Veenendaal ◽  
M. Torello-Raventos ◽  
T. R. Feldpausch ◽  
T. F. Domingues ◽  
F. Gerard ◽  
...  
Keyword(s):  
South America ◽  
Woody Plant ◽  
Canopy Cover ◽  
Woody Vegetation ◽  
Canopy Closure ◽  
Forest Transition ◽  
Vegetation Types ◽  
Forest Species ◽  
Stable States ◽  
Transition Zones

Abstract. Through interpretations of remote sensing data and/or theoretical propositions, the idea that forest and savanna represent "alternative stable states" is gaining increasing acceptance. Filling an observational gap, we present detailed stratified floristic and structural analyses for forest and savanna stands mostly located within zones of transition (where both vegetation types occur in close proximity) in Africa, South America and Australia. Woody plant leaf area index variation was related in a similar way to tree canopy cover for both savanna and forest with substantial overlap between the two vegetation types. As total woody plant canopy cover increased, so did the contribution of middle and lower strata of woody vegetation to this total. Herbaceous layer cover also declined as woody cover increased. This pattern of understorey grasses and herbs being progressively replaced by shrubs as canopy closure occurs was found for both savanna and forests and on all continents. Thus, once subordinate woody canopy layers are taken into account, a less marked transition in woody plant cover across the savanna-forest species discontinuum is observed compared to that implied when trees of a basal diameter > 0.1m are considered in isolation. This is especially the case for shrub-dominated savannas and in taller savannas approaching canopy closure. An increased contribution of forest species to the total subordinate cover is also observed as savanna stand canopy closure occurs. Despite similarities in canopy cover characteristics, woody vegetation in Africa and Australia attained greater heights and stored a greater concentration of above ground biomass than in South America. Up to three times as much aboveground biomass is stored in forests compared to savannas under equivalent climatic conditions. Savanna/forest transition zones were also found to typically occur at higher precipitation regimes for South America than for Africa. Nevertheless, coexistence was found to be confined to a well-defined edaphic/climate envelope consistent across all three continents with both soil and climate playing a role as the key determinants of the relative location of forest and savanna. Taken together these observations do not lend support the notion of alternate stable states mediated through fire-feedbacks as the prime force shaping the distribution of the two dominant vegetation types of the tropical lands.

Fire and open ecosystems

2019 ◽  
pp. 97-120
Author(s):  
William J. Bond
Keyword(s):  
Vegetation Structure ◽  
Open Systems ◽  
Fire Regime ◽  
Alternative Stable States ◽  
Fire Regimes ◽  
Fire Effects ◽  
Emergent Property ◽  
Stable States ◽  
Mosaic Landscapes ◽  
Patterns And Processes

Can fire account for the widespread occurrence of open ecosystems? This chapter explores fire as a major consumer shaping vegetation in diverse regions worldwide. The concept of fire regime helps explain the diverse influences of fire on vegetation structure. Fire regimes select compatible growth forms from the species pool. These, in turn, create the fuel which in large part determines the fire regime. Experimental evidence can show whether fire is a major determinant of vegetation structure or merely an emergent property of ecosystems determined by climate and soils. Whether fires consume closed forests or stop at their margins will determine the dominant vegetation in mosaic landscapes. A mechanistic framework for analysing processes influencing fire effects on the boundary is introduced with examples. Pyrophilic open systems in mosaics with pyrophobic closed forests have been considered as examples of Alternative Stable States. Recent evidence for the patterns and processes expected by ASS theory are discussed.

scholarly journals Assessment of Maize Growth and Development with High- and Medium-Resolution Remote Sensing Products

Agronomy ◽  
2021 ◽  
Vol 11 (5) ◽  
pp. 940
Author(s):  
Rocío Ballesteros ◽  
Miguel A. Moreno ◽  
Fellype Barroso ◽  
Laura González-Gómez ◽  
José F. Ortega
Keyword(s):  
Remote Sensing ◽  
Precision Agriculture ◽  
Vegetation Index ◽  
Normalized Difference Vegetation Index ◽  
Landsat Imagery ◽  
Canopy Cover ◽  
Remote Sensing Data ◽  
Multilinear Regression ◽  
Area Index ◽  
Canopy Development

The availability of a great amount of remote sensing data for precision agriculture purposes has set the question of which resolution and indices, derived from satellites or unmanned aerial vehicles (UAVs), offer the most accurate results to characterize vegetation. This study focused on assessing, comparing, and discussing the performances and limitations of satellite and UAV-based imagery in terms of canopy development, i.e., the leaf area index (LAI), and yield, i.e., the dry aboveground biomass (DAGB), for maize. Three commercial maize fields were studied over four seasons to obtain the LAI and DAGB. The normalized difference vegetation index (NDVI) and visible atmospherically resistant index (VARI) from satellite platforms (Landsat 5TM, 7 ETM+, 8OLI, and Sentinel 2A MSI) and the VARI and green canopy cover (GCC) from UAV imagery were compared. The remote sensing predictors in addition to the growing degree days (GDD) were assessed to estimate the LAI and DAGB using multilinear regression models (MRMs). For LAI estimation, better adjustments were obtained when predictors from the UAV platform were considered. The DAGB estimation revealed similar adjustments for both platforms, although the Landsat imagery offered slightly better adjustments. The results obtained in this study demonstrate the advantage of remote sensing platforms as a useful tool to estimate essential agronomic features.

scholarly journals Trends and gaps of the scientific literature about the effects of fire on Brazilian Cerrado

2018 ◽  
Vol 18 (1) ◽  
Author(s):  
Filipe Viegas de Arruda ◽  
Diego Guimarães de Sousa ◽  
Fabrício Barreto Teresa ◽  
Vitor Hugo Mendonça do Prado ◽  
Hélida Ferreira da Cunha ◽  
...  
Keyword(s):  
International Institutions ◽  
Fire Management ◽  
Scientific Literature ◽  
Fire Suppression ◽  
Biotic Interactions ◽  
Federal District ◽  
Fire Effects ◽  
Fire Frequency ◽  
Brazilian Cerrado ◽  
Number Of Publications

Abstract Fire management is an important issue in the Brazilian Cerrado, since both anthropogenic high intensity fires and complete fire suppression can reduce the biodiversity in this biome. In this paper, we highlight the trends in scientific literature about fire effects in the Cerrado, aiming to detect possible gaps and to indicate directions of future scientific research. We searched for articles in the periodic database Web of Knowledge from 1991 to 2016, and observed an increase in the number of publications throughout the years. Most articles were associated with Brazilian institutions (58%), followed by those with collaboration between Brazilian and international institutions (33%), and those published by authors exclusively from international institutions (9%). Most articles addressed the effects of fire on biodiversity (77%), followed by articles about abiotic environment (19%), and then biotic interactions or interactions between organisms and environment (4%). The most studied taxonomic group was plants (75%), followed by mammals (8%) and insects (6%), with the remaining taxa comprising about 11% of publications. The Federal District was the federative unit with the greatest number of studies (31%). The majority of studies was conducted in areas with fewer fire events, whereas areas with major incidence of fires are poorly studied. Our data shows that studies on the effect of fires on the Brazilian Cerrado are geographically and taxonomically biased. This lack of knowledge limits the extrapolations about the effects of fire on this biome. Therefore, we emphasize the need for investment in research in areas with high fire frequency and also for an increase in knowledge about these effects on the biota, especially on the fauna. This action is fundamental to support the development of public policies for effective and directed fire management in the Cerrado.

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