Forest diversity plays a key role in determining the stand carbon stocks of Mexican forests

Arasa-Gisbert, R., Vayreda, J., Román-Cuesta, R.M., Villela, S.A., Mayorga, R., Retana, J. (2018) Forest diversity plays a key role in determining the stand carbon stocks of Mexican forests. Forest Ecology and Management. 415-416: 160-171.
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Doi: 10.1016/j.foreco.2018.02.023

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Pacific and Atlantic oceanic anomalies and their interaction with rainfall and fire in Bolivian biomes for the period 1992–2012

Roman-Cuesta R.M., Rejalaga-Noguera L., Pinto-Garcia C., Retana J. (2014) Pacific and Atlantic oceanic anomalies and their interaction with rainfall and fire in Bolivian biomes for the period 1992–2012. Climatic Change. : 0-0.
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Doi: 10.1007/s10584-014-1246-5

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Bolivia is located at the crossroad of the major climatic influences of Northern and Southern-South America, which turns this country into a natural laboratory to investigate the interactions between ocean-climate and fire variability. We chose two oceanic indices: MEI (multivariate ENSO Index) and AMO (Atlantic Multidecadal Oscillation) to select the three most representative years for four oceanic conditions: El Niño, La Niña, AMO, and standard years (understood as years with little ocean influences), for the period 1992–2012. We investigated how i) rainfall (dry vs wet seasons) and ii) fire responded in five Bolivian biomes (Tropical Moist Forests, Tropical Dry Forests, Tropical Grasslands, Tropical Montane, and Seasonally Flooded ecosystems) under these oceanic conditions. Bolivia showed a strong rainfall increase in El Niño years in both seasons (wet/dry), while AMO showed the strongest droughts in both seasons. La Niña showed a bipolar response with rainfall increases in the wet season and a very marked rainfall decrease in the dry season. Drought significantly increased fire numbers in AMO years, being the most significant fire condition and suggesting a larger fire influence of the Atlantic than the Pacific at the national level. Surprisingly, the amount of fire was very large under normal years (STD) and similar to fire levels under La Niña, suggesting generalized fire conditions in the country, except for El Niño years that bring rainfall excess and little fire. The most fire-affected biomes were the seasonally flooded and dry forests, followed by the grassland/savannah biome. Montane areas showed the least fire, but satellite fire omission is well known in the Andean region.

Llegeix més

Characterising fire spatial pattern interactions with climate and vegetation in Colombia

Armenteras-Pascual D., Retana-Alumbreros J., Molowny-Horas R., Roman-Cuesta R.M., Gonzalez-Alonso F., Morales-Rivas M. (2011) Characterising fire spatial pattern interactions with climate and vegetation in Colombia. Agricultural and Forest Meteorology. 151: 279-289.
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Doi: 10.1016/j.agrformet.2010.11.002

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Vegetation burning in tropical countries is a threat to the environment, causing not only local ecological, economic and social impacts, but also large-scale implications for global change. The burning is usually a result of interacting factors, such as climate, land-use and vegetation type. Satellite-derived monthly time series datasets of rainfall, burned area and active fire detections between December 2000 and 2009 were used in this study. A map of vegetation types was also used to determine these factors' spatial and temporal variability and interactions with the total amount of burned area and active fires detected in Colombia. Grasslands represented the vegetation most affected by fires every year in terms of burned area (standardised by their total area), followed by secondary vegetation, pasture and forests. Grasslands were also most affected by active fires, but followed closely by pasture, agricultural areas, secondary vegetation and forests. The results indicated strong climate and fire seasonality and marked regional difference, partly explained by climatic differences amongst regions and vegetation types, especially in the Orinoco and Caribbean regions. The incidence of fire in the Amazon and Andes was less influenced by climate in terms of burned area impacted, but the strength of the ENSO phenomenon affected the Orinoco and the Andes more in terms of burned area. Many of the active fires detected occurred in areas of transition between the submontane and lowland Andes and the Amazon, where extensive conversion to pasture is occurring. The possible high impact of small fires on the tropical rainforest present in this transition area and the Amazonian rainforest deserves more attention in Colombia due to its previous lack of attention to its contribution to global change. © 2010 Elsevier B.V.

Llegeix més

Factors influencing the formation of unburned forest islands within the perimeter of a large forest fire

Román-Cuesta R.M., Gracia M., Retana J. (2009) Factors influencing the formation of unburned forest islands within the perimeter of a large forest fire. Forest Ecology and Management. 258: 71-80.
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Doi: 10.1016/j.foreco.2009.03.041

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Large forest fires have recently increased in frequency and severity in many ecosystems. Due to the heterogeneity in fuels, weather and topography, these large fires tend to form unburned islands of vegetation. This study focuses on a large forest fire that occurred in north-eastern Spain in 1998, which left large areas of unburned vegetation within its perimeter. Based on a satellite post-fire severity map we searched for the relative influence of biotic and abiotic factors leading to unburned island formation. We divided the area of the fire into individual units we called "slopes" which were meant to separate the differential microclimatic effects of contrasted aspects. The number of unburned islands and their areas were related to 12 variables that influence their formation (i.e. land cover composition, aspect, steepness, forest structure, two landscape indices and weather variables). We hypothesized that unburned vegetation islands would concentrate on northern aspects, in less flammable forests (i.e. broadleaf species) and higher fragmentation to interrupt the advance of fire. While north and western aspects did have a higher presence of unburned vegetation islands, our study suggests greater presence of islands in slopes that are larger (i.e. more continuous areas with relatively homogeneous aspect), with greater proportions of forest cover, with higher wood volumes and with lower proportions of broadleaf species. Climate also played a role, with relative humidity and wind speed positively and negatively correlated to island formation, respectively. Unburned vegetation was more frequent on slopes with lower diversity of land covers and higher dominance of one land cover in the slope. Since slopes with only one land cover (i.e. forests) had more islands than slopes with multiple cover types, we infer that under severe meteorological conditions, fragmented forests can be more affected by wind and by water stress, thus burning more readily than forests that are protected from this edge phenomenon. These results would reinforce forest management strategies that avoid linear features (fire-lines and fire-breaks), to enhance fuel treatments that focus on areas and minimize fragmentation. © 2009 Elsevier B.V. All rights reserved.

Llegeix més

A quantitative comparison of methods for classifying burned areas with LISS-III imagery

Román-Cuesta R.M., Retana J., Gracia M., Rodríguez R. (2005) A quantitative comparison of methods for classifying burned areas with LISS-III imagery. International Journal of Remote Sensing. 26: 1979-2003.
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Doi: 10.1080/01431160512331299315

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Environmental agencies frequently require tools for quick assessments of areas affected by large fires. Remote sensing techniques have been reported as efficient tools to evaluate the effects of fire. However, there exist few quantitative comparisons about the performance of the diverse methods. This study quantitatively evaluated the accuracy of five different techniques, a field survey and four satellite-based techniques, in order to quickly classify a large forest fire that occurred in 1998 in Solsonès (north-east Spain) by means of an IRS LISS-III image. Three pure classes were determined: burned area, unburned vegetation, and bare soil; along with a non-pure class that we called mixed area. These selected techniques were included into a tree classifier to investigate their partial contribution to the final classification. The most accurate methods when focusing on pure classes were those directly related to the spectral characteristics of the pixel: Reflectance Data and Spectral Unmixing (82% of overall accuracy), versus the poorer performances of Vegetation Indices (70%), Textural measures (72%) and the field survey (68.6%). Since no image processing technique was applied to the Raw Reflectance Data, it can be considered the most cost-effective method, and the tree classifier reinforces its importance. The results of this study reveal that time consuming and expensive methods are not necessarily the most accurate, especially when potentially easily distinguishable classes are involved. © 2005 Taylor & Francis Group Ltd.

Llegeix més