National and regional determinants of tropical deforestation in Colombia

Armenteras D., Cabrera E., Rodríguez N., Retana J. (2013) National and regional determinants of tropical deforestation in Colombia. Regional Environmental Change. 13: 1181-1193.
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Doi: 10.1007/s10113-013-0433-7

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Global tropical deforestation continues to occur at high rates despite political attention. National-level forest baselines are being established all over the world to guide the implementation of several policy mechanisms. However, identifying the direct and indirect drivers of deforestation and understanding the complexity of their interlinkages are often difficult. We first analyzed deforestation between 1990 and 2005 at the national level and found an annual deforestation rate of 0.62 %. Next, we performed separate analyses for four natural regions in Colombia and found annual deforestation rates between 0.42 and 1.92 %. Using general linear models, we identified several direct causes and underlying factors influencing deforestation at the national level: rural population density, cattle, protected areas, and slope. Significant differences in deforestation rates and causes were found across regions. In the Caribbean region, drivers of loss are urban population, unsatisfied basic needs, slope, and precipitation and four land use variables (illicit crops, pastures, cattle, and fires). In the Orinoco region, crops are the main driver of forest loss, and in the Amazonian region, deforestation is primarily due to fires related to the colonization front. Policy mechanisms will have to take into account regional patterns to successfully balance development and forest preservation in Colombia. © 2013 Springer-Verlag Berlin Heidelberg.

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Forest fragmentation and edge influence on fire occurrence and intensity under different management types in Amazon forests

Armenteras D., González T.M., Retana J. (2013) Forest fragmentation and edge influence on fire occurrence and intensity under different management types in Amazon forests. Biological Conservation. 159: 73-79.
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Doi: 10.1016/j.biocon.2012.10.026

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The ecological characteristics of forest edges have been intensively studied in the Amazon region, but the occurrence and intensity of fires as large-scale edge effects are less well known, as is the role of different types of management in modifying this relationship. We used remote sensing techniques to examine the relationship between forest fragmentation, fire and management across NW Amazonia. Our study was based on forest data for 2005 and on active fire data from the MODerate-resolution imaging Spectro-radiometer (MODIS), with information on the occurrence and strength of fires based on fire radiative power (FRP) data. We analyzed the fragmentation and fire occurrence and intensity in a 50 × 50. km grid. We also calculated the distance at which edge-related fires occur in the forest interior and outside the forest edge. Forest fragmentation had a significant impact on fire occurrence and fire intensity, supporting the hypothesis that the more fragmented a forest is, the higher the degree of biomass combustion. These results are in agreement with the occurrence of an edge effect on both the occurrence and the intensity of fire. The different types of management in the region influence the occurrence and intensity of fire, whereas fire as a large-scale edge effect occurs independent of the management type. Finally, we suggest that a high connectivity in protected areas and indigenous reserves and also in outside areas should be encouraged to minimize edge-driven fire processes. © 2012 Elsevier Ltd.

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Response of ant functional composition to fire

Arnan X., Cerda X., Rodrigo A., Retana J. (2013) Response of ant functional composition to fire. Ecography. 36: 1182-1192.
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Doi: 10.1111/j.1600-0587.2013.00155.x

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Little is known about the impact of disturbances on functional diversity and the long-term provisioning of ecosystem services, especially in animals. In this work we analyze the effect of wildfire on the functional composition of Mediterranean ant communities. In particular, we asked whether a) fire changes functional composition (mean and dissimilarity of trait values) at the community level; and b) such fire-induced functional modification is driven by changes in the relative abundance-dominance of species or by a replacement of species with different traits. We sampled ant communities in burned and unburned plots along 22 sites in a western Mediterranean region, and we computed two complementary functional trait composition indices ('trait average' and 'trait dissimilarity') for 12 functional traits (related to resource exploitation, social structure and reproduction) and with two different datasets varying in the way species abundance is considered (i.e. abundance and occurrence data). Our results suggest a set of functional responses that seem to be related to direct mortality by fire as well as to indirect fire-induced modifications in environmental conditions relevant for ants. Trait average of colony size, worker size, worker polymorphism and the ratio between queen and worker size, as well as the trait dissimilarity of the proportion of behaviorally dominant species and of liquid food consumption, and overall functional diversity, were higher in burned than in unburned areas. Interestingly, different patterns arise when comparing results from abundance and occurrence data. While the response to fire in trait averages is quite similar, in the case of trait dissimilarity, the higher values in response to fire are much more marked when considering occurrence rather than abundance data. Our results suggest that changes in trait average are driven at the same time by replacement of species with different traits and by changes in the relative abundance-dominance of species, while fire promotes a higher diversity of functions that is primarily driven by rare species that are functionally unique. Overall, we observed major fire-induced changes in functional composition in Mediterranean ant communities that might have relevant consequences for ecosystem processes and services. © 2013 The Authors.

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Soil carbon stocks and their variability across the forests, shrublands and grasslands of peninsular Spain

Doblas-Miranda E., Rovira P., Brotons L., Martinez-Vilalta J., Retana J., Pla M., Vayreda J. (2013) Soil carbon stocks and their variability across the forests, shrublands and grasslands of peninsular Spain. Biogeosciences. 10: 8353-8361.
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Doi: 10.5194/bg-10-8353-2013

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Accurate estimates of C stocks and fluxes of soil organic carbon (SOC) are needed to assess the impact of climate and land use change on soil C uptake and soil C emissions to the atmosphere. Here, we present an assessment of SOC stocks in forests, shrublands and grasslands of peninsular Spain based on field measurements in more than 900 soil profiles. SOC to a depth of 1 m was modelled as a function of vegetation cover, mean annual temperature, total annual precipitation, elevation and the interaction between temperature and elevation, while latitude and longitude were used to model the correlation structure of the errors. The resulting statistical model was used to estimate SOC in the ∼8 million pixels of the Spanish Forest Map (29.3 × 106 ha). We present what we believe is the most reliable estimation of current SOC in forests, shrublands and grasslands of peninsular Spain thus far, based on the use of spatial modelling, the high number of profiles and the validity and refinement of the data layers employed. Mean concentration of SOC was 8.7 kg m-2, ranging from 2.3 kg m-2 in dry Mediterranean areas to 20.4 kg m -2 in wetter northern locations. This value corresponds to a total stock of 2.544 Tg SOC, which is four times the amount of C estimated to be stored in the biomass of Spanish forests. Climate and vegetation cover were the main variables influencing SOC, with important ecological implications for peninsular Spanish ecosystems in the face of global change. The fact that SOC was positively related to annual precipitation and negatively related to mean annual temperature suggests that future climate change predictions of increased temperature and reduced precipitation may strongly reduce the potential of Spanish soils as C sinks. However, this may be mediated by changes in vegetation cover (e.g. by favouring the development of forests associated to higher SOC values) and exacerbated by perturbations such as fire. The estimations presented here provide a baseline to estimate future changes in soil C stocks and to assess their vulnerability to key global change drivers, and should inform future actions aimed at the conservation and management of C stocks. © 2013 Author(s).

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Future variability of droughts in three Mediterranean catchments

Lopez-Bustins J.A., Pascual D., Pla E., Retana J. (2013) Future variability of droughts in three Mediterranean catchments. Natural Hazards. 69: 1405-1421.
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Doi: 10.1007/s11069-013-0754-3

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In the present study, we analyze the magnitude and frequency of long-term droughts throughout the present century in Catalonia in the north-eastern Iberian Peninsula (Spain). In fact, this western Mediterranean region has recently suffered one of the most extreme dry episodes (2006-2008) in the last decades. This calls for further study of future perspectives of drought variability at the local scale. We selected three medium-sized catchments on the Catalan littoral: Fluvià, Tordera and Siurana. We employed both instrumental and simulated temperature and rainfall data to calculate two multi-scalar drought indices: the Standardized Precipitation Index (SPI) and the Standardized Precipitation Evapotranspiration Index (SPEI). Instrumental data consisted of several weather stations for a recent period: 1984-2008. Future projections covering the 2001-2100 period were extracted from a dynamical downscaling procedure at a 15-km horizontal grid resolution, nesting the mesoscale model MM5 into the atmosphere-ocean coupled model ECHAM5/MPI-OM, performed by the Meteorological Service of Catalonia. We calculated 24-month SPI and SPEI values for the instrumental and simulated periods, and no changes were found in drought variability for the early twenty-first century. For the mid-century, high climatic variability was detected, as extremely dry and wet periods might alternate according to the SPI values. At the end of the present century, we generally detected, particularly in the dry catchment of southern Catalonia, Siurana, more severe and longer droughts than the last extreme drought (2006-2008). There is a need to implement appropriate and specific adaptation strategies for water management of each catchment over the next decades to reduce the risk of the forecasted drought conditions. © 2013 Springer Science+Business Media Dordrecht.

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Post-fire invasion and subsequent extinction of Conyza spp. in Mediterranean forests is mostly explained by local factors

Pino J., Arnan X., Rodrigo A., Retana J. (2013) Post-fire invasion and subsequent extinction of Conyza spp. in Mediterranean forests is mostly explained by local factors. Weed Research. 53: 470-478.
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Doi: 10.1111/wre.12040

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This work explored the invasion patterns of Conyza species in Mediterranean pine forests after fire and identified their main correlates through a temporal study approach. We hypothesised that wildfires might favour Conyza spp. invasion in these forests, but only transiently and depending on fire regime. We recorded Conyza spp. invasion and subsequent extinction in plots from species' occurrence and cover in vegetation surveys. We also explored the association of Conyza spp. presence and cover with a set of climatic, landscape and local (plot) factors using GLZ and GLM. We assessed changes in significant factors over time with a Wilcoxon test for paired samples. Evidence for Conyza spp. establishment was found in two-thirds of the study plots, with an invasion peak 2 years after fire. Local factors related to resource availability, including high fire severity, low soil stoniness and total vegetation cover and high herbaceous cover, were significantly correlated with Conyza occurrence in plots at the invasion peak. However, Conyza cover was always low (≤6%) and populations did not persist more than several years, thus becoming rarer as plant cover increased. Landscape and climatic factors showed no association with Conyza occurrence. In conclusion, wildfires favour transient invasion of European Mediterranean pine forests by Conyza spp. Invasion is mostly enhanced by local fire severity and constrained by subsequent vegetation recovery, while it is poorly explained by climate and landscape, either current or historical. © 2013 European Weed Research Society.

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Land use and land cover change in the Colombian Andes: Dynamics and future scenarios

Rodriguez Eraso N., Armenteras-Pascual D., Alumbreros J.R. (2013) Land use and land cover change in the Colombian Andes: Dynamics and future scenarios. Journal of Land Use Science. 8: 154-174.
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Doi: 10.1080/1747423X.2011.650228

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Land use and land cover changes (LUCC) are recognized as one of the most relevant drivers of biodiversity loss in ecosystems. Through the analysis of satellite images, this article quantifies the LUCC that occurred between 1985 and 2008 in the Colombian Andes. Four submodels of changes were analyzed: deforestation, crop intensification, conversion to pastures, and abandonment. We associated these changes with demographic, socioeconomic, and abiotic variables and to some attractors of landscape change, and finally we have considered three scenarios of change: reference, increase in pasture, and crop intensification. The dynamics of LUCC were dominated by systematic transitions between crops, pastures, and secondary vegetation. Of all the submodels, pasture conversion has an important contribution in terms of accuracy rate (84%), and the most relevant variables for explaining land cover changes in the region were elevation, soil type, and distance to roads, cities, and pastures. Our simulations suggest that the pasture conversion scenario would have the biggest impact in natural ecosystems and could cause the loss of 28-30% of the cover area by 2050. The results indicate some that these hotspots of change are currently still under a good conservation state with large extension of forests. © 2013 Copyright Taylor and Francis Group, LLC.

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Effectiveness of protected areas in the Colombian Andes: Deforestation, fire and land-use changes

Rodríguez N., Armenteras D., Retana J. (2013) Effectiveness of protected areas in the Colombian Andes: Deforestation, fire and land-use changes. Regional Environmental Change. 13: 423-435.
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Doi: 10.1007/s10113-012-0356-8

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Protected areas (PAs) are one of the most common conservation strategies to halt biodiversity loss. However, little is known about their current effectiveness and how they could behave under projected scenarios of change, especially in the mountain ecosystems of the Andean region. In this study, we assess the role of protected areas against deforestation and fire incidence in the Colombian Andes and how variables associated with biophysical and context drivers such as the size, year of creation and geographic location of the PAs affect their effectiveness. For the long-term, we have addressed the question of how effective these areas will be under three different scenarios of change for the period between 2020 and 2050, including a reference scenario and two scenarios of increasing pastureland and croplands. The results obtained indicated that both deforestation and fire levels were significantly lower inside protected areas than outside their borders. Concerning variables affecting deforestation and fire, only the type of ecosystem affected these processes in this study. The magnitude of forest loss was different between the analysed scenarios and depended on the location of the PAs. The PAs located in the Western Mountain Range presented the largest values of deforestation but the lowest number of fire incidences. This finding could be related to the presence of processes other than fire, such as illegal logging or selective extraction. The largest losses are expected in the PAs associated with the Eastern and Central mountain ranges, whereas the Western Mountain range will have the lowest loss. We conclude that although the Andes Mountains are a highly transformed and dynamic region, the current PAs have been effective barriers for deforestation and fire. However, the creation of new areas and the maintenance of the current PAs should take into account the interaction with the surrounding population, especially in those areas that are more sensitive to change. © 2012 Springer-Verlag Berlin Heidelberg.

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Patterns and drivers of regeneration of tree species in forests of peninsular Spain

Vayreda J., Gracia M., Martinez-Vilalta J., Retana J. (2013) Patterns and drivers of regeneration of tree species in forests of peninsular Spain. Journal of Biogeography. 40: 1252-1265.
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Doi: 10.1111/jbi.12105

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Aim: Our study aimed to identify and explore the main factors that influence tree recruitment of multiple species at a regional scale across peninsular Spain, an understanding of which is essential for predicting future forest species composition in the face of ongoing environmental change. The study focused on the dynamics of the key transition phase from saplings to adult trees. Location: The forests of peninsular Spain. Methods: We used the extensive network of plots sampled in two consecutive Spanish national forest inventories (> 30,000 plots) to identify the factors that determine regeneration patterns of the 10 most abundant forest species of Spain at relatively large temporal (c. 10 years) and spatial scales (across Spain): five coniferous species of Pinus (pines) and five broadleaved species of the genera Fagus and Quercus. We fitted separate generalized linear models for the pine species and the broadleaved species to assess the response of sapling abundance and ingrowth rate to the spatial variability of climate (temperature, water availability and recent warming), forest structure (tree density, understorey and overstorey canopy cover, and basal area change) and disturbances (previous forest logging, wildfires and grazing). Results: Mean sapling abundance was four times higher for broadleaved species than for pines, while mean annual ingrowth was twice as high. Sapling abundance and ingrowth rate were mainly determined by stand structure, both in pines and broadleaved trees. The direct effects of disturbances and climate were comparatively smaller, and there was no detectable effect of recent warming. Main conclusions: The higher values of ingrowth rate of broadleaved species can be explained by their ability to maintain a higher sapling bank due to their greater shade tolerance. This differential response of pines and broadleaved species to canopy closure suggests a probable increase in broadleaved species at the expense of pines. This transition could occur earlier in stands with faster canopy closure dynamics. Spatially explicit, mixed-species demographic models incorporating both the ingrowth and the tree mortality components are needed for predicting the composition of future forests. © 2013 Blackwell Publishing Ltd.

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Patterns of Forest Decline and Regeneration Across Scots Pine Populations

Vilà-Cabrera A., Martínez-Vilalta J., Galiano L., Retana J. (2013) Patterns of Forest Decline and Regeneration Across Scots Pine Populations. Ecosystems. 16: 323-335.
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Doi: 10.1007/s10021-012-9615-2

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To predict future changes in forest ecosystems, it is crucial to understand the complex processes involved in decline of tree species populations and to evaluate the implications for potential vegetation shifts. Here, we study patterns of decline (canopy defoliation and mortality of adults) of four Scots pine populations at the southern edge of its distribution and characterized by different combinations of climate dryness and intensity of past management. General linear and structural equation modeling were used to assess how biotic, abiotic, and management components interacted to explain the spatial variability of Scots pine decline across and within populations. Regeneration patterns of Scots pine and co-occurring oak species were analyzed to assess potential vegetation shifts. Decline trends were related to climatic dryness at the regional scale, but, ultimately, within-population forest structure, local site conditions, and past human legacies could be the main underlying drivers of Scots pine decline. Overall, Scots pine regeneration was negatively related to decline both within and between populations, whereas oak species responded to decline idiosyncratically across populations. Taken together, our results suggest that (1) patterns of decline are the result of processes acting at the plot level that modulate forest responses to local environmental stress and (2) decline of adult Scots pine trees seems not to be compensated by self-recruitment so that the future dynamics of these forest ecosystems are uncertain. © 2012 Springer Science+Business Media New York.

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