Shrub clearing as Active Management strategy to control land abandonment in the Central Spanish Pyrenees: The effects and the limits

<p>The Mediterranean mountains have been subject to significant land abandonment processes during the second half of the 20th century.  The subsequent natural revegetation following abandonment in rural areas has been widely documented to have significant implications on the hydrological cycle and the vegetation dynamics. The Spanish Pyrenees, are one of the most affected areas by these land transformations which could threaten their importance for water supply and agricultural activities in the downstream lowland areas.</p><p>Management strategies of these abandoned areas have been debatable during the last decades between scientists, policy-makers and stakeholders. Active Management strategy through shrub clearing is one of the proposed practices that have shown advantages to deal with land abandonment in some regions of Spain. Nevertheless, little is known on the effects of this practice on the hydrological cycle and water resources in abandoned areas. In this study we used the Regional Eco-Hydrological Simulation System RHESSys to estimate shrub clearing effects on water resources in the Aisa valley in the Central Spanish Pyrenees, subject to land abandonment and natural revegetation processes during the past decades. Our results show an increase of annual streamflow and a decrease of annual evapotranspiration following shrub clearing. Nevertheless, the magnitude of these changes may decrease with the age of abandonment and climate change.</p>

Gestión activa frente a matorralización: buscando el equilibrio entre conservación y explotación en montaña

The mountains of Europe, especially in the Mediterranean, have undergone a significant process of revegetation since the mid-20th century with the spread of shrublands and forests in succession stages. This leads to negative effects (degradation of pasture, accumulation of biomass with the subsequent increase in fire risk, loss or trivialized of cultural landscapes, etc.) and other positive ones (greater rewilding of landscapes, recovery of forest life, more CO2 fixation, less soil erosion, etc.). Thus, two alternatives must be put forward: either allow the rewilding process to continue, or intervene in the region to reduce the negative effects of revegetation.In this paper, the literature forms the base for a discussion on the main interventions in the territory: extensive livestock grazing, combined with prescribed fires and shrub clearing. Prescribed fires are found to be insufficient to control the spread of shrublands, and in some cases promotes its regrowth (Echinospartum horridum), as well as degrading the pasture land and increasing soil erosion. On the other hand, clearing shrubland has positive effects: a reduction in wildfires, increased livestock numbers, and improved indicators of heterogeneity and fragmentation of the landscape.

Flammability descriptors of fine dead fuels resulting from two mechanical treatments in shrubland: a comparative laboratory study

Mechanical treatments are traditionally used to modify the fuel complex in shrubland, but information about their actual effectiveness in reducing the risk of wildfire initiation is scarce. The effects of two mechanical fuel treatments (shrub clearing with crushing and manual removal) on flammability in a shrubland community in north-western Spain were compared. Three months after treatment, laboratory tests using a point-ignition source were conducted on the fine dead fuels to analyse the effect of type of treatment and fuel moisture content (FMC) under two conditions: (1) flaming; or (2) glowing+wind ignition source. Fuel load effect within each treatment was also studied. Time-to-ignition, flaming duration, number of burnt sides of the sample and fuel consumption ratio were assessed. Logistic models were developed to assess ignition and sustained combustion probabilities. Type of treatment and FMC significantly affected flammability under both experimental conditions tested. Slow smouldering was observed in fuels subjected to shrub clearing and removal, whereas crushing fuels were rapidly burnt with flaming phase combustion. In general, shrub clearing and removal appeared to be more effective in reducing wildfire hazard in these shrubland communities.