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T. Curt & J. Pausas 2010. Are changes in fire regime threatening cork oak-shrubland mosaics
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- the fire severity for cork oak was modeled by two levels of fire response: low (i.e. low
mortality and high resprouting rate for cork oak) versus high (high mortality and low
resprouting rate for cork oak)
The persistence of all plants was assessed at the end of the simulations using the total
abundance of all cohorts, and the abundance of four cohorts representing the life stages (i.e.
seeds, immature individuals, mature trees, and mature high trees). In order to analyze the spatial
changes of the mosaics we also compared the spatial patterning of cork oak and of the whole
mosaic before and after the simulations. For this purpose we assessed the ‘total edge length’
(McGarigal et al., 2002), this statistics being expected to be a good indicator of species’ spatial
interactions (Pausas, 2006). We also tested the spatial autocorrelation for species richness at the
end of simulations by computing the Moran’s I index (Cliff and Ord 1981). The comparison of
the effect of different fires regimes on the mosaics was done using multiple analyses of variance
(MANOVA) with the variables describing species abundance, richness and patterning as
dependent variables and the variables of fire regime as independent variables.
3. Result
The multiple analyses of variance (Table 1) indicated that the overall abundance of cork (i.e. the
number of cells in which cork oak was present whatever the cohort) was quite stable among all
the simulations runs. It varied from 46.5 to 62% of the landscape (mean value 50.7% with a
coefficient of variation of 6.6%) while the area at the beginning of all simulations was 50% of
the landscape. The total abundance of cork oak after simulation did not relate to the type of
mosaic: large and small patches of cork oak woodlands resulted in similar cork oak abundance
under a similar fire regime. Likewise, the different cohorts of cork oak (i.e. from seeds to
mature high trees) were not significantly affected by the size of the woodland patches at the
beginning of simulation. Conversely, all the variables of the fire regime clearly impacted the
abundance of cork oak in the landscape (Table 1): its overall abundance decreased with low fire
recurrence and small fires. While the presence of cork oak in the landscape was quite stable
among simulations, the different cohorts behaved differently. Seeds were more abundant with a
mean fire interval of 30 to 40 years. Immature individuals were more abundant at a 20-years fire
interval and with large fires. Mature cork oak trees tended to increase with longer fire intervals
but not statistically significantly. High mature trees that form the overstory increased at low fire
recurrence, and with low severity and small fires. In all the simulations, lower disturbance by
fire (i.e. long fire-free intervals, small fires and low-severity fires) favored the development of
mature cork oak woodlands dominated by mature trees, with fewer immature individuals.
Forest Landscapes and Global Change-New Frontiers in Management, Conservation and Restoration. Proceedings of the IUFRO Landscape Ecology
Working Group International Conference, September 21-27, 2010, Bragança, Portugal. J.C. Azevedo, M. Feliciano, J. Castro & M.A. Pinto (eds.)
2010, Instituto Politécnico de Bragança, Bragança, Portugal.