Direct Regeneration Is Not the Only Response of Mediterranean Forests to Large Fires. Rodrigo, A., Retana, J., & Picó, F. X. 85(3):716–729.
Direct Regeneration Is Not the Only Response of Mediterranean Forests to Large Fires [link]Paper  doi  abstract   bibtex   
It is widely accepted that the postfire recovery in Mediterranean plant communities is carried out by direct regeneration, i.e., the fast recovery of a plant community with the same species pool that it had immediately prior to disturbance. However, there is evidence that not all plant species in the Mediterranean basin survive fire in all situations, suggesting that the direct regeneration process might not apply to all situations. We analyze whether the main combinations of forest tree species (up to 16) of the western Mediterranean basin exhibit a postfire direct regeneration process. Based on data from field surveys, we have developed a stochastic model to predict the medium-term forest dynamics. In general, Quercus species (resprouters) and the pines Pinus halepensis and P. pinaster (seeders that produce abundant seedlings) showed direct regeneration patterns. In contrast, forests of P. nigra, P. sylvestris, and P. pinea (seeders that produce few seedlings) changed to other situations after fire. This outcome was validated by additional data from plots with known fire history. These results did not support completely the direct regeneration model, since only half of the combinations of tree species analyzed exhibited a $>$50\,% probability of recovering the original prefire situation after fire. This partial failure of direct regeneration evidences the need for reconsidering restoration and conservation plans for Mediterranean ecosystems after fire. [Excerpt: Discussion] [::Postfire direct regeneration in Mediterranean forests] The results indicated that forest types with the highest resilience were those of resprouter species (Q. ilex, Q. cerrioides, and Q. suber) or with efficient seedling recruitment after fire (P. halepensis and P. pinaster). However, only 7 out of 16 forest types analyzed in this study had a .50\,% probability of recovering the prefire forest type after fire. Particularly, monospecific and mixed forests of P. nigra, P. sylvestris, and P. pinea exhibited low or nil stasis after fire (Tables 3 and 4) and had high probabilities of change toward states dominated by different Quercus species or grasslands. As a result, the postfire regeneration of many of these forest types cannot be interpreted as a direct regeneration process because the composition and structure of the new postfire forest type were completely different from those of the prefire forest type. The resilience of P. halepensis and P. pinaster was due to high initial seedling densities (Table 2). These species overcome the destruction caused by fires through very powerful postfire regeneration based on their ability to safeguard seeds in a long-term permanent seed bank on the serotinous cones of the canopy, which open after the passage of fires (Saracino et al. 1993, Daskalakou and Thanos 1996, Broncano 2000). However, there was a high variability in germination of these species among plots and, as a consequence, the high probability of changing to other forest types observed in mixed forests of these pines (Fig. 5). The almost complete absence of P. nigra and P. sylvestris in the postfire scenarios can be attributed to very low seedling density after fire. They do not have serotinous cones, and their seeds are dispersed in late winter to spring (Skordilis and Thanos 1997). As most seeds have already germinated in late spring (A. Rodrigo, personal observation), they are burned as seedlings during summer fires, which are the most common in the Mediterranean region. In the case of P. pinea, its low presence after fire is not due to low seedling density (Table 2), but to high seedling mortality in the first years after fire. The probability that these forests may change toward states dominated by Quercus species or grasslands depends on topographical and/or management features that favor or hinder the establishment of Quercus individuals under the overstory of pines (Espelta et al. 1995, Broncano et al. 1998). The high stasis of the three Quercus species is due to their resprouting ability, although they show different strategies. Q. ilex and, to a lesser extent, Q. suber, produce a large number of resprouts per individual after fire (Espelta et al. 1999), which causes strong intraindividual competition and high mortality through time. On the other hand, Q. cerrioides produces fewer resprouts per individual (Espelta et al. 2003), but shows lower mortality than the former species. Stem density of the three species 30 years after fire was quite similar to the prefire situation with both resprouting strategies [...] [] Overall, the results of this study suggest that the historical idea that direct regeneration of Mediterranean plant species to fire was a feedback mechanism protecting Mediterranean ecosystems from the continuous human impact during millennia should be regarded with care. Mediterranean forests may change considerably due to fire. By a similar reasoning, other recent works also show that posthurricane regeneration of tropical mangroves is more complex than direct regeneration models proposed for other tropical forests affected by hurricanes, and where regeneration is dominated by resprouting (Baldwin et al. 2001). Considering the high biodiversity of the Mediterranean Basin, which is one of the hotspots that should receive particular priority at a worldwide scale (Myers et al. 2000), the inability of postfire regeneration exhibited by some Mediterranean forests under the present fire regime might have important consequences of loss of biodiversity, not only of trees, but of many other plant and animal species affected by community-scale changes. This shows the need to reconsider management and restoration plans for Mediterranean species and ecosystems in response to fire, which should also include the real possibility that some species or communities do not recover from fire in the way that would be expected based on classical theory.
@article{rodrigoDirectRegenerationNot2004,
  title = {Direct Regeneration Is Not the Only Response of {{Mediterranean}} Forests to Large Fires},
  author = {Rodrigo, Anselm and Retana, Javier and Picó, F. Xavier},
  date = {2004-03},
  journaltitle = {Ecology},
  volume = {85},
  pages = {716--729},
  issn = {0012-9658},
  doi = {10.1890/02-0492},
  url = {http://mfkp.org/INRMM/article/13797221},
  abstract = {It is widely accepted that the postfire recovery in Mediterranean plant communities is carried out by direct regeneration, i.e., the fast recovery of a plant community with the same species pool that it had immediately prior to disturbance. However, there is evidence that not all plant species in the Mediterranean basin survive fire in all situations, suggesting that the direct regeneration process might not apply to all situations. We analyze whether the main combinations of forest tree species (up to 16) of the western Mediterranean basin exhibit a postfire direct regeneration process. Based on data from field surveys, we have developed a stochastic model to predict the medium-term forest dynamics. In general, Quercus species (resprouters) and the pines Pinus halepensis and P. pinaster (seeders that produce abundant seedlings) showed direct regeneration patterns. In contrast, forests of P. nigra, P. sylvestris, and P. pinea (seeders that produce few seedlings) changed to other situations after fire. This outcome was validated by additional data from plots with known fire history. These results did not support completely the direct regeneration model, since only half of the combinations of tree species analyzed exhibited a {$>$}50\,\% probability of recovering the original prefire situation after fire. This partial failure of direct regeneration evidences the need for reconsidering restoration and conservation plans for Mediterranean ecosystems after fire.

[Excerpt: Discussion] [::Postfire direct regeneration in Mediterranean forests] The results indicated that forest types with the highest resilience were those of resprouter species (Q. ilex, Q. cerrioides, and Q. suber) or with efficient seedling recruitment after fire (P. halepensis and P. pinaster). However, only 7 out of 16 forest types analyzed in this study had a .50\,\% probability of recovering the prefire forest type after fire. Particularly, monospecific and mixed forests of P. nigra, P. sylvestris, and P. pinea exhibited low or nil stasis after fire (Tables 3 and 4) and had high probabilities of change toward states dominated by different Quercus species or grasslands. As a result, the postfire regeneration of many of these forest types cannot be interpreted as a direct regeneration process because the composition and structure of the new postfire forest type were completely different from those of the prefire forest type. The resilience of P. halepensis and P. pinaster was due to high initial seedling densities (Table 2). These species overcome the destruction caused by fires through very powerful postfire regeneration based on their ability to safeguard seeds in a long-term permanent seed bank on the serotinous cones of the canopy, which open after the passage of fires (Saracino et al. 1993, Daskalakou and Thanos 1996, Broncano 2000). However, there was a high variability in germination of these species among plots and, as a consequence, the high probability of changing to other forest types observed in mixed forests of these pines (Fig. 5). The almost complete absence of P. nigra and P. sylvestris in the postfire scenarios can be attributed to very low seedling density after fire. They do not have serotinous cones, and their seeds are dispersed in late winter to spring (Skordilis and Thanos 1997). As most seeds have already germinated in late spring (A. Rodrigo, personal observation), they are burned as seedlings during summer fires, which are the most common in the Mediterranean region. In the case of P. pinea, its low presence after fire is not due to low seedling density (Table 2), but to high seedling mortality in the first years after fire. The probability that these forests may change toward states dominated by Quercus species or grasslands depends on topographical and/or management features that favor or hinder the establishment of Quercus individuals under the overstory of pines (Espelta et al. 1995, Broncano et al. 1998). The high stasis of the three Quercus species is due to their resprouting ability, although they show different strategies. Q. ilex and, to a lesser extent, Q. suber, produce a large number of resprouts per individual after fire (Espelta et al. 1999), which causes strong intraindividual competition and high mortality through time. On the other hand, Q. cerrioides produces fewer resprouts per individual (Espelta et al. 2003), but shows lower mortality than the former species. Stem density of the three species 30 years after fire was quite similar to the prefire situation with both resprouting strategies [...]

[] Overall, the results of this study suggest that the historical idea that direct regeneration of Mediterranean plant species to fire was a feedback mechanism protecting Mediterranean ecosystems from the continuous human impact during millennia should be regarded with care. Mediterranean forests may change considerably due to fire. By a similar reasoning, other recent works also show that posthurricane regeneration of tropical mangroves is more complex than direct regeneration models proposed for other tropical forests affected by hurricanes, and where regeneration is dominated by resprouting (Baldwin et al. 2001). Considering the high biodiversity of the Mediterranean Basin, which is one of the hotspots that should receive particular priority at a worldwide scale (Myers et al. 2000), the inability of postfire regeneration exhibited by some Mediterranean forests under the present fire regime might have important consequences of loss of biodiversity, not only of trees, but of many other plant and animal species affected by community-scale changes. This shows the need to reconsider management and restoration plans for Mediterranean species and ecosystems in response to fire, which should also include the real possibility that some species or communities do not recover from fire in the way that would be expected based on classical theory.},
  keywords = {*imported-from-citeulike-INRMM,~INRMM-MiD:c-13797221,~to-add-doi-URL,disturbances,forest-fires,forest-resources,mediterranean-region,pinus-halepensis,pinus-nigra,pinus-pinaster,pinus-pinea,pinus-sylvestris,postfire-recovery,quercus-cerrioides,quercus-ilex,quercus-suber,wildfires},
  number = {3}
}
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