Satellite Evidence of Decreasing Resilience in Mediterranean Plant Communities after Recurrent Wildfires. Díaz-Delgado, R.; Lloret, F.; Pons, X.; and Terradas, J. 83(8):2293–2303.
Satellite Evidence of Decreasing Resilience in Mediterranean Plant Communities after Recurrent Wildfires [link]Paper  doi  abstract   bibtex   
Vegetation recovery from fire has been widely studied at the stand level in many types of terrestrial ecosystems, but factors controlling regeneration at the landscape scale are less well known. Over large areas, fire history, climate, topography, and dominant type of vegetation may affect postfire response. Increased fire frequency, as is occurring in some mediterranean-type ecosystems, may reduce ecosystem resilience, i.e., the ability to recover the pre-disturbance state. We used the Normalized Difference Vegetation Index (NDVI) from Landsat imagery to monitor vegetation recovery after successive fires in a 32$\mkern1mu$100-km2 area of Catalonia (northeastern Spain) between 1975 and 1993. In areas burned twice, NDVI patterns indicated that regrowth after 70 mo was lower after the second fire than after the first. This trend was observed several years after burning, but not immediately following fire. Green biomass after the second fire significantly increased with longer intervals of time between fires. There was also a positive correlation between postfire NDVI and mean rainfall, whereas a negative correlation was found between NDVI and solar radiation. Forests dominated by resprouting Quercus spp. were more resilient to fire, but they showed a larger decrease in resilience after the second fire than did forests dominated by Pinus spp. that regenerate from seed. We conclude that the use of time series satellite images may help to gain further insights in postfire vegetation dynamics over large regions and long time periods. [Excerpt] [...] Although fires may be considered as a natural disturbance, shifts in current fire regime in relation to historical records have been observed in some regions. Reduced fire recurrence has been shown in circumboreal forests (Flannigan et al. 1998), coniferous forests of western North America (Heyerdahl et al. 2001), and temperate forests of North America and Mexico (Covington and Moore 1994, Fule´ and Covington 1999). On the other hand, higher fire recurrence, higher fire intensity, or larger burned area has been reported for tropical forests (Goldammer 1999) and some mediterranean shrublands and forests (Moreno et al. 1998, Keeley et al. 1999). Global warming may increase fire occurrence in these ecosystems (Rambal and Hoff 1998, Goldammer 1999). Therefore, a great concern has arisen about the effects of changes in disturbance regime on ecosystems, and particularly on the ecosystem-level consequences of increased fire frequency (Lavorel et al. 1998, Cochrane et al. 1999, Keeley et al. 1999). We investigated the relationship between fire recurrence and postfire revegetation in a coastal area of the Mediterranean Basin. We considered this revegetation in terms of green biomass resilience, that is, the level of postfire green biomass in relation to pre-fire levels. We also examined the role of several environmental parameters, such as climate, topography, and dominant overstory species, in determining ecosystem resilience. [...] [Results] [...] Differences were [...] found in the recovery after the second fire between the two main types of forests: those dominated by resprouting oaks (Quercus ilex and Q. suber) and those dominated by non-resprouting pines (Pinus halepensis, P. sylvestris, and P. nigra). Oak forests showed higher resilience values than former pine forests after the second fire (one-way ANOVA, F1,23 = 8.8, P = 0.006, n = 25; measurements at 38 mo after fire). However, when comparing resilience after the first and second fires, we observed that the ability to regenerate after the second fire decreased less in pine forests than in oak forests (measurements at 38 mo after the fire: pines, two-tailed paired t test, t = 1.05, P = 0.36, n = 4 fires; oaks, two-tailed paired t test, t = 2.65, P = 0.037, n = 7 fires; Fig. 6). [...] [Discussion] [...] Overall, resilience is higher in holm-oak forests, but pine forests show lower resilience decrease after the second fire. Holm-oak forests are, in general, a dense community, dominated by woody resprouters that regenerate quickly after fire. The rate of recovery might decrease after the second fire because of lower resprouting success and because of the absence of a fast-growing herbaceous layer in these communities. In contrast, pine forests may show lower resilience after six years because tree canopy development from seedlings initially is slower than from re-sprouts. However, open pine forests in the region have greater understory green biomass than do evergreen oak forests. [\n][...] Site characteristics also contribute to explaining postfire regeneration (López-Soria and Castell 1992, Christensen 1993). The positive relationship found between the resilience values after the first and second fires suggests that the same factors determining postfire recovery (site productivity and biological potential to regenerate, i.e., life-history characteristics of the species present in the community) are operating at both times. This result also indicates that good regeneration after the first fire is not at the expense of the regenerative potential after the second fire. Rainfall, in particular, plays an important role in the ecosystem response to fire, as shown by the positive correlation between resilience and mean rainfall. In mediterranean ecosystems, seedling establishment has a seasonal pattern because it requires moist conditions (Specht et al. 1983, Keeley 1986). However, short-term effects of rainfall in the year immediately following the fire event have not been correlated to resilience, probably because resprouting is highly determined by resources previously stored in underground organs (Canadell and López-Soria 1998). [...]
@article{diaz-delgadoSatelliteEvidenceDecreasing2002,
  title = {Satellite Evidence of Decreasing Resilience in {{Mediterranean}} Plant Communities after Recurrent Wildfires},
  author = {Díaz-Delgado, Ricardo and Lloret, Francisco and Pons, Xavier and Terradas, Jaume},
  date = {2002-08},
  journaltitle = {Ecology},
  volume = {83},
  pages = {2293--2303},
  issn = {0012-9658},
  doi = {10.1890/0012-9658(2002)083[2293:SEODRI]2.0.CO;2},
  url = {https://doi.org/10.1890/0012-9658(2002)083[2293:SEODRI]2.0.CO;2},
  abstract = {Vegetation recovery from fire has been widely studied at the stand level in many types of terrestrial ecosystems, but factors controlling regeneration at the landscape scale are less well known. Over large areas, fire history, climate, topography, and dominant type of vegetation may affect postfire response. Increased fire frequency, as is occurring in some mediterranean-type ecosystems, may reduce ecosystem resilience, i.e., the ability to recover the pre-disturbance state. We used the Normalized Difference Vegetation Index (NDVI) from Landsat imagery to monitor vegetation recovery after successive fires in a 32{$\mkern1mu$}100-km2 area of Catalonia (northeastern Spain) between 1975 and 1993. In areas burned twice, NDVI patterns indicated that regrowth after 70 mo was lower after the second fire than after the first. This trend was observed several years after burning, but not immediately following fire. Green biomass after the second fire significantly increased with longer intervals of time between fires. There was also a positive correlation between postfire NDVI and mean rainfall, whereas a negative correlation was found between NDVI and solar radiation. Forests dominated by resprouting Quercus spp. were more resilient to fire, but they showed a larger decrease in resilience after the second fire than did forests dominated by Pinus spp. that regenerate from seed. We conclude that the use of time series satellite images may help to gain further insights in postfire vegetation dynamics over large regions and long time periods.

[Excerpt] [...] Although fires may be considered as a natural disturbance, shifts in current fire regime in relation to historical records have been observed in some regions. Reduced fire recurrence has been shown in circumboreal forests (Flannigan et al. 1998), coniferous forests of western North America (Heyerdahl et al. 2001), and temperate forests of North America and Mexico (Covington and Moore 1994, Fule´ and Covington 1999). On the other hand, higher fire recurrence, higher fire intensity, or larger burned area has been reported for tropical forests (Goldammer 1999) and some mediterranean shrublands and forests (Moreno et al. 1998, Keeley et al. 1999). Global warming may increase fire occurrence in these ecosystems (Rambal and Hoff 1998, Goldammer 1999). Therefore, a great concern has arisen about the effects of changes in disturbance regime on ecosystems, and particularly on the ecosystem-level consequences of increased fire frequency (Lavorel et al. 1998, Cochrane et al. 1999, Keeley et al. 1999). We investigated the relationship between fire recurrence and postfire revegetation in a coastal area of the Mediterranean Basin. We considered this revegetation in terms of green biomass resilience, that is, the level of postfire green biomass in relation to pre-fire levels. We also examined the role of several environmental parameters, such as climate, topography, and dominant overstory species, in determining ecosystem resilience. [...]

[Results] [...] Differences were [...] found in the recovery after the second fire between the two main types of forests: those dominated by resprouting oaks (Quercus ilex and Q. suber) and those dominated by non-resprouting pines (Pinus halepensis, P. sylvestris, and P. nigra). Oak forests showed higher resilience values than former pine forests after the second fire (one-way ANOVA, F1,23 = 8.8, P = 0.006, n = 25; measurements at 38 mo after fire). However, when comparing resilience after the first and second fires, we observed that the ability to regenerate after the second fire decreased less in pine forests than in oak forests (measurements at 38 mo after the fire: pines, two-tailed paired t test, t = 1.05, P = 0.36, n = 4 fires; oaks, two-tailed paired t test, t = 2.65, P = 0.037, n = 7 fires; Fig. 6). [...]

[Discussion] [...] Overall, resilience is higher in holm-oak forests, but pine forests show lower resilience decrease after the second fire. Holm-oak forests are, in general, a dense community, dominated by woody resprouters that regenerate quickly after fire. The rate of recovery might decrease after the second fire because of lower resprouting success and because of the absence of a fast-growing herbaceous layer in these communities. In contrast, pine forests may show lower resilience after six years because tree canopy development from seedlings initially is slower than from re-sprouts. However, open pine forests in the region have greater understory green biomass than do evergreen oak forests. 

[\textbackslash n][...] Site characteristics also contribute to explaining postfire regeneration (López-Soria and Castell 1992, Christensen 1993). The positive relationship found between the resilience values after the first and second fires suggests that the same factors determining postfire recovery (site productivity and biological potential to regenerate, i.e., life-history characteristics of the species present in the community) are operating at both times. This result also indicates that good regeneration after the first fire is not at the expense of the regenerative potential after the second fire. Rainfall, in particular, plays an important role in the ecosystem response to fire, as shown by the positive correlation between resilience and mean rainfall. In mediterranean ecosystems, seedling establishment has a seasonal pattern because it requires moist conditions (Specht et al. 1983, Keeley 1986). However, short-term effects of rainfall in the year immediately following the fire event have not been correlated to resilience, probably because resprouting is highly determined by resources previously stored in underground organs (Canadell and López-Soria 1998). [...]},
  keywords = {*imported-from-citeulike-INRMM,~INRMM-MiD:c-12106420,~to-add-doi-URL,ecosystem-resilience,forest-fires,forest-regeneration,forest-resources,mediterranean-region,pinus-spp,quercus-spp,spain,wildfires},
  number = {8}
}
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