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Consequences Of Forest Fires On The Corsican Nuthatches

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ENDEMYS

The study examined the effects of two large wildfires on the population size of the endangered Corsican nuthatch bird in Corsica. Field studies before and after the fires in 2000 and 2003 showed sharp declines in the number of nuthatch territories of 37.5-50% immediately after the fires. Habitat characteristics like the minimum length of burned pine crown predicted nuthatch absence, with presence most likely when at least one pine had less than 2.5m of crown burned. The declines were likely due to simultaneous loss of shelter, nest sites and food from the fires. The habitat remained unfavorable for several years after the fires as the forest regenerated.

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Pasquale MONEGLIA, EPHE, CEFE (UMR 5175)
Consequences Of Forest Fires On The Corsican Nuthatches
Because of its forest habitat, its restricted range, and its small population size, the Corsican nuthatch is one of the rare Mediterranean birds most threatened by fire. Large fires may have different consequences for a bird population depending on 1. the characteristics of the fire (e.g., size, severity, patchiness, time since fire) 2. changes in vegetation structure 3. increase or depletion of food 4. nest-site availability 5. increase in predation
The present study aims : • to measure the effect of two large wildfires on nuthatch abundance, • to identify the habitat characteristics and level of fire severity that best explained the local presence or absence of the nuthatches after the fire, so as to recommend appropriate conservation strategies and forestry practices after fire.
Consequences Of Forest Fires On The Corsican Nuthatches
 Study area: • The forest of Tartagine-Melaja : In August 2003, a wildfire burned 1 836 ha of forest and maquis. The study area (680 ha) included the whole burned forest except areas that had been logged for timber before the fire. • The forest of Corte-Restonica : In August 2000, a wildfire burned 2 371 ha ha of forest and maquis. The study area (224 ha) included most of the habitat of nuthatches affected by fire.
ï‚ž In the forest of Tartagine-Melaja, in May and June 1992 (i.e., before the fire), the nuthatch territories were exhaustively mapped on a ca. 300 ha. After the fire, i.e. during springs 2004 and 2005, we mapped the nuthatch territories on the whole study area ï‚ž In the forest of Corte-Restonica, the nuthatch territories were exhaustively mapped before the fire (1992) and after the fire (i.e. during springs 2004 and 2005) on whole area study
 Study area : • The forest of Tartagine-Melaja  Plot sampling: • After mapping of nuthatch territories, we recorded 39 plots within nuthatches after fire (territories occupied in 2004, or in 2005, or both) • In addition, 22 plots without nuthatches after fire were selected randomly using a GIS (Arcview software).
 Habitat measurements:  On the 39 occupied plots and the 22 empty plots, we defined 3 circular sub-plots, each of them with a radius of ca. 11.40 m. The centres of the three subplots were 50 m away from each other on a straight and generally horizontal line. The centre of the median sub-plot corresponded, depending on the case, (i) to a nest, (ii) to a contact with a territorial bird, if the nest was not found, or (iii) to the centre of a randomly selected square without nuthatch.  Within each sub-plot, we measured five variables on all Corsican pines whose diameter at breast height (DBH) was greater than 10 cm: (i) DBH, (ii) height of the tree, (iii) height of blackened trunk, (iv) height of the lowest branch of the crown, (v) height of the lowest branch with green foliage  In the statistical analysis, the three subplots were lumped together into one plot, corresponding to a surface of ca. 1 225 m².
From the field measurements we calculated several secondary variables, and selected among them seven variables for the modelling : 1. the number of trees on the plot (NT), 2. the diameter of the largest pine on the plot (Dmax), 3. the height of the smallest pine (Hmin), 4. the length of the longest pine crown (before fire) on the plot (LCmax), 5. the number of dead pines (NDT), 6. the minimum height of blackened trunk (HBTmin), 7. the smallest length of pine crown burned (SLCB), i.e., the length of the burned crown measured on the pine which has been the least affected by the fire on the plot (measured from the lowest branch of the crown upwards to the first green branch).
ï‚ž Data analysis: Based on these seven variables, we modelled the presence-absence of the nuthatch using multiple logistic regressions. Starting from full models, each of them including a set of variables and all their interactions, the selection was performed through a backward procedure using R software. We first explored two categories of variables separately (step 1): (i) four dendrometric variables (NT, Dmax, Hmin, LCmax), (ii) three fire severity variables (NDT, HBTmin, SLCB). After having identified the best model in each category from its p value (using AIC instead of the probabilities lead to the same results), we merged all the selected explanatory variables and continued the selection process until the final model, where all the variables were significant (step 2). Significance is given at the 5% level.
Consequences Of Forest Fires On The Corsican Nuthatches
r r %U %U %U %U r %U %U %U %U %U %U %U %U %U %U %U N EW S 0 300 600 900 1200 m. Zone prospectée Années d'occupation des territoires %U 1992-2004-2005-2007 %U 1992-2004-2005 %U 1992-2004 %U 1992-2007 %U 1992 r 2004-2005 r 2004-2007 r 2004 %U %U %U %U %U %U %U %U %U %U %U %U %U r r %U %U %U %U %U %U %U %U %U %U %U r r r r r r rr r rrrr r r r r r r r r r r r r rr N EW S 0 300 600 900 1200 m. Zone prospectée uniquement en 2004 et 2005 Zone prospectée en 1992, 2004 et 2005 Années d'occupation des territoires %U 1992-2004-2005 %U 1992-2004 %U 1992-2005 %U 1992 r 2004-2005 r 2004 r 2005
Année Nombre de territoires Corte-Restonica Tartagine-Melaja (ZONE-B) 1992 15 24 2000 incendie - 2003 - incendie 2004 11 15 2005 9 13 2007 5 - in the two Corsican pine forests where nuthatches have been monitored before and after fire, the number of territorial birds has sharply declined in the first spring after fire: by - 37.5 % on Tartagine-Melaja and - 50% on Restonica. The decrease in abundance observed in the study area appears to result from the fire The habitat seems to remain unfavourable for nuthatches for several years after fire. We did not observe any trend toward a restoration of nuthatch numbers in the first two years after fire in Tartagine-Melaja forest, nor even in the first seven years after fire in Restonica forest . The decline for several years after the fire may result to (i) the mortality of individuals remained on their territory during the first years following the disturbance (site tenacity), and (ii) non- recruitment of new nuthatches due to unfavorable habitat
the modelling procedure selected the smallest length of crown burned as the only variable significantly (at the 5% level) explaining nuthatch presence. The regression coefficients show that the smaller the length of crown burned, the more likely was the presence of the nuthatch after the fire (intercept = 0.925, slope = -0.388). The probability of occurrence of the bird was greater than 0.5 when the smallest length of crown burned on a pine of the plot was less than 2.5 m (cf. Fig.). In other words, the nuthatch tends to be absent in severe burns when all the pines have more than 2.5 m of burned crown. 0 0,1 0,2 0,3 0,4 0,5 0,6 0,7 0,8 0,9 1 0 1 2 3 4 5 6 7 ProbabilityofoccurrenceoftheNuthatch Smallest length of crown burned (m) Probability of occurrence of the Corsican Nuthatch as a function of the smallest length of Corsican pine crown burned (with 90% confidence intervals)
The fire can have different effects, not exclusive and depending generally on its severity, that could explain the decline of nuthatches in burned areas: The simultaneous decrease of shelters, of nest sites, and of food resources probably forces nuthatches to leave the burned stands. Emigration resulting from a shortage of seeds has been described in the related Red-breasted nuthatch Sitta canadensis, especially after fire. Nuthatches breed in dead and soft wood where the pairs excavate holes. The fire usually burns most of the available snags, so that it may be difficult for birds to find nest-sites in the short term before new snags are available (several years may be required for the dead wood of the pines killed by fire to become soft enough to permit the excavation of new nest sites by the nuthatch). The seeds of Corsican pine are the main food resource for nuthatches. Even if the opening of cones by fire makes numerous unburned seeds available during the days immediately following the fire, the production of new seeds is much reduced in burned areas. Fire may cause an increase in the abundance of predators. Woodpeckers in general and Great Spotted Woodpeckers Dendrocopos major (a nest predator of nuthatch), in particular, usually increase in abundance after fire, increasing the risk of predation for nuthatch. The disappearance of a fraction of the canopy, increasing the distances between crowns, is prejudicial to forest birds that need cover as protection against predators.
The habitat seems to remain unfavourable for nuthatches for several years after fire. We did not observe any trend toward a restoration of nuthatch numbers in the first two years after fire in Tartagine-Melaja forest, nor even in the first seven years after fire in Restonica forest. There are several long-lasting effects of fire: i. where there is woodland regrowth after fire, even when the regeneration of the pines is successful the habitat, when completely burned, remains unfavourable for 60-120 years, i.e., the estimated time for stand maturity ii. the natural regeneration of Pinus nigra after fire is low iii. seed production decreases for several years after fire iv. Corsican pines suffer delayed mortality as other Mediterranean pines
ï‚ž As with other passerines, the nuthatch seems to show a high site- tenacity after a moderate disturbance. Owing to the irregular topography of the Corsican mountain forests, the severity of the fire varies from place to place, resulting in a mosaic of patches burned to different degrees. The nuthatch is absent only in the most burned areas. This mosaic pattern tempers the impact of large wildfires on the population. ï‚ž Our results show that the nuthatch is likely to be absent when all the pines have more than 2.5 m of burned crown on the plot, and present when at least one pine has less than 2.5 m of crown burned (i.e., the threshold at which the presence and absence of the nuthatch are equally probable). Thus a burned stand should not be clear-cut in the latter case. The use of such criteria could help the selection of plots to be cut where salvage logging is necessary.

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Consequences Of Forest Fires On The Corsican Nuthatches

  • 3. Because of its forest habitat, its restricted range, and its small population size, the Corsican nuthatch is one of the rare Mediterranean birds most threatened by fire. Large fires may have different consequences for a bird population depending on 1. the characteristics of the fire (e.g., size, severity, patchiness, time since fire) 2. changes in vegetation structure 3. increase or depletion of food 4. nest-site availability 5. increase in predation
  • 4. The present study aims : • to measure the effect of two large wildfires on nuthatch abundance, • to identify the habitat characteristics and level of fire severity that best explained the local presence or absence of the nuthatches after the fire, so as to recommend appropriate conservation strategies and forestry practices after fire.
  • 6. ï‚ž Study area: • The forest of Tartagine-Melaja : In August 2003, a wildfire burned 1 836 ha of forest and maquis. The study area (680 ha) included the whole burned forest except areas that had been logged for timber before the fire. • The forest of Corte-Restonica : In August 2000, a wildfire burned 2 371 ha ha of forest and maquis. The study area (224 ha) included most of the habitat of nuthatches affected by fire.
  • 7. ï‚ž In the forest of Tartagine-Melaja, in May and June 1992 (i.e., before the fire), the nuthatch territories were exhaustively mapped on a ca. 300 ha. After the fire, i.e. during springs 2004 and 2005, we mapped the nuthatch territories on the whole study area ï‚ž In the forest of Corte-Restonica, the nuthatch territories were exhaustively mapped before the fire (1992) and after the fire (i.e. during springs 2004 and 2005) on whole area study
  • 8. ï‚ž Study area : • The forest of Tartagine-Melaja ï‚ž Plot sampling: • After mapping of nuthatch territories, we recorded 39 plots within nuthatches after fire (territories occupied in 2004, or in 2005, or both) • In addition, 22 plots without nuthatches after fire were selected randomly using a GIS (Arcview software).
  • 9. ï‚ž Habitat measurements:  On the 39 occupied plots and the 22 empty plots, we defined 3 circular sub-plots, each of them with a radius of ca. 11.40 m. The centres of the three subplots were 50 m away from each other on a straight and generally horizontal line. The centre of the median sub-plot corresponded, depending on the case, (i) to a nest, (ii) to a contact with a territorial bird, if the nest was not found, or (iii) to the centre of a randomly selected square without nuthatch.  Within each sub-plot, we measured five variables on all Corsican pines whose diameter at breast height (DBH) was greater than 10 cm: (i) DBH, (ii) height of the tree, (iii) height of blackened trunk, (iv) height of the lowest branch of the crown, (v) height of the lowest branch with green foliage  In the statistical analysis, the three subplots were lumped together into one plot, corresponding to a surface of ca. 1 225 m².
  • 10. From the field measurements we calculated several secondary variables, and selected among them seven variables for the modelling : 1. the number of trees on the plot (NT), 2. the diameter of the largest pine on the plot (Dmax), 3. the height of the smallest pine (Hmin), 4. the length of the longest pine crown (before fire) on the plot (LCmax), 5. the number of dead pines (NDT), 6. the minimum height of blackened trunk (HBTmin), 7. the smallest length of pine crown burned (SLCB), i.e., the length of the burned crown measured on the pine which has been the least affected by the fire on the plot (measured from the lowest branch of the crown upwards to the first green branch).
  • 11. ï‚ž Data analysis: Based on these seven variables, we modelled the presence-absence of the nuthatch using multiple logistic regressions. Starting from full models, each of them including a set of variables and all their interactions, the selection was performed through a backward procedure using R software. We first explored two categories of variables separately (step 1): (i) four dendrometric variables (NT, Dmax, Hmin, LCmax), (ii) three fire severity variables (NDT, HBTmin, SLCB). After having identified the best model in each category from its p value (using AIC instead of the probabilities lead to the same results), we merged all the selected explanatory variables and continued the selection process until the final model, where all the variables were significant (step 2). Significance is given at the 5% level.
  • 13. r r %U %U %U %U r %U %U %U %U %U %U %U %U %U %U %U N EW S 0 300 600 900 1200 m. Zone prospectée Années d'occupation des territoires %U 1992-2004-2005-2007 %U 1992-2004-2005 %U 1992-2004 %U 1992-2007 %U 1992 r 2004-2005 r 2004-2007 r 2004 %U %U %U %U %U %U %U %U %U %U %U %U %U r r %U %U %U %U %U %U %U %U %U %U %U r r r r r r rr r rrrr r r r r r r r r r r r r rr N EW S 0 300 600 900 1200 m. Zone prospectée uniquement en 2004 et 2005 Zone prospectée en 1992, 2004 et 2005 Années d'occupation des territoires %U 1992-2004-2005 %U 1992-2004 %U 1992-2005 %U 1992 r 2004-2005 r 2004 r 2005
  • 14. Année Nombre de territoires Corte-Restonica Tartagine-Melaja (ZONE-B) 1992 15 24 2000 incendie - 2003 - incendie 2004 11 15 2005 9 13 2007 5 - in the two Corsican pine forests where nuthatches have been monitored before and after fire, the number of territorial birds has sharply declined in the first spring after fire: by - 37.5 % on Tartagine-Melaja and - 50% on Restonica. The decrease in abundance observed in the study area appears to result from the fire The habitat seems to remain unfavourable for nuthatches for several years after fire. We did not observe any trend toward a restoration of nuthatch numbers in the first two years after fire in Tartagine-Melaja forest, nor even in the first seven years after fire in Restonica forest . The decline for several years after the fire may result to (i) the mortality of individuals remained on their territory during the first years following the disturbance (site tenacity), and (ii) non- recruitment of new nuthatches due to unfavorable habitat
  • 15. the modelling procedure selected the smallest length of crown burned as the only variable significantly (at the 5% level) explaining nuthatch presence. The regression coefficients show that the smaller the length of crown burned, the more likely was the presence of the nuthatch after the fire (intercept = 0.925, slope = -0.388). The probability of occurrence of the bird was greater than 0.5 when the smallest length of crown burned on a pine of the plot was less than 2.5 m (cf. Fig.). In other words, the nuthatch tends to be absent in severe burns when all the pines have more than 2.5 m of burned crown. 0 0,1 0,2 0,3 0,4 0,5 0,6 0,7 0,8 0,9 1 0 1 2 3 4 5 6 7 ProbabilityofoccurrenceoftheNuthatch Smallest length of crown burned (m) Probability of occurrence of the Corsican Nuthatch as a function of the smallest length of Corsican pine crown burned (with 90% confidence intervals)
  • 16. The fire can have different effects, not exclusive and depending generally on its severity, that could explain the decline of nuthatches in burned areas: The simultaneous decrease of shelters, of nest sites, and of food resources probably forces nuthatches to leave the burned stands. Emigration resulting from a shortage of seeds has been described in the related Red-breasted nuthatch Sitta canadensis, especially after fire. Nuthatches breed in dead and soft wood where the pairs excavate holes. The fire usually burns most of the available snags, so that it may be difficult for birds to find nest-sites in the short term before new snags are available (several years may be required for the dead wood of the pines killed by fire to become soft enough to permit the excavation of new nest sites by the nuthatch). The seeds of Corsican pine are the main food resource for nuthatches. Even if the opening of cones by fire makes numerous unburned seeds available during the days immediately following the fire, the production of new seeds is much reduced in burned areas. Fire may cause an increase in the abundance of predators. Woodpeckers in general and Great Spotted Woodpeckers Dendrocopos major (a nest predator of nuthatch), in particular, usually increase in abundance after fire, increasing the risk of predation for nuthatch. The disappearance of a fraction of the canopy, increasing the distances between crowns, is prejudicial to forest birds that need cover as protection against predators.
  • 17. The habitat seems to remain unfavourable for nuthatches for several years after fire. We did not observe any trend toward a restoration of nuthatch numbers in the first two years after fire in Tartagine-Melaja forest, nor even in the first seven years after fire in Restonica forest. There are several long-lasting effects of fire: i. where there is woodland regrowth after fire, even when the regeneration of the pines is successful the habitat, when completely burned, remains unfavourable for 60-120 years, i.e., the estimated time for stand maturity ii. the natural regeneration of Pinus nigra after fire is low iii. seed production decreases for several years after fire iv. Corsican pines suffer delayed mortality as other Mediterranean pines
  • 18. ï‚ž As with other passerines, the nuthatch seems to show a high site- tenacity after a moderate disturbance. Owing to the irregular topography of the Corsican mountain forests, the severity of the fire varies from place to place, resulting in a mosaic of patches burned to different degrees. The nuthatch is absent only in the most burned areas. This mosaic pattern tempers the impact of large wildfires on the population. ï‚ž Our results show that the nuthatch is likely to be absent when all the pines have more than 2.5 m of burned crown on the plot, and present when at least one pine has less than 2.5 m of crown burned (i.e., the threshold at which the presence and absence of the nuthatch are equally probable). Thus a burned stand should not be clear-cut in the latter case. The use of such criteria could help the selection of plots to be cut where salvage logging is necessary.