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Postfire epicormic resprouting

September 22nd, 2017 No comments

Many plants resprout from basal buds after disturbance, and this is common in shrublands subjected to high-intensity fires [1]. However, resprouting after fire from epicormic (stem) buds is globally far less common. In a recent paper we review the ecology and evolution of this mechanism [2]. Many plants can generate epicormic shoots after light disturbances (e.g., browsing, drought, low intensity fires, insect defoliation, strong winds), but this does not mean they generally resprout epicormically after fire, as the heat of a fire may kill epicormic buds if they are not well protected (e.g., by a thick bark). The most well-known examples of epicormic resprouting are many species of eucalypts (Fig. 1A below), the cork oak (Quercus suber [3], Fig. 1B below), and Pinus canariensis ([4], Fig. 1C, D below). There are other pines and oaks that also resprout epicormically, and many species from savannas, especially those from the Brazilian savannas (cerrado) where many trees have a thick corky bark [5].

Epicormic resprouting has appeared in different lineages and on different continents and thus it is an example of convergent evolution in fire-prone ecosystems. It is an adaptation to a regime of frequent fires that affect tree crowns. It has probably been favoured where productivity is sufficient to maintain an arborescent growth form, fire intensity is sufficient to defoliate the tree canopy crown, and fire frequency is high (in conifers, too high for serotiny to be reliable) [2]. Given the high resilience of forest and woodlands dominated by epicormic resprouters, these species are good candidates for reforestation projects in fire-prone ecosystems [3].

Figure: Examples of postfire epicormic resprouting after a crown fire from very different lineages: (A) Eucalyptus diversicolor 18 months after fire in Western Australia. (B) Quercus suber woodland 1.5 years postfire in southern Portugal. (C) Pinus canariensis woodland a few years after fire; (D) epicormic resprouts of P. canariensis 3 months postfire. Photos by G. Wardell-Johnson (A); F.X. Catry (B) and J.G. Pausas (C, D), from [2].

References
[1] Pausas, J.G., Pratt, R.B., Keeley, J.E., Jacobsen, A.L., Ramirez, A.R., Vilagrosa, A., Paula, S., Kaneakua-Pia, I.N. & Davis, S.D. 2016. Towards understanding resprouting at the global scale. New Phytologist 209: 945-954. [doi | wiley | pdf | Notes S1-S4]

[2] Pausas J.G. & Keeley J.E. 2017. Epicormic resprouting in fire-prone ecosystems. Trends in Plant Science 22: xx-xx. [doi | pdf]

[3] Aronson J., Pereira J.S., Pausas J.G. (eds). 2009. Cork Oak Woodlands on the Edge: conservation, adaptive management, and restoration. Island Press, Washington DC. 315 pp. [The book]

[4] Pinus canariensis, jgpausas.blogs.uv.es/2017/05/07

[5] Dantas V. & Pausas J.G. 2013. The lanky and the corky: fire-escape strategies in savanna woody species. Journal of Ecology 101 (5): 1265-1272. [doi | pdf | suppl.]

More information on: epicormic resprouting | cork oak | pines

Chile 2017 fires: fire-prone forest plantations

September 16th, 2017 No comments

During the 2016/17 fire season in central Chile, wildfires burned about 600,000 ha, a record for the region (most of the area burned between 18-Jan and 5-Feb, 2017). Two factors are considered the main responsible of such a large area burned: (1) an intense drought with strong head waves (January was the hottest month in record), and (2) the fact that the region is covered by large and dense tree plantations that create a continuous fuel bed. The tree planted are two alien species: Pinus radiata and Eucalyptus sp., from California and Australia, respectively. Most burned area (+60%) were plantations, and if we standardize the area burned in relation to the area with each landuse in the region (plantations, native forest, grasslands, agriculture) we see that the plantations were more affected by fire than expected by their area in each region; and this contrast with the other landuses (Figure 1, [1]). That is, tree plantations were an important driver for the large area burned (highly flammable).

Interesting is that the two species planted not only are highly flammable, they also have very good (although very different) postfire regeneration mechanisms, because both are originally from fire-prone ecosystems and have adapted to coupe with crown fires. Pinus radiata have serotinous cones (closed cones that open with fire) and showed an extraordinary “natural” seedling regeneration postfire (Figure 2 top), while those eucalytps planted show epicormic (stem) resprouting that allows a quick canopy recovery (even young trees, Figure 2 bottom). All suggest that these plantations were born to burn!

Figure 1: Analysis of the areas affected by fires according to types of use (forest plantations, native forest, Scrubland + pastures, and agricultural areas), in relation to what is available in each of the 4 regions that have burned the most (V, RM, VI, VII are: Valparaiso, Metropolitana, O’Higgins, and Maule). Positive data means that fire has positively selected this type of use (it has burned more than expected by the area it occupies); the negative data indicate that fire tends to avoid such landuse. There is a strong tendency for plantations to burn more than expected according to their abundance in the landscape (positive values), while native forests, scrub, or agricultural areas are burned similar or less than expected according to their abundance (negative values). The region VII (Maule) is the most extreme in positive selection of plantations and negative of other uses. Elaborated on the basis of official SIDCO-CONAF data (Chile) [1].

 


Figure. 2. Postfire regeneration of tree plantations. Top: Extraordinary postfire seedlings regeneration of Pinus radiata (adult trees are dead). Bottom: epicormic resprouting of eucalypts (mixed with dead pines). Photos from early September (ca. 7 months after fire), in the Nilahue Barahona fire (O’Higgins region, Chile).

References

[1] Incendios en Chile 2017, jgpausas.blogs.uv.es/2017/02/10

More information on:  Chile and fires | Serotiny | Epicormic resprouting

 

Pinus canariensis

May 7th, 2017 No comments

The last post was about Pinus brutia [1] from the Eastern Mediterranean basin. Another pine of the mediterranean group (Pinaster group) is Pinus canariensis, endemic of Canary Islands, in the north west of Africa (in the Atlantic). P. canariensis have a thick bark and resprouts vigorously from stem buds (epicormic resprouting) after crown fires. In addition, it produce serotinous cones, a clear adaptation to recruit after fire [2,3]. Very few other trees have strong adaptations to both survival and regeneration postfire; P. canariensis is among the best fire-adapted trees in the world, likely to survive very different fire regimes.

Pictures of Pinus canariensis (by JG Pausas except mid-right from NASA).
· Top-left: 5 years after a crown-fire (La Palma, Canary Is.).
· Mid-left: plantation 2 years after fire (Vall d’Ebo, Alicante, eastern Spain; planted in the 50s).
· Bottom-left: Contrasted response of Pinus halepensis (left; fire-killed serotinous pine) and P. canariensis (right, resprouting) two years after fire (Alicante, eastern Spain).
· Top-, bottom-right: epicormic resprouts 3 months after fire (Tenerife, Canary Is.).
· Mid-right: a fire plume from a wildfire in La Palma (Canary Is.).

References
[1] Pinus brutia, jgpausas.blogs.uv.es, 19 Apr 2017

[2] Keeley J.E., Pausas J.G., Rundel P.W., Bond W.J., Bradstock R.A. 2011. Fire as an evolutionary pressure shaping plant traits. Trends Plant Sci. 16: 406-411. [doi | sciencedirect | trends | pdf | For managers]

[3] Pausas, J.G. 2015. Evolutionary fire ecology: lessons learned from pines. Trends Plant Sci. 20: 318-324. [doi | sciencedirect | cell | pdf]

 

Fire adaptations in Mediterranean Basin plants

September 7th, 2015 No comments

Few days ago a botanist colleague ask me whether there were some fire adaptations in the plants of the Mediterranean Basin, similar to those reported in other mediterraenan-climate regions. So I realised that researchers working on other topics may not be aware of the recent advances in this area. Here is my brief answer, i.e., some examples of species growing in Spain that show fire adaptations; this is by no means an exhaustive list, but a few examples of common species for illustrative purpose. You can find a description of these adaptations and further examples elsewhere [1, 2, 3, 4]. It is also important to note that plants are not adapted to fire per se, but to specific fire regimes, and thus some adaptations my provide persistence to some fire regimes but not to all [1]. That is, species that exhibit traits that are adaptive under a particular fire regime can be threatened when that regime changes.

  • Serotiny (canopy seed storage): Pinus halepensis, Pinus pinaster, with variability in serotiny driven by different fire regimes [5, 6]
  • Fire-stimulated germination: There are examples of heat-stimulated germination, like many Cistaceae (e.g., Cistus, Fumana [7, 8]) and many Fabaceae (e.g., Ulex parviflorus, Anthyllis cytisoides [7, 8]), as well as examples of smoke-stimulated germination like many Lamiaceae (e.g., Rosmarinus officinalis, Lavandula latifolia [7]) or Coris monspeliensis (Primulaceae [7]). There are also examples of species with smoke-stimulated seedling growth (Lavandula latifolia [7])
  • Resprouting from lignotubers: Arbutus unedo, Phillyrea angustifolia, Juniperus oxycedrus, many Erica species (e.g., E. multiflora, E. arborea, E. scoparia, E. australis) [4, 17]
  • Epicormic resprouting: Quercus suber [9, 10], Pinus canariensis [4]
  • Fire-stimulated flowering: Some monocots like species of Asphodelus, Iris, Narcissus [11, 12]
  • Enhanced flammability: Ulex parviflorus shows variability of flammability driven by different fire regimes [13] and under genetic control [14]. Many Lamiaceae species have volatile organic compounds that enhance flammability (e.g., Rosmarinus officinalis [16]).
  • Thick bark and self-pruning (in understory fires): Pinus nigra [3,15]

 

fireadaptations2

References

[1] Keeley et al. 2011. Fire as an evolutionary pressure shaping plant traits. Trends Plant Sci 16:406-411. [doi | pdf]

[2] Keeley et al. 2012. Fire in Mediterranean Ecosystems. Cambridge University Press. [book]

[3] Pausas JG. 2012. Incendios forestales. Catarata-CSIC. [book]

[4] Paula et al. 2009. Fire-related traits for plant species of the Mediterranean Basin. Ecology 90:1420-1420. [doi | pdf | BROT database]

[5] Hernández-Serrano et al. 2013. Fire structures pine serotiny at different scales. Am J Bot 100:2349-2356. [doi | pdf]

[6] Hernández-Serrano et al. 2014. Heritability and quantitative genetic divergence of serotiny, a fire persistence plant trait. Ann Bot 114:571-577. [doi | pdf]

[7] Moreira et al. 2010. Disentangling the role of heat and smoke as germination cues in Mediterranean Basin flora. Ann Bot 105:627-635. [doi | pdf]

[8] Moreira B and Pausas JG. 2012. Tanned or Burned: the role of fire in shaping physical seed dormancy. PLoS ONE 7:e51523. [doi | plos | pdf]

[9] Pausas JG. 1997. Resprouting of Quercus suber in NE Spain after fire. J Veget Sci 8:703-706. [doi | pdf]

[10] Catry et al. 2012. Cork oak vulnerability to fire: the role of bark harvesting, tree characteristics and abiotic factors. PLoS ONE 7:e39810. [doi | pdf ]

[11] Postfire flowering: Narcissusjgpausas.blogs.uv.es 2 May 2015

[12] Postfire blooming of Asphodelous, jgpausas.blogs.uv.es 5 Apr 2014

[13] Pausas et al. 2012. Fires enhance flammability in Ulex parviflorus. New Phytol 193:18-23. [doi | pdf]

[14] Moreira et al. 2014. Genetic component of flammability variation in a Mediterranean shrub. Mol Ecol 23:1213-1223. [doi | pdf]

[15] He et al. 2012. Fire-adapted traits of Pinus arose in the fiery Cretaceous. New Phytol 194:751-759. [doi | pdf | picture]

[16] Flammable organic compounds: Rosmarinus officinalis, jgpausas.blogs.uv.es 2-Oct-2015

[17] Paula et al. 2016. Lignotubers in Mediterranean basin plants. Plant Ecology [doi | pdf | suppl. | blog]

 

Afrotropical and neotropical savannas are different

July 29th, 2013 No comments

Savannas are typically ecosystems dominated by grasses with a variable tree density (e.g., [1]). However, the savanna biome is very large, it occurs in different continents, and includes a large variability in the vegetation structure and composition. Fire and herbivory are the main disturbance factors shaping savannas worldwide and because the different climatic conditions and the different evolutionary histories among different savannas, fire and herbivory regimes also varies among savannas. Because plants are not adapted to fire and herbivory “per se” but to specific regimes of herbivory and fire [2], we expect different strategies to cope with these disturbances in different savannas. In this framework, we have recently compared savannas from Africa and from South America (afrotropical and neotropical savannas respectively) [3]: Afrotropical savannas have a dryer climate and are more intensely grazed than neotropical savannas, and thus the amount of available fuel is typically lower in afrotropical than in the neotropical savannas. Consequently fires tend to be more intense in neotropical savannas. In afrotropical conditions, young woody plants tend to grow quickly in height to soon locate the canopy above the flame zone before the next fire, and above the browsing height. Thus these plants tend to have a pole-like or lanky architecture (the lanky strategy). In contrast, in neotropical savannas where herbivory pressure is lower they require a thick corky bark for protection against relatively intense fires (the corky strategy) [3]. Despite the two fire escape strategies appear in both Africa and South America, we suggest that the lanky strategy is more adaptive in afrotropical savannas, while the corky strategy is more adaptive in neotropical savannas [3].


Figure: Diospyros hispida A.DC. (Ebenaceae), a South American example of a plant with the corky strategy. Although the trunk was fully burned one year earlier (dark branches and trunk), the bark protected the lateral buds which enabled epicormic resprouting and the formation of lateral resprouts (light grey branches). This photo was taken in Emas National Park (cerrado ecosystem, Brazil) at the beginning of the rainy season (2011) when this deciduous plant starts to produce new leaves (Photo: V.L. Dantas). For an example of the lanky strategy see [4].

References:
[1] Dantas V., Batalha, MA & Pausas JG. 2013. Fire drives functional thresholds on the savanna-forest transition Ecology 94:2454-2463. [doi | pdf | blog]

[2] Keeley J.E., Pausas J.G., Rundel P.W., Bond W.J., Bradstock R.A. 2011. Fire as an evolutionary pressure shaping plant traits. Trends Plant Sci. 16(8): 406-411. [doi | trends | pdf]

[3] Dantas V. & Pausas J.G. 2013. The lanky and the corky: fire-escape strategies in savanna woody species Journal of Ecology 101: 1265-1272 [doi | pdf]

[4] Archibald, S. & Bond, W.J. 2003. Growing tall vs growing wide: tree architecture and allometry of Acacia karoo in forest, savanna, and arid environments. Oikos, 102: 3-14.

 

Bark harvesting and Cork oak vulnerability to fire

July 11th, 2012 No comments

Cork oak (Quercus suber) is a strong fire-resistant tree species thank to is very thick and insulating corky bark [1-4]. In fact it is the only European tree with the capacity to resprout from epicormic buds in the canopy after an intense crown-fire [1]. However, the bark of the cork oak is periodically harvested for cork production (mainly for bottle tops but also for other uses, [2]) and thus bark harvesting increases the vulnerability of the tree to fire. In a recent paper we quantified the response of cork oak (tree mortality, stem mortality, and crown recovery) after fire [5]. The results showed that fire vulnerability was higher for trees with thin bark (young or recently debarked individuals) and decreased with increasing bark thickness until cork was 3–4 cm thick. This bark thickness corresponds to the moment when exploited trees are debarked again, meaning that exploited trees are vulnerable to fire during a long period. Exploited trees were also more likely to be top-killed than never-debarked trees, even for the same bark thickness. Additionally, vulnerability to fire increased with burn severity and with tree diameter, and was higher in trees burned in early summer or located in drier south-facing aspects. All these aspects need to be considered when managing cork oak woodlands specially nowadays that fire activity is increased [6]. Increasing the length of the cork harvesting cycle would increase the time during which the trees have a thicker bark and are better protected against fire injury. Since cork is the main economical income from these forests, stopping bark exploitation might be unrealistic in most cases. However, in fire-prone areas where conservation and tourism are the main objectives, stopping bark explotation would likely be the most effective option to increase ecosystem resilience to fire. The valorisation of many other services provided by cork oak forests [7] could create economic incentives to decrease the bark-exploitation dependency of these systems in the future.


Foto: Cork oak  resprouting from epicormic buds (By F. Catry)

References

[1] Pausas, J.G. 1997. Resprouting of Quercus suber in NE Spain after fire. J. Veg. Sci. 8: 703-706. [doi | pdf]

[2] Aronson, J., J. S. Pereira, and J. G. Pausas (eds). 2009. Cork Oak Woodlands on the Edge: Ecology, Adaptive Management, and Restoration. Island Press, Washington, DC. [web of the book]

[3] Pausas J.G. 2009. Convergent evolution. jgpausas.blogs.uv.es, 8/Nov/2009. [link]

[4] Pausas J.G. 2011. Bark thickness: a world record? jgpausas.blogs.uv.es, 3/Jan/201. [link]

[5] Catry F., Moreira F., Pausas J.G., Fernandes P.M., Rego F., Cardillo E. & Curt T. 2012. Cork Oak vulnerability to fire: the role of bark harvesting, tree characteristics and abiotic factors. PLoS ONE 7: e39810. [doi | pdf ]

[6] Pausas J.G. & Fernández-Muñoz S. 2012. Fire regime changes in the Western Mediterranean Basin: from fuel-limited to drought-driven fire regime. Climatic Change 110: 215-226. [doi | springer | pdf]

[7] Bugalho M.N., Caldeira M.C., Pereira J.S., Aronson J., & Pausas J.G. 2011. Mediterranean Cork oak savannas require human use to sustain biodiversity and ecosystem services. Frontiers in Ecology and the Environment 9: 278-286. [doi | pdf | blog]

 

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