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Posts Tagged ‘resprouting’

Postfire resprouting of Chamaerops humilis

March 18th, 2016 No comments

“A few, but only a few species of palms, are, like our Coniferae, Quercineae, and Betulineae, social plants : such are the Mauritia flexuosa, and two species of Chamaerops, one of which, the Chamaerops humilis, occupies extensive tracts of the ground near the Mouth of Ebro and in Valencia …” — Alexander von Humboldt (1848)

Chamaerops humilis (Mediterranean dwarf palm) is the only native palm in continental Europe, and the northernmost naturally occurring palm in the world. It is native to the western Mediterranean Basin, occurring along the Mediterranean cost of Spain (as mentioned by Humboldt), Portugal, France, Italy, Malta, Morocco, Algeria, and Tunisia. The other palm occurring in the Mediterranean Basin is Phoenix theophrasti, a rare palm growing in the Crete island and in the southern Turkey [MedTrees].

Humboldt probably did not know that Chamaerops humilis resprouts very quick after fire (at that time fire was not considered as part of the natural processes). The resprouting of this species does not necessary come from new dormant buds (as in most typical resprouters) but from the normal apical buds protected from the fire by the leaf bases in the stem.The first resprouting leaves often show the typical burned-brown-green pattern of the photo below. This is because in palms (and in all monocots), the meristem is at the base of the leaves (more protected), and thus even burned leaves can still grow from the base and showing the upper part burned. In addition, C. humilis can generate basal suckers from an underground rhizome. C. humilis often flowers very quickly after fire, together with the first leaves (upper photo). Overall it is very resilient to recurrent fires.

Chamaerops-humilis
Chamaerops humilis (one of the few ‘social palms’ following Humboldt) 2-3 months postfire in the Valencia region (eastern Spain; photos: JG Pausas)

References

Humboldt, A. von (1848). Aspects of nature (original title: Ansichten der Natur, 3rd ed).

 

Olive trees resprouting

February 22nd, 2016 No comments

The typical image on a cultivated olive tree (Olea europaea) is a short squat tree with a thick gnarled trunk. Below are some olive trees with a slightly different shape, after being burned twice in different wildfires (1994 and 7/2015) in Montán (Castelló, eastern Spain). Before 1994 these trees were single-stemmed with the typical thick trunk; they were planted long ago for olive production. The 1994 fire killed the main stem and the tree produced many resprout from the base, around the trunk (it became multi-stemmed). In 2015 in burned again killing those 21 year-old resprouts and producing many new ones (the green ones in the pictures, 7 month-old resprouts). The 2015 fire also consumed the main stem that had died in the 1994 fire, including the base of the stem, and thus it produced a hole in the middle of the tree (second picture). This is quite common.

Olea resprouting 1
Olea resprouting 2
Photos: Olive trees (Olea europaea) resprouting after two fires (1994, 7/2015; JG Pausas 2/2016).

More on resprouting: Lignotubers | Resprouting at the global scaleEvolutionary ecology of resprouting and seedingPhysiological differences between resprouters and seedersTo resprout or not to resprout | Differences between resprouters and non-resprouters | Fire, drought, resprouting: leaf and root traits |

 

Lignotubers

November 17th, 2015 1 comment

Lignotubers are swollen woody structures located at the root-shoot transition zone of some plants; they contain numerous dormant buds and starch reserves [1]. They are ontogenetically programmed, that is, they are not the product of repeated disturbances; and thus they can be observed at very early stages of the plant development (other types of basal burls may be a response to multiple disturbances). Lignotubers enables the plant to resprout prolifically after severe disturbances that remove the aboveground biomass, thus they are considered adaptive in fire-prone ecosystems [2]. Lignotubers are not well-known in many floras because they are often below-ground (i.e., detected only after excavation) and because they are often confused by other non-ontogenetically determined basal burls; thus some reports of lignotubers in the literature are mistakes. In a recent review [1] we provide examples of species with a clear evidence of lignotubers in the Mediterranean basin, together with detailed morphological and anatomical description of lignotubers in saplings. The species with lignotuebers in the Mediterranean basin include many Erica species (e.g. E. arborea, E. scoparia, E. australis, E. lusitanica, E. multiflora), the two Arbutus species (A. unedo, A. andrachne), Rhododendron ponticum, Viburnum tinus, Phillyera angustifolia, Quercus suber (not obvious macroscopically!), Tetraclinis articulata and Juniperus oxycedrus (but not in all populations!). Please let me know (email address here) if you know of other Mediterranean basin species with lignotubers! Thanks

lignotubers
Figures: Examples of lignotubers for Mediterranean basin species. A Juniperus oxycedrus (resprouting after fire). B Viburnum tinus. C Arbutus unedo. D Quercus suber (not a clear basal swelling). E Olea europaea. F Phillyrea angustifolia (adult), G Phillyrea angustifolia (saplings). In many species (e.g., V. tinus, A. unedo and P. angustifolia) the lignotuber is only evident after excavating the root-shoot transition zone.

References

[1] Paula S., Naulin P.I., Arce C., Galaz C. & Pausas J.G. 2016. Lignotubers in Mediterranean basin plants. Plant Ecology  [doi | pdf | suppl.]

[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 | pdf | For managers]

 

Resprouting at the global scale

November 2nd, 2015 No comments

Plant resprouting (i.e., the ability to form new shoots after destruction of living tissues from disturbance) is often considered a simple qualitative trait and used in many ecological studies. However, resprouting is a trait that increases fitness under many different disturbance types, occurs in a wide range of environments, is widespread in many lineages, and is morphologically very diverse. In a recent paper we review some of the complexities and misunderstandings of resprouting and highlight that cautions is needed when using resprouting ability to predict vegetation responses across disturbance types and biomes [1]. There are marked differences in resprouting depending on the disturbance type, and fire is often the most severe disturbance because it includes both defoliation and lethal temperatures. In the mediterranean biome, there are differences in functional strategies to cope with water deficit between reprouters (dehydration avoiders) and non-resprouters (dehydration tolerators) [1,2]; however, there is little research to unambiguously extrapolate these results to other biomes, and some of the extrapolations seems to be incorrect. In addition, resprouting in the mediterranean biome tends to be binary, that is, species are either resprouters or non-resprouters [3], and intermediate cases are evolutionary unstable [4]; however this is not necessary true in other biomes (e.g., in the tropics). Furthermore, predictions of vegetation responses to changes in disturbance regimes require consideration of not only resprouting but also other relevant traits (e.g., seeding, bark thickness) and the different correlations among traits observed in different biomes [5]; models lacking these details would behave poorly at the global scale. Overall, the lessons learned from a given disturbance regime and biome, like crown-fire mediterranean ecosystems, can guide research in other ecosystems but should not be extrapolated at the global scale.

 

Cistus-Quercus

Fig: Fire allows the coexistence of species with very different strategies: Cistus albidus seedling (left) and Quercus coccifera resprout (right) 10 months after a high intensity fire in eastern Spain (Cortes de Pallás fire, 2012, Valencia). Cistus albidus  is a drought semi-deciduous nonresprouter (obligate postfire seeder ) with a physiological drought-tolerant behavior; Quercus coccifera  is an sclerophyllous (evergreen) obligate resprouter with drought-avoiding traits [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 | pdf] — New paper!

[2] Vilagrosa A., Hernández E.I., Luis V.C., Cochard H., Pausas, J.G. 2014. Physiological differences explain the co-existence of different regeneration strategies in Mediterranean ecosystems. New Phytologist 201: 1277-1288. [doi | pdf ]

[3] Pausas, J.G., Bradstock, R.A., Keith, D.A., Keeley, J.E. & GCTE Fire Network. 2004. Plant functional traits in relation to fire in crown-fire ecosystems. Ecology 85: 1085-1100. [pdf | esa | doi]

[4] Pausas J.G. & Keeley J.E., 2014. Evolutionary ecology of resprouting and seeding in fire-prone ecosystems. New Phytologist 204: 55-65. [doi | wiley | pdf]

[5] Pausas, J.G. 2015. Bark thickness and fire regime. Functional Ecology 29:317-327. [doi | pdf | suppl.]

 

Odena fire: 55 days postfire

October 17th, 2015 No comments

The 27th of July a wildfire in Òdena (Anoia, central Catalonia, NE Spain) burned ca. 1200 ha, mainly of Pinus halepensis forest [1]. Here some details 55 days after the fire:

Top: limit of the fire, with the Montserrat mountains in the background. Middle: resprouting of understory plants; Arbutus unedo in the right. Bottom left: concentration of pine nuts around an ant nest. Bottom right: Genista scorpius resprouting. Photos by J. Garcia-Pausas (top, bottom right), A. Mazcuñan (bottom left), JG Pausas (middle).

[1] Odena fire: first visitors, jgpausas.blogs.uv.es 10-08-2015

Ecology and evolution in fire-prone ecosystems

February 28th, 2015 2 comments

During the last years I’ve been working in many topics related to fire ecology and plant evolution in ecosystems subject to recurrent fires (mainly mediterranean and savanna ecosystems). Because I believe knowledge should be spread around easily, I make my results available to the public in my web page (see publications list) and in this blog. However, having the cumulative list of paper published each year is not very convenient for people searching for a specific topic. For this reason, I’m rearranging most of my articles by topics as follows:

1. Fire history
2. Fire regime: climate & fuel
3. Fire traits (resprouting, postfire germination, serotiny, bark thickness, flammability, data & methods)
4. Fire & plant strategies (in Mediterranean ecosystems, in pines, in savannas, community assembly)
5. Fire & evolution
6. Some fire-adapted species (Pinus halepensis, Quercus suber, Ulex parviflorus)
7. Fire & vegetation modelling
8. Plant-animal interactions
9. Restoration & conservation

See: fire-ecology-evolution.html

Some papers may be repeated if they clearly fit in more than one topic; some papers, mainly old ones, do not fit well in any of these topics and have not been included (at least at the moment), they still can be found in the section of publications sorted by year. I’m still working on this rearrangement, so some modifications are possible; and any comment is welcome.
I hope this is useful for somebody!

Publications: by year | by topic | books

 

Evolutionary ecology of resprouting and seeding

July 15th, 2014 No comments

There are two broad mechanisms by which plant populations persist under recurrent fires: resprouting from surviving tissues, and seedling recruitment [1]. Species that live in fire-prone ecosystems can have one of these mechanisms or both [1]. In a recent review paper [2], we propose a model suggesting that changes in evolutionary pressures that modify adult (P) and juvenile (C) survival in postfire conditions (Fig. 1 below) determine the long-term success of each of the two regeneration mechanisms, and thus the postfire regeneration strategy: obligate resprouters, facultative species and obligate seeders (Fig. 2). Specifically we propose the following three hypotheses: 1) resprouting appeared early in plant evolution as a response to disturbance, and fire was an important driver in many lineages; 2) postfire seeding evolved under conditions where fires were predictable within the life span of the dominant plants and created conditions unfavorable for resprouting; and 3) the intensification of conditions favoring juvenile survival (C) and adult mortality (P) drove the loss of resprouting ability with the consequence of obligate-seeding species becoming entirely dependent on fire to complete their life cycle, with one generation per fire interval (monopyric life cyle). This approach provides a framework for understanding temporal and spatial variation in resprouting and seeding under crown-fire regimes. It accounts for patterns of coexistence and environmental changes that contribute to the evolution of seeding from resprouting ancestors. In this review, we also provide definitions and details of the main concepts used in evolutionary fire ecology: postfire regeneration traits, postfire strategies, life cycle in relation to fire, fire regimes (Box 1), costs of resprouting (Box 2), postfire seeding mechanisms (Box 3), and the possible evolutionary transitions (Box 4).

 

Fig2_sm
Fig. 1 : Main factors affecting adult and offspring seedling survival (P and C, respectively), and thus the P/C ratio, in fire-prone ecosystems (from Pausas & Keeley 2014 [2]).

 

Fig3_sm

Fig. 2: The changes in the probability of resprouting along an adult-to-offspring survival (P/C) gradient are not linear but show two turning points related to the acquisition of key innovations: the capacity to store a fire-resistant seed bank (postfire seeding), and the loss of resprouting capacity. Changes in P/C ratio may be produced by different drivers (Fig. 1) which drove the rise of innovations during evolution, e.g., during the increasing aridity from the Tertiary to the Quaternary (from Pausas & Keeley 2014 [2]).

 

Refecences

[1] Pausas, J.G., Bradstock, R.A., Keith, D.A., Keeley, J.E. 2004. Plant functional traits in relation to fire in crown-fire ecosystems. Ecology 85: 1085-1100. [doi | pdf | esa | jstor]

[2] Pausas J.G. & Keeley J.E. 2014. Evolutionary ecology of resprouting and seeding in fire-prone ecosystems. New Phytologist 204: 55-65 [doi | wiley | pdf]

 

Physiological differences between resprouters and seeders

November 9th, 2013 No comments

The ability to resprout and to recruit after fire are two extremely important traits for the persistence in fire-prone ecosystems [1,2], and they define three life histories: obligate resprouters, obligate seeders (non-resprouters), and facultative seeders. After a fire, obligate seeders die and recruit profusely from the seeds stored in the seed bank [3-5]. In contrast, resprouters survive after fire and their above-ground tissues regenerate from protected (often below-ground) buds by using stored carbohydrates [6]. Facultative seeders not only recruit profusely after fire, but are also able to resprout. In fact, seeders and resprouters have different regeneration niches: seedling regeneration of obligate resprouters is not linked to fire, and they recruit during the inter-fire period under sheltered conditions (i.e., under vegetation cover), while seedling regeneration of seeders occurs in open postfire environments. Given the marked difference in water availability between microsites under vegetation and microsites open to the sun under Mediterranean conditions, seedlings of resprouters and seeders are subjected to different water-stress conditions, and thus they are expected to have different physiological attributes. Despite these differences, resprouters and seeders co-exist, are often well-mixed on local and landscape scales [7,8], and represent the two main types of post-fire regeneration strategies in Mediterranean ecosystems [2].

A recent study demonstrates marked differences in physiological attributes between seedlings of seeders and resprouters [9]: Seeders show a range of physiological traits that better deal with water-limited and highly variable conditions (e.g., higher resistance to xylem cavitation, earlier stomatal closure with drought, higher leaf dehydration tolerance), but they are also capable of taking full advantage of periods with high water availability (greater efficiency in conducting water through the xylem to to sustain high gas exchange rates when water is available). Conversely, resprouter species are adapted to more stable water availability conditions, favoured by their deeper root system, but they also display traits that help them resist water shortages during long summers.

Previous studies already showed marked differences between seeders and resprouters in a range of attributes: resprouters tend to exhibit a deeper root-system, while seedling root structure of seeders are more efficient in exploring the upper soil layer [10]. Leaves of seeders show higher water use efficiency (WUE) and higher leaf mass per area (LMA; i.e., higher sclerophylly, lower SLA) [11]. Seeds of seeder species are more tolerant to heat shocks and have greater heat-stimulated germination [3]. All these differences support the idea that they are distinct syndromes with different functioning characteristics at the whole plant level and suggest that they undertook different evolutionary pathways [12].

Figure: Coexistence of resprouters (R+) and seeders (R-) in postfire conditions near Valencia, Spain. (Foto: A. Vilagrosa).

 

References:

[1] Pausas, J.G., Bradstock, R.A., Keith, D.A., Keeley, J.E. & GCTE Fire Network. 2004. Plant functional traits in relation to fire in crown-fire ecosystems. Ecology 85: 1085-1100. [jstor |[pdf | Ecological Archives E085-029]

[2] Keeley J.E., Bond W.J., Bradstock R.A., Pausas J.G. & Rundel P.W. 2012. Fire in Mediterranean Ecosystems: Ecology, Evolution and Management. Cambridge University Press. [The book]

[3] Paula S. & Pausas J.G. 2008. Burning seeds: Germinative response to heat treatments in relation to resprouting ability. Journal of Ecology 96 (3): 543 – 552. [doi | pdf]

[4] Moreira B., Tormo J., Estrelles E., Pausas J.G. 2010. Disentangling the role of heat and smoke as germination cues in Mediterranean Basin flora. Annals of Botany 105: 627-635. [doi | pdf | blog]

[5] Moreira B. & Pausas J.G. 2012. Tanned or burned: The role of fire in shaping physical seed dormancy. PLoS ONE 7(12): e51523. [doi | plos | pdf | blog]

[6] Moreira B., Tormo J, Pausas J.G. 2012. To resprout or not to resprout: factors driving intraspecific variability in resprouting. Oikos 121: 1577-1584. [doi | pdf]

[7] Verdú M, & Pausas JG 2007. Fire drives phylogenetic clustering in Mediterranean Basin woody plant communities Journal of Ecology 95 (6), 1316-323 [doi | pdf]

[8] Ojeda, F., Pausas, J.G., Verdú, M. 2010. Soil shapes community structure through fire. Oecologia 163:729-735. [doi | pdf | blog]

[9] Vilagrosa A., Hernández E.I., Luis V.C., Cochard H., Pausas, J.G. 2014. Physiological differences explain the co-existence of different regeneration strategies in Mediterranean ecosystems. New Phytologist 201 : xx-xx [doi | pdf | suppl.] – NEW

[10] Paula S. & Pausas J.G. 2011. Root traits explain different foraging strategies between resprouting life histories. Oecologia 165:321-331. [doi | pdf | blog]

[11] Paula S. & Pausas J.G. 2006. Leaf traits and resprouting ability in the Mediterranean basin. Functional Ecology 20: 941-947. [doi | pdf | blog]

[12] Verdú M. & Pausas J.G. 2013. Syndrome-driven diversification in a Mediterranean ecosystem. Evolution 67: 1756-1766. [doi | pdf | blog]

 

Fire-stimulated flowering

May 25th, 2013 No comments

Some plant species flower profusely and quickly after fire (fire-stimulated flowering). Compared with resprouting or postfire seeding, this trait is relatively unknown outside of South Africa and Australia [1, 2]. It is considered one of the adaptations of some resprouting species to live in recurrently burn environments. There are some of these species that rarely flower without a fire (obligate postfire flowering) while others can flower in the absence of fire but they produce more flowers after it (facultative postfire flowering). One example I had the chance to observe recently in Central America is Bulbostylis paradoxa (Cyperaceae; Figure below); it is a very flammable plant that grow in savannas and dry forest of Central/South America and the Caribbean. Local foresters told me that they have never seen this species flowering in absence of fire, and that they start flowering next day after the fire.


Figure: Bulbostylis paradoxa (Cyperaceae) one month after a fire in Santa Rosa National Park, Costa Rica (fotos: J.G. Pausas, May 2013).

References:
[1] Bytebier B., Antonelli A., Bellstedt D.U., Linder H. P. 2011. Estimating the age of fire in the Cape flora of South Africa from an orchid phylogeny. Proc. R. Soc. B, 278: 188-195.

[2] Lamont B.B., Downes K.S. 2011. Fire-stimulated flowering among resprouters and geophytes in Australia and South Africa. Plant Ecol. 212: 2111-2125.

 

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]

 

New Book: Fire in Mediterranean Ecosystems

March 13th, 2012 No comments

Finally the new fire ecology book by Keeley et al. (2012) has been published:



For more information, table of contents, etc, see here.

Cambridge UP (ukusaau), Amazon (ukusajp), eBooks

To resprout or not to resprout

January 25th, 2012 No comments

Resprouting is a mechanism that allows individual plants to persist in disturbance-prone ecosystems. It is often considered a binary trait, defining species as resprouters or non-resprouters [1]. Although this dichotomous classification accounts for a high proportion of the interspecific variability in resprouting, it does not account for the intraspecific variability, as not all individuals of resprouting species successfully resprout [2], even if they are subject to a similar disturbance. In a recent paper, we proposed a conceptual model that disaggregates the process of resprouting into three sequential steps: initial ability to resprout, resprouting vigour and post-resprouting survival [3]. Intraspecific variability in resprouting supported the importance of: a) the pre-disturbance state of the plant (i.e. plant size and stored resources) on the initial ability to resprout and on the resprouting vigour, and b) the initial post-disturbance capacity to acquire resources (i.e., resprouting vigour) on the post-resprouting survival. The proposed three-step model of resprouting provides a mechanistic description of the factors driving intraspecific variability in resprouting.

Figure: Probability of initiating resprouting (as a function of starch concentration in roots), resprouting vigor (as a function of pre-disturbance plant size), and survival (as a function of the resprouting vigor), for Linum suffruticosum [see pictures] in the Valencia (eastern Spain). From Moreira et al. (2012) [2]

References

[1] Pausas, J.G., Bradstock, R.A., Keith, D.A., Keeley, J.E. & GCTE Fire Network. 2004. Plant functional traits in relation to fire in crown-fire ecosystems. Ecology 85: 1085-1100. [jstor | pdf]

[2] Catry F.X., Rego F., Moreira F., Fernandes F.M., Pausas J.G. 2010. Post-fire tree mortality in mixed forests of central Portugal. For. Ecol. Manage. 206: 1184-1192. [doi | pdf | post]

[3] Moreira B., Tormo J, Pausas J.G. 2012. To resprout or not to resprout: factors driving intraspecific variability in resprouting. Oikos [doipdf]

Differences between resprouters and non-resprouters

October 1st, 2011 No comments

Resprouting is a very important process in plants living in disturbance-prone ecosystems, and the December issue of the journal Plant Ecology is going to be dedicated to this topic (Ecology of plant resprouting in fire-prone ecosystems). During the recent years, and starting from the PERSIST project, we have been comparing functional traits between resprouters and non-resprouters in Mediterranean fire-prone ecosystems, and the last comparison (physiological traits [5]), is included in this special issue. Resprouters and non-resprouters are two plant syndromes in Mediterranean ecosystems that also differ in their evolutionary history [1]. Resprouters tend to exhibit a deeper root-system than non-resprouters that inverse less resources on roots. So one could think that resprouters are better adapted to drought. However, both resprouters and non resprouters coexist, and non-resprouters counteract their lower root allocation by different traits that confer higher drought resistance [2]. Non-resprouters have higher drought resistance at leave level because they have higher water use efficiency (WUE) and higher leaf mass per area (LMA; i.e., higher sclerophylly, lower SLA) [3]. The seedling root structure of non-resprouters also allows them to more efficiently explore the upper soil layer [4]. A recent paper also shows that, when water is non-limiting, non-resprouters showed a better performance of leaf gas exchange traits (higher assimilation, stomatal conductance and transpiration) than resprouters [5]; that is non-resprouters have higher efficiency in resource capture, and thus a better capacity to take advantage of water when it is freely available. In addition, resprouters and non-resprouters also differ in their post-fire germination, as non-resprouters tend to have a greater capacity to both (i) persist after fire by means of recruiting (greater heat-tolerance) and (ii) increase their population after fire (greater heat-stimulated germination), than resprouters [4]. All these results suggest that resprouters and non-resprouters are two contrasted syndromes or functional types in the Mediterranean Basin [6].

Figure: Arbutus unedo resprouting after a fire.

References:

[1] Pausas J.G. & Verdú M. 2005. Plant persistence traits in fire-prone ecosystems of the Mediterranean Basin: A phylogenetic approach. Oikos 109: 196-202. [pdf |doi]

[2] Pausas J.G. 2010. Fire, drought, resprouting: leaf and root traits. URL: jgpausas.blogs.uv.es, 22/Oct/2010.

[3] Paula S. & Pausas J.G. 2006. Leaf traits and resprouting ability in the Mediterranean basin. Functional Ecology 20: 941-947. [pdf | [doi]

[4] Paula S. & Pausas J.G. 2011. Root traits explain different foraging strategies between resprouting life histories. Oecologia 165:321-331. [doipdfblog]

[5] Hernández E.I., Pausas J.G. & Vilagrosa A. 2011. Leaf physiological traits in relation to resprouter ability in the Mediterranean Basin. Plant Ecology 212:1959-1966 [doi| pdf]

[4] Paula S. & Pausas J.G. 2008. Burning seeds: Germinative response to heat treatments in relation to resprouting ability. Journal of Ecology 96 (3): 543 – 552. [pdf | doi]

[6] Pausas, J.G., Bradstock, R.A., Keith, D.A., Keeley, J.E. & GCTE Fire Network. 2004. Plant functional traits in relation to fire in crown-fire ecosystems. Ecology 85: 1085-1100. [pdfjstor] [Ecological Archives E085-029]

Fire, drought, resprouting: leaf and root traits

October 22nd, 2010 No comments

Drought and fire are prevalent disturbances in Mediterranean ecosystems. Plant species able to regrow after severe disturbances (i.e. resprouter life history) have higher allocation to roots and higher water potential during the dry season than coexisting non-resprouting species. However, non-resprouters have higher survival rate after summer drought. We expect that, to counteract their shallow-rooting systems and to maximize seedling survival, non-resprouters have traits that confer higher water-use efficiency and higher efficiency in soil resource acquisition than resprouters.

Some time ago we tested this prediction in relation to leaf traits [1] and found that non-resprouters have higher leaf mass per area (LMA; i.e. lower specific leaf area, SLA), leaf dry matter content (LDMC), area-based leaf nitrogen content (LNCa) and integrated water-use efficiency (δ13C) than resprouters, suggesting that they have higher potential for structural resistance to drought and higher water-use efficiency than resprouters.

In a recent paper we have now tested the prediction for root traits in seedlings [2]. We found that non-resprouters have higher specific root length (SRL) and longer, thinner and more branched lateral roots, especially in the upper soil layers. The external links (i.e. the most absorptive root region) are also more abundant, longer, thinner and with higher SVR for non-resprouters. Thus seedling root structure of non-resprouters species allows them to explore more efficiently the upper soil layer, whereas seedling roots of resprouters will permit both carbon storage and deep soil penetration.

Whereas resprouters tend to maximize the surface and the efficiency of the organs for carbon uptake to ensure carbohydrate storage for resprouting (eg, higher SLA), non-resprouters maximize the root surface (eg, higher SRL), since their survival and growth may be limited by soil resources.

[1] Paula S. & Pausas J.G. 2006. Leaf traits and resprouting ability in the Mediterranean basin. Functional Ecology 20: 941-947. [doi | pdf]

[2] Paula S. & Pausas J.G. 2011. Root traits explain different foraging strategies between resprouting life histories. Oecologia 165:321-331 [doi | pdf]

Specific Root Length

Relationship between average root diameter and specific root length (SRL; log-scale) for resprouting (R+, closed symbols) and non-resprouting (R-, open symbols) species. Intraspecific variability is indicated by segments emerging from each symbol. From Paula & Pausas (Oecologia [2]).

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