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Posts Tagged ‘regeneration’

Postfire blooming of Asphodelous

April 5th, 2014 No comments

The 4th of February, 2014, a forest fire burnt ca. 200 ha in Segorbe, near Valencia, eastern Spain. Two months later (1st April 2014), few plants had started to resprout, others had started to germinate, but there were three species that had resprouted very quickly and were already flowering: Asphodelous cerasiferus (= A. ramosus; Spanish: gamón), Iris lutescens, and Asparagus horridus; the first showed an spectacular blooming (pictures below).

Asphodelus-bloom
Spectacular postfire bloom of Asphodelous cerasiferus in Segorbe, near Valencia, Spain (photos by MC Castellanos & JG Pausas, two months after fire).

Proyecto VIRRA

February 28th, 2014 No comments

El proyecto “El papel del fuego en la Variabilidad Intraespecífica (fenotípica y genética) de plantas del matoRRAl mediterráneo (VIRRA)” finalizó hace unos meses. Aquí se puede ver un resumen y los principales productos de este proyecto: enlace.

Ulex parviforus_juli_sm

La aliaga (Ulex parviflorus) es una de las principales especies estudiadas en VIRRA [1, 2].

[1] Ulex born to burn, jgpausas.blogs.uv.es, 9/Nov/2011

[2] Ulex born to burn (II): genetic basis of plant flammability,  jgpausas.blogs.uv.es, 25/Jan/2014

Serotiny

November 16th, 2013 No comments

Serotiny is the delayed seed release for more than a year by retaining the seeds in a woody structure [1]. This implies an accumulation of a canopy seed bank. Serotiny confer fitness benefits in environments with frequent crown-fires, as the heat opens the cones and seeds are dispersed in the post-fire bed which is rich in resource and the competition and predation are low. It is typical of many Proteaceae and some conifers, like some pine species [1, 2; figure below].

Two recent papers analyse the serotiny of two mediterranean pines Pinus halepensis and Pinus pinaster [3, 4]. P. halepensis show higher proportion of serotinous cones than P. pinaster, but the latter retain the cones for longer [3]. The two species show high variability of serotiny within and between populations, but they show a clear pattern of higher serotiny in populations subject to high frequency of crown-fires than those living in areas where crown-fires are rare or absent. This is true either considering serotiny as the proportion of serotinous cones or as the age of the cones stored. Compared with other pines worldwide, the strength of the fire-serotiny relationship in P. pinaster is intermediate, and in P. halepensis is among the highest known [3]. For P. halepensis (the species with higher % serotiny), populations in high fire recurrence regimes have higher fine-scale spatial aggregation of serotiny than those inhabiting low fire recurrence systems. This phenotypic spatial structure generated by fire could be a consequence of the spatial genetic structure of the population. The second study used genomic tools to search for a genetic association for serotiny [4]. The analysis of 384 SNPs of 199 individuals of P. pinaster (in 3 populations included in the previous study [3])  shows that 17 loci were associated with serotiny and explain all together ca. 29% of the serotiny variation found in the field. All these results adds further evidence to the emerging view that fire shapes intraspecific variability of traits and generates phenotypic divergence between populations [5, 6, 7].

Figure: Serotinous cones of Pinus pinaster (Foto: K.B. Budde)

References:

[1] 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]

[2] He T, Pausas JG, Belcher CM, Schwilk DW, Lamont BB. 2012. Fire-adapted traits of Pinus arose in the fiery Cretaceous. New Phytologist 194: 751-759. [doi | wiley | pdf (suppl.)]

[3] Hernández-Serrano A., Verdú M., González-Martínez S.C., Pausas J.G. 2013. Fire structures pine serotiny at different scales. American Journal of Botany 100: 2349-2356 [doi | amjbot | pdf | supp.]

[4] Budde, K. B., Heuertz, M., Hernández-Serrano, A., Pausas, J.G., Vendramin, G.G., Verdú, M. & González-Martínez, S.C. 2014. In situ genetic association for serotiny, a fire-related trait, in Mediterranean maritime pine (Pinus pinaster Aiton). New Phytologist  201: 230-241 [doi | pdf]

[5] 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 in Plant Science 16(8): 406-411. [doi] [trends] [pdf]

[6] Pausas, J. G., Schwilk, D. W. 2012. Fire and plant evolution. New Phytologist, 193:301-303. [doi | wiley | pdf]

[7] Pausas J.G., Alessio G., Moreira B. & Corcobado G. 2012. Fires enhance flammability in Ulex parviflorusNew Phytologist 193: 18-23. [doi | wiley | pdf]

 

Smoke-stimulated recruitment

September 16th, 2013 No comments

In many plant species from mediterranean ecosystems, germination is promoted by fire [1]; this effect may be driven by the heat [e.g., 2-4] or by the chemicals produced by the fire (e.g., smoke, 4,5]). Most information regarding to smoke-stimulated germination in the Mediterranean Basin comes from a few experiments performed in laboratory conditions. This approach does not consider factors that occur in the field, such as species interactions, density-dependent processes or the fact that seeds spent time in the soil. A recent field experiment performed in eastern Spain show that smoke increase overall seedling recruitment, specially seedlings of annual plant species [6]. However, despite most species had higher seedling establishment in the smoke than in the control subplots, there were very few species in which the effect of smoke was statistically significant, suggesting that the community response to smoke cannot be inferred from individual species; it is the sum of small differences in each species towards the same direction that produces a significant pattern at community scale. This emerging property of the community is often neglected by only considering germination experiments in the laboratory. The results also suggest that the effect of smoke in annual species of the Mediterranean Basin might be more relevant than previously thought.

References
[1] 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]

[2] 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]

[3] Moreira B. & Pausas J.G. 2012. Tanned or burned: The role of fire in shaping physical seed dormancy. PLoS ONE 7: e51523. [doi | plos | pdfblog]

[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. [pdf | doi | post]

[5] Smoke-stimulated germination, jgpausas.blogs.uv.es, 2/Dec/2011.

[6] Tormo, J., B. Moreira, and J. G. Pausas. 2014. Field evidence of smoke-stimulated seedling emergence and establishment in Mediterranean Basin flora. Journal of Vegetation Science 25: 771-777 [doi | wiley | pdf]

Seed dormancy as a fire adaptation in Mediterranean ecosystems

December 6th, 2012 1 comment

Plant species with physical seed dormancy are common in mediterranean fire-prone ecosystems. Because fire breaks seed dormancy and enhances the recruitment of many species, this trait might be considered adaptive in fire-prone environments [1]. However, to what extent the temperature thresholds that break physical seed dormancy have been shaped by fire (i.e., for post-fire recruitment) or by summer temperatures in the bare soil (i.e., for recruitment in fire-independent gaps) remains unknown [1]. In a recent paper published in PLoS ONE [2], we tested these two alternatives in six woody species (21 populations) occurring in fire-prone areas across the Mediterranean Basin (Spain and Turkey). Seeds from different populations of each species were subject to heat treatments simulating fire (i.e., a single high temperature peak of 100ºC, 120ºC or 150ºC for 5 minutes) and heat treatments simulating summer (i.e., temperature fluctuations; 30 daily cycles of 3 hours at 31ºC, 4 hours at 43ºC, 3 hours at 33ºC and 14 hours at 18ºC).

The results showed that fire treatments broke dormancy and stimulated germination in all populations of all species. In contrast, summer treatments had no effect over the seed dormancy for most species and only enhanced the germination in Ulex parviflorus, although less than the fire treatments. That is, the results suggest that in Mediterranean species with physical dormancy, the temperature thresholds necessary to trigger seed germination are better explained as a response to fire than as a response to summer temperatures (see Figure below). The high level of dormancy release by the heat produced by fire might enforce most recruitment to be capitalized into a single post-fire pulse when the most favorable conditions occur. This supports the important role of fire in shaping seed traits [3]. Given that seed dormancy is heritable, demonstrating that it provides higher chances of recruitment (i.e., higher potential fitness benefits) in response to fire than in response to summer temperatures suggests the temperature threshold for breaking dormancy might be an adaptation to fire [1, 4].

Figure: Germination (%) in fire conditions (y axis) versus germination (%) in summer conditions (x axis) for 6 species (21 populations across the Mediterranean basin). Intraspecific variability (i.e., among populations) is indicated by small symbols (mean population value) emerging from the large symbol (mean species value). The 1:1 line is also shown (dotted line). Species considered are: Cistus albidus, Cistus creticus, Cistus parviflorus, Cistus salviifolius, Fumana thymifolia, and Ulex parviflorus.

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

[2] Moreira, B. and J. G. Pausas. in press. Tanned or burned: The role of fire in shaping physical seed dormancy. PLoS ONE 7(6): e39810. [doi | pdf]

[3] Moreira B., Tavsanoglu Ç., Pausas J.G. 2012. Local versus regional intraspecific variability in regeneration traits. Oecologia 168: 671-677. [doi | pdf]

[4] Pausas J.G. & Schwilk D.W. 2012. Fire and plant evolution. New Phytol., 193, 301-303. [doi | wiley | pdf]

Life 15 days after the large fires in Valencia

July 22nd, 2012 4 comments

Few days ago two simultaneously large fires occurred very near to Valencia city [1]: The first affecting Dos Aguas and surroundings (ca. 29000 ha burned), and the second in Andilla and surroundings (ca. 19000 ha burned). The fires burned under extreme fire whether conditions (strong drought, high temperature and strong dry wind [Foehn type wind]). 15 days after the fire, I visited area burned around Dos Aguas and took these pictures showing the postfire life activity; several species already started to resprout and pines were dispersing their seeds. In addition I saw several lizards, different birds and a fox, all in the middle of the recently burned area, quite far from the edge of the fire.

A. Chamaerops humilis (en: Mediterranean dwarf Palm, es: palmito, cat: margalló)

B. Resprout of Quercus coccifera (en: Kermes oak, es: coscoja, cat: garric, coscoll)

C. Resprout of Daphe gnidium (en: flax-leaved daphne, es: torvisco, cat: matapoll). The high intensity of the fire is clear from the thick remaining branch.

D. Post-fire seed dispersal of the serotinous cones of Pinus halepensis (en: Aleppo Pine , es: pino carrsco; cat: pi blanc).

 

[1] Incendios forestales en Valencia, Junio 2012, jgpausas.blogs.uv.es, 4/Julio/2012.

 

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]

Cork oak acorn production

January 20th, 2012 No comments

Cork oak (Quercus suber, from the western Mediterranean Basin[1]) is a weird oak. In most oak species, acorn maturation pattern is clear and fixed. In some species acorns mature in one year, in others acorn require two years for maturation. This trait is not fixed in Cork oak, some trees have annual acorns, some others have mainly biennial acorns, and some trees have both. This is why when we relate Cork acorn production with climatic variables the relation is very weak (explained variance < 8%), much weaker than for other oaks. However, after the trees being grouped according to their dominant acorn maturation pattern (annual or biennial), weather parameters account for 44% of the variability in acorn crops, with trees with annual acorns exhibiting mast fruiting in years with reduced spring frost and shorter summer droughts and trees with biennial acorns showing the opposite pattern [2]. Thus, conditions that negatively affect annual production could be beneficial for biennial production (and vice versa). The ability to modulate the acorn production pattern of a given year according to the environmental conditions could be regarded as an example of phenotypic plasticity for facing variable and uncertain climatic conditions, such as those in Mediterranean ecosystems. To what extent other oaks living under variable and stressful conditions behave similarly remains to be explored.

Figure: Recently debarked Cork oak and cork oak landscape in eastern Spain (foto: J. Cortina)

[1] 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]

[2] Pons, J. and J. G. Pausas. 2012. The coexistence of acorns with different maturation patterns explains acorn production variability in Cork oak. Oecologia [doipdf]

Other post on Cork oak:

  • Conservation of cork oak ecosystems, Mar 14th, 2011 [link]
  • Bark thickness: a world record?, Jan 3rd, 2011 [link]
  • Wine supporting biodiversity, Jan 5th, 2010 [link]
  • Cork Oak Woodlands on the Edge, Oct 14th, 2009 [link]

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]

Intraspecific plant variability and the spatial scale

September 24th, 2011 No comments

Variability is a fundamental characteristic of life and the raw material for natural selection, driving speciation and diversification processes. Traditional biogeographical theory would predict that plants in populations that are close each other (e.g., few km) should be more similar among them, than plants in distant populations (e.g., 100s or 1000s km). This is because biogeographical processes such as migration, glacial/interglacial climatic fluctuations and isolation should cause distant plant populations to diverge, and thus enhance intraspecific variability at large scales, while gene flow through close populations should reduce divergences. In contrast, in a recent paper we suggest that in fire prone-ecosystems, where fire may generate local heterogeneity, local variability in traits related to regeneration are quite large, overriding the variability at the larger scale [1]. Studying post-fire regeneration traits in Cistus salviifolius and Lavandula stoechas, in eastern Iberia (IB, Spain) and in south-western Anatolia (AN, Turkey), we found that the trait variability within each region is larger than between regions (separated by about 2600 km, with the sea in the middle). The traits studied were seed size, seed dormancy and germination stimulation by head and by smoke. The two studied species exhibited germination stimulated by the fire-related cues; and independently of the region, the different populations of each species had a similar pattern of response. That is, Cistus salviifolius was stimulated by heat and Lavandula stoechas was mainly stimulated by smoke, although heat also exhibited a positive effect on the latter species (see also [2] for more details on heat- and smoke- stimulated germination). All these results supports the prominent role of fire as an ecological and evolutionary process across the Mediterranean Basin, producing trait variability and shaping biodiversity [3, 4].

References

[1] Moreira B., Tavsanoglu Ç., Pausas J.G. 2012. Local vs regional intraspecific variability in regeneration traits. Oecologia 168: 671-677 [doi | pdf]

[2] 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.[pdf| doiblog]

[3] Pausas J.G. & Keeley J.E. 2009. A burning story: The role of fire in the history of life. BioScience 59: 593-601 [doi | pdfpost]

[4] 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 in Plant Science 16(8): 406-411. [doi | pdf | For managers]

Fire and alien plants

November 25th, 2010 No comments

In Mediterranean Basin ecosystems, fires are frequent, and post-fire regeneration is tipically based on native species, that is, there is no invasion of alien species after fire. However, this is not the case in the other Mediterranean climatic regions, where fire frequencies higher than their natural (historic) fire regime favors the invasion of alien plants. This is specially the case in the Mediterranean ecosystems of Chile, where recurrent fires play a little role on the evolutionary history. In Chile, fires appeared with the indigenous settlements, and increased exponentially since the time of the Spanish invasion (1536). This increase in fires, together with heavy grazing, has reduced the native matorral and increased the invasive species. In a recent paper, Gómez-Gonzalez et al. [1] show that fire open the window for the establishment of annual plants, and most of them are alien (from the Mediterranean Basin). The successful establishment of alien annuals was due to their ability to maintain rich seedbanks in burned areas and to the greater propagule arrival compared to native species (annuals or perennials). Thus the results demonstrate that fire is a relevant factor for the maintenance of alien-dominated grasslands in the Chilean matorral and highlight the importance of considering the interactive effect of seed rain and seedbank survival to understand plant invasions patterns in fire-prone ecosystems.

[1] Gómez-González S, Torres-Díaz C., Valencia G, Torres-Morales P, Cavieres L.A., and Pausas J.G (in press). Anthropogenic fires increase alien and native annual species in the Chilean coastal matorral. Diversity and Distributions 17: 58-67 [doi | pdf]

invasion-fumaria_sm
Figure: Chilean matorral recently burnt showing the invasion of Fumaria capreolata (flowering), and annual alien species original from Europe (Foto by S. Gómez-González).

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]).

Post-fire tree mortality, central Portugal

August 26th, 2010 No comments

In September 2003, a mixed forest of central Portugal (Tapada Nacional de Mafra) burned in a large crown fire. We surveyed the survival of more than 700 trees during 4 years postfire. The results are detailed in a recent paper by Catry et al. (2010, [1]) ; the table below provides a summary on the proportion of the trees that  (a) died, (b) survived but were top-killed (stem and crown mortality) and resprouted from the base, and (c) the stem survived, after 4 years postfire (for tree mortality, the value observed after the first year is given in brackets).

a) Tree mortality b) Stem mortality (basal resprouting) c) Stem survival
Castanea sativa (20) 83 0 17
Crataegus monogyna (0) 7 86 7
Fraxinus angustifolia (0) 0 15 85
Olea europaea sylvestris (0) 0 97 3
Pistacia lentiscus (0) 0 100 0
Quercus coccifera (0) 10 89 1
Quercus faginea (2) 14 75 11
Quercus suber (1) 1 0 99
Pinus pinaster (84) 95 0 5
Pinus pinea (77) 85 0 15

Most pines (P. pinaster and P. pinea) died and few, specially of P. pinea, were little affected by fire; there were a significant positive relationship between crown damage and tree mortality.
Most broadleaved trees survived the fire, and whether the stem survived or died (and resprouted from the base) were related to bark thickness and char height (i.e. fire severity). Castanea sativa showed the highest tree mortality, mostly due to post-resprouting mortality after the first year. Fraxinus angustifolia, Olea europaea and Pistacea lentiscus showed no mortality at all; most Olea and Pistacea individuals resprout from the base, while for Fraxinus the crown of most trees were unaffected. The low effect of fire in Fraxinus angustifolia is probably due to the topographic positions where this species occurs; in addition theses trees are quite tall and with relatively thick bark. Quercus coccifera and Q. faginea showed low mortality and most trees resprouted from the base. Quercus suber showed almost no mortality and almost all trees showed epicormic resprouting, due to their extremely thick and insulating bark [2, 3].

References

[1] 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]

[2] Pausas, J.G. 1997. Resprouting of Quercus suber in NE Spain after fire. J. Veg. Sci. 8: 703-706. [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] [Ch 1, the tree]

[Update] see: “To resprout ot not to resprout”, Jan 25th, 2012.

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