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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.

 

Fire shapes savanna-forest mosaics in the Brazilian cerrado

May 14th, 2013 No comments

Cerrado is the name of a tropical fire-prone mosaic of savanna and forest in Brazil. In a recent paper [1], we showed that in cerrado landscapes, despite the existence of a great variety of community structure (from open savannas to closed forests; Figure below), there are two well-defined stable states of community function, each associated with contrasting levels of community closure (open and closed environments) and maintained by different fire regimes. Soil properties, phylogenetic and non-phylogenetic beta-diversities, and most of the plant functional traits presented a threshold pattern along the community closure gradient with coinciding breakpoints, providing strong evidence of a functional threshold along the forest-savanna gradient. Open environments consisted of communities growing on poor soil and dominated by short species with early investments in thick barks, low wood density and with thick and tough leaves (high toughness and low specific area). In contrast, closed communities grow in more fertile soils and include plants having the opposite functional attributes. Moreover, we found contrasting fire regimes on the two sides of the threshold, with open formations showing shorter fire intervals than closed formations and a switch from communities dominated by fire-resistant plants to communities dominated by shade tolerant species that compensate for their lack of fire resistance by efficiently closing the canopy (i.e., reducing flammability). Overall, these results are consistent with the theoretical model of fire-plant feedbacks as main drivers of the coexistence of two stable states, savanna and forest. In this context, we provide the first field-based evidence for a community-level threshold separating two vegetation states with distinct functional and phylogenetic characteristics and associated with different fire regimes.

Top: A woodland cerrado (cerrado sensu stricto) six months after a fire, with several top-killed trees and a developed layer of resprouting vegetation; and one of the sampled closed forests.
Middle: A dense woodland cerrado (cerrado denso); one example of a typical thick-barked species found in open communities (Anadenanthera peregrina (Benth.) Reis, Fabaceae); a transitional zone between dense savannas and forests.
Bottom: A typical open savanna at the early rainy season, with tall flammable grasses and small trees and shrubs.
Photo credits: V. Dantas, G. Sartori, V. Cadry, J.G. Pausas, F. Noronha, A. Favari. See [1].

References

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

 

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