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Post-burning regeneration of the Chaco seasonally dry forest: germination response of dominant species to experimental heat shock

Jaureguiberry, Pedro, Díaz, Sandra
Oecologia 2015 v.177 no.3 pp. 689-699
Mediterranean climate, drought, ecosystems, fires, forests, germination, graminoids, heat shock response, heat tolerance, heat treatment, photoperiod, plant communities, seed dispersal, seeds, Argentina, El Gran Chaco
Plant species of the Chaco seasonally dry forest of central Argentina have presumably been under a low evolutionary pressure to develop specialized fire-response traits, such as heat-stimulated germination. Nevertheless, other historical factors such as seasonal drought and/or endozoochorus dispersal could have led some species to develop heat-tolerant seeds. Therefore, heat-tolerant germination should be more common than heat-stimulated or heat-sensitive germination. To test this, we exposed seeds of 26 dominant species from the Chaco region to a broad range of experimental heat treatments and incubated them for 30 days at 25 °C and 12 h photoperiod. We then scored the percent germination and classified them as heat-stimulated, heat-tolerant or heat-sensitive based on their germination following heat treatments relative to control. Seventeen species showed heat-tolerant germination, including all native graminoids. Seven species showed heat-stimulated germination, under the less-intense heat treatments. Only two species showed heat-sensitive germination. Endozoochory had no influence on germination responses. We suggest that, unlike Mediterranean-climate ecosystems, fire was not a major evolutionary force in the development of Chaco forests, and our results provide greater understanding of the potential response of Chaco plant communities in the face of increasingly frequent fires.