Probability of germination after heat treatment of native Spanish pines

Abstract

Spanish pine forests exhibit a high degree of resilience to frequent wildfires. For this reason, they have been considered as active pyrophytes. However, the primary evidence of the fire response of some of the seven Spanish pines suggests that they are not real pyrophytes because germination enhancement has not been detected. In order to investigate the germination response of the Spanish pine seeds after heating, seeds were submitted to different treatments at varying temperatures (50-130 C) and exposure times (1-15 min) to simulate responses to different fire regimes and situations. The probability of germination after heating was mod- elled by means of multiple logistic regressions using temperature, time and their interaction as predictors. Very predictive models were found for all the pines, except for Pinus pinea. Seeds germinate readily without treatment, losing their viability within a short time and showing a slight protection from fire. The results suggest that, despite the fact that these pines all occur in fire-prone envi- ronments, their germination behaviour has clearly not evolved in relation to fire alone. Furthermore, seed behaviour is not related to the general syndromes described as typical of fire-evolved plants. Whereas most of the Mediterranean seeders base their efficient recruitment after wildfires on the presence of hard-coated seeds, most of the Mediterranean pines have attempted other strategies with some variants related to prolific seed production. Only P. pinea regeneration after wildfires depends on the existence of fire- resistant and hard-coated seeds. (© Inra/Elsevier, Paris.) heat treatments / Mediterranean pine forests / multiple logistic regression / seed germination / wildfires Rsum -Probabilit de germination des graines de pins d'origine espagnole aprs traitement par chauffage. Les pins espagnols montrent un haut degr de rsilience aux feux frquents. Pour cette raison, ils ont t considrs comme des pyrophytes actifs. Cependant, l'vidence premire de la rponse au feu de certaines des sept espces de pins espagnols suggre qu'elles ne sont pas de relles pyrophytes car aucune augmentation de germination n'a t observe. Afin de connatre la rponse la germination des graines aprs chauffage, des graines furent exposes diffrents traitements de gradients de temprature (50 C 130 C) et de dure (1 min 15 min) afin de simuler la rponse diffrents rgimes de situation de feu. La probabilit de germination aprs chauffage a t modlise au moyen de rgressions multiples logistiques utilisant la temprature, la dure d'exposition et leur interaction comme variables prdictives. De trs bons modles prdictifs ont t tablis pour tous les pins, except pour Pinus pinea. Les graines germent dj sans traitement, perdent rapidement leur capacit germinative et montrent une faible protection au feu. Les rsultats sugg- rent que, en dpit du fait que tous ces pins soient localiss dans un environnement propice l'incendie, il est clair que leur comportement germinatif n'a pas uniquement volu en relation avec les feux. En outre, le comportement des graines n'est pas reli au syndrome gnral dcrit comme typique de l'volution des plantes sous l'influence du feu. Alors que la plupart des semenciers mdi- terranens basent leur efficiente rgnration aprs passage du feu sur l'existence de graines tguments pais, la plupart des pins mditerranens ont tabli d'autres stratgies avec des variantes relies une production prolifique de graines. Aprs incendie, seule la rgnration de P. pinea dpend de l'existence de graines rsistantes au feu et avec des tguments pais. ( © Inra/Elsevier, Paris.) chauffage / forts de pins mditerranens / rgression multiple logistique / germination des graines / feu sauvage