Aleppo Pine (Pinus Halepensis) Postfire Regeneration: the Role of Canopy and Soil Seed Banks

Abstract

Pinus halepensis (Aleppo pine), is the dominant tree of a large fraction (26%) of the Greek coniferous forests; this species is an endemic pine of the Mediterranean Rim and well adapted to fire. Its regeneration is accomplished exclusively through seeds, thus its soil and canopy seed banks are of paramount importance for postfire resilience. Cone opening and seed dispersal were investigated in unburned forests of Attica (Greece) and it was found that Pinus halepensis trees maintain a significant percentage of the yearly cone crop (40-80%) closed, thus creating a persistent, canopy seed bank. Full viability of enclosed seeds was maintained for at least three years in canopy storage; moreover, preliminary results concerning the viability of seeds enclosed within the cones for four to more than 50 years showed a gradual reduction of both final percentage and rate of germination. Nevertheless, cones of up to 20 years of age contained a considerable fraction of germinable seeds. On the other hand, Aleppo pine forms only a short-lived (transient) soil seed bank; this bank was particularly abundant after a fire, as a result of the fire-induced cone opening. The germinable seed portion, although quite important prior to the start of the rainy season, was rapidly depleted, and at the end of the rainy season it was virtually absent in both burned and unburned forests. It is therefore concluded that postfire Aleppo pine seedling recruitment takes place almost exclusively during the first year after the fire and depends upon the germination of seeds in a transient soil bank which is produced by the postfire dispersal of pine seeds stored in the canopy seed bank.

Understanding long-term post-fire regeneration of a fire-resistant pine species

“…In our field research, germination rate from released seeds was 2-18 %, a much lower value compared with germination rates measured under laboratory conditions (20-80 %) (Escudero et al 2002;Calvo et al 2013). However, this is a typical value for species with recalcitrant seeds in field conditions, which are viable only the first months after release, as is the case for P. halepensis (Daskalakou and Thanos 1996).…”

“…Circles represent outliers and asterisks extreme values. Similar letters indicate no significant differences according pair-wise PERMANOVA test (p<0.05) with 9999 permutations (Daskalakou and Thanos 1996;Skordilis and Thanos 1997;Tapias et al 2001). The release of Aleppo pine seeds during dry weather events (also called weak serotiny or xeriscence) is considered an advantage for the establishment in an ecological scenario where potential competitors have been suppressed (Espelta et al 2011;Nathan et al 1999).…”

Effects of climate, tree age, dominance and growth on δ15N in young pinewoods

“…), a 2.7 ha stand originated by natural regeneration after a wildfire that in August 1991 completely destroyed the original plantation of Pinus pinaster Aiton. In these circumstances, seedling recruitment takes place almost exclusively during the first year after the fire and depends upon the germination of seeds in a transient soil bank that is produced by the postfire dispersal of pine seeds stored in the canopy seed bank (see Daskalakou andThanos, 1996, andVega et al, 2008). Therefore, although originated from natural post-fire regeneration, the result is an even-aged stand.…”

Tree density and site quality influence on Pinus halepensis Mill. reproductive characteristics after large fires

“…Also, these results give an idea of the possible future development of pine stands. The reproductive characteristics selected were based on the measurement of variables commonly used in similar studies: the number of strobili and cone types [24]; cone weight and volume and seed number per cone [44]; and the number of sound seeds, viability and germination rates [12,43]. If a new fire occurred before the tree reached the reproductive phase, post-fire natural regeneration might be deficient [10,43] which produces important environmental impacts as risk of soil loss, loss of biodiversity, loss of carbon sink, etc.…”