Post-fire regeneration patterns of Pinus nigra in a recently burned area in Mount Taygetos, Southern Greece: The role of unburned forest patches
Introduction
Pinus is one of the oldest genera of the plant kingdom. Today, more than 100 species belong to Pinus, making it the richest gymnosperm genus in the northern hemisphere (Mirov, 1967, Vidakovic, 1991, Scaltsoyiannes et al., 2009). Along the Mediterranean Basin, nine species of the genus Pinus can be found, representing an important vegetation component that covers more than 13 million hectares across a broad gradient of altitudes (Barbéro et al., 1998). It has been suggested that the periodic occurrence of fire has favored the expansion of pines (Quézel, 1980, Thanos and Marcou, 1991, Agee, 1998, Richardson and Rundel, 1998). In order to understand the current pattern of pine distribution their evolution in relation to fire must be taken into account (Keeley, 2012).
Although fire is thought to be an important ecological factor associated with pine-dominated forest ecosystems, not all pine forests share the same fire regime (Agee, 1998). According to Keeley (2012) pines can be classified into two main groups. The first group comprises species that are distributed in environments where fire is not a regular environmental feature and are characterized as fire-avoiders. The second and largest group includes fire-adapted species commonly found in fire-prone landscapes. Nevertheless, no species can be considered as fire-adapted in general; plant species are adapted to a particular fire regime (Pausas and Keeley, 2009).
Pinus nigra J.F Arnold (black pine) is a fire-resistant tree species provided that it is exposed to low intensity surface fires (Fulé et al., 2008, Touchan et al., 2012). Bark thickness is considered the main trait related to the species’ resistance to fire (Tapias et al., 2004), although post-fire survival is also influenced by tree age and the level of crown and stem damage (Ordóñez et al., 2006, Fernandes et al., 2012). P. nigra appears to endure fire return intervals (FRIs) ranging from 30 to 750 years (Leys et al., 2014), although it can withstand FRIs shorter than 30 years (Christopoulou et al., 2013).
On the other hand, during the recent decades there is an increasing trend of high severity crown fires occurring in black pine forests in the western (Ordóñez et al., 2005, Ordóñez et al., 2006, Fernandes et al., 2008) and eastern part of southern Europe (Kakouros and Chrysopolitou, 2010, Christopoulou et al., 2013). This trend may pose a threat to the existence and conservation status of black pine, especially under scenarios of global warming, which are projected to profoundly affect wildfire frequency and intensity (Moriondo et al., 2006, Giannakopoulos et al., 2009, Fyllas and Troumbis, 2009).
P. nigra does not maintain a canopy seed bank (Habrouk et al., 1999, Ordóñez et al., 2005), so its regeneration after crown fires relies on surviving local seed sources, which may be rare or nonexistent (Trabaud and Campant, 1991, Retana et al., 2002, Ordóñez et al., 2004, Ordóñez, 2004, Pausas et al., 2008). The natural post-fire recovery of burned stands depends almost exclusively on long-distance seed dispersal from neighboring unburned patches or sparse surviving individuals of the species (Retana et al., 2002, Ordóñez and Retana, 2004, Ordóñez et al., 2005, Ordóñez et al., 2006, Arianoutsou et al., 2010). Nevertheless, the dispersion of seeds to the burned area does not necessarily imply an adequate recruitment (Retana et al., 2012). A number of abiotic and biotic factors, such as vegetation and soil cover (Trabaud and Campant, 1991), intra- and inter- specific competition (Trabaud and Campant, 1991, Ordóñez et al., 2006) and post-dispersal seed predation (Ordóñez and Retana, 2004, Kerr et al., 2008) can strongly mediate black pine post-fire recruitment.
The aim of the current study was to investigate the post-fire regeneration patterns of P. nigra in the Taygetos mountain range at Southern Greece, which was heavily affected by the 2007 high severity crown fire, which was one of the most extreme natural disasters in the country’s recent history (Koutsias et al., 2012). The specific objectives of the study were: (1) to examine the role of unburned stands in the re-establishment of P. nigra in burned areas through seed dispersal and (2) to explore the effects of environmental variables and microhabitat characteristics upon black pine seedlings and saplings densities. The results of this study are expected to support restoration and fire management practices in P. nigra forests.
Section snippets
Study area
Mount Taygetos is the highest (2407 m) and longest mountain range of the Peloponnese, Southern Greece. Coniferous forests cover the altitudinal zone between 800 and 1600–1700 m and are dominated by P. nigra J.F. Arnold and Abies cephalonica Loudon (Greek fir). The main geological substrates are limestone and phyllite-quartzite (Bornovas and Rondogianni-Tsiambaou, 1983). A meteorological station situated near the study area (Touristiko Taygetou 1310 m above sea level), reported a mean annual
Size and structure of Pinus nigra regenerating population
A total number of 2952 black pine seedlings and saplings were recorded in all study sites. At the edges of unburned patches mean pine density was 0.406 individuals/m2 (4060 individuals/ha), with median density varying from 0.000 to 0.500 individuals/m2. Mean regeneration density was higher near the unburned patch (d < 10 m) compared to all other distance classes (Table 2; Fig 2a). Five years after fire, the regeneration in the completely burned areas remained practically nil, with a mean density
Discussion
Fire is a natural component of Black pine forest ecosystems (Leys et al., 2014). P. nigra is a fire-resistant tree species provided that it is exposed to low intensity surface fires (Fulé et al., 2008, Touchan et al., 2012), even if they are recurrently occurring (Christopoulou et al., 2013). Nonetheless, in cases of large and severe fires its post-fire recovery depends mainly on seed availability as the species is not serotinous (Habrouk et al., 1999, Ordóñez et al., 2005, Dodson and Root, 2013
Implications for management
The results obtained can provide important guidelines for management of black pine forests as well as for other forest ecosystems with similar ecological characteristics, by taking into account the expected future increase in fire activity. In cases of extended crown fires, spatial identification of low regeneration/vulnerable areas would be of key importance for allocating restoration practices. Removing dead trees and coarse woody debris from the landscape should be avoided as apart from soil
Acknowledgments
This research was financed by the European project FUME (Grant Agreement No. 7243888). We would like to thank Dr Dimitris Kazanis for his contribution in sites selection and Dr Magdalini Pleniou for her help in the satellite image analysis. We are also grateful to Ioannis Karamitsos for providing the climate data from Mt Taygetos (http://www.weather-messinia.gr/index.html). Additional thanks to George Seintis for his help in field work. Finally, the authors would like to express their thanks to
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