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The Effects of Ash and Black Carbon (Biochar) on Germination of Different Tree Species


Forest fires generate large amounts of ash and biochar, or black carbon (BC), that cover the soil surface, interacting with the soil’s constituents and its seedbank. This study concerns reproductive ecology assessments supported by molecular characterisation to improve our understanding of the effects of fire and fire residues on the germination behaviour of 12 arboreal species with a wide geographic distribution. For this purpose, we analysed the effects of three ash and one BC concentration on the germination of Acacia dealbata Link, A. longifolia (Andrews) Willd., A. mearnsii De Wild., A. melanoxylon R. Br., Pinus nigra Arnold, P. pinaster Aiton, P. radiata D. Don, P. sylvestris L., Quercus ilex L., Q. pyrenaica Willd., Q. robur L., and Q. rubra L. Each tree species was exposed to ash and BC created from its foliage or twigs (except for Q. rubra, which was exposed to ash and BC of Ulex europaeus L.). We monitored germination percentage, the T50 parameter, and tracked the development of germination over time (up to 1 yr). The BC of A. dealbata, P. pinaster, and Q. robur was analysed by pyrolysis-gas chromatography-mass spectrometry (PY-GC-MS) to assess the molecular composition. In six species, ash inhibited the germination, while in another five species, germination was not affected by ash or by BC. In Q. rubra, ash and BC stimulated its germination. This stimulating effect of the BC on Q. rubra is likely to be related to the chemical composition of the ash and BC obtained from Ulex feedstock. The BC of U. europaeus has a very different molecular composition than the other BC samples analysed, which, together with other factors, probably allowed for its germination stimulating effects.


Los incendios forestales generan gran cantidad de ceniza y biocarbones o carbón negro (CN) que cubren la superficie del suelo, interaccionando con los constituyentes del suelo y con banco de semillas. Este estudio se centra en evaluar la ecología reproductiva apoyada en la caracterización molecular para implementar nuestro conocimiento de los efectos del fuego y sus productos en el comportamiento germinativo de 12 especies de árboles con amplia distribución geográfica. Para ello, analizamos el efecto de tres concentraciones de ceniza y una de CN sobre la germinación de Acacia dealbata Link, A. longifolia (Andrews) Willd., A. mearnsii De Wild., A. melanoxylon R. Br., Pinus nigra Arnold, P. pinaster Aiton, P. radiata D. Don, P. sylvestris L., Quercus ilex L., Q. pyrenaica Willd., Q. robur L. y Q. rubra L. Cada especie arbórea fue expuesta a ceniza y CN obtenido a partir de hojas y ramas finas de la propia especie (excepto Q. rubra que fue expuesta a ceniza y CN de Ulex europaeus L.). Calculamos el porcentaje de germinación, el T50 y la distribución de la germinación a lo largo del tiempo (hasta 1 año). El CN de A. dealbata, P. pinaster y Q. robur fue analizado por pirólisis-cromatografía de gases-espetrometría de masas (PI-CG-EM) para determinar su composición molecular. En seis especies, la ceniza inhibió la germinación mientras que en otras cinco especies la germinación no fue modificada ni por la ceniza ni por CN. En Q. rubra la ceniza y el CN estimularon su germinación. Este efecto estimulador del CN sobre Q. rubra parece estar relacionado con la composición química de la ceniza y el CN obtenido de Ulex. El CN de U. europaeus tiene una composición molecular muy diferente de las otras muestras de carbón analizadas, lo cual junto con otros factores, probablemente permitió sus efectos estimuladores.


Fire is and has been an important ecological and evolutionary factor in world ecosystems for millions of years, perhaps since terrestrial vegetation existed (Trabaud 1981, Pausas 2004). Nowadays, forest fires are a serious environmental problem with millions of hectares burnt every year, affecting many human beings, destroying ecosystems, and contributing to climate change (Pausas 2004). Wildfires can decrease or completely eliminate plant cover, thereby altering rainfall interception, evapotranspiration rates, and hydrological surface processes and cycles (Cerdà and Doerr 2008) through complex interactions that generally culminate into increased erosion rates. Moreover, severe burning can affect a wide range of soil properties including nutrient availability, pH, organic matter content, texture, and structure (Certini 2005).

Among the direct consequences of wildfires is the formation of ash and black carbon (BC) layers that (1) contribute to the modification of the aforementioned physical and chemical soil properties, and (2) alter germination behaviour (rate, time, etc.) of the seeds of many species (Reyes and Casal 1998). These seeds can be present in the soil’s pre-fire seed-bank or can originate from the seed rain after the fire. Kemball et al. (2010) demonstrated that the type of ash influences the germination percentage of tree species, and Solaiman et al. (2012) showed that the type and quantity of BC influences the germination rate.

The solid organic residue of incomplete combustion known as BC includes materials such as char, charcoal, soot, and pyrogenic graphite (Knicker 2011). Black C has recently found a new use in agronomy as biochar (e.g., Lehmann et al. 2006). BC can, but does not always, improve soil water retention capacity, increase the pH, enhance aggregate stability, reduce leaching, and generally increase soil productivity, while it also has a potential for climate change mitigation through C sequestration (Schmidt and Noack 2000, Masiello 2004, Jeffery et al. 2011). However, the effects of BC on germination and their relation to BC molecular composition are poorly understood. Therefore, laboratory studies on the alteration of seed behaviour in the presence of BC are of great interest.

Acacia, Pinus, and Quercus are plant genera that provide much forest cover and biomass in fire-prone ecosystems around the world. For the present study of the effects of ash and BC on seed germination parameters, we selected four species from each of these genera: Acacia dealbata Link, A. longifolia (Andrews) Willd., A. mearnsii De Wild., A. melanoxylon R. Br., Pinus nigra Arnold, P. pinaster Aiton, P. radiata D. Don, P. sylvestris L., Quercus ilex L., Q. pyrenaica Willd., Q. robur L., and Q. rubra L. Apart from their wide distribution, these species are very important from ecological, silvicultural, and cultural viewpoints. The four species of Acacia that were studied are native to different regions of Australia (López-González 2006), but have anthropogenically expanded worldwide through ornamental use and subsequent invasive potential. Also, A. mearnsii is one of the most dangerous invasive species in the world (Invasive Species Specialist Group 2014). Many species of Acacia generally have low natural germination rates that increase after a fire event (Mucunguzi and Oryem-Origa 1996, Arán et al. 2013). The genus Pinus is distributed mainly in the temperate regions of the Northern Hemisphere: P. nigra and P. pinaster are native to the Mediterranean Basin, P. radiata is native to three different areas of central-coastal California, and P. sylvestris forms extensive forests in Europe and Asia (Richardson and Rundel 1998). These four members of the genus Pinus, P. radiata in particular, have expanded significantly in timber plantations (Kral 1993, Lavery and Read in Richardson and Rundel 1998). The Pinus species usually have aerial seed banks that protect the seeds during a fire and are released afterwards (Reyes and Casal 2002). Thermal shock does not stimulate their germination (Reyes and Casal 1995).

The distribution of Quercus genera covers all of Europe, and Q. robur is a species that can be found forming extensive natural forests from the north of Norway to the south of Sicily, and from Ireland to the Balkan, Ural, and Caucasus mountains. Q. pyrenaica is a Mediterranean species with a reduced area of natural growth, extending through southern France, the Iberian Peninsula, northwest Morocco, and has also been cited in north Italy. The populations of Q. ilex are a dominant component of many sclerophyllous forests that at one time dominated vast areas of the Mediterranean region. The geographic distribution of this species is centered on the Mediterranean Basin (Castroviejo et al. 1999). Q. rubra is native to the eastern USA and Canada. It is currently grown in many regions of the world, mainly for timber production. In comparison with the genera of Acacia and Pinus, the Quercus species produce smaller amounts of seeds that are comparably large in size, and with higher natural germination rates (Reyes and Casal 2006). They do not contain aerial seed banks but seedling banks instead. Aerial parts of seedlings may be top-killed by fire, but can resprout if the root system is sufficiently developed. High temperatures do not enhance the germination of Quercus (Valbuena and Tárrega 1998) and damage the seedlings.

Soil humidity is one of the climatic variables with strong influence on the emergence and establishment of seedlings (Classen et al. 2010). During a fire, soil humidity is reduced, but the ash and BC layer reduces the evaporation afterwards. Despite the likely importance of ash and BC from wildfires on germination behaviour, there are few studies on the subject (González-Rabanal and Casal 1995; Reyes and Casal 1998, 2004; Kemball et al. 2006, 2010) and the results are highly variable. We undertook laboratory experiments using the above species incubated in ash and BC preparations.

The hypothesis is that the fire agents (ash and BC) will stimulate, inhibit and accelerate, or delay the germination behaviour of the studied species.


The biological material used in this study were seeds of A. dealbata, A. longifolia, A. mearnsii, A. melanoxylon, P. nigra, P. pinaster, P. radiata, P. sylvestris, Q. ilex, Q. pyrenaica, Q. robur, and Q. rubra. The seeds of Acacia and Quercus were handpicked in natural populations and in plantations of the northwest of the Iberian Peninsula during the seed dispersal season (Acacia in spring and Quercus in autumn). The seeds of Quercus were stored at 4 °C until the beginning of the experiments (between 1 and 2 months). Seeds from four Pinus species were obtained from different parts of the Iberian Peninsula through the seed collection service of DGCONA (Direction General de Conservación de la Naturaleza). We did not apply stratification because the seeds of the Spanish populations of these species do not require such treatment in order to germinate (Reyes and Casal 1995, Reyes and Casal 2006, Arán et al. 2013) and we did not scarify the seeds in order to focus on the effects of ash and BC.

The ash and BC were obtained by burning leaves and fine branches in a combustion stove for 20 minutes. When possible, we used ash and BC from their corresponding feedstocks, but in case such materials were not available, we selected shrub species from their understory, and we did not perform BC treatments in Pinus species (Table 1). Gorse (Ulex europaeus) was chosen as the substitute ash or a BC treatment as it is geographically widespread and especially abundant in the fire-prone shrublands and woodlands of northwest Spain. After the combustion reaction, the ash (between 0.4 mm and 1 mm diameter) and BC (>1 mm diameter) were separated by sieving.

Table 1 Applied treatments to each species and ash and BC (Black C) sources used.

The BC samples from selected species of each genus (Q. ilex, P. pinaster and A. dealbata, thought to be representative of their respective genera) and U. europaeus were analysed by pyrolysis-gas chromatography-mass spectrometry (PY-GC-MS) to assess their molecular properties, using an Agilent 6890 gas chromatograph, Agilent 5975 mass spectrometer (Agilent Technologies, Santa Clara, California, USA) and CDS Pyroprobe 5000 (CDS Analytical, Oxford, Pennsylvania, USA). The pyrolysis temperature was 750 °C for 10 seconds. Main peaks were quantified according to characteristic fragment ions. A detailed description of the technique and its application to BC is provided in Kaal et al. (2012), which includes a description of the gas chromatographic program used. Even though Pinus-derived BC was not studied here, we analysed BC of P. pinaster for the sake of completeness and future studies.

The treatments performed were: Control, Ash-Low, Ash-Medium, Ash-High, and BC. Five replicates of 25 seeds were used for each species and each treatment. Acacia and Pinus seeds were placed on double-thickness filter paper in 9 cm diameter Petri dishes, and Quercus seeds were placed on perlite in 12 cm × 20 cm trays. The filter paper and perlite do not interfere in the germination response. The amount of ash used in the different treatments was based on the quantities of ash per hectare measured by Soto et al. (1997) in a fire of moderate intensity: Ash-Low: 0.25 g (3.93 kg ha−1), Ash-Medium 0.50 g (7.86 kg ha−1), and Ash-High 1 g (15.72 kg ha−1). The ash and BC were placed in the trays and Petri dishes in which the seeds were deposited. The BC treatment was performed by incubating the Quercus seeds sown in 1.0 g BC per tray (41.5 g m−2 of BC), which is within the range observed for forest fires by Ohlson and Tryterud (2000), and Acacia and Pinus species in 0.26 g of BC per Petri dish, an adequate amount considering the size of the Petri dishes. Initially, 10 ml of distilled water was added to the Petri dishes, with additional water being applied periodically (at the same time as the determination of germination parameters) to keep the seeds moist (assuring that at least one-third of its surface was in contact with water). Germination was counted every Monday, Wednesday, and Friday during the germination period of each species. A seed was considered to have germinated when its radicle had extended beyond the teguments by at least 1 mm (Côme 1970). The experiments took place spanning a period of several years and some treatments were not applied to all species (Table 1). The data obtained were used to calculate the germination percentage, the T50 rate (the time required to reach 50 % of germination), and the distribution of germination time.

For statistical analysis, using SPSS 15.0 (IBM SPSS Statistics, Armonk, New York, USA), we used the SQRT [ACOS (germination percentage ÷ 100)] transformation on the percentage data. First, the species and treatment factors were analysed using two one-way ANOVAs: one for germination percentage data and the other for the T50 data. Significant interactions between these two fixed factors were observed in both ANOVAs, which implied that the main effects could not be interpreted (Underwood 1997, Quinn and Keough 2002). Then one-way ANOVAs were performed to analyse the effect of the “treatment” factor in each species separately. The level of significance (0.05) was adjusted following Benjamini and Yekutieli (2001) to 0.1625 to reduce the Type I error when several analyses are made to study the same hypotheses. In those analyses in which significant differences between the treatments were shown, the corresponding Duncan tests were performed to determine which treatments caused the differences detected. For two species (A. mearnsii and P. radiata), post hoc T50 tests were not undertaken since at least one treatment had less than two cases.


Molecular Composition of Black Carbon

All BC samples produced significant amounts of monocyclic (benzene, toluene, C2-benzenes, C3-benzenes) and polycyclic (indenes, naphthalenes, fluorene, anthracene, phenanthrene, biphenyl) aromatic hydrocarbons (MAHs and PAHs) (Figure 1). These compounds, together with the N-containing pyrolysis product benzonitrile, represent strongly charred material. The Quercus and Pinus BC pyrolysates consisted almost completely of these compounds (92 % and 87 % of total quantified peak area [TQPA], respectively). The Acacia BC produced, apart from the aforementioned MAHs, PAHs, and benzonitrile (63 % of TQPA), significant peaks of benzaldehyde (11 %) and levoglucosan (21 %). Considering the absence of other polysaccharide markers that would have been produced from intact cellulose, this levoglucosan probably existed as trapped volatiles in micropores. The Ulex BC produced only 36 % MAHs, PAHs, and benzonitrile combined, in addition to large amounts of benzaldehyde (45 %), benzyl alcohol (11 %), and benzoic acid (6 %). The extraordinarily large proportion of benzaldehyde probably originated from dehydration of the corresponding benzyl alcohol during pyrolysis. The benzene:toluene and naphthalene:C1-naphthalenes ratios (Kaal and Rumpel 2009) were much higher for the Quercus BC (5.4 and 54, respectively) than for the Acacia (0.7 and 4), Ulex (0.7 and 9) and Pinus (1.0 and 5.1). These ratios were considered indicative of the abundance of alkyl-based cross bridges between aromatic groups and therefore a reverse indication of the degree of aromatic polycondensation.

Figure 1

Total ion current chromatograms after pyrolysis-GC-MS of the black carbon samples analysed. Asterisks correspond to peaks from analytical contamination (column bleed).

Germination Percentage

The Control germination percentages varied widely between species (Figure 2). The ANOVA applied to the 12 species detected highly significant differences among species (P < 0.001) and among treatments (P < 0.001). In general, high germination rates, between 42 % and 97 %, were found for the species of the genera Pinus and Quercus, while low rates, between 2 % and 18 %, were found for the species of Acacia, except for A. melanoxylon, which reached 54 %. However, as the interaction between species and treatment also turned out to be significant (P < 0.001), we applied an additional ANOVA to the data of each species separately. Three different germination behaviours were obtained:

  1. 1)

    No significant differences among treatments were detected in A. mearnsii, A. melanoxylon, Q. ilex, Q. pyrenaica, and Q. robur;

  2. 2)

    Germination was significantly inhibited by the three ash treatments (P < 0.005) in A. dealbata and by the Ash-Medium and Ash-High treatments (P < 0.05) in A. longifolia. In the four species of pine, the ash treatment significantly inhibited (P < 0.001) germination and this effect was stronger with increasing ash concentration.

  3. 3)

    The only Quercus species that showed significant differences between treatments (P < 0.005) was Q. rubra. In Q. rubra, results were very different from those obtained with the other species, which may be related to the particular compositions of the Ulex-derived ash and BC: the treatments Ash-Medium and BC both stimulated germination, with BC increasing germination by 30 %.

Figure 2

Mean percentage germination (±SD) reached by each species with each treatment. BC = black carbon.

The period required to reach 50 % germination varied significantly among species (Figure 3). Each genus has a particular T50 pattern, with Pinus being the fastest to germinate followed by Acacia and, lastly, Quercus. With the control treatment, rates varied from 5 days to 10 days in the Pinus species studied, to 22 days to 70 days in the Acacia species, to 87 days to 112 days in the Quercus species. The ANOVA applied to the T50 data detected highly significant differences between species (P < 0.0001) and the interaction (species × treatment) was also significant (P < 0.005), which is indicative of differential responses to treatment for every species. Using the Duncan test, five groups of species were detected: (1) the four species of Pinus and A. mearnsii with the shortest average T50; (2) A. dealbata and A. longifolia with T50 values between 23 days and 27 days; (3) Q. ilex, Q. rubra, and A. melanoxylon between 47 days and 55 days; (4) Q. pyrenaica with 73 days; and (5) Q. robur with an average T50 of 102 days. Analysing each species separately, we only found significant differences in treatments in the T50 of A. dealbata (P < 0.001), A. melanoxylon (P < 0.005), and Q. ilex (P < 0.05). The most striking result is that the Ash-Medium and Ash-High treatments significantly accelerate germination of A. dealbata. In A. melanoxylon, the Ash-Low and Ash-Medium treatments slow down germination, and in Q. ilex, BC produces that same effect. In the other species, no significant differences were detected between control and ash or BC treatments.

Figure 3

T50 (in days) and SD reached by each species with each treatment. BC = black carbon.

Temporal Distribution of Germination

The temporal distribution of germination was different for the species studied, even though there were certain similarities among species of the same genus (Figure 4). Pinus species took between 10 days and 20 days to complete their germination, Acacia about three months, Q. rubra and Q. ilex about 5 months, and Q. pyrenaica and Q. robur approximately one year. The responses to ash and BC treatments were also different. In the Pinus genus, during the first days, Control germination exceeded that of the treatments. For Acacia, the effects of the treatments on germination became visible only after 8 days and were less intense. For Quercus, germination was high and prolonged over time. The four Quercus species tested with Ash-Medium and BC treatments gave higher germination rates than the Control treatment during virtually the whole period, even though at the end the germination rates levelled out in all species except in Q. rubra. This last result is probably related to the different ash and BC used on Q. rubra and not an inherent difference between Q. rubra seeds behaviour with respect to the other Quercus species.

Figure 4

Temporal distribution of germination for each species and their treatments. BC = black carbon.


From the molecular properties of the BC samples, the results suggested that thermal impact was strongest for the Quercus BC, followed by Pinus, Acacia, and finally Ulex. All BC samples should be considered as strongly charred specimens, well past the phase of transition chars according to the scheme of Keiluweit et al. (2010). In comparison with laboratory-produced BC thermosequences under anaerobic conditions, they would have formed at an equivalent temperature of 450 °C to 600 °C (Kaal et al. 2012), which is well within the range generally considered suitable for biogeochemically “stable” or “recalcitrant” BC production (IBI 2012). The gorse BC sample produced large amounts of benzaldehyde, benzyl alcohol, and benzoic acid, which have not been observed previously in BC pyrolysates, at least not in such high proportions, and they were not abundant in anaerobically produced laboratory BC from Ulex wood (Kaal et al. 2012), suggesting that they are a result of the specific formation conditions such as condensation of leaf products.

Obviously, the high variability in the Control germination rates is related to the reproductive strategies acquired by each genus, developed through evolution. In A. mearnsii, A. melanoxylon, Q. ilex, Q. pyrenaica, and Q. robur, the different treatments had no significant effects on germination behaviour. The species of the Quercus and Pinus genera produce seeds with soft coats, while the seeds of Acacia have hard coats on which temperature shock has a special role in germination by physically breaking the dormancy (Rivas et al. 2006, Aran et al. 2013). The species with soft seed coats tend to show high Control germination rates as compared to species with hard seeds coats. Usually, germination of hard seeds is stimulated by heat or other agents that produce scarification (Ferrandis et al. 1999, Kimura and Islam 2012) and this explains the low germination percentages in Acacia. A lack of germination response to ash treatment has also been documented for species such as Calluna vulgaris (L.) Hull, Erica umbellata L., or Salvia iodantha Fernald. (González-Rabanal and Casal 1995, Zuloaga-Aguilar et al. 2011). In A. dealbata, A. longifolia, and the four Pinus species, the ash treatments usually inhibited germination and this effect increased with increasing ash concentration. These results are consistent with those of Trabaud and Casal 1989, Reyes and Casal 2004, and Kemball et al. 2010. According to González-Rabanal and Casal (1995), the decrease of germination percentages can be related to the sensitivity of seeds to the high osmotic pressure induced by the ash.

For Q. rubra, the results were very different as ash and BC both stimulated germination behaviour, which is probably a consequence of the particular chemical composition of the gorse-derived ash and BC applied to this species. Firstly, the ash of U. europaeus, which has N-fixation nodules in its root system, has a much higher N content (12 g kg−1) than the 6 g kg−1 for pine species (Soto et al. 1997, Solla-Gullón et al. 2004). Light et al. (2005) and Downes et al. (2013) showed that N-rich ashes are stronger germination stimulating agents than N-poor analogues. For the gorse BC, on the other hand, the molecular properties showed that it had been subjected to the weakest thermal modification and produced remarkably high proportions of benzaldehyde, benzyl alcohol, and benzoic acid, probably of the same benzoic acid-based precursor. These substances may be responsible for inhibiting the development of fungi and bacteria (Tfouni and Toledo 2002, Drăcea et al. 2008). The seeds of Q. rubra germinate for almost five months and during this period they are often subjected to microbial attack from bacteria and fungi that would have been present on the seeds when they were picked in the field (even though they may also enter the system in the laboratory itself). Therefore, the particular nature of the gorse BC may have protected the Q. rubra seeds against this microbial attack, thereby enhancing its germination rate. On the contrary, the BC of the Quercus genus is devoid of benzaldehyde and benzyl alcohol, thereby not exerting such protection to the seeds of the other Quercus species studied. In the Mediterranean Basin, the number of species that are chemically stimulated by a fire agent (BC, ash, or smoke) is much smaller (Keeley and Baer-Keeley 1999, Reyes and Trabaud 2009), while physical stimulation (heat shock) is more common (Rivas et al. 2006, Moreira et al. 2010).

The T50 results are similar to those of other studies that found short germination rates in Pinus species (Neeman et al. 1993; Reyes and Casal 1995, 2001; Escudero et al. 1997; Álvarez et al. 2007), intermediate mean rates in Acacia and Quercus species (Li and Romane 1997, Valbuena and Tárrega 1998, Aref et al. 2011, Zuloaga-Aguilar et al. 2011, Arán et al. 2013), and very long rates in some Quercus species (Reyes and Casal 2006). Some ash treatments accelerate germination of A. dealbata significantly, whereas the most common response found was the non-modification of germination time (González-Rabanal and Casal 1995, Escudero et al. 1997, Reyes and Casal 1998).

In the Pinus genus, it is common to find short germination distribution periods as well (Escudero et al. 1997, Ganatsas and Tsakaldimi 2007). In the Acacia genus, germination distribution in response to treatments was delayed and less pronounced. Other studies with different species of the Acacia genus found both early (Aref et al. 2011) and medium germination (Zuloaga-Aguilar et al. 2011). In the Quercus genus, germination was high and prolonged over time, coinciding with the findings of Li and Romane (1997).

In a post-forest fire scenario, Pinus species would germinate quickly if sufficient water is available in the soil, but the inhibiting effect of ash on its germination will create few seedlings (Reyes et al. 2015). Acacia species initiate their germination rapidly and they maintain high germination rates over the first three months despite of the presence of ash or BC, and during this period the ash and BC may get substantially diluted or eliminated through runoff, thereby mitigating the inhibitive effect of ash and BC after these three months (Rumpel et al. 2009). The Quercus species, on the one hand, have such a long germination time that their seeds can take advantage of the time when environmental features are more advantageous for germination and, on the other hand, are less sensitive to physical and chemical conditions than other species. In Q. rubra, BC stimulates germination but it does not change its time distribution trend. The regeneration of plant populations after fire depends on many factors such as the wildfire season (Trabaud 1981), local climatic regimes, weather conditions following wildfire, and especially fire severity (Kemball et al. 2006). After severe fire events, the ash quantity on the soil may be very small and then the inhibitive effects of ash on germination will be reduced.


The twelve tree species studied show different responses to the fire agents (ash and BC), both in their germination percentages and their times. In the species studied of the Acacia and Pinus genera, ash and BC either do not modify germination, or they inhibit it. In three species of Quercus, none of the agents modify germination and, in turn, both stimulate it in Q. rubra. The U. europaeus BC sample has a particular molecular composition producing abundant benzoic acid and benzyl alcohol upon pyrolysis, contrary to the other BC samples analysed. Its stimulating effect on the germination of Q. rubra seeds may be related to these components.

More studies are needed to give further insight into the causes of the differential germination response of these species to ash and BC generated by forest fires. Even though this study was focused on twelve important forest ecosystem taxa, studies on the different effects of ash and BC in silvicultural and agricultural contexts involving BC amendments are urgently needed. Finally, the results suggest that multidisciplinary attempts are fundamental to unravel the complexity of the interactions between ash, BC, and seed germination behaviour in fire-affected areas.

Literature Cited

  1. Álvarez, R., L. Valbuena, and L. Calvo. 2007. Effect of high temperatures on seed germination and seedling survival in three pine species (Pinus pinaster, P. tisylvestris and P. nigra). International Journal of Wildland Fire 16: 63–70. doi: 10.1071/WF06001

    Article  Google Scholar 

  2. Aran, D., J. García-Duro., O. Reyes, and M. Casal. 2013. Fire and invasive species: modifications in the germination potential of Acacia melanoxylon, Conyza canadensis and Eucalyptus globulus. Forest Ecology and Management 302: 7–13. doi: 10.1016/j.foreco.2013.02.030

    Article  Google Scholar 

  3. Aref, I.M., H.A.E. Hashim, T.A. Shahrani, and A.I. Mohamed. 2011. Effects of seed pretreatment and seed source on germination of five Acacia spp. African Journal of Biotechnology 10(71): 15901–15910. doi: 10.5897/AJB11.1763

    Article  Google Scholar 

  4. Benjamini, Y., and D. Yekutieli. 2001. The control of false discovery rate under dependency. Annals of Statistics 29: 1165–1188. doi: 10.1214/aos/1013699998

    Article  Google Scholar 

  5. Castroviejo, S., S. Talavera, C. Aedo., C. Romero-Zarco, L. Sáez, F.J. Salgueiro, and M. Velayos, editors. 1999. Flora Ibérica 3. Real Jardín Botánico, Consejo Superior Investigaciones Cientificas, Madrid, Spain. [In Spanish.]

    Google Scholar 

  6. Cerdá, A., and S. Doerr. 2008. The effect of ash and needle cover on surface runoff and erosion in the immediate post-fire period. Catena 74: 256–263. doi: 10.1016/j.catena.2008.03.010

    Article  Google Scholar 

  7. Certini, G. 2005. Effects of fire on properties of forest soils: a review. Oecology 143: 1–10. doi: 10.1007/s00442-004-1788-8

    Article  Google Scholar 

  8. Classen, A.T., R.J. Norby, C.E. Campany, K.E. Sides, and J.F. Weltzin. 2010. Climate change alters seedling emergence and establishment in an old-field ecosystem. PLoS ONE 5(10): e13476. doi: 10.1371/journal.pone.0013476

    Article  PubMed  PubMed Central  CAS  Google Scholar 

  9. Côme, D. 1970. Les obstacles à la germination. Masson, Paris, France. [In French.]

    Google Scholar 

  10. Downes, K.S., M.E. Light, M. Posta, L. Kohout, and J. van Staden. 2013. Comparison of germination responses of Anigozanthos flavidus (Haemodoraceae), Gyrostemon racemiger and Gyrostemon ramulosus (Gyrostemonaceae) to smoke-water and the smoke-derived compounds karrikinolide (KAR1) and glyceronitrile. Annals of Botany 111: 489–497. doi: 10.1093/aob/mcs300

    Article  PubMed  PubMed Central  CAS  Google Scholar 

  11. Drăcea, O., C. Larion, M.C. Chifiriuc, I. Raut, C. Limban, G.M. Niţulescu, C.D. Bădiceanu, and A.M. Israil. 2008. New thioureides of 2-(4-methylphenoxymethyl) benzoic acid with antimicrobial activity. Roum Arch Microbiol Immunol 67(3–4): 92–97.

    PubMed  Google Scholar 

  12. Escudero, A., S. Barrero, and J.M. Pita. 1997. Effects of high temperatures and ash on seed germination of two Iberian pines (Pinus nigra ssp. salzmannii, P. sylvestris var. iberica). Annals of Forest Science 54: 553–562. doi: 10.1051/forest:19970605

    Article  Google Scholar 

  13. Ferrandis, P., J.M. Herránz, and J.J. Martínez-Sánchez. 1999. Effect of fire on hard-coated Cistaceae seed banks and its influence on techniques for quantifying seed banks. Plant Ecology 144: 103–114. doi: 10.1023/A:1009816309061

    Article  Google Scholar 

  14. Ganatsas, P.P., and M.N. Tsakaldimi. 2007. Effect of light conditions and salinity on germination behaviour and early growth of umbrella pine (Pinus pinea L.) seed. Journal of Horticulture Science and Biotechnology 82(4): 605–610.

    Article  Google Scholar 

  15. González-Rabanal, F., and M. Casal. 1995. Effect of high temperatures and ash on germination of ten species from gorse shrubland. Vegetatio 116: 123–131. doi: 10.1007/BF00045303

    Article  Google Scholar 

  16. IBI [International Biochar Initiative]. 2012. Standardized product definition and product testing guidelines for biochar that is used in soil. <>. Accessed 10 June 2012.

  17. Invasive Species Specialist Group. 2014. Global invasive species database: 100 of the world’s worst invasive alien species. <>. Accessed 14 October 2014.

  18. Jeffery, S., F.G.A. Verheijen, M. van der Velde, and A.C. Bastos. 2011. A quantitative review of the effects of biochar application to soils on crop productivity using meta-analysis. Agricultural Ecosystems and Environment 144: 175–187. doi: 10.1016/j.agee.2011.08.015

    Article  Google Scholar 

  19. Kaal, J., and C. Rumpel. 2009. Can pyrolysis-GC/MS be used to estimate the degree of thermal alteration of black carbon? Organic Geochemistry 40: 1179–1187. doi: 10.1016/j.orggeochem.2009.09.002

    Article  CAS  Google Scholar 

  20. Kaal, J., A. Martínez Cortizas, O. Reyes, and M. Soliño. 2012. Molecular characterization of Ulex europaeus biochar obtained from laboratory heat treatment experiments—a pyrolysis-GC/MS study. Journal of Analytical and Applied Pyrolysis 95: 205–212. doi: 10.1016/j.jaap.2012.02.008

    Article  CAS  Google Scholar 

  21. Keeley, J.E., and M. Baer-Keeley. 1999. Role of charred wood, heat-shock and light in germination of postfire phrygana species from the eastern Mediterranean Basin. Israel Journal of Plant Science 47: 563–576. doi: 10.1080/07929978.1999.10676746

    Article  Google Scholar 

  22. Keiluweit, M., P.S. Nico, M.G. Johnson, and M. Kleber. 2010. Dynamic molecular structure of plant biomass-derived black carbon compounds (biochar). Environmental Science and Technology 44: 1247–1253. doi: 10.1021/es9031419

    Article  PubMed  CAS  Google Scholar 

  23. Kemball, K.J., G.G. Wang, and R.A. Westwood. 2006. Are mineral soils exposed by severe wildfire better seedbeds for conifer regeneration? Canadian Journal of Forest Research 36: 1943–1950. doi: 10.1139/x06-073

    Article  CAS  Google Scholar 

  24. Kemball, K.J., R.A. Westwood, and G.G. Wang. 2010. Laboratory assessment of the effect of forest floor ash on conifer regeneration. Canadian Journal of Forest Research 40: 822–826. doi: 10.1139/X10-027

    Article  Google Scholar 

  25. Kimura, E., and M.A. Islam. 2012. Seed scarification methods and their use in forage legumes. Research Journal of Seed Science 5: 38–50. doi: 10.3923/rjss.2012.38.50

    Article  Google Scholar 

  26. Knicker, H. 2011. Pyrogenic organic matter in soil: its origin and occurrence, its chemistry and survival in soil environments. Quaternary International 243: 251–263 doi: 10.1016/j.quaint.2011.02.037

    Article  Google Scholar 

  27. Kral, R. 1993. Pinus. Pages 373–398 in: Flora of North America Editorial Committee, editor. Flora of North America: North of Mexico, Volume 2. Oxford University Press, England, United Kingdom.

    Google Scholar 

  28. Lehmann, J., J. Gaunt, and M. Rondon. 2006. Biochar-char sequestration in terrestrial ecosystems—a review. Mitigation and Adaptation Strategies for Global Change 11: 403–427. doi: 10.1007/s11027-005-9006-5

    Article  Google Scholar 

  29. Li, J., and F.J. Romane. 1997. Effects of germination inhibition on the dynamics of Quercus ilex stands. Journal of Vegetation Science 8: 287–294. doi: 10.2307/3237358

    Article  Google Scholar 

  30. Light, M.E., B.V. Burger, and J. van Staden. 2005. Formation of a seed germination promoter from carbohydrates and amino acids. Journal of Agricultural Food Chemistry 53: 5936–5942. doi: 10.1021/jf050710u

    Article  PubMed  CAS  Google Scholar 

  31. López-González, G. 2006. Los árboles y arbustos de la Península Ibérica e Islas Baleares. Vol. 2. Ediciones Mundi-Prensa, Madrid, Spain. [In Spanish.].

    Google Scholar 

  32. Masiello, C.A. 2004. New directions in black carbon organic geochemistry. Marine Chemistry 92: 201–213. doi: 10.1016/j.marchem.2004.06.043

    Article  CAS  Google Scholar 

  33. Moreira, B., J. Tormo, E. Estrelles, and J.G. Pausas. 2010. Disentangling the role of heat and smoke as germination cues in Mediterranean Basin flora. Annals of Botany 105: 627–635. doi: 10.1093/aob/mcq017

    Article  PubMed  PubMed Central  CAS  Google Scholar 

  34. Mucunguzi, P., and H. Oryem-Origa. 1996. Effects of heat and fire on the germination of Acacia sieberiana D.C. and Acacia gerrardii Benth. in Uganda. Journal of Tropical Ecology 12: 1–10. doi: 10.1017/S0266467400009275

    Article  Google Scholar 

  35. Neéman, G., I. Meir, and R. Neéman. 1993. The effect of ash on the germination and early growth of shoots and roots of Pinus, Cistus and annuals. Seed Science and Technology 21: 339–349.

    Google Scholar 

  36. Ohlson, M., and E. Tryterud. 2000. Interpretation of the charcoal record in forest soils: forest fires and their production and deposition of macroscopic charcoal. Holocene 10: 519–525. doi: 10.1191/095968300667442551

    Article  Google Scholar 

  37. Pausas, J.G. 2004. Changes in fire and climate in the eastern Iberian Peninsula (Mediterranean Basin). Climate Change 63: 337–350. doi: 10.1023/B:CLIM.0000018508.94901.9c

    Article  Google Scholar 

  38. Quinn G.P., and M.J. Keough. 2002. Experimental design and data analysis for biologists. Cambridge University Press, England, United Kingdom. doi: 10.1017/CBO9780511806384

    Book  Google Scholar 

  39. Reyes, O., and M. Casal. 1995. Germination behaviour of 3 species of the genus Pinus in relation to high temperatures suffered during forest fires. Annals of Forest Science 52: 385–392. doi: 10.1051/forest:19950408

    Article  Google Scholar 

  40. Reyes, O., and M. Casal. 1998. Germination of Pinus pinaster, P. tiradiata and Eucalyptus globulus in relation to the amount of ash produced in forest fires. Annals of Forest Science 55: 837–845. doi: 10.1051/forest:19980707

    Article  Google Scholar 

  41. Reyes, O., and M. Casal. 2001. The influence of seed age on germinative response to the effects of fire in Pinus pinaster, Pinus radiata and Eucalyptus globulus. Annals of Forest Science 58: 439–447. doi: 10.1051/forest:2001137

    Article  Google Scholar 

  42. Reyes, O., and M. Casal. 2002. Effect of high temperatures on cone opening and on the release and viability of Pinus pinaster and P. tiradiata seeds in NW Spain. Annals of Forest Science 59: 327–334. doi: 10.1051/forest:2002028

    Article  Google Scholar 

  43. Reyes, O., and M. Casal. 2004. Effects of forest fire ash on germination and early growth of four Pinus species. Plant Ecology 175: 81–89. doi: 10.1023/B:VEGE.0000048089.25497.0c

    Article  Google Scholar 

  44. Reyes, O., and M. Casal. 2006. Seed germination of Quercus robur, Q. tipyrenaica and Q. ilex and the effects of smoke, heat, ash and charcoal. Annals of Forest Science 63: 205–212. doi: 10.1051/forest:2005112

    Article  Google Scholar 

  45. Reyes, O., and L. Trabaud. 2009. Germination behaviour of 14 Mediterranean species in relation to fire factors: smoke and heat. Plant Ecology 202: 113–121. doi: 10.1007/s11258-008-9532-9

    Article  Google Scholar 

  46. Reyes, O., J. García-Duro, and J. Salgado. 2015. Fire affects soil organic matter and the emergence of Pinus radiata seedlings. Annals of Forest Science 72: 267–275. doi: 10.1007/s13595-014-0427-8

    Article  Google Scholar 

  47. Richardson, D.M., and P.W. Rundel. 1998. Ecology and biogeography of Pinus: an introduction. Pages 3–48 in: D.M. Richardson, editor. Ecology and Biogeography of Pinus. Cambridge University Press, England, United Kingdom.

    Google Scholar 

  48. Rivas, M., O. Reyes, and M. Casal. 2006. Influence of heat and smoke treatments on the germination of six leguminous shrubby species. International Journal of Wildland Fire 15: 73–80. doi: 10.1071/WF05008

    Article  Google Scholar 

  49. Rumpel, C., A. Ba, F. Darboux, V. Chaplot, and O. Planchon. 2009. Erosion budget and process selectivity of black carbon at meter scale. Geoderma 154: 131–137. doi: 10.1016/j.geoderma.2009.10.006

    Article  CAS  Google Scholar 

  50. Schmidt, M.W.I., and A.G. Noack. 2000. Black carbon in soils and sediments: analysis, distribution, implications, and current challenges. Global Biogeochemical Cycles 14: 777–793. doi: 10.1029/1999GB001208

    Article  CAS  Google Scholar 

  51. Solaiman, Z.M., D.V. Murphy, and L.K. Abbott. 2012. Biochars influence seed germination and early growth of seedlings. Plant and Soil 353: 273–287. doi: 10.1007/s11104-011-1031-4

    Article  CAS  Google Scholar 

  52. Solla-Gullón, F., M.P. Taboada, R. Rodríguez-Soalleiro, and A. Merino. 2004. Respuesta inicial del aporte de cenizas de biomasa arbórea en el estado nutricional de una plantación joven de Pinus radiata D. tiDon. Investigaciones Agrarias: Sistemas y Recursos Forestales 13(2): 281–293. [In Spanish.]

    Google Scholar 

  53. Soto, B., R. Basanta, and F. Diaz-Fierros. 1997. Effects of burning on nutrient balance in an area of gorse Ulex europaeus L. scrub. The Science of Total Environment 204: 271–281. doi: 10.1016/S0048-9697(97)00185-X

    Article  Google Scholar 

  54. Tfouni, S.A.V., and M.C.F. Toledo. 2002. Determination of benzoic and sorbic acids in Brazilian food. Food Control 13(2): 117–123. doi: 10.1016/S0956-7135(01)00084-6

    Article  CAS  Google Scholar 

  55. Trabaud, L. 1981. Man and fire: impacts on Mediterranean vegetation. Pages 523–537 in: F. di Castri, D.W. Goodall, and R.L. Specht, editors. Mediterranean-type shrublands. Elsevier, Amsterdam, The Netherlands.

    Google Scholar 

  56. Trabaud, L., and M. Casal. 1989. Réponses des semences de Rosmarinus officinalis à différents traitements simulant une action de feu. Acta Oecologica-Oecologia Applications 10: 355–366. [In French.]

    Google Scholar 

  57. Underwood, A.J. 1997. Ecological experiments: their logical design and interpretation using analysis of variance. Cambridge University Press, England, United Kingdom.

    Google Scholar 

  58. Valbuena, L., and R. Tárrega. 1998. The influence of heat and mechanical scarification on the germination capacity of Quercus pyrenaica seeds. New Forestry 16: 177–183. doi: 10.1023/A:1006578802038

    Article  Google Scholar 

  59. Zuloaga-Aguilar, S., O. Briones, and A. Orozco-Segovia. 2011. Seed germination of montane forest species in response to ash smoke and heat shock in México. Acta Oecologica 37: 256–262. doi: 10.1016/j.actao.2011.02.009

    Article  Google Scholar 

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This study was carried out within the Project 10MDS200007PR, financed by the Xunta de Galicia; the Project AGL2013-48189-C2-2-R, financed by the Ministerio de Economía y Competitividad, Spain; and FEDER. The authors would like to thank F. Díaz-Fierros and M. Casal for their valuable suggestions, and X. Mouriño for his help locating A. mearnsii.

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Correspondence to Otilia Reyes.

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Reyes, O., Kaal, J., Arán, D. et al. The Effects of Ash and Black Carbon (Biochar) on Germination of Different Tree Species. fire ecol 11, 119–133 (2015).

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  • Acacia
  • ash
  • black carbon
  • germination
  • Pinus
  • Quercus