Ecological Engineering 71 (2014) 80–86

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Mulch application as post-fire rehabilitation treatment does not affect vegetation recovery in ecosystems dominated by obligate seeders Víctor M. Santana a,b,∗ , Josu G. Alday b , M. Jaime Baeza a a Fundación de la Generalitat Valenciana Centro de Estudios Ambientales del Mediterráneo (CEAM), Parque Tecnológico Paterna. C/Charles Darwin, 14, E-46980 Paterna, Valencia, Spain1 b School of Environmental Sciences, University of Liverpool, Liverpool L69 3GP, United Kingdom

a r t i c l e

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Article history: Received 12 November 2013 Received in revised form 7 May 2014 Accepted 11 July 2014 Keywords: Mediterranean Basin Seedling emergence Seedling establishment Seedling survival Soil erosion Woody chips

a b s t r a c t Mulching treatments have been successfully tested for reducing soil erosion in the first years after fire. However, little is known about their possible negative effect on vegetation regeneration. The aim of this work is to assess the effect of mulch application (woody chips) on the regeneration of Mediterranean Basin ecosystems dominated by obligate seeders. For this purpose, two different mulch ratios (1 and 2 kg m−2 ) were applied immediately after fire as a post-fire rehabilitation treatment. Soil micro-environmental modifications were tested by monitoring soil temperature and moisture. Vegetation regeneration was assessed by monitoring seedling emergence, seedling establishment, species richness and plant cover during the following three years. Mulch application modified micro-environmental conditions as soil temperature lowered and soil moisture increased. However, no significant effects were found in the final establishment of individuals, plant cover and species richness. In addition, application ratios of 2 kg m−2 increased the seedling survival of obligate seeders species. Mulch application reduced only seedling emergence in one species (Cistus albidus) in the 2 kg m−2 treatment, but did not affect final establishment. The lack of negative effects on vegetation regeneration is of paramount importance in the ecosystems studied as all plant individuals die and the root system protecting the soil must be completely restored by new individuals. Rapid vegetation establishment and growth will help reduce the “window of disturbance” for soil erosion, which occurs until vegetation is recovered. In conclusion, woody chip applications may be a suitable post-fire rehabilitation treatment as they have no negative effects on vegetation regeneration. © 2014 Published by Elsevier B.V.

1. Introduction Wild fire is a major agent of land degradation in the Mediterranean Basin (Shakesby, 2011). Apart from destroying vegetation cover and producing heat-induced changes in soil properties (e.g., soil water repellence, aggregate stability, organic matter losses; Certini, 2005), wild fire is characterised by a drastic increase of runoff and soil erosion (Shakesby and Doerr, 2006; Varela et al., 2010). Removal of the protective litter and vegetation layers from the soil surface by fire produces a ‘window of disturbance’, which allows sediment transportations in later rainfall (Prosser and

∗ Corresponding author at: The University of Liverpool, School of Environmental Sciences, Nicholson Building, Liverpool, L69 3GP, United Kingdom. Tel.: +44 01517955172. E-mail address: [email protected] (V.M. Santana). 1 http://www.ceam.es. http://dx.doi.org/10.1016/j.ecoleng.2014.07.037 0925-8574/© 2014 Published by Elsevier B.V.

Williams, 1998). This erosion normally peaks during the first rainstorms and declines over time as vegetation regenerates (Mayor et al., 2007). In the last few decades, socio-economical and climatic causes have led to a significant increase in the number of fires and areas burned in the Mediterranean Basin (Pausas and Fernández˜ Munoz, 2012). Consequently, there is growing concern about the possible triggering of soil degradation processes after wild fires (Pausas et al., 2008), especially if we consider that wild fires in the Mediterranean Basin occur mainly in summer and that these areas are affected yearly by torrential rainfall in late summer and ˜ autumn (de Luís et al., 2005; Penarrocha et al., 2002). The application of mulch as a rehabilitation treatment against runoff and soil erosion after fires has been widely tested in Mediterranean areas in recent years (Calvo et al., 2012). This treatment consists in spreading organic material (e.g., wheat straw or wood chips) over soil immediately after a fire and just before the first autumn rainfall. Generally, this application has obtained satisfactory results, including significant reductions in runoff and soil

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erosion (Badia and Marti, 2000; Bautista et al., 1996; Fernández et al., 2011; Groen and Woods, 2008; Wagenbrenner et al., 2006), although highly variable reductions can be obtained depending on the mulch type and the application ratio (Fernández et al., 2011; Prats et al., 2012). Nevertheless, studies about mulching effects on vegetation regeneration are still scarce and remain controversial (Dodson and Peterson, 2010). Mulch application can modify the micro-environmental conditions of treated sites and influence plant regeneration. For example, mulch can benefit plant establishment and growth at water-stressed sites by reducing soil temperatures and retaining soil moisture (Badia and Marti, 2000; Bautista et al., 1996; Robichaud et al., 2000). In contrast, this treatment can act as a physical barrier for plant establishment, especially when accumulated in deep piles (Dodson and Peterson, 2010; Izhaki et al., 2000). Moreover, some studies have found no effects on seedling growth, vegetation cover or species richness (Dodson and Peterson, 2010; Kruse et al., 2004). Hence it is necessary to disentangle the possible effects of mulch application on vegetation regeneration, especially if we consider that this recovery is a key factor for reducing the ‘window of disturbance’ after fire. The socio-economic changes and the associated abandonment of agricultural lands that have occurred in the Mediterranean Basin in the last few decades have led to an increasing number of ecosys˜ tems in early succession stages (Pausas and Fernández-Munoz, 2012). These ecosystems are dominated mainly by shrub species that accumulate large amounts of standing dead fine fuels which increase the probability of fire occurrence and land degradation (Baeza et al., 2011; Saura-Mas et al., 2010). These shrubs are mostly obligate seeders with hard coated seeds which base their regeneration on persistent soil seed banks (Verdú, 2000). These obligate seeders are normally characterised by a pulse of germination and establishment in the autumn following the fire (Santana et al., 2012). Initially, it was assumed that this pulse was produced by the breakage of seeds physical dormancy as a result of fire heat. However, it has been recently observed that soil temperature fluctuations occur immediately after fire in summer may also play a determining role in breaking seed dormancy, being more important than fire temperatures in some cases (Baeza and Roy, 2008; Santana et al., 2013). The mulch application effect on micro-environmental conditions can buffer soil temperatures thus diminishing obligate seeders recovery by reducing seed germination. A good understanding of the possibility that vegetation recovery is lacking in this kind of ecosystems is of vital importance to reduce soil degradation processes. It should be taken into account that after a wild fire, all obligate seeder individuals die and the root system protecting the soil must be completely restored by new established individuals. This contrasts, for example, with the communities dominated by resprouter species where root systems are practically unaffected (Pausas et al., 2008). In this paper, we attempt to address these issues by testing the effect of different mulch ratios (1 and 2 kg m−2 ) after wild fire on the regenerative capacity of three main obligate seeders species in the Mediterranean Basin ecosystems: Cistus albidus, Ulex parviflorus and Rosmarinus officinalis. These issues may be of vital importance in improving mulching application methods to reduce soil erosion, while favouring species regeneration. The experiment was performed at three different sites burned experimentally in 2006 by measuring the mulch effects on seedling emergence and seedling establishment over a 3-year period. Total vegetation cover and species richness were also assessed. Here we hypothesise that mulch application: (1) will reduce the recovery of obligate seeders by reducing temperature fluctuations on the soil surface, thus limiting obligate seeders emergence; (2) in contrast, mulch application will increase the survival of obligate seeders of emerged seedlings by increasing soil moisture content; and finally (3) mulch

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application will modify plant cover and species richness by affecting the micro-environmental conditions in the establishment phase. 2. Material and methods 2.1. Study area The study was carried out inland in the Valencian Community (southeast Spain) at three sites: Onil (38◦ 39 N–0◦ 39 W), Pardines (38◦ 40 N–0◦ 39 W) and Ayora (39◦ 07 N–0◦ 57 W). In all cases, the study sites were old-field terraces that had been abandoned ca. 50–60 years ago and had a well-documented history of exploitation and fire occurrence (Santana et al., 2010). Their altitudes range between 900 and 1050 m.a.s.l., and their climate is typically Mediterranean. Mean annual rainfall ranges between 466 mm (Onil) to 537 mm (Ayora). Summer drought is pronounced from June to August, with no more than 65 mm of rain at any site. The mean annual temperature is approximately 14 ◦ C, and the mean maximum temperature for the hottest month (July) is 30 ◦ C. To minimise environmental variability between sites, all the sites were oriented north, located on marls and their soils were Calcaric cambisols (Anon, 1988). At the time of our study, vegetation was a shrub-land dominated by several obligate-seeding species. The woody stratum was composed mainly of the shrubs C. albidus (Cistus hereafter), U. parviflorus (Ulex hereafter) and R. officinalis (Rosmarinus hereafter), whereas the herbaceous stratum consisted of perennial resprouting species, mainly the grass Brachypodium retusum. There were a few isolated individuals of woody resprouting species like Quercus coccifera and Juniperus oxycedrus. 2.2. Experimental fires and mulching treatments At each site (Onil, Pardines and Ayora), an experimental plot of 30 × 20 m was selected in spring 2006. All three sites were burned by an experimental fire in June 2006, and only a 1-week separation was left between each fire (see Santana et al., 2011 for more details of experimental burnings). In order to test the effect of mulching on vegetation response, a 10 × 10 m square subplot was laid out within each experimental plot at each site, and 15 points within this subplot were chosen randomly from a 1 × 1 m grid (five points for each mulch treatment per site; see below). At each point, we set a permanent 0.5 × 0.5 m quadrat where mulch was manually applied. Mulch treatments were applied as follows: (i) control with no mulch application (Control hereafter), (ii) mulch at the 1 kg m−2 rate (1 kg hereafter); (iii) mulch at the 2 kg m−2 rate (2 kg hereafter). The mulch applied at each site consisted in woody chip particles produced from the slash of Pinus halepensis stems. Mulch particles were no bigger than 2 cm and 0.5 cm thick, and were applied by considering their moisture (Mean: 7.9%, SD: 0.4, n = 8). Treatments were applied approximately 1 week after fire and resulted in soil cover values of ca. 60% (1 kg) and 95% (2 kg). Mulch depths did not exceed 1 cm. Treatments were in accordance with the typical application ratios of woody chips in Mediterranean areas (e.g., 0.4 kg m−2 in Fernández et al., 2011; 0.87–1.75 kg m−2 in Prats et al., 2012). 2.3. Micro-environment monitoring After mulch applications, we monitored soil temperature and soil moisture to check the effect of mulching on changing soil micro-environmental conditions. First, the continuous soil temperature in the absence of treatments (Control) was recorded at a 1-cm depth over a 2-month period in summer 2006 (from July 21 to September 21). At each site, temperature was recorded hourly

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with a temperature probe (Hobo® Event, Onset Computer Corporation, Bourne, MA, USA). Sensors were inserted horizontally in untreated soils at the desired depth, and then soil was restored as closely as possible to its original state. Second, the buffering effect of treatments was assessed by means of protected diodes buried at a 1-cm depth. These diodes were placed in the middle of each 0.5 × 0.5 m quadrat where mulching treatments were applied (45 in all). Temperature was measured at midday when temperatures are higher, and also when the buffering effect can reach a higher value. Records were taken weekly during 5 weeks in August and September. Soil moisture was monitored with a Tektronik 1502C metallic cable tester (Tektronik, Beaverton, OR, USA) in the first 5 cm of the soil profile. Records were also taken weekly from the end of July to November 2006.

2.4. Vegetation recovery monitoring We studied the seedling dynamics after the mulch applications of the three dominant seeder species (Cistus, Rosmarinus and Ulex). All together, the relative cover of these species was greater than 75% in the shrub layer of the ecosystems studied (Santana et al., 2012). Seedling emergence and survival were monitored in the above-described quadrats every 2 months, from October 2006 to June 2009 (16 monitoring times). To facilitate their identification during subsequent samplings, seedlings were tagged with colour-coded rings to indicate time of germination, while their coordinates within the quadrat were recorded. The fate of each seedling was tracked throughout the study period. Germination of Mediterranean Basin shrubs occurs preferentially during the wet seasons of autumn and spring, whereas it is negligible in summer (Santana et al., 2012). Therefore to simplify the analyses of our data, we pooled the emergent seedlings into two annual cohorts according to their time of emergence. The seedlings which emerged in the October and December samplings were considered autumn cohorts, whereas those that emerged in February, April and June were pooled in the spring cohort of the respective years. The last monitoring of the survival of previously emerged seedlings was done in September 2009 (after the last summer drought period). In addition, total plant cover and species richness were assessed visually in each monitoring quadrat (n = 45) two years after the experimental fire (June 2008) to check the mulching effect.

Moreover, the cover and richness of the different life-forms were also recorded following the Raunkiaer (1934) classification (i.e., nanophanerophytes, chamaephytes, hemicryptophytes and terophytes).

2.5. Statistical analysis All the statistical analyses were carried out using the R programme (version 2.14.2., Development Core Team 2012, Vienna, Austria). The soil temperature and soil moisture differences in summer 2006 among the three mulch treatments were analysed by a generalised linear mixed model (GLMM). We used mulching treatments as fixed effects, while permanent quadrats, sites and sampling dates (repeated measures analysis) were included as random effects (Bolker et al., 2009). Similarly, the GLMMs were used for analysing the differences in seedling emergence, seedling establishment, vegetation cover and species richness between mulch treatments. For this purpose, we used total emergences and establishments at the end of a 3-year sampling (June 2009). Mulching treatments were used as fixed effects, while permanent quadrats and sites were included as random effects. Each model was performed twice after changing its baseline to compare the three treatments between them. All the models were fitted using a Poisson error distribution and a log-link function (Crawley, 2007). The GLMMs were fitted by means of the GLMM-PQL package (Bolker et al., 2009). Seedling survival for the different mulching treatments and for the three dominant species was analysed with the Survival package (Crawley, 2007). The survival curves of each cohort were estimated with a non-parametric Kaplan–Meier analysis. As the censored data, we took the seedlings that were alive at the end of the study and those checked as being alive upon the intermediate samplings, but which were not detected in later samplings. Then the shape differences in the survival curves between treatments were tested by log-rank tests (Pyke and Thompson, 1986). Since the cohorts were not equally abundant and most seedling emergence occurred in the first autumn after the fire (79.2% of emergences), we provide only results for the autumn 2006 cohort. For this analysis, the seedlings for the three sites in the same census were pooled in order to reach a density of at least 1 individual m−2 (Quintana et al., 2004; Santana et al., 2012). However, it was possible to perform this analysis only

Fig. 1. Soil temperatures experienced after the experimental fires in summer 2006. (A) Frequency of daily maximum temperatures assessed for burned areas during a 63-day period (21 July to 21 September) at a 1-cm depth of the soil profile. (B) Temperature buffer of mulching treatments vs. the Control squares at midday. The values for this graph were the difference of the mean values assessed at five treatment points on the same day. Measurements were taken 5 times spaced over 7–10 days (n = 5). Bars represent the standard error.

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Fig. 2. Soil moisture with different mulching treatments in 2006. Bars represent the standard error (n = 5).

in Cistus and Ulex seedlings because of the low individual densities of Rosmarinus.

3.2. Seedling emergence, seedling establishment, plant cover and richness

3. Results

During the 3-year study period, 1640 seedlings were recorded. The most abundant species was Cistus (1391 seedlings in all), followed by Ulex (207 seedlings in all) and Rosmarinus (42 seedlings in all). Seedling emergence was higher in the autumn than in the spring cohorts (95% vs. 5%), especially in the first autumn after the fire. The first autumn cohort accounted for 79.2% of all the seedlings that emerged during the 3-year study period (79.6% for Cistus, 79.7% for Ulex and 65.9% for Rosmarinus). The seedling emergence for Cistus decreased significantly in the 1 kg (df = 40, t-value = −2.054, P = 0.046) and 2 kg (df = 40, tvalue = −3.884, P < 0.001) treatments if compared with Control, where 1 kg obtained intermediate values between the other two treatments (Fig. 3A). However, mulching had no significant effect on the established Cistus seedlings three years after the fire (Control vs. 1 kg, P = 0.445; Control vs. 2 kg, P = 0.241) (Fig. 3B). In contrast, mulching treatments did not affect Ulex and Rosmarinus seedlings emergency and establishment, and only the seedling emergence in Rosmarinus was marginally significant between Control and 2 kg (df = 40, t-value = −1.911, P = 0.063) (Fig. 3A and B). At the same time, that is two years after applying the mulching treatments, no significant differences in plant cover and species richness of the different life forms considered were found (P > 0.1 in all cases) (Fig. 4A and B).

3.1. Soil temperature and soil moisture The daily maximum soil temperature in the next summer after the fire ranged more frequently between 50 ◦ C and 60 ◦ C for the Control treatment (Fig. 1A). The 1 kg and 2 kg treatments significantly buffered soil temperature as compared to Control (Fig. 1B). Approximately, 1 kg reduced the soil temperature by between 0.25 ◦ C and 2.5 ◦ C (GLMM, df = 218, t-value = −2.219, P = 0.027), while 2 kg reduced the soil temperature by between 1.65 ◦ C and 3.75 ◦ C (df = 218, t-value = −4.511, P < 0.001; Fig. 1B). Significant differences in soil temperature were also found between 1 kg and 2 kg (df = 218, t-value = −2.293, P = 0.023), and 2 kg showed a greater buffering capacity than 1 kg (Fig. 1B). Soil moisture increased with mulch applications (Fig. 2). Significant differences were observed between Control and 1 kg (GLMM, df = 394, t-value = 2.474, P = 0.014), and between Control and 2 kg (df = 394, t-value = 5.125, P < 0.001). In addition, the soil moisture between 1 kg and 2 kg also significantly differed as 2 kg obtained higher moisture values than 1 kg (df = 394, t-value = 2.683, P = 0.007). Another interesting point is that the differences among treatments were greater when soil moisture increased (Fig. 2).

Fig. 3. Seedlings emerged (A) and established (B) after a 3-year mulching treatment. Different lower case letters indicate the significant differences between treatments (GLMM, P < 0.05). Bars represent the standard error (n = 15).

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Fig. 4. Vegetation cover (A) and species richness (B) after a 2-year mulching treatment. Bars represent the standard error (n = 15).

3.3. Seedlings survival Mortality was generally higher during the first months after germination for the Cistus and Ulex seedlings. This pattern is very clear during the first winter-spring after germination. Afterwards, mortality became much lower throughout the 3-year study period, with very few losses during summer periods (Fig. 5). The Cistus survival percentages were generally lower than those of Ulex (Table 1). For Cistus, the Log-Rank comparisons of the survival curves showed that survival was significantly better in 2 kg (29%) vs. Control and 1 kg (18–21%), and no differences were found between Control and 1 kg. A similar pattern was obtained for Ulex, with better survival in 2 kg (61%) as compared to Control and 1 kg (ca. 36%) (Fig. 5, Table 1).

Table 1 Number of emerged seedlings and percentage of survival at the end of the study for the autumn 2006 cohort. The effect of mulching treatments on the survivorship of the seedlings of each species was compared by Log-Rank tests. Treatment

Cistus Control 1 kg 2 kg Ulex Control 1 kg 2 kg

Emerged (individuals)

Survival (%)

Log-rank comparison 1 kg

2 kg <0.001 0.019

545 347 148

18.2 21.9 29.6

0.3

63 61 41

36.5 36.1 61

0.953

0.009 0.008

4. Discussion Suitable mulch application after wild fire may not impede natural vegetation recovery in Mediterranean Basin ecosystems dominated by obligate seeders. This study shows that mulch application (woody chips) had no significant effect on vegetation recovery three years after fire. This overall result is supported by

the lack of differences between the mulching treatments and controls in Rosmarinus and Ulex seedlings emergence, establishment of the three obligate seeders, and the plant cover and richness of the different life-forms. As most obligate seeders and herb species are established during the first post-fire years, the resultant community may maintain its composition over time without significant

Fig. 5. Kaplan–Meier survival curves for the autumn 2006 cohorts. Data represent means ± SE. AUT = autumn, SPR = spring, Sep = September (early autumn).

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changes (Santana et al., 2012). At the same time, the mulch application increased the seedling survival of obligate seeders species during the first three years. Therefore, besides being an effective soil protection method for Mediterranean areas (Badia and Marti, ˜ et al., 2012; Fernández et al., 2000; Bautista et al., 1996; Díaz-Ravina 2011; Prats et al., 2012), the application of mulching at the 1 kg m−2 and 2 kg m−2 rates can be a satisfactory tool from the vegetation restoration point of view. This is of relative importance in such ecosystems dominated by obligates seeders, where all individuals die after wild fires and the root system protecting soil must be completely restored by new individuals. These results are in agreement with other mulch application works conducted in the USA (Dodson and Peterson, 2010; Peterson et al., 2009) and in other Mediterranean Basin areas (Badia and Marti, 2000; Bautista et al., 1996), where vegetation regeneration was not affected by such treatments or even improved. Contrary to our hypothesis, the mulch application did not limit the species emergence of Ulex and Rosmarinus, but reduced only the emergence of Cistus seedlings. In particular, ca. 34% of Cistus emergences were reduced in comparison to the Control when 2 kg of mulch was applied. These reductions may be caused by mulching’s capacity to modify the soil micro-environment towards less suitable conditions for seed germination and seedling emergence. In fact, we observed that mulch application buffered soil temperature, which is a very important factor for breaking seed dormancy in the three obligate seeders studied (Santana et al., 2013). In our study, the maximum soil temperature was buffered in ca. 1.7–3.8 ◦ C in the 2 kg treatment if compared to Control, thus reducing the extreme temperature fluctuations that break seed dormancy. Therefore, these results support the hypotheses that the daily soil temperature fluctuations which occur in summer after fires play an important role in breaking seed dormancy in species with hard coated seeds (Baeza and Roy, 2008; Santana et al., 2013). Nevertheless, it is worth noting that other micro-environment modifications may be determinants in this seed germination and seedling emergence reduction. For example, mulch application can reduce the incident light in the first centimetres of soil, a factor that stimulates seed germination (Baeza and Roy, 2008; Roy and Sonie, 1992). At the same time, the physical barrier created by mulch application may also impede seedling emergence, although it has been suggested that mulch piles higher than 2–5 cm are required to have a significant effect (Dodson and Peterson, 2010; Izhaki et al., 2000). Further research is therefore needed to definitively disentangle the relative impact of these different micro-environmental conditions on the seedling emergence of Mediterranean Basin obligate seeders. Three years after the experimental fires, seedling establishments per species were equal for all the treatments applied (Control, 1 kg and 2 kg). It is interesting to note that despite the 2 kg treatment reduced Cistus seedling emergence, this had no effect on the total amount of seedlings established. This is probably due to the highest mortality observed in the Control treatments vs. 2 kg, which may buffer the initial differences. Mulch application modified the soil micro-environment at our experimental sites by increasing soil moisture; i.e., the 2 kg treatment retained ca. 4% more soil moisture on average than Control, and 2% more than 1 kg. This increase in soil moisture may benefit the seedling survival at water-stressed sites in initial seedling establishment stages (Robichaud et al., 2000). In fact, the largest differences in soil moisture between treatments were found in the first autumn-winter after fire, at the highest level of annual moisture, and when the main events of seedling emergence and establishment occurred. It has been postulated that soil moisture is probably one of the most limiting factors for seedling survival during these first stages in Mediterranean ecosystems (Lloret et al., 2005; Moreno et al., 2011; Quintana et al., 2004). Otherwise, it may be also possible

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that mulch application increased seedling survival by protecting emerged seedlings from torrential rainfall and water runoff. In the Mediterranean Basin, torrential rainfall occurs normally in autumn, ˜ precisely when seedlings are emerging (Penarrocha et al., 2002). In fact, it has been observed that these heavy rains can significantly increase the mortality of the species studied (Cistus, Ulex, Rosmarinus) by being directly buried by transported sediment, or by being totally or partially un-hearted (de Luís et al., 2005). The results reported here, therefore, support our second hypotheses that mulch application enhances seedling survival by improving either moisture conditions or physical protection. As a consequence, the woody chips mulch application appears to be a suitable management strategy to improve vegetation establishment and survival after wild fires in similar ecosystems of the Mediterranean Basin. After mulch application, rapid vegetation establishment and growth will help to reduce the “window of disturbance” after wild fires (Mayor et al., 2007; Prosser and Williams, 1998). Moreover, if vegetation is composed of different life-forms the community complexity and stability will be increased, improving the restoration process (Alday et al., 2011, 2012). Here, our results do not support our hypothesis which states that mulch application will modify plant cover and richness by affecting micro-environmental conditions. Two years after the mulching application, the plant cover and species richness of the different life-forms showed no significant differences if compared with Controls. This suggests that applying woody chips mulch (here at the 1 kg and 2 kg ratios) after a wildfire has no negative effect on short-term vegetation establishment and diversity. These results agree with recent studies into mulching application after wildfires in pine woodlands of the USA, where no clear effects were observed in species richness (Dodson and Peterson, 2010). Nonetheless, still very little is known about the possible effects of mulch application on species richness, especially in Mediterranean ecosystems. In any case, the low plant cover values obtained after three years in the controls and the two mulch treatments (cover values within the 9.5–12% range) suggest that a longer time frame will be needed to achieve the complete regeneration of these Mediterranean areas. Mulch application and its possible effects on vegetation regeneration still face a number of future challenges. In this paper, we observe that mulch application in the form of woody chips is an effective treatment to increase soil moisture and seedling survival. In addition, this treatment has not negative effects on other vegetation regeneration aspects, such as species richness and plant cover. Nevertheless, more efforts need to be made in order to accurately determine optimal mulch application rates. In this paper, we take a step forward by observing that discrete application rates, by increasing from 1 kg m−2 to 2 kg m−2 , imply a change from no clear effect on seedling emergence and survival to significant impacts. In addition, further research is required to ascertain whether other commonly applied mulch types, i.e. wheat straw, have similar effects on the vegetation recovery of Mediterranean ecosystems dominated by obligate seeders. It would be also interesting to ascertain the upper mulch rate application threshold that has a negative impact on species regeneration by acting as a physical barrier. Finally within the on-going climate change frame, mulch application treatments may prove to be an effective tool for maintaining the regeneration capacity of soil seed banks. Over the next decades, an increase in air and soil temperatures is expected which may lead to wider temperature fluctuations in bare soils (Giorgi and Lionello, 2008; Ooi, 2012). This may release the physical dormancy of many seeds which remain ungerminated after fire, thus compromising the efficiency of the bet-hedging mechanism (Ooi, 2012). Similarly, higher air temperatures and the predicted drier conditions may produce seed bank net losses by increasing seedling

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mortality in early establishment stages, and before seedlings reach their reproductive age (del Cacho et al., 2012). Therefore, microhabitat modifications by reducing soil temperatures and increasing soil moisture, as achieved by woody chips mulching, can be an effective measure to reduce potential losses in soil seed banks after perturbations. 5. Conclusion Mulch application (woody chips) as a post-fire rehabilitation treatment has no negative effects on plant regeneration in Mediterranean Basin ecosystems dominated by obligate seeders. This fact is of paramount importance since all the individuals in these ecosystems die after wild fires and the root system protecting soil must be completely restored by new individuals. Rapid vegetation establishment and growth will help to reduce the “window of disturbance” for soil erosion that occurs until vegetation is recovered. Mulch application modifies micro-environmental conditions by lowering soil temperatures and increasing soil moisture. However, no significant effects on the final establishment of individuals, plant cover and species richness were observed. In addition, the application ratios of 2 kg m−2 increased the seedling survival of obligate seeders species. In conclusion, woody chip applications may prove to be a suitable post-fire rehabilitation treatment to reduce post-fire soil erosion as it does not extend the “window of disturbance” by adversely affecting vegetation regeneration. Acknowledgments V.M. Santana has been supported by a VAli + d post-doctoral grant awarded by the Generalitat Valenciana (Valencian Regional Government). J.G. Alday has been supported by Basque Country Government post-doctoral grant (DEUI BFI-2010-245). This research has been carried out as part of the RESILIEN (CGL 2011-30515-C02-02) and the Consolider-Ingenio 2010 (GRACCIE CSD2007-00067) projects. CEAM is supported by the Generalitat Valenciana. References Alday, J.G., Marrs, R.H., Martínez-Ruiz, C., 2011. Vegetation convergence during early succession on coal wastes: a six-year permanent plot study. J. Veg. Sci. 22, 1072–1083. Alday, J.G., Marrs, R.H., Martínez-Ruiz, C., 2012. Soil changes during early succession on coal wastes: a six-year permanent plot study. Plant Soil 353, 305–320. Anon, 1988. Soil map of the world. In: World Soil Resources, FAO Report 60. FAOUNESCO, Rome, Revised legend. Badia, D., Marti, C., 2000. Seeding and mulching treatments as conservation measures of two burned soils in the central Ebro valley, NE Spain. Arid. Soil Res. Rehab. 13, 219–232. Baeza, M.J., Roy, J., 2008. Germination of an obligate seeder (Ulex parviflorus) and consequences for wildfire management. For. Ecol. Manage. 256, 685–693. Baeza, M.J., Santana, V.M., Pausas, J.G., Vallejo, V.R., 2011. Successional trends in standing dead biomass in Mediterranean basin species. J. Veg. Sci. 22, 467–474. Bautista, S., Bellot, J., Vallejo, V.R., 1996. Mulching treatment for postfire soil conservation in a semiarid ecosystem. Arid. Land Res. Manage. 10, 235–242. Bolker, B.M., Brooks, M.E., Clark, C.J., Geange, S.W., Poulsen, J.R., Stevens, M.H.H., White, J.S.S., 2009. Generalized linear mixed models: a practical guide for ecology and evolution. Trends Ecol. Evol. 24, 127–135. Calvo, L., Baeza, J., Marcos, E., Santana, V., Papanastasis, V.P., 2012. Post-fire management of shrublands. In: Moreira, F., Arianoutsou, M., Corona, P., De las Heras, J. (Eds.), Post-Fire Management and Restoration of Southern European Forests. Springer, New York, NY, pp. 293–320. Certini, G., 2005. Effects of fire on properties of forest soils: a review. Oecologia 143, 1–10. Crawley, M.J., 2007. The R Book. John Wiley, Chichester. de Luís, M., Raventós, J., González-Hidalgo, J.C., 2005. Fire and torrential rainfall: effects on seedling establishment in Mediterranean gorse shrublands. Int. J. Wildland Fire 14, 413–422. ˜ del Cacho, M., Saura-Mas, S., Estiarte, M., Penuelas, J., Lloret, F., 2012. Effect of experimentally induced climate change on the seed bank of a Mediterranean shrubland. J. Veg. Sci. 23, 280–291.

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