Multiproxy analysis for the paleobiogeographical reconstruction of the relict forests of the Serranía de Ronda during the Holocene (Baetic System,Spain)

Abstract

The mountains of the southern Iberian Peninsula are important biodiversity hotspots. They are also home to several relict species that are threatened with extinction in the face of global change. One of the best examples is the Serranía de Ronda, a system of mountainous reliefs located at the western end of the Baetic Cordillera. Its tree cover includes, among other unusual taxa, endemic formations such as the Spanish fir (Abies pinsapo) and Portuguese oak (Quercus faginea) forests. However, despite the ecological exceptionality of this mountainous area, little is known about its paleobiogeography. To remedy this, in this research we take a multidisciplinary approach based on the application of several different paleoecological disciplines, of which pedoanthracology is the main methodological tool. Six new soil surveys were performed, which were added to the existing pedoanthracological network, making a total of 43 soil sampling sites. The taxonomic analysis revealed several taxa, such as Abies, Fraxinus, Pinus and Pinus sylvestris-type, which are currently absent in several of the sampled sites. After contextualizing the 36 new radiocarbon dates obtained, the results confirm the antiquity of certain paleoendemic forests in the Serranía de Ronda, and the important role played by certain mountain enclaves as refuges for conifers such as A. pinsapo and Pinus sylvestris-type during the Pleistocene-Holocene transition. The dissemination of the results of this research will enable them to be implemented in the different strategies of adaptive management of the most threatened forests of the Serranía de Ronda.

Keywords

Baetic Range endangered species Holocene paleoendemic conifers pedoanthracology vegetation dynamics

Introduction

The Mediterranean bioclimatic region is the second most important biodiversity hotspot in the world, with as many as 25,000 plant species (Médail et al., 2004; Myers et al., 2000). This exceptional ecological richness is the result of a very long and complex biogeographical history (Molina-Venegas et al., 2017; Rey-Benayas et al., 2002). In this sense the location of the European mountain systems, especially those situated in the southern part, in a transition zone between temperate and tropical climates, has played a fundamental role in the evolution of certain plant taxa during different historical periods as refugia for flora and as a bridge between the continents of Africa and Europe (Médail and Diadema, 2009; Medail and Quezel, 1997).

Together with this, the Mediterranean basin has since time immemorial been a leading center of human settlement and development, which has had a significant negative impact on this inherited biological wealth (Blondel, 2006). The imprint of humanity on the plant cover intensified during the Neolithic (Carrión, 2012), a period in which the environmental conditions of the Holocene period began to improve (Jalut et al., 2000).

At the same time, the western Mediterranean is currently one of the most vulnerable regions on Earth in the face of global change (Cramer et al., 2018). Its mountains are expected to have to withstand greater exposure to environmental changes than other mountain areas of the planet (Giorgi, 2006; Thuiller et al., 2005). This problem will have an even greater impact on the Iberian Peninsula, one of the main centers of plant diversity with more than 6000 plant taxa, of which about 22% are endemic (Aedo et al., 2017).

Within the Baetic Cordillera, one of the most outstanding mountain ranges in this sense is the Serranía de Ronda (western Baetic Range), a vast mountain territory with large areas of forest. Its forests are made up of formations of conifers (pines and firs) and of broad-leaved (cork oaks, Portuguese oaks, holm oaks and riparian trees), which together form a vegetation landscape of great ecological value in which man has played a decisive role (Gómez-Zotano and Olmedo-Cobo, 2021). As a result, there has been a lot of recent research into the current situation of certain taxa (Gómez-Zotano and Olmedo-Cobo, 2021; López-Quintanilla, 2013). This includes studies of their habitat, references from historical sources or species distribution models (SDM), varied approaches that provide an important body of information about the recent dynamics and the current state of certain plant formations. This information has also served as a framework of reference for the different conservation and forestry restoration policies carried out in recent years in this part of the Baetic Cordillera.

However, these approaches offer a very limited temporal resolution, which means that our knowledge of the evolutionary dynamics of the plant landscape in the Serranía de Ronda is sketchy (Gómez-Zotano and Olmedo-Cobo, 2021; Gómez-Zotano et al., 2017). There are very few reconstructions over a broad timeframe which enable us to identify the different factors that may have favored the adaptation, fragmentation and extinction of certain plant taxa (Alba-Sánchez et al. (2018, 2019); Pardo-Martínez et al., 2022). All of this in spite of the proven value of paleoecological sources for forest conservation and management purposes (Carracedo-Martín et al., 2017; Robin et al., 2013), especially when combined with data obtained from ecological monitoring (Alba-Sánchez and López-Sáez, 2013).

These paleoecological sources include for example the study of pollen microremains, although there have been very few analyses of this kind in the areas where the Spanish fir currently grows (Alba-Sánchez et al., 2019). Another innovative method is pedoanthracology, the study of non-archeological soil charcoals, an important approach given that fire has been one of the main agents modeling the plant landscape over the course of history, and is a key element for explaining the great diversity of species associated with the Mediterranean climate (Bond and Keeley, 2005). This technique has been successfully applied in the mountains in the north and center of the Iberian Peninsula. Cunill (2010) and Cunill et al. (2012, 2013) pioneered the application of pedoanthracology in the Pyrenees, while García-álvarez et al. (2017) did likewise in the Central System. For their part, Beato-Bergua et al. (2019) applied this technique to the study of Taxus baccata in the Asturian Massif Central (Cantabrian Mountains). Research of this kind in our study area in the south of the Iberian Peninsula began more recently (Gómez-Zotano et al., 2017; Pardo-Martínez, 2020). In this context, the Baetic Cordillera is an excellent laboratory for the study of the spatial and temporal components of global change and the processes it entails. This analysis also provides complementary perspectives which enable a paleoclimatic and paleo-environmental interpretation to be performed (Cunill et al., 2013; Saltré et al., 2013).

The main objective of this research was to obtain a first overview of the composition and dynamics of the forests of the Serranía de Ronda. To this end, in this study we adopted a multi-proxy approach to this question based on the application of different paleoecological disciplines, of which pedoanthracology is the main methodological tool. Over the course of this research, we discovered taxa that once grew in sampling sites where they are no longer present today. This information, contextualized with 36 new radiocarbon dates in addition to the 74 that had previously been obtained, has provided revealing data on the composition and dynamics of the forests of the Serranía de Ronda at different times during the Holocene. It highlights the role played by various mountain enclaves as refuges for certain species of conifer – and in particular of Abies pinsapo and Pinus sylvestris-type – after the Last Glacial Maximum. The dissemination of the results of this research will enable their implementation in different strategies for the conservation and adaptive management of the most endangered forests and their habitats in the Serranía de Ronda.

Methods

Study area

The Serranía de Ronda (Figure 1) is located in the extreme south-west of the Baetic Cordillera (in the provinces of Cádiz, Málaga and Sevilla). It is a natural, mountainous, densely forested area, which hosts a wide variety of plant species due to the particular combination of Mediterranean climate, orography and rocky outcrops (Gómez-Zotano and Olmedo-Cobo, 2021).

Within this territory, as established by Pérez-Latorre et al. (2021), there are at least four functional groups of forests (evergreen, marcescent, conifers and deciduous riparian), which in turn can be divided into 12 main forest types, that are represented by species such as: holm oaks (Quercus rotundifolia), cork oaks (Quercus suber), carobs (Ceratonia siliqua), Portuguese oaks (Quercus faginea), oaks (Quercus pyrenaica), pines (Pinus pinaster), firs (Abies pinsapo), poplars (Populus alba), alders (Alnus glutinosa), elms (Ulmus minor), ash trees (Fraxinus angustifolia), and willows (Salix pedicellata). These are distributed across the territory in different ways depending on the litho-edaphic and bioclimatic conditions. Together they form a plant landscape in which humans have played a fundamental role in the past and present distribution of the forest canopy (Alba-Sánchez et al., 2019; Castañeda-Fernández, 2008; Castillo-Rodríguez, 2000; Gómez-Zotano and Olmedo-Cobo, 2021).

From a biogeographical point of view, most of the study area falls within the Baetic province (Rondeño, Bermejense and Antequerano sectors) with certain smaller areas belonging to the Tingitano-Onubo-Algarviense province (Aljíbico subsector) (Pérez-Latorre et al., 1998, 2019; Rivas-Martínez, 2011). The floristic singularity of this territory is completed by the fact that it hosts an important number of endemic and/or endangered taxa of which the most significant are: A. pinsapo, Q. faginea subsp. alpestris, Atropa baetica, Narcissus bugei, Sarcocapnos baetica subsp. baetica, Saxifraga bourgeana, Stahelina baetica, Ilex aquifolium, and Taxus baccata (Pérez-Latorre et al., 2021).

Methodology

In order to carry out the multiproxy analysis on which this research is based, various different methodologies were applied, such as palynology, historical references, species distribution models (SDM), and pedoanthracological analysis. This last procedure was the main methodological tool applied, based on protocols defined by Talon et al. (1998) and adapted by Cunill (2010) and Cunill et al. (2013). The work was divided into the following phases:

1. Fieldwork. During this phase of the work a total of six new soil sampling sites were excavated in different parts of the Serranía de Ronda: Arroyo de los Lobos 1 and 2, Cascajares 2, 3 and 4, and La Nava. These were in addition to the 37 existing ones (see Olmedo-Cobo et al., 2021; Pardo-Martínez et al., 2022; Figure 1). This brings the network of pedoanthracological sampling sites for the Serranía de Ronda as a whole to 43. We then described the edaphic profile of each sample, having differentiated between 2 (II) and 8 (VIII) levels. Between 3 and 15 kg of soil samples were taken for each of these levels.

2. Laboratory work. The second phase, carried out in our laboratory, involved the following tasks:

a. Sieve, while damp, the soil samples collected in the field. For this purpose, standardized 50 cm sieves were used with mesh gaps of 0.8, 2, and 5 mm. Once they had been sieved, each sample was dried in the open air.

b. Weighting the residual samples. The lithological fragments of more than 5 mm – from each of the sampling levels established–, were weighed in order later to calculate the anthracomass. They were then discarded.

c. Separation of the charcoals. Manual selection of the charcoal using a binocular loupe.

d. Taxonomic identification. Once selected, the taxon of each charcoal was identified using an Olympus BX51 reflected light optical microscope (x50-400). The maximum number of fragments identified by sampling level was 100 units. The taxa of the charcoal fragments were identified by consulting several atlases of comparative wood anatomy (Schweingruber, 1990; Vernet et al., 2001).

e. Radiocarbon dating. Thirty-six charcoal fragments from different taxa were subjected to radiocarbon dating in the following specialized laboratories: Poznan Radiocarbon Laboratory (Poznan, Poland) and the Alfred-Wegener-Institut (Bremerhavem Germany). These 36 charcoal fragments consisted of 13 fragments of Pinus sp., 9 of P. sylvestris-type, 7 of Abies sp., 4 of Pinus pinaster and 3 of Quercus sp. Later, the dated samples were calibrated using Oxcal 4.3 software and the IntCal20 database (Reimer et al., 2020), 2 sigma (95% probability).

The pedoanthracological sampling was complemented with a palynological analysis at one of the sampling points. In this case, the sediment core, measuring 235 cm, was collected using a Rolatec RL-48-L drill equipped with a hydraulic piston. The ¹⁴C datings (10 in total) were performed using accelerator mass spectrometry (AMS) at the Scottish Universities Environmental Research Centre (United Kingdom). The samples were treated according to the chemical methodology proposed by Faegri and Iversen (1989) and Moore et al. (1991), which comprises an initial attack with HCl and subsequent washings with NaOH. The sediment was then concentrated in heavy liquid in order to separate pollen and non-pollen palynomorphs (Goeury and De Beaulieu, 1979), and finally treated with HFl. Pollen concentration was estimated by adding a Lycopodium tablet to each sample (Faegri and Iversen, 1989; Stockmarr, 1971).

At the same time, we reviewed all the palynological studies conducted to date in the western sector of the Baetic Cordillera. This biogeographical study was complemented with analysis of both the historical sources with a timescale dating back to the 16th century and the available SDMs (Alba-Sánchez and López-Sáez, 2013; Alba-Sánchez et al., 2010; Gutiérrez-Hernández, 2018; López-Tirado and Hidalgo, 2014; Navarro-Cerrillo et al., 2006; Sánchez-Salguero, 2007). This enabled us to obtain paleoecological and prospective information about the different tree taxa present in the Serranía de Ronda.

Results and discussion

Pedoanthracological analysis

The six new soil samplings conducted in our latest research are in addition to those carried out in the Serranía de Ronda over the last few years. This brings the number of pedoanthracological sampling sites to 43. This extensive network enabled us to obtain a large volume of charcoal fragments.

The anthracomass values showed great diversity, with very low values being found at Cascajares 3 (66 mg/kg) and very high values at Arroyo de los Lobos 2 (8337 mg/kg). In other locations in the Serranía de Ronda the dynamics are similar, as shown by Olmedo-Cobo et al. (2021) and Pardo-Martínez et al. (2022). In this respect, we found some sites with very low anthracomass values, such as Majada del Toro (1.4 mg/kg), Líjar (5.2 mg/kg) and Jarastepar 2 (9.3 mg/kg), and others with very high anthracomass values, such as Palmitera 2 (7066.3 mg/kg), Palmitera 3 (7831.6 mg/kg), or Palmitera 1 (137,379.3 mg/kg).

A total of 1040 charcoal fragments were subjected to taxonomical analysis. Eighty-five percent (884 samples) of these fragments were validly identified. An additional 5.3% of the samples analyzed could only be identified as angiosperms, while gymnosperms accounted for 1.3%. In the remaining 8.7% of the samples (85 fragments) we were unable to make any taxonomic classification whatsoever, due to processes of structural deformation, vitrification and/or the presence of fungi. These new samplings brought the total number of fragments identified in all 43 sampling sites in the Serranía de Ronda pedoanthracological network to 6751. Of these, 63.6% (4297 samples) were successfully identified, while a further 11% could only be identified as angiosperms and 4% as gymnosperms. Taxonomic identification proved impossible in 21.3% of the samples (1441 fragments).

By taxa, the most common was the Quercus genus, with 26.2%, in line with the results obtained by Olmedo-Cobo et al. (2021) and Pardo-Martínez et al. (2022). In the Serranía de Ronda as a whole, this genus accounts for 26.2% of all the fragments and was present in 37 of the 43 sampling sites. Families such as rosaceae and leguminosae accounted for 26.1% and 12.4% of the taxonomic identifications, respectively (5.8% and 4.5% considering the entire pedoanthracological network). Other taxa, such as Pinus (5.8%), ericaceae (2.9%), Pinus sylvestris-type (2%), Rhamnus (1%), and Abies (0.1%), had much lower percentages. Taxonomic diversity increases significantly in the Serranía de Ronda as a whole, including, in addition to those already mentioned, genera such as Acer, Arbutus, Daphne, Erica, Fraxinus, Lonicera, Pistacia, Rhamnus, Salix, and Taxus. In any case, these accounted for just 2.4% of all the validly identified fragments (Figure 2).

In general, the taxa identified in this study coincide with the plant species growing today in the different localities analyzed. However, in certain enclaves we identified taxa that are no longer present today. These include for example the charcoal fragments of relict conifers such as Abies sp. found in Arroyo de los Lobos 2; Pinus sp. in Cascajares 1; and P. sylvestris-type in Arroyo de los Lobos 1 and Cascajares 4.

These results are in addition to the ancient populations previously identified by Olmedo-Cobo et al. (2021) and Pardo-Martínez et al. (2022) in other locations in the Serranía de Ronda, such as Abies sp. in Palmitera 1, Jarastepar 2, Fuenfría Alta; and Pinus sp. in Puerto de los Valientes, Cañada del Cuerno, Sierra del Pinar 1, Jarastepar 2 and Tablón.

In Cañada de Enmedio, for its part, fragments from deciduous genera such as Fraxinus and Salix (Table 1, Figure 3) were found by Olmedo-Cobo et al. (2021).

Table 1.

Anthracomass values and taxonomic identifications for each of the pedoanthracological samplings conducted in the Serranía de Ronda as a whole.

Samplings carried out during the present investigation
Sites	Anthracomass (mg/kg)	Taxa identified		Identified taxa currently absent
Arroyo de los Lobos 1	124.5			Pinus sylvestris-type
Arroyo de los Lobos 2	8337			Abies sp.
Cascajares 2	151.7			—
Cascajares 3	66			—
Cascajares 4	211.1			Pinus sylvestris-type
La Nava	118.8			—
Samplings carried out in previous investigations
Sites	Anthracomass (mg/kg)	Taxa identified		Identified taxa currently absent
Arroyo del Toro	15.3			—
Cancha de Almola	25.7			—
Cañada de Enmedio	1039.4			Fraxinus sp.
Cañada del Cuerno	27.5			Pinus sp.
Cascajares 1	17.6			Pinus sp.
Cerro Barretos	1461.1			—
Cerro de los Sauces	287.5			—
Fuenfría Alta	651.7			Abies sp.
Jarastepar 1	25			—
Jarastepar 2	9.3			Abies sp. and Pinus sp.
Jardón 1	289.5			—
Jardón 2	185.2			—
Líjar	5.2			—
Llanos de Rabel	80.3			—
Los Reales 1	1965			—
Los Reales 2	2115.2			—
Los Reales 3	197.1			—
Los Reales 4	98.4			—
Majada del Toro	1.4			—
Navacillo 1	39.7			—
Navacillo 2	22			—
Navacillo 3	136.5			—
Palmitera 1	137,379.3			Abies sp.
Palmitera 2	7066.3			—
Palmitera 3	7831.6			—
Palmitera 4	99.6			—
Pilones 1	118.4			—
Pilones 2	143			—
Puerto de la Encina	234.3			—
Puerto de Lifa	9.6			—
Puerto de los Valientes	475.7			Pinus sp.
Puerto del Hoyo	413.7			—
Sierra de los Pinos	30.8			—
Sierra del Pinar 1	8285			Pinus sp.
Sierra del Pinar 2	129.8			—
Tablón	186.4			Pinus sp.
Terril	49.7			—
Legend
Abies sp.	Pinus pinaster		Salix sp.
Acer sp.	Pinus sylvestris-type		Taxus baccata
Fraxinus sp.	Quercus sp.		Other categories: : : : : : : :
Juniperus sp.	Deciduous Quercus		Angiosperm
Leguminosae	Evergreen Quercus		Gymnosperm
Pinus sp.	Rosaceae		Unclear

Source: Drawn up by the authors on the basis of data compiled by Olmedo-Cobo et al. (2021) and Pardo-Martínez et al. (2022).

A total of 36 new radiocarbon dates were obtained, in addition to the 74 obtained previously for the Serranía de Ronda as a whole (see Olmedo-Cobo et al. (2019a, 2019b, 2021); Pardo-Martínez et al., 2022). The chronologies range from 14,013–13,440 to 235 years cal. BP (Table 2).

Table 2.

Ages obtained for 110 charcoal fragments subjected to radiocarbon ¹⁴C dating.

Radiocarbon dates obtained during the present investigation
PALMITERA 1
Taxa	Lab. Code	Level/Sampling depth (cm)	AMS ¹⁴C age (BP)	Age cal. BP
Pinus pinaster	5181.1.1	V (52–80)	7236 ± 103	8385–7932
Pinus pinaster	5178.1.1	III (21–32)	6847 ± 36	7853–7678
Pinus pinaster	5180.1.1	V (52–80)	6794 ± 33	7751–7856
Pinus pinaster	5179.1.1	IV (32–52)	4760 ± 33	5660–5403
PUERTO DE LOS VALIENTES
Taxa	Lab. Code	Level/Sampling depth (cm)	AMS ¹⁴C age (BP)	Age cal. BP
Abies sp.	6247.1.1	I (0–18)	3072 ± 17	3428–3297
Abies sp.	6248.1.1	III (56–85)	1597 ± 59	1748–1424
Abies sp.	6246.1.1	I (0–18)	1135 ± 16	1239–1040
JARASTEPAR 2
Taxa	Lab. Code	Level/Sampling depth (cm)	AMS ¹⁴C age (BP)	Age cal. BP
Pinus sp.	6245.1.1	II (21–55)	10,059 ± 96	11,976–11,337
Pinus sp.	6242.1.1	I (0–21)	10,006 ± 93	11,888–11,311
Pinus sp.	5164.1.1	I (0–21)	9782 ± 42	11,327–11,227
Pinus sp.	6244.1.1	I (0–21)	9675 ± 97	11,311–10,801
Pinus sp.	6243.1.1	I (0–21)	9126 ± 22	10,422–10,297
SIERRA DEL PINAR 1
Taxa	Lab. Code	Level/Sampling depth (cm)	AMS ¹⁴C age (BP)	Age cal. BP
Pinus sp.	5168.1.1	III (20–44)	145 ± 20	310–126
Abies sp.	5167.1.1	III (20–44)	132 ± 20	280–80
Abies sp.	5166.1.1	III (20–44)	127 ± 22	280–80
Abies sp.	5165.1.1	III (20–44)	136 ± 23	276–77
CAÑADA DEL CUERNO
Taxa	Lab. Code	Level/Sampling depth (cm)	AMS ¹⁴C age (BP)	Age cal. BP
Pinus sp.	6241.1.1	II (23–36)	3630 ± 16	4119–3956
CASCAJARES 1
Taxa	Lab. Code	Level/Sampling depth (cm)	AMS ¹⁴C age (BP)	Age cal. BP
Pinus sp.	6253.1.1	III (81–112)	9261 ± 88	10,311
Pinus sp.	6251.1.1	III (81–112)	9153 ± 97	10,234
Pinus sp.	6252.1.1	III (81–112)	8583 ± 94	9494
Pinus sp.	6250.1.1	II (51–81)	7473 ± 84	8234–8110
Pinus sp.	6249.1.1	I (0–51)	139 ± 56	236
TABLÓN
Taxa	Lab. Code	Level/Sampling depth (cm)	AMS ¹⁴C age (BP)	Age cal. BP
Pinus sp.	6256.1.1	III (33–64)	11767 ± 108	14,013–13,440
Quercus sp.	6255.1.1	III (33–64)	8594 ± 22	9643–9566
Quercus sp.	6254.1.1	III (33–64)	151 ± 54	235
TERRIL
Taxa	Lab. Code	Level/Sampling depth (cm)	AMS ¹⁴C age (BP)	Age cal. BP
Quercus sp.	6257.1.1	III (60–93)	1560 ± 16	1500–1455
ARROYO DE LOS LOBOS 1
Taxa	Lab. Code	Level / Sampling depth (cm)	AMS ¹⁴ C age (BP)	Age cal. BP
Pinus sylvestris-type	7990.1.1	III (32–55)	9560 ± 124	10,645
ARROYO DE LOS LOBOS 2
Taxa	Lab. Code	Level/Sampling depth (cm)	AMS ¹⁴C age (BP)	Age cal. BP
Abies sp.	6792.1.1	III (17–39)	108 ± 23	289–94
CASCAJARES 4
Taxa	Lab. Code	Level/Sampling depth (cm)	AMS ¹⁴C age (BP)	Age cal. BP
Pinus sylvestris-type	7992.1.1	II (15–45)	7472 ± 26	8352–8267
Pinus sylvestris-type	7997.1.1	III (45–96)	7473 ± 25	8352–8267
Pinus sylvestris-type	7993.1.1	II (15–45)	7352 ± 25	8339–8103
Pinus sylvestris-type	6793.1.1	III (45–96)	7361 ± 23	8333–8103
Pinus sylvestris-type	7996.1.1	II (15–45)	7405 ± 28	8244–8134
Pinus sylvestris-type	7995.1.1	II (15–45)	7386 ± 25	8238–8112
Pinus sylvestris-type	7998.1.1	III (45–96)	7335 ± 25	8105
Pinus sylvestris-type	7994.1.1	II (15–45)	7300 ± 104	8013
Radiocarbon dates obtained in previous investigations
PALMITERA 1
Taxa	Lab. Code	Level/Sampling depth (cm)	AMS ¹⁴C age (BP)	Age cal. BP
Abies sp.	5173.1.1	V (52–80)	8707 ± 37	9931–9616
Abies sp.	5174.1.1	V (52–80)	8573 ± 35	9719–9551
Abies sp.	5176.1.1	V (52–80)	8549 ± 36	9552
Abies sp.	5175.1.1	V (52–80)	8300 ± 40	9266–9206
Abies sp.	5177.1.1	V (52–80)	8155 ± 39	9245–9076
Abies sp.	5170.1.1	V (52–80)	8003 ± 128	9236–8615
Abies sp.	5171.1.1	V (52–80)	8057 ± 111	8672
Abies sp.	Poz-83921	V (52–80)	7300 ± 50	8342–8053
Pinus pinaster	Poz-78857	V (52–80)	7300 ± 40	8092
Abies sp.	5169.1.1	IV (32–52)	7142 ± 34	8001–7944
Abies sp.	Poz-78851	IV (32–52)	6480 ± 40	7516–7356
Abies sp.	5172.1.1	V (52–80)	6239 ± 35	7224–7085
Abies sp.	Poz-78852	IV (32–52)	5710 ± 40	6651–6473
Abies sp.	Poz-83920	V (52–80)	5840 ± 40	6607–6573
Abies sp.	Poz-83922	IV (32–52)	5770 ± 40	6553–6523
Pinus pinaster	Poz-78854	IV (32–52)	4965 ± 35	5899–5668
Abies sp.	Poz-83924	IV (32–52)	4605 ± 35	5441–5145
Quercus sp.	Poz-78850	II (9–21)	50 ± 30	295–103
Pinus pinaster	Poz-78849	I (0–9)	70 ± 30	293–101
Quercus sp.	Poz-78929	III (21–32)	90 ± 30	289–94
Quercus sp.	Poz-78853	IV (32–52)	120 ± 30	279–79
Quercus sp.	Poz-78856	V (52–80)	135 ± 30	254–77
Quercus sp.	Poz-78848	I (0–9)	140 ± 30	242–76
CAÑADA DE ENMEDIO
Taxa	Lab. Code	Level/Sampling depth (cm)	AMS ¹⁴C age (BP)	Age cal. BP
Acer sp.	Poz-113830	III (30–45)	955 ± 30	998–865
Deciduous Quercus	Poz-113272	III (30–45)	890 ± 30	979–802
Deciduous Quercus	Poz-113273	III (30–45)	825 ± 25	852–760
Fraxinus sp.	Poz-113271	III (30–45)	825 ± 30	750
Acer sp.	Poz-113832	II (11–30)	480 ± 30	612–568
Abies sp.	Poz-113828	III (30–45)	200 ± 30	326–208
Abies sp.	Poz-113846	I (0–11)	180 ± 30	322–137
Abies sp.	Poz-113848	II (11–30)	180 ± 30	322–137
Abies sp.	Poz-113827	II (11–30)	170 ± 30	320–131
Abies sp.	Poz-113270	I (0–11)	50 ± 30	295–103
Abies sp.	Poz-113784	II (11–30)	15 ± 30	295–103
Abies sp.	Poz-113847	II (11–30)	80 ± 30	291–79
Abies sp.	Poz-113829	II (11–30)	115 ± 30	280–80
Abies sp.	Poz-113826	II (11–30)	125 ± 30	276–78
LOS REALES 1
Taxa	Lab. Code	Level / Sampling depth (cm)	AMS ¹⁴C age (BP)	Age cal. BP
Abies sp.	Poz-83919	III (36–61)	8860 ± 50	9810
Pinus pinaster	Poz-78861	II (10–36)	6200 ± 40	7274–7052
Pinus pinaster	Poz-78886	III (36–61)	6070 ± 40	7197–6863
Pinus pinaster	Poz-78862	III (36–61)	6170 ± 40	7017
Abies sp.	Poz-83918	II (10–36)	6160 ± 40	7014
Pinus pinaster	Poz-83916	III (36–61)	6140 ± 40	7006–6974
Abies sp.	Poz-78858	I (0–10)	200 ± 30	326–208
Abies sp.	Poz-78859	I (0–10)	195 ± 30	325–143
Abies sp.	Poz-78885	I (0–10)	60 ± 30	294–102
Pinus pinaster	Poz-78860	I (0–10)	110 ± 30	282–82
LOS REALES 2
Taxa	Lab. Code	Level / Sampling depth (cm)	AMS ¹⁴C age (BP)	Age cal. BP
Abies sp.	Poz-82525	IV (33–52)	3270 ± 30	3516–3476
Pinus pinaster	Poz-83915	I (0–7)	2895 ± 30	3011
Pinus pinaster	Poz-82528	III (18–33)	2405 ± 30	2715–2419
Pinus pinaster	Poz-82524	IV (33–52)	1955 ± 30	2220–2031
Pinus pinaster	Poz-82526	IV (33–52)	2005 ± 30	2135–2104
Abies sp.	Poz-82527	III (18–33)	1800 ± 30	1832–1674
Abies sp.	Poz-83914	I (0–7)	45 ± 30	295–103
Abies sp.	Poz-83913	II (7–18)	40 ± 30	295–103
Abies sp.	Poz-83912	II (7–18)	110 ± 30	282–82
PUERTO DE LOS VALIENTES
Taxa	Lab. Code	Level/Sampling depth (cm)	AMS ¹⁴C age (BP)	Age cal. BP
Pinus sp.	Poz-113775	IV (XXX)	3860 ± 35	4294–4225
Deciduous Quercus	Poz-113776	IV (85–108)	1065 ± 30	1092–991
Abies sp.	5160.1.1	IV (85–108)	1197 ± 73	1030
Deciduous Quercus	Poz-113268	II (18–56)	630 ± 30	622
Abies sp.	Poz-113772	IV (85–108)	360 ± 30	491–385
Acer sp.	Poz-113774	IV (85–108)	285 ± 30	420–226
Abies sp.	Poz-113771	I (0–18)	345 ± 30	383
FUENFRÍA ALTA
Taxa	Lab. Code	Level/Sampling depth (cm)	AMS ¹⁴C age (BP)	Age cal. BP
Abies sp.	Poz-113773	I (0–18)	335 ± 30	380
Abies sp.	Poz-113780	III (45–78)	8740 ± 50	9619
Abies sp.	Poz-113779	I (0–14)	4970 ± 35	5897–5668
Abies sp.	Poz-113778	I (0–14)	5015 ± 35	5726–5679
Pinus sp.	Poz-113781	III (45–78)	3590 ± 35	4123–3800
Pinus sp.	Poz-113269	IV (78–94)	3650 ± 40	3939–3921
Deciduous Quercus	Poz-113783	III (45–78)	1510 ± 30	1564–1380
Deciduous Quercus	Poz-113782	I (0–14)	1095 ± 30	1023–1003
JARASTEPAR 2
Taxa	Lab. Code	Level/Sampling depth (cm)	AMS ¹⁴C age (BP)	Age cal. BP
Abies sp.	5162.1.1	I (0–21)	9038 ± 121	9830
Abies sp.	5163.1.1	I (0–21)	8861 ± 122	9669–9629
Abies sp.	5161.1.1	I (0–21)	8637 ± 40	9606

Source: Drawn up by the authors on the basis of data collected by Olmedo-Cobo et al. (2019a, 2019b, 2021) and Pardo-Martínez et al. (2022).

Pollen analysis

The results show the conclusions arising from the only paleo-palynological survey carried out to date in the Serranía de Ronda (see Alba-Sánchez et al., 2019) (Figure 4). The survey was performed in a wetland in an area known as the Cañada de Enmedio, in the Sierra de las Nieves National Park. On the basis of these palynological records, it was possible to identify changes in land use, and the evolution of the Spanish fir forests over the last eight centuries (1180 AD to the present). In this last section, the decline of Abies pinsapo can be observed in recent centuries. During the Islamic period, there was little human impact on the A. pinsapo forest whose structure remained relatively stable. However, a process of degradation began as a result of the intensification of human activities during the Christian period. Both the size and the biodiversity of these forests were affected by deforestation to provide wood for shipbuilding, mining, the wider commercial use of charcoal, extensive agriculture, livestock-farming and grazing. The latest sequence of the sedimentary record reveals that around the beginning of the 20th century, the mountains around Ronda were subject to severe deforestation, although the conservation measures implemented in the last few decades have allowed a slight recovery and densification of the fragmented populations of A. pinsapo. Finally, and as a consequence of progressively hotter, drier conditions due to global warming, in recent years there has been an important extension in the populations of Quercus rotundifolia.

Historical information

The historical documentary sources offer a general perspective on the vegetation in the Serranía de Ronda since the 17th century onward. A detailed study of these sources revealed that the landscape was dominated by conifer and broadleaf forests. As regards the most unusual formations in ecological and landscape terms, which include the A. pinsapo, Spanish fir forests, the earliest references appear in the 17th century in various municipal ordinances and in inventories of wood used to supply the Spanish Navy or for building houses (see Becerra, 2006; Gil, 2002; Gómez-Zotano, 2004, 2006; Gómez-Zotano and Olmedo-Cobo, 2021). The information about the Spanish fir in the General and Specific Questions from the Ensenada Land Survey, from the mid-18th century (Gómez-Zotano and Olmedo-Cobo, 2021) is also of great interest, as are the written accounts of travelers and naturalists gathered by Guzmán et al. (2013) and López-Quintanilla (2013).

As regards P. pinaster, it has been confirmed that it grew naturally in certain enclaves in the Serranía de Ronda, such as the Sierra Bermeja (Gómez-Zotano, 2004; Olmedo-Cobo et al., 2019a, 2019b). In 1752 the Marqués de la Ensenada Land Survey referred to the peridotite outcrops as “barren land by nature which produces nothing,” with the exception of the places that hosted a population of “pinos bravíos” (the adjective “bravíos” refers to wild pines, i.e. to a native population), a fact also mentioned by the cartographer Tomás López in 1780 (Gómez-Zotano, 2004).

A great deal of information is available on broadleaf species, and in particular the Quercus genus, of which the most commonly worked species was the holm oak. Various sources, such as the documents about the demarcation of the land boundaries in Castillo-Rodríguez, 2000 and those from the ironworks in Marbella, mention the existence of cork oak and holm oak trees in certain areas of the Sierra del Real (Gómez-Zotano, 2004). As regards the Portuguese Oak, the first references appear in the 16th century in the General Archives of Simancas and in municipal ordinances from the town of Benaoján (Becerra, 2021; Urbaneja, 2021). Later, various different documents and field journals by 19th and 20th century naturalists continue to indicate the presence of Portuguese Oaks in various parts of the Serranía de Ronda, from the Valley of the River Guadiaro to the Sierra de las Nieves passing through Ubrique, Grazalema or Cortes de la Frontera, as highlighted by Castillo-Rodríguez (2021), De Benito (2021), Urbaneja (2021), and Vargas-Jiménez (2021). In spite of that, all the historic references refer to the common Portuguese oak (Q. faginea), and there are no reliable historical mentions of the genuine mountain Portuguese oaks (Q. faginea subsp. alpestris), apart from those relating to the first material collected for this species by the Swiss botanist, Pierre Edmond Boissier, in 1837.

Species distribution models

The main species distribution models indicate an overall decline in the forest mass in the southern part of the Iberian Peninsula. Special interest has been shown in the models applying to the A. pinsapo (Alba-Sánchez and López-Sáez, 2013; Alba-Sánchez et al., 2010; Gonzalez-Hernandez et al., 2021; Gutiérrez-Hernández, 2018; Navarro-Cerrillo et al., 2006, 2013; Sánchez-Salguero, 2007), based on patterns of suitability and multivariable regressions to establish different degrees of potentiality regarding the previous presence of this species in the mountains in the south and south-east of Spain (Serranía de Ronda, Sierras de Almijara-Tejeda, Sierra Nevada, Sierras de Cazorla-Segura and Sierra de Aitana).

As regards the Serranía de Ronda, Sánchez-Salguero (2007) established optimum potentiality for the Spanish fir in the highest levels of the main mountain systems in the province of Cadiz (Sierra del Pinar, Sierra del Endrinal, Sierra del Caíllo, Sierra de Líbar, and Sierra de los Pinos).

Other models, such as those developed by Navarro-Cerrillo et al. (2006, 2013), show enlarged maps for the group of mountain systems which currently host A. pinsapo: Sierra de las Nieves, Sierra Bermeja, and Sierra de Grazalema. The results show high potentialities based on two fundamental requirements: high average altitude and north-facing.

For their part, the models developed by González-Hernández et al. (2021) highlight the mismatch between the current niche and the reproductive niche of A. pinsapo in response to a changing climate. These authors observed a change in the altitude range, where the young trees are migrating upwards (or northwards) toward cooler and wetter climates leaving behind the older generations of trees to try to survive at lower altitudes. Mature trees may show some degree of resilience to less-than-ideal conditions, surviving in areas where seedlings can no longer establish themselves, so making it difficult for the species to complete its life-cycle.

At a broader geographical scale, perhaps the most interesting studies are those by Alba-Sánchez and López-Sáez (2013) and Alba-Sánchez et al. (2010), who created a suitability model for A. pinsapo for the Baetic Cordillera as a whole. The analysis of this model shows that the highest suitability levels were restricted to the Rondeño sector of the Baetic Province, the enclave currently hosting the only populations of Spanish fir in the Iberian Peninsula. At the same time the model broadens the habitability area for this species to other mountain systems in the south and east of the Iberian Peninsula, such as Sierra Gorda, Sierra Tejeda, Sierra Nevada, Sierra de Cazorla, Sierra de Alcaraz, Sierra de Aitana, Sierra de Alfaro, and Sierra de Mondúver, although the suitability rates are significantly lower in the more easterly mountain systems.

Lastly, and in order to analyze the progression of the different ecological niches for A. pinsapo in the current context of climate change, the Regional Government of Andalusia has developed various different prospective models as part of a project called “Escenarios locales de cambio climático. Clasificación del Índice de distribución potencial del Pinsapo (Abies pinsapo) (Junta de Andalucía, 2014).” These models show the progression of the potential enclaves of A. pinsapo in three large periods: from 2011 to 2014, from 2014 to 2017 and from 2071 to 2099, taking the period 1961–2000 as the period of reference. The results show a progressive decline in the area of potential habitability of the Spanish fir at the end of this century. These findings are in line with the conclusions reached by Gutiérrez-Hernández (2018), who by assembling models for the ecological niche of A. pinsapo with a horizon at the year 2100, estimated drastic potential and actual reduction in the species during the coming decades. This regressive dynamic is also applicable to other tree species from the Serranía de Ronda of great interest in ecological and landscape terms, such as Quercus rotundifolia, Quercus suber, P. pinaster, and Castanea sativa, taxa whose potential habitability areas also seem likely to decline in the coming years.

New paleoecological data about the composition and dynamics of the forests in the Serranía de Ronda

During the present research, pedoanthracological analysis was systematically applied to 6 new sites in the southwestern end of the Baetic Cordillera. In this way, we discovered ancient populations of conifers such as Abies sp. and P. sylvestris-type that are currently absent in several of the sites sampled. The latter is particularly interesting because it is not currently present in any of the mountainous reliefs that make up the Serranía de Ronda. These findings were contextualized with information from other available sources, and data from previous research by Olmedo-Cobo et al. (2019a, 2019b, 2021) and Pardo-Martínez et al. (2022). This allowed for a much broader understanding of the paleoecological dynamics of the vegetation in the Serranía de Ronda. The data obtained suggest that trees played a much greater role in certain enclaves in the Serranía de Ronda. This phenomenon has also been observed in large parts of the European continent where, after the ice receded to (almost) its present-day distribution, most of the forests in Europe reached their maximum size (Giesecke et al., 2017; Zanon et al., 2018).

In the case of Abies sp., the dates obtained by carbon dating for a total of 51 charcoal fragments – 7 in this study – confirmed a larger distribution area in mountain areas over the course of the last millennia than there is today, in line with the conclusions reached by Linares (2011). The earliest records suggest that the Spanish fir was present in locations such as Palmitera 1 (Sierra Palmitera), Fuenfría Alta (Sierra de las Nieves) and Jarastepar 2 (Sierra del Oreganal), with remains dating from between 9931–9616 and 9619 years cal. BP, as reported by Olmedo-Cobo et al. (2021) and Pardo-Martínez et al. (2022). These data reveal the role that may have been played by these enclaves during the migration of the Spanish fir over the course of the last millennia. In this way, localities such as Palmitera 1, Fuenfría Alta and Arroyo de los Lobos 2 – the last one much more recently – may have provided a physical connection between the populations in the Sierra de las Nieves and the Sierra Bermeja. For its part, Jarastepar 2 could have acted as a link between the Spanish fir forests in the Sierra de las Nieves National Park and the Sierra de Grazalema Natural Park. This past distribution range seems to follow a similar pattern to that shown on the maps produced by Euforgen (2022), which show a uniform extension of Abies sp. through all the main mountain systems in the Serranía de Ronda. These maps do not in fact depict the real situation today but could show the past distribution of this species. In the same way, all the paleo-populations of Abies discovered coincide with the potential domains established by the different available models (Alba-Sánchez and López-Sáez, 2013; Alba-Sánchez et al., 2010; Gonzalez-Hernandez et al., 2021; Gutiérrez-Hernández, 2018; Navarro-Cerrillo et al., 2006, 2013; Sánchez-Salguero, 2007).

At the same time, when the new carbon dating results obtained for P. pinaster in various locations in the Serranía de Ronda are combined with the existing ones, they seem to indicate on the one hand, the dynamism of the pine forest, which apparently replaced the Spanish fir (e.g. in Fuenfría Alta) about 6000 years ago, as noted by Olmedo-Cobo et al. (2021). This dynamic was accentuated about 4500–4000 years ago, due to hotter and drier conditions in the western Mediterranean (Jiménez-Moreno et al., 2013; Mauri et al., 2015). The results also reveal that the Spanish fir forests coexisted with P. pinaster at altitudes of over 1200 masl in Sierra Palmitera in certain phases of the early and Mid-Holocene, with ages of between 9931–9616 and 5441–5145 years cal. BP. In addition, the chronologies for P. pinaster have allowed us to confirm its status as an autochthonous plant on the ultramafic substrata of Sierra Bermeja (Olmedo-Cobo et al., 2019a, 2019b).

The identification of the Pinus genius in localities such as the Cañada del Cuerno (Sierra de las Nieves) during the Mid-Holocene (4119–3956 years cal. BP), indicates that the long-lived, monospecific, Spanish fir forests existing today may have been enriched intermittently with Pinus sp. Once again, the climatic bonanza that characterized this period known as the Holocene Climatic Optimum (Davis et al., 2003; Kalis et al., 2003) could perhaps explain the expansion of the pine forest into the Spanish fir forest. Later, when conditions became favorable for the Spanish fir, the pine forest must have begun to decline until it finally disappeared from this sector of the Sierra de las Nieves. In addition, the lack of Abies charcoal in the pedoanthracological record, together with the presence of numerous ancient trees seems to strengthen the role played by the Spanish fir in this area during the last centuries (Olmedo-Cobo et al., 2021).

Pinus sp. has also appeared in the localities of Cascajares 1 and Puerto de los Valientes, with chronologies ranging between 10,311 and 8234–8110 years cal. BP in the first case and between 4294 and 4225 years cal. BP in the second. These findings seem to confirm the past presence of pine forests in both these enclaves where they no longer exist today. This information, together with the identification of ancient charcoals from practically the same era of deciduous Quercus (presumably attributable to Q. faginea subs. alpestris) and Abies in Puerto de los Valientes, appears to confirm the existence of strips of mixed forest at high altitudes in the Sierra de las Nieves (Olmedo-Cobo et al., 2021). This circumstance would also allow us to hypothesize about the greater area covered by trees in mountainous areas in the past, as highlighted in historical accounts (Castillo-Rodríguez, 2002; Gómez-Zotano, 2004). The relative scarcity of trees today would confirm the tendency toward deforestation over the last centuries, as mentioned earlier.

Pinus sp. has also been found at the western end of the Serranía de Ronda, specifically in the Sierra del Pinar in Grazalema. The ages obtained via carbon dating reveal that this taxon was present in this Sierra in the period 310–126 years cal. BP. These dates are practically contemporary with those offered by three charcoal fragments from the Abies genus (between 280–80 and 276–77 years cal. BP) and seem to confirm the existence of mixed forest (fir-pine) in this enclave, less than 3 centuries ago. Together with this, the high anthracomass value of the fragments found in this locality (8285 mg/kg) offers an insight into the important impact that fire seems to have had in recent periods in this area. This coincides with the gradual withdrawal of the fir forests in this sector since the beginning of the Modern Age, as can be inferred from different historical references compiled by Guzmán et al. (2013). The burning of forests and the conversion to agricultural and grazing land, coinciding with better topographic conditions, seem to have intensified during the wars arising from the Christian reconquest of Al-Ándalus (15th and 16th centuries), and in the fight for survival produced by the lack of cultivated land (16th and 19th centuries). The severe fire damage caused to these forests may also have led to a significant decline in the area occupied by the Spanish fir and presumably also by pine forests.

Charcoal belonging to the Pinus genus has also been identified at altitudes of less than 800 masl in the Sierra del Tablón, a mountainous spur that forms the northern boundary of the Serranía de Ronda. The sole charcoal fragment was dated at 14,013–13,440 years cal. BP, the oldest in the present study. It proved impossible to exactly identify the species and we were therefore obliged to hypothesize about which pine trees featured most in the tree canopy in this enclave during the Pleistocene-Holocene transition, a stage of great paleo-environmental importance (García-Alix et al., 2021; López-Sáez et al., 2008). Badal et al. (2013) confirmed the existence of orophile (mountain-loving) pine forests toward the end of the Solutrean (±16,000 years cal. BP) in the south of the Iberian Peninsula at altitudes of up to 1000 masl. During this period the Sierra del Tablón would have been subject to the influence of the upper supra-mediterranean and the lower oro-mediterranean bioclimatic levels, while the coastal strip would have been dominated by mesomediterranean conditions (Aura-Tortosa et al., 2002). On top of that, various palynological and anthracological records performed in locations near the Sierra del Tablón have detected the presence of P. sylvestris-type on the southwestern flank of the Baetic Cordillera between 1000 and 10,000 years ago (Carrión, 2012; López-Sáez et al., 2008). This hypothesis was reinforced by the discovery of P. sylvestris-type charcoal in localities such as Cascajares 4 and Arroyo de los Lobos 1 (Sierra Blanca de Igualeja), and of various fragments of Pinus sp. dating back more than 10,000 years in Jarastepar 2 (Sierra del Oreganal), all of which were situated above 1100 masl (Pardo-Martínez et al., 2022). All of these findings confirm the possible role that the Sierra del Tablón may have played as a refuge after the Last Glacial Maximum, a period when certain sub-alpine pine forests must have shown great resilience in different sectors of the Baetic Cordillera (Rubiales et al., 2010). During the Holocene, the chronologies obtained for three fragments of Quercus sp. confirm the presence of this taxon over the last 10,000 years. Similarly, the progressive trend toward hotter, drier environmental conditions in the south of Spain (Cacho et al., 2001; Jalut et al., 2000) is likely to favor the disappearance of the pine forest, giving way to more thermophile taxa such as evergreen Quercus sp. (Carrión, 2012). This dynamic continues today and coincides with the classification established by Rivas-Martínez (2011), who stated that the potential vegetation in the Sierra del Tablón corresponds to sclerophyll, thermo-mesomediterranean holm oak and Portuguese oak forests, today enriched with thermophile species such as Pistacia lentiscus and Arbutus unedo, as evidenced by the pedoantracological record.

Fragments from the Fraxinus and Salix genera appear in the charcoal record from the Cañada de Enmedio sampling site (Sierra de las Nieves), although these taxa do not grow in this locality today. However, they would seem to have played a relatively secondary role, accounting respectively for just 8.7% and 0.7% of the fragments detected, as noted by Olmedo-Cobo et al. (2021). This fact, together with the signal obtained for other taxa which currently have a fairly minor presence within the plant system in this enclave, would suggest greater heterogeneity in the arboreal stratum in the past. The presence of these minor taxa, together with the dates obtained for Fraxinus, and those obtained for Acer (998–865 and 612–568 years cal. BP) and deciduous Quercus. (979–802 and 852–760 years cal. BP), suggest that the long-living, practically monospecific Spanish fir forest that we see today was probably accompanied by different deciduous genera over the course of the last millenium. Later, and as inferred by the last palynological survey carried out in the study area, it seems that a situation that was unfavorable for the conservation of forests developed until well into the 17th century (Alba-Sánchez et al., 2019). Later, the modern era brought with it the progressive decline in the forest mass, with repeated forest fires and intensive deforestation processes, which led to a notable reduction in the surviving tree formations, including the Spanish fir forest (Guzmán et al., 2013). This modern phase of degradation of the forests is highlighted by the most recent carbon dating records obtained for carbon fragments of Abies sp. in this enclave with ages ranging between 343–80 and 324–101 years cal. BP. This confirms the role played by fire during the last centuries in the configuration of the plant landscape in this sector.

Importance of fire in the dynamics of the floresta during the Holocene

Forest fires have been a key factor in the configuration of the plant landscape in the western Mediterranean (Bond and Keeley, 2005; Turner et al., 2008; Vannière et al., 2008). There is ample evidence of the important role played by fire in the genesis of present-day plant ecosystems in the north and center of the Iberian Peninsula (López-Sáez et al., 2014; Pérez-Obiol et al., 2016). In the south, however, despite of being a territory that is extremely vulnerable to forest fires, paleo-geographic research into this question has been relatively limited (Global Paleofire Database, 2022; Harrison et al., 2022; Sweeney et al., 2022).

The new datings we obtained – 36 in total –, together with those obtained during earlier research by Olmedo-Cobo et al. (2019a, 2019b, 2021) and Pardo-Martínez et al. (2022), provide an excellent framework of reference to expand our knowledge of forest fires at the western end of the Baetic Cordillera during the Holocene (Figure 5). They also provide a considerable volume of information for the Global Paleofire Database, offering very precise data about the different episodes of fire in the Serranía de Ronda throughout the Holocene. The 110 radiocarbon dates available for the whole of the Serranía de Ronda show that there were two hiatuses between 6500–5800 and 5200–4300 years cal. BP, periods during which no carbon fragments were detected. This suggests that there were fewer fires in these periods, a possibility corroborated by the evidence of cooling between the two Holocene Climatic Optimums (Davis et al., 2003; Ilvonen et al., 2022), and to the very limited human presence in medium and high altitudes of the Serranía de Ronda during the initial period of the Neolithic era in Andalusia (Mid-Holocene), at which time there were settlements in nearby areas on the Andalusian coast and in the depression of Ronda (Castaño-Aguilar, 2021; Ramos-Muñoz et al., 2017). On this question, the very limited available information seems to some extent to match the results obtained in this study by highlighting that the period running between 7500 and 5200 years cal. BP was one of optimum conditions for mesophyte species and the period with the lowest level of fires (Carrión, 2002; Carrión et al., 2003).

Taken together, the data show higher levels of fire in the study area over the last 2000 years in line with the different historical accounts. Forty-nine charcoal fragments were carbon-dated from this period. This trend can be extended to other parts of the south and south-west of Andalusia, as evidenced by the palynological records (Carrión, 2012). This was exacerbated by the increasing intensification of agricultural production and seems to have been the primary cause of the deterioration of the natural environment of the Serranía de Ronda (Gómez-Zotano and Olmedo-Cobo, 2021; Ramos-Muñoz et al., 2017).

In much more recent periods, the increased frequency and virulence of forest fires has been verified in different localities in the study area such as Sierra de Tolox and Sierra Bermeja, in which a total of 2500 and 16,542 ha respectively have been burnt during the last 50 years (Martos-Martín and Gómez-Zotano, 2021; Millán-Madrid and Martínez-Murillo, 2021).

Conclusions

The present study has provided new data to improve our paleobiogeographic knowledge of certain relict forests at the southwestern end of the Baetic Cordillera, an area where there is a serious lack of such information. The results of this research have been added to the existing database, so creating an important source of hard data on the dynamics of the forests of the Serranía de Ronda during the Holocene. Likewise, the 110 radiocarbon dates – 36 of them obtained in this study – are an essential source for the paleogeographical study of forest fires in the south of the Iberian Peninsula.

The wide network of pedological sampling carried out over the last few years has enabled us to find ancient populations of taxa that are currently absent in some of the localities sampled. The data highlight the role played by certain physiographical enclaves as refuges for flora over the course of the Holocene. Mountain ranges such as the Sierra del Oreganal and the Sierra Palmitera seem likely to have acted as important ecological corridors that facilitated links between the three separate unconnected masses of A. pinsapo that exist today.

Various fragments of Pinus sylvestris-type were found amongst the soil samples. This is the first pedoanthracological evidence of this taxonomic group in this sector of the Baetic Cordillera. Mountain areas such as the Sierra del Tablón and the Sierra Blanca de Igualeja seem likely to have acted as important post-glacial refuges for certain mountain-loving pine forests during the Pleistocene-Holocene transition. These locations must once have formed the south-western boundaries of the high mountain pine forests in the first stages of the Holocene, before they were progressively restricted toward their current distribution area.

At the same time, the complementary nature of the different sources of information that have come together in the multi-proxy approach applied in this research have revealed the greater importance and diversity of the tree cover in the study area during the last millennia. This gives us a much more accurate picture of the past vegetation and allows us to contextualize it with the different environmental and anthropic conditions that have prevailed in the Serranía de Ronda at different times during the Holocene.

This paleoecological information could be of great value for understanding the environmental dynamics that have contributed to shaping our current plant landscape. As a result, it could be an effective tool for the adaptive management of the most endangered forests in the face of global change. To this end, it is important to continue broadening our paleoecological knowledge of the mountains in the south of the Iberian Peninsula as a future line of research. This will involve extending the current network of pedoanthracological and palynological surveys to the rest of the Baetic Cordillera.

Supplemental Material

sj-jpg-1-hol-10.1177_09596836231185835 – Supplemental material for Multiproxy analysis for the paleobiogeographical reconstruction of the relict forests of the Serranía de Ronda during the Holocene (Baetic System, Spain)

Supplemental material, sj-jpg-1-hol-10.1177_09596836231185835 for Multiproxy analysis for the paleobiogeographical reconstruction of the relict forests of the Serranía de Ronda during the Holocene (Baetic System, Spain) by Rubén Pardo Martínez, José Antonio Olmedo Cobo, José Gómez Zotano and Francisca Alba Sánchez in The Holocene

Supplemental Material

sj-jpg-2-hol-10.1177_09596836231185835 – Supplemental material for Multiproxy analysis for the paleobiogeographical reconstruction of the relict forests of the Serranía de Ronda during the Holocene (Baetic System, Spain)

Supplemental material, sj-jpg-2-hol-10.1177_09596836231185835 for Multiproxy analysis for the paleobiogeographical reconstruction of the relict forests of the Serranía de Ronda during the Holocene (Baetic System, Spain) by Rubén Pardo Martínez, José Antonio Olmedo Cobo, José Gómez Zotano and Francisca Alba Sánchez in The Holocene

Footnotes

Funding

The author(s) disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: This research has been supported by a contract for University Teacher Training (Formación de Profesorado Universitario) (Ref. 18/03023) from the Spanish Ministry of Education, Culture and Sports (Ministerio de Educación, Cultura y Deportes del Gobierno de España), and research projects financed by the State Research Agency (SRA) and European Regional Development Fund (ERDF): PALEOPINSAPO (CSO2017-83576-P), PALEOPINSAPO II (PID2022-141592NB-100), MED-REFUGIA (RTI2018-101714-B-I00) and TED2021-132631B-I00; Andalusian Plan for Research, Development and Innovation: Oromed-Refugia (P18-RT- 4963); and ERDF Operational Programme in Andalusia (EU regional programme): ForestMed (A-RNM-688-UGR20).

ORCID iDs

Rubén Pardo Martínez

Francisca Alba Sánchez

Supplemental material

Supplemental material for this article is available online.

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