This paper investigates the Holocene vegetation dynamics for
Burmarrad in Northwest Malta and provides a pollen-based quantitative
palaeoclimatic reconstruction for this centrally located Mediterranean
archipelago. The pollen record from this site provides new insight into the
vegetation changes from 7280 to 1730 cal BP which correspond well with
other regional records. The climate reconstruction for the area also provides
strong correlation with southern (below 40
Interpreting the complex relationship between vegetation dynamics, climate change, and anthropogenic activities during the Holocene is important for understanding past societies and their environment (Weiner, 2010; Walsh, 2013). Palynology, the study of pollen and spores (e.g. Erdtman, 1943; Faegri and Iversen, 2000; Moore et al., 1991; Traverse, 2008), has been an important element in this interpretation and has been central to environmental reconstruction since the early 20th century (MacDonald and Edwards, 1991). The analysis of pollen grains extracted from sediment cores from terrestrial and marine environments, as part of an interdisciplinary approach, provides quantitative data on the past changes in vegetation compositions (e.g. Behre, 1981; Giesecke et al., 2011; Sadori et al., 2013a), revealing valuable palaeoecological information that can assist with climate reconstructions (e.g. Bartlein et al., 2011; Mauri et al., 2015). Over the past 25 years there has been a growing body of knowledge relating to Holocene vegetation changes particularly within the Mediterranean. This region is considered a hotspot of biodiversity (Médail and Quézel, 1999) as well as a climate change “hotspot” (Giorgi and Lionello, 2008). Recent research has highlighted possible anthropogenic influences along with the, often hard to separate, climatic signal through palaeoenvironmental reconstruction, such as to the west (Carrión et al., 2007; Estiarte et al., 2008; López Sáez et al., 2002; Pantaléon-Cano et al., 2003), centrally (Bellini et al., 2009; Calò et al., 2012; Combourieu Nebout et al., 2013; Di Rita and Magri, 2012; Noti et al., 2009; Peyron et al., 2011; Sadori et al., 2013b; Tinner et al., 2009), as well as in eastern areas (Bottema and Sarpaki, 2003; Finkelstein and Langgut, 2014; Hajar et al., 2010; Jahns, 2005; Kaniewski et al., 2014; van Zeist et al., 2009).
Numerous studies have highlighted the climatic contrast between the western versus eastern and northern versus southern sides of the Mediterranean Basin during the Holocene (Brayshaw et al., 2011; Jalut et al., 2009; Magny et al., 2012; Roberts et al., 2011, Peyron et al., 2013). It is generally considered that environmental change was primarily nature-dominated in the wetter early Holocene and human-dominated in the warmer, drier late Holocene (Berger and Guilaine, 2009), with the mid-Holocene (6–3 ka BP) remaining a “melange” (Roberts et al., 2011); therefore focus is often placed on this mid-Holocene climatic transition (Collins et al., 2012; Fletcher et al., 2013; Mercuri et al., 2011; Pérez-Obiol et al., 2011; Vannière et al., 2011).
Within the Mediterranean, the centrally located Maltese archipelago (Fig. 1a) provides a key site to study these dynamics in an island context during the Holocene. However, with no peat bogs or lake deposits, suitable sites for palaeovegetation data collection are very limited; notwithstanding this situation some recent research has been carried out on coastal areas (Carroll et al., 2012; Djamali et al., 2012; Fenech, 2007; Marriner et al., 2012).
The purpose of this study is to expand on the current knowledge of the
Holocene vegetation dynamics on this strategically located archipelago,
positioned almost midway between the western and eastern edges of the
Mediterranean, through the study of a terrestrial core taken from Burmarrad,
the second largest flood plain, on the Maltese Islands (Fig. 1d). This will allow for:
completing the previous results from Burmarrad obtained by
Djamali et al. (2012), that covered a shorter period during the early to mid-Holocene (7350–5600 cal BP); a new palaeovegetation reconstruction from 7280 to 1730 cal BP for
NW Malta; the first quantitative palaeoclimatic reconstruction for the Maltese
islands.
It is hoped that the more interdisciplinary research conducted both within this archipelago and other Mediterranean locations will provide more data to enable concise reconstructions of the fluctuating vegetation assemblages and climatic variations present over the Holocene. This information, in turn, might provide a better understanding of the various processes and factors affecting not only past but also present and future landscapes.
The Maltese archipelago (latitude:
35
Study area.
Selection of plant taxa characteristic of the main Maltese vegetation communities (adapted from Schembri, 1997; Stevens et al., 1995).
The archipelago's vegetation, similar to other Mediterranean islands and coastal areas, is strongly affected by intense summer heat and low precipitation, as well as increasing anthropogenic activity in recent millennia (Grove and Rackham, 2001; Roberts, 2014). Presently, the three main semi-natural vegetation types are garrigue, steppe, and maquis (Table 1), while there are a few much smaller communities developed as woodlands, in freshwater and on rocky habitats, on sand dunes and in coastal wetlands; these smaller communities are significant due to the rare endemic species found within them (Schembri, 1997).
Current evidence for the archipelago establishes human occupation on the islands at about 7200 years ago, with the initial settlers originating from Sicily (Blouet, 2007). During the period covered by the BM2 core the islands have undergone a succession of occupiers; during the Neolithic, Temple, and Bronze periods (Trump, 2002), as well as the Historical period with Phoenician, Punic, and Roman settlements (Bonanno, 2005).
The climate of the archipelago (Fig. 1c) is considered to be typically
Mediterranean (Chetcuti et al., 1992), with mild, wet winters and hot, dry
summers, while the spring and autumn seasons are short (Blondel et al.,
2010). The annual precipitation is 530 mm, with 70 % of this rainfall
occurring between October and March, though much is lost to
evapotranspiration (Anderson, 1997). The northwesterly wind
(
The Burmarrad area where the BM2 core was taken (Fig. 1d) is currently an agricultural plain with a number of settlements, along with patches of maquis, garrigue, and steppe along its edges, as well as one small remnant stand of indigenous olive trees. Though hard to date, the latter are considered to be up to 1200 years old (Grech, 2001). Terracing with rubble walls for agricultural purposes can also be found on the rocky slopes of the catchment area. The present agricultural plain is subject to seasonal flooding; however, before silting in, there is strong archaeological evidence to suggest that it was used as a natural anchorage up until at least Roman times (Gambin, 2005; Trump, 1972). The earliest evidence for occupation in this area is in the form of a prehistoric tomb at San Pawl Milqi dating to 6050–5750 BP (Locatelli, 2001). The fluctuating cultural changes since this time have influenced the widespread landscape transformation during the Holocene not only in this area, but also throughout the archipelago.
Through the Franco-Maltese ANR project PaleoMed (C. Morhange, leader), a number of cores have been taken from locations on the Maltese archipelago with the aim of probing the islands' environmental history. A multi-disciplinary team has been investigating a number of bodies of evidence including sediments, charcoal, pollen, and shells. A mid-Holocene section of the BM1 sediment core has been examined (Djamali et al., 2012); while geoarchaeological analysis of the Burmarrad area has been undertaken by Marriner et al. (2012).
A percussion corer (diameter 10 cm) was used to extract the BM2 core. The 10 m long core was sampled at regular 5–10 cm intervals, while the top 2 m was not considered due to proximity to the surface. The methodology used to define the sedimentary environments is based on high-resolution sedimentological and palaeoecological data (ostracods and marine molluscs); the initial facies descriptions (such as colour and lithofacies) were conducted under standardized laboratory conditions (see Marriner et al., 2012).
Pollen extraction was undertaken following the classic method described by
Moore et al. (1991). Each of the 1 cm
A mean total count of at least 300 terrestrial pollen grains was used for
each sample – this amount is considered sufficient to provide a fossil
assemblage census (Benton and Harper, 2009). Pollen identification was
undertaken using the IMBE's pollen reference collection and the pollen
atlases of Europe and North Africa (Reille, 1992, 1995, 1998) along with the
pollen atlas of Central Europe (Beug, 2004). Cereal-type pollen was described
as Poaceae > 45
NPPs were identified using a number of references:
Cugny (2011), Mudie et al. (2011), Haas (1996), van Geel (1978), and Macphail
and Stevenson (2004). Pollen percentages were calculated in TILIA, while pollen
percentage diagrams were created using TGview (Grimm, 2004/5). Final diagrams were redrawn and amended in Adobe Illustrator. The
pollen diagram taxa have been grouped according to ecology and life form:
trees and shrubs, herbs, aquatic and hygrophilous species, coprophilous
associated species, and NPPs. Microcharcoals (woody not herbaceous particles)
smaller than 10
Radiocarbon dates obtained from the Burmarrad BM2 core.
This paper presents the results of pollen analysis carried out on 48 samples collected from the BM2 core between the depths 210 and 1000 cm. Some parts of the core did not provide any palynological material to be represented in the diagram (in particular the section between 450 and 240 cm).
Use of only one method for pollen-based palaeoclimate reconstructions could reduce the robustness of the results obtained (Birks, 2011; Brewer et al., 2008), therefore a multi-method approach was utilized for the climatic reconstruction based on the BM2 data set. The chosen approach has been successfully used in studies throughout the Mediterranean area (Peyron et al., 2013; Sadori et al., 2013a). Three methods were chosen: the modern analogue technique “MAT” which compares past assemblages with modern assemblages (Guiot, 1990); the weighted averaging “WA” method (Ter Braak and Van Dam, 1989); and the weighted average-partial least square technique “WAPLS” (Ter Braak and Juggins, 1993). The MAT is the only one based on a comparison of past pollen assemblages to modern pollen assemblages, while the WA and WAPLS are transfer functions that require a statistical calibration between environmental variables and modern pollen assemblages; Peyron et al. (2013) provide a comprehensive outline of these three approaches. The climate parameters estimated from the Burmarrad core are the temperature of the coldest month (MTCO) and the seasonal precipitation. Calculations for the winter and summer precipitations are based on the sum of the months: December, January, February and June, July, August respectively.
BM2 sedimentary profile and age–depth model interpolated curve.
The BM2 core has been subdivided into five lithostratigraphic zones (Fig. 2), recording a general transition from upper estuarine, through marine, to a marsh/fluvial environment. The visual core description is as follows: the lower part of the sequence is predominately composed of grey silts (Unit 1a: 1000–800 cm) followed by slightly darker grey silts (Unit 1b: 800–710 cm) both deposited in an estuarine environment, grey shelly sands (Unit 2: 710–460 cm) deposited under marine conditions, marshy muds (Unit 3: 460–300 cm) and marshy muds with oxide mottling (Unit 4: 300–210 cm), and finally, at the upper part, brown sandy clays (Unit 5: 210–0 cm). The two latter sedimentary units display different degrees of pedogenesis. No pollen samples were taken from the top 200 cm surface section due to the considerable biologic and anthropogenic activity that this layer is regarded to have undergone.
Burmarrad simplified pollen diagram: selected percentage curves and
pollen concentration versus depth. Mediterranean arboreal taxa:
Burmarrad pollen percentage diagram versus depth: trees and shrubs. The pollen percentages are calculated using the pollen sum of all terrestrial pollen counted; it excludes Cyperaceae and other aquatic/hygrophilous species, NPPs, and undetermined/indeterminable grains.
Burmarrad pollen percentage diagram versus depth: herbaceous taxa. The pollen percentages are calculated using the pollen sum of all terrestrial pollen counted; it excludes Cyperaceae and other aquatic/hygrophilous species, NPPs, and undetermined/indeterminable grains.
Four radiocarbon dates, calibrated using IntCal09 and Marine09 (Reimer et al., 2009) have been used for the BM2 core (Table 2). The samples used for the dating consisted of two charcoal pieces, one grain, and one wood fragment. An age model based on these four dates was constructed using the R-code Clam (Blaauw, 2010); this is obtained by repeated random sampling of the dates' calibrated distributions to produce a robust age–depth model through the sampled ages, displayed in the linear interpolation diagram (Fig. 2).
Results of the Accelerator Mass Spectrometry (AMS) dating are provided in Fig. 2. The lowest part of the core is radiocarbon dated to approximately 7280 cal BP while the top corresponds to approximately 1730 cal BP. The interpolated curve is quite steep in the midsection of this diagram. This may be an indication of anthropogenic activity in this area causing accelerated runoff and rapid infill of the plain during this period (Gambin, 2005; Marriner et al., 2012). Although all chronology should be treated with caution, it is noted that there is good correlation between the BM1 (Djamali et al., 2012) and BM2 cores. Reworking processes in low-energy ria environments such as these tends to be low; furthermore to overcome reservoir issues we have dated charcoal and short-lived plant material. Our interpretations are based on a chronological timescale established according to four radiocarbon dates; we assume that sedimentation rate in the intervals between the dating points remains relatively constant; however, we do not exclude the possibility that in some depths, some changes in sedimentation rate may have occurred leading to slightly different ages for the observed environmental variations.
From the BM2 core only 48 of the 57 spectra are recorded in the pollen diagram due to poor pollen concentration (hiatus between depth 450 and 240 cm). Two other smaller hiatuses appear in the record due to core recovery issues (940–890 and 680–600 cm). The pollen concentration in the core generally was poor; however, the preservation of the grains was, on the whole, satisfactory. There was sufficient diversity of taxa to reflect pollen contributions from a number of habitats, including wetland as well as a variety of dry ground environments.
The pollen diagram provides percentages for all the terrestrial and aquatic pollen counted, as well as that of spores, microcharcoal, microforaminifera, and dinoflagellates; the pollen sum was calculated using terrestrial pollen totals only. No taxa were omitted from the pollen diagram. However, pollen productivity and dispersal levels (Hevly, 1981) and possible preservation variability (Havinga, 1971) have been considered (Figs. 3–6).
A total of 98 pollen and spore types were identified, including 17 arboreal pollen (AP) taxa and 56 non-arboreal pollen (NAP) taxa, the latter comprising herbs and weed species. With regard to NPP type, 17 different taxa were identified (Fig. 6). Following Cushing (1967) the diagram has been divided into Local Pollen Assemblage Zones (LPAZ) – these five zones are based on principle terrestrial taxa changes.
Burmarrad pollen percentage diagram versus depth: aquatic/wetland taxa and NPPs. The pollen percentages are calculated using the pollen sum of all terrestrial pollen counted; it excludes Cyperaceae and other aquatic/hygrophilous species, NPPs, and undetermined/indeterminable grains.
Synthesis of cultural phases, LPAZs (local pollen assemblage zones), sediment, vegetation dynamics, and climatic reconstruction: BM2 core, Malta.
The lower part of this zone (980 cm) is radiocarbon dated to
This zone is characterized by a very significant rise in AP taxa, increasing
to a maximum of 65 % (880 cm). The majority of this AP is comprised of
This zone is radiocarbon dated to
The middle part of this sequence (720 cm) is radiocarbon dated to
The middle part of this sequence (500 cm) is radiocarbon dated to
This last analysed section of the core has two notable AP species peaks,
though as a whole sequence LPAZ5 records the lowest AP record of 10 %
dropping from 18 %, while NAP taxa remain high at 82–90 %. Firstly,
the start of LPAZ5 has a significant
A quantitative climate reconstruction has been performed for Malta on the BM2 pollen sequence. The results (Fig. 8) include: temperature, MTCO (mean temperature coldest month), and winter and summer precipitation. The findings are compared and contrasted with other Mediterranean climate reconstructions (see Sect. 5.2).
Between ca. 7000 and 4800 cal BP the temperature (MTCO) is fairly stable at
around 11
Comparison between pollen-inferred climate for Malta
(35.9
Winter precipitation displays much more variability than summer. Although reconstructed values differ following different methods (MAT, WAPLS, and WA) they illustrate the same trends. From 7000 to 4600 cal BP both winter and summer precipitation are generally high and tend to decrease especially after 6000 cal BP. The period between 4500 and 3800 cal BP is characterized by low winter precipitation indicating a dry period. Again there is no fluctuation displayed between 3700 and 2000 cal BP due to a break in the sequence. Between 2000 and 1800 cal BP precipitation values are under the present-day ones.
A number of studies have highlighted the problem of disentangling the human- and climate-induced changes in the Mediterranean region (e.g. Behre, 1990; Pons and Quezel, 1985; Sadori et al., 2004; Roberts et al., 2011; Zanchetta et al., 2013). More often than not it may be a fluctuating combination of these two forces driving the changes rather than a single factor, with one amplifying or even moderating the vegetation signals provided in the palynological record. While it is acknowledged that vegetation patterns can vary even within small island settings such as Malta (Hunt, 2015), the BM2 core provides insight into both changing vegetation dynamics and hydroclimatic fluctuations in the Burmarrad valley system from 7280 to 1730 cal BP.
Trump (2002) states that evidence of the first settlers in Malta, around 7200–7000 BP, is found at the Skorba and Ghar Dalam prehistoric sites. These original occupiers coming from Sicily (Blouet, 2007), brought with them knowledge in tool making (stone, wood, and bone) and agricultural practices (Pace, 2004), as well as crop (barley, lentils, emmer, and club wheat) and domesticated animals such as sheep, goats, cattle, and pigs (Trump, 1972). However, the exact date when humans arrived in Malta remains a key question. Broodbank (2013) postulates that permanent Mediterranean island settlements were probably preceded by early visitations. However, these remain “archaeologically invisible” (Colledge and Conolly, 2007). The Mediterranean Sea, as well as other areas such as the Persian Gulf (Wells, 1922), were being sailed as early as 9950 cal BP. Even before the Holocene epoch, during the Upper Palaeolithic and Younger Dryas, coastal and island crossings were taking place (Broodbank, 2006, 2013); given the inter-island visibility and this early movement of seafarers, it is plausible that the Maltese islands may have been visited, and possibly temporarily occupied, before being permanently settled during the Neolithic.
Much of southern mainland Europe saw decreasing deciduous woodland areas
(from the early Neolithic onwards, Delhon et al., 2009). This vegetation does
not appear abundant on the Maltese Islands during this period (Carroll et
al., 2012; Djamali et al., 2012), though it has been postulated that
deciduous forest was the dominant vegetation at this time (Grech, 2001).
Evidence for the environment during this early Neolithic period in Burmarrad
suggests an initially open landscape at ca. 7280–6700 cal BP surrounding a
large palaeobay during the maximum marine transgression period (Marriner et
al., 2012) with mainly non-arboreal pollen and aquatic/wetland taxa. Recorded
species indicating this environment are
Although the evidence from the BM2 core and the BM1 core (Djamali et al.,
2012) points to this area having an open landscape, it is necessary to
highlight that there are Maltese archaeological records from the Neolithic
period from other locations. Such evidence might point to a different more
“woody” environment, such as the discovery of
Many of the key anthropogenic pollen indicators (API) used in different parts
of the Mediterranean region, such as primary crop species (
These initial traces of palynological evidence, mainly based on NAP taxa
which are, due to their phenology, considered more sensitive and responsive
to environmental change (Markgraf and Kenny, 2013), coincide with
archeological evidence for nearby permanent dwelling structures on the island
(Pace, 2004; Trump, 2002), as well as abundant microcharcoals – the latter
might be indicative of landscape modification through the use of fire, which
has been recorded during the same time period in neighbouring Sicily (Noti et
al., 2009) as well as throughout other Mediterranean areas (Vannière et
al., 2011), although climate-driven fire events cannot be discounted (Sadori
et al., 2015a). Nonetheless, the extent to which these first recorded settlers
actually impacted the landscape from its “original state” is hard to
decipher without pre-occupation data. What is clear is that arboreal pollen
was extremely low in this catchment area during the early Neolithic, and
those tree species actually recorded in the pollen sequence, such as
The three cultural phases of the Maltese Neolithic period are delineated mainly by changes in pottery styles, the initial style being almost identical to pottery found in Stentinello, Sicily (Trump, 2004). These remains have been recovered from both the Ghar Dalam cave and the Skorba huts, the latter located very close to the Burmarrad catchment area (Fig. 1b), as well as fragments for other locations in the archipelago including Gozo. It is highly probable that during this first Ghar Dalam phase (Fig. 7) many more geographically important sites around the island were being settled (Pace, 2004), while farming customs and practices were possibly undergoing adaptation. The first temples were built later – ca. 5450 cal BP during the Ġgantija phase (Fig. 7).
The major recorded change in the landscape is from a predominantly open
herbaceous and wetland environment, to a much more closed evergreen arboreal
cover. At ca. 6700 cal BP there is a rapid expansion of
Similar rapid and large expansion of
With regard to NAP taxa, the level recorded is the lowest within the whole
sequence, with particularly low percentages of nitrophilous taxa, supporting
the theory of dense scrubland, that would restrict the growth of other plant
species. Chenopodiaceae taxa use, as a possible indictor of a nitrophilous
environment, is treated with caution. Many in this taxon are known halophytes
(Grigore et al., 2008) and possess a close association with aridity (Pyankov
et al., 2000); therefore their use, especially given this coastal zone
context, is always in conjunction with other key taxa. Additionally, there is
the lowest level of Poaceae, including Cerealia-type
(
Burmarrad's palaeo-lagoon is still present during this period, with key indicator species such as dinoflagellates reaching their highest level; these are primarily marine organisms (Traverse, 2008). Their presence confirms the lower estuarine environment at the site recorded in both BM1 (Djamali et al., 2012; Marriner et al., 2012) and BM2 (this study).
The Temple period in Malta lasted between 6050 and 4450 cal BP; this period is unique to the archipelago (Pace, 2004). To date, nowhere else in the world are there freestanding stone buildings (such as Haġar Qim, Mnajdra, and Ġgantija, Fig. 1b) dating to this period. The first temple structure is dated to ca. 5450 cal BP, built during the Ġgantija phase (Fig. 7). The purpose of these buildings is thought to be for ritual purposes, for the estimated 10 000 people settled on the islands at this time (Trump, 2002).
During this temple-building phase there is a notable increase of
With this increase in
The Bronze Age in Malta occurred between 4450 and 2650 cal BP (Fig. 7), and is divided into three phases representing different colonizations of these islands: Tarxien Cemetery, Borg-In-Nadur, and Bahrija, the latter settlers co-inhabiting the island with the Borg-In-Nadur people for about 200 years (Pace, 2004). Trump (2004) suggests that the difference in cultures between the Temple and Bronze Age is so apparent that it is possible that the islands passed through a phase of abandonment, though this remains the subject of an ongoing debate. During the Bronze Age, fortified settlements were built on strategically located hilltops complete with underground food storage facilities known as “silo-piths” (Buhagiar, 2007), while dolmen structures (possibly used for the burial of cremated remains) were also constructed. Even though there is evidence that these Bronze Age people built dwellings and undertook agricultural activity, including livestock management and possible crop rotation (Fenech, 2007), the previous Temple Period, with its megalithic temple civilization, is considered culturally and economically superior (Buhagiar, 2014). The population of the islands during the Bronze Age is suggested to have been smaller than that of the Temple period (Blouet, 2007), though their impact on the landscape can still be traced. One such impact found around the islands is the ancient cart rut tracks. These parallel channels are incised into the limestone rock (Hughes, 1999) – 22 such networks have been recorded in the Burmarrad catchment area alone (Trump, 2004). There has been speculation on the origin, use, and date of these cart ruts since they were first referenced in 1647 by Gian Francesco Abela, one of Malta's earliest historians (Hughes, 1999; Mottershead et al., 2008). Although it is not this paper's purpose to delve into their much-debated chronology and use, it is pertinent to point out that at least some are suggested to be Bronze Age in origin (Trump, 2004).
Throughout the early and mid-Bronze Age, arboreal species in the Burmarrad catchment area are decreasing in abundance, while herbaceous taxa are increasing, suggesting the opening up of the landscape. Furthermore, the increased microcharcoal concentration at the start of this sequence might indicate the use of slash-and-burn to this end. This increase in fire activity around 4500 cal BP is also noted in southern Sicily at Gela di Biviere (Noti et al., 2009) and slightly earlier (5000 cal BP) at Lago Pergusa (Sadori and Giardini, 2007). It is also observed as a general trend in the Mediterranean from around 4000–3000 cal. BP (Vannière et al., 2011). The cause of this increased fire activity is suggested to be partly due to human activity and associated disturbances.
Pastoral activity plant indicators (such as
The early part of the Bronze Age in this area is also marked by a rise in
This increasing human pressure on the landscape during the Bronze Age is not isolated to the Maltese archipelago or the central Mediterranean area (Mercuri, 2014) it has also been recorded throughout the whole region, between 5000 and 3000 cal BP, as societies and their associated ecological disturbances become more apparent (Sadori and Giardini, 2007; Mercuri et al., 2015). Sadori et al. (2011) note two signals within the Mediterranean; the first corresponds to a climate event of 4300–3800 BP (Magny et al., 2009), that of a sudden and brief episode between 4400 and 4100 cal BP which initially affects the arboreal pollen concentration followed by the percentages (generally being accompanied by human presence indicators), then a second between 3900 and 3400 BP, which they suggest is slightly longer and involved intensive land exploitation.
Towards the latter part of this period in Burmarrad (ca. 3600 cal BP) the
remaining Mediterranean arboreal taxa decline again. However, there is a
distinct increase in
In addition, towards the middle of the Bronze Age period, there is a gradual
decline in nitrophilous and pastoral taxa (Fig. 3), perhaps indicating a
reduction in the amount of livestock within the catchment area. On the other
hand, there is an increase in Poaceae as well as a considerable rise in
The BM2 core sequence (Fig. 7) covers the first three phases of the historical period: Phoenician 2750–2430 BP, Punic 2430–2168 BP, and Roman 2168–1404 BP (Pace, 2004), although palynological data are currently only available for the period 1972–173 cal BP. At the beginning of the second Punic War the islands changed from Carthaginian to Roman rule, forming part of the Sicilian province (Bonanno, 2005). However, for about the first three hundred years the Punic culture, detectable in pottery styles and inscriptions, persisted (Blouet, 2007). Seventeen Roman period sites have been linked to the production and exportation of olive oil on the islands (Gambin, 2005), along with extensive port remains, such as quays and various buildings including warehouses, around the Marsa area (Gambin, 2004/5), being in close proximity to the Grand Harbour, a naturally sheltered ria. Following Roman occupation in 2168 BP, archaeological remains and textual evidence both suggest that Malta was producing refined textiles and that some islanders were living in sophisticated dwellings such as a typical domus located in Rabat (Bonanno, 2005). The Burmarrad area also has archaeological evidence of Roman occupation. Evidence includes large oil-producing Roman villas (San Pawl Milqi and Bidnija), burial complexes (Bonanno, 2005), along with ceramic deposits datable to the Punico-Roman period from the silted ancient harbour (Gambin, 2005).
The last part of the core sequence for the Burmarrad plain dates to the
mid-Roman phase (1972–1730 cal BP). The landscape in the catchment area at
this time appears relatively open –
When interpreting pollen data, possible long-distance transport, including that of cereals, should be considered (Birks and Birks, 1980; Court-Picon et al., 2005). Another consideration regarding Poaceae, including cereals and other crop species, is that pollen dispersal and its potential deposition is dependent on harvesting methods (Hall et al., 2013). Furthermore, it has been suggested by López-Merino et al. (2010) that crop cultivation may decrease the herbaceous plant community abundance, while abandonment can have the opposite effect. This increase in cultivated species and corresponding decrease in herbaceous taxa can be noted in the pollen record of Burmarrad during this time, although attention must be placed on the over- or under-representation situation caused by a plant's life cycle. Under-represented taxa, such as cereals, are considered to produce low quantities of pollen that are poorly dispersed (Court-Picon et al., 2006). This can cause over-representation of extra-local and regional pollen that is anemophilous in nature. Furthermore, pollen production of local Poaceae taxa in intensive livestock areas has been suggested to be low due to overgrazing (Hjelle, 1998; Mazier et al., 2006), which possibly would also allow for over-representation of extra-local and regional pollen, although Ejarque et al. (2011) observed contrasting results in their modern pollen-rain study.
Another notable increase is that of
The interpretation that
With regard to
Other notable changes include higher levels of microcharcoal, compared to the
Bronze Age, which can also be observed at Lago Preola, Sicily (Calò et
al., 2012). Additionally, there is the highest peak of both
Synthesis of general trends and key events indicating Malta's reconstructed climatic position (all data, except Burmarrad, from Peyron et al., 2013).
The Holocene climate has fluctuated both spatially and temporally on a global scale (Mayewski et al., 2004) as well as within the Mediterranean Basin (e.g. Brayshaw et al., 2011; Jalut et al., 2009; Magny et al., 2002, 2011; Roberts et al., 2011; Mauri et al., 2015). Human impacts have affected the natural vegetation of the Mediterranean since the mid-Holocene, but disentangling the climatic and anthropogenic causes of vegetation change is complex. Our climatic reconstruction seems consistent with independent records from the Mediterranean such as lake levels from Sicily (Fig. 8) or speleothems from Israel (Magny et al., 2012; Bar-Matthews and Ayalon, 2011), and large-scale paleoclimate reconstruction (Mauri et al., 2015). This reconstruction provides valuable insight into the palaeoclimate of this centrally situated archipelago between 7280 and 1730 cal BP, allowing for comparisons to be made with other reconstructions undertaken within the Mediterranean region (Figs. 8 and 9).
The trends observed within the Burmarrad sequence are comparable to other southern Mediterranean climate reconstructions, particularly Sicilian and southern Italian mainland sites (Peyron et al., 2013). The temperature for Malta is slightly warmer than that recorded at Lago Pergusa, Sicily (Sadori et al., 2013b), which is situated at a higher altitude (667 m a.s.l.); however, the overall pattern of fluctuation is similar (Fig. 8). This difference may be due in part to the more southerly latitude of the Maltese islands. Orography is another factor that may create both regional and local variances in Mediterranean heat wave, wind, and cyclonic activity (Gladich et al., 2008; Lionello et al., 2006; Sotillo et al., 2003). The Maltese archipelago's relatively small area and low-lying terrain differ greatly from Sicily's larger and much more mountainous area.
The reconstructed MTCO temperature for Burmarrad can be summarized as warm in
the early Holocene, followed by instability after 4800 cal BP, particularly
between 4100 and 3700 cal BP with a minimum at 7
Peyron et al. (2013) propose a north–south divide for Italy, similar to that
seen in the eastern Mediterranean (Dormoy et al., 2009; Kotthoff et al.,
2008, 2011), which supports the mid-Holocene opposing summer precipitation
hypothesis for the Mediterranean; that of a reduced summer precipitation for
northern sites (above 40
Burmarrad's winter precipitation pattern and quantity is, on the whole,
comparable with Lago Pergusa (Fig. 8). Both areas are subject to an increase
in winter precipitation between 7000 and 5500 cal BP, followed by a slight
decrease until just before 5000 cal BP. Djamali et al. (2012) suggest that
the early Holocene (7350–6960 cal BP) was relatively dry, favouring steppe
vegetation in the Maltese islands (as well as some other Mediterranean
sites). This was most probably due to the indirect effect of the subtropical
monsoon intensifications, with the maximum moisture availability occurring
during the time of
Based on results from Sicily's Lago Pergusa (pollen-based) and Lago Preola (lake-level), Magny et al. (2011) describe the pattern of Holocene precipitation as having a maximum winter and summer wetness between 9800–4500 cal BP, followed by declining winter and summer wetness. This is largely consistent with findings from Burmarrad. These changing moisture levels during the Holocene have been linked to significant societal changes. Sadori et al. (2015b) propose that periods of increased humidity, over the last 2000 years, coincided with both agricultural and demographic expansions. While Weiss and Bradley (2001) suggest that, around 4250 BP, a number of cultures were at their economic peak, such as Mesopotamia's Akkadian empire, Egypt's Old Kingdom civilization and Palestine, Greece, and Crete's Early Bronze societies; however, these once flourishing areas declined rapidly after 4150 BP possibly due to severe drought and cooling. The event has been recorded elsewhere in the world and seems to have acted at a global scale (Booth et al., 2005). The impact of drought events on the human socio-economy, and the consequent impacts on the landscape, should thus not be underestimated, as has been recently suggested by Sharifi et al. (2015) for the continental Middle East. These increases in aridity not only affect the vegetation communities directly but also indirectly by altering the anthropogenic pressure on the local landscape, both directly in those regions, as well as wherever the displaced people migrate. This combined effect is not confined to the eastern Mediterranean at this time. Closer to the Maltese archipelago, Noti et al. (2009) suggest that at Gela di Biviere, Sicily, between 5000 and 4000 cal BP, the anthropogenic impact occurring on the landscape is probably influenced by the climatic changes.
As well as the north–south divide, there are also east–west differences in
moisture that have been recorded in the Mediterranean during the early
Holocene (Roberts et al., 2011; Vannière et al., 2011), whereby during
the early Holocene the northeastern region underwent a period of increased
winter precipitation up until 6000 BP followed by a decline, whereas south
of the Dead Sea, Hunt et al. (2007) suggest a general
decrease in precipitation through the early to mid-Holocene, and in the
western region, though less pronounced, the maximum increases occurred
between 6000 and 3000 BP before declining to current levels (Roberts et al.,
2011); see Zielhofer and Faust (2008) for mid–late Holocene fluctuations
recorded in Tunisia. Therefore, given Malta's central location, finding its
“climatic” position poses an interesting task. The first part is fairly
simple: lying below 40
This paper presents vegetation dynamics from ca. 7280 to 1730 cal BP for Burmarrad in Northwest Malta, along with a pollen-based climate reconstruction for this archipelago. The vegetation changes recorded within the catchment area correspond well with those observed in the shorter early to mid-Holocene sequence of BM1 core, as well as those from neighbouring southern sites in coastal Sicily. If vegetation changes in Burmarrad are similar to those in coastal Sicily then it may be possible to infer similarities to other areas within Malta itself, or at least it can be “reasonably assumed”, though such assumptions would have to be tested.
This inference might also be supported by the fact that Malta has a relatively low topographic variability and is almost completely located within the same bioclimatic and vegetation belt (Thermo-Mediterranean) similar to that of coastal Sicily. In such a context, the slightly varying responses of biomes/vegetations to hydroclimatic trends as observed in highland vs. lowland Sicily (e.g. in Pergusa versus Gorgo Basso) would not be observed in Malta.
The climatic reconstruction is based on the pollen record from this northwestern region; however, the island is relatively small in size and therefore our interpretations can probably be taken for the area as a whole. The reconstruction also provides strong correlation with climatic reconstructions conducted for southern Mediterranean sites. The main findings are as follows.
Between ca. 7280 to 6700 cal BP (early Neolithic period) the results record an initially open landscape at the site, surrounding a large palaeobay, with arboreal pollen taxa at their lowest levels.
From ca. 6700 cal BP dense
From ca. 4450 cal BP the landscape became more open again, coinciding with
the start of the Bronze Age on the archipelago. Notably, fire events also
increase during this period as do indications of increased soil erosion
(
During the early Roman occupation period the landscape is still fairly open
with an increase in
Through continued interdisciplinary research both on this archipelago and other Mediterranean locations more precise reconstructions of vegetation assemblages and climatic variations can be provided for the Holocene. These robust and comprehensive data sets can provide information on the various processes and drivers influencing not only past but also present and future landscapes. The question of Holocene climate- or human-driven environmental change remains a tricky one. An alternative approach might be to consider these two factors, which Sadori et al. (2013) emphasize have a “synergy”, as interactive or dual-action for at least the mid-Holocene onwards; in this way it might bring us closer to a better understanding and appreciation of the continually evolving Mediterranean “living mosaic” landscape.
The authors would like to thank Nicholas Vella from the Department of Archaeology at the University of Malta for the kind use of the Zeiss Light Microscope, Edwin Lanfranco for sharing his extensive knowledge on local vegetation, Dr Saviour Formosa for the DTM layer of NW Malta, and Dr Lyudmila Shumilovskikh (IMBE) for her expertise in NPP identification. This research was partially funded by the ANR Paleomed project (09-BLAN-0323-204 01). Edited by: N. Combourieu Nebout