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VI/2/2015
INTERDISCIPLINARIA ARCHAEOLOGICA
NATURAL SCIENCES IN ARCHAEOLOGY
homepage: http://www.iansa.eu
Humans and Water in Desert “Refugium” Areas: Palynological Evidence of
Climate Oscillations and Cultural Developments in Early and Mid-Holocene
Saharan Edges
Anna Maria Mercuri
a
, Assunta Florenzano
a*
, Carlo Giraudi
b
, Elena A. A. Garcea
c
a
Laboratorio di Palinologia e Paleobotanica, Dipartimento di Scienze della Vita, Università di Modena e Reggio Emilia, viale Caduti in Guerra 127,
41121 Modena, MO, Italy
b
ENEA C. R. Saluggia, Strada per Crescentino 41, 13040 Saluggia, VC, Italy
c
Dipartimento di Lettere e Filosofa, Università di Cassino e del Lazio Meridionale, via Zamosch 43, 03043 Cassino, FR, Italy
1. Introduction
The concept of a
refugium
is frequently combined with
that of mountains in desert ecosystems (Quézel 1997;
Anthelme
et al.
2008; Migliore
et al.
2013).
Evolutionary
and
ecological
refuges have different chronological and
spatial scales (Quézel, Martinez 1960; Maley 1981, 2010;
Bennet, Provan 2008; Watrin
et al.
2009; Davis
et al.
2013),
but both may be recognised in the history of currently hyper-
arid regions. Although there are different approaches to this
matter, in general, refugia are regarded as places where the
local microclimate was different from the regional climate,
and therefore organisms may have retreated,
persisted in
or
expanded from
, under changing environmental conditions
(according to the habitat-based defnition of refugia by
Keppel
et al.
2012). Under dry or cold climate oscillations,
for example, organisms have a higher chance of survival in
these places.
With regard to deserts, including current ethnographic
evidence (Mandaville 2011; di Lernia
et al.
2012), it is
especially evident that, little by little, water has triggered
the movements of plants, animals and humans. Across the
history of desert regions, organisms have followed water,
and when climate conditions became drier and water basins
and rivers reduced their distribution or fow, then humans
have reached the same refuges where water and plants have
already concentrated (Kuper, Kröpelin 2006; Mercuri 2008a;
Florenzano
et al.
2016).
This leaves open the question as to whether the plant cover
near places of water (or wetlands) is natural or anthropogenic.
Saharan anthropic deposits from archaeological sites, located
along wadis or close to lakes, and sedimentary sequences from
permanent and dried basins, have demonstrated that water has
been an attractive environmental feature especially during
periods of drought (
e.g.
, Smith
et al.
2005; Garcea 2013a).
Volume VI ● Issue 2/2015 ● Pages 151–160
*Corresponding author. E-mail: assunta.forenzano@unimore.it
ARTICLE INFO
Article history:
Received: 30
th
April 2015
Accepted: 21
st
December 2015
Key words:
palaeoecology
pollen
wet habitats
archaeology
climate change
Libya
Niger
ABSTRACT
Saharan anthropic deposits from archaeological sites, located along wadis or close to lakes, and
sedimentary sequences from permanent and dried basins demonstrate that water has always been
an attractive environmental feature, especially during periods of drought. This paper reports on two
very different examples of Holocene sites where “humans and water” coexisted during dry periods,
as observed by stratigraphic, archaeological and palynological evidence. Independent research was
carried out on the Jefara Plain (Libya, 32°N) and the Gobero area (Niger, 17°N), at the extreme
northern and southern limits of the Sahara, respectively.
The histories of the Jefara and Gobero areas, as revealed by the archaeological and palaeoenvironmen-
tal reconstructions, suggest that these areas were likely to have been visited and exploited for a long
time, acting as anthropic refugia, and therefore they have been profoundly transformed. Human presen-
ce and actions have conditioned the local growing of plants and selected a more or less synanthropic
fora. Today, modern conservation strategies should take into consideration that water reservoirs, which
are crucial for the long-term conservation of biodiversity, have provided refugia in the past just as they
presently do under global warming conditions.
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Anna Maria Mercuri, Assunta Florenzano, Carlo Giraudi, Elena A. A. Garcea: Humans and Water in Desert “Refugium” Areas: Palynological Evidence
of Climate Oscillations and Cultural Developments in Early and Mid-Holocene Saharan Edges
152
This paper reports on two, very different, examples of
evidence concerning “humans and water” as observed in
the stratigraphic, archaeological and palynological studies
carried out on Holocene deposits at the extreme limits of
northern and southern Sahara.
2. The case studies
The two case studies reported in this paper come from the
Jefara Plain (Libya, 32°N) to the north and the Gobero
region (Niger, 17°N) to the south of the present Sahara
desert (Figure 1). They currently lie at the margins of the
widest desert of the world, both regions that are known to
receive more rainfall and have greater vegetation cover than
the central regions. Central Sahara lies between 18º and 30º
N, its annual rainfall is below 25 mm, and its underground
aquifers sometimes penetrate through to the surface resulting
in oases (White 1983).
The areas of the Jefara and Gobero have been studied using
an interdisciplinary approach that involved environmental
investigations in the general archaeological research.
Palaeoenvironmental reconstructions resulted from an
integration of archaeological, geological, sedimentological
and palynological studies in the two areas. In fact, they
are both multipoint sites characterised by a complex set
of sedimentary and cultural contexts (Giraudi 1995; 2005;
Barich
et al.
2006; Garcea, Giraudi 2006; Sereno
et al.
2008;
Barich 2013; Garcea 2013a).
Pollen analyses resulted in a very laborious and time-
consuming procedure. Many sandy and organic-poor types
of sediment were treated for pollen extraction through
sieving and foating procedures (van der Kaars
et al.
2001;
Florenzano
et al.
2012). Although several grams of sediment
were processed, quite a lot of samples were sterile and
others showed very low pollen concentration (expressed
as pollen grains per gram = p/g). Nevertheless, pollen in a
good state of preservation was found in several samples. The
high interest of these contexts, commonly associated with
archaeological deposits and radiocarbon dating, encouraged
the accomplishment of these pollen analyses and gave the
possibility to compare the pollen data with the other results
obtained from different analyses.
2.1 Case study 1: the Jefara Plain (Libya; 32°00′ N,
11°41′ E; c. 230 m asl; c. 7800–4600 cal BP)
At the northern fringes of the Sahara desert, Quaternary
sedimentary sequences were identifed in the Jefara Plain in
front of the northern scarp of the Jebel Gharbi, a mountain
range in northwestern Libya. These sequences were mostly
formed of dark-grey palustrine sediments interbedded with
aeolian deposits; these were studied in order to establish
the timing of marsh formation and the periods of increased
groundwater fow (Giraudi
et al.
2013). Moreover, a number
of Neolithic archaeological features, especially hearths,
suggested that human frequentation had occurred on a
seasonal basis for those transiting between the Mediterranean
coast and the mountain range and the pasture of livestock
(Lucarini 2013).
As the geomorphologic and stratigraphic features of the
Jebel Gharbi and the Jefara Plain showed that Holocene
sediments were rather discontinuous in this area, since
they had been subjected to strong wind defation and
erosion by ephemeral streams, two sites about 300 m apart,
SJ-06-87 and SJ-06-88, where the aeolian sediments were
interbedded with dark palustrine sediments, were selected
Figure 1.
Location map of the sites
discussed in the text: 1 – Jefara Plain;
2 – Gobero area; 3 – Chott Rharsa basin;
4 – Tadrart Acacus Mountains.
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Anna Maria Mercuri, Assunta Florenzano, Carlo Giraudi, Elena A. A. Garcea: Humans and Water in Desert “Refugium” Areas: Palynological Evidence
of Climate Oscillations and Cultural Developments in Early and Mid-Holocene Saharan Edges
153
for pollen analyses (Giraudi
et al.
2013). Six radiocarbon
dates made on organic dark sediments demonstrated that
these sediments accumulated during a period of about
three thousand years. Pollen samples were taken from the
same sediments (Figure 2). About 200 pollen grains were
counted on average in nine samples. Counts of Non Pollen
Palynomorphs (especially algae; van Geel 2001), and
microscopical particles of charcoal, helped to complete the
palaeoecological information.
The palynofacies from the two sites looked different.
The mean pollen concentration was very low (800 p/g in
SJ 06-88, and <100 p/g in SJ 06-87)
but a high number of
taxa (more than 100 taxa, from 14 to 47 per sample) was
observed. The pollen diagram shows a dominance of pollen
from herb plants (Figure 3). Trees were insignifcant with a
mean percentage sum of 6%, and prevalence of
Tamarix
and
Ficus,
followed by
Salvadora persica
and
Capparis
. Pollen
of anemophilous trees included the deciduous
Quercus
and
Betula
, and conifers, such as
Pinus
and
Cedrus
, that derived
from long-distance transport from the Mediterranean area.
These types of records may be interpreted as indicators of
wind fuxes that, generally, are more intense during dry
climate phases (Lézine
et al.
2011; Mercuri 2015). In these
spectra, Poaceae and Cyperaceae were ubiquitous together
with different taxa of Chenopodiaceae, Asteraceae and
Plantago
. Altogether, the prevalent vegetation of the Jefara
Figure 2.
Sedimentary sequence and pollen
sampling from the sites SJ-06-87 and SJ-06-88
in the Jefara Plain (from Giraudi
et al.
2013,
modifed).
Figure 3.
Pollen diagram of the samples from the Jefara Plain.
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IANSA 2015 ● VI/2 ● 151–160
Anna Maria Mercuri, Assunta Florenzano, Carlo Giraudi, Elena A. A. Garcea: Humans and Water in Desert “Refugium” Areas: Palynological Evidence
of Climate Oscillations and Cultural Developments in Early and Mid-Holocene Saharan Edges
154
Plain was a shrub forest of alluvial plains or a wadi vegetation
(with
Ficus
,
Capparis
,
Salvadora persica
and
Tamarix
) with
extended grassland and a water pool where the water level
probably changed seasonally.
Among the high biodiversity of herbs, the most interesting
evidence is the high values of
Plantago
(
P. afra
-type,
P.
lanceolata
-type,
P.
undiff.) and
Urtica-
type
dioica
, together
with charcoal particles > 200 μm. Large microcharcoals are
evidence of local fres, and might have been produced by
freplaces (Clark 1988; Sadori
et al.
2015).
Plantago
species
grow on trampled layers, while
Urtica
species include
nitrophilous plants. Plantains also grow well in sandy soils,
where trampling causes compaction and a reduction of soil
water porosity, and moisture content is higher in the upper
layers of the soils due to capillarity (Noë, Blom 1981).
Signifcant values of
Plantago
pollen are evidence of trampling
in the relevant depositional phases (Behre 1981). An increase
of humans or animals enriched the soils with organic matter,
favouring also the local growth of nettles. Therefore, pollen
grains of
Plantago
and
Urtica-
type
dioica
are usually linked to
the spread of human landscapes during the late Mid-Holocene
in regions facing the Mediterranean basin (Mercuri
et al.
2012). In the Jefara, the archaeological evidence is not always
clear, but the combination of pollen and microscopic charcoal
was interpreted as evidence of “trampling, organic enrichment
and fres”. This relative increase of human frequentation at the
sites is evident in the layers dated to around 6.7 and 5.0 ka
BP, and especially in the last part of this period (P1 and P2 in
Figure 3). This probably depended, partly or principally, on
the local availability of water.
Besides pollen from plants of wet environments, algal
remains are the most unambiguous record from water
places.
Cymatiosphaera
is related to brackish water with
high nutrient content, and may live in the surface sediments
of intertidal marshes (Medeanic 2006; Mudie
et al.
2010).
Also, the rare records of
Pseudoschizaea circula
,
together
with other Zignemataceae spores, indicate brackish water or
fresh water. These algae are an index of fresh and/or brackish
water at the sites, signalling the local presence of a low water
level during phases of the Mid-Holocene.
In the wider Saharan region, a desiccation of the eastern
Sahara is known to have occurred at around 6.3–6.2 ka BP,
while in central Sahara the beginning of a shift towards more
permanent aridity has been registered from approximately
6.0 ka BP onwards (Mercuri
et al.
2011; Cremaschi
et al.
2014), and the spread of psammophilous vegetation marking
current hyperarid habitats occurred at around 5.4 ka BP. In
the Sahara, in general, two major Holocene wet periods are
known from palaeoenvironmental records: the frst dated
between about 10.5 ka BP and 8.5 ka BP, and the second
dated between about 7.5 and 4.5 ka BP (Cremaschi
et al.
2010). The wet phases found in its sedimentary sequences
correlate with the phases of expansion of the Saharan lakes
(Figure 4). Water table levels increased at 7.5–5.8 ka BP, and
at around 5.5–5.0 ka BP (Chott Rharsa basin, Tunisia; Swezey
et al.
1999). The pollen diagram from the Jefara shows a dry
phase at the bottom (high Chenopodiaceae+Asteraceae), and
then the expansion of grasslands (high Poaceae+Cyperaceae;
Figure 3). As mentioned above, the local availability of water
is evident because a rich biodiversity of hygrophilous plants,
aquatics and algal remains was observed in the samples dated
at around 6.7 and 5.0 ka BP. High values of aquatics were
actually recorded at around 5.5–5.0 ka BP, during a period of
local expansion of xerophytes (Figure 3).
Therefore, we can conclude that the permanence of water
encouraged humans and animals to move around and live in
the area even during expansions of xerophilous vegetation
and dry climatic phases.
Figure 4.
Holocene climatic and
environmental phases in the Jefara Plain
(modifed from Giraudi
et al.
2013).
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Anna Maria Mercuri, Assunta Florenzano, Carlo Giraudi, Elena A. A. Garcea: Humans and Water in Desert “Refugium” Areas: Palynological Evidence
of Climate Oscillations and Cultural Developments in Early and Mid-Holocene Saharan Edges
155
2.2 Case study 2: the Gobero Lake (Niger; 16°55′ N,
9°30′E; c. 560 m asl; c. 10,000–3800 cal BP)
During the Holocene humid periods, a lake formed in the
Gobero basin and a spillway connected the Gobero area with
Lake Chad. During the Early and Mid-Holocene periods,
human settlements were established on the shores of the
ancient lake and over 200 burial sites within the settlements
were found and assigned to the Pre-Pastoral (c. 9.5–8.2 ka BP)
Figure 5.
The Gobero area: a – Gobero basin and catchment area; b – Map of the Gobero area with the sites (modifed from Garcea 2013a).
Figure 6.
Stratigraphy of the Gobero Lake
showing subsequent lacustrine units (l.u.)
and aeolian units (a.u.), main vegetation
cover, and cultural periods (modifed from
Giraudi 2013).
0 5 km
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Anna Maria Mercuri, Assunta Florenzano, Carlo Giraudi, Elena A. A. Garcea: Humans and Water in Desert “Refugium” Areas: Palynological Evidence
of Climate Oscillations and Cultural Developments in Early and Mid-Holocene Saharan Edges
156
and Pastoral (c. 7.1–4.5 ka BP) cultural phases
.
Besides the
archaeological contexts, the chronological framework of the
site is based on OSL and radiocarbon dating (Sereno
et al.
2008).
Pollen analyses were carried out on samples taken
from the burial sites (close to the skeletons; G1 and G3)
and stratigraphic test excavations in the dried lake (GO1;
Figure 5). The pollen record from the lake provided pollen
that was less disturbed by human infuence than that
collected from the burial sites. On the other hand, pollen
analyses from the burial sites revealed some human plant
uses (Mercuri
et al.
2013). The combined evidence of pollen
spectra from both the burial sites and dried lake allowed us to
infer vegetational and environmental changes. Stratigraphic
correlations showed that the lake record belongs to the Mid-
Holocene phase, dating from about 7575–7485 to 6880–6670
cal BP (Lacustrine Unit 4 in Giraudi 2013; Giraudi, Mercuri
2013, 118). Its stratigraphy was made by subsequent
lacustrine and aeolian units corresponding to wet and dry
climatic phases, and different cultural phases
(Figure 6).
The pollen samples were collected from several lakebeds
and burial deposits associated with wet phases. Among
the 31 pollen samples taken from eleven lakebeds, pollen
spectra could only be obtained from site GO1. A very low
pollen concentration, even <100 p/g, and only a few number
of pollen taxa (<10 taxa) were found in the samples from
the other exposures of lake sediments, showing that selective
corrosion had affected the pollen. Thinned exines, probably
resulting from hydration / dehydration cycles in the lakes,
were usually observed.
Eight pollen samples were taken from the lacustrine unit
(l.u. 4 in Figure 6), in about 53 cm of sandy and silty sediments
of GO1. About 300 pollen grains per sample were counted on
average. Mean pollen concentration was low (440 p/g), but
quite a high number of taxa (90, from 14 to 36 per sample)
was observed. The pollen diagram shows a dominance of
Poaceae and Cyperaceae suggesting the presence of open
grassland, and a few shrubs possibly surrounding the margins
of the lake (Figure 7). Trees were insignifcant with a mean
percentage sum of 9%. The hygrophilous tree
Ficus
prevails
testifying to a continuous presence of water – at least in the
upper surface layer water table.
Capparis
has an isolated
peak, and Chenopodiaceae includes the small psammophilous
shrub
Cornulaca monacantha
-type. Pollen of anemophilous
trees from the Mediterranean basin, especially
Quercus
ilex
-type, deciduous
Quercus
and
Pinus
, comes from long-
distance transport by wind. In the herb-dominated spectra,
Urticaceae (
Laportea
-type) and
Plantago afra
-type are
common with Asteraceae and
Zygophyllum
. Herb plants of
wet environments, including limno-telmatophytes, such as
Phragmites
and
Typha
, characterise the spectra.
Two main pollen zones, represented here in the diagram
(Figure 7), were distinguished:
•
at the bottom (zone GO1-a, 53–22 cm, around 7.5 ka
BP), pollen concentration is very low;
Ficus
is present
together with
Capparis
and
Salvadora
, which grow in
wadi communities. Freshwater communities are well-
represented especially by
Typha
, growing along the
lake shores, while Chenopodiaceae refect salt and dry
environments in the area.
•
at the top (zone GO1-b, 21–5 cm, around 6.8 ka BP)
there is an increase in pollen concentration, together
with pollen of
Typha
, and foating aquatics needing
permanent water, such as
Nymphaea
and
Potamogeton
,
whereas xerophytes decrease. Algal elements and
microscopic charcoal particles were observed in one
(20 cm-deep) sample.
These zones refect two subsequent phases in the life of
the lake, a locally drier phase in the bottom part, and seasonal
oscillations of water levels. As different plant communities
and habitats are represented in the same pollen spectrum,
they suggest a mosaic of wet environments, grassland and
sandy dunes matching different habitats and seasons around
the lake and in the region. Cattails and other plants provided
food, woody plants gave fuel, and, in general, plants were
collected for multipurpose uses (Mercuri 2008b).
Figure 7.
Pollen diagram of GO1 lakebed showing two main pollen zones.
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Anna Maria Mercuri, Assunta Florenzano, Carlo Giraudi, Elena A. A. Garcea: Humans and Water in Desert “Refugium” Areas: Palynological Evidence
of Climate Oscillations and Cultural Developments in Early and Mid-Holocene Saharan Edges
157
Combined with the record from the burial sites, the pollen
from Gobero shows major vegetational changes occurring
in the area during the Early and the Middle Holocene
(Figure 8). Sedimentological and pollen data suggest that,
during the Early Holocene, the environment was more
humid and became progressively drier with a climatic
warming in the Middle Holocene. At this time, some humid
episodes still occurred, but seasonality was enhanced. The
landscape was covered by grassland of a Sahelian-type in
the rainy seasons, although xerophilous plants spread in the
dry seasons. Towards the fnal phase of human occupation,
around 5.0–4.0 ka BP, psammophilous shrubs spread in
sandy places with the encroaching of the Sahara, leading to
the gradual abandonment of the site. As the local conditions
did not seem as dry as in other northwestern African areas, a
persistence of signifcant local wet conditions still occurred
at Gobero for a short period of time (around 4.1–3.7 ka BP)
within a generally dry climatic phase.
The archaeological reconstruction shows that, during the
Pre-Pastoral period, hunter-gatherers settled only in some
restricted locations that offered certain crucial resources,
such as water bodies (Garcea 2013a; Garcea
et al.
2013).
Once people had begun to choose the richest available patch
of land and water body, they were forced into sedentism. In
order to cope with decreasing resources, they based their
subsistence on the consumption of a wide range of plants that
offered a constant available resource. During the Pastoral
period, when the climate became more instable, the Gobero
palaeolake offered a very favourable and exceptional location
for a base camp. In fact, when water supplies are limited, as
was the case in southern Sahara, lakes play a determining
role in reducing the mobility of herders. Furthermore, when
water availability continued to decrease, settling at Gobero
was probably not only an effcient logistical choice, but an
economic necessity to exploit the resources that were still
available on the spot.
3. Discussion
Research in the Saharan and Mediterranean regions has often
suggested that cultural developments sometimes show trends
that can correspond to climatic changes (Brooks
et al.
2005;
Cremaschi 2002; Kuper, Kröpelin 2006; Mercuri 2008a;
Cremaschi, Zerboni 2009; Roberts
et al.
2011; Maley,
Vernet 2013). The main events of profound change in the
environmental and cultural systems occurred at around 8.2,
6.0 and 4.2 ka BP (Mercuri
et al.
2011). During these periods
not all the responses were the same, but it is possible that
such dry and cool events triggered human adaptation to
new environmental conditions. Many palaeoenvironmental
archives, for example, have suggested that the Mediterranean
Figure 8.
Selected plant associations
from pollen analysis of the Gobero area
(burial sites and lakebed), and their trends
in lacustrine units (l.u.) (modifed from
Giraudi, Mercuri 2013).
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Anna Maria Mercuri, Assunta Florenzano, Carlo Giraudi, Elena A. A. Garcea: Humans and Water in Desert “Refugium” Areas: Palynological Evidence
of Climate Oscillations and Cultural Developments in Early and Mid-Holocene Saharan Edges
158
natural vegetation was transformed into a cultural landscape in a
fairly gradual way (Mercuri 2014). The Saharan environments
underwent dramatic changes that considerably affected their
ecosystems, and human settlements or their movements,
during the Holocene. Archaeological sites are, therefore,
reliable archives of both climate and human infuences and
their impact (Mercuri 2008a; Cremaschi
et al.
2014).
The interpolation of palaeoenvironmental and
archaeological data suggests that around the Gobero Lake
there was an ecosystem dynamic similar to that observed
around the marshlands of the Jefara Plain. At the northern
fringes of the Sahara desert, human frequentation of the
Jefara Plain relatively increased at around 6.7–5.4 ka BP. This
probably depended on the local availability of water and this
encouraged humans and animals to move and live in the area
even during drought periods. A similar ecosystem dynamic
was observed at the Gobero Lake area (Giraudi
et al.
2013).
In the central Sahara highlands and mountains (such as,
for example, the Tadrart Acacus), although psammophilous
vegetation began its expansion after approximately 6.2 ka BP,
a change in grassland composition with an increase of more
drought-resistant grass species took place at around 5.4 ka BP,
and a spread of xerophilous plants followed the increasing
aridity in places like the wadi Teshuinat area (Mercuri 2008a).
South of it, in the wadi Takarkori area, an almost continuous
human occupation of rock shelters occurred since the
beginning of the Holocene. The pollen content of the Takarkori
rockshelters highlighted a reduction of water availability
in the region at c. 8.2 ka BP. However, the persistence of
water resources inside the central Saharan massifs allowed a
continuous human frequentation, even during the dry period.
This confrms that these mountains acted as a refuge for human
groups, which in the same period modifed their subsistence
strategies, including the exploitation of domesticated animals
in their subsistence base (Cremaschi
et al.
2014).
At Gobero, people could beneft from the advantage of
living in ecological and social conditions that are typical
of edge zones (see Garcea 2013b). These areas are able to
offer high biodiversity and social interactions with different
groups, providing opportunities to incorporate a wide suite
of adaptive responses. In the case of Gobero – sedentism,
as a settlement strategy developed by the local pastoralists –
probably caused some contrary effects of over-exploitation,
which may have become fatal in the long-run. This has been
demonstrated, for example, by the pollen research carried
out in the Tadrart Acacus. During phases of decrease of
water availability all over the desert, over-grazing during
the Middle and Late Pastoral cultural phases contributed
to accelerating the desertifcation of such an ecologically-
sensitive area (Mercuri 2008a; 2008b).
4. Conclusion
A strong link exists between humans and water – and this
is deeply rooted in the biological nature of living organisms
and is evident in the general development of human cultures;
but in deserts, where “water” is the major limiting factor
for life, this is even more stringent. In fact, a small change
in water distribution, such as might occur under recurrent
climate oscillations, can cause non-negligible changes in
both vegetation distribution and cultural adaptations to the
environment.
Before the desertifcation of modern times, both the
Gobero Lake and the Jefara marshlands seem to have acted
as microrefugia – as they were restricted areas of favourable
environmental conditions within regions of largely
unfavourable climate; they acted as ecological refuges and
were able to provide shelter under the existing highly variable
climatic conditions of the Early and Middle Holocene.
The presence of water in these Saharan basins was
particularly attractive for humans, and the “sites with water”
had, in the past just as it is today, the invaluable role of being
nourishing places for living beings, and refugia for plants,
animals and humans. Such places offered more favourable
conditions for life during critical phases, such as dry
oscillations, due, for example, to a decrease in precipitation
and a lowering of the water table and small superfcial lakes.
In this sense they have always acted as biodiversity hotspots
that provided the sole source of water for living organisms.
The history of the Jefara, and especially that of Gobero,
as revealed by the archaeological and palaeoenvironmental
reconstructions, suggests that such sites at the edges of the
desert – at its most northern and southern limits – have been
visited and exploited for a long time, and therefore have
been profoundly transformed, especially when they acted
as anthropic refugia. The presence of humans and their
action have conditioned the local growing of plants and
have selected a more or less synanthropic fora. Modern
conservation strategies should take into consideration the
fact that water reservoirs, which are crucial for the long-
term conservation of the Sahara-Sahel biodiversity today
(Vale
et al.
2015), have provided refugia in the past – as they
presently do under global warming conditions.
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