The Representativeness of Olea Pollen from Olive Groves and the Late Holocene Landscape Reconstruction in Central Mediterranean

Abstract

Modern pollen spectra are an invaluable reference tool for paleoenvironmental and cultural landscape reconstructions, but the importance of knowing the pollen rain released from orchards remains underexplored. In particular, the role of cultivated trees is in past and current agrarian landscapes has not been fully investigated. Here, we present a pollen analysis of 70 surface soil samples taken from 12 olive groves in Basilicata and Tuscany, two regions of Italy that exemplify this cultivation in the Mediterranean basin. This study was carried out to assess the representativeness of Olea pollen in modern cultivations. Although many variables can influence the amount of pollen observed in soils, it was clear that most of the pollen was deposited below the trees in the olive groves. A rapid decline in the olive pollen percentages (c. 85% on average) was found when comparing samples taken from IN vs. OUT of each grove. The mean percentages of Olea pollen obtained from the archeological sites close to the studied orchards suggest that olive groves were established far from the Roman farmhouses of Tuscany. Further south, in the core of the Mediterranean basin, the cultivation of Olea trees was likely situated ~500–1,000 m from the rural sites in Basilicata, and dated from the Hellenistic to the Medieval period.

Full text

ORIGINAL RESEARCH
published: 20 October 2017
doi: 10.3389/feart.2017.00085
Frontiers in Earth Science | www.frontiersin.org 1October 2017 | Volume 5 | Article 85
Edited by:
Encarni Montoya,
Instituto de Ciencias de la Tierra
Jaume Almera (CSIC), Spain
Reviewed by:
Josu Aranbarri,
University of the Basque Country
(UPV/EHU), Spain
Donatella Magri,
Sapienza Università di Roma, Italy
*Correspondence:
Rita Fornaciari
rita.fornaciari@unimore.it
Specialty section:
This article was submitted to
Quaternary Science, Geomorphology
and Paleoenvironment,
a section of the journal
Frontiers in Earth Science
Received: 30 July 2017
Accepted: 05 October 2017
Published: 20 October 2017
Citation:
Florenzano A, Mercuri AM, Rinaldi R,
Rattighieri E, Fornaciari R, Messora R
and Arru L (2017) The
Representativeness of Olea Pollen
from Olive Groves and the Late
Holocene Landscape Reconstruction
in Central Mediterranean.
Front. Earth Sci. 5:85.
doi: 10.3389/feart.2017.00085
The Representativeness of Olea
Pollen from Olive Groves and the Late
Holocene Landscape Reconstruction
in Central Mediterranean
Assunta Florenzano 1, Anna Maria Mercuri 1, Rossella Rinaldi 1, Eleonora Rattighieri 1,
Rita Fornaciari 1, 2
*, Rita Messora 1, 2 and Laura Arru 2
1Laboratorio di Palinologia e Paleobotanica, Dipartimento di Scienze della Vita, Università di Modena e Reggio Emilia,
Modena, Italy, 2Plant Physiology Lab, Dipartimento di Scienze della Vita, Università di Modena e Reggio Emilia, Reggio Emilia,
Italy
Modern pollen spectra are an invaluable reference tool for paleoenvironmental and
cultural landscape reconstructions, but the importance of knowing the pollen rain
released from orchards remains underexplored. In particular, the role of cultivated trees is
in past and current agrarian landscapes has not been fully investigated. Here, we present
a pollen analysis of 70 surface soil samples taken from 12 olive groves in Basilicata and
Tuscany, two regions of Italy that exemplify this cultivation in the Mediterranean basin.
This study was carried out to assess the representativeness of Olea pollen in modern
cultivations. Although many variables can influence the amount of pollen observed in
soils, it was clear that most of the pollen was deposited below the trees in the olive
groves. A rapid decline in the olive pollen percentages (c. 85% on average) was found
when comparing samples taken from IN vs. OUT of each grove. The mean percentages
of Olea pollen obtained from the archeological sites close to the studied orchards suggest
that olive groves were established far from the Roman farmhouses of Tuscany. Further
south, in the core of the Mediterranean basin, the cultivation of Olea trees was likely
situated ∼500–1,000 m from the rural sites in Basilicata, and dated from the Hellenistic
to the Medieval period.
Keywords: Olea europaea L., pollen, surface soil, archeological site, Basilicata, Tuscany, Roman landscape
INTRODUCTION
The olive tree is an important marker of the Mediterranean cultural landscapes. Molecular,
archaeobotanical, and paleoenvironmental data are acknowledged as essential for reconstructing
the history of the domesticated olive tree (Zohary and Hopf, 2000; Newton et al., 2014). Together
with the walnut and chestnut trees, the present geographical distribution of genetic diversity in Olea
europaea L. was perhaps more influenced by human activities than by its natural migration and
colonization (Bottema and Woldring, 1990; Baldoni et al., 2006), a view confirmed by the frequent
recovery of this pollen in the deposits from archeological sites (Mercuri et al., 2013). Accordingly,
Olea pollen may be regarded as an indicator of human presence and activity in a certain
area. However, the species includes both wild and domesticated subspecies (O. europaea L. ssp.
sylvestris and O. europaea L. ssp. europaea, respectively) that have quite similar pollen morphology

Florenzano et al. The Representativeness of Olea Pollen
(Roselli, 1979; Ribeiro et al., 2012; Messora et al., 2017).
Another problem arises from the fact that O. europaea is an
evergreen xerophilous tree, whose growth is promoted by a
warming climate (Moriondo et al., 2013). Recent studies have
demonstrated that a seasonal analysis is required to establish
robust relationships between the Mediterranean climate and olive
development (Aguilera et al., 2015); therefore, an increasing
trend in the pollen curves may have ambiguous significance
in the diagrams from the Mediterranean Holocene records.
Palynologists have concluded that Olea pollen may be considered
both a proxy of warming and drought conditions, as well as
the product of a fruit-bearing plant dispersed and cultivated by
humans. High percentages of this pollen recovered in the spectra
from archeological sites, or from human-influenced off-sites, can
reasonably result from a process of cultivation. However, it is not
clear how much “high” may be the percentage of Olea pollen in
modern agrarian landscapes. Today, Olea pollen is common and
among the most abundant airborne pollen in the Mediterranean
countries (e.g., Galán et al., 2004; Ziello et al., 2012; Mercuri,
2015). In aerobiology, volumetric spore traps were placed in olive
groves to study the phenology and the delayed pollination season
of olive groves located at higher altitudes (in SE Spain: Aguilera
and Valenzuela, 2012). Nevertheless, the amount of pollen that
fell to the ground and was trapped in sediments below olive trees
and near modern groves has not yet been systematically assessed.
In this paper, we discuss the representativeness of Olea pollen
in surface soil samples taken from modern Italian olive groves,
with the aim of contributing to the interpretation of past pollen
spectra. To our best knowledge, this is the first study of surface
soil sediments from this widespread type of crop cultivation. This
is somewhat surprising, considering that knowledge of current
pollen rain may be the best reference tool for understanding
and reconstructing the environments and agrosystems of the
past (e.g., Cañellas-Boltà et al., 2009; Fall, 2012; Davis et al.,
2013). Since most pollen-based landscape reconstructions are
based on sophisticated quantitative pollen analyses and modeling
estimates, this paper instead proposes a basic observational test
to provide much-needed reference data for the complex and
fragmented Mediterranean landscapes during the late Holocene.
This simpler approach can improve our understanding of the
historical development of Mediterranean cultural landscapes.
The same methodology, but applied in a different approach,
was used by Vermoere et al. (2003) to compare the modern
and subfossil pollen assemblages through “modern analogs” and
multivariate statistics in their study of an “olive landscape” in SW
Turkey (Sagalassos).
Today, most of the total area with olive groves is estimated to
lie in the Mediterranean basin, with the highest olive production
quantities occurring in Spain and Italy (FAOSTAT, 2017;
Figure 1). The focus of our palynological research is centered on
the olive plantations located in Italy, a country extraordinarily
rich of agroforestry traditions and olive cultivars of the central
Mediterranean basin (Rühl et al., 2011). Such cultivation is
widespread in the central-southern regions and the islands where
the local environmental conditions are most favorable to olive
growth. For our study, we selected Tuscany and Basilicata, two
of the most productive agrarian regions in Italy, with large olive
groves in their territories (Pisante et al., 2009;Figure 2). These
regions couple modern plantations, characterized by different
cultivars, with an impressive record of archeological sites
preserving evidence of long-term agricultural activity carried out
for millennia (Florenzano, 2013; Vaccaro et al., 2013; Bowes et al.,
2015). Therefore, we have the opportunity to directly compare
past (archeological) and present (olive grove) pollen spectra from
the same areas. The results should be useful for assessing the
significance of this pollen and tree in the late Holocene history of
these two regions, which can serve as an exemplar for the entire
peninsula.
MATERIALS AND METHODS
Pollen Sampling and Study Areas
Surface soils were collected from 12 olive groves: five were
located in Basilicata (B1–5, cultivated along the Bradano River,
in the province of Matera) and seven in Tuscany (T1–7, grown
in the commune of Cinigiano, in the province of Grosseto;
Figure 2). These two regions have quite heterogeneous soil
structures, ranging from alluvial soils along the rivers to marine-
origin sandy-gravel deposits in the hinterlands (Pieri et al., 1996;
Costantini and Righini, 2002).
The climate of the two regions has a typical Mediterranean
seasonality, with rainy winters and dry summers, but with
regional differences depending on the latitude and elevation. In
Basilicata, the climate is influenced by both the hydrographic
basin of the Bradano River and the Ionian Sea, while in Tuscany
it is by the warm current from the Tyrrhenian Sea (mean annual
temperatures from both regions: from 13 to 16◦C; mean annual
rainfall: from 300 to 700 mm. Data from regional meteorological
archives of Archivio Meteo Storico).
Mediterranean vegetation characterizes the two regions,
although mesophilous plant associations are also distributed in
the studied areas. In Basilicata, broadleaved deciduous forests are
the dominant vegetation communities of the inner lands, whereas
Pinus halepensis Mill. forest are spread along the coast (Blasi,
2010). A widespread occurrence of woodlands composed of
evergreen sclerophylls and broadleaf deciduous trees and shrubs
characterize the southern Tuscany vegetation (Selvi, 2010). Some
pine tree stands (Pinus nigra J. F. Arnold, P. pinaster Aiton,
P. pinea L., and P. halepensis) now cover this territory after
being reforested over the last two centuries (Ciabatti et al., 2009).
The olive groves include different cultivars, commonly organized
in mixed plantations of variable size and expansion (Figure 3).
In this study, each olive grove was selected to be the farthest
away possible from other groves in the same area (Florenzano
et al., 2011). However, in Basilicata and Tuscany olive groves
account approximately for c. 11% of the Italian territory planted
with olive trees, and the density of these tree cultivations is
so high that they often color and characterize the landscape of
these two regions (from ISTAT—National Institute of Statistics
2011: Basilicata: 31.350 ha, and Toscana: 97.241 ha of olive
orchards).
Two samples were taken from the center of each plantation
(IN), and four samples from the peripheral positions (OUT),
at a distance of c. 250–500 and 1,000 m depending on
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Florenzano et al. The Representativeness of Olea Pollen
FIGURE 1 | Distribution map showing the production quantities by country, estimated in tons of olives (in the legend) redrawn from FAOSTAT database for 2017.
FIGURE 2 | Map of Italy showing the locations of the 12 olive groves studied in Basilicata (B, Southern Italy) and Tuscany (T, Central Italy). The cultivars of Olea
europaea L. ssp. europaea cultivated in these olive groves are reported at the right (B) and left (T) of the map. The labels of the olive groves (B1–5, and T1–7) follows
the list embedded in the Figure 2 graphic.
geomorphologic and anthropogenic limits, but always along the
SE and the NW transects.
A total of 70 samples were collected from bare ground—not
covered by grass—“by cutting” out an c. 2-cm thick portion
of the surface soils. One of the IN samples was picked up
according to the method of sampling “by pinches” (e.g., used
in forensic palynology; Horrocks et al., 1998; Bryant and Jones,
2006): soil sub-samples were taken from several points over
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Florenzano et al. The Representativeness of Olea Pollen
FIGURE 3 | Surface pollen samples taken from the olive groves located in Basilicata (B) and Tuscany (T), Italy; the geographical coordinates, size of the plantation,
and type of sampling are shown. a, maximum length; b, maximum width; IN, samples taken from the center of the olive groves; OUT, peripheral samples. The olive
grove extent is that for the sampling year (2010 for Basilicata, 2011–13 for Tuscany). Bottom left: the model of pollen sampling in the olive groves.
a c. 1 m2area, mixed, and put into a single small plastic
bag per sample. Since the pollination of different cultivated
crops occurs at different periods, normally between April and
June in the western and central Mediterranean (Fornaciari
et al., 2000; Osborne et al., 2000), the samples were collected
in the spring or summer seasons, i.e., immediately before
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Florenzano et al. The Representativeness of Olea Pollen
(early April) or after (July) the blooming periods of the olive
trees.
Reference Data from Archeological
Literature
Data from the archeological layers were obtained from the
pollen analyses of 12 sites located in Basilicata (BI–VII)
and in Tuscany (TI–V)—as part of multidisciplinary research
carried out by independent projects (for list and references
see Table 1)—and selected to compare the presence of Olea
in modern and past pollen spectra. The archeological sites
were mainly rural settlements and farmhouses belonging to
different cultural periods, from Hellenistic to Medieval in
Basilicata, and from the Augustean Roman age in Tuscany.
The chronology of the sites was mainly determined by their
archeological materials (e.g., pottery), and to a lesser extent
by radiocarbon dates and layer correlations. Based on both
the pollen data and archeological evidences, environmental
reconstructions emphasize the importance of oliviculture in the
past economies of these lands (Florenzano, 2013; Bowes et al.,
2017). In Basilicata, the Greek and Roman settlements were
characterized by well-developed economic activities, including
agricultural and pastoral practices (Florenzano and Mercuri,
2012). An organized road network and an efficient irrigation and
drainage system characterized this land (Carter and Prieto, 2011).
After a period of crisis linked to the fall of the Roman Empire
(ca. 4–11th century AD), agricultural practices resumed during
the Medieval period, and included olive cultivations within
the monastic communities (Sogliani and Marchetta, 2010). In
Tuscany, the archaeobotanical and archeological data point
to a phase of intensive land use in the late Republican/early
Imperial date (ca. 1st century BC/1st century AD). Along
with the significant presence of cereals, the grape vines, and
olives attest to the importance of Mediterranean crops in
rural contexts, which were small and mainly occupied on a
temporary/short-period basis (Rattighieri et al., 2013; Bowes
et al., 2015).
Pollen Analysis
An amount of 2–5 g of wet weight per sample of surface soil
sediment was treated for pollen extraction (Florenzano et al.,
2012). Lycopodium spores were added for the calculation of
pollen concentration (expressed in pollen grains per gram =p/g).
The method involves deflocculation with Na-pyrophosphate
10%, sieving with nylon filter of 7 µm mesh, carbonate
dissolution with HCl 10%, acetolysis (Erdtman, 1960) to remove
part of the organic substance, enrichment with heavy liquid (Na-
metatungstate hydrate) to concentrate the pollen with flotation,
dissolution of silicates with HF 40%. The residues were mounted
in slides, fixed in glycerol jelly and sealed with paraffin. Pollen
counts (up to about 500 pollen grains per sample) were carried
out under 400x with a light microscope. For the purpose of
this research, we counted only Olea,Pinus, and the number of
total pollen grains in the Pollen Sum. Olea was identified as
trizonocolpate-colporate pollen with reticulate exine, and a polar
axis of ∼20 µm. Pinus is a high pollen producing tree, and has a
saccatae pollen with a maximum diameter of c. 70 µm in many
species (e.g., P. nigra—Accorsi et al., 1983;Pinus pinea—Accorsi
et al., 1978; Desprat et al., 2015). As Pinus was an important
component of some pollen spectra, obtaining the pine values
helped us assess the underestimation of Olea pollen in several
olive groves.
Pollen values reported in the Results section below are the
mean pollen concentrations or percentages calculated from the
TABLE 1 | Percentage of Olea pollen from the archeological sites close to the modern olive groves studied in this paper, and relevant references.
Archeological site (label and name) Archeological chronology Number of pollen samples Olea % Main references
Mean Max
BASILICATA
B I - Pizzica H 5 2.5 11.8 Florenzano and Mercuri, 2012
B II - Fattoria Fabrizio H 10 2.6 4.6 Florenzano et al., 2013;
Florenzano, 2014
B III - Pantanello R 12 0.4 2.1 Florenzano and Mercuri, 2012,
2017
B IV - Sant’Angelo Vecchio H-R 27 1.9 13.1 Florenzano, 2016
B V - Difesa San Biagio H 9 0.7 1.8 Mercuri et al., 2010
B VI - Miglionico M 10 0.8 2.4 Florenzano, 2013
B VII - Altojanni M 7 1.6 6.5 Mercuri et al., 2010
TUSCANY
T I - San Martino R 8 <0.1 0.2 Rattighieri et al., 2013
T II - Colle Massari R 4 0.2 0.4 Bowes et al., 2015, 2017
T III - Podere Terrato R 11 <0.1 0.4 Bowes et al., 2015, 2017
T IV - Case Nuove R 15 0.1 1.0 Vaccaro et al., 2013
T V - Poggio dell’Amore R 5 0.1 0.3 Bowes et al., 2015, 2017
The detailed pollen analyses are reported in Florenzano (2013) (Basilicata) and Rattighieri (2016) (Tuscany). H, Hellenistic; R, Roman; M, Medieval.
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Florenzano et al. The Representativeness of Olea Pollen
average data of the two (IN) or four (OUT) pollen samples per
olive grove.
Pollen Data Elaboration
Data were imported into Microsoft Excel 2013 and used to
make the graphs. Data elaborations show the trends of olive
pollen deposition at three distances from their source (IN,
500 and 1,000 m). Their linear trends were based on the
coefficient of determination (R2) by using linear analysis tools.
Principal component analysis (PCA) was performed, by using the
XLSTAT 2014 software, to display the distribution of the samples
(variables) with respect to Olea,Pinus, and the total pollen from
other taxa observed in the samples.
RESULTS
The pollen analysis from surface soils (Table 2) shows that
the total pollen concentrations are always significant, ranging
from min. c. 20,000 p/g (B5, higher IN than OUT) to max.
c. 130,000 p/g (T2, higher OUT than IN). One half of the
samples IN contains higher total concentrations than OUT.
The total pollen concentrations are higher in Tuscany than
in Basilicata (73,138 vs. 40,137 p/g on average), possibly
reflecting the different soil composition and richness of organic
matter.
The mean percentage of Olea pollen in the samples was similar
between the two regions (T =29.8% vs. B =29.3%). The IN
samples had significant percentages of Olea, from 8% in B4 to
58% in B1, but only three olive groves showed Olea at >50% for
the IN spectra (B1, B5, and T4). In five IN samples, Olea occurred
at <20% (B2, B3, B4; T2, T7); these values, however, reached to
30–40% when Pinus was excluded from the counts. The highest
Olea percentages came from the sites B1 (IN: c. 58%) and T4 (IN:
c. 53%). However, the more extensive olive groves (B5 and T3;
Figure 3) had lower values (IN: c. 51% in B5, and c. 23% in T3).
This indicated that an evident relationship was lacking between
the size and representativeness of Olea pollen taken from the
center of an olive grove.
The presence of Olea strongly decreased for OUT, at 500 m (2–
9%), whereas Olea values were more variable for OUT at 1,000 m
(Table 2;Figure 4). In some cases (B2, B4), an increase in Olea
percentage is observed reflecting the pollen rain from other olive
trees/groves growing in the area.
The PCA (Figure 5) allowed for the comparison of pollen
spectra and sites, and separated them along the distance and
composition features. In the sectors III and II, the IN samples—
taken from the center of olive groves—are concentrated with the
highest Olea percentages; moreover, samples with a significant
presence of Pinus are concentrated in sector II. By contrast, most
of the OUT samples taken at 500 m and 1,000m from the groves
center, were plotted in the sectors I and IV; hence this revealed
that other taxa influenced these spectra.
DISCUSSION
The Representativeness of Olea in the
Olive Orchards
As expected, Olea pollen was consistently present in the pollen
spectra from the olive groves. Generally, we know that pollen
released from trees is transported, in part, by wind through the
canopy, and partly is trapped by the foliage and eventually falls
by gravity in the wood (McKibbin, 2006). The local signal and
the anemophilous pollination are predictive of a good amount
of Olea pollen grains in and around the groves. Although this
pollen is one of the main components in the airborne pollen
rain of Mediterranean countries, the yearly percentage of Olea
pollen is not usually reported, and so direct comparison between
such aerobiological data and soil pollen spectra is not possible
(Ziello et al., 2012). Data from airborne pollen monitoring by
the station of Matera (years 2005–2006, by ARPAB) suggested
that Olea pollen is generally less represented in the air than
in the surface soil layers (Florenzano et al., 2011), a pattern
TABLE 2 | Results of the pollen analyses: concentration (p/g =pollen per gram) of all the pollen grains found in the soil surface samples, and the percentages of Olea
pollen counted in the IN and OUT samples of each plantation.
Olive grove Total pollen concentration (p/g) Olea pollen (%)
Label Number of pollen samples Total IN OUT IN 500 m 1,000 m Mean
B1 6 31,620 25,337 34,761 58.4 7.6 4.4 23.5
B2 6 71,746 40,002 87,617 11.1 1.5 6.4 6.3
B3 6 22,338 20,746 23,134 18.7 2.8 / 9.1
B4 6 55,097 75,992 44,649 7.6 2.1 4.0 4.6
B5 6 19,884 27,200 16,226 50.9 4.0 3.1 19.3
T1 6 73,450 123,290 48,531 26.6 3.4 2.2 10.7
T2 6 127,836 72,232 164,905 13.2 1.6 / 4.6
T3 6 49,154 42,804 52,329 22.8 9.0 5.3 12.4
T4 6 79,093 99,066 65,777 52.8 2.3 / 23.2
T5 6 31,844 32,720 30,968 28.6 4.0 / 16.3
T6 4 45,146 43,968 46,323 48.6 2.1 / 25.3
T7 6 105,441 229,453 43,435 16.2 1.9 1.1 6.4
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Florenzano et al. The Representativeness of Olea Pollen
FIGURE 4 | Trends of Olea pollen deposition observed in the olive groves: (A) IN and 500 m (for all 12 sites), and (B) IN, 500 and 1,000 m (for seven sites: the sites
without samples at 1,000 m were excluded). R2=coefficient of determination.
FIGURE 5 | Principal component analysis (PCA; elaboration: XLSTAT 2014) for the 70 samples from the 12 studied olive groves. The modern pollen spectra shows
that the percentage of Olea depends on the distance from the olive groves (sector III), and on the presence of Pinus (II) or other taxa (IV, I).
also evident for Prunus orchards (Mercuri, 2015). The pollen
of Olea was c. 7–11% of the yearly pollen rain, while, in our
study, it was 13% on average in the IN and OUT surface soil
samples of the B-groves (this value was calculated from the
Table 2 data). Nevertheless, we found that Olea pollen had very
variable percentages (2–58%) depending on the IN and OUT
point locations of sampling. We found that, in general, the
highest values of Olea pollen were recorded in those samples
taken from the center of the plantation but no relationship
between the size of the olive groves and the amount of olive pollen
accumulated in these IN samples. We estimated that the highest
values observed in the IN samples, from B1 and T4, sharply
dropped from c. 58–53 to c. 5% at 500 m. Hence, Olea pollen
could be estimated to decrease by 61–96% in the first few hundred
meters from its source. Accordingly, Adams-Groom et al. (2017)
showed that most pollen from isolated trees [Carpinus betulus
L., Cedrus atlantica (Endl.) Manetti ex Carrière, Juglans nigra L.,
and Platanus acerifolia (Aiton) Willd.] was deposited beneath the
canopy (range 63–94%), following an exponentially decreasing
curve. An exponential decline was also observed in Vitis pollen as
function of its distance away from the vineyard edge: Vitis pollen
can be detected within vineyard soils, but rapidly reaches very low
concentrations (<0.1%) or disappears altogether in soils outside
vineyards (Turner and Brown, 2004). In the surface soil pollen-
deposition patterns of hornbeam, cedar, walnut, and plane pollen,
the tailing-off began at the outer edge of the canopy; the amount
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Florenzano et al. The Representativeness of Olea Pollen
of pollen deposited at 50 m was <2.6% and at 100 m it was
<0.2% of total deposition in the samples for any tree (Adams-
Groom et al., 2017). Bunting (2002), who studied modern pollen
deposition in and around woodlands, by using moss polsters
and surface sediments from small lakes, also found that local
woody pollen percentages generally reached background levels
of <100 m from the woodland edge. The rapid decline of tree
pollen grains with distance is reported from additional studies
(e.g., Broström et al., 2005), which often remark on the 100-m
threshold from the woodland edge for the dramatic decrease of
tree pollen (Tinsley and Smith, 1974).
The slope of imaginary lines connecting each percentage
value at the IN and 500 m sampling sites was negative for
each olive grove we considered. This confirms a substantial
decrease of pollen deposition at 500 m (Figure 4A). Farther,
however, the percentages remain fairly constant, or even increase
in the samples taken at 1,000 m sites, and thus inconsistent with
the previous one (Figure 4B). A plausible explanation for this
result is that the great density of olive groves in the studied
areas (mentioned above) caused an abundant pollen emission
of airborne pollen in the relevant sampled areas. Many factors
likely contributed to the variability of Olea pollen percentages in
our samples. For example, aerobiological data report that olive-
growing areas act as good Olea pollen sources but give contribute
differently to the airborne pollen rain depending on the prevalent
wind direction and the size of groves (Hernandez-Ceballos et al.,
2012). Besides the extent of olive groves, the tree size- and age-
distributions, the gap between the sampling date and the start
of the pollination period (April), the tree density and canopy
closure, the abundance of overrepresented pollen from other
taxa in the pollen spectra (Pinus), the occurrence of particular
agricultural practices (e.g., plowing), and the spread of olive
groves or the presence of wild olive specimens in the same area,
are all variables capable of influencing our olive grove spectra.
The Pollen Evidence of Past Olive Groves
near Archeological Sites
Our results obtained from the modern pollen spectra may help
to interpret spectra from archeological sites (Table 3). The mean
percentages of olive pollen from the archeological sites located in
Basilicata suggest that the olive groves were c. 500 m in distance
from BI, BII, BIV, and BVII, yet >500 m from BIII, BV, and
BVI. According to these data, oliviculture was one of the most
relevant features of the past landscape and economy of Basilicata
(Florenzano, 2013). Although Mediterranean vegetation was
prevalent in southern Italy, the influence of wild olive does
not seem to have had significant incidence in the past spectra
from this region: according to the archeological and historical
literature, olive cultivation was spread since the 7–6th century
BC and favored by the Greek colonization. From that period
onward, this crop has largely influenced the agrarian system of
this territory (van der Mersch, 1994; De Siena, 2001).
The archeological sites located in Tuscany always had very low
Olea pollen values (≤0.2%), suggesting that the olive groves were
not distributed within 1,000 m of the Roman farmhouses of the
Cinigiano district. This is due, in part, to the fact that the sites
TABLE 3 | Percentage of Olea pollen from the archeological sites of Basilicata and
Tuscany, in relation to the distance from the center of an olive grove.
Distance Olea pollen (%)
Modern olive groves Archeological sites
BASILICATA
IN 7.6–58.7 No sites
500 m 1.5–7.6 2.5 (B I), 2.6 (B II), 1.9 (B IV), 1.6 (B VII)
>500 m <1.5 0.4 (B III), 0.7 (B V), 0.8 (B VI)
TUSCANY
IN 13.2–58.8 No sites
500 m 1.6 - 9 No sites
>500 m <1.6 <0.1 (T I, T III), 0.2 (T II), 0.1 (T IV, T V)
The estimated distance was based on the results obtained from the soil samples of the
modern olive groves. The labels of the archeological sites (B I–VII, and T I–V) follow the list
in Table 1.
were small facilities, mainly used seasonally to process cereals,
or for animal husbandry, so that herbaceous crops cultivated
for food and fodder especially influenced the pollen spectra.
However, the low values of Olea pollen are recurrent in these sites
of Tuscany. Although the Roman agriculture was intensive and
complex, we can conclude that oliviculture was not a landscape
feature of this region at that time.
A net of off-sites helps to reconstruct the history of this plant
in the Italian peninsula. In southern Italy, many off-site records
contain Olea pollen dating back to the early Holocene (Pergusa
lake and Gorgo Basso in Sicily: Sadori and Narcisi, 2001; Tinner
et al., 2009; Lago di Trifoglietti in Calabria: Joannin et al., 2012).
Afterwards, the fairly continuous curve of Olea begins at c. 6500
cal BP during the mid-Holocene (Lago Salso and Lago Alimini
Piccolo in Apulia: Di Rita and Magri, 2009; Di Rita et al., 2011;
Lago Battaglia: Caroli and Caldara, 2007). From c. 3,600 cal
BP onward, Olea curves increase in Lago Alimini Piccolo and
Lago di Pergusa (c. 20% in both sites), but also increasing in
Lago Battaglia at c. 3,100 and 2,600 cal BP. Similarly, in central
Italy, some off-site cores show the occurrence of Olea during
the early Holocene (Lago dell’Accesa in Tuscany: Drescher-
Schneider et al., 2007), with its continuous presence from c. 7,300
to 7,000 cal BP also at Lago del Greppo (Vescovi et al., 2010). In
Tuscany, at Lago di Massaciuccoli (Mariotti Lippi et al., 2007),
Olea pollen is present in traces amounts, and found only in the
layers dating to the Roman Age; also elsewhere in the region, Olea
was discontinuously recorded in low amount (Mariotti Lippi
et al., 2015; Mariotti Lippi in verbis). Then, at c. 2,800–2,700
cal BP, Olea increased together with Juglans and Castanea, and
with cereals and other anthropogenic indicators, thus clearly
showing the development of cultural/agrarian systems (at Lago
di Vico, Lago dell’Accesa and Lago Battaglia: Magri and Sadori,
1999; Caroli and Caldara, 2007; Drescher-Schneider et al., 2007).
These data show the general chronological trend of olive pollen
from traces to high percentages in the Holocene off-sites (e.g.,
Lago Alimini Piccolo), but the meaning of Olea presence in the
off-site and on-site cores is different (Mercuri et al., 2013). We
must remember that these records are from areas that lie within
the distribution of wild olive trees. In lake records, where we
Frontiers in Earth Science | www.frontiersin.org 8October 2017 | Volume 5 | Article 85

Florenzano et al. The Representativeness of Olea Pollen
cannot expect the growth of olive trees at the sampling locations,
the presence of pollen from these trees does not strictly mean
that they were cultivated. The high amounts of Olea in these
records (>2%) may be evidence of (mixed) wild stands that
occurred besides the plantations in the area (as regional pollen
rain is recorded in off-sites); hence, the significance of this pollen
requires careful consideration of the chronology and proximity
of archeological sites to the off-site.
CONCLUSIONS
Our data show that olive trees can depict a significant picture in
pollen spectra, and that their highest percentages are evidence of
the local presence of cultivations in a given area. Low percentages
of Olea pollen may be interpreted as being the result of long-
distance transport, while percentages of >2% may indicate the
presence of plantations at least 1,000 m from the sampling
point(s).
Olea pollen from modern olive groves provides a reference-
tool that is useful for paleoenvironmental reconstructions (as
generally attested: Davis et al., 2013), and it is important to
know the role of olive cultivation in the development of cultural
landscapes. As mentioned above, the significance of olive pollen
in past spectra is sometimes controversial, since the presence
of wild trees enlarge the signal of the species, and the warming
phases have a role in spreading olive trees in the Mediterranean
landscapes.
The transformation of natural to human-influenced
environments (Zanchetta et al., 2013; Mercuri and Sadori,
2014), from the local to trans-regional spatial scales (Mercuri,
2014), may be tracked by observing the presence and trends of
Olea both in and near the archeological sites. Our work suggests
the cultivation of olive trees has been a long-time activity along
the Bradano River in Basilicata, whereas it is a relatively recent
one for the agrarian landscape of the Cinigiano district in
Tuscany. The research reported in this paper, carried out in
two regions with a strong agriculture vocation, shows that the
long tradition in olive cultivation marks the present and past
pollen spectra, and that it clearly remains evident in the current
Mediterranean landscapes.
AUTHOR CONTRIBUTIONS
AM and AF planned the research, and wrote the paper
with the cooperation of RF; RR, ER, and AF made pollen
sampling and analyses; RF made statistic and graphical
elaborations; RM and LA studied olive grove distribution and
pollen morphology. All authors read and approved the final
manuscript.
FUNDING
This work was supported by the national-funded project
SUCCESSO-TERRA (Human societies, climate, environment
changes and resource exploitation/sustainability in the
Po Plain at the Mid-Holocene times: the Terramara;
Ministero del’Istruzione, dell’Università e della Ricerca
PRIN-20158KBLNB).
ACKNOWLEDGMENTS
Archaeological sites are listed in the BRAIN database (http://
brainplants.unimore.it/). Meteorological data are available
from Archivio Meteo Storico (https://www.ilmeteo.it/portale/
archivio-meteo/Montescaglioso?refresh_cens; https://www.
ilmeteo.it/portale/medie-climatiche/Cinigiano?refresh_ce).
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Conflict of Interest Statement: The authors declare that the research was
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Copyright © 2017 Florenzano, Mercuri, Rinaldi, Rattighieri, Fornaciari, Messora
and Arru. This is an open-access article distributed under the terms of the Creative
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