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Agroforestry SystemsAn International Journal incorporatingAgroforestry Forum ISSN 0167-4366 Agroforest SystDOI 10.1007/s10457-014-9733-2

Floristic diversity of valonia oaksilvopastoral woodlands in Greece

Michael S. Vrahnakis, GeorgeFotiadis, Anastasia Pantera, AndreasPapadopoulos & Vasilios P. Papanastasis

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Floristic diversity of valonia oak silvopastoral woodlandsin Greece

Michael S. Vrahnakis • George Fotiadis •

Anastasia Pantera • Andreas Papadopoulos •

Vasilios P. Papanastasis

Received: 3 July 2013 / Accepted: 25 July 2014

� Springer Science+Business Media Dordrecht 2014

Abstract Valonia oak (Quercus ithaburensis subsp.

macrolepis (Kotschy) Hedge and Yaltirik), a deciduous

species grown in the xerothermic conditions of the east

Mediterranean zone of Europe, forms woodlands of

open canopy that permits adequate light to reach the

ground thus sustaining an exceptionally rich flora. In

Greece, these woodlands are mainly used for livestock

grazing and considered important silvopastoral systems.

Nowadays, most of them are abandoned and degraded as

a result of inappropriate management. For the effective

evaluation and sustainable management of these wood-

lands and the establishment of reliable monitoring

systems, a detailed analysis of their plant diversity

characteristics across Greece is needed. This paper aims

at determining and comparing floristic diversity mea-

sures as well as at assessing the impact of human

activities on vegetation and floristic diversity of the most

characteristic valonia oak silvopastoral woodlands of

Greece. It was found that the truncated log-normal

model adequately predicts the species abundance data

for eleven out of the twelve woodlands. From the

statistical comparison of the diversity indices Q-statis-

tic, Berger–Parker dominance index and Shannon-

Wiener measure of equitability, three groups of these

woodlands can be distinguished (a) the high-richness

group of Pentalofos, Lesvos, Lakonia and Thesprotia,

(b) the medium-richness group of Kriti Island, Alex-

androupoli, Strofylia and Galaxidi, and (c) the low-

richness group of Kea Island, Amfilohia, Almyros and

Lilaia. However, the Renyi’s diversity ordering diagram

showed that, generally, in low levels of entropy

inconsistency is the rule and no clear pattern of diversity

is extracted reflecting the impact of complex factors.

Among them, those related to management seem to

mostly determine plant diversity of valonia oak silvo-

pastoral woodlands, with abiotic factors having an

occasionally supporting role. Changes of species rich-

ness and evenness due to livestock grazing as well as

acorn and wood harvesting are further discussed.

Keywords Quercus ithaburensis subsp.

macrolepis � Community organization � Monitoring �Diversity ordering � Human activities

Introduction

Numerous threatened woodland ecosystems of Europe

are found in the Mediterranean biodiversity ‘‘hotspot’’

M. S. Vrahnakis

Department of Forestry and Management of Natural

Environment, Technological University of Thessaly,

43100 Karditsa, Greece

G. Fotiadis � A. Pantera (&) � A. Papadopoulos

Department of Forestry and Natural Environment

Management, TEI of Central Greece, 36100 Karpenissi,

Greece

e-mail: panteranatasa@gmail.com

V. P. Papanastasis

Faculty of Forestry and Natural Environment, Aristotle

University, 54124 Thessaloniki, Greece

123

Agroforest Syst

DOI 10.1007/s10457-014-9733-2

Author's personal copy

area (sensu Myers et al. 2000), rich in endemic

elements (Di Castri and Mooney 1973; Quezel 1985;

Greuter 1991, 1994; Thompson 1999; Verdu et al.

2003; Quezel and Medail 2003). Among them, the

silvopastoral woodlands of Quercus ithaburensis

Decaisne generate conservation challenges of first

priority (Quezel 1976; Papanastasis 2002; Pantera

2002; Papadopoulos et al. 2002; Dafis and Kakouros

2006). Q. ithaburensis is a deciduous oak tree species,

endemic of east-Mediterranean zone of Europe. It has

two subspecies: a) Q. ithaburensis (Kotschy) Hedge

and Yaltirik subsp. ithaburensis (tabor oak), found

mostly in Anatolia (Turkey) and the Middle East

(western Asia), and b) Q. ithaburensis subsp. macrol-

epis (Kotschy) Hedge and Yaltirik, hereafter referred

as valonia oak, found mostly in South-East Italy,

Albania, Greece, and west Anatolia (Quezel and

Bonin 1980; Quezel and Barbero 1985; Kaplan and

Gutman 1999). Valonia oak is well adapted to the

xerothermic conditions of the east Mediterranean by

developing open canopies that permit adequate light to

reach the ground floor thus favoring the growth of a

rich flora (Papanastasis 2002). According to a recent

classification of European wood pastures (Bergmeier

et al. 2010), valonia oak woodlands together with the

dehesa-type sclerophyllous woodlands of the west

Mediterranean form the habitat type ‘‘Meridional old-

growth wood-pastures’’, which are bioclimatically

determined by air temperature and the distance from

the coast. However, research on the geographical and

ecological characteristics of valonia oak ecosystems is

relatively limited (Dufour-Dror and Ertas 2004) and

has been carried out mainly in Turkey (Inal 1959) and

Greece (Athanasiadis 1986; Pantera 2001; Papadopo-

ulos et al. 2002, 2003; Pantera et al. 2009).

Past human exploitation has resulted to the degra-

dation of valonia oak woodlands. During the seven-

teenth to nineteenth century, valonia oak woodlands

provided significant products sustaining rural econo-

mies in the east Mediterranean (Karschon 1982;

Giannakopoulou 2002). It is estimated that from the

wider area of Xiromero, western Greece, acorn

production of 385 tons was exported to the markets

of central Europe in nineteenth century (Giannako-

poulou 2002). Its wood was used as firewood and

building material as well as in naval industry. Its

tannins-rich acorns were used in pharmacy, tannery

and dyeing industry and as a feed to animals while its

foliage served as animal fodder during winter. The

understorey layer, rich in grasses and forbs of high

quality and quantity, sustained livestock husbandry for

centuries. All these uses indicate that valonia oak

woodlands are an important silvopastoral system,

equivalent to the dehesas and the montados of the west

Mediterranean (Papanastasis 2002).

Over the years, large areas of valonia oak woodlands

have been gradually transformed to arable lands,

grazing lands or urban areas. Solitary old trees or small

thickets are frequently found inside cultivated areas

indicating that valonia oak woodlands were deforested

in the past and reclaimed for agricultural purposes.

Woodland remnants bear signs of unsustainable use

either from livestock husbandry or over-logging. Today,

remnants of pure valonia oak woodlands consisted of

old trees are mainly restricted to the foothills of

mountainous complexes (Pantera et al. 2009). Their

area is estimated to more than 29,500 ha, mostly

extending along the coastal areas of Greece, in the

Aegean islands, and in the island of Crete (Kriti)

(Pantera 2002; Pantera et al. 2009).

According to Bergmeier et al. (2010), wood pastures

such as the ones of valonia oak are of special importance

at the European level since they constitute transitions

between woodlands and grasslands, with exceptional

structural and compositional characteristics not com-

monly found in either of them. The compositional aspect

of biodiversity and especially of the forest-like floristic

elements is of great importance; its consideration is an

important instrument, especially when maintenance and

protection of threatened ecosystems are the main

priorities (Grill and Cleary 2003; Martınez-Morales

2005; Dıaz et al. 2005; Behera et al. 2005). For the

valonia oak silvopastoral woodlands of Greece in

particular, information about floristic diversity is scarce

and restricted to woodlands of western Greece (Papan-

astasis and Gogos 1983; Pantera 2001). The necessity

and importance of a full registration of vegetation

elements of valonia oak silvopastoral woodlands of

Greece are dictated from the characteristic habitats and

biotopes they form. They are mentioned in the technical

handbook of CORINE land cover system (code: 41.791)

and the annexes of the 92/43/EC Regulations (code:

9350). However, Bergmeier et al. (2010) stressed the

need for re-examining and expanding the protection

measures of initiatives to include these systems together

with their traditional management practices.

According to Platis (2002), for the effective eval-

uation and sustainable management of valonia oak

Agroforest Syst

123

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woodlands and the establishment of reliable monitor-

ing systems, a detailed description of vegetation and

an evaluation of their biodiversity characteristics are

needed. The objectives of this paper were to determine

and compare several floristic diversity measures and

explore the impact of human activities in valonia oak

silvopastoral woodlands.

Study area

In Greece, valonia oak woodlands are mainly found in

the Quercetalia ilicis zone (dominated by evergreen

broadleaved species—maquis or phryganic vegeta-

tion) and partly in the xerothermic limit of the

deciduous broadleaved oak forests zone (Quercetalia

pubescentis) (Dafis 1973; Athanasiadis 1986). Based

on the distribution map produced by Pantera et al.

(2009), twelve well-defined valonia oak woodlands

scattered throughout Greece were selected, namely the

woodlands of Pentalofos (Pent), Alexandroupoli

(Alex), Almyros (Almy), Amfilochia (Amfi), Galaxidi

(Gala), Kea (Kea), Kriti (Krit), Lakonia (Lako),

Lesvos (Lesv), Lilaia (Lila), Strofilia (Stro) and

Thesprotia (Thes) (Fig. 1).

The most common management practice in all

these woodlands is grazing by livestock, mainly sheep

and goats. This activity is applied in a communal way

because woodlands are state-owned areas allowed to

be grazed without specific regulation by local live-

stock owners. As a result, the intensity of grazing is

often unregulated; either too low resulting in the

overgrowth of the understory vegetation or too heavy,

particularly around animal sheds and watering points.

Both practices have a negative impact on tree regen-

eration which appears to be the main problem in all

these woodlands composed of mainly old trees. A

minor practice currently carried out is firewood

collection. However, it has become a major one in

some woodlands over the last few years due to

economic crisis thus threatening their existence due to

Fig. 1 Distribution of well-

defined stands of valonia

oak silvopastoral woodlands

in Greece

Agroforest Syst

123

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Ta

ble

1S

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Agroforest Syst

123

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over-logging and necessitating their conservation. In

the meantime, an initiative to re-establish an ancient

practice, i.e. collecting acorns for tannery, has recently

appeared in valonia oak woodlands grown in some

islands.

Materials and methods

Data collection

For each valonia oak woodland, abiotic data were

collected (Table 1). They included mean altitude

and slope measured in situ by a hypsometer;

geological substrate based on the geological map

produced by the Institute of Geological and Mineral

Research of Greece (Bornovas and Rontogianni

1983); water pH and soil organic matter, two

critical parameters for grazed woodlands (Papana-

stasis 1986; Papaioannou 2004) were also mea-

sured, after randomly taking ten surface soil

samples (0–15 cm deep) in each woodland in the

spring of 2005. Bioclimate was based on the

bioclimatic map of Mavrommatis (1980), and

winter severity, critical for valonia oak distribution

(Pantera et al. 2009), was also measured based on

information derived from the Meteorological Ser-

vice of Greece (1999). Other additional information

included management data for acorn and wood

harvesting, grazing activity in terms of stocking

rate expressed in sheep equivalents (SE) per hectare

(after Pratt and Rasmussen 2001), burning condi-

tion and protection status (Table 1). This later

information was derived from the state services in

charge of land management.

The floristic research was conducted in the wood-

lands in mid-spring to early-summer of 2005 and

2006. Preliminary floristic data were collected in 2005

for each woodland and served to define the 2006

sample size. The formula used was the following

(Southwood and Henderson 2000):

n ¼ s=Ex� �2

where, x: mean number of species found inside a 0.25-

m2 metal square quadrat, placed on relatively homog-

enous sites (in terms of physiognomy of the understory

vegetation), s: standard deviation, and E: the prede-

termined standard error as a decimal of the mean (5 %

was judged adequate).

Given the inherent difficulty in defining the exact

number of individuals per plant taxon found in a

sampling unit (mostly associated to asexual plant

propagation), a modified quadrat was used. The four

sides of the original quadrat (0.5 9 0.5 m2) were sub-

divided so that 25 smaller quadrats of 0.01 m2 each

were produced within it. Subsequently, abundance

data were taken as number of presences (i.e. number of

small quadrats where a species was present). This

method, although it restricts the number of presences

of a taxon to a maximum of 25, is quite attractive as it

minimizes labor cost, and hence the total sampling

cost (Wiegert 1962; Cochran 1977; Krebs 1999).

The upper-story vegetation (standing trees/shrubs)

was recorded to determine its structural characteristics

(Table 1) and included crown aerial interception and

vegetation vertical profile in terms of % canopy

coverage for the three strata: trees, shrubs and herbs, as

well as the mean height of tree layer measured by a

hypsometer.

Data analysis

Soil analyses and plant identification were conducted

in the Soil Analysis and Forest Botany Laboratories of

the Department of Forestry and Management of

Natural Environment, Technological University of

Central Greece, Karpenissi. Soil samples were air

dried prior to analysis. Soil pH was measured electro-

metrically in a 1:1 v/v soil–water suspension (Mc Lean

1982) and soil organic matter by the wet oxidation

method (Nelson and Sommers 1982).

Chorological analysis was performed by means of

the chorological spectrum following Oberdorfer’s

system of geographical partition of Europe into major

floristic units (Oberdorfer 1990) in order to estimate

the effect of Mediterranean climate on the physiog-

nomy of vegetation. The classification of floristic

elements into major life forms was based on Raunki-

aer’s (1910) system as modified by Ellenberg (1956).

Classification was based on Garcke (1972), Pignatti

(1982), Davis (1969), Strid (1986) and Oberdorfer

(1990). Nomenclature of taxa follows Dimopoulos

et al. (2013).

In order to arrange the twelve valonia oak wood-

lands along the structural, abiotic gradients and define

the continuity or not of the vegetation units the

Detrended Correspondence Analysis (DCA) was

applied by using the CANOCO software, ver. 4.5

Agroforest Syst

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(ter Braak and Smilauer 2002). She values of each

structural, abiotic and management factor were

entered the DCA. The percentage values of cover

were square-root transformed prior to their analysis,

while the option of down-weighing rare species, i.e.

for species with very low abundance, was not chosen.

Also, for the qualitative variables, numerical scores

were used. Specifically, for the dominant geological

substrate, a score of 1 was assigned in the case of

presence and 0 for absence; for bioclimate, the scores

were 1 for humid (95 \ Q2 \ 150), 0.5 for sub-humid

(50 \ Q2 \ 95), and 0 for semi-arid (25 \ Q2 \ 50),

while for the winter type the scores were 1 for cool

(0 \ m\3 �C), 0.5 for temperate (3 \ m\7 �C) and 0

for warm (7 \ m \ 10 �C), where Q2: pluviothermic

ratio, and m: mean minimum temperature of the

coldest month (Emberger 1971). Finally, scores

assigned for wood harvesting (1: applied, 0: none),

for acorn harvesting (1: applied, 0: none), for wildfire

events in the last 20 years (1: yes, 0: no), and for

protection status (1: yes, 0: no).

Given the enormous literature on floristic diversity

parameters, problems related to a standard and widely

accepted quantification are often met. The diversity

analyses used in this research combined procedures

developed by Southwood (1978), Routledge (1979)

and Krebs (1999).

At first, fitting of a series of statistical distributions

(species abundance models sensu Magurran (2004)) to

the data was explored. Thus, an insight of the

community organization of valonia oak silvopastoral

woodlands was obtained. The distributions used were

the geometric series (Motomura 1932), log series

(Fisher et al. 1943), log normal (truncated) (Preston

1948; Pielou 1975) and broken-stick (MacArthur

1957).

Secondly, an estimation of species richness was

attempted to obtain an overall view of the potential

species number that valonia oak woodland may

sustain. For this purpose, the sample rarefaction

method was applied (Sanders 1968 corrected by

Hulbert 1971 and Simberloff 1972; Heck et al.

1975). The method estimates how the species number

in a selected sample changes with the number of

individuals. It uses the number of individuals in the

selected sample as a measure of effort. To incorporate

the sampling effort and infer about the ranking of

woodlands according to their species richness, the

rarefaction method was applied in five scales, i.e. for

sampling efforts of 100, 500, 1,000, 2,000, and 3,000

quadrats. Two versions of the rarefaction method were

applied: a finite (sampling performed without replace-

ment) and an infinite (sampling performed with

replacement). Also, the standard error of the estimate

was calculated. The method, estimates the expected

number of species in a random sample of n individuals

(E(Sn)) (Krebs 1999):

EðSnÞ ¼XS

i¼1

1�

N � Ni

n

!

N

n

!

2

66664

3

77775

where S: total number of species found, Ni: number of

individuals per species i, N = R Ni, n = value of

sample size chosen for standardization (n B N),

N

n

!

: N!/n! (N - n)!, i.e. number of combinations

of n individuals that can be chosen from a set of

N individuals.

Finally, a numerical profile of a-diversity was

outlined by calculating the: (a) Q-statistic, to obtain an

arithmetic indication of diversity, (b) Shannon-Wiener

measure of equitability (JH), to express the level of

uniformity (or evenness) of distribution of individuals

per species, and (c) the Berger–Parker dominance

index (d), to obtain a measure of the numerical

importance of the most abundant species. Among

several indices tested, the quantification of diversity

was chosen to be made by the parametric Q-statistic,

since it takes into account the distribution of species

abundances but does not actually entail fitting a model

(Kempton and Taylor 1978). Q-statistic is the measure

of the interquartile slope of the cumulative species

abundance curve and provides an indication of the

diversity of the community with no weighing either

towards very abundant or very rare species (Magurran

2004). It is based on the distribution of species

abundances and is given by the formula:

Q ¼

12

nR1 þPR2�1

R1þ1

nr þ 12

nR2

ln R2

R1

� �

where nr = the total number of species with abun-

dance R, R1 and R2 = 25 and 75 % quantiles, nR1 and

nR2 = the number of species in the class where R1 and

Agroforest Syst

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R2 falls, respectively. The Shannon–Wiener measure

of equitability (JH) is given by the formula

JH ¼ H=log Sð Þ, where H is the Shannon–Wiener

measure of a-diversity and S as above. The Berger–

Parker’s index of dominance is given by the formula

d ¼ Nmax=N, where Nmax is the number of individuals

of the most abundant species, and N as above. For the

a-diversity estimates (i.e. Q-statistic, d, and JH) the

confidence limits were calculated with the use of the

percentile bootstrap technique. The 95 % confidence

intervals were the 2.5 and 97.5 percentiles of the

bootstrap distribution of the estimate (Southwood and

Henderson 2000).

After calculating a-diversity estimates (Q, d, JH), a

statistical pair-wise comparison of the estimates for

each valonia oak woodland was undertaken by using

the randomization test proposed by Solow (1993). The

test re-sampled 10,000 times from a distribution of

species abundances produced by a summation of two

samples. Firstly, the difference (delta, d) between

observed indices of diversity from two samples (i.e.

valonia oak woodlands) was calculated. Then, two t-

tests were performed: (a) a two-sided test, where the

null hypothesis that diversities are equal is tested, by

estimating the number of simulated |d| (after 10,000

randomizations) that are greater than the observed |d|,

and thus calculated the estimated probability that

diversities are equal (values lower than 0.05, i.e. a

proportion of 500 over 10,000 randomizations, indi-

cate that diversities are statistically different), and

(b) a one-sided t test, where the null hypothesis that the

diversity of sample 1 is statistically higher than

diversity of sample 2 is tested, by estimating the

number of simulated d (after 10,000 randomizations)

that are greater than the observed d and thus calculated

the estimated probability that diversity of sample 1 is

greater than sample 2; values lower than 0.05 indicate

that diversity of sample 1 is greater than sample 2,

while values over 0.95, i.e. a proportion of 9,550 over

10,000 randomizations, indicate that sample 2 is more

diverse than sample 1.

Finally, to compare the twelve woodlands in terms

of overall diversity and to define their comparability,

the Renyi’s family equation (Renyi 1961, 1970; Hill

1973) was used. By generating a family of diversity

indices, it is possible to define comparable communi-

ties. This becomes useful when non-parametric indi-

ces of diversity are used for diversity ordering

(Tothmeresz 1995). In a plant community composed

of N species, the pi is the proportional abundance

(often measured as number of individuals) of the i-th

species (i = 1, 2, …, N) such that 0 B pi B 1 andPN

i¼1 pi ¼ 1. Hill (1973), considering that standard

diversity indices measure different aspects of the

partition of abundance between species, proposed a

generalized formulation of diversity by defining a

continuum of possible diversity measures. For a

relative abundance vector P = (p1, p2, …, pM), Renyi

(1970) defined a generalized entropy of order a as

Ha ¼ 11�a

lnPN

i¼1 pai , a C 0. While standard diversity

indices supply point descriptions of community

structure, according to the Renyi’s parametric diver-

sity family there is a continuum of possible diversity

measures that differ in their sensitivity to changes of

the relative abundances of dominant and rare species

as a function of the parameter a (Ricotta 2003).

Accordingly, rather than as a single-point summary

statistics, diversity is seen as a scaling process from

community species richness to its dominance concen-

tration that takes place not in the real but in the

topological data space (Podani 1992). By plotting the

Renyi index to a range of values for generalized

entropy of order a, the diversity ordering diagram is

produced that offers insights for the behaviour of

diversity with increasing levels of entropy. In addition,

the diagram helps to define incompatible communities

in terms of diversity. The biological justification for

using the Renyi’s family equation in studying plant

diversity is found in Ricotta (2003).

Diversity analyses were facilitated by the means of

the software program Species Diversity and Richness,

ver. 4.00, �Pisces Conservation Ltd, 2006, designed

by P.A. Henderson and R.M.H. Seaby.

Results

Ecology: vegetation

Table 1 shows the values of the 18 structural, abiotic

and management factors studied. Tree cover ranged

from 35 % (Gala) to 78 % (Stro), shrub cover from

5 % (Lila) to 75 % (Gala) and herb cover from 24 %

(Lako) to 82 % (Gala). Mean tree height ranged from

5.6 m (Lesv) to 12 m (Thes, Lila, and Stro) and

altitude from 3 m (Stro) to 721 m (Lila) a.s.l. In Almy

and Stro, valonia oak forests are found in plain areas,

Agroforest Syst

123

Author's personal copy

while in the other localities in relatively steep areas

with a maximum slope of 45 % in Lila. Limestone is

the dominant geological substrate, while in the plain

areas of Almy and Stro valonia oak forests are found

on alluvial deposits and in Lesv on volcanic substrate.

Soil pH ranged from 4.4 (Kea) to 7.4 (Amfi) and the

organic matter percentage from 1.0 % (Lako) to 8.9 %

(Almy). Bioclimate ranged from semi-arid (Kea) to

humid (Thes, Pent, Amfi), and winters from warm

(Kriti, Kea) to cool (Alex, Almy). For management

factors, finally, acorn harvesting was practised in four,

wood harvesting in six, wildfire occurred in four and

protection is applied to two out of the twelve

woodlands while the stocking rate ranged from zero

to 6.06 SE/ha.

Understory vegetation differentiates into (a) herba-

ceous and shrubby vegetation in the humid areas

(western Greece), and (b) shrubby and phryganic

vegetation in the semi-arid areas; complex vegetation

understory is found in sub-humid areas. Floristically,

Mediterranean elements dominate over sub-Mediter-

ranean and Eurasiatic ones, supporting the character-

ization of valonia oak as a typical Mediterranean

woodland (Fig. 2). Therophytes dominate uniformly

over the other life forms, with a mean presence of

42.49 % for all woodlands, followed by hemicrypto-

phytes (29.56 %) and phanerophytes (13.44 %).

Commonness: consistency

A total of 302 plant taxa were identified. The most

common were Galium aparine (present in 11 wood-

lands), Asphodelus ramosus subsp. ramosus, Sherar-

dia arvensis and Bromus sterilis (in 10 woodlands),

Asparagus acutifolius and Cynosurus echinatus (in 9

woodlands), Geranium purpureum (in 8 woodlands),

Phlomis fruticosa, Torilis arvensis, Ranunculus nea-

politanus and Dactylis glomerata (in 7 woodlands).

DCA revealed a geographical consistency of the

vegetation in terms of species abundances at least for

the adjacent woodlands of Almy, Thes, Amfi, Pent,

and Lako (Figs. 3, 4). For the two axes, the cumulative

percentage variance of species x environment and

management relations equals to 36.4 %. This pattern

is interrupted for those woodlands found either on

islands (Lesv, Kea, Krit) or remote areas (Alex). The

presence of species with defensive mechanisms and

thus of low selectivity was high and typical in the

understorey vegetation. Such species with long awns

and thistles were Bromus sterilis in 10 woodlands,

Cynosurus echinatus and Asparagus acutifolius in 9

woodlands, and Acanthus spinosus and Euphorbia

acanthothamnos in 7 woodlands. Additionally, some

species of low palatability were Galium aparine in 11

woodlands, Asphodelus ramosus subsp. ramosus in 10

woodlands, Geranium purpureum in 8 woodlands, and

Phlomis fruticosa, E. dendroides and Torilis arvensis

in 7 woodlands.

The ordination of species abundance data along

with the abiotic variables revealed a clear discrimina-

tion of species abundance of Alex due to shrub cover

and cool winter (Fig. 3). Alluvial deposits seem to

affect species abundance of Stro, and volcanic

substrate discriminated species abundance of Lesv.

For Gala, tree height affected species abundance.

When ordination of species abundance along man-

agement gradient was attempted, it revealed that Stro

was highly affected by protection status while wood

harvesting and fires mostly affected the species

abundance of valonia oak woodlands in Alex

(Fig. 4). Grazing seems to have affected species

abundance of Krit, Pent, Lako, while Kea was highly

affected by acorn harvesting.

Species abundance models

Generally, in most cases the truncated log-normal

model adequately fits the species abundance

(Table 2). This is the case for eleven out of the twelve

woodlands, while by using a more relaxed statistical

criterion (i.e. lower level of significance), other

models may fit too (data not shown). For example, in

the case of Stro all four examined models may fit (for

geometric: v(0.05, 5)2 = 54.73 with P = 0.060, for log

series: v(0.05, 5)2 = 9.10, P = 0.105, for truncated log-

normal: v(0.05, 5)2 = 1.28, P = 0.937, and for broken

stick: v(0.05, 5)2 = 7.38, P = 0.194).

Species richness

The poorest woodland in terms of species richness was

Lila (21 plant species encountered), and the woodland

of Pent was the richest (115 plant species). The other

woodlands were found between these two extremes;

the group of Almy (30 species), Amfi (31), Kea (36),

Gala (39), Stro (40), and Alex (62), which was close to

Lila extreme, and the group of Krit (68), Thes (77),

Lako (80), and Lesv (84), which was close to Pent

Agroforest Syst

123

Author's personal copy

Fig. 2 Chorological

spectrum of the floristic

elements of the twelve

valonia oak silvopastoral

woodlands (where Med:

Mediterranean, Smed: Sub-

Mediterranean, Euras:

Eurasiatic, Omed/Osmed:

East Mediterranean/East

Sub-Mediterranean. Rest

includes North, Greek

endemics, Cosmopolitan,

Continental, Balkan

endemics, Alpine, Sub-

Cosmopolitan, Cultivated,

Greek Subendemic, and

Subatlantic/West

Mediterranean)

Agroforest Syst

123

Author's personal copy

extreme. The pattern was not changing by increasing

sampling effort. For an effort of 3,000 quadrats, the

sorting of woodlands in ascending order was Lila

(21.00 for finite estimations), Almy (31.00), Amfi

(31.00), Gala (39.00), Stro (41.00), Alex (62.00), Krit

(67.32), Thes (75.97), Lako (78.90), Lesv (82.88), and

Pent (111.63) (Fig. 5). The same general pattern was

apparent when infinite rarefaction was applied.

Species diversity

Q statistic showed that the silvopastoral woodlands of

Pent were far more diverse than the other silvopastoral

woodlands (Tables 3, 4). By ranking the twelve

silvopastoral woodlands according to their Q values

it was found that the woodland of Pent (QPent = 31.78)

was in the first position and statistically higher than

those of Lesv (QLesv = 20.44, P = 0.0010**), Lako

(QLako = 19.13, P = 0.0002***), Thes (QThes =

17.83, P \ 0.0001***), Krit (QKrit = 16.76, P \0.0001***), and Alex (QAlex = 16.13, P \0.0001***) who formed the second group in order.

The silvopastoral woodlands of Lila (QLila = 7.07) and

Almy (QAlmy = 6.43) attained the significantly lowest

Q values between the twelve silvopastoral woodlands.

Regarding the Berger-Parker’s values of domi-

nance, the silvopastoral woodlands of Kea

(dKea = 0.333), and Almy (dAlmy = 0.312) had the

significantly highest values among the twelve wood-

lands, not significantly different between each other

(P = 0.2914 NS) (Tables 3, 4). For both woodlands,

apart from the dominance of valonia oak (373 records

out of a total of 1,143 for Kea, and 287 out of 919 for

Almy), there were other species with high levels of

dominance, like Sarcopoterium spinosum (62) for Kea

and Asphodelus ramosus subsp. ramosus (120) and

Galium aparine (73) for Almy. The woodland of Pent

retained high values of dominance as the value of

Berger-Parker’s index of dominance (dPent = 0.301)

was not statistically different from that of Almy

(P = 0.4784 NS) but significantly lower than Kea

(P = 0.0306*). Apart from the presence of valonia

oak in Pent (1,374 records out of a total 4,569), other

dominant species were Asphodelus ramosus subsp.

ramosus (297) and Phlomis fruticosa (286).

Consistency seems to exist with respect to the

dominance index of Berger-Parker (d) and the index of

equitability of Shannon–Wiener (JH) as both indexes

Fig. 3 Diagram of all species abundance data along the first

two DCA axes with explanatory variables passively projected

onto the ordination space. The explanatory variables concern the

sum per valonia oak woodland of the relative abundances of the

species, the environmental variables Alt (altitude), Incl (incli-

nation), OM (organic matter), pH, Biocl (bioclimatic type),

geological substrate (Lim: limestone, Volc: volcanic, Dep:

deposits) and physiognomy of vegetation variables Tree (cover

of trees), Shrubs (cover of shrubs), Herb (cover of herbs), and

Height (height of trees) as well

Fig. 4 Diagram of all species abundance data along the first

two DCA axes with explanatory variables passively projected

onto the ordination space. The explanatory variables concern the

sum per valonia oak woodland of the relative abundances of the

species, as well as the management variables Fores (Wood

production), Fir (Fire), Prot (Protection), Acor (Acorn

production)

Agroforest Syst

123

Author's personal copy

were inversely related (Table 3). Indeed woodlands

with high values of JH were associated with low

dominance (d). This implies that woodlands with the

individual plants of each species evenly distributed

into species showed low levels of dominance. For

example, the woodland of Gala was found in the last

position in terms of the dominance index of Berger-

Parker (or in the first when the inverse term 1/d is

considered) with dGala = 0.120, and in the first

position when the index of equitability of Shannon-

Wiener (JHGala = 0.864) was considered. Con-

versely, the woodland of Kea showed relatively

high levels of dominance (dKea = 0.333), sorting

this woodland in the first position in terms of

dominance, and low levels of equitability

(JHKea = 0.737), sorting this woodland in the tenth

position in terms of equitability. Woodlands of Gala

and Lila (JHLila = 0.859) formed a statistical supe-

rior group in terms of equitability, not statistically

different between each other (data not shown), while

the woodland of Pent was found in the last position

in terms of equitability (JHPent = 0.713).

The Renyi’s diversity ordering diagram showed

that generally the low level of entropy inconsistency is

the rule. Indeed, many intersections existed when

scale parameter varied between 0 and 2 (Fig. 6). After

the value of 2, the number of intersections is getting

lower and diversity profiles are more evenly

distributed.

Discussion

From all tested abundance models, i.e. geometric

series, log series, log normal (truncated) and broken-

stick, it was found that the statistical model of log

normal exhibited a better fit to the abundance data for

almost all valonia oak woodlands, with respect to the

niche-based models of geometric series and broken

stick. The geometric series model describes commu-

nities where few species are dominant and situations

with maximal niche preemption (Ferreira and Petrere

2008), while the broken stick emphasizes species

richness and implies that an ecological factor is evenly

shared between species (Higgins and Strauss 2008).

The statistical log series model seems to be the case

when a community is organized on a small number of

abundant species and large species rarity, and better

reflects temporally organized community patterns

(e.g. Kaltsas et al. 2012). The log normal community

assembly supports the assumption for sequential

breaking of empty niche space in community forma-

tion, proposed by Sugihara (1980). Accordingly, each

species entering the community uses niche space

successively and proportionally to its abundance,

while the size of niche space does not affect its

probability to be subdivided. Also, the community

formation is heavily based on an ecological or

evolutionary process (Sugihara 1980) (e.g. succession

in our case). Although the lognormal distribution is

Table 2 Model statistics and Chi square test of significance (v(0.0052

,df)) for geometric, log series, truncated log normal, and broken

stick models fitted to species abundance data obtained from the twelve valonia oak silvopastoral woodlands

Geometric Log series Trunc log normal Broken stick

Alex (df = 6) nf v2 = 4.47, P = 0.484 v2 = 3.29, P = 0.655 nf

Almy (df = 6) nf nf nf nf

Amfi (df = 5) nf nf v2 = 7.08, P = 0.214 nf

Gala (df = 5) v2 = 33.67, P = 0.670 nf v2 = 2.42, P = 0.788 v2 = 7.25, P = 0.203

Kea (df = 5) nf v2 = 11.04, P = 0.087 v2 = 3.29, P = 0.772 v2 = 7.43, P = 0.191

Krit (df = 8) nf v2 = 11.15, P = 0.132 v2 = 2.54, P = 0.924 nf

Lako (df = 8) nf nf v2 = 5.12, P = 0.645 nf

Lesv (df = 8) nf nf v2 = 7.23, P = 0.406 nf

Lila (df = 4) v2 = 27.25, P = 0.128 v2 = 2.79, P = 0.248 v2 = 2.38, P = 0.666 v2 = 2.39, P = 0.495

Pent (df = 7) nf nf v2 = 3.58, P = 0.827 nf

Stro (df = 5) v2 = 54.73, P = 0.060 v2 = 9.10, P = 0.105 v2 = 1.28, P = 0.937 v2 = 7.38, P = 0.194

Thes (df = 8) nf nf v2 = 7.63, P = 0.367 nf

nf non fitted

Agroforest Syst

123

Author's personal copy

often associated with large, undisturbed communities

(so called default distribution), Matossian et al. (2012)

argues that this is rather attributed to the mathematical

properties when large data set are used. They found

that such distribution fits the plant species abundance

data, after 10 years from a severe disturbance (wild

fire) in a Mediterranean forest community of low

elevation zone. Our study, although shorter, seems to

support this idea, since valonia oak woodlands are

found in a successional stage after long lasting human

caused influences.

By statistically comparing the diversity measures of

Q-statistic, Berger-Parker dominance index and Shan-

non–Wiener measure of equitability, calculated for

each woodland, it is evident that there is not a clear and

consistent ranking of the woodlands. This is often the

case when an ordering of diversity is asked; given the

availability of large number of indices and the

emphasis they placed either on species richness or

species abundance and evenness. Also, the response of

each index to impacts of ecological or other factors is

different. According to Kindt et al. (2006), studies

merely based on a single index of diversity to rank

communities obtain erroneous results. In this respect,

the diversity ordering diagrams of Renyi’s shed more

light (Tothmeresz 1995). Nevertheless, the inspection

of temporal and spatial changes of the indices may

serve as basis to depict the impact of management

actions in monitoring programmes.

When inspecting the whole range of the scale

parameter, that reflects a gradient of the system

entropy in the diversity ordering profiles of the valonia

oak woodlands, no clear pattern is obtained, since

several intersections of diversity lines are apparent.

For entropy values over 2, a more clear order of the

diversity lines was established. Such complex

responses of diversity lines may be attributed to the

ecological (abiotic conditions) and management fac-

tors that either lead to communities of high evenness

(e.g. Galaxidi, Lilaia in our case) or to communities

with high species richness (e.g. Pentalofos, Lakonia),

or both (e.g. Alexandroupoli, Lesvos Island).

The results show that plant diversity of valonia oak

silvopastoral woodlands is determined mostly by

management factors, while abiotic conditions play a

supporting role only in some cases. This is not

surprising since management history is a regulating

factor of diversity in such ecosystems (Alados et al.

2004; Caballero et al. 2009). Three groups of valonia

oak silvopastoral woodlands in respect to their species

richness and/or evenness may be distinguished. The

first group includes the woodlands of Pentalofos,

Lesvos, Lakonia and Thesprotia and it is characterized

by high species richness. Although these woodlands

have a relatively high canopy tree cover, the applied

stocking density deemed as moderate (Kyriazopoulos

et al. 2009) seems to be a controlling factor for

retaining high species richness, since it constrains

shrub encroachment. Generally, in Mediterranean

landscapes shrub encroachment is negatively associ-

ated with plant species richness. It is well documented

that as shrub assemblages become thicker total species

richness declines (Merou and Vrahnakis 1999; Alados

et al. 2004; Vrahnakis et al. 2005; Papadimitriou et al.

Fig. 5 Changes of estimated species richness per sampling efforts of 100, 500, 1000, 2000 and 3000 quadrats, after individual-based

finite rarefaction (vertical bars represent standard errors)

Agroforest Syst

123

Author's personal copy

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123

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2004) and biodiversity is favoured by adjusting shrub

cover to 15-50 % (Papachristou 1997; Papanastasis

1999; Pearson et al. 2006; Vrahnakis 2008). Equita-

bility seems to be regulated by the long cessation

time of acorn harvesting; long periods of cessation

lead to high levels of equitability (like in Lesvos) and

low periods lead to low equitability levels (like in

Pentalofos). Besides livestock grazing, acorn har-

vesting seems to contribute to the high species

richness as in Pentalofos. For the valonia oak

woodland of Thesprotia, wood harvesting and wild-

fires had the most important role in the increased

species richness. Generally it has been shown that

disturbances due to management activities result in

the creation of open spaces which elevate biodiver-

sity in the ecosystems (Sirami et al. 2010; Perez

Campana and Valenzuela Montesa 2014). The fact

that the high biodiversity is related to the volcanic

substrate in the Lesvos island has been already

underpinned by other authors too (Arianoutsou-

Faraggitaki 1985; Margari et al. 2009).

The second group includes the silvopastoral wood-

lands of Kriti, Alexandroupoli, Strofylia and Galaxidi,

characterized by medium levels of species richness,

which are also determined by management factors. As

far as livestock grazing is concerned, the stocking

rates applied were either light in the latter three or

heavy in the case of island of Kriti. It has been shown

that if livestock grazing is ceased a rapid change in

species composition takes place, followed by stabil-

ization (e.g. Marriott et al. 2009). This stabilization is

reflected by a rather uniform distribution of individual

plants into species (evenness). However, in the case of

Kriti Island, overgrazing resulted in low plant species

evenness and high dominance values. They included

nitrophilous species, like Oxalis pes-caprae, Galium

aparine and Asphodelus ramosus subsp. ramosus.

The last group consists of the silvopastoral wood-

lands of Kea Island, Amfilohia, Lilaia and Almyros

that are characterized by low species richness and low

or medium evenness. These results should be attrib-

uted not only to the relatively high stocking rates

combined with acorn or wood harvesting in the three

former woodlands, but also to the protection from all

these activities in the latter site suggesting that

complete banning of human activities in these eco-

systems does not favour floristic diversity.

Biological diversity is an important property of an

ecosystem determining its overall function (Loreau

et al. 2002). This property is often realised by its

patterns in space and time (Rosenzweig 2005; Dengler

2005). Thus, the determination of patterns of diversity

and its components is an important instrument,

especially when conservation of threatened ecosys-

tems and landscapes are the main priorities (Grill and

Cleary 2003; Martınez-Morales 2005; Dıaz et al.

2005; Behera et al. 2005; Bergmeier et al. 2010). The

exploration of diversity patterns of the valonia oak

silvopastoral woodlands of Greece showed that special

attention must be drawn when conservation measures

are to be designed and implemented. Specific studies

must be carried out in the near future concerning the

restoration of the traditional human activities in the

valonia oak silvopastoral woodlands so that their

overall diversity in terms of species richness and

evenness is increased.

Acknowledgments This research was conducted in the

framework of the research project ‘‘Ecology of Valonia Oak

Forests in Greece’’ (2005–2007), under the ‘‘EPEAEK,

ARCHIMEDES II programme’’ and was co-funded by the

European Social Fund (75 %) and the Greek Government

(25 %).

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