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Identifying biodiversity indicators in a forest ecosystem.
Vassiliki I. Kati1 and. Haritakis I. Papaioannou2.
Sustainable forest management would be much easier if we could implement conservation actions
targeting only one biological group with the certainty that other biological groups would be sufficiently
protected as well. We attempt to identify such surrogate groups for biodiversity conservation. The
indicator value of six taxonomic groups is tested. These are vegetation, orchids, Orthoptera, aquatic
herpetofauna, terrestrial herpetofauna and small terrestrial birds. Standard quadrats are used for
vegetation sampling, time constraint visits are conducted for orchids and aquatic herpetofauna
sampling, random transects of fixed length are conducted for Orthoptera and terrestrial herpetofauna
sampling and finally acoustic point counts of unlimited distance are carried out for bird sampling. In
total, 36 sites of 20ha maximum surface each one, are sampled in the forest of Dadia reserve (N.E.
Greece), representing 18 Corine habitat types. For every targeted group we select the ideal set of sites
optimizing its conservation (100% of species conserved, using a complementary algorithm. We
calculate afterwards the average comparative species loss of the remaining non-targeted groups that is
maintained inside the network of the indicator group, as well as the average species loss of overall
biodiversity. Results reveal that in general a complementary network designed in favor of one targeted
group does not guarantee the conservation of other groups as well. Among the studied groups, the
optimal vegetation network is a very good surrogate for the conservation of aquatic herpetofauna (0%
species loss) and of birds (4% species loss). It is also proved to be the best biodiversity shortcut (17%
species loss). In conclusion, the maintenance and enhancement of vegetation diversity in the forest
ecosystem of Dadia reserve proves to be beneficiary for the conservation of aquatic herpetofauna, birds
and overall biodiversity.
Biodiversity, conservation, indicator, complementarity, networks
I. INTRODUCTION
Conservation decision would be much easier if we could implement conservation actions targeting only
one biological group with the certainty that other biological groups would be sufficiently protected as
well. Most of conservation studies assume but do not prove such indicator relationships and propose
conservation measures on the basis of this assumption. However, the indicator value of species or
taxonomic groups is a great question in conservation biology and requires rigorous testing (Reyers and
van Jaarsveld 2000).
The current study explores the indicator value of six different taxonomic groups, as potential surrogates
for the conservation of other groups and the whole of biodiversity, taking as a case study a forest
ecosystem: Dadia reserve in Greece. By definition, the ideal reserve system for the conservation of one
taxonomic group is a set of sites selected in a complementary way (Howard et al. 1998; Williams et al.
1996; Lombard 1995; Price 1995; Saetersdal 1993). On this basis, we form the ideal reserve network
for the conservation of one targeted taxonomic group and we calculate the average percentage of
species loss of the other no-targeted groups inside it, in order to test its indicator value for the no-
targeted groups.
II. METHODS
Study area
The study area is situated in northeastern Greece, in the region of Thrace, at longitude between 26° 00'
and 26°19' and at latitude between 40°59' and 41°15'. The whole study area covers 43,000ha, of which
42,450ha belong to the forest reserve of "Dadia-Lefkimmi-Soufli complex", as it is officially cited. The
reserve was created in 1980, due to its high ornithological value for birds of prey; hosting one of the
two European populations of black vulture (Aegipius monachus). It is forest-dominated area (70% of
the reserve), belonging mainly to the Quercion frainetto alliance and to the Fagion moesiaca alliance.
The main vegetation type is Aegean pine woods (Pinus brutia).
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Sampling sites
Thirty-six sites, having from 2 to 20ha surface, are sampled. They represent 18 different habitat types
or combinations of habitat types, according to the typology of CORINE database (Devillers et al. 1996)
(Table 1).
TABLE 1: Main vegetation types, number of Corine habitats and number of sites sampled.
Vegetation type N. of Corine habitats
N. of sites
Forests 8 18
Scrubs 3 4
Heaths 1 2
Grasslands 3 5
Agricultural land 2 4
Mosaics 1 3
Total 18 36
Indicator selection
The concept of biodiversity is represented by a complementary set of six different indicator groups
(Pearson 1995; Noss 1990), having different ecological and spatial needs: vegetation (tree and bush
species), Orthoptera, orchids, aquatic herpetofauna (amphibians and terrapins), terrestrial herpetofauna
(lizards and tortoises) and small terrestrial birds.
Sampling methods
Sampling methods are summarized in table 2. Vegetation was qualitatively sampled with the help of
three standard quadrats of [25m*25m], randomly located in each site (Kent and Coker 1994). Orchids
were recorded in a qualitative way, using visits of fixed time duration. Sampling repeated twice during
springtime for two successive years (1998-99). Species were identified in situ (Delforge 1994). Semi-
quantitative data were collected during Orthoptera sampling, counting individuals during transects of
30m and 90m for open sites (shadow less than 60%) and closed (shadow more than 60%) sites
respectively. Each site was sampled by two transects. Sampling repeated three times: late spring,
summer, autumn. Species were identified stereoscopically (Willemse 1985). Time constraint visits were
conducted for collecting presence-absence data for aquatic herpetofauna (Crump and Scott 1994).
Sampling was carried out once during early spring at dusk for acoustic identification of species
choruses, and three more times during early spring, spring and summer for visual identification of
adults, larvae and egg masses. We used random transects of 300m fixed length, counting individuals of
terrestrial herpetofauna (Krebs 1989). Sampling repeated during early spring, late spring and summer.
Small terrestrial birds were identified acoustically, using the point count method of unlimited distance
(I.P.A) (Blondel et al. 1970). Up to five sampling stations were carried out in each site. Sampling
repeated twice during early spring and late spring.
TABLE 2: Sampling methods and sampling organization of the six taxonomic groups studied.
GROUP Type of data
Sampling
method
Sampling
surface
Number
Repetition Total
VEGETATION Qualitative Quadrats 25m*25m 108 1 108
ORCHIDS Qualitative
Time constraint
visits
- 36 4 144
ORTHOPTERA Semi-
quantitative
Transects 30m (open habitats)
90m (closed habitats)
72 3 216
AQUATIC
HERPETOFAUNA
Qualitative
Time constraint
visits
- 1 4 144
TERRESTRIAL
HERPETOFAUNA
Semi-
quantitative
Transects 300m 40 3 120
BIRDS Semi-
quantitative
I.P.A.
(point counts of
10min)
Unlimited distance 155 2 310
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Indicator value
We considered each time one of the six groups as an indicator and the total of the rest five groups as
parameter BD5, representing the idea of biodiversity. For every indicator group we selected an optimal
reserve network, where all species were maintained within the minimum land surface. To do so, we ran
an optimal random selection algorithm (Kati 2001) in S.A.S. system (1985), which carried out 20,000
permutations for a given number of sites λ and produced 20,000 random combinations of λ sites. The
algorithm calculated the number of species that was included inside every site combination and
pinpointed the combination including the maximum number of species. This one was the optimal
solution of the λ most complementary sites.
We tested the indicator value of each targeted group by assessing the comparative species loss of each
one of the no-targeted groups and of BD5, inside the optimal network of the indicator group. In
practice, we extracted the percentage of species of every non-targeted group from the percentage of
species of the indicator group, which were maintained inside the optimal network of the targeted group,
at every step of the λ sites included in the reserve network. We calculated afterwards the average of the
λ differences produced. Ideally, when the network targeting the indicator group is equally beneficiary
for the non-targeted groups, the difference would be zero. The smaller is the difference, the more the
indicator value of the targeted group increases.
III. RESULTS
Sampling resulted in the record of 55 species of trees and bushes, 25 orchid species (Kati et al. 2000),
39 Orthoptera species (Kati and Willemse in press), 10 species of aquatic herpetofauna, 10 species of
terrestrial herpetofauna and 72 species of small terrestrial birds (Kati 2001).
A two-way table (table 3) quantifies the comparative species loss of the non-targeted groups when we
take action for the benefit of the indicator group. We used the average of the λ values of comparative
species loss as a scale-independent parameter to assess the indicator status of each group. Cell values
are the averages of all λ substractions. Small cell value means great indicator value.
TABLE 3: Comparative species loss (average % of λ sites) of the non-targeted groups inside the
complementary network of the indicator group and mean species loss of BD5.
Targeted
group
λ
sites
loss
BD5
Species loss of the non-targeted groups
Vegetation
Orchids
Orthoptera
Aquatic
herpeto
fauna
Terrestrial
herpetofauna
Birds
Vegetation 9 17% 0% 45% 18% -4% 25% 4%
Orchids 4 41% 58% 0% 31% 55% 23% 41%
Orthoptera 6 38% 54% 30% 0% 56% 19% 31%
Aq. herpetofauna 4 37% 24% 67% 40% 0% 38% 19%
Ter. herpetofauna
2 60% 65% 69% 50% 80% 0% 40%
Birds 8 32% 21% 67% 21% 16% 34% 0%
According to the results of table 3, we conclude that in Dadia forest reserve:
a) the optimal vegetation network succeeds to conserve more of overall biodiversity (BD5)
b) the optimal vegetation network favors more aquatic herpetofauna and birds
c) the optimal orchid network favors more terrestrial herpetofauna
d) the optimal Orthoptera network favors more terrestrial herpetofauna and orchids
e) the optimal aquatic herpetofauna network favors more birds and vegetation
f) the optimal terrestrial herpetofauna network doesn't favor the other groups sufficiently
g) the optimal bird network favors more aquatic herpetofauna.
IV. DISCUSSION
Indicators for other taxa
In general, the complementary network designed in favor of one group does not guarantee the
conservation of other groups as well.
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From the above relationships, only the complementary vegetation network is a very good surrogate for
the conservation of birds and aquatic herpetofauna in the study area. Each step of conservation action
for the benefit of vegetation is also for the benefit of the aquatic herpetofauna and for birds, as the
comparative percentage of species loss is very small (<5%).
One possible explanation for the positive vegetation - amphibian relationship is humidity. In our study
area, the aridity is a stress factor for the aquatic life. Besides, the humidity probably favors the
vegetation development, under the arid climatic context of the study area. As a result, it happens that
the set of sites with water points is rich in both vegetation and aquatic species on the whole.
As far as the good surrogate relationship of vegetation for small terrestrial birds is concerned, many
bird studies support the positive correlation between bird diversity and tree diversity (Peck 1989)
between bird diversity and the structural complexity of the vegetation (Farina 1981; Prodon and
Lebreton 1981; Blondel et al. 1973).
Indicators for biodiversity
According to our results, it doesn’t seem to exist a general congruence between the complementary
network of one indicator group and of biodiversity. Conservation decision should then target many
different taxonomic groups without the illusion that “what is good for one targeted taxon is good for
everything”.
From all the studied groups, the optimal vegetation network seems to result in the least biodiversity
loss (17%). One could argue that this is the result of scale effect, because we include 9 sites in
vegetation network and fewer sites in other networks. However, we compared the average percentages;
these normalized value are scale-independent. Although the optimal vegetation network seems to
conserve more of biodiversity in comparison with the other groups, we draw the attention to the very
weak surrogate character of the vegetation network for orchid conservation.
Plant communities have a keystone role in the ecosystem as they provide habitat for dependent fauna
(Ferris and Humphrey 1999; Simberloff, 1998). Our results reveal that forest management should focus
on the increase of vegetation diversity, through the maintenance of forest openings and the
enhancement of structural vegetation complexity. The high vegetation diversity reflects high landscape
heterogeneity and favors biodiversity conservation.
Finally, we should emphasize that our conclusions refer only to the habitats of our study area and to the
frame of the current sampling; therefore we cannot extrapolate them to other ecosystems as well. We
need to prove the surrogate relationship many times, in different scales and in different ecosystems in
order to use it with certainty in conservation biology.
V. CONCLUSIONS
Our results can be summarized in the following points:
The indicator relationship of taxonomic group as a surrogate for the conservation of other
taxonomic groups and of biological diversity overall, should always be tested, because we
found in general low efficiency of the complementary network of one taxonomic group to
conserve species of another taxonomic group and to conserve overall species richness.
The complementary network of vegetation species is a good surrogate for the conservation of
bird and aquatic herpetofauna species.
Forest management should be orientated towards the enhancement of vegetation diversity,
because it is the best biodiversity shortcut in comparison with the other groups studied.
ACKNOWLEDGEMENTS
We are grateful to the Institute Bodossaki and to the Institute Alexandros Onassis, which funded the
current research, under a frame of a Ph.D. scholarship for biodiversity issues.
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