LATVIJAS UNIVERSITĀTE
Digna Pilāte
SAUSZEMES GLIEMEŽU SUGU DAUDZVEIDĪBA MEŽĀ UN TO
IETEKMĒJOŠIE FAKTORI LATVIJĀ
DIVERSITY AND DETERMINING FACTORS OF
TERRESTRIAL SNAILS IN FORESTS IN LATVIA
Promocijas darba kopsavilkums
Bioloģijas nozare
Zooloģijas apakšnozare
Summary of the thesis for doctoral degree in Biology
(speciality - Zoology)
Rīga, 2007
IMPORTANCE OF THE THEME
Snails are ones of the most frequently occurring organisms in terrestrial
ecosystems. Despite of that the study of diversity of snail species and factors
affecting it in forests and in other terrestrial ecosystems has not been
performed in Latvia till now. Snails play an important role in the turnover of
organic substances, and they are a natural source of calcium for many
animals. Some snail species occur only in forests and they have adapted to
certain ecological niches. Their distribution is slow, therefore they are
sensitive to human-induced changes in environment. Due to their sedentary
life-style and limited distribution capacity snails are prospective
bioindicators.
The actual diversity of snails in the forest was not known until this
research. The state policy on nature protection and forest management
harmonised in line with the principles of biodiversity preservation set in
Europe called for the need to begin this study. Information about the
occurrence of many snail species, including rare and endangered species and
their distribution was outdated and there was no data at all about the
situation of snail populations in Latvia. As a result of this research for the
first time the information was acquired on populations of many rare and
endangered species in forest habitats.
Over the last years forest utilisation has become more intensive also in
Latvia, thus the survival of rare and endangered snail species outside the
boundaries of the protected nature territories and preservation of species
diversity in commercially managed forests become topical issues. Until this
research it was not known how forest management affects snail diversity in
Latvia. Only survey results produced in other countries could be used to
assess these effects. Also the development of bioindicator system for natural
forest habitats has become a topical issue.
GOAL AND TASKS OF THE RESEARCH
The main goal of the study was to estimate the diversity of terrestrial
snail species in forest habitats and to define the factors influencing it in
Latvia, including the populations of endangered and protected species. The
tasks were such:
• to study the snail fauna and diversity of species in forest habitats;
• to analyse the structure of snail communities in forest habitats;
• to determine the most essential factors influencing the species
composition of snail communities and species diversity;
• to assess the forest management impact and the importance of forest
biodiversity structures;
• to identify snail species that are forest habitats and natural forest
indicators in Latvia;
• to establish the occurrence of protected and endangered species and
vitality of populations in the surveyed areas.
SUMMARY OF SCIENTIFIC CONCLUSIONS
This is the first study on the diversity of snail species and the factors
influencing it in forest habitats in Latvia. Until the beginning of the research,
more than 50-year-old data and the results of the studies performed in other
countries were used to describe the snail fauna, populations of species and
ecology. Yet the results of the studies performed in other countries cannot be
automatically applied to Latvia due to different climatic conditions, forest
growing conditions and forest management, what was proved by this
research. The geographic distribution and occurrence of species also differ in
the territory of Latvia.
For the first time in Latvia the snail fauna was surveyed in such forest
habitats as pine forests, spruce forests and black alder forests. Further on
analysing the snail fauna in coniferous forests, the pine forests and the
spruce forests are viewed separately. The surveys in black alder forests
revealed that these forests are abundant in the snail fauna. For the first time in
Latvia the study focused on diversity of snail species, snail communities and
their composition, and species occurrence in forest habitats. These results
were used in 1998 developing the inventory methodology of natural forest
habitats for the Latvian State Forest Service and Regional Forestry Board of
Östra Götaland as well as training forest ecologists from 1997 to 1999.
The research revealed the most important factors affecting the structure
of snail communities and diversity of species. For the first time over the last
100-120 years the impact of forest management on the diversity of snail
species was assessed and the importance of forest biodiversity structures was
evaluated. On the basis of this research the first list of indicatorspecies of
natural forest habitats was compiled. In this research for the first time in
Latvia the analysis of forest habitat indicatorspecies and natural forest
indicatorspecies was performed.
The condition of populations of endangered and protected species was
ascertained in the surveyed areas. For the first time in Latvia the place of
these species within the snail communities and their occurrence in various
forest habitats were determined, the impact of forest management on the
populations was also assessed. These results were used in the Natura 2000
database, in the database of the Latvian Environment Agency and in the
development of nature protection plans for some specially protected nature
territories in Latvia.
During the survey two species - Vertigo genesii (Gredler, 1856) and V.
moulinsiana Dupuy, 1849 were found for the first time in Latvia. They are
included in Annex II of the EU Species and Habitat Directive listing the
species for the conservation of which a protected territory should be set up.
CONTENTS OF THE PAPER
Material and methodology
1. Description of Research Sites
The fieldwork was performed from 1995 to 1997 in the period from
May till September in the territories of Slītere, Aizkraukle, Līvbērze and
Mežole forest districts. These territories differ by their geographical location,
relief, climate, prevailing vegetation and history of the performed forest
management activities. These territories include representative areas of
natural forests.
The studies were carried out in all classes of natural forests occurring in
Latvia: dry and swampy boreal coniferous forests (Cl. Vaccinio-Piceeted), dry
and swampy European broad-leaved forests (Cl. Querco-Fageted) and
Eurosiberian alder swamps (Cl. Alnetea glutinosae), in five forest habitats spruce forests, pine forests, broad-leaved forests, black alder swamps and
deciduous forests of pioneer tree species.
Altogether 42 sampling plots were selected. In each forest district
several similar forest habitats were surveyed in order to compare the
acquired results among forest plots with a differing background of forest
management activities and with a different number of forest biodiversity
structures (hereafter - BDS). Considering ecological requirements of forest
snails to their habitat (vegetation, shading, humidity, deadwood), 54 forest
BDS were selected as the most important ones. The inventory of the BDS
accountable for the snail diversity was performed in 1995 marking the
existing BDS in the particular sampling plot.
The impact of forest management over the last 100-120 years was
assessed using the forest survey results of Slītere forestry (1985), Līvbērze
forestry (1989), Aizkraukle forestry (1992), Mežole forestry (1995) and
materials from the State Archives of Latvia - maps and reports (Suško 1998).
The impact of forest management was evaluated applying a 5-point system: 1 no impact; 2 - low impact (felling of separate trees or reasonable draining);
3 - medium impact (a single clear cut); 4 - strong impact (two clear cuts); 5 very strong impact (numerous clear cuts, establishment of plantation forests,
draining).
2. Collection and Processing of Samples, Identification of Species
Snails were studied applying three methods - the so-called volumesampling method, the so-called area-sampling method and gathering them
by hand (Balogh 1958, Valovirta 1996, Dunger, Fiedler 1997).
The volume-sampling method was used in 1995. One sampling plot
with an area of 10 × 20 m was marked in each homogenous habitat. Walking
in a zigzag pattern, litter was taken by hand after each two steps and sifted
into a litter sieve (10 mm) separating coarse litter - leaves, branches, stems
and cones. Overall 42 litter samples with the total volume of each sample 5 1
were collected. Samples were air dried and then sifted through soil sieves (5
mm, 3 mm, 2,5 mm, 2 mm, 1 mm). Snail shells were picked out with
tweezers, looking through a magnifying glass. This method was used not
only to determine the composition of snail species but also to analyse the
occurrence of protected and endangered species.
The area-sampling method was used for collection of samples in 1997. A
sampling plot was chosen in each habitat where surveys were conducted
along a 25 m transect line. The sampling plot was selected in a homogenous
habitat (except for sampling plots EMI and EM32). A litter_sample
(altogether 25 samples) was collected each meter along the entire transect
with a biocenometer (20 × 20 cm). Each sample was sifted through a litter
sieve. Samples were air dried and then separately sifted through soil sieves.
Snail shells were picked out with tweezers, looking through a magnifying
glass. Altogether 1,050 litter samples were collected in 42 sampling plots.
The data was used for statistical analysis.
Snails were gathered by hand from tree trunks and decaying wood
both within the boundaries of a sampling plot and in the surveyed habitat.
This method was used in 1995 to determine the species composition because
certain species can rarely be found in the litter.
Species were identified according to M.P. Kerney (Kerney et al. 1983). In
addition the publications of I. M. Liharev (Лихарев 1962) and В. М.
Pokryszko (Pokryszko 1990) were used to determine families of the snail
species Clausiliidae and Vertiginidae. The snail classification according to
M.P. Kerney (Kerney et al. 1983) was applied. The gathered materials are
stored at the Natural History Museum of Latvia.
3. Assessment of Ecological Factors
Several ecological factors were measured, defined and assessed in
each sampling plot: thickness of the litter/moss layer (cm); the pH of a
humus layer of the soil; percentage of deciduous trees (%); age of a forest
stand (years); humidity inside a forest stand in a sampling plot (groups).
4. Analysis of Data
All data was summarised in Excel tables. The number, dominance or
percentage, density, occurrence classes and diversity of species were
analysed using the classifications of species and sampling plots and
ordination methods - TWINSPAN (Two-way indicator species analysis),
DECORANA (Detrended Correspondence Analysis) (Hill 1979, Hill, Gauch
1980) and an indicatorspecies analysis (Dufrene, Legendre 1997). The
results of all three survey methods are used in the analysis of species
composition of the protected and endangered species in sampling plots and
habitats. The data acquired on the basis of materials gathered by the areasampling method in 1997 was used to analyse the species diversity (the
number of species, Shannon-Wiener index, summary domination index), the
domination structure of species, density of populations and occurrence
classes of species in each habitat. A data matrix, which was acquired
summing up the number of species and specimens collected in 25 samples
along one transect of each sampling plot, was used in data analyses. This
data was used in the TWINSPAN classification, DECORANA ordination
and the analysis of indicatorspecies.
For each sampling plot (except for sampling plots EMI and EM32)
the domination or proportion of each species was determined (p =
d/D*100%) (Fjodorov, Giljmanov 1980) and the average density of snails
was estimated (summing up the number of specimens collected in samples
along one transect and attributing the figure to 1 m2). The domination
structure was drawn up according to Schwerdtfeger (Schwerdtfeger 1975).
The occurrence classes of species were estimated according to
Schwerdtfeger (Schwerdtfeger 1975) (F= 100*b/a). The occurrence classes
were divided according to Tischler (Tischler 1979).
In order to characterise the diversity of species the following diversity
indices were calculated: number of species (S); Shannon-Wiener index
(Shannon, Weaver 1962; Hair 1980; Liepa et al. 1991);
S
(HS = -Σ(p)(log p)
i=l
summary domination (Simpson) index (C = Σ p ) (Odum 1975).
The ecological groups of snail species are distinguished according to
bibliographic sources.
The significance of correlation coefficients is assessed according to the
table of critical values (rα;n) (Liepa 1974).
Main Results
1. Snail Fauna and Diversity of Species in Forest Habitats
The results were acquired collecting 22,964 snail specimens. Overall 51
snail species were found belonging to 19 families, constituting 61.2% of the
total number of terrestrial snail species known in Latvia. It proves that forests
are ones of the most abundant habitats in Latvia by species number. The
largest number of terrestrial snail species was found in sampling plots in
deciduous forests with pioneer tree species and in sampling plots in broadleaved forests, i.e. 53.49% of Latvia's terrestrial snail species and 90.2% of
the total number of species identified during the survey (Table 1). The
diversity indices of snail species in deciduous forests with pioneer tree
species were highest. In pine forests the lowest number of terrestrial snail
species was identified, i.e. 23% of the total number of terrestrial snail
species known in Latvia and approximately 39% of the species identified in
forests during the survey. In pine forests the diversity indices of snail species
were lowest. In spruce forests and black alder forests a similar number of
terrestrial snail species was identified (Table 1). The number of species
identified in spruce forests constitutes 45.1% of the total number of Latvia's
terrestrial snail species (74.5% of the number of species identified during the
survey) and in black alder forests - 45% of the total number of Latvia's
terrestrial snail species (76% of the number of species identified during the
survey).
The results of the survey of the snail fauna in broad-leaved forests and in
deciduous forests with pioneer tree species coincide with the references to the
abundance of species in deciduous forests mentioned in many
bibliographical sources (Ehnström, Waiden 1986, Niemelä 1997; Лихарев
1962, Шилейко 1978, Лихарев, Виктор 1980) and this fact is also proved by
other studies performed in Latvia (Petersons 1932, 1933, Pilāte 1997, 2000b;
2003a,d,e; Suško 1998; Dreijers, Stalažs 2000; Barševskis et al. 2002). Till
1995 the studies of the snail fauna and species diversity in pine forests, spruce
forests and black alder forests practically were not carried out in Latvia.
Usually in bibliographical sources pine forests and spruce forests are not
viewed separately but combined into coniferous forests where the snail fauna
is described as poor and in such forests up to 10 snail species occur (Лихарев
1962; Шилейко 1978; Лихарев, Виктор 1980; Kerney et al. 1983; Spuris
1998; Rudzīte 1999), however, this survey revealed 20 species in pine forests
and almost twice as many in spruce forests. The conclusion that in pine
forests the snail fauna is poorer than in other forest habitats correspond to the
results of other studies (Pilāte 1997, 2003a, 2000e). The opinions differ
regarding swampy forest types. A Shileyko (Шилейко 1978) characterises
swampy forests as poor in snail species yet the studies performed by other
scientists (Ehnström, Waiden 1986, Niemelä 1997, Pilāte 2000b,d, Waidén
2001) along with this study prove that swampy black alder forests are rather
abundant in the snail fauna. One of the four species included in Annex II of
the EU directive was identified in the black alder forest habitat - Vertigo
moulinsiana (European Communities 1992).
2. Ecological Factors Determining Structure of Snail Communities and
Species Diversity
A statistically significant positive correlation was found between the
number of snail species, density and Shannon-Wiener index and the pH level
of the humus layer of the soil and percentage of deciduous trees. With the
increase of the litter/moss layer, the indices of species diversity decline,
however, a statistically significant negative correlation was established
between thickness of the litter/moss layer and the number and density of
species. There is a statistically significant negative correlation between the
summary domination index and the pH level of the humus layer of the soil
and percentage of deciduous trees, and a statistically significant positive
correlation between the summary domination index and thickness of the
litter/moss layer.
According to the TWINSPAN classification two clusters appear in the
first division - cluster *0 with 31 sampling plots and cluster *1 with nine
sampling plots (Figure 1).
Cluster *0 includes sampling plots mainly from broad-leaved forests,
deciduous forests with pioneer tree species, black alder forests and mixed
spruce forests. Altogether there are 47 snail species (Table 2) in the cluster,
therefore the selected forests can be considered to be the most abundant
forests by the number of snail species. Cluster *0 is characterised by 20
species (Table 2).
Cluster * 1 includes sampling plots marked mostly in pine forest and
spruce forest habitats (Figure 1). Cluster *1 comprises 15 species (Table 2)
therefore they can be described as poor forests considering the number of
snail species. Cluster * 1 is characterised by eight species (Table 2).
In the second division cluster *00 appears within cluster *0 with seven
sampling plots and cluster *01 appears with 24 sampling plots (Figure 1).
Cluster *00 comprises sampling plots selected in broad-leaved forests.
Cluster *00 is characterised by 25 snail species (Table 2).
Cluster *01 includes 24 sampling plots which mainly represent
swampy and mixed spruce forests, black alder forests and deciduous forests
with pioneer tree species (Figure 1). The number of snail species in the
forests selected in this cluster is larger than in cluster *00. Cluster *01 is
characterised by 18 species (Table 2).
In the second division cluster *10 appears from cluster *1 with four
sampling plots and cluster *11 appears with five sampling plots (Figure 1). In
both clusters the selected sampling plots represent pine forests and spruce
forests, and one black alder forest which appears in cluster * 11. There are 13
snail species in cluster *10 and eight of them are characteristic of the cluster
(Table 2). In cluster * 11 there are 11 snail species and four of them are
characteristic of the cluster (Table 2).
In the third TWINSPAN classification cluster *010 and cluster *011
appear for cluster *01 (Figure 1). The sampling plots of both clusters
represent a very similar habitat composition, only humidity conditions differ.
Comparatively the most humid conditions are in habitats selected in cluster
*011. In cluster *011 the number of snail species is smaller than in cluster
*010 (Table 2). The habitats selected in cluster *011 are characterised by 17
species. This cluster includes wetland species Vertigo antivertigo, V.
moulinsiana, Zonitoides nitidus and Carychium minimum that do not occur in
other clusters or their occurrence class in them is lower. The habitats
selected in cluster *010 are characterised by 23 species (Table 2).
Among the sampling plots classified according to TWINSPAN there are
several plots where the number of the occurring snail species is small -up to
15 species. The poorest sampling plots constitute 2 to 12 snail species. The
habitats where the number of the occurring snail species is lowest are pine
forests, dry spruce forests and spruce plantations. Those sampling plots where
more than 15 snail species can be found are considered to be most abundant,
e.g. broad-leaved forests, deciduous pioneer forests, wet spruce forests and
black alder forests. In few cases quite many species can also be found in
swampy pine forests.
In the broad-leaved forests (cluster *00) singled out among the
sampling plots classified according to TWINSPAN, there is a smaller
number of snail species than mostly in deciduous forests with pioneer tree
species, black alder forests and wet spruce forests (cluster *01). It might be
caused by the diversity of habitats combined in cluster *01. Wetland species
(Cochlicopa nitens, Vertigo genesii, V. moulinsiana) supplement the species
identified in these forests. 25 snail species are characteristic of broad-leaved
forests where there are more than 90% of deciduous trees, and 18 species are
characteristic of the other forest habitats (except pine forests and planted
spruce forests). The composition of species characteristic of habitats is
similar but there are several snail species (Acicula polita, Bradybaena
fruticum, Cepaea hortensis, Clausula pumila, Macrogastra ventricosa,
Succinea putris, Trichia hispida), which most often and in larger numbers
occur in broad-leaved forests. There are seven species (Columella aspera, C.
edentula, Euconulus fulvus, Nesovitrea hammonis, N. petronella, Punctum
pygmaeum and Vertigo substriata) among the species characteristic of forest
habitats, which are identified in all forest habitats with a high occurrence
class. These can be regarded as ecologically adaptive species.
The eigenvalues (λl=0,219, λ2=0,12) of the first DCA axis and the
second DCA axis are higher than the eigenvalue (λ3=0,069) of the third
DCA axis. The eigenvalue of the third DCA axis is the lowest and it explains
some changes in ecological conditions.
The first DCA axis explains the gradient of deciduous - coniferous
forests and ecological conditions - proportion of deciduous trees, the pH of
the humus layer of the soil and thickness of the litter/moss layer (Figure 2). In
the direction of the first DCA axis to the right from the vertical line almost
all selected sampling plots represent coniferous forests - spruce forests and
pine forests (Figure 2). These are both natural and planted forests. The richest
forest habitats in snail species - mostly deciduous forests
(deciduous forests with pioneer tree species, broad-leaved forests, black
alder forests and also some spruce forests are found to the left from the
vertical line on the first DCA axis.
A statistically significant correlation is seen between the second DCA
axis and proportion of deciduous trees - it increases upwards in the
direction of the second DCA axis and is the only one of indices, which
correlates with this DCA axis. In comparison with the first DCA axis and
the third DCA axis, forest management impact - it increases upwards in the
direction of the second DCA axis - shows the highest correlation value with
the second DCA axis. Perhaps the second DCA axis explains the gradient
of forests affected - unaffected by forest management. The third DCA axis
can be viewed as the gradient of dry - swampy forests because there is a
statistically significant correlation between this axis and humidity level in
the forest stand.
The occurrence class is highest in forests of 10 snail species
(Carychium tridentatum, Cochlicopa lubrica, Columella aspera, C.
edentula, Euconulus fulvus, Nesovitrea hammonis, N.petronella, Punctum
pygmaeum, Vertigo substriata, Vitrea crystallina) (Table 2). They were
found in almost all sampling plots and in the surveyed forest habitats (yet
not so often in pine forests) and usually they occur all together in snail
communities.
The acronyms of the snail species characterising mostly pine forests
and planted spruce forests (Columella aspera, C. edentula, Discus
ruderatus, Euconulus fulvus, Nesovitrea hammonis, N.petronella, Punctum
pygmaeum, Vertigo substriata, Vertigo pusilla and V. ronnebyensis) are
encircled with a black line (Figure 3).
The acronyms of species occurring in deciduous forests as well as in
natural spruce forests are separated with a dashed line (Figure 3). In the
middle part of the first DCA axis yet closer to the second DCA axis there
are acronyms of those snail species the occurrence classes of which in
deciduous forests are higher than in coniferous forests.
A statistically significant correlation is seen between the first DCA
axis and 23 snail species. Only one of these species - Vertigo ronnebyensis has a statistically significant positive correlation. The other 22 species
(Acanthinula aculeata, Acicula polita, Aegopinella nitidula, Aegopinella
pura, Arion circumscriptus, Bradybaena fruticum, Carychium tridentatum,
Cepaea hortensis, Clausilia pumila, Cochlicopa lubrica, Cochlodina
laminata, Columella edentula, Macrogastra plicatula, M. ventricosa,
Perforatella bidentata, Punctum pygmaeum, Succinea oblonga, S. putris,
Trichia hispida, Vertigo pusilla, Vitrea crystallina, Vitrina pellucida) have
a statistically significant negative correlation. The number of specimens of
these species and consequently also the density of their populations
considerably decreases in coniferous forests and increases in deciduous
forests. These 22 snail species can most likely be found together in
deciduous forests than in coniferous forests.
A statistically significant correlation is seen between 11 snail species
and the second DCA axis. The acronyms of these species are encircled with a
dashed line (Figure 3). There is a statistically significant negative
correlation between three snail species (Acanthynula aculeata, Clausilia
bidentata and Spermodea lamellata) and the second DCA axis and there is a
statistically significant positive correlation with the species Carychium
minimum, Punctum pygmaeum, Ruthenica filograna, Succinea oblonga, S.
putris, Vertigo antivertigo, V. moulinsiana and Zonitoides nitidus.
A statistically significant positive correlation is found between the third
DCA axis and six species (Carychium minimum, С tridentatum, Oxychilus
alliarius, Perforatella bidentata, Succinea putris and Zonitoides nitidus). The
density of these snail populations grows with the increase of humidity. There
is a statistically significant negative correlation between the third DCA axis
and nine snail species (Bulgarica сапа, Clausilia cruciata, Discus ruderatus,
Limax cinereoniger, Macrogastra plicatula, Ruthenica filograna, Vertigo
ronnebyensis, Vallonia costata and Succinea oblonga). With the increase of
humidity, the proportion of these snail species decreases within the snail
community.
According to bibliographical sources, the snail diversity, distribution and
occurrence are mostly affected by vegetation (Лихарев 1962, Fog 1979). The
analysis of ecological conditions shows that snail diversity in forests
considerably depends on the percentage of deciduous trees. According to
bibliographical sources, many terrestrial snail species occur in shady
deciduous and mixed forests (Лихарев 1962, Шилейко 1978, Лихарев,
Виктор 1980, Kerney et al. 1983, Rudzīte 1999) where snails are protected
against the sun and desiccation (Лихарев, Виктор 1980, Ehnström, Waiden
1986, Hylander et al. 2004). In deciduous forests litter complies with snails'
ecological requirements (Лихарев 1962, Шилейко 1978, Лихарев, Виктор
1980). Pine forests are insolated and more exposed to sunlight, which
adversely affects snails (Лихарев 1962, Шилейко 1978, Лихарев, Виктор
1980). Planted spruce forests are shady, yet they either lack deciduous trees or
their proportion is very small.
Usually the diversity of snails is larger in sites with neutral or alkaline
soil (Wäreborn 1969,1970,1992; Valovirta, Heino 1994) because calcium is
the main component of snail shells and slime (Шилейко 1978, Лихарев,
Виктор 1980). The research results show that snail diversity grows with the
increase of the pH of the humus layer of the soil, and the reaction of the
humus layer is interrelated with the percentage of deciduous trees.
The survey revealed that the diversity of snail species is higher in
forests with a thinner litter and moss layer. These are broad-leaved forests.
Plants and their remains are source of nutrition for many terrestrial snails,
and litter in deciduous forests is a suitable place for refugees (Ehnström,
Waiden 1986, Corsmann 1989, Hylander et al. 2004). In pine forests and
planted spruce forests where the layer of litter and moss is thickest, the
diversity of snail species is low. In deciduous forests the litter layer mostly
consists of leaves and the moss layer is much thinner but in coniferous
forests the moss layer is thick and the litter layer mostly consists of needles
(Liepa 2003). The litter in coniferous forests gives an acid reaction but in
deciduous forests - a neutral reaction (Kāposts 2003). Needles are not
suitable for snail nutrition (Лихарев 1962, Шилейко 1978, Лихарев,
Виктор 1980).
The analysis of ecological conditions shows that humidity does not
considerably affect the parameters characterising the diversity of snail
species. Humidity mostly affects species composition of snail communities,
species occurrence and the domination structure of species. Two species
(Vertigo antivertigo, V. moulinsianä), which do not occur in drier forest
types, were recorded in swampy forests. Some species (Carychium minimum,
Succinea oblonga, Zonitoides nitidus) most often occur in swampy forests
than in drier forest types.
3. Analysis of Indicatorspecies
As a result of the indicatorspecies analysis, 12 indicatorspecies have
been identified among 47 terrestrial snail species found in forests in 1997.
These indicatorspecies are characteristic of one of the five sampling plot
groups that were selected depending on the forest habitat. Indicatorspecies
were not identified in pine forests. In deciduous forests with pioneer tree
species two indicatorspecies were selected Cochlicopa lubrica and Vitrea
crystallina. One indicatorspecies Discus ruderatus was identified for spruce
forests. Two indicatorspecies Carychium minimum and Zonitoides nitidus
were identified for black alder forests. Seven indicatorspecies were selected
(Aegopinella pura, Bradybaena fruticum, Columella edentula, Punctum
pygmaeum, Trichia hispida, Vitrina pellucida and Vertigo pusilla) for broadleaved forests. A wetland species Columella edentula and adaptive species
Punctum pygmaeum, Trichia hispida and Vitrina pellucida are common and
frequently occur in various forest habitats, in meadows, greenery or dunes
(Rudzīte 1999; Pilāte 2003 b). Therefore these species cannot be used as
indicatorspecies of broad-leaved forests.
As a result of the analysis of natural forest indicatorspecies, three
indicatorspecies have been identified. Indicatorspecies were identified only
for two groups of the five sampling plot groups selected depending on the
degree of forest management impact. Two indicatorspecies Clausilia
bidentata and Oxychilus alliarius were selected for the forest group with no
forest management impact. One indicatorspecies Clausilia pumila was
determined for the forest group where clear cutting was performed twice. All
three selected indicatorspecies are forest species and they are rare in Latvia.
During the previous studies carried out in Latvia the analysis of forest
habitat indicatorspecies and indicatorspecies of forest management impact
have not been performed. Bibliographical sources (Suško 1998; Ek et al.
1998; Lārmanis et al. 2000; Priedītis 2002; Pilāte 2003c) contain information
about natural forest indicatorspecies the biological cycle of which indicates
the continuity of certain forest structures or processes. The species that are
attached to a certain habitat and the existence of which depends on the
management type of this particular forest habitat (habitat specialist species)
are singled out among these indicatorspecies. Only in Estonia the analysis of
indicatorspecies of environment quality has been performed (Söderman et al.
2000).
The indicatorspecies analysis shows that natural forest indicatorspecies
(Bulgarica сапа, Clausilia cruciata, Clausula dubia, Limax einer eoniger,
Macrogastra latestriata and Ruthenica filograna) that are mentioned in
several bibliographical sources (Suško 1998; Ek et al. 1998; Lārmanis et al.
2000; Priedītis 2002; Pilāte 2003c) show a high, yet not a statistically
significant indicator value for forests that are felled only once. Perhaps the
snails of these species are resistant to a single clear cut, however, after
repeated forest felling the populations of these species may decline or even
disappear because the study revealed that in forests, which had been largely
affected by management activities, mostly in planted forests, there are no
indicatorspecies or their number has diminished.
4. Diversity of Snail Species in Forests Affected by Management
Activities
In the forest generally, from the statistical point of view, the forest
management impact does not considerably influence the indices
characterising species diversity (the number of species, Shannon-Wiener
index, summary domination index). With the increase of the forest
management impact, on the whole, the number of species, density of
specimens and Shannon-Wiener index in the forest slightly decline, but the
summary domination index increases. As the forest management impact
becomes stronger, the number of species diminishes mostly in spruce forests
(Figure 4).
Probably one of the reasons why the gradient of a natural-affected
forest is insignificant in forests is the fact that almost half of the surveyed
sampling plots are wet and swampy forests and that the percentage of
deciduous trees exceeds 50% in almost 2/3 of the sampling plots. The
Swedish studies (Prior 1985, Hylander et al. 2004) assessing the impact of
clear cuts on snail diversity established that in swampy forests clear cuts do
not affect snail diversity as much as in dry forests. Deciduous trees also play
an important role in preservation of snail diversity after clear cutting
(Strayler et al. 1986, Hawkins et al. 1997, Waiden 1998, Ну lander et al.
2004).
The results of the Swedish research show that after clear-cutting the
number and density of snail species decrease within two to three years
(Hylander et al. 2004). Bibliographical sources contain various information
about the time period needed for the recovery of the species after clearcutting - it might take a couple of years, nine years or even more (Strayler et
al. 1986, Hawkins et al. 1997). The research results lead to a conclusion that
in the first years after clear-cutting the number of snail species declines yet
the species may recover already in 15 years. Perhaps it is very important for
the regenerated forests to border on habitats abundant in the snail fauna.
Several authors (Strayler et al. 1986; Hawkins et al. 1997) state that broadleaves and shrubs, which prevail in deciduous pioneer forests, play a
decisive role in determining time when after a prolonged disturbance in a
pioneer stages the number and density of snail species would be the same as
in an unaffected forest.
A statistically significant correlation is found between the number of
snail species and the number of forest BDS, however, the number of BDS
does not influence the Shannon-Wiener index and the summary domination
index. Yet there are sites comprising only seven to ten BDS but with the
almost identical number of snail species as in sites with 20 or 25 BDS. A
statistically significant positive correlation is seen between the number of
snail species and those groups of BDS which are characteristic of deciduous
trees, moss and lichen layer, shrubs and undergrowth. There is no
statistically significant correlation between the Shannon-Wiener index and
any of the BDS groups. The BDS group characterising of the deadwood has a
comparatively larger effect on the Shannon-Wiener index. A statistically
significant correlation is seen between the summary domination index and
the BDS group characteristic of deciduous trees.
5. Protected and Endangered Snail Species
During the survey 14 protected snail species were identified (Acicula
polita, Bulgarica сапа, Cochlicopa nitens, Cochlodina orthostoma,
Clausilia bidentata, Clausilia dubia, Clausilia cruciata, Clausilia pumila,
Ena obscura, Limax cinereoniger, Macrogastra latestriata, Ruthenica
filograna, Spermodea lamellata and Vertigo genesii), for the protection of
three of those species Clausilia cruciata, Macrogastra latestriata and
Vertigo genesii micro-reserves should be established. Two of the four
species included in Annex II of the EU Species and Habitat Directive were
identified - Vertigo genesii and V. moulinsiana, for the conservation of
which a specially protected nature territory should be established. Eleven of
the endangered species of Latvia's Red Book were identified {Acicula polita,
Aegopinella nitidula, Bulgarica сапа, Cochlicopa nitens, Cochlodina
orthostoma, Clausilia bidentata, Clausula dubia, Clausilia cruciata,
Clausula pumila, Ruthenica filograna, Vertigo ronnebyensis).
The study revealed that the largest populations of rare and endangered
species occur in the forests where management activities had not been
performed and in the forests that had been slightly or moderately affected by
forest management. In numerously felled forests and in planted spruce
forests only some specimens of these species are found or they do not occur
at all. According to bibliographical sources (Fog 1979; Ehnström, Waiden
1986; Müller et al. 2005) several species (Acicula polita, Bulgarica сапа,
Clausilia dubia, Cochlicopa nitens, Ena obscura, Vertigo genesii,
Spermodea lamellata) are sensitive not only to felling but also to grazing,
draining and planting of trees because the habitats of these species are
related to the structures of natural forests, e.g. large diameter trees, fallen
trees, deadwood.
Main Conclusions
• Altogether 51 snail species were identified in forests, constituting
61.2% of the total number of terrestrial snail species known in Latvia. In
forests the snail fauna can be described as rich. Two species Vertigo
genesii and V. moulinsiana are new species to Latvia's fauna.
• Pine forests and spruce plantations are ranked as poor habitats of the
snail fauna but deciduous forests and natural spruce forests are
abundant in the snail fauna. The lowest diversity of snail species is in
pine forests but it is highest in deciduous forests with pioneer tree
species and in broad-leaved forests.
• The percentage of deciduous trees (the number of snail species in
forest habitats increases with the growth of the percentage of
deciduous trees), the pH of the humus layer of the soil and thickness of
the litter and moss layer mostly determine the diversity of snail species
and the number of species characteristic of habitats. The humidity of a
forest stand mostly affects the occurrence of snail species and the
domination structure of snail communities. The diversity of snail
species in forests is not directly related to the age of a forest stand.
• The largest part of snail species prevailing in forest habitats occurs
frequently and is widely distributed in Latvia. Five species Columella
edentula, Discus ruderatus, Nesovitrea hammonis, N. petronella and
Vitrea crystallina have been identified in all sampling plots, these are
ecologically most adaptive species in forests.
• Forest management activities (mostly clear cuts and planting of trees) in
forests generally do not considerably affect diversity of species if there are
a comparatively large proportion of deciduous forests, wet or swampy
forests or rich snail fauna. Multiple felling and planting of trees largely
influence snail diversity in spruce forests and in broad-leaved forests. The
domination structure of the species changes due to human activities. In this
respect a snail community of pine forests is the most sensitive one.
• The number of snail species declines after a clear cut. The regeneration of
species population depends on the remained forest BDS that are
significant to snails and on the abundance of the snail fauna in the
neighbouring territories.
• The number of BDS, which are significant to snails, is smaller in forests
strongly affected by management activities than in natural forests. With
the decrease of the number of BDS, which are significant to snails, the
number of snail species also considerably decreases. The diversity of snail
species depends on those groups of forest BDS which are characterising of
deciduous trees, shrubs, moss and lichen layer, shrubs and undergrowth.
• Among the snail species identified in forests, Aegopinella pura,
Bradybaena fruticum, Columella edentula, Punctum pygmaeum, Trichia
hispida, Vertigo pusilla and Vitrina pellucida are considered to be
indicatorspecies of a broad-leaved forest habitat. One indicatorspecies
Cochlicopa lubrica was selected for forests with pioneer tree species. One
indicatorspecies Discus ruderatus was identified for spruce forests. Two
indicatorspecies Carychium minimum and Zonitoides nitidus were selected
for black alder forests. Three species (Clausilia bidentata, Clausilia pumila
and Oxychilus alliarius) were identified as indicatorspecies of natural
forests.
• During the survey 14 species {Acicula polita, Bulgarica сапа, Clausilia
bidentata, С. cruciata, C. dubia, C. pumila, Cochlicopa nitens,
Cochlodina orthostoma, Ena obscura, Limax cinereoniger, Macrogastra
latestriata, Ruthenica filograna, Spermodea lamellata and Vertigo genesii)
were found in forests of 21 protected terrestrial snail species in Latvia.
Two species Vertigo genesii and V.
moulinsiana are included in Annex II of the EU directive. Snails of
protected and rare species do not occur or in separate cases only some
specimens can be found in the forests strongly affected by forest
management activities.
APPROBATION
The research results were presented at four international conferences (on
preservation of Fennoscandian biodiversity - in Petrozavodsk, Russia, in 2000,
on survey and preservation of biodiversity in the Baltic region - in Daugavpils,
in 2001, 2003 and 2005) and at two international symposiums -on the
diversity and preservation of Nordic nature in Kuhmo, Finland, in 2000 and
at 1st Baltic Symposium on Malacology "Diversity and conservation of
European molluscan fauna" in Riga, in 2006 as well as at the 8th annual
scientific conference of the Daugavpils Pedagogic University in 2000.
AUTHOR'S EDUCATION AND SCIENTIFIC EXPERIENCE
Education:
1983 - 1990 Faculty of Biology, University of Latvia,
1995 - 2000 Doctoral Programme at the University of Latvia
Scientific Experience:
• "Latvia's natural forests. Study on biodiversity structures, dependent
species and forest history", WWF Latvia - Pasaules Dabas fonds, (19951996);
• "Inventory of woodland key habitats", State Forest Service, Regional
Forestry Board of Östra Götaland (1997 - 1999);
• "Inventory of woodland key habitats in Gauja Nature Park",
• „Inventory of snail fauna in Gauja Nature Park", Gauja NP (2000)
• „Development of biodiversity indication system of grey dunes" (2001 2004);
• The study funded by the JSC "LVM"- "Development of monitoring
methodology for the management of natural forest habitats and its
approbation", Latvian Forestry Research Institute "Silava" (2004);
• The study funded by the Forest Development Fund - "Development of
forest management models without clear cutting", Latvian Forestry
Research Institute "Silava" (2005);
• "Implementation of bog habitat preservation plan in Latvia", Latvian
Fund for Nature (2005);
• Survey of snail fauna in Augšdaugava, Natural History Museum of
Latvia (1991- 1996);
• Survey of snail fauna in Katleži forests, Natural History Museum of
Latvia (2000);
• Inventory of Ena montana sites, Natural History Museum of Latvia
(2001);
• Survey of snail fauna in Karelia, on Kizhi Archipelago and in Zaonezje
region, Natural History Museum of Latvia, Kizhi museum-reserve (2003)
• Survey of snail fauna in Ludza region, Ludza Local History Museum
(2004-2005)
PLACE AND TIME OF RESEARCH
The research has been carried out at the University of Latvia and at the State
Agency "The Natural History Museum of Latvia" from 1995 to 2005.
ACKNOWLEDGEMENTS
This research was initiated as part of the project "Latvia's natural
forests - study on biodiversity structures, dependent species and forest
history" performed by the WWF Latvia under the guidance of Uvis Suško.
I want to express my gratitude to my academic adviser Voldemārs
Spuņģis. Special thanks to Uvis Suško for the opportunity and inspiration to
develop my study. I would also like to thank Uvis Suško for allowing me
access to information he had compiled about the history of forest
management in the surveyed areas. I would like to thank Valdis Pilāts and
Māris Pilāts, as well as Andis Liepa and Kaspars Liepiņš for their support in
collection of materials and transportation. Very special thanks to Valdis
Pilāts for translation and valuable remarks he made during the performance of
the research. Many thanks to Uvis Suško, Normunds Priedītis, Kristaps Vilks,
Māra Pakalne and Guntis Brumelis for consultations in data interpretation.
Particular thanks to Normunds Priedītis for his valuable comments and
recommendations on this research. For his assistance in identification of
species, I would like to thank Edgars Dreijers. Special thanks to Katja
Matveijena from Finland who helped obtain the necessary literature. Many
thanks to Skaidrīte Ruskule, head of the Natural History Museum of Latvia,
Guna Bagrade, deputy director, staff members of the Zoology Department Nikolajs Savenkovs, Una Bērziņa, Jānis Dreimanis, Dmitrijs Boiko and
colleagues Anatolijs Beļajevs and Egita Zviedre for their assistance in
preparation of this study. I would also like to thank Arvīds Barševskis and my
children - Māris Pilāts and Katrīna Pilāte for their moral support.