A N N A L E S H I S T O R I C O - N A T U R A L E S M U S E I N A T I O N A L I S H U N G A R I C I Volume 88. Budapest, 1996 pp. 69-77.

Seed bank of Pinus nigra plantations in dolomite rock grassland habitats, and its implications

for restoring grassland vegetation

P. CSONTOS 1, A . HORÁNSZKY 1 . T. KALAPOS 1 & L . L Ő K Ö S 2

^Department of Plant Taxonomy and Ecology, Eötvös Loránd University (ELTE) H-1083 Budapest, Ludovika téri, Hungary

9 Department of Botany, Hungarian Natural History Museum

H-1087 Budapest, Könyves Kálmán krt, 40, Hungary

CSONTOS, P., HORÁNSZKY, A., KALAPOS, T. & LŐKÖS, L . (1996): Seed bank of Pinus nigra plantations in dolomite rock grassland habitats, and its implications for restoring grassland vegetation. -Annls hist.-nat. Mus. nain. hung. 88: 69-77.

Abstract - Dolomite grasslands of the Hungarian Central Range represent high botanical value, preserving several relic and endemic species and associations. These areas were extensively afforested with the alien black pine (Pinus nigra ARN.) during this century. Recently, restoration of the dolomite grassland vegetation started in nature reserves. Therefore, the soil seed bank of the black pine plantations was studied to evaluate its possible role in grassland restoration. Germination tests indicated an impoverishment of the seed bank of the former grassland vegetation under the studied 55-year-old forests. This trend increased with higher density of tree-canopy (92.4 seeds/sqm at 65% - and 39.6 seeds/sqm at 8 0 % canopy cover. Six dolomite grassland components maintained a long-term persistent seed bank: Campanula sibirica, Colutea arborescens, Filipendu-la vulgaris, Polygala amara, Teucrium montanum and Viola rupestris. The relatively high ratio of wind dispersed seeds of weeds or species from other natural communities implies that the removal of black pine over large areas would lead to the dominance of these species. In order to promote the immigration and establishment of the dolomite rock grassland species, a successive cutting system is proposed. With 2 tables.

I N T R O D U C T I O N

Grasslands developed on shallow, rocky soils of dolomite hills form one of the characteristic landscapes in the Hungarian Central Range. The intense physical weathering o f exposed dolomite bedrock and the associated downward movement of rock debris along steep slopes slow down soil formation processes and prevent the establishment of forest vegetation. It also produces a wide variety of microhabitats with contrasting microclimate. As a consequence, the natural grassland vegetation is rich in species and contains several relic and endemic elements. It is hypothesized that these grasslands served as réfugia for lowland steppe species during the Pleistocene glaciation periods. The characteristic vegetation of this landscape was recognized as early as the turn of the last century (BORBÁS 1900), and later the theories of its existence and role in the vegetation history o f the Carpathian Basin were developed (ZÓLYOMI 1942, 1952).

Earlier this century the grassland habitats of dolomite plateaux and hillsides were afforested wi th the non-indigenous Pinus nigra A R N . ( H É D E R 1 9 5 3 ) , causing significant changes in the original vegetation ( B O R l l i n i 1 9 5 6 , B Ó D I S 1 9 9 3 ) . Some further unfavourable effects o f the black-pine plantations are briefly summarized from a nature conserva-tional point o f view by CSONTOS & L Ő K Ö S ( 1 9 9 2 ) .

Recently a strong need has emerged for the restoration of the previous grassland vegetation in the place of existing pine plantations within nature reserves. However, one may doubt the success of restoration efforts because the herb layer seems to be increasingly changed and impoverished with increasing age and canopy closure of the pine stands ( B O R H I D I 1956 , B Ó D I S 1 9 9 3 ) . Sometimes this process terminates in a "nudum" type forest understory in the case o f old stands (above 5 0 years) ( B O R H I D I 1 9 5 6 ) .

Therefore, when these forests are cut for grassland restoration purpose the following must be considered:

a) How big is the risk o f soil erosion? (Especially where the black pine forests exist on steep slopes.)

b) Are the grassland species able to recolonize the areas even i f seed sources are relatively far away?

c) Do the grassland species have significant seed bank in the soil to support successful recolonization?

The last question is studied in this paper. Direct seed bank study o f dolomite grasslands has not been done yet in Hungary,

however V l R Á G H & GERENCSÉR's ( 1 9 8 8 ) paper on a secondary steppe community contains seed bank data for some species in common with dolomite grasslands. Papers dealing with various vegetation types of the Atlantic Europe, though large in number, generally consider different species pools ( V Y V E Y 1 9 8 9 « , b). However, some studies under ecological conditions more or less similar to our case (such as investigations on some limestone grasslands, or habitats should maintain limestone grassland, i f undisturbed) reported poorly developed seed bank beneath the standing vegetation (DONELAN & T H O M PSON 1 9 8 0 , G R A H A M & H U T C H I N G S 1 9 8 8 ) , while other authors found a somewhat better developed seed bank, but mainly composed by subordinated species of the studied grasslands ( R Y S E R & GlGON 1 9 8 5 , POSCHLOD etal. 1 9 9 1 ) . The papers above generally agreed on discussing the vulnerability and difficulties of re-establishment of these species-rich communities.

The purpose of this study is to describe the soil seed bank under black pine plantations on dolomite grassland habitats and to discuss some implications of this for the restoration o f the grassland vegetation.

M A T E R I A L S A N D METHODS

The research area is located about 20 km NW of Budapest, near the village Pilisszentiván, at an elevation of 300 m. This hilly region is formed by Triassic dolomite and due to the continuous physical erosion of its bedrock, steep slopes and shallow soils are characteristic of the area. Within the research area several hillsides are covered by Pinus nigra of which the following two were selected for soil seed bank studies:

Stand 1 - Above the cliff named "Ördög-torony". Average tree height is 10 m; stand age (Pinus) 55 years; diameter at chest height is 20.3 cm (S.d. 4.6); mean cover of the tree-layer is 65%. Share of tree species: Pinus nigra 40% and Fraxinus ornus 25%. The ash forms a spontaneous, uneven-aged, lower tree layer (with mean age of 25.2 years (S.d. 12.3).

Stand 2 - The inner zone of the "Fehér-hegy". Average tree height is 16 m; stand age 55 years; diameter at chest height is 17.1 cm (S.d. 4.2); mean cover of the tree-layer is 80%. Pure stand of Pinus nigra.

From both stands 17,500 enr soil were collected in 36 pieces of 6 cm deep soil prisms taken at random, on 24th October, 1991. The freshly fallen layer of needles was removed before cutting out the prisms. During winter the soil was kept outside and protected from light and additional seed rain. From 8th April, 1992, the samples were exposed to light and kept moist in a greenhouse of the University Botanical Garden. Emerging seedlings were identified then removed at weekly intervals. For seedling identification we used the Seedling Herbarium of the Botanical Department of the Hungarian Natural History Museum and the works by CSAPODY (1968) and M U L L E R (1978). In some cases seedlings were transplanted into flower-pots and raised till flowering stage.

The standing vegetation of the two Pinus nigra plantations was sampled twice in 1993 (4th May and 25th June), by using five, 5 m x 5 m quadrats at each site. The percentage cover of each species was recorded, based on eye estimation, and the average cover values were calculated. Regarding data of different sampling times the higher cover values were considered for each species when the final tables were put together.

Nomenclature follows TUTIN et at. (1964-1980).

RESULTS A N D DISCUSSION

Altogether 52 individuals were identified in the germination tests, and these seedlings belonged to 28 species (Tables 1 and 2).

The seed numbers per square metre were: 105.6 at the less closed tree-canopy (stand 1 ) and 66 under the pure pine forest (stand 2). I f we consider values published for various grassland vegetations, like limestone grasslands ( R Y S E R & GlGON 1985) or short-grass-, mixed grass- and Fescue prairie (RiCE 1989), where 400-8000 seeds/sqm are stored in the soil, then a considerable depletion of seed bank is obvious under the 55 year old pine plantations. Additionally, more than two thirds of the species were represented by single seeds only, again a sign of seed bank depletion (see Tables 1 and 2).

A similar rate of seed bank impoverishment was detected (32 seeds/sqm) in a calcareous grassland when the original surface was covered by 1.6-1.8 m deep soil layer for 32 years ( H E N D R Y et al. 1995), while depletion of woodland seed banks due to coniferi-zation was discussed by W A R R etal. (1994).

The highest number of seeds were detected for Carex humilis (8 seeds; 26.4 seeds/sqm). However it was also present in the standing vegetation and occasionally may produce seeds under the shade of the pine forests.

Beside Carex humilis, which occurred in both stands, in Stand 1 a further three species were present both in the seed bank and in the standing vegetation. However, the compositional similarity between seed bank and standing vegetation was extremely low ( T H O M P S O N & G R I M E 1979). Additionally an increasing dissimilarity was detected parallel wi th the share of Pinus nigra in the canopy.

Table 1. Results of soil seed bank and standing vegetation studies at Stand 1 ("Ördög-torony"). (B = species probably originated from the Botanical Garden, G = members of the original rock grassland communities, N = members of native communities other than rock grasslands, W = weeds and alien neophytes)

Species groups No. of seedlings Average cover (%)

Calamagrostis epigejos N 4

Campanula sibirica G 2

Cardamine. impatiens N 1 Colutea arborescens G 1

Epilobium tetragonum N 1 Filipendula vulgaris G 1 Poa annua B 1

Polygala amara G 1 Salix caprea B

Solidago canadensis w 1

Sonchus asper W 1 Viola rupestris G

undet. grass 1

undet. herb 1

Asperula tinctoria G 1 0.70

Carex humilis G 8 5

Reseda lutea G(W) 1 0.40

Taraxacum officinale s. 1. W 1 0.05

Tree layer (total cover 65%)

Pinus nigra 50

Fraxinus ornus 25

Shrub layer (total cover 10%)

Berberis vulgaris 0.25

Pinus nigra 2

Quercus petraea 0.25

Fraxinus ornus 8

Herb layer (total cover 25%)

Allium senescens ssp. montanum 0.10

Anthericum ramosum 1.50

Berberis vulgaris 0.30

Biscutella laevigata 0.05

Species groups No. of seedlings Average cover (%)

Brachypodium sylvalicum 0.20

Brotnus pannonicus 13

Campanula rapunculoides 0.05

Campanula rotundifolia 0.70

Cardaminopsis arenosa 0.05

Cytisus supinus 0.25

Euphorbia cyparissias 0.40

Fraxinus ornus 2.50

Galium glaucum 0.05

Galium mollugo 0.20

Geum urbanum 0.05

Hieracium murorum s. 1. 0.04

Peucedanum oreoselinum 0.05

Phyteuma orbiculare 0.25

Poa nemoralis 2.50

Polygonatum odoratum 0.30

Quercus cerris 0.05

Äoja canina 0.04

Solidago virgaurea 0.05

Stachys recta 0.10

Teucriuin chamaedrys 0.05

Thalictrum minus ssp. pseudominus 0.05

Veronica officinalis 0.10

Veronica spicata 0.10

Wo/a odorata 0.10

Wo/fl reichenbachiana 0.05

No. of species in the seed bank 18(16)*

Total nr. of individuals 32 (28)

No. of seeds/sqm 105.6 (92.4)

* Values in parentheses are without Group " B "

The species found in the germination tests can be sorted into the fol lowing four groups:

Group "G" - Members of the rocky grassland communities (marked by "G" in the Tables). Altogether 8 or 9 species fall into this group, of which the following six were found only in the seed bank and not in the standing vegetation: Campanula sibirica, Co-

groups:

Table 2. Results of soil seed bank and standing vegetation studies at Stand 2 ("Fehcrdiegy") (for abbreviations see Table 1)

Species groups No. of seedlings Average cover (%)

Artemisia vulgaris W 1

Berteroa incana W 1

Cardamine impatiens N 1

Chenopodium album W 1

Conyza canadensis W 2

Poa annua B I

Populus alba B I

Populus nigra cv. italica B 4

Stellaria media s. 1. B 2

Teucrium montanum G 3

undet. herb 1. 1

undet. herb 2. 1

Carex humilis G 1 0.50

Tree layer (total cover 80%)

Pinus nigra 80

Herb layer (total cover 2%)

Allium senescens ssp. montanum 0.10

Anthericum ramosum 0.30

Bromus pannonicus 0.05

Campanula rotundifolia 0.50

Campanula sihirica 0.05

Euphorbia cyparissias 0.10

Festuca pallens 0.30

Galium aparine 0.05

Galium austriacum (). 10

Koeleria macrantha 0.05

Prunus mahaleb 0.10

Quercus petraea 0.10

Quercus pubescens 0.10

Taraxacum officinale s. 1. 0.10

Thalictrum minus ssp. pseudominus 0.10

Veronica spicata 0.10

Species groups Nr of seedlings Average cover (%)

Vincetoxicum hirundinaria 0.05

Viola reiche nbachiana 0.05

No. of species in the seed bank 13(9)*

Total nr. of individuals 20(12)

No. of seeds/sqm 66 (39.6)

* Values in parentheses arc without Group "B"

lutea arborescens, Filipendula vulgaris, Polygala amara, Teucriurn montanum and Viola rupestris. Because these species probably disappeared during the early stage of pine plantation development, their seed bank character can be considered as "long term persistent" according to T H O M P S O N ' S method ( T H O M P S O N 1993). Additional data are given by P O S C H L O D etal. (1991) who rendered a persistent seed bank probable for Teucriurn montanum. Wi th respect to Campanula sibirica seeds from deep soil layers of several samples taken from xerotherm grasslands were found germinable (A. S E N D T K O , pers. comm.). It may be worth mentioning that the species of this group, with persistent seed bank are subordinated components of the dolomite rock grassland communities. A s imilar phenomenon is reported for the composition of the persistent seed bank of chalk grasslands (RYSER & GiGON 1985, G R A H A M & H U T C H I N G S 1988, P O S C H L O D et al.

1991). Group "N" - Members of native communities other than the rock grasslands. Out

of the three species in this group those with wind dispersed seeds contributed most (Ca-lamagrostis epigeios and Epilobium tetragonum). The additional Cardamine impatiens is a forest species, therefore it may have occasionally grown in the area since it was afforested or the seeds were introduced by zoochory.

Group "W" - Weeds and alien neophytes. This group counts seven species o f which 4 are wind dispersed: Conyza canadensis, Solidago canadensis, Sonchus asper, Taraxacum officinale. A further three species are common weeds of disturbed places. These presumably were introduced at the time of afforestation and may have been producing seeds for some subsequent years. Except Berteroa the other two may belong to the next " B " group as well .

Group "B" - Species probably originated from the Botanical Garden. From the five species put here Poa annua and Stellaria media were frequent weeds in the greenhouse where the soil samples were placed. Mature specimens of Populus nigra cv. italica are found in the vicinity of the green house and penetration o f their fluffy seeds through the air passages was observed. A similar origin is supposed for the further two Salicaceae species {Populus alba and Salix capraea).

According to the main types of origin of seeds in the experiment 58.3% can be considered autochtonous, while 41.7% allochtonous. From the latter 66.6% of seeds were an-emochorous.

CONCLUSIONS

Under the studied black pine plantations the over-all paucity of seeds in the soil -especially when members of the dolomite grassland vegetation are taken into account -makes the landscape restoration difficult, since we can not expect considerable regeneration from buried seeds (cf. G R A H A M & H U T C H I N G S 1988, D O N E L A N & T H O M P S O N 1980

and WARRera/ . 1993). A n additional risk factor is that the majority of the dolomite grassland species lack

effective dispersal methods, but wind dispersed seeds of other vegetation types are already present in the seed bank.

Fol lowing massive disturbances like clear felling or forest fires wind dispersed species w i l l obviously colonize the habitat immediately ( P O S C H L O D & J O R D A N 1992). In our case Calamagrostis epigeios and Conyza canadensis, are the most likely to form dense populations following disturbance.

Considering the results, our suggestions for landscape restoration are the fol lowing: In the first place a network o f glades should be cut in the forest, with width about

double the tree height of the surrounding stands. Following establishment of grassland vegetation on these glades their width should repeatedly be enlarged until neighbouring glades jo in each other. The execution of the enlarging operation cannot be more frequent than at every fourth year, since J Á R Ó et al. (1988) found a three year recovery time of soil variables (e. g. decomposition of needle carpet, humus content and -quality) by monitoring a Pinus nigra clearcut area, and the recolonization of grassland species which are lack o f seed bank can be expected in the third year after clearing ( P O S C H L O D & JORD A N 1992).

* * *

A c k n o w l e d g e m e n t s - Special thanks are due to K. THOMPSON (Sheffield) who critically revised the first version of the manuscript. Discussion with A. SENDTKO (Freiburg) is also acknowledged. We arc grateful to I . IsÉPY and I . PINTÉR for allowing us to work in the greenhouse of the University Botanical Garden. This research was supported by the Hungarian Scientific Research Fund (OTKA No. 3167) .

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Catalogue of Palaearctic Diptera edited by Á. SOÓS, L. PAPP and P. OOSTERBROEK

Volume 1 Trichoceridae - Nymphomyiidae The Catalogue contains the basic taxonomic, nomenclatorial and

distribution data of all species occurring in the Palaearctic Region with the fundamental morphological features for the majority of the fly groups.

Contents: Introduction to Volumes 1-13 (Á. SOÓS and L. PAPP). History of the Catalogue of Palaearctic Diptera. Structure. Genera and their type-species. Species names, type-localities. Distribution. Literature data, references. Dates of publication. Readers. Acknowledgements and closing remarks. List of contributors (Vols 1-13). Type-species designations in Volume 1. New names proposed in Volume 1. Families: Trichoceridae (C. D A H L ) . Tanyderidae (R. W A G N E R ) . Blephariceridae (P . Z W I C K ) . Deuterophlebiidae (L. JED-L I C K A ) . Tipulidae (P. OOSTERBROEK and B R . T H E O W A L D ) . Cylin-drotomidae (Á. SOÓS and P. OOSTERBROEK) . Limoniidae (E. N. S A V C H E N K O , P. OOSTERBROEK and J. S T A R Y ) . Ptychopteridac (R. R O Z K O S N Y ) . Nymphomyiidae (L. J E D L I C K A ) . Bibliography. Index.

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