UDC 574.472.42 FEATURES OF GRASS AND SUBSHRUB REPRODUCTION IN FOREST PHYTOCOENOSES

The north-east region of Ukraine stands out from the other regions including the Carpa­thians­ for­ high­ forest­ cover.­Grass­and­ subshrub­ layer­ significantly­ affects­ the­ formation of tree layer (the early stages of forest demutation). The study is conducted in forest phytocoenoses of the National Nature Park “Desniansko-Starogutsky” and the adjacent territories. The study objects are model plant species of grass and subshrub layer (Aegopodium podagraria L., Asarum europaeum L., Calluna vulgaris (L.) Hull, Carex pilosa Scop., Molinia caerulea (L.) Moench., Stellaria holostea L., Vaccinium myrtillus L., Vaccinium vitis-idaea L.), each presented by 3–5 coenopopulations. Two main types of reproduction are found in forest grasses and subshrubs: seed (or by spores in spore-bearing plants) and vegetative. In case of generative reproduction, an important biological characteristic is the so-called reproductive effort, which characterizes the contribution of organic matters and energy to the reproductive process. An important common feature of reproduction of the vast majority of forest grasses is the ability for vegetative reproduction and clone formation. It is established that the main indicators of generative reproduction of clone forming plants of grass and subshrub layer depend on plant­species,­and­are­ influenced­by­the­ecological­and­coenotic­factors.­ It­has­been­ found that the smallest contribution (2 %) to the reproduction organs is characteristic of C. vulgaris, and the highest contribution (almost 50 %) is found in the coenopopulations of M. сaerulea. Overall, generativity of the studied plants of grass and subshrub layer is determined by the ecological and coenotic factors, and, therefore, is consistently varied from association to association.


INTRODUCTION
The north-east region of Ukraine stands out from the other regions including the Carpa thians for high forest cover. Many works are primarily focused on the description of ve ge tation of this region, forest phytocoenoses in particular [2,8,12,13,16,19,20,23,29]. According to geobotanical zoning, the area where the study has been conducted belongs to the European broad-leaved forests, Eastern-European province, and covers two subprovinces -the Eastern European, and the Polisky and Podilsky and

RESULTS AND DISCUSSION
Reproduction in a broad sense is the process by which female parents generate some or other germs (diasporas) able to form new individuals that are genetically similar to female parents. Three main types of reproduction were found in forest plants: sexual, asexual and vegetative. Metasperms and gymnosperms are characterized by sexual and vegetative reproduction. One type of reproduction is often dominated. Vegetative reproduction often prevails in forest grasses. R. Ye. Levina [18] rightly emphasized that "from the point of view of the species viability strategy, vegetative reproduction and regeneration justify themselves only in combination with seed reproduction". This combination in reality is observed in plants of the lower layers of forest ecosystems.
Seed reproduction is a multiple-stage process. The first stage is the formation of generativebuds,flowersandflowering,whichisdeterminedbytheconditionofparent plant. The second stage is a complex mechanism of pollination and fertilization, which depends not only on the condition of plants, but also as on the functions of agents provi-The end of the Table 1 ding transportation of pollen. Ripening of seeds and fruits is mainly due to the vital condition of parent plants, whereas their dispersion is almost entirely dependent on external agents (excluding such phenomenon as autochory). A few monographs deal with these importantissues:problemsoffloweringandpollination(monographK.FegriK. and L. van der Pale [10], problems of seed dispersion (monograph. R. Ye. Levina [17]). Methods of plant reproduction study [1] are also well developed.
Thestudyofreproductivebiologyandecologyrequirestheexplicitidentificationof a set of signs characterizing this process on all its stages, and must be recorded in the study of reproduction. Speaking from the perspective of forest ecology, quantitative traitsofreproductionareofparticularimportance:numberofflowersproducedbythe plant, magnitude of reproductive effort, number of diasporas both per individual and per unit of surface area and the like.
Incaseofseedreproduction,thekeyandcriticalstagesareasfollows:flowering and its duration, pollination, fruit and seed ripening, dispersion, preservation of seeds in the soil and the ability to form soil seed banks.
Two main types of reproduction are found in forest grasses and subshrubs: seed (or by spores in spore-bearing plants) and vegetative. Three special reviews [6,15,31] focus on the features of life cycle and reproduction of this group of plants.
Forestgrassesandsubshrubsduetothehighspeciesdiversityarecharacterizedby a wide variety of methods of pollination and seed dispersal [24]. However, in a way, the nature of reproduction of plants of the lower forest layer is a contrast to reproduction of forest forming woody species. Various forms of zoophily, especially entomophily, are predominant in the pollination of grasses and subshrubs of forest ecosystems, and zoochory is dominant among the mechanisms of fruit and seed dissemination -fruits are mostly juicy, seeds may have appendages used as food by insects. In general, animals play a leading role in pollination and distribution of diasporas of plants of the lower forest layer. This has a positive effect on the sustainable conservation of such species in the ecosystemthatdependsonthevarietyandsufficientnumberofspeciesofforestfauna.
Lackofnichespecializationinthepollinationprocessisadistinctivespecificfeatureofforestgrassesinthetemperatezone.Flowersareusuallywhiteorbrightcolored, mostly actinomorphic, so insects with different body shape and size can get nectar and spread pollen. About 40 % of the species of forest grasses of forest ecosystems of the temperate zones have autogamy [4]. But, basically, the researchers record pollination deficitinforestgrassesasoneofthekeyreasonsforthelowleveloffruiting.
When studying a large group of individuals of Actaea spicata in 25 different locations,J.P.Dahlgrenetal [9]foundthatin83%ofcases,floweringoftheseplantsis determined by soil temperature and stand and herbaceous layer density. Accordingly, theearliestfloweringplantswerefoundonsouth-facingslopes.
The range of pollinators in entomophilous species is very wide: bees, bumblebees, butterflies,beetlesandothergroupsofinsects.Therearevariousdefensorstoprevent self-pollination. In Oxalis acetosella, flowers are cleistogamous, they have shortened internodescomparedtonormalflowers.Thesignsofnectarintheformofpinkveinsare well expressed on the petals of this plant.
Havingasufficientlybroadsetofdefensorsthatprovideflowerpollination,forest grasses are often characterized by a low level of fruit inception which depends on the lack of pollination [11]. According to the data collected by T. Asman and others [3] for over20years,pollendeficitisacharacteristicfeatureofthereproductiveprocessof forest grasses and subshrubs.
In general, all types of grasses and subshrubs are characterized by some partial divergenceinfloweringpeaks.Thisisanimportantadaptivetraitthatallowsplantsto improvethechancesoffairlycompletepollinationofflowers.Anegativefactorforpollination of nemoral and boreal species of forest grasses is forest fragmentation. In these conditions,thecompositionofentomofaunaisdramaticallychanging,andinsufficient flowerpollinationofplantsofgrassandsubshrublayerinthefragmentedforestsisbecoming wide-scale [30]. The size of seeds and fruits in forest grasses and subshrubs is very diverse. It ranges from big to the so-called dust-like seeds (representatives of the Orchid family). And the supply of nutrients in seeds varies accordingly [28].
The level of the production process in plants of the lower layer is largely dependent on the vitality of individuals. It in turn is determined by many factors. The structure of phytogeneous fields of forest forming species plays a significant role among them. T. V. Paal [21] has found out that in Vaccinium vitis-idaea the number of established fruitswithinphytogeneousfieldsofspruceissignificantlylowerthanoutsidesuchfields. The activity of phytophages is even more important. Animals destroy up to 80 % of fruits [24] in Actaea spicata.
Resulting effect of the renewal process of a number of plant species of grass and subshrub layer depends on the establishment of soil bank of diasporas, its species composition, duration of preservation of viability and the overall size of bank by diasporas. In broad-leaved forests, the composition of soil seed bank is dominated by diasporas of not indigenous forest species but species of open habitats [22]. In a series of papers of V. V. Petrov [25,26,27] it is shown that the soil supply of diasporas in coniferous indigenous forests is not large and usually comprises 1000-1500 pieces/m 2 . Among forest species, the composition of soil seed bank often includes the seeds of birch and some species of forest grasses and subshrubs (Carex pilosa and Rubus idaeus). Depending on forest type, seeds may be concentrated in some cases in litter, while in others -mainly in the mineral soil layer.
In the study of seed reproduction of forest grasses in the mixed coniferous-broad leaved forest of Bryansk region, N. Y. Bohdanova [7] found out that in some cases their seeds can be spread to a distance of 1 km, but more often cover smaller distances. The studied plant species were characterized by autochory (shoots lodging, balistochory, amphicarpy), synzoochory (myrmecochory, seed dispersal by mouse-like rodents, birds), endozoochory. All studied species were characterized by the combination of different methods of seed dispersal.
In case of generative reproduction, an important biological characteristic is the socalled reproductive effort, which characterizes the contribution of organic matters and energy to the reproductive process. Methods of its calculation are different and depend on the life forms of plants. In most cases, reproductive effort is the proportion of phytomass of reproductive structures of the total phytomass of plant and expressed in percentage [32].
An important common feature of reproduction of the vast majority of forest grasses is the ability for vegetative reproduction and clone formation.
It is established that the main indicators of generative reproduction of clone forming plantsofgrassandsubshrublayerdependonplantspecies,andareinfluencedbythe ecological and coenotic factors ( Betuleto-Pinetum coryloso-aegopodiosum, have been studied. The weight of generative plant organs ranges from 0.7 to 1.5 g and is the greatest in Querceto-Pinetum coryloso-aegopodiosum association. The value of RE comprises 10.9-15.8 % and is the highest in Quercetum coryloso-aegopodiosum association. This is confirmed by the data of M. G. Bashtovy [5] according to which magnitude of reproductive effort is an expression of tactics of plant protection against stress factors. The study of coenopopulations of A. europaeum was carried out in three associations (I. Quercetum coryloso-asarosum, II. Pinetum coryloso-asarosum, III. Querceto-Pinetum asarosum). The proportion of generative individuals in A. europaeum populations comprised 21.3-58.7 % and was the highest in association of Querceto-Pinetum asarosum. The weight of generative structures was 0.3-0.4 g at RE being from 17.7 to 25.6 %. The highest value of RE was also in Querceto-Pinetum asarosum association.
M. caerulea is represented by three populations, limited to the following associations: I. Pinetum myrtilloso-moliniosum, II. Querceto-Pinetum franguloso-molinioso-hylocomiosum, III. Betuleto-Pinetum moliniosum. The percentage of generative individuals in forest ecosystems amounted to 11-20 % and was the greatest in Betuleto-Pinetum moliniosum association. The total weight of generative structures was in the amplitude of 1.2-1.4 g, and RE amounted to 34.0-41.7%. The minimum value of RE was in Betuleto-Pinetum moliniosum association.
Conclusions. The study of 8 model plant species of grass and subshrub layer in forest ecosystems of the north-eastern part of Ukraine, represented by 27 populations was conducted. It was found out that the smallest contribution to the reproduction organs is characteristic for C. vulgaris amounting to 2 %, and the highest one for coenopopulations of M. сaerulea (almost 50 %). Overall, generativity of the studied plants of grass and subshrub layer is determined by the ecological and coenotic factors, and therefore is consistently varied from association to association.