ISSN 1067-4136, Russian Journal of Ecology, 2017, Vol. 48, No. 1, pp. 10–20. © Pleiades Publishing, Ltd., 2017. Original Russian Text © E.G. Kolomyts, 2016, published in Ekologiya, 2016, No. 6, pp. 403–413.
Buffer Boreal Forests as an Evolutionary Phenomenon in the Pacific Ecotone of Northern Eurasia E. G. Kolomyts Institute of Ecology of the Volga Basin, Russian Academy of Sciences, Tolyatti, 445003 Russia e-mail:
[email protected] Received June 16, 2015
Abstract—The results of landscape-ecological surveys in the Komsomolsk Nature Reserve (the Lower Amur region) have been used as a basis for empirical–statistical modeling of the spatial organization of floristic phratries and forest types that characterize the Amur sub-Pacific as part of the continental marginal part of the megaecotone. Trends in the evolutionary forest-forming processes are described. Mechanisms have been revealed for the origin of buffer forest communities, including spruce–broadleaf and nemoral fir–spruce forests of the Manchurian–Okhotian phratry. Forests of this phenomenal buffer flora are distinguished by extremely high parameters of structural and functional development and have reached the state approaching the evolutionary climax. The previously advanced concepts of the Pacific ecotone of Northern Eurasia as a focus of evolutionary processes in the continental biosphere have been confirmed. Keywords: boreal ecotone, buffer forest communities, floristic phratries, forest types, phytomass, productivity, empirical–statistical modeling DOI: 10.1134/S1067413616060072
acterizes certain key points on the evolutionary trajectory of terrestrial biogeosystems on the islands and continental margin. The Pacific megaecotone of Northern Eurasia lies in the global belt of convergence of matter and energy fluxes on the land surface and is connected with tectonically mobile Earth’s crust. Beginning from the mid-Mesozoic, it has been a source region for the formation of continental part of the biosphere. This region has provided conditions for the development of focal biocoenotic processes (Yurtsev, 1974), formation of high-rank plant and animal taxa (Panfilov, 2005), and emergence of new stable components in phytocoenological structures (Krishtofovich, 1946; Bobrov, 1980). Illustrative in this respect is experience in studies on paleo- and biogeography of Beringia and Hultenia, the closest parts of northeastern Asia and northwestern America that had repeatedly jointed together in the past (Hulten, 1968; Hopkins, 1972; Brigham-Grette, 2000). We regard the Pacific megaecotone as a natural laboratory for studying the patterns of evolutionary biogenesis at the current stage of development of the continental biosphere (Kolomyts, 1987). Thus, analysis of a more complex ecotonal object— a hierarchical system of geoecotones at regional and topological levels under different morphostructural and macroclimatic conditions—is a new step in the development of the theory and methods of studies on biogeographic ecotones.
Ecotonal biogeosystems are the most dynamic structural–functional units of the biosphere that are characterized by increased intensity of matter–energy and clear manifestation of new evolutionary tendencies in the environment (Odum, 1971; Ricklefs, 1976; Sochava, 1979; Kolomyts, 2005). Lateral fluxes and corresponding landscape connections in geoecotones account for the spatiotemporal ordering of natural complexes at all hierarchical levels, from a continental or oceanic sector to a biogeocenosis (Landscape Boundaries…, 1992; Ekotony v biosfere, 1997). Most of relevant studies in Russia and abroad deal with local phytoecotones and concentrate on the problem of discreteness and continuity of plant cover, biodiversity, and distribution of species and communities over gradients of abiotic factors and at the boundaries of contrasting natural environments. This paper presents our experience in studies on biogeocoenotic1 processes and phenomena in the continental marginal sector of the Pacific megaecotone of Northern Eurasia. Analysis is performed using the example of the regional Amur boreal bioclimatic ecotone, which is a component of the above megaecotonal system (Kolomyts, 1987). The age series of geoecotonal objects (on the geological time scale) in this case char1 The
term “biogeocoenose” (in exactly this spelling) was proposed by the renowned Russian geobotanist Academician V.N. Sukachev (1960), the founder of biogeocoenology as a new science of the 20th century (Sukachev, 1972).
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IDEOLOGY OF SCIENTIFIC INQUIRY The Pacific megaecotone of Northern Eurasia is a three-dimensional structure that has arisen due to processes resulting in three types of biosphere ecotonization: with respect to latitudinal zones (macroclimatic), longitudinal sectors (macroorograhic), and altitudinal belts (mesooroclimatic). This is clearly reflected in the pattern of formations in the plant cover (Ekologo-fitotsenoticheskie…, 1977). Conditions on the continental margin are characterized by high meridional hydrothermal gradients complicated by mountain–valley topography. Such conditions provide for the development of sharply contrasting phytocoenotic and landscape structures at the regional and local levels, with the consequent high patchiness of natural ecosystem and frequent zonal and altitudinal inversions. This is favorable for the formation of ecotonal (buffer) biotic communities, which have become widespread in the study region (Sochava, 1980). Growing for a long time under monsoon climate, the plant cover of the temperate belt within the megaecotone has been developing continuously. The transition from the Tertiary to the Quaternary in the flora and vegetation occurred relatively smoothly (Krishtofovich, 1946; Sochava, 1946), being accompanied by migration of certain elements of the Tertiary flora from the north to south and back to the north and by invasion of plants characteristic of cold climate (Yuzhnaya chast’…, 1969). Such a specific evolutionary process resulted in gradual transformation of thermophilic Tertiary suboceanic formations into more temperate formations adapted to sharp seasonal hydrothermal contrasts (Urusov, 1993). As a consequence, not only mixed Korean pine–broadleaf but also conifer forests have a compound flora distinguished by multispecies composition, heterogeneity of phytocoenotic components in all layers, and the presence of numerous Tertiary relicts. Their characteristic features include complex, entangled interspecific relationships and multiformity of the forest-forming process itself, which are accounted for by age-dependent, centennial, and progressive successions of forest communities that give rise to certain genetic series of plant groups (Kolesnikov, 1956; Bobrov, 1980). OBJECTS, MATERIAL, AND METHODS The Far East branch of the Eurasian boreal bioclimatic ecotone (Bazilevich et al., 1986; Kolomyts, 1995) encompasses mountain–valley systems of the Lower Amur region, which Sochava (1980) includes in the sub-Pacific, a geographic space of Mesozoic geological age at the continental margin that represents the transition from the Cenozoic volcanogenic neoPacific (which extends over islands, peninsulas, and the ocean coast) to the much more ancient (Paleozoic) paleo-Pacific included in the Siberian Platform. The structural “core” of this part of the boreal ecotone RUSSIAN JOURNAL OF ECOLOGY
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is represented by the subtaiga zone (Sochava, 1979). The Komsomolsk State Nature Reserve is located in this zone. In its territory, a large-scale landscape–ecological survey was conducted as described (Kolomyts, 2008) in 2011, 2012, and 2014 by specialists of the reserve headed by P.S. Petrenko. They obtained information on 76 qualitative and quantitative parameters characterizing the structural and functional state of forest ecosystems from 55 test plots within the survey area. Two categories of phytocoenological formations were studied: floristic phratries (Sochava, 1946) and groups of forest types (Kolesnikov, 1956). A phratry is a regional typological units of the highest rank (phytocoenomere) that comprises different classes of plant formations and hierarchically corresponds to two phytocoenochores, i.e., regions with latitudinal and altitudinal zonality (Sochava, 1979). A group of forest types is an assemblage of tree species that reflects a certain stage of the forest-forming process characteristic of given site conditions. Four basic phratries were distinguished: Manchurian mesophilic (Mm), Manchurian xerophilic (Mx), Okhotian (Okh), and Angaridian (An). The process of migration and regional differentiation of the Tertiary pra-Manchurian–northern Japanese formation (Sochava, 1946), which resulted in individualization of the above basic floras, had also been accompanied by their integration (intermixture with each other) in habitats with favorable conditions, with consequent formation of sustainable buffer (transitional) phratries. In the Amur sub-Pacific, we distinguished two buffer phratries—Manchurian–Okhotian (MO) and Manchurian–Angaridian (MA)—and the following groups of forest types: (1) broadleaf (Bl), (2) Cedar (Korean pine)–broadleaf (СB), (3) spruce–broadleaf (SB), (4) fir–spruce (FS), (5) larch (La), and (6) forest-bog (FB), with the last group comprising larch peat-moss bog forests (a.k.a. mari). Different components of living forest phytomass and indices of its production were calculated as discrete parameters characterizing autotrophic biogenesis (Glazovskaya, 1981) as the ascending branch of forest functioning. They included the phytomass of wood (BW), total skeletal phytomass (BS), aboveground phytomass of undergrowth and understory (BB), total green phytomass (BV), green phytomass of ground vegetation layer (BG), total aboveground phytomass (BL), total above- and belowground phytomass (BC), and annual production of aboveground skeletal phytomass (PS), green phytomass of herbaceous layer (PV), total green phytomass (PG), and total living phytomass (PC). All these parameters were calculated based on general and regional tables of biological productivity of complete (normal) stands (Shvidenko et al., 2008) using the average values of tree height, diameter, and age for each tree species and of stand density (the initial parameters recorded during forest inventory in the 2017
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test plots). In addition, two integrated indices of autotrophic biogenesis were calculated: the index of ecological efficiency of production process in forest phytocoenoses (EEP = PC/BC) and the coefficient of annual aboveground phytomass turnover (CR = PV/BL). The descending branch of biological turnover was evaluated according to the theory of soil-forming processes (Duchaufour, 1968; Glazovskaya, 1981; Polivanov, 1984; etc.), using an indirect approach based on soil characteristics: the thickness of horizons А0 and А1, their ratio, and acidity. This allowed us to reveal, in first approximation, the most general features of the detrital branch of metabolism, such as the rates of dead organic matter decomposition under certain thermo- and hydroedaphic conditions and the relationship between mineralization and humification as two antagonistic processes of detritogenesis. Empirical–statistical modeling was performed by information theory methods (Kustler, 1957; Puzachenko and Skulkin, 1981) using two basic parameters of relationships between components: standardized coefficient of interrelation C(A,B) between phenomenon A and factor B and partial coefficient of connection Сij between individual gradations (states) of phenomenon (ai) and factor (bj). The second parameter served to determine the system of ecological niches for each value (gradation) of phenomenon A in the space of factor B values; i.e., binary ordination of characters was performed. New approaches were developed to substantively interpret the results of informational modeling of natural ecosystems. A matrix of significant Сij > 1 values was used to construct corresponding plots where gradations of the phenomenon were arranged in order of increase (or decrease) in their ecological dominants with respect to gradations of a given factor. Then an enveloping curve passing through the dominants was plotted, which provided a fairly clear idea of the most significant tendency in the relationship of interest. Many characteristics of forest ecosystems have not only their main ecological niche with respect to a certain factor (with the corresponding ecological dominant and “fuzzy” part) but also a kind of enclave separated from the niche itself by more than one gradation of the factor in the plot of partial coefficients of relationship. The appearance of disjunctions within phytocoenotic ranges is indicative of migration of species and entire communities, which contributes to the evolution of plant cover as a whole (Vasil’ev, 1946). The existence of enclaves is evidence for incessant migration processes in the phytobiota and for the dynamicity of these forest formations. Each enclave may be regarded as a transgressive localization of the phenomenon of interest at alternative values of the relevant factor but under the effective influence of other factors that create similar conditions for the existence of this phenomenon.
Since the dominant part of the ecological niche corresponds to optimal conditions of its formation (Puzachenko, 1996), it was considered that the location of each optimum is the focus of spread (transgression) of the phenomenon toward the existing enclave, with the deviation of the enclave from the niche being regarded as the vector of local transgression of the phenomenon. Attention was also paid to the cells of binary phenomenon–factor ordination where Сij ≤ 1. These were the areas of sporadic distribution of the phenomenon along the gradient of the factor (including the formation of an enclave in many cases). The system of ecological niches served as a basis for calculating the taxonomic norm of a certain functional character for a given object. To this end, we used the central values of all gradations of the factor and matrices of standardized partial coefficients of connection for the object, which were included in calculations as “weight” coefficients. The norm, or the weighted average value of the functional character (Ramensky, 1971), was determined by adding up the products of multiplying the central values of all its gradations by the weight coefficient corresponding to a given gradation of the phenomenon (object). RESULTS OF MODELING AND DISCUSSION Zonation of Forests with Respect to Elevation and Slope Aspect and Formation of Buffer Communities The pattern of natural zonation is more diverse in the mountains than in the plains, which is reflected in the furtherance of Dokuchaev’s theory of geographic zonality (Gartsman, 1971). The superposition of two sources of regional differentiation of the mountain terrain—morphotectionic and macroclimatic—accounts for a variety of zonal phenomena that depend on latitude, elevation, horizontal and aspect-dependent atmospheric circulation, barrier function, and solar exposure. Being combined together, they give rise to complex forms of so-called dislocational zonation. In this concept, zonation is tightly linked with the notion of vector (gradient) and defined as consistent, spatially ordered directionality of change in the properties of geo(eco)systems and their individual components. To reveal the forest-forming role of dislocational zonation, the low-mountain oroclimatic system of the model territory was represented in terms of superposition of the two leading abiotic factors: elevation a.s.l. (A) and slope aspect (B). Three altitudinal belts (hence, three gradations of factor A) were distinguished within the range of our test plots: А1, 20–110 m; А2, 110–310 m; and А3, 310–680 m a.s.l. The first belt comprised plain and foothill areas and the lower parts of mountain slopes; the second, the middle (major) parts of slopes and the tops of low mountains; and the third, the upper parts of slopes and high ridgetops. Taking into account basic climate-forming processes in the Amur region of the Far East (Yuzhnaya
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Mx
MO
An
(a) MA
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(b) Okh
Mm
Bl
SB
FB
La
СB
FS
Elevation–aspect zonation
A1B1 I
I
II
II
III
III
A4B0 A1B2 A2B1 A2B2 A3B1 A3B2 K(A; B) = 0.143 1
2 8
K(A; B) = 0.181
3
4
5
6
7
9
Fig. 1. Binary ordination of (a) floristic phratries and (b) forest types with respect to the factor of elevation–aspect zonation: (1) ecological dominant; (2) the “fuzzy” part of ecological niche; (3) trajectory connecting ecological dominants; (4) ecological niche space; (5) enclave; (6) zone of sporadic distribution of the phenomenon within a given range of factor gradations; (7) direction of possible transgression of the phenomenon from its ecological dominant; (8) direction of transgression of basic phratries (or forest type groups), with intermixing between them and formation of buffer phratries or forest type groups; (I, II, III) the upper, middle, and lower zones of low-mountain belt.
chast’…, 1969), all mountain slopes in the model territory were divided into two opposite categories with regard to aspect (and, therefore, solar–circulation exposure). The first category (В1) comprised slopes of NW–N–NE–E aspects. These shaded slopes are not only under strong impact of the winter continental monsoon, which brings severe weather with little snow, but also are exposed to the strong cooling and drying influence of the Okhotsk high-pressure system during the growing season. These are the coldest and least moistened habitats within each altitudinal belt. Category В2 comprised SW–S–SW–W slopes, which are well insolated, protected from the winter monsoon, and receive sufficient precipitation from lowpressure systems coming from northeastern China and the bordering Far Eastern seas. Hence, the warmest and well-moistened habitats have been formed on these slopes. A special group included subhorizontal areas В0 of foothill plains and valleys of small rivers (А4), where the adverse effect of winter climate inversions manifests itself. Binary ordination of the above phytocoenological indicators with respect to the factor of dislocational zonation (Fig. 1), with sufficiently high C(A;B)2, proRUSSIAN JOURNAL OF ECOLOGY
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vides evidence that, in the continental monsoon climate, elevation-dependent bioclimatic zonation is manifested selectively, being markedly disturbed because of contrasting insolation conditions. The coefficients of interrelation C(A;B) of floristic phratries and forest type groups with elevation are 0.126 and 0.102, whereas those with slope aspect (i.e., solar exposure) are higher: 0.174 and 0.157, respectively. It may well be that alteration of altitudinal zonation by the combined factor of solar–circulation exposure is explained by the dualism of the southern Far East regional bioclimatic system itself. This concerns commensurate manifestations of latitudinal zonation of the suboceanic type (broadleaf forests ↔ mixed forests ↔ dark conifer forests) and longitudinal sectoral zonation of the eastern continental margin type. The role of the latter manifests itself primarily in the expansion of larch forests (representatives of the Angaridian flora) along river valleys (lowland forests) and over the NW– 2 It
should be noted that the standardized coefficient of interrelation C(А; В) = 0.19 corresponds to a correlation coefficient of about 0.7 (Puzachenko and Skulkin, 1981), with the values C(А; В) ≥ 0.07 being considered statistically significant (Kolomyts, 1995).
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N–NE slopes in the middle low-mountain belt (mountain forests). In the same band and on the slopes of the same aspects, intermixing between the Angaridian flora and the xerophilic Manchurian flora has given rise to multistory larch forests with broadleaf tree species that belong to the buffer Manchurian– Angaridian phratry. The Manchurian floristic phratries themselves— the main phytocoenological representatives of the Amur sub-Pacific—also show no definite confinement to a certain altitudinal belt. Broadleaf and cedar–broadleaf forests occur almost all over the lowmountain altitudinal profile, even if sporadically, and have two ecological dominants: (1) xerophytic in the plains and foothills and (2) mesophytic on the southerly and southwesterly slopes in the upper zone of mountain ridges. The dominant region for fir–spruce forests lies in the same zone but on slopes of northeasterly aspect. This is the next type of forest formations with respect to altitudinal distribution, which is represented by the Okhotian flora. Thus, elevationdependent zonation begins to manifest itself in this case, but only on slopes of certain aspects where conditions for this are most favorable. The transgression of Mx and Okh floras from the upper to the middle parts of well-insolated slopes and their intermixture have resulted in the formation of spruce–broadleaf forests. However, forest of the same buffer phratry are similarly widespread in the foothills, with an enclave on the southerly slopes of the lower mountain belt. A characteristic ecological consequence of dislocational zonation in the sub-Pacific is that representatives of different faunas selectively interpenetrate forest communities growing in certain altitudinal belts or on slopes of certain aspects. The correlation between forest type groups and their constitutive floristic phratries is very high: (C(A, B) = 0.313), which is evidence for the oroclimatically predetermined stability of the florogenesis of any given forest type. This stability is also confirmed by the fact that the ecological niches of floristic phratries and forest type groups in the space of dislocational zonation are fairly discrete (Fig. 1). They have only an insignificant fuzzy component and consist mainly of the dominant part and numerous enclaves. Florogenesis has undergone territorial subdivision depending on different combinations of elevation and slope aspect (solar–circulation exposure), with consequent formation of corresponding phytocoenotic structures. This appears to be one of the factors accounting for the origin of well-known floristic diversity and species saturation of forests in the Amur sub-Pacific (Kolesnikov, 1956; Nakamura and Krestov, 2005). Broadleaf forests consist mainly of species from the Manchurian flora (up to 80–100% in the tree stand), with its Mm and Mx types being almost equally represented (52 and 48%, respectively). However, this does
not apply to cedar–broadleaf forests, where the overstory and understory have the richest floristic composition. They contain approximately equal proportions of Mm and Mx communities (21 and 25%) and also of forests transitional to the Okhotian flora, which include fir–spruce stands (up to 15%). However, dominance in the forest type group (with a probability of up to 32%) belongs to buffer MA associations, where larch (Larix gmelinii and L. cajanderi) accounts for no less than 30% of tree stand (55–80% probability of dominance). Thus, considerable invasion of species from the continental Angaridian flora (primarily larch) and suboceanic Ayan dark conifer forests to northern Korean pine forests of the Lower Amur region may be regarded as characteristic for the florogenetic structure of the main zonal forest formation of the Amur boreal ecotone. On the other hand, larch forests— “legitimate” representatives of the Angaridian phratry—have an even greater admixture of buffer MA communities (up to 43%). In addition, the Manchurian–Angaridian flora is represented in forests of the Okhotian flora; i.e., transgression of larch (20%) is also observed in mixed forests of the Lower Amur region. Korean pine–broadleaf forests are more humid (mesophilic) than broadleaf forests with oak (mesoxerophilic). The buffer Manchurian–Okhotian forest communities have been formed due to intermixing of species from the Ayan fir–spruce forests with representatives of cedar forests, where the general humidity level is the closest to that in the former group. This forest-forming process has involved the well-known phenomenon of substitution of cedar by Yeddo spruce (Kolesnikov, 1956; Nakamura and Krestov, 2005). As a result, spruce–broadleaf forests have two equivalent dominant floristic regions: they can either remain the buffer Manchurian–Okhotian type or pass to the Okhotian phratry. The arena of local contacts between the basic phytocoenological representatives of the sub-Pacific and paleo-Pacific in the Amur boreal ecotone is confined to lowland plains and foothills, with both these groups occurring mainly in flat-interfluve (plakor) areas. Their ecological dominants on mountain slopes are separated depending on solar exposure, being localized on slopes with high and moderate insolation for the broadleaf forests of Mm phratry and on shaded slopes for the larch forests of An phratry. Dominants of the two buffer floristic phratries (МО and МА) have been formed in territorially close altitudinal belts (at elevations of 110 to 310 m). Intermixing between the Okhotian and Manchurian floras proceeded from the upper low-mountain belt (the dominant focus of Ayan fir–spruce forests) downslope, toward the dominant of the ecological niche of mountain mesophilic cedar forests. The formation of SB forests, i.e., Yeddo spruce invasion to ash–oak–linden
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(a) MA Okh An Mx Mm MO
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(b) La FS СB SB FB Bl
(c) An MA Mx Okh Mm MO V Quality class
Slope aspect
NW–N–NE NE–E–SE NW–W–SW Horizontal SW–S–SE
IV III II I
K(A; B) = 0.128
K(A; B) = 0.150
K(A; B) = 0.149
Fig. 2. Binary ordination of (a, c) floristic phratries and (b) forest type groups with respect to the factor of slope aspect and stand quality class. For designations, see Fig. 1.
communities, occurred mainly on moderately insolated or, less frequently, shaded slopes, where the ecological dominant of this buffer МО phratry has eventually shifted. Moreover, its dominant has proved to be located 100–200 m lower than that of the mountain Mm phratry. With respect to solar–circulation exposure, distinct differentiation is observed between SB and FS forests, on the one hand, and CB forests, on the other hand (Figs. 2a, 2b). The Ayan fir–spruce forests are widespread on all slopes with moderate insolation and also expand to slopes of northerly aspects. However, the ecological dominant for forests of the Okh flora is on the westerly slopes open to moisture-laden air masses. At the same time, the dominance region of broadleaf forests of the basic Mx flora includes southerly (wellinsolated) and easterly (least moistened) slopes. Transgression of mountain broadleaf forests from easterly slopes to fir–spruce forests on westerly slopes has resulted in the development of buffer MO formation (spruce–broadleaf forests) on the latter slopes. In turn, the downslope spread of fir–spruce forests along river valleys and their invasion into broadleaf Mm forests have given rise to enclaves of this buffer phratry in the plains. Thus, two polar-opposite floras, Manchurian mesophilic and Angaridian, have dominance regions at almost the same elevations (from foothills to ridgetops), on slopes with similar conditions of solar exposure (generally moderate, but with prevalence of wellinsolated slopes for the Mm flora and shaded slopes for the An flora) and similar meso- and microtopography (slope angle 0–16 degrees). However, the buffer (intermediate) MA flora grows both in plakor areas and on ridgetops, with the initial Mm and An floras intermixing with each other and larch expanding to cedar–broadleaf forests. Broadleaf forests with oak (the Mx flora) also grow in the same habitats, which is a consequence of aridization of mesophilic Manchurian forests. RUSSIAN JOURNAL OF ECOLOGY
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Therefore, the actual mosaic pattern of the above floras in the low-mountain Lower Amur sub-Pacific is not strictly fixed to the geomorphological framework. Its formation appears to be governed mainly by the bioclimatic system, and in particular by centennial and supracentennial climate fluctuations and ectogenetic successions of the forest vegetation itself. Zonal Groups of Forests and Formation Mechanisms of Buffer Communities The zonal geographic structure of floristic phratries is reflected in the ground vegetation layer, which A.K. Kajander defined as an indicator of biologically equivalent habitats (cited from Sukachev, 1972). Of special interest in this respect are Manchurian phratries as basic for the formation of forest cover in the Amur sub-Pacific. The ground vegetation layer in forest of the Mm phratry largely consists of a complex of boreal + nemoral species (dominants) (40%) and a major enclave of purely boreal herbaceous species (a total of 74%). In contrast, this total proportion in the Manchurian xerophytic flora (broadleaf forest with oak) does not exceed 19%, in the absence of boreal species. The dominance region is represented by boreal–nemoral species (62% probability), and the fuzzy part of the niche, by equal proportions of boreal + nemoral complex and nemoral–boreal species. The zonal structure of buffer floristic sheds some light on the mechanism of their formation (Fig. 3). In the buffer Manchurian–Okhotian flora, boreal– nemoral herbaceous species are prevalent (47% probability), although there also are purely boreal species (up to 20%). The latter are a heritage from the basic Okhotian flora, where their proportion reaches 100%. Since boreal–nemoral species are absent in the Manchurian mesophytic flora, it appears that the buffer MO phratry has originated due to the mixing of the Manchurian mesophytic (rather than xerophytic) flora with the Okhotian flora. The mixing of the same Manchurian mesophytic flora with the Angaridian flora has given rise to the buffer MA phratry. This fol2017
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B+N
Zonal groups B BN
NB
An
Mx
B Zonal groups
A1B1 A4B0 Elevation–aspect zonation
Floristic phratries Okh Mm MA MO
A1B2
NB B+N BN
A2B1
K(A; B) = 0.167 A2B2 A3B1 A3B2 K(A; B) = 0.196
Fig. 3. Ecological niches of zonal forest groups in the space of elevation–aspect zonation and of floristic phratries in the space of zonal geographic groups: (B) boreal, (NB) nemoral–boreal, (B + N) boreal and nemoral (in equal degrees), and (BN) boreal– nemoral. For other designations, see the text and Fig. 1.
lows from the dominant position of boreal + nemoral species in both Mm flora (40% probability) and MA flora (54%) and from a considerable presence of boreal species in the Mm flora (34%), with their proportion of the An flora being 73%. Thus, both buffer phratries, Manchurian–Okhotian and Manchurian–Angaridian, have been formed on the basis of the same Manchurian mesophytic phratry. Compared to the xerophytic variant of the Manchurian flora, it proved to be much closer to other basic phratries (MO and An) with respect to the factor of biologically equivalent habitats. Functional Organization of Forest Ecosystems Characterization of forest ecosystem functioning was based on discrete parameters of autotrophic biogenesis in Glazovskaya’s (1981) terms, i.e., the stocks of different components of living phytomass and indices of primary production. These are the output parameters of the biogeochemical turnover (Bazilevich and Rodin, 1971) that characterize the efficiency of abiotic resource utilization by phytocoenoses (Utekhin, 1977). Sharp contrasts between the structural patterns of forests in the Amur boreal ecotone (see above) also manifest themselves in the stocks of living phytomass components (Table 1), while annual production indices in different groups of forests are relatively similar (Table 2). This appears to be one of the striking eco-
logical consequences of unique forest-forming processes in the sub-Pacific (Kolesnikov, 1956). Judging from ecological dominants and taxonomic norms, the highest stocks of wood and aboveground living phytomass are characteristic of forests on slopes with high or moderate insolation and on f lat ridgetops. This is where the fuzzy parts of ecological niches of different forest type groups converge to each other. In particular, these are Korean pine–broadleaf, fir–broadleaf, and nemoral fir–spruce forests of the same buffer MO phratry. Dominant BS stocks over 265 t/ha occur in 73% of cases, and the probability of ВС > 320 t/ha is 63%. Forests on well-insolated slopes are also distinguished by the largest amounts of understory and undergrowth. The shaded slopes of low mountains are occupied mainly by fir–spruce and spruce–broadleaf forests, where the stocks of wood and herbaceous phytomass are 1.5 times lowed because of insufficient hat supply in summer. The stocks of aboveground and total phytomass are also reduced (Table 1). The green phytomass of the understory and undergrowth comprises no more than 3–7%. This is evidence that heat supply is the limiting factor of forest productivity in the Amur boreal ecotone. Low stocks of living forest phytomass are also characteristic of foothills and small river valleys, where lowland cedar forests of the Mm flora and birch forest and larch mari of the Angaridian flora occur along with fir–spruce and larch forests. Reduction in wood
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BUFFER BOREAL FORESTS Table 1. Taxonomic norms of phytomass in forests of different floristic phratries, t/ha Phytomass (see the text) BW BS BB BG BV BL BC
mountain Ayan fir–spruce forests and lowland larch mari (PS = 0.4–1.0) → broadleaf forests with oak of the Manchurian xerophilic flora (PS = 1.0–3.2) → spruce–broadleaf and cedar–broadleaf forests (PS = 3.3–4.4) → larch forests of the buffer Manchurian– Angaridian phratry (PS ≤ 6.5). With respect to dominants of total phytomass production (t/ha per year), forest communities form the following series: Okhotian fir–spruce forests (≤5.0) → Manchurian mesophilic cedar–broadleaf forests (6.5–9.0) → Manchurian– Okhotian larch forests (9.0–11.0) → Manchurian– Okhotian spruce–broadleaf forests and Manchurian xerophilic broadleaf forests with oak (11.0–13.8).
Floristic phratries Mm
Mx
МО
Okh
95.10 110.13 1.33 0.66 6.12 121.06 140.30
122.60 138.35 2.42 0.58 9.24 153.02 197.36
251.18 279.21 2.14 2.29 11.27 284.78 330.04
МА
17
An
131.75 79.10 70.70 139.98 92.10 67.61 1.31 0.68 1.56 2.34 0.47 1.51 10.85 4.74 3.31 136.88 91.00 81.96 170.42 124.68 96.94
Almost all forest type groups and floristic phratries fit into a narrow range of relatively low values of the integrated parameters of autotrophic biogenesis (Table 2). The minimum annual turnover of aboveground phytomass is characteristic of Ayan fir– spruce forests and larch forests growing in transitional microlandscapes, mainly on shaded slopes. Similar to them are mountain and plain spruce–broadleaf forests of the buffer MO flora. A wide range of higher values of the turnover coefficient have been calculated for Manchurian broadleaf and cedar–broadleaf forests.
phytomass is especially distinct. Thee habitats are well warmed in summer, and phytomass production is limited not by summer heat supply but rather by excess soil moistening and deep freezing in winter. An intermediate position between the polar-opposite phytomass stocks in the above optimal and pessimal habitats is occupied by upland natural complexes of foothill plains, where broadleaf, cedar–broadleaf, and spruce–broadleaf forests of the Manchurian and Manchurian–Okhotian floras are dominant. Relatively low stocks of wood and total skeletal phytomass (about 35–40% of probable BW ≤ 90 t/ha) are indicative of imperfect bioclimatic conditions for tree vegetation in high-plain habitats. In Utekhin’s (1977) terms, these forest communities acquire a certain adaptive structure that counterbalances reduction in the phytomass stocks of tree stands. This adaptation manifests itself in increased productivity of the ground vegetation layer, compared to pessimal habitats (up to and over 0.95–2.80 t/ha), and in the development of the shrub layer and consequent enhancement of its productivity. Models of partial relationships allowed the arrangement of forest communities into series in order of increasing productivity. The series based on annual skeletal phytomass production (t/ha) is as follows:
The results of analyzing the descending (detrital) branch of biological turnover are as follows. The least productive Ayan fir–spruce of the Okhotian phratry, which grow in sites with low temperatures and soil overmoistening, are characterized by a low rate of organic matter decomposition and slow evolution of infiltration organic matter. Processes of forest litter mineralization are likewise retarded in larch forests, where the thickness of humus horizon (more correctly, mixed A0A1 horizon) reaches the maximum values (Table 3). This is evidence for a low rate of biological turnover. Spruce–broadleaf forests of the buffer MO phratry stand out against this contrasting background of its detrital branch. They produce the maximum amounts of green phytomass, but the rate of litter decomposition in these forests is lower than the annual rate of plant debris input, since soil temperatures are relatively low.
Table 2. Taxonomic norms of productivity (t/ha per year), integrated parameters of autotrophic biogenesis, and the average age of forest-forming tree species in forests of different floristic phratries and forest type groups Floristic phratries
Forest type groups
Parameter PS PG PV PC EEP CR Age, years
Mm
Mx
МО
Okh
МА
An
Bl
CB
SB
FS
La
2.56 – 5.17 7.68 0.050 0.036 101
2.84 – 6.44 9.45 0.051 0.040 83
2.82 – 5.63 9.08 0.031 0.022 133
2.01 – 3.50 5.61 0.034 0.021 116
4.01 – 4.50 9.34 0.092 0.039 39
2.38 – 3.26 5.62 0.069 0.084 64
2.77 0.71 5.25 8.07
2.58 0.49 6.36 9.52
2.51 3.37 5.36 8.10
2.39 0.92 2.93 6.02
4.16 1.28 4.02 8.57
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Table 3. Taxonomic norms of soil morphological parameters in different forest type groups Forest type groups Parameter Bl
CB
SB
FS
La
FB
Thickness of horizon А0
5
6
10
6
6
8
Thickness of horizon А1
7
8
15
12
15
14
Thickness of horizon А2
17
22
29
15
29
2
Thickness of horizon В
39
43
35
17
34
40
А0/A1 ratio
0.71
0.90
0.67
0.50
0.40
0.57
(А0 + A1)/B ratio
0.32
0.33
0.71
1.12
0.62
0.55
The proportion of necromass that is mineralized and utilized for plant nutrition is also reduced in Manchurian–Okhotian forests. The synthesis of humic substances in their soils is enhanced, resulting in the increasing thickness of humus horizon. Consequently, the entire humus profile reaches the maximum depth (Table 4) and even extends to the illuvial horizon B where the processes of illuviation, pseudopodzolization, and pedogenic weathering are especially active. Therefore, it may be considered that, in the series of forest formation considered above, the soils of Manchurian–Okhotian forests are the most mature, i.e., the closest to the equilibrium (climax) state. CONCLUSIONS Experience in empirical–statistical modeling of forest ecosystem structure and functioning in the Lower Amur sub-Pacific provides a basis for certain conclusions that accentuate the evolutionary character of the forest-forming process in the region, which has been based on the floristic richness of forest phytocoenoses and the diversity of their successional changes. In particular, this concerns the formation of buffer for-
est communities characteristic of ecotonal systems, such as forests of the Manchurian–Okhotian phratry derived from the two basic phratries, Manchurian mesophilic and Okhotian ones. Manchurian–Okhotian spruce–broadleaf and nemoral fir–spruce forests are distinguished from those of the basic and other phratries primarily by a more strongly developed tree layer of high quality class (Fig. 2c), but they retain the high floristic diversity of tree stand, undergrowth and ground vegetation characteristic of Manchurian forests. These buffer forest formations also have the highest parameters of living organic matter production, including skeletal, green, and total phytomass. The rate of necromass decomposition is retarded, and the forest litter reaches the maximum thickness. However, the decrease in organic matter mineralization is accompanied by intensification of the synthesis of humic substances, and the thicknesses of the humus soil horizon and humus profile also reach high values (Table 4). Finally, the processes of illuviation, pseudopodzolization, and pedogenic weathering are especially active, and therefore the soils of these forests most closely approach the evolutionary climax. Thus, what has taken place in the study region is not merely transzonal intermixing of the Manchurian mesophilic and Okhotian floras but rather the formation of buffer forest ecosystems with a better developed structure and more diverse functioning, compared to the ecosystems of the basic floras. Forests of the Manchurian–Okhotian phratry have most closely approached the evolutionary climax in Krishtofovich’s (1946) terms, i.e., the ultimate, highest stage of vegetation development under given zonal–regional climatic conditions. This stage is reached due to migration processes in the plant cover (Vasil’ev, 1946), i.e., those driving forces of its evolution that provide for the formation of buffer forest communities. This confirms the previously advanced concepts of the Pacific ecotone of Northern Eurasia as a focus of evolutionary processes in the continental biosphere (Yurtsev, 1974; Kolomyts, 1987; Panfilov, 2005). In contrast, the formation of the Manchurian– Angaridian buffer phratry has not been accompanied
Table 4. Standardized partial coefficients of interrelation between the thickness of soil humus profile and floristic phratries and forest type groups (boldfaced values indicate dominant zones of ecological niches) Thickness of humus profile, cm 6–10 10–16 16–22 22–31 31–58
Floristic phratries (C(A,B) = 0.093)
Forest type groups (C(A,B) = 0.075)
Mx
Mm
Okh
МА
An
МО
Bl
CB
FS
La
0.45 0.24
0.18 0.57 0.26
0.20 0.16 0.43 0.22
0.13
0.13 0.10 0.09 0.43 0.27
0.14 0.22 0.20 0.16 0.28
0.23 0.37 0.17
0.22 0.35 0.08 0.13 0.22
0.29 0.12 0.42 0.17
0.13 0.10 0.09 0.43 0.25
0.30
0.29 0.31 0.27
0.23
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SB 0.18
0.39 0.61
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by such a structural and functional effect. With respect to all the test parameters, its communities are intermediate between forests of the basic phratries, and only the measures of floristic diversity of the tree stand and undergrowth are similar to those in Manchurian xerophilic forests. The data presented above show that the latitudinal (north ↔ south) zonal transgression of tree and shrub species and phytocoenoses as a whole in the continental marginal sector of the Eurasian Pacific megaecotone has been manifested much more distinctly and produced a far stronger effect on the forest cover of the region, compared to the longitudinal (east ↔ west) transgression. The forest-forming process of the first group has obviously prevailed over that of the second group, which could take place only on condition of long-term, sustainable retention of oceanic features in the regional climatic system of the Amur sub-Pacific. ACKNOWLEDGMENTS This study was supported by the Russian Foundation for Basic Research, project no. 14-05-00032-a. REFERENCES Armand, A.D., Sharp and gradual timberlines as a result of species interaction, in Landscape Boundaries: Consequences for Biotic Diversity and Ecological Flows, New York: SpringerVerlag, 1992, pp. 360–378. Bazilevich, N.I. and Rodin, L.E., Productivity and element turnover in natural and cultivated phytocenoses (data on the Soviet Union), in Biologicheskaya produktivnost’ i krugovorot khimicheskikh elementov v rastititel’nykh soobshchestvakh (Biological Productivity and Turnover of Chemical Elements in Plant Communities), Moscow: Nauka, 1971, pp. 5–32. Bazilevich, N.I., Grebenshchikov, O.S., and Tishkov, A.A., Geograficheskie zakonomernosti struktury i funktsionirovaniya ekosistem (Geographic Patterns of Ecosystem Structure and Functioning), Moscow: Nauka, 1986. Bobrov, E.G., Some features of the recent history of flora and vegetation in the southern Far East, Bot. Zh., 1980, vol. 65, no. 2, pp. 172–183. Brigham-Grette, J., New perspectives on Beringian Quaternary paleogeography, stratigraphy, and glacial history, Quat. Sci. Rev., 2000, vol. 20, pp. 15–24. Duchaufour, Ph., Precis de pedologie. L’Evolution des soil, Paris, 1968. Ekologo-fitotsenoticheskie kompleksy Aziatskoi Rossii (opyt kartografirovaniya) (Ecophytocenotic Complexes of Asian Russia: Experience in Mapping), Sochava, V.B., Ed., Irkutsk: Inst. Geogr. Sibiri i Dal’nego Vostoka, Sib. Otd. Akad. Nauk SSSR, 1977. Ekotony v biosfere (Ecotones in the Biosphere), Zaletaev, V.S., Ed., Moscow: RASKhN, 1997. Gartsman, I.N., Problems of geographic zonality and discontinuity of hydrometeorological fields under conditions of mountain monsoon climate, Tr. DVNIGMI, 1971, no. 35, pp. 3–31. RUSSIAN JOURNAL OF ECOLOGY
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Translated by N. Gorgolyuk
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