The Development of Grassland Communities

The area around the village of Golovnino at the southern end of Kunashir Island is a region where grassland communities have developed. Herb-Sasa (west of the village of Golovnino), Artemisia-Anaphalis-herb-Sasa (Paltusov Cape) and Sasa-Sieversia-Achillea-Carex-herb assemblages (Ivanovskii Cape) are identified on terrace like surfaces [14]. The area has forest vegetation that dates to 2000 14C yr BP. Today the area is covered in grasslands [19]. South Temperate broad-leaved forests arose at the beginning of the Late Holocene (3790±70 BP, GIN-8443) in whose composition, given the dominance of Quercus, one would have found such thermophylic species as Juglans, Ulmus, Corylus, as well as Carpinus and Fagus that today are restricted to Hokkaido Island. V. M. Urusov holds that the three latter species have been absent from the Kuril Islands since the second half of the Pleistocene [48]. Climatic conditions were warmer than today and the average annual temperature was 2°C degrees higher [19]. With the cooling in the first half of the Late Holocene (2730±60 BP, GIN-8442), birch groves quickly colonized the area and many thermophylic species disappeared from the composition of oak forests.

West of the outlet of the Golovnina River, on a 12-15 meter high terrace like surface (section 5395), a profile of meadow-sod soil was studied at a polygenic soil profile that exhibits weak signs of podzolization. The top of the profile is represented by meadow soddy soil. Two buried soils appear in the lower portion of the profile. Contemporary vegetation is a herbaceous-mixed grass meadow with Sasa. Cover is 100%; height up to 50 cm. The pollen spectra from the soil cover demonstrate that bush-herbaceous groups covered this area in the second half of the Late Holocene. Pollen spectra from the buried soils fix a sharp drop in temperature: pollen composition is dominated by pollen similar in morphology to the Betula sect. Nanae pollen (Figure 2).

Figure 2. Percentage pollen diagram for soil profiles near Golovnino Village (section 5395) and near Lagunnoe Lake (section 2396), Kunashir Island.

Birch bushes are not observed in the south of the islands of the Kuril chain [4, 49]. It could be that the pollen found belongs to Betula tatevakiana, an endemic encountered on Hokkaido Island in marshes in the area of Nemuro Peninsula. The pollen might be a product of B. fruticosa, a species broadly distributed on the Japanese islands.

Bush-herbaceous groups developed on loamy substrate in supersaturated conditions, which is demonstrated by the high content of Cyperaceae pollen (up to 50%) and by the presence of Bryales that is gradual disappearing from the spectra. Sedge and sedge-grass associations are the most widely developed. Alnaster, which is broadly distributed in the contemporary vegetation groups on the coastline of southern Kunashir Island, begins to dominate in the upper portion of the profile. The large volume of Quercus pollen demonstrates that, apparently, this portion of the profile was formed in the lesser Holocene optimum, toward the end of the final two millenniums (14C-data 630±60 BP, GIN-8955, probably renewed).

The pollen spectra obtained from the surface horizon of soil reflect a grassland community with a somewhat different composition. These are mixed herbaceous meadows that have a significant portion of Artemisia, Cichoriaceae pollen and that have developed in good drainage conditions. The horizon is formed of well sorted humus sand whose accumulation is associated with the onset of aeolian processes in the Little Ice Age. Aeolian cover from this period is especially well distributed on the south of the Sea of Okhotsk coastline of Kunashir Island [20, 36]. The fern Coniogramme, which is usually found in the cover of valley forests, is among the spores that are encountered.

Although grassland communities in this portion of the island have existed for a relatively long time (at least since 2500 14C yr BP), the rise of contemporary grasslands in the renewed, highly productive substratum occurred around 300 14C yr BP. Species remaining from Japanese gardens also make up part of the composition. This portion of the island is located in a zone influenced by volcanic ash from Hokkaido Island; this ash has enriched the soil with nutrients.

Grasslands on the Sea of Okhotsk side of the Yuzhno-Kurilskii Isthmus have existed since at least the lesser Holocene optimum (Figure 2). A grassland soil profile (section 2396) was studied. Three buried soils were uncovered in the lower portion of the profile. Mixed grass meadows are now present. Fossil soil appears at the base of the profile; it is dark loam that formed in warm climatic conditions between the end of the Middle and the beginning of the Late Holocene (14C-data 4090±70 BP, GIN-9624). Rare coniferous pollen, grasses and spores are encountered in the fossil soil. Mixed grass meadows were distributed at this site in the second half of the Late Holocene; these were characterized by tall, diverse grass taxa (Figure 2). The slopes of Fregat and Otdelnaya Mountains were covered with dark coniferous, spruce-fir forests with pockets of birch. Remainders of South Temperate forests on the shore of Lagunnoe Lake date from the Holocene optimum. A thick soil profile formed in the Late Holocene with the addition of volcanic ash. The phase of active volcanic ash depositions on Kunashir Island is dated to 1700-1300 14C yr BP [19, 20]. Sand buildup improved drainage of the substratum and this enabled such species as Poaceae, Asteraceae, Artemisia, Cichorium, Caryophyllaceae to develop in dry habitats. Pollen from these species increased from 43% to 75%. The pollen spectra from a thin surface soil that is covered by a layer of finely sorted volcanic ash demonstrate that following the Little Ice Age the floristic composition of grassland communities did not undergo significant modification.

Grassland communities in the north of Kunashir Island, the Kruglovskii Isthmus and Lovtsov Peninsula are located in a zone affected by volcanic ash from Tyatya Volcano. These volcanic ash depositions exerted an especially strong influence on grassland communities on that part of the isthmus where volcanic ash fall was heavy. Volcanic ash has at time completely covered the soil. A shallow strait that was blocked from the Pacific Ocean by a barrier wall probably existed in the Middle Holocene, at the site where the isthmus was located in the end of Middle Holocene - beginning Late Holocene. The low isthmus located at this site was repeatedly closed by thick layers of tephra, the result of which is that the tephra grew to 20 meters in height. The radiocarbon age of fossil soils exposed in the creek valley that runs into Dlinnoe Lake demonstrates that the last, rather heavy eruptions of Tyatya Volcano occurred around 3500 and 2000 14C yr. BP (14C-data 3570±90 BP, GIN-9646, 1780±40 BP, GIN -9645). Pollen spectra obtained from fossil soils and that are mixed with continental depositions reflect the broad development of mixed grass meadows on the isthmus (content of grass pollen is 28-29%), this, at least in the beginning of the Holocene. The vegetation of dry (Artemisia, Asteraceae, Caryophyllaceae) and wet (Thalictrum, Apiaceae, Sanguisorba, Ranunculaceae, Polygonum, Rumex, Primulaceae) habitats contain grass pollen. The percentage of pollen associations for dry meadows found in the surface soil atop tephra remains below 13%. The richness of the species composition of the grassland on the isthmus might be explained by the repeated renewal of the soil profile and by the large volume of nutrients entering with the tephra.

An analysis of fossil soils in dunes on the Sea of Okhotsk side of the Lovtsov Peninsula dates meadow vegetation to the Little Ice Age portion of the Holocene optimum (14C-data from fossil soils in dunes 630±140 BP, GIN-9643, 270±80 BP, GIN-9642). In the pollen spectra, along with grass associations found in well drained areas (Asteraceae - up to 38%, Artemisia - up to 30%, Poaceae - up to 13%, Cichorium, Sanguisorba), the pollen spectra show that hydrophilous Apiaceae, Cyperaceae, Thalictrum and by other representatives of the family Ranunculaceae, Polygonum, Liliaceae, Iridaceae, Primulaceae, Polemoniacea played a large roll (up to 45%).

Development of stone birch forests with Pinus pumila and grassland communities on Iturup Island, features characteristic of areas north of Vetrovoi Isthmus occurred over an extended period of time. An important floristic boundary cuts across this region [3, 42, 48]. Studies of fossil soils in volcanic ash cover that are located in Parusnaya Bay at an elevation of 40 meters show that grassy communities were a sufficiently stable component of the landscape in the second half of the Late Holocene. The age of aeolian cover is estimated to correspond to the second or third generation volcanic aeolian sands for the Southern Kuils, whose formation took place during a cooling period between 1700-1300 BP and in the Little Ice Age [19, 36]. Pollen spectra from fossil soils at the base of the profile (Figure 3) demonstrate the broad development of alder forests on drained territory of Vetrovoi Isthmus in the middle of the Late Holocene. Arboreal pollen from Poaceae, and Poaceae-.Artemisia assemblages in dry habitats that are mixed with forb-mix-grass associations dominate the upper horizons of the fossil soils. The pollen spectra from a contemporary soil profile demonstrate the distribution of Pinus pumila, whose grass pollen composition responds to mix grass meadow communities. Representatives of the genus Botryhium are noted among the ferns.

Figure 3. Percentage pollen diagram of eolian-paleosol cover on the coast of Parusnaya Inlet, Iturup Island (section 1198).

The abundance and large species diversity of mosses on Itirup Island contrasts to the grassland communities in the south of Kunashir Island.

The herbaceous communities on marshy, accumulative plains found along the coastlines also vary in age. The accumulative forms at the head of Yuzhno-Kurilskii Bay and in the lower drainage of the Rogachevka and Saratovka Rivers are the oldest examples on Kunashir Island. Their formation began in the second half of the Middle Holocene, which is demonstrated by the presence of dune ridges that were formed during the regression during the cooling period that occurred around 4500-4700 years ago and that now block low, marine terraces [20]. Herbaceous communities on the marshy plain in the Serebryanka River valley have a unique floristic composition and are distinguished by a high variety of species. The rich vegetation is possibly a result of habitat variety in areas with different saturation regimes, given the underlying substratum, and is related to the relatively long development period for vegetation cover in the alternating climatic conditions characteristic of the Middle and Late Holocene. Storm depositions in the inner portion of the isthmus are covered in dark coniferous forest that displaced South Temperate forests during the Holocene optimum. It is possible that some species in modern herbaceous communities are inherited from the Holocene optimum.

A low, accumulative valley in the lower drainage of the Saratovka and Rogachevka Rivers was formed at the end of the Middle Holocene. A ridge of dunes that stretches along the shore and that separates a low, marine terrace (section 896) began to form during the cooling at the cusp of the Middle and Late Holocene, this demonstrated by radiocarbon dating of the fossil and illuvial-humus soils (3300±200 BP, GIN-9639, 2650±150 BP, GIN-9638). Herbaceous communities at this site have existed since at least the beginning of the Late Holocene and have been in combination with dark coniferous forests that have birch and broad-leaved species covering surrounding slopes (Ulmus, Quercus, Juglans, Carpinus, Tilia). The pollen composition of herbaceous taxa reflects the development of mixed grass associations (Figure 4). A significant variety of mosses is found, which contrasts to grassland communities at the southern end of the island. The presence of Potamogeton pollen shows that lakes in the deflation basin have existed for at least 3000 years. The formation of soil with a loamy composition and that contains volcanic ash from the Tyatya Volcano, and that serves as a water-resistant horizon, is probably the reason for their formation amidst the dunes. The spread of grass pollen and spores across the profile shows that on the whole the structure of herbaceous communities in the Late Holocene did not change significantly.

The development of marshy-herbaceous communities occurred in younger, low marine terraces in the southeast of Kunashir Island. Accumulative deposits began to form around 3000 years ago, and at Veselovskii Spit - around 2000 years ago [19, 16]. Soil cover was studied on a terrace two meters above sea level (section 4196), one kilometer to the north of the outlet of Belozerskaya River. The profile revealed meadow sod and the buried, polygentic profile. The soil profile includes three buried soil horizons. Contemporary vegetation is a forbic mix-grass meadow. Middle Holocene age fossil soil appears at the base of the profile (C-data 5630±50 BP, GIN-9620). Pollen spectra from this soil horizon are primarily composed of grass pollen that belong to grass communities (Figure 5). The question of the preservation of woody pollen is, however, not entirely clear. Spores and pollen are not found at the top of this horizon. Fossil soil formed at the beginning of the Late Holocene is layered higher.

Figure 4. Percentage pollen diagrams for paleosols from dunes near Rogachevka and Saratovka River mouths (section 898), and soil profile near Otradnoe Village (section 3895), Kunashir Island.
Figure 5. Percentage pollen diagram for soil profile on 2 m terrace, located in 1 km northward Belozerskaya River, Kunashir Island (section 4196).

The structure of the pollen spectra demonstrates that on the coast, South Temperate broad-leaved forests existed at the south end of the island until the beginning of the Late Holocene. Radiocarbon dating obtained for this horizon is for a period from 3280±70 BP, GIN-9619 until 2440±120 BP, GIN-9617 and the sample may be somewhat renewed. The soil includes three volcanic ash seams of rhyolitic and dacitic composition that correspond to volcanic eruptions on Hokkaido Island. Such exotic species as Podocarpus, Taxodiaceae, which along with Fagus and Pterocarya pollen may have been brought in from Japanese Islands, were discovered in the Kuril Islands. Redeposition of this pollen is hardly likely since the saturation of the pollen deposition of the Golovnin River glomerate is extremely low [31]. Such an interpretation suggests that predominant southerly winds (Okhotsk-Aleut atmospheric circulation type, according the A. M. Polyakova [30]) were the most typical for the spring and summer seasons in the warm phase of the Holocene. Abundant Potamogeton pollen (up to 20%) demonstrates the proximity of nearby lake bodies. Accumulative deposits probably began to form on the southeast portion of Kunashir Island at this time. These were a result of a series of ocean depositions that led to the establishment of marshy areas and numerous small lakes.

The cooling in the second half of the Late Holocene marks a sharp increase in the percent of Betula sect. Nanae and Alnaster pollen. Grassland communities expanded and the percentage of grass pollen in the pollen spectra grew significantly. Ferns, including the genus Osmunda, played a large role in grassland associations. The later development of grassland communities on expanding, sandy accumulative deposits is a feature of the lesser Holocene optimum. Aeolian material improved drainage and Artemisia (up to 40%) and the forbs (more than 50%) played a large role in grassland communities, despite a general decline in the variety of grassland taxa. It is possible that Sasa-mixed herbaceous communities on the slopes of Golovnin Volcano played the determining role in the spectrum represented in the surface soil horizon. The woody vegetation at the south of Kunashir Island is dark coniferous and birch forests with small oak groves.

The age of the lowland Sernovodskii Isthmus is from the Late Holocene. The most ancient portion of the isthmus, formed at the end of the Middle Holocene, is located on the Sea of Okhotsk side of the island and is cut off by dunes formed between the Middle and Late Holocene. Marshy lowlands on the Pacific Ocean side of the isthmus formed in the Late Holocene (14C-data 2220±80 BP, GIN-7895). In the first half of the Late Holocene this portion of the island was covered in mixed coniferous broad-leafed forest [19]. Given supersaturated conditions at the lowland's initial stage of formation, sphagnum moss and alder associations expanded broadly; in the Middle to Late Holocene they were quickly replaced by mixed herbaceous communities that included ferns and forbs. The upper portion of the peatlands were heavy in sand that probably arose from aeolian materials and that show the presence of volcanic ash from Mashu Volcano on Hokkaido Island.

Grasslands on the Vetrovoi Isthmus of Iturup Island belong to relatively young formations. Despite the fact that a strait existed on the isthmus in the inter-glacial period, the surface deposits of the isthmus are of a much younger age. The rise in sea level in the Middle and Late Holocene transgression period [34, 35] did not entirely submerge the isthmus. Dunes, with a series of thin fossil soils on the Sea of Okhotsk side of Vetrovoi Isthmus, contrast to second generation dunes on Kunashir Island [20, 36]. A ridge of dunes along the Pacific Ocean side of the isthmus that arose in the Little Ice Age characteristically lack fossil soils. The surface of the isthmus is universally covered in loom more than 2 meters thick and that is saturated with angular fragments of vulcanite that could possibly have a lahar origin. The age of these deposits is around 1280±110 BP, GIN-10494. Grassland vegetation began to colonize the isthmus during the cooling period that, along with unfavorable strong wind conditions, led to the formation of pseudo-alpine communities. The vegetation on the isthmus has been subjected to serious anthropogenic impact: a landing strip, warehouses and a series of villages were located here, leading to the introduction of weed and exotic species into the association. Grasslands on the coastal lowland near Kurilsk of Iturup Island have natural origin too. These grassland landscape existed last 2000 yr. PB [35].

There are, along with natural climate driven grasslands on the islands, grassland communities that formed as a result of timber harvest that was conducted until the mid 20th century. Intensive harvest took place on the slopes of Mendeleev Volcano [22, 40]. The Sasa associations containing thin birch groves on the slopes of Golovnin Volcano are probably also a result of timber harvest. The recent formation of these grassland communities is clearly shown in the pollen spectra for these soil profiles. The grasslands in the area of Otradnoe Peninsula on Kunashir Island may also have their origin in human activity. An abundance of grass pollen (40%) is found only in the surface layer of the soil (Figure 5). During the less Holocene optimum (14C-data 1090±40 BP, GIN-8952) dark coniferous fir -spruce forests with fern understory were spread along this area. Spruce forest also covered dune fields in Golovnin Bay. Spruce roots have been discovered in-situ in the first fossil soil layer.

The grasslands on the shoreline of Kuibyshevsky Bay and the isthmus of the same name that colonized areas where larch and birch-larch forests were harvested on Iturup Island are a result of anthropogenic impact. A high content of grass pollen (37-45%) is noted for this region only in the pollen spectra for fossil soils in dunes located near Maloe Lake. Radiocarbon dating of the age of the upper soil horizon (650±40 BP, GIN-8951) shows that a series of fossil soils formed at the end of the Late Holocene. The composition of the grasses corresponds to the formation of Poaceae-Artemisia-mixed herb groups of Poaceae-Artemisia-herb assemblages on dune ridges and moist Carex-Poaceae associations with Sphagnum, Ranunculaceae in marshy areas of the deflation basin. Forest type spectra whose grass pollen content does not exceed 1-3% are characteristic for soils in the central portion of the isthmus. The predominance of wood and shrub pollen species is characteristic of fossil soils in the dune field on the coastline of Kasatka Bay and for the soil profile at 14-16 meters on a terrace like surface in the area of Burevestnik Peninsula. It is interesting to note that the percent of Pinus s/g Haploxylon pollen increases sharply only in the upper portions of soil profiles. Apparently, as cooling occurred, a series of volcanic ash deposit in the 1600-500 14C yr BP period led to a much broader distribution of Pinus pumila on the Pacific Ocean coastline of the island. The volcanic ash has a primarily basaltic and andesite-basaltic content. Its origin is probably the volcanoes in the Ivan Groznyi group. The regular appearance of Pinus s/g Diploxylon pollen in the pollen spectra from the soil profile near Burevestnik Peninsula confirms the hypothesis of V. M. Urusov about the existence of a refugium Pinus parviflora in the region of Kuibyshevskii isthmus in the Holocene [48].

A polygenic soil profile (Figure 6) has been studied in the western portion of Zeleniy Island on terrace like surface at an elevation of 8-9 meters. The area has mixed grass meadows. The contemporary soil is sod-humic on buried layered ash soil. Two fossil profiles appear at the foundation.

Figure 6. Percentage pollen diagram for soil profiles of Zeleniy Island (section 15903).

From the upper portion of the first fossil soil 14C-data 1640±60 BP, GIN-12557 have been obtained, and from the base of the profile - 14C-data 6130±130 BP, GIN-12558. Grass pollen (up to 56%) and spores (up to 62%) dominate the pollen spectra. The pollen content is diverse and is dominated by Asteraceae (up to 68.6%), Artemisia (up to 59%), Sanguisorba (up to 33%), Poaceae (up to 12%) that reflects development of mix grass meadows with rich species diversity. Polypodiaceae spores dominate. There is abundant Lycopodium. Soil under grassland on Tanfiliev Island has similar profile with Middle Holocene paleosol (14C-data 4240±120 BP, GIN-13461). The pollen spectra show that grassland communities on the island existed at least from the Middle Holocene, and possibly throughout the enter Holocene [33, 37]. Similar data were obtained for Nemuro Peninsula (Hokkaido Island) [15, 24] and Yururi Island near Eastern Hokkaido [25].

Pollen spectra for peatland profiles on Shikotan Island show that forests were well developed in the Middle and Late Holocene [33]. Forests began to decrease at the end of the Late Holocene, possibly in response to ocean impacts in a context of general cooling. Forests were preserved in limited areas, on the western side of the island that were protected by ancient volcanoes from the cooling effects of the Pacific Ocean. Fires and timber harvest may also be reasons for the destruction of small forest areas. The Sasa grasslands with dense sod hamper to progress of forest vegetation restoration. Forest vegetation begins to occupy the places with broken soil cover (old roads, fields).

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