Geography and Natural Resources 30 (2009) 355–358
Changes in the cenoflora of dark-coniferous forests of the Northern Baikal region under current climate warming O. A. Anenkhonov * Institute of General and Experimental Biology SB RAS, Ulan-Ude Received 14 February 2008
Abstract Calculations of the activity indices and species richness of belt-zonal elements of the flora of dark-coniferous forests have been done in order to reveal the presence of climatogenic changes. It was found that there is an increase in activity of the species of the dark-coniferous belt-zonal group peculiar to these forests. It is suggested that this phenomenon is associated with current climate warming. It is concluded that with increasing climate warming and with the persisting tendency for its humidification, in the lower belt of the mountains there will be taking place an enhancement in the landscape role of dark-coniferous forests through succession from light-coniferous forests to them. Keywords: flora, dark-coniferous forests, climatogenic successions, climate warming, Baikal region.
Formulation of the problem
Description of the study area
In most regions across the globe, the currently recorded climate warming leads to changes in composition, structure and functioning of plant ecosystems; this is particularly true for the temperate, Subarctic and Arctic zones [1]. Some of the previously made predictions as to the magnitude of temperature rise [2]and, accordingly, the displacement of the boundaries of natural zones by the year 2000 [3] have lacked support from any known factual evidence. Nevertheless, there are sufficiently dramatic changes in ecosystems which are associated with climate warming, such as the displacement of phenological phenomena [4], and the expansion of thermophilic plant species [5, 6]. On the other hand, many changes have a latent character which manifests itself only through a detailed analysis of the parameters of ecosystems. Specifically, they include the directional changes in floristic composition of natural vegetation cover providing evidence of a transformation of ecosystems. As shown in our earlier publication [7], these processes reflect changes in the habitat conditions of light-coniferous forests of the Northern Baikal region toward a warming. This paper is a continuation of the studies into the tendencies for changes in vegetation composition associated with changes of climate.
In some zones of the Northern Baikal region, dark-coniferous forests have a relatively high landscape significance. In the study areas: the Upper-Angara depression, on the western and eastern macroslopes of the southern part of the Barguzinsky Range, and on the northeastern macroslope of the Svyatoi Nos Peninsula, dark-coniferous forests occur predominantly in areas of sporadic permafrost, permafrost islands and discontinuous permafrost. River valleys are the most characteristic habitats of dark-coniferous forests in the region. On the mountain slopes, watersheds and in the upper part of the forest zone, formation of these forests occurs only under the conditions of a humid climate which is characterized by the following parameters: average annual precipitation 500–1000 mm/year, snow cover thickness 70–140 cm, the sum of active above-zero temperatures 1400–1500 0С, and the January and July temperature averaged over many years varies from –20 to –24 0С and from 12 to 16 0С, respectively. The average annual temperature lies between 0 and –0.5 0С [8–11]. In accordance with the botanical-geographical regionalization of the Lake Baikal watershed basin [8], the areas used in our investigation refer to the Pribaikalskaya province of high-mountain dark-coniferous and light-coniferous forests and golets vegetation and, within its confines, to two districts. The Upper-Angara depression belongs to the Angara district of dark-coniferous and light-coniferous forests, open
* Corresponding author. E-mail address:
[email protected] (O. A. Anenkhonov)
Copyright © 2009 IG SB, Siberian Branch of RAS. Published by Elsevier B.V. All rights reserved doi:10.1016/j.gnr.2009.11.009
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O. A. Anenkhonov / Geography and Natural Resources 30 (2009) 355–358
woodlands and golets vegetation; the areas of the Barguzinsky Range and of the Svyatoi Nos Peninsula refer to the Chivyrkui-Ina district of dark-coniferous and light-coniferous forests and golets vegetation. Materials and methods The analysis of the floristic composition of dark-coniferous forests used 45 geobotanical descriptions of plant communities. The classification of vegetation was generated through the use of the TURBO(VEG) software package [12] within the framework of the ecologo-floristic approach (the Braun-Blanquet approach) according to which dark-coniferous forests refer to the class Vaccinio-Piceetea Br.-Bl. in Br.-Bl., Siss. et Vlieger 1939, and their floristic composition was taken in our study as the cenoflora, which is consistent with contemporary tenets of comparative floristics [13, 14]. The ecologo-geographical groups of species were determined according to [15] with some refinements. The lightconiferous, dark-coniferous and preboreal groups were identified in the floristic complex; the meadow and aquatichelad groups were recognized in the azonal complex, and the species of the high-mountain and general-belt mountain complex were represented by the montane group. The analysis of the relationships of activity ranks and species richness for the ecologo-geographical groups of the cenoflora was carried out following the scheme reported in [16]. For the species of the cenoflora the activity indices were determined according to [17], and class intervals were calculated for the species richness of the ecologo-geographical groups of species. Accordingly, the activity was calculated by the formula ,
(1)
where R is activity, А is the sum of coverages of the species of the belt-zonal group in a given syntaxon, В is the occurrence frequency of the species of the belt-zonal group in a syntaxon, and N is the number of descriptions. To calculate the class intervals, the following formula is used ,
(2)
where С is the class interval, xmax is the maximum value of partial activity or of the number of species, xmin is the minimum value of partial activity or of the number of species, and k is the number of belt-zonal groups. The analysis disregards the species that are encountered singly in the set of descriptions or have obviously extremely low activity indices: Doronicum altaicum Pall., assigned to the high-altitude group proper, and the adventitious Fallopia convolvulus (L.) A. Löve. Their presence in a given cenoflora can be determined by accidental factors.
Results and discussion Forest-forming species of dark-coniferous forests of the Northern Baikal region are represented by Siberian fir (Abies sibirica Ledeb.), and by Siberian stone pine (Pinus sibirica Du Tour). Spruce forests (of Picea obovata Ledeb.) in the region have no landscape significance and occur as narrow fragmented strips along rivers. The species composition of dark-coniferous forests is regarded as an ancient formation that has been evolving since the Tertiary Period and has profound linkages with the preboreal flora [15, 18, 19]. As part of the investigations, it was established that the cenoflora of the dark-coniferous forests includes 128 species of vascular plants. It is dominated by the species of the forest floristic complex, whereas the involvement of the species of the azonal and, especially, high-mountain and mountain general-belt complexes is insignificant. Syntaxonomically, the dark-coniferous forests of the Northern Baikal region are currently represented by one order, two unions, and five associations. Analysis of the activity and species richness of dark-coniferous forests points to a consistency of the rank indices both in activity and in species richness for almost all ecologo-geographical groups of species (see the table). The sole exception is provided only by the dark-coniferous group where the activity class of species is little more than the class of species richness. Such an exceeding may betoken the onset of the more favorable conditions for the species of this group in the recent past. Species richness and activity indices of belt-zonal geographical cenofloral groups of dark-coniferous forests belonging to the class Vaccinio-Piceetea Index
Belt-zonal group ММ
LС
DC
PB
MD
AH
Total coverage of species, %
81.0
1344.0
1169.5
197.5
98.0
51.5
Frequency of species occurrence
18
323
275
16
38
15
Species richness
5
60
41
9
6
7
Activity, points
0.85
14.64
12.60
1.25
1.36
0.62
6
1
3
6
6
6
6
1
1
6
6
6
0
0
+2
0
0
0
Species richness class Activity class Difference
Note. Groups: ММ – montane, LС – light-coniferous, DC – dark-coniferous, PB – preboreal, MD – meadow, AH – aquatichelad.
O. A. Anenkhonov / Geography and Natural Resources 30 (2009) 355–358
To determine the particular conditions which should be considered favorable for the species of the dark-coniferous ecologo-geographical group, it is necessary to consider their ecological preferences. Siberian fir (Abies sibirica) is the main cenoformer of the forests under consideration – it is an atmospheric-moisture demander and avoids territories with continuous permafrost [20–23]. Nevertheless, it can also grow on frozen ground occurring near the surface [20]. Such conditions are unfavorable for fir, however; in such a case, it is merely a component of forest communities. Furthermore, fir is sensitive to soil moisture, and excessive as well as insufficient moisturization is unfavorable for it. Nevertheless, it grows quite well on wet soils, but under good drainage conditions. Therefore, fir forests are largely associated with areas which are characterized by a relatively humid climate. Siberian stone pine (Pinus sibirica) is noted for its ability to grow under somewhat worse conditions as regards the temperature regime and moisturization [22]. Favorable for dark-coniferous forests are, in the general case, the conditions characterized by a moderate heat reserve without any considerable temperature fluctuations (both diurnal and annual), and by a sufficient, yet not excessive, soil moisturization [24]. In the Baikal region, areas with favorable conditions for dark-coniferous forests are contiguous with territories dominated by continuous or discontinuous permafrost. There is no question that under climate warming, the most conspicuous signs of changes in vegetation cover can be found in such areas. The cenoflora of the dark-coniferous forests used in this study includes an extensive variety of shade-loving moderately thermophilic mesophytes and mesohygrophytes. Such species are the most numerous and constitute the core of the dark-coniferous ecologo-geographical group. As regards the other groups forming part of the cenoflora of dark-coniferous forests, high indices of activity and species richness correspond to the light-coniferous ecologo-geographical group. Ecologically, its species are more heliophilic and somewhat more cryophilic. The species of these two belt-zonal groups predominate in the cenoflora of dark-coniferous forests both in the quantity and in the phytocenotic role. The species of the preboreal ecologo-geographical group are the most heatloving among the components of the cenoflora of dark-coniferous forests. Whilst their activity is relatively low, it obviously exceeds the activity of the other groups which are few in number (see the table). The species richness of this group shows a comparable level with the other groups. This suggests that there is an incipient (still very weak) tendency for an enhancement of the cenotic positions of the preboreal species in dark-coniferous forests. If such a view is true, then it is safe to assume that the reason behind this has to do with an improvement in heat availability of the habitats of darkconiferous forests, which must obviously be associated with general climate warming. The species of the other belt-zonal groups in the cenoflora of dark-coniferous forests are few in number and show
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low activity. The species of the montane group are relatively cryophilic, and their presence in this cenoflora is due to the mountainous character of the region under consideration. The presence of species of the meadow and aquatic-helad groups is predetermined by good running-water humidification of the ecotopes of dark-coniferous forests occurring at the bottoms of river valleys, while the temperature factor has a secondary role for these species. Dark-coniferous species are soil- and air-moisture demanding and show poor frost resistance. As demonstrated by a florogenetic analysis of vegetation cover [15] and palaeogeographical reconstructions based on spore-pollen spectra [25, 26], maximum development of dark-coniferous forests in the Baikal region corresponded to the Atlantic phase of the Mid-Holocene (the climate optimum phase). Subsequently, dark-coniferous forests were being supplanted by light-coniferous and small-leaved forests during the subboreal phase of the Mid-Holocene and over the course of the Late Holocene, with decreasing temperatures and with a decrease in atmospheric precipitation combined with an enhanced continentality of climate. This leads us to suggest that a climate warming concurrent with an increase in humidity must result in an expansion of the growing area of dark-coniferous forests. In the Baikal region, a warming is due to the rise in winter temperatures [27, 28] and, hence, there is an attenuation of the negative (for dark-coniferous species, and firs in particular) impact of the low winter temperature factor. It follows that the detected tendency for an increase in the activity of the species cenogenetically associated with darkconiferous forests may be thought of as the initial stage of the future expansion of dark-coniferous forests and a gradual replacement of other forest types by them, primarily lightconiferous forests predominating in the Northern Baikal region. Furthermore, there is no question that dark-coniferous forests will spread first to territories with thin sporadic permafrost and permafrost islands which are endowed with higher heat availability when compared with zones of discontinuous and continuous permafrost. Note that the escalating encroachment of the evergreen coniferous species, i.e. forest-producers of the dark-coniferous taiga (Siberian stone pine, fir and spruce), into the zone dominated by light-coniferous larch forests was also recorded on the Middle-Siberian Plateau [29, 30]. Conclusion Indirect evidence for the relationship between the enhancement of the landscape positions of dark-coniferous forests (for the most part, fir, Siberian stone pine and Siberian stone pine-fir forests) with climate warming is provided by their more extensive occurrence on the territories of Siberia for which the relatively high indices of the sum of active temperatures combine with a relatively low coefficient а continentality [31]. In the region under consideration in the past there occurred a similar tendency during the phase of the Holocene Climate Optimum.
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