Spruce-fir forests have a tendency to de- cline in the southern portion of their range on the Sikhote-Alin (Man’ko & Gladkova 2001). Several waves of decline occurred over exten- sive areas in the recent past, including the last, in 1970–1980, in the central Sikhote-Alin (Man’ko 1987, Man’ko & Gladkova 1993, 1995, Man’ko et al. 1998). Stand dieback started with the simultaneous death of several trees in 1972, not necessarily the oldest trees in the stand. After 1978 the area of dead stands increased, and the patches of dead trees merged. In 1983 the total area of dead forest was not considered a large-scale decline, but the subsequent merging of existing breakdown sites and appearance of new patches caused canopy degradation over an area of 140 km2 (Kamibayashi et al. 1994).
According to Man’ko et al. (1998), forest decline is expressed as death of canopy trees preceded by appearance of dead branches along the mid-stem and yellowing needles on the whole stem. The authors discovered that stem death tended to increase with increasing diameter and that it was mainly fir that was dying. The dead trees ranged between 100 and 160 years old, and dying stands were uneven- aged. The young sub-canopy spruce genera- tion did not suffer when the canopy trees dis-
appeared but rather tended to grow better. Spruce and fir saplings successfully regener- ated the stands with dead canopies.
Analyses and experiments carried out in dying or dead forests did not show a definite factor causing the forest decline. The authors hypothesize that drought during the growing season may play a crucial role, citing the complex mechanisms of forest response to water stress and various accompanying stresses. These include excesses of various elements (Zn, Li, Ni, Co, Pb, Ti) in the soil, fungal diseases in the dead centers, and con- sequent damage by insects (Man’ko et al. 1998, Man’ko & Gladkova 2001).
6.4 Phytocenotic diversity
Dark-conifer vegetation in the boreal zone of eastern Russia involves two basic types of spruce forest: Formation Piceeta ajanensis, widely occurring in continental as well as in- sular regions, and at high elevations in north- eastern China; and Formation Piceeta glehnii, a rare vegetation type occurring locally on the islands (southernmost Sakhalin, Iturup and Kunashir). The largest mass of Picea glehnii forest occurs on Hokkaido (Tatewaki 1943). Classification of dark-conifer forests of east- ernmost Russia is shown in Table 5.12.
Table 5.12. Classification of dark-conifer forests, with indicator species, ecology, and topographical position of association
groups. Abbreviations for edatopes as in table 5.7.
Grex associationum Indicator plants Edatope Topography, aspect
Formatio: Piceeta ajanensis Classus associationum: Piceeta purum
Piceeta purum fruticulosa Vaccinium vitis-idaea, Diphasiastrum complanatum, Gymnocarpium dryopteris
SD, P–MN
Steep southern slopes
Piceeta purum nano-herbosa taigae
Maianthemum bifolium, M. dilatatum, Linnaea bo- realis, Chamaepericlymenum canadense
F, MN Gentle slopes at differ- ent elevations
Piceeta purum hylocomiosa Hylocomium splendens, Pleurozium schreberii, Ptil- ium crista-castrensis
SD–F, P–MN
Flats and gentle northern slopes
Piceeta purum filicosa Diplazium sibiricum M, MN Small terraces on moun- tain slopes
Piceeta purum grandiherbosa Senecio cannabifolius, Calamagrostis langsdorffii, Athyrium felix-femina
M–VM, MN–R
Moist river valleys
Piceeta purum sphagno- ledosa
Ledum palustre, Sphagnum fuscum, Polytrichum commune
VM, P–MN
Poorly drained valleys
Classus associationum: Piceeta abietosium nephrolepis
Abieto-Piceeta fruticulosa Vaccinium vitis-idaea, Diphasiastrum complanatum, Orthilia secunda
SD, P–MN
Northern steep slopes
Abieto-Piceeta nanocaricosa taigae
Carex callitrichos, Pseudocystopteris spinulosa SD, MN–R
Insolated steep slopes
Nemoreto-Piceeta herbosa nemoretae
Dryopteris crassirhizoma, Aconitum umbrosum, Thalictrum tuberiferum
F–M, MN–R
Gentle (<20°) southern slopes and river valleys
Nemoreto-Piceeta filicosa Dryopteris expansa, Leptorumohra amurensis, Diplazium sibiricum, Phegopteris connectilis
F, MN–R Gentle (<20°) northern slopes
Nemoreto-Piceeta nano- herbosa taigae
Maianthemum bifolium, Chamaepericlymenum ca- nadense, Carex falcata, C. xyphium
F, MN Gentle slopes and ter- races
Abieto-Piceeta hylocomiosa Hylocomium splendens, Pleurozium schreberii, Rhytidiadelphus triquetrus, Pleurosiopsis ruthenica
SD–F, MN
Gentle and medium slopes and flats
Abieto-Piceeta oplopanaxosa elati
Oplopanax elatus, Euonymus macroptera, Carex xyphium
F–M, R Micro-terraces on moun- tain slopes
Abieto-Piceeta grandi-filicosa Cornopteris crenulatoserrulata, Koniogramme in- termedia, Athyrium filix-femina
VM, MN–R
Well-drained river val- leys
Abieto-Piceeta grandi- caricosa
Carex appendiculata, Ledum palustre, Calama- grostis langsdorffii
VM–W, MN–R
Poorly-drained valleys
Classus associationum: Piceeta abietosium sachalinensis
Abieto sachalinensis-Piceeta sasosa
Sasa kurilensis, S. senanensis, Ilex rugosa, Skimmia repens F–M, MN–R Gentle slopes Abieto sachalinensis-Piceeta hylocomiosa
Hylocomium splendens, Pleurozium schreberi, Pleuroziopsis ruthenica
F, P–MN Gentle northern slopes
Abieto sachalinensis-Piceeta filicosa taigae
Leptorumohra amurensis, Dryopteris expansa F–M, MN–R
Gentle concave slopes
Abieto sachalinensis-Piceeta nano-herbosa taigae
Maianthemum dilatatim, Linnaea borealis, Vaccin- ium praestans
F, MN Gentle slopes and ter- races
Abieto sachalinensis-Piceeta sphagno-ledosa
Ledum palustre, Rubus chamaemorus, Sphagnum fuscum, Vaccinium uliginosum, Carex schmidtii
VM–W, VP–MN
Poorly drained river valleys
Formatio: Piceeta glehnii
Classus associationum: Piceeta glehnii laricetosium dauricae
Lariceto-Piceeta glehnii sphagno-ledosa
Ledum palustre, Sphagnum fuscum, Betula midden- dorffii, Rubus chamaemorus
W, VP–P Poorly drained valleys
Lariceto-Piceeta glehnii nano-herbosa taigae
Maianthemum dilatatum, Ilex rugosa, Sphagnum girgensohnii
M–VM, MN
6.4.1 Piceeta ajanensis – Picea ajanensis