Kanji Namikawa

Disturbance history and tree establishment in old‐growth Pinus koraiensis‐hardwood forests in the Russian Far East

. Dendro-ecological studies were undertaken to document the disturbance history in two old-growth mixed Pinus koraiensis-hardwood forests in the southern part of the Sikhote-Alin mountains in the Russian Far East. Establishment of four common canopy conifers, Abies holophylla, A. nephrolepis, P. koraiensis and Picea ajanensis, and three common canopy hardwoods, Acer mono, Betula costata and Tilia amurensis, were also inferred from population age structures and spatial dispersion patterns. Growth releases on increment cores suggested that peak periods of growth releases indicating partial canopy disturbances have repeatedly occurred over the past 230 yr at intervals from ca. 35 to 100 yr. Slight releases and suppressions other than the peak releases occurred in many years of both histories, suggesting the formation of smaller-scale canopy gaps. Despite the predominance of anthropogenic fires in Primorskiy Kray at present, destructive fires had not affected either forest. Wind disturbances and low intensity fires are likely factors controlling the dynamics of the forests. Under the disturbance regime, P. koraiensis has maintained its populations through its dependence on canopy gaps for establishment. Age distribution and gap dependence of P. ajanensis, A. nephrolepis and A. mono suggested continuous establishment of these species under a closed canopy, whereas occasional establishment of T. amurensis was derived largely from vegetative reproduction. Restricted establishment of A. holophylla and B. costata suggested a variety in kinds of disturbance throughout the histories. Continuous habitation of the study area by P. koraiensis is likely under the disturbance regime without destructive fires.

Stand dynamics during a 12-year period in a second-growth stand in a cool temperature forest in northern Japan

In 1981 and 1993, trees over 2 m high were measured and mapped to clarify stand dynamics in two permanent plots of 0.1 ha in a secondary, cool temperate, mixed broadleaf/conifer forest after logging in the Tomakomai Experiment Forest, central Hokkaido, northern Japan. The species could be placed in two groups according to the change in basal area and density, and annual height growth:Quercus mongolica var.grosseserrata, Phellodendron amurense, Prunus sargentii andTilia japonica (Group I: GI) showed episodic regeneration and/or fast height growth;Acer mono, Acer palmatum var.matsumuae andSorbus alnifolia (Group II: GII) showed continuous regeneration and/or slow height growth. The age distribution of stems over 10 cm in d.b.h. suggests synchronous regeneration of GI and GII species. Vertical stratification was promoted during the 12-year period by the difference in annual height growth between the two species groups. Additional tree censuses in both remnant old-growth stands and second-growth stands after large scale blowdowns demonstrated thatQ. mongolica var.grosseserrata is most dominant in stands varying in the stages of development. Disturbance history and successional trends in dominant species implied that stand-devastating disturbances were responsible for the regeneration ofQ. mongolica var.grosseserrata in the study forest.

Stand dynamics during a 12 year period in an old-growth, cool temperate forest in northern Japan

In 1979 and 1991, trees over 2.0 m high were measured and mapped together with their crown projections to clarify stand dynamics and shifts in canopy dominants during this period, in a permanent plot of 0.525 ha in an old-growth, cool temperate mixed forest of Mt Moiwa, Central Hokkaido, northern Japan. During this period, an abundant recruitment of trees was observed after some canopy trees were felled by a typhoon in 1981 leaving gaps in the canopy. Vigorous recruitment was observed forTilia japonica, Acer mono andPrunus ssiori. These species had different regeneration sites in relation to canopy state. NeitherUlmus japonica norKalopanax pictus had any recruits during the 12 year period even in gaps. The equilibrium composition of tree species projected from transition probability analysis also implied the above shift of dominant species during the 12 year period in the plot and suggested that the present forest is not in an equilibrium state.

Decline in gene diversity and strong genetic drift in the northward-expanding marginal populations of Fagus crenata

The species distribution of Fagus crenata, or Japanese beech, in the Japanese archipelago shifted northward during phytogeographical changes that occurred during the Pleistocene and Holocene epochs. Presently, the continuous natural distribution of beech reaches north to the Kuromatsunai Depression of Hokkaido Island, Japan. In addition, dozens of marginal patches and isolated individuals north of the continuous distribution have been observed. F. crenata grows remarkably well among these small-scattered northern marginal populations, which must have originated from seeds dispersed beyond the northern limit of the continuous beech forest. It is conceivable that the distribution of F. crenata is still in the process of expanding northward. We investigated the genetic structure of 33 beech populations to evaluate the population gene diversity at the leading northern edge of the range expansion. We analyzed 12 nuclear microsatellite loci in each of the 1,693 individuals. Genetic diversity parameters such as expected heterozygosity and allelic richness were clearly lower in the northernmost populations. We found genetic differentiation in the northernmost distribution range (FST = 0.045, G′ST = 0.242). STRUCTURE analysis revealed that the southwestern continuous populations consisted of homogeneous ancestral clusters. However, northeastern marginal populations consisted of mixtures of highly differentiated clusters with higher levels of genetic drift than found in the continuous populations.

Stand structure and establishment process of an old-growth stand in the mixed deciduous broadleaf/conifer forest of Mt. Moiwa Forest Reserve, central Hokkaido, Northern Japan

Stand structure of an old-growth forest was studied by tree (≥4.0 cm in DBH) census in a main plot of 1.3 ha and 8 additional plots (0.525 ha in total) located in the Mt. Moiwa Forest Reserve, central Hokkaido, northern Japan. Major tree species with ≥1.0% of the relative basal area and of relative number of trees (Acer mono, A. mono var.mayrii, Kalopanax pictus, Magnolia kobus var.borealis, M. obovata, Prunus ssiori, Tilia japonica, andUlmus laciniata) have positive values of skewness in DBH, which shows the abundance of smaller-sized stems. All stems over 1.3 m high in the main plot were mapped to clarify the relationship between stem densities and canopy states. Although advances from sapling (>1.3 m tall and <4.0 cm DBH) to small tree (10.0 cm ≤ DBH <25 cm) for all major component species, exceptP. ssiori andU. laciniata, were independent of canopy states, those ofP. ssiori andU. laciniata depended on canopy gaps.Betula spp. was the most abundant gap makers, butT. japonica andA. mono (including var.mayrii) were dominant species in the main plot. This suggests the shift of dominant species in the forest of the study site. Historical records of disturbance demonstrated that selective cuttings of conifers during the late 19th century were responsible for the dominance ofBetula spp. and the subsequent shift of dominant species. This fact suggests that artificial disturbance plays an important role in the establishment ofTilia japonica-Acer mono forest considered to be a climax of the mixed deciduous broadleaf/conifer forests.