Old-growth Mixed Forest Research Articles

Climate change impacts on stand structure and competitive interactions in a southern Swedish spruce–beech forest

It is believed that European beech (Fagus sylvatica L.) will increase its competitive ability at its northern range margin in Scandinavia due to climate change. In mixed old-growth forests of beech and Norway spruce (Picea abies (L.) Karst.) at Siggaboda nature reserve (southern Sweden), stand structure characteristics were sequentially recorded in the years 2004, 2005 and 2007 as well as growth in stem diameter using tree-coring analyses. Using these measurements, we studied the effects on stand dynamics of an extreme storm event (2005 “Gudrun” hurricane), drought and heat (mid-summer 2006, spring 2007) and subsequent bark beetle attacks on spruce (growing season 2007), overlaid with warming tendencies. The storm, which caused disastrous damage in many stands nearby, had comparatively little impact on the structure of the spruce–beech stand. All together, only 32 trees (19 spruces, 10 beeches, 3 other species) per hectare were thrown or broken mainly in the leeward direction (NE) or impacted by secondary damage by uprooted neighbour trees; this represents 7% of the total tree number and 11% of the growing stock. Diameter and height structure did not change significantly. However, the 2006 drought and the 2007 attack of biotic agents changed the stand structure and composition strongly due to the death of about 19% of the dominating older spruce trees that accounted for 35% of total stand volume. This resulted in a considerable increase in beech’s contribution to stem number (4% increase) and wood volume of the living stand (7% increase). A comparison of diameter growth of beech and spruce during the periods 1894–1949 and 1950–2005 showed a distinct decrease in growth superiority of spruce during the last 50 years. These results support the idea of a northward migration of European beech as a nemoral tree species in Sweden, due to a higher tolerance to the abiotic and biotic threats accompanying climate change and an increased competitive ability compared to boreal tree species Norway spruce.

Clonal structure and diversity of Cryptomeria japonica along a slope in a cool-temperate, old-growth mixed forest in the snowy region of Japan

To clarify patterns of clonal growth along a slope for Cryptomeria japonica (L.f.) D. Don, which can regenerate by layering resulting from snow pressure, we analyzed the spatial genetic structure with respect to slope position and in relation to stem size in a cool-temperate, old-growth mixed forest in the snowy region of Japan. For the genetic analysis, five polymorphic microsatellite markers developed for C. japonica were used. Spatial autocorrelation analyses revealed a significant positive association of ramets (trees) with the same genotype as the result of clonal growth at around <6 m regardless of slope position for understory trees (≥50 cm stem length and <10 cm diameter at breast height (DBH)). This clonal patch size almost corresponded to the clustering scale for overstory trees (≥10 cm DBH) belonging to the same genet. For understory trees in three subplots established along a slope, the size distribution of ramets within a clone (genet) followed an inverse J-shaped distribution without small ramets being distributed peripherally. These results suggest that each clone of C. japonica is maintained continuously in a relatively restricted area where it establishes, regardless of slope position, which could contribute to the high clonal and genetic diversity of C. japonica in this forest.

Regeneration of Cryptomeria japonica on a sloping topography in a cool-temperate mixed forest in the snowy region of Japan

Cryptomeria japonica D. Don shows a limited distribution on and around ridges in its native habitat. To clarify the regeneration process of this species, we analysed spatial patterns among five size classes on a slope extending from a ridge to a valley bottom, and growth patterns of understorey trees related to their slope position, in a cool-temperate old-growth mixed forest in Japan. Although the largest size-class trees ([Formula: see text]20 cm diameter at breast height (DBH)) were confined to the upper part of the slope, understorey size-class trees ([Formula: see text]50 cm stem length and <10 cm DBH) extended their range below the upper regions by layering. The annual growth of understorey size class stems increased towards the lower slope in relation to the understorey light conditions. However, snow pressure injured understorey trees and killed many regenerating medium-sized trees on the steeply inclined expanding site. These results indicate that increased snow pressure, influenced by slope topography, may inhibit the clonal expansion of C. japonica. We concluded that snow pressure gradient on a sloping topography strongly influences the regeneration success of C. japonica, restricting its distribution to ridges in natural forests in snowy regions.

Densities of large living and dead trees in old-growth temperate and boreal forests

We recorded and reviewed densities and basal areas of large living and dead trees in old-growth forest in Europe. Recorded densities were similar to those reported from old-growth forests in eastern North America, but lower than in northwestern North America. Based on our results we suggest that, 10–20 living trees per ha with dbh>70 cm may have been typical values for many central European and south Scandinavian virgin forests. In boreal forests, it was probably common with at least 20 living trees per ha with dbh>40 cm. Basal areas of living trees in mixed old-growth forests in central Europe and southern Sweden were 34–40 m 2 per ha on dry ground and about 60 m 2 per ha in wet alder–ash–spruce forests. Densities of large trees (dbh>40 cm) were twice as high in the latter forest type than on dry ground in Białowieża forest, Poland. Based on our results, we propose the following generalizations to be further tested in other old-growth temperate and boreal forests: 1. Among all standing trunks (including high stumps) about 10% are dead, but this proportion increases for the largest trees. The proportion of standing trees that are dead seem to be independent of total basal areas. Based on this, we suggest that the volume of dead wood is directly proportional to the productivity of old-growth forests. 2. Standing dead trees (snags) are on average larger than downed dead trees. Trees with dbh>40 cm often dominate the basal area and volume of standing dead trees and living trees. 3. About 30% (20–40%) of the basal area and volume of dead trees is standing in old-growth forests. This proportion seems to be independent of total volume of dead wood. Large disturbances by fire, strong winds and insects may temporarily change these proportions considerably in individual stands.

Distribution and conservation status of the Mt Mangana stag beetle, Lissotes menalcas (Coleoptera: Lucanidae)

Lissotes menalcas (the Mt Mangana Stag Beetle) is an obligate log dwelling beetle and is presently classified as vulnerable under the Tasmanian Threatened Species Protection Act 1995. The distribution, habitat and conservation status of this species were investigated through a combination of collation of known locations and searches for the in decaying logs across likely areas of occurrence. L. menalcas was found to have a wide distribution in south eastern Tasmania and is now recorded from 34 localities. The species was found in a variety of wet forest habitats from old-growth mixed forest through to 23-year-old wet eucalypt silvicultural regrowth. About 12% of wet eucalypt forest within the predicted range of L. menalcas is formally reserved, and another 14% on Crown land is unlikely to be subject to logging. L. menalcas appears to tolerate both wildfire and clear felling with regeneration burning. Because the species depends on an ongoing supply of rotting logs for its long-term survival, plantation development will probably lead to the elimination of the species from such areas. Analysis of the likely impact of plantation establishment within its range over the next ten years indicates that it will not reach levels that would lead it to be considered as vulnerable. Thus, it is recommended that the status of the species be changed from vulnerable to rare. However, there is a need to determine the ecological sustainability of present forest management practices in relation to the decaying-log habitat and to continue to monitor the extent of clearing and modification of the species' habitat.

Seedling success of Tsuga sieboldii along a microtopographic gradient in a mixed cool-temperate forest in Japan

Emergence and establishment of Tsuga sieboldii seedlings were monitored for six years in an old-growth mixed forest in Japan, to clarify the reason why adult T. sieboldii trees are distributed only on convex slopes. T. sieboldii seedlings germinated on exposed soils without broad-leaved litter cover on both convex and concave slopes, but they died out from concave slope during the first two years after germination. Along a gradient from convex to concave slope, litter cover became higher and surface soil erosion became severer, and T. sieboldii seedlings died at the plots with severe surface soil erosion. Other environmental variables, such as relative illuminance, vegetation cover of seedling layer and soil water potential were not significantly different between convex and concave slopes. We concluded that the restricted seedling establishment of T. sieboldii to convex slope is determined by stability of surface soils and broad-leaved litter cover.

A Floristic Comparison of Vascular Species in Tasmanian Oldgrowth Mixed Forest With Regeneration Resulting From Logging and Wildfire

About 20% of Tasmania's wet eucalypt forest is mixed forest, i.e. having a rainforest understorey and a eucalypt overstorey. While one-third of the mixed forest is formally reserved, much of the remainder is subject to logging on an 80-100 year rotation which is insufficient for the redevelopment of mature mixed forest. The routine silvicultural regeneration treatment for wet eucalypt forests is to clearfell, burn and sow with eucalypt seed. A comparison of the Vascular floristics of 20-30-year-old silvicultural and wildfire regeneration with oldgrowth mixed forest showed that most species common in oldgrowth mixed forest were represented in approximately similar frequencies in silvicultural regeneration and wildfire regeneration. The major floristic difference between the two regeneration types was the much lower frequency of oldgrowth epiphytic fern species in silvicultural regeneration and a higher frequency of a sedge species often associated with disturbed areas. However, after a single logging treatment, the vascular plant floristics of silvicultural regeneration were sufficiently similar to wildfire regeneration to assume that, in the absence of further logging or fires, the silvicultural regeneration could become mature mixed forest and eventually rainforest. Further work is required to determine whether regrowth mixed forest can be logged at 80-100 years and still retain sufficient rainforest elements to eventually return to mixed forest within the life span of the dominant eucalypts. The critical factor in the silvicultural perpetuation of mixed forest may be rotation length rather than regeneration treatment.