Mature Coniferous Forest Research Articles

A Late-glacial–Holocene Fossil Insect Succession from Vallée des Merveilles, French Alps, and its Paleoecological Implications

We studied the composition of assemblages of fossil insects from the Quaternary in the high- altitude Lac Long Inférieur located at 2090 m a.s.l in the “Vallée des Merveilles” (southern French Alps). The insect assemblages extracted from the lake sedimentary sequence were divided into five faunal units, which enable us to reconstruct the evolution of paleoenvironments from the Würmian ice retreat to the present. Our results indicate that the periglacial desert was replaced by steppic environments, followed by the rise of the treeline and the establishment of a mature conifer forest, which ended in the final collapse of the forest cover. Human action was clearly responsible for this last event, but in contrast to other alpine sites, agropastoral activities around the lake itself were not clearly indicated by insect data. Comparisons between insect and pollen data for the same sedimentary sequence agreed in most cases, but these two approaches have a complementary value when they are applied on the same site.

Environmentally sensitive plot-scale timber harvesting: impacts on suspended sediment, bedload and bank erosion dynamics

The impact on sediment pollution of environmentally sensitive harvesting of a 15ha plot (20% of the catchment area) of mature coniferous plantation forest in the 0·89km2Afon Tanllwyth catchment, Plynlimon, was investigated for 12 months before harvesting began and a further 18 months after. The results revealed: (a) a steepening of the suspended sediment concentration vs. discharge rating curve resulting in a 39% increase in suspended sediment yield (as compared to the adjacent forested Hafren catchment) during the year in which the harvesting operations took place; (b) a statistically significant increase in main channel bank erosion rates, as compared with the nearby Afon Cyff; main channel banks are estimated to have contributed around 80% of the total catchment suspended sediment yield during the two year period (1995–1996), and (c) no significant change in bedload yields over the duration of the study, though a longer post-harvesting time series of bedload data will be required to properly assess the impact of the harvesting operation upon bedload yields. Forest management implications of these findings are discussed in detail with respect to the existing Forest and Water guidelines.

STATUS OF AMERICAN MARTENS IN COASTAL FORESTS OF THE PACIFIC STATES

American martens (Martes americana) are associated strongly with mature conifer forests and once occurred throughout the mountains of the coastal Pacific states. We sought to document the distribution of martens in this region using historical records and to understand recent change in their distribution. We described the distribution of martens from 1900 to 1949 using museum and trapping records and compared it to recent (1989-1998) detections at camera and track-plate stations. Martens were detected at only 12 of the 237 (5.1%) survey sample units in coastal California, Oregon, and Washington. Martens are absent from most of the historical range of the Humboldt marten (M. a. humboldtensis) in California and also may have declined on the Olympic Peninsula of Washington. Few data exist from northwestern Oregon and southwestern Washington, but the limited amount of protected public land and absence of reported road kills are reasons for concern for populations in this region. Martens still occur in the central and southern coastal mountains of Oregon. Our results suggest that conservation of martens in coastal forests will require new initiatives to protect existing populations and new efforts to document all populations of martens in this region. Conservation measures should include a reevaluation of timber harvest plans that affect habitat in coastal forests, interagency cooperation on a coastal marten conservation assessment, and the collection of new survey information, especially on private lands in southwestern Washington and northwestern Oregon.

Survival, ranging, habitat choice and diet of the Northern Goshawk Accipiter gentilis during winter in Northern Finland

The winter ecology of the Northern Goshawk Accipiter gentilis was studied in northern Finland in 1991‐95. The data consist of 26 radiomarked hawks, of which 331 day and 299 night positions were located. Average range size was 9894 ha for males (minimum convex polygon, n= 4) and 6282 ha for females (n= 11). Ranges calculated by the 75% harmonic mean contour gave range areas of 3283 ha for males (n= 3) and 2753 ha for females (n= 11). Harmonic mean centres concentrated near human settlements, implying better food availability there compared with woodland areas. Some Goshawks preyed upon animals living in the city dump in late winter. Goshawks preferred deciduous and mature conifer forests and avoided open areas such as fields and bogs. They also avoided very heterogeneous sites. The winter diet consisted mostly of Mountain Hares Lepus timidus (30.9%), Red Squirrels Sciurus vulgaris (23.6%), Brown Rats Rattus norvegicus (12.7%) and forest grouse Tetraonidae (27.1%), of which Black Grouse Tetrao tetrix was the most important (14.5%). By weight, hares constituted 70% of the biomass consumed.

Clief and Deciduous Tree Nests of Marbled Murrelets in Southwestern British Columbia

We report on nests of radio-marked marbled murrelets (Brachyramphus marmoratus) nesting in unusual habitats in southwestern British Columbia. We found 1 confirmed and 2 probable marbled murrelet nest sites on cliffs. These represent the 1st substantiated accounts of ground nesting in this species south of Alaska. In addition, we found a marbled murrelet nesting in a 130 (?5)-yr-old red alder (Alnus rubra) deciduous tree. A survey of available nesting sites in both the nest tree patch and the mixed coniferous-deciduous stand adjacent to this deciduous nest tree indicated most potential nesting trees were deciduous and that deciduous trees had a higher density of potential nesting sites. These unusual sites represent a very small proportion (7% of confirmed sites, 3% of suspected sites) of nest sites found in British Columbia using radio telemetry. Both confirmed nest sites consisted of a platform with heavy epiphyte cover and an adjacent flyway, similar to nests found in mature coniferous forest.

Cumulative effects of roads and logging on landscape structure in the San Juan Mountains, Colorado (USA)

In the southern Rocky Mountains of temperate North America, the effects of Euro-American activities on disturbance regimes and landscape patterns have been less ubiquitous and less straightforward in high-elevation landscapes than in low-elevation landscapes. Despite apparently little change in the natural disturbance regime, there is increasing concern that forest management activities related mainly to timber harvest and to the extensive network of roads constructed to support timber harvest, fire control, and recreation since the late 1800s have altered disturbance regimes and landscape structure. We investigated the magnitude of change in landscape structure resulting from roads and logging since the onset of timber harvest activities in 1950. We found limited evidence for significant impacts in our study area when all lands within the landscape were considered. The relatively minor changes we observed reflected the vast buffering capacity of the large proportion of lands managed for purposes other than timber (e.g., wilderness). Significant changes in landscape structure and fragmentation of mature forest were, however, evident on lands designated as suitable timberlands. Roughly half of the mature coniferous forest was converted to young stands; mean patch size and core area declined by 40% and 25%, respectively, and contrast-weighted edge density increased 2- to 3-fold. Overall, roads had a greater impact on landscape structure than logging in our study area. Indeed, the 3-fold increase in road density between 1950–1993 accounted for most of the changes in landscape configuration associated with mean patch size, edge density, and core area. The extent of area evaluated and the period over which change was evaluated had a large impact on the magnitude of change detected and our conclusions regarding the ecological significance of those changes. Specifically, the cumulative impact on landscape structure was negligible over a 10-year period, but was notable over a 40-year period. In addition, the magnitude of change in landscape structure between 1950–1993 varied as a function of landscape extent. At the scale of the 228 000 ha landscape, change in landscape structure was trivial, suggesting that the landscape was capable of fully incorporating the disturbances with minimal impact. However, at intermediate scales of 1000–10 000 ha landscapes, change in landscape structure was quite evident, suggesting that there may be an optimal range of scales for detecting changes in landscape structure within the study area.

Survey of Songbirds during a Spruce Beetle (Dendroctonus rufipennis) Outbreak on the Kenai Peninsula, Alaska

A spruce beetle (Dendroctonus rufipennis) epidemic in southcentral Alaska has caused extensive mortality to spruce trees and a change in forest stand structure. Because a change in forest vegetation can influence composition and abundance of forest birds, we at- tempted to assess the type and magnitude of change in bird populations within 2 forest stands on the Kenai Peninsula that were undergoing differing levels of spruce beetle infestation. In addition, we compared bird populations occupying a salvage-logged forest site with those in the other forest stands. During our survey period (1994 to 1998), species composition and abun- dance of land birds differed across the sampled forest stands. Avian species diversity and rich- ness was greatest in the early successional stage of the logged forest and least in the heavily infested forest stand where many spruce trees killed by the spruce beetle had fallen to the ground. As predicted, ground nesting and foraging bird species increased where trees had fall- en or were removed. Conversely, the abundance of mature conifer forest birds, such as Town- send's warblers (Dendroica townsendi) and ruby-crowned kinglets (Regulus calendula) decreased in those forest stands that lost overstory structure. Townsend's warblers declined in abundance through time, potentially due to the loss of mature conifers for nest sites. Bird abundance was greater within the lightly infested stand in 1996, possibly due to immigration of birds from less suitable habitats. Because forest stand characteristics will continue to change through time fol- lowing the spruce beetle epidemic, we suggest that songbird communities will also remain dy- namic in response to changing habitats.

Aboveground Net Primary Production and Leaf-Area Index in Early Postfire Vegetation in Yellowstone National Park

Aboveground net primary production (ANPP) and leaf-area index (LAI) of lodgepole pine (Pinus contorta var. latifolia Engelm. ex Wats.) saplings and aboveground productivity of herbaceous vegetation components were determined 9 years after the 1988 fires in Yellowstone National Park (YNP). Measurements were made in four sites representing a wide range of early postfire vegetation present in YNP, including high-density lodgepole pine, low-density lodgepole pine, and two nonforest stands. LAI of the pine saplings and total ANPP (trees plus herbs) generally increased with increasing sapling density, from 0.002 m2 m−2 and 0.25 Mg ha−1 year−1 in the infertile nonforest stand (100 pine saplings ha−1) to 1.8 m2 m−2 and 4.01 Mg ha−1 year−1 in the high-density pine stand (62,800 saplings ha−1). Aboveground herbaceous productivity was not strongly correlated with sapling density, but appeared to be influenced by soil fertility. In the high-density pine stand, tree ANPP and LAI were within the lower range of values reported for similar mature coniferous forests. This finding suggests that at least some ecosystem processes (related to ANPP and LAI) may have nearly recovered after only 9 years of postfire succession, in at least some of the young forests developing after the 1988 Yellowstone fires.

Influence of Forest Structure and Diseases on Nest-Site Selection by Red-Breasted Nuthatches

Empirical studies of the effects of forestry on cavity-nesting birds largely neglect weak cavity excavators and instead focus on large, strong cavity excavators such as woodpeckers (Picidae). Weak cavity nesters tend to be smaller and may be less limited by the availability of large trees but more dependent on suitably softened wood. In this paper, we describe availability, use, and preference for nesting habitat of a small cavity-nesting bird, the red-breasted nuthatch (Sitta canadensis), in mature coniferous forest in southeastern British Columbia. We describe nesting habitat at 3 spatial scales: (1) the level of forest stands proposed for logging (cutblocks), which ranged from 8.1 to 18.4 ha in size; (2) the level of 0.04-ha patches of forest centered on nest trees (nest plots); and (3) the level of individual nest trees. In addition to considering basic structural habitat features, we analyzed the relation between nesting use and several factors related to forest health, including Armillaria root disease (Armillaria ostoyae), stemwood decay, mountain pine beetle (Dendroctonus ponderosae) infestation, and dwarf mistletoe (Arceuthobium spp.). Red-breasted nuthatches nested at higher densities on cutblocks with more dead trees (snags) and higher levels of root disease. Within nest plots, we also detected a preference for nesting in Armillaria-infected trees. Cavity nesting of nuthatches was influenced by both forest structure and the disease agents that contribute to it. We recommend that standing diseased and dead trees be retained in patches during logging operations. Retention of such trees in distinct patches more likely satisfies requirements for worker safety and for limiting the spread of diseases than does retention of single dead and diseased trees throughout cutblocks. Wildlife values not only should be incorporated into timber harvesting regulations but also should be considered when planning activities designed to improve forest health for timber production.

Microsite Controls on Tree Seedling Establishment in Conifer Forest Canopy Gaps

Tree seedling establishment and growth were studied in experimental canopy gaps to assess the effect of heterogeneity of regeneration microsites within and among gaps in mature conifer forests. Seedlings were studied for two years in closed-canopy areas and in recently created gaps ranging in size from 40 to 2000 m2 in four stands of mature (90–140 yr) and old-growth (>400 yr) Douglas-fir forest in the western Cascade Range of central Oregon and southern Washington, USA. We examined the relative importance of substrate type, shade from logs and shade cloth, density of understory vegetation, gap size, and forest age on the success of Pacific silver fir (Abies amabilis), Douglas-fir (Pseudotsuga menziesii), and western hemlock (Tsuga heterophylla). Seedlings originating from seed sown on experimental microsites were compared with seedlings regenerating naturally on a range of microsites. Seedling establishment was greater on decayed wood than on forest floor or mineral soil in closed-canopy areas, particularly for Tsuga. Differences in establishment among substrates declined with increasing gap size, although establishment on the forest floor tended to be low in portions of large gaps exposed to direct solar radiation. In exposed areas, shade from woody debris and shade cloth facilitated establishment for all species, while shade from understory vegetation aided the establishment of Pseudotsuga but not that of Tsuga. Establishment in shaded portions of gaps declined with vegetation and shade-cloth cover. Seedling size increased with gap size, decreased with level of shade, and tended to be greatest on forest floor and lowest on decayed wood. Establishment and growth of the different species was related to differences in seed mass and tolerance of environmental extremes. Heterogeneity at the seedling scale (<10 cm) often overrode larger-scale environmental gradients (>2 m) associated with gap size and within-gap position. Thus the gap partitioning hypothesis, which emphasizes gap size and within-gap position, may be too simple to account for the role of microsite heterogeneity and species’ regeneration traits on the development of mature forests.

MICROSITE CONTROLS ON TREE SEEDLING ESTABLISHMENT IN CONIFER FOREST CANOPY GAPS

Tree seedling establishment and growth were studied in experimental canopy gaps to assess the effect of heterogeneity of regeneration microsites within and among gaps in mature conifer forests. Seedlings were studied for two years in closed-canopy areas and in recently created gaps ranging in size from 40 to 2000 m2 in four stands of mature (90–140 yr) and old-growth (>400 yr) Douglas-fir forest in the western Cascade Range of central Oregon and southern Washington, USA. We examined the relative importance of substrate type, shade from logs and shade cloth, density of understory vegetation, gap size, and forest age on the success of Pacific silver fir (Abies amabilis), Douglas-fir (Pseudotsuga menziesii), and western hemlock (Tsuga heterophylla). Seedlings originating from seed sown on experimental microsites were compared with seedlings regenerating naturally on a range of microsites. Seedling establishment was greater on decayed wood than on forest floor or mineral soil in closed-canopy areas, particula...

Seasonal Habitat Selection by Marten in an Untrapped Forest Preserve

American marten (Martes americana) are often associated with mature conifer-dominated forests; however, marten may require complex vertical and horizontal woody structure, rather than a coniferous overstory. To evaluate whether marten prefer forests with a mature conifer overstory, we investigated landscape-and stand-scale habitat selection of 38 (20 M, 18 F) resident (≥25 locations collected during ≥3 months), nonjuvenile (≥1 year [YR]) marten in a forest preserve in northcentral Maine where trapping and timber harvesting had been excluded for >35 years. At the landscape scale, nearly all of the available habitat was used by marten. Further, composition of forest types within home ranges of radiocollared resident marten was similar to areas outside of home ranges. At the stand scale, marten used forest types disproportionately (P = 0.03) from availability within their home ranges during summer (1 May-31 Oct), but exhibited no apparent selection (P = 0.83) during winter. During summer, stands with substantial spruce-budworm (Choristoneura fumiferana)-caused mortality (<50% overstory canopy closure) had the highest selection index. No significant difference in stand-scale selection was detected among mature, well-stocked coniferous, deciduous, or mixed forest types during summer or winter. Mature, well-stocked coniferous forest was the least abundant forest type in home ranges of both sexes in both seasons, whereas mature, well-stocked deciduous forest was the most abundant. Further, much variability was observed in the amount of coniferous (range 0.8-36.3%) and deciduous (range 6.3-66.1%) habitat occurring in marten home ranges. Nine of 10 adult females captured in late spring were lactating, despite that their home ranges composed only 3-36% (median = 10.5%) mature coniferous forest. Our results suggest that marten do not require a dense or coniferous forest overstory and are consistent with the hypothesis that vertical and horizontal structure may be more important habitat components than age or species composition of the forest overstory. Thus, forest practices, such as on-site delimbing, cull-tree retention, and slash management may provide opportunities to maintain use of regenerating forest habitat by marten after harvesting. Structural complexity often may be associated with age and species composition of forests; however, conservation practices should consider structural attributes that functionally, influence the quality of forested habitats for marten, rather than merely age, species composition, and canopy closure of the forest overstory.

The Relative Importance of Nesting and Foraging Sites in Selection of Breeding Territories by Townsend's Warblers

We investigated habitat selection by the Townsend's Warbler (Dendroica townsendi), a Neotropical-Nearctic migrant that breeds primarily in mature coniferous forests. From 1993 to 1994, we compared the features of habitat selected for nest sites and foraging sites with those selected for territories in mature, mixed coniferous-deciduous forests in south-central Alaska. We also tested the prediction that large conifers are selected for nesting and foraging sites. Females placed nests in relatively large white spruce (Picea glauca) and consistently chose nest trees that were within areas of higher densities of large white spruce than were generally available. Nesting areas also had a higher density of small white spruce than was generally available, which may have been important in concealing nests from predators. Vegetation features selected for foraging differed from those selected for nesting and varied seasonally. Foraging was concentrated in medium-sized white spruce during the prehatching stage and became more generalized across coniferous and deciduous vegetation during the posthatching stage. Adults foraged in large white spruce in direct proportion to their availability on the study areas. Territories, which encompassed both nesting and foraging areas, were heterogeneous in vegetation structure and floristics. Areas selected for territories clearly reflected availability of the large white spruce selected for nest sites but did not reflect selection of medium white spruce for foraging. Characteristics of habitats varied with specific resource needs, but the distribution of Townsend's Warblers was most strongly related to specific habitat requirements for nest sites.

High rates of nitrification and nitrate turnover in undisturbed coniferous forests

THE importance of nitrate (NO–3) in the internal nitrogen cycle of undisturbed coniferous ecosystems has not been widely recognized1,2. Nitrate concentrations in soils from these forests tend to be low, and assays measuring net nitrification usually show exceedingly slow rates3,4. It may be, however, that microbial assimilation of NO–3 is substantial in these soils, and that net nitrification rates greatly underestimate gross rates5. Here we use a 15N isotope-dilution technique in intact soil cores to measure gross rates of nitrification and microbial assimilation of NO–3 in eleven undisturbed forest ecosystems of New Mexico and Oregon. We found that gross nitrification rates were surprisingly high in all of the forests examined. Net nitrification rates poorly predicted gross rates because the soil microbial communities had the capacity to assimilate almost all of the NO–3 produced. To our knowledge, this is the first report of gross nitrification and NO–3 assimilation rates in intact soil samples from a large number of contrasting forest ecosystems. Our results contradict previous assumptions that nitrification rates are low in mature coniferous forests and suggest that current models greatly underestimate the role of the microbial community in preventing NO–3 loss.

Predation Risk and Shifts of Foraging Sites in Mixed Willow and Crested Tit Flocks

Field studies have demonstrated interspecific niche separation between the Willow Tit Parus montanus and the Crested Tit P. cristatus in mixed-species flocks using mature coniferous forest. The dominant Crested Tit prefers the upper parts in pine, while the Willow Tit forages lower in the canopy. Foraging niche shifts of these species were studied when they foraged alternately in mature pine forest and in areas with saplings. In the saplings, where flying predators are unable to attack prey in the lower part of the canopy because of the dense branch structure there, Crested Tits switched to forage in the lower parts. As the subordinate species, Willow Tits foraged lower in the mature forest and higher up in the saplings, thus in both cases using more exposed parts of the canopy. Predation risk from Sparrowhawks Accipiter nisus seemed to be high. Since Crested Tits used the safest sites in both habitats, tits seem able to evaluate predation risk and adjust their habitat use. The spatial segregation of foraging niches in flocks of wintering tits can be explained by their response to habitat gradients in predator exposure.

Potential for mobility and population variability in similar-sized mammals and birds

Interspecific differences in population variability (fluctuations or cycles) can be due to environmental variability, different trophic interactions or differences in movement behaviour under severe circumstances. To establish the most important factor, variations in numbers of small mammals and passerine birds were examined during 11 years along transect lines extending from mature coniferous forests out into cleared areas, thus providing the potential for recording temporal variation at least in suboptimal habitats. Coefficients of variation did not correlate with sample means and were considerably higher in mammals than in birds. Spatial variation was usually larger than temporal variation, except for two small mammal species. Tropical migrants among the passerines demonstrated especially low temporal variation. Correlations with extrinsic variables (variation in weather and food supply) were only observed in resident mammals and birds. The differences in variability between the two vertebrate classes ...

The trout ( Salmo trutta L.) populations of the headwaters of the Rivers Severn and Wye, mid-Wales, UK

Brown trout ( Salmo trutta L.) populations were studied in two contrasting headstream systems in mid-Wales. An electrofishing survey in 1979 compared the long-term effects on trout populations in the upper Severn and upper Wye systems of mature conifer forest (Severn) and sheep pasture (Wye), respectively, and identified a previously unknown trout population in the upper Severn. In June 1979, brown trout were found in six out of seven stations in the Wye system. In the Severn system trout were found at only one station out of 10. Population densities and biomasses ranged from 0 to 0.32 fish m −2 and 0–5.6 g m −2 in the Wye and the age composition of the samples indicated good recruitment in most years. In the Severn station, population density was c.0.05 fish m −2 and biomass was c.3.1 g m −2. There was evidence of irregular recruitment. Growth in the Wye system could be described in terms of an asymptotic length of 21.5 cm, a von Bertalanffy [1] growth constant (K) of 0.34 and a I-group mean length in June of 7.9 ± 0.95 cm (95% C.L.). Growth in the Severn population appeared to be similar to but rather more rapid than, that in the Wye. The population of the upper Severn occupies a stream area of c.1700 m 2 and probably fluctuates between c.50 and c.400 individuals. Complete or partial isolation is likely to have occurred within the last 55 years. Acidification of upland streams often causes local extinction of trout. The occurrence of this small population in the Hafren may indicate that this is an acid tolerant strain, or that the water in the relevant portion of the Hafren is better buffered than previously supposed, or that the population is maintained by occasional incursions of spawners from further downstream.

Density of organic carbon in soil at coniferous forest sites in southern Finland

More detailed knowledge of the density of organic carbon in soils of boreal forests is needed for accurate estimates of the size of this C stock. We investigated the effect of vegetation type and associated site fertility on the C density at 30 mature coniferous forest sites in southern Finland and evaluated the importance of deep layers to the total C store in the soil by extending the sampling at eight of the sites to the depth of ground water level (2.4–4.6 m). The C density in the organic horizon plus 1 m thick mineral soil layer ranged from 4.0 kg/m2 to 11.9 kg/m2, and, on the average, increased towards the more productive vegetation types. Between the depth of 1 m and the ground water level the C density averaged 1.3–2.4 kg/m2 at the studied vegetation types and these layers represented 18–28% of the total stock of C in the soil. The results emphasize the importance of also considering these deep layers to correctly estimate the total amount of C in these soils. At the least fertile sites the soil contained about 30% more C than phytomass, whereas at the more fertile sites the amount of C in soil was about 10% less than the amount bound in vegetation.

Factors influencing the changes in Cs levels with time in boreal-forest plants in Sweden

The distribution and turnover of radiocesium from the reactor accident at Chernobyl in 1986 has been monitored in boreal forest vegetation in Sweden since 1986. The purpose has been to characterise the distribution of 137Cs in plants and biotopes over time. The study was mainly performed in an experimental forest where the fall-out in 1986 was 23 000 (S.D. 11 000) Bq/m2137Cs. In addition, we included 36 sites in a radius of ∼ 200 km from the experimental forest representing a range of ground deposition levels from 8000 to 80 000 Bq/m2 of 137Cs. Significant differences in 137Cs activity were found between plant species. The highest concentration in 1986 was 48 000 Bq per kg 137Cs dry mass in Nymphaéa cándida, and the lowest was 31 Bq per kg 137Cs dry mass (Epilobium angustifolium). We found a weak, but significant, correlation between ground deposition and cesium concentration in Betula pubescens and Vaccinum myrtillus. A significant decline in 137Cs levels occurred between 1986 and 1990. The cesium level in bilberry declined faster in young mixed forests (5- to 10-year-old clear cuttings) than in mature coniferous forests.

Factors influencing the changes in 137Cs levels with time in boreal-forest plants in Sweden

The distribution and turnover of radiocesium from the reactor accident at Chernobyl in 1986 has been monitored in boreal forest vegetation in Sweden since 1986. The purpose has been to characterise the distribution of 137Cs in plants and biotopes over time. The study was mainly performed in an experimental forest where the fall-out in 1986 was 23 000 (S.D. 11 000) Bq/m 2 137Cs. In addition, we included 36 sites in a radius of ∼ 200 km from the experimental forest representing a range of ground deposition levels from 8000 to 80 000 Bq/m 2 of 137Cs. Significant differences in 137Cs activity were found between plant species. The highest concentration in 1986 was 48 000 Bq per kg 137Cs dry mass in Nymphaéa cándida, and the lowest was 31 Bq per kg 137Cs dry mass ( Epilobium angustifolium). We found a weak, but significant, correlation between ground deposition and cesium concentration in Betula pubescens and Vaccinum myrtillus. A significant decline in 137Cs levels occurred between 1986 and 1990. The cesium level in bilberry declined faster in young mixed forests (5- to 10-year-old clear cuttings) than in mature coniferous forests.