Impacts of hemlock looper defoliation on growth and survival of balsam fir, black spruce and white birch in Newfoundland, Canada

Hemlock looper (Lambdina fiscellaria fiscellaria (Guen.)) is an economically damaging defoliator that undergoes periodic outbreaks in Newfoundland, Canada. It defoliates and causes extensive tree mortality to its primary host, balsam fir (Abies balsamea [L.] Mill.). We quantified tree survival using data from permanent sample plots (PSPs) and growth reduction or release using dendrochronology, and related these impacts to defoliation severity determined from annual aerial defoliation survey data. Such impact relationships are necessary as a fundamental input to a Decision Support System. Growth and survival of balsam fir, black spruce (Picea mariana (Mill.) B.S.P.) and white birch (Betula papyrifera Marsh.) were assessed from 1996 to 2008 in 48 Newfoundland Forest Service PSPs, selected based on four classes of defoliation severity. Two years of severe (71-100%) defoliation resulted in almost complete mortality for balsam fir, 10 years after defoliation, whereas survival was 70-80% for black spruce and white birch. Lower defoliation severity (1-2 years of moderate (31-70%) or 1 year of severe) resulted in approximately 60% survival for balsam fir and no reduction in survival for black spruce and white birch. Maximum growth reduction of balsam fir was 10-15% with 1 year of moderate-severe defoliation, 35-40% with 2 years of moderate defoliation, and about 50% with 2 years of severe defoliation. Growth recovered to pre-defoliation rates 5 years after defoliation ceased in all severity classes. Growth reduction and recovery of black spruce were more variable and lower than for balsam fir, and white birch exhibited only minor (<10%) growth reduction during the defoliation year or 1 year after defoliation. Control measures should focus on avoiding severe defoliation for two consecutive years.     

Availability of standing trees for large cavity-nesting birds in the eastern boreal forest of Québec,Canada

Large cavity-nesting birds depend on large-diameter trees for suitable nest sites. The increased spatial extent of commercial timber harvesting is modifying forest structure across the land base and may thus compromise the availability of large trees at the landscape scale. In this study, our objectives were to (1) characterize the availability of large living and dead trees in old-growth stands dominated by different tree species and surficial deposits that encompass the range of natural cover types of eastern Québec's boreal forest; (2) analyze the distribution of trees among decay-classes; and (3) compare the availability of large trees in unharvested, remnant, and harvested stands for the entire range of decay-classes. A total of 116 line transects were distributed across unharvested forests, remnant linear forests, and cutblocks in cutover areas. Unharvested forest stands (black spruce [Picea mariana], balsam fir [Abies balsamea]–black spruce, balsam fir–white spruce [Picea glauca] and balsam fir) reflected a gradient of balsam fir dominance. The remnant forests selected were isolated for 5–15 years. Analyses were performed at two diameter cut-off values. Trees with DBH ≥20 cm were considered for availability of total trees whereas trees with DBH ≥30 cm were considered for availability of large trees. Forest stands comprised high proportions of standing dead trees (33% of all stems, 8% were large dead stems). Availability of total and large standing trees increased with the dominance of balsam fir in stands. Forest stands located on thick surficial deposits showed higher densities of large dead trees for every stand type suggesting a higher productivity on those sites. Availability of stems according to decay-classes showed a dome-shaped distribution with higher densities of snags in intermediate decay stages. However, for large stems, black spruce stands showed a significantly lower availability that was consistent across all decay-classes. In linear remnant forests, pure balsam fir stands were absent. Remnant stands thus showed a much lower availability in large trees when compared with unharvested balsam fir stands. Clearcuts had the lowest densities of dead trees across sampled stands. Current even-aged management practices clearly affect availability and recruitment of large trees, therefore forest-dwelling wildlife relying on these structures for breeding is likely to be affected by large-scale harvesting in coniferous boreal forests.     

Forest regeneration 50 years following partial cutting in mixedwood ecosystems of southern Quebec,Canada

The impact of winter harvesting on regeneration 50 years after an experimental diameter-limit cutting was examined in mixed deciduous–coniferous ecosystems of southern Quebec, Canada. The study was conducted in La Mauricie National Park, Quebec, Canada. Regeneration data in two balsam fir (Abies balsamea (L.) Mill.), red spruce (Picea rubens Sarg.), sugar maple (Acer saccharum Marsh.), and yellow birch (Betula alleghaniensis Britt.) ecosystem types were analyzed. Comparisons between uncut and cut stands were obtained from a total of 63 sample plots. For both ecosystems, there were no significant differences between uncut and cut plots for regeneration density and stocking. The most abundant regeneration species were balsam fir, red spruce, sugar maple, red maple (Acer rubrum L.), yellow birch and American beech (Fagus grandifolia Ehrh.). The type of diameter-limit cutting described in the study did not affect regeneration density and stocking but its impact on productivity, timber quality and genetics is still unknown.     

Representing site productivity in the basal area increment model for FVS-Ontario

The utility of site index as a predictor variable in models for complex, mixed species stands is limited because the site index concept is not well suited for these stand types. Additionally, there is no standard protocol of estimating site index for uneven-aged mixed species stands, which is evident in permanent sample plot (PSP) and co-operative (COOP) data sets available from the Province of Ontario, Canada. Under such circumstances, an alternative to site index in a basal area increment model was explored, using a combination of climate and Forest Ecosystem Classification (FEC) variables from the Ontario boreal region. Among the four candidate climate variables chosen, mean annual temperature (MAT) explained the most variability in basal area increment for the four selected tree species – trembling aspen (Populus tremuloides Michx.), balsam fir (Abies balsamea (L.) Mill.), jack pine (Pinus banksiana Lamb.), and black spruce (Picea mariana (Mill.) B.S.P.). Our results indicated that a combination of the climate variable, MAT, and FEC explained a substantially higher proportion of variation in the basal area increment than site index alone. Thus, climate and FEC variables are superior substitutes in the basal area increment model even when error-free site index values are possible to obtain.     

Can the impact of deer browsing on tree regeneration be mitigated by shelterwood cutting and strip clearcutting?

Silvicultural treatments creating large canopy openings failed to restore regeneration of balsam fir (Abies balsamea (L.) Mill.) due to browsing pressure from white-tailed deer (Odocoileus virginianus Zimmermann). Consequently, we tested two alternative silvicultural treatments aimed at improving balsam fir establishment on Anticosti Island (Québec, Canada). In 1998 and 1999, we set up shelterwood seed cutting using three harvest intensities (0, 25 and 40% of basal area) and strip clearcutting with scarification using three different strip widths (15, 30 and 45 m), both with fenced and unfenced regeneration plots, in balsam fir stands. After 8 years, shelterwood seed cutting did not allow the establishment of new balsam fir seedlings, nor the development of unbrowsed balsam fir seedlings. In the strip clearcutting, deer browsing suppressed growth of palatable species in all strip widths. This favoured the development of unpalatable species, especially white spruce (Picea glauca (Moench) Voss). Our study demonstrates that the use of silvicultural treatments alone is unlikely to restore balsam fir regeneration on Anticosti Island, as long as the deer population remains higher than 20 deer/km².     

Height–diameter equations for boreal tree species in Ontario using a mixed-effects modeling approach

Height–diameter relationships based on stand characteristics (trees/ha, basal area, and dominant stand height) were investigated for balsam fir, balsam poplar, black spruce, jack pine, red pine, trembling aspen, white birch, and white spruce using data from permanent growth study plots in northern Ontario, Canada. Approximately half the data were used to estimate model parameters with the rest used for model evaluation. Multiple Chapman–Richards functions with parameters expressed in terms of various stand characteristics were fit to determine the best models for predicting height.     

Precommercial thinning as a silvicultural option for treating very dense conifer stands

Lack of available workforce in motor-manual operations has led to increased interest in mechanized precommercial thinning (PCT) treatments. We evaluated 15 years of growth and yield development of a very dense (27,000 stems ha^–1) balsam fir (Abies balsamea (L.) Mill) and black spruce (Picea mariana (Mill.) B.S.P.) stand after six PCT treatments: (1) motor-manual (MAN), (2) motor-manual with crop tree release (MAN-C), (3) mechanized (MEC), (4) mechanized with residual patches (MEC-P), (5) semi-mechanized (mechanized followed by motor-manual, MEC-S), and (6) unthinned control (CON). Compared to CON, both MAN and MEC-S increased height of balsam fir study trees by 53–56% and diameter at breast height (DBH) by 57–58%. MAN-C and MEC-S increased DBH of black spruce study trees by 15–31% over all other treatments. The proportion of merchantable basal area (BA) was higher in MAN (62%) and MEC-S (56%) than in CON (22%) and MEC (25%), without a reduction in total BA. PCT treatments that provided a uniform distribution of potential crop trees (MAN, MEC-S) performed better than MAN-C and MEC-P, while MEC yielded the poorest responses. Our findings highlight the need to develop new tailored mechanized systems for high wood production and low operational cost.     

Canopy disturbance and intertree competition: implications for tree growth and recruitment in two yellow birch–conifer stands in Quebec, Canada

Composition, structure, and species-specific patterns of recruitment and growth were characterized in two yellow birch (Betula alleghaniensis Britt.)–conifer stands in Quebec, Canada, to improve our understanding of the dynamics of these complex ecosystems. The mixture of mid- and shade-tolerant species in the canopy, the inverse J-shape stem diameter distribution, and the age distribution were indicative that the two stands were in a late-successional stage. Recruitment of mid-tolerant species above 1.3 m in height appeared to be periodic and synchronized with historical spruce budworm (Choristoneura fumiferana Clem.) outbreaks, while the coniferous component of these mixedwood stands recruited continuously. Results suggest that recruitment of yellow birch and red maple (Acer rubrum L.) requires disturbances of a certain intensity that affect at least 25 % of the forest cover. In contrast, balsam fir (Abies balsamea (L.) Mill.) and red spruce (Picea rubens Sarg.) can recruit under the canopy without relying on moderate or large canopy disturbances. Results suggest that the historical disturbance regime, and differences in shade tolerance between species, largely govern the contemporary composition of these stands. This study improves the comprehension of mechanisms that regulate the dynamics of yellow birch-conifer stands and will be useful for the subsequent elaboration of forest management strategies.     

The impact of hemlock looper (Lambdina fiscellaria fiscellaria (Guen.)) on balsam fir and spruce in New Brunswick, Canada

In 1989, the first recorded outbreak of hemlock looper (Lambdina fiscellaria fiscellaria (Guen.)) occurred in New Brunswick, Canada. Data were collected from ten plots established in an area infested from 1992–1994, to assess impacts of hemlock looper. Ocular and branch sample assessments of current defoliation and ocular assessments of total defoliation (all age classes of foliage) were conducted for balsam fir (Abies balsamea [L.] Mill.), white spruce (Picea glauca [Moench] Voss), and black spruce (Picea mariana (Mill.) B.S.P.). Stand response was assessed and related to cumulative defoliation. Ocular assessments were found to accurately estimate defoliation, which was significantly related to tree mortality. Ninety-two percent of balsam fir trees that had cumulative defoliation >90% died. Mortality of balsam fir was significantly (p < 0.05) related to tree size, in both lightly and severely defoliated plots; trees with DBH <11 cm sustained 22–48% higher mortality than larger trees. Mortality of balsam fir, in terms of both percent stems/ha and m³/ha merchantable volume, increased exponentially in relation to three estimates of cumulative (summed) plot mean defoliation. The strongest relationships (r² = 0.75–0.79) were between mortality and the ocular defoliation assessment for 1990–1993 foliage. Tree mortality caused by the looper outbreak ranged from 4–14% stems/ha in lightly defoliated and from 32–100% in severely defoliated plots; merchantable volume killed was 3–14 m³/ha and 51–119 m³/ha, respectively. Relationships between mortality and defoliation were similar when defoliation was assessed for 1987–1993 and 1990–1993 foliage age classes.     

Spatial distribution of late-successional coniferous species regeneration following disturbance in southwestern Québec boreal forest

Remnant tree stands left intact following a disturbance constitute the sole seed banks available for regeneration of coniferous species that neither bear serotinous cones nor reproduce vegetatively. The success of regeneration of tree species on these disturbed sites is, therefore, dependent on the distance from potential seed sources. The regeneration of balsam fir (Abies balsamea (L.) Mill.), white spruce (Picea glauca (Moench) Voss) and white cedar (Thuja occidentalis L.) was studied at two sites in Québec’s southwestern boreal forest in order to quantify the influence of remnant stands on spatial distribution of regeneration. The first site is located in an area that burned in 1944 while the second site is located in an area that was clear-cut in the mid-1980s. Canonical correspondence analyses were used to determine the respective contributions of environmental data and spatial variables to the pattern of spatial distribution of regeneration. The results reveal that distance from a remnant stand is the most important variable in explaining spatial distribution of regeneration when compared to environmental variables such as soil type, drainage, slope and altitude. The plots of regeneration density against distance from a remnant stand for both the burned site and logged site show that regeneration density decreases abruptly with distance from a remnant stand. Furthermore, spatial autocorrelation analyses (Moran’s I) indicate that even small remnant zones can significantly influence the pattern of spatial distribution of regeneration for the three species studied. The results presented here suggest that where preestablished regeneration is not abundant enough, alternative silvicultural systems such as strip clear-cutting or seed-tree systems could be used instead of cuts with protection of regeneration and soils (CPRS).     

Effects of the overstory on the diversity of the herb and shrub layers of Anatolian black pine forests

Understory plants are important components of forests because they are responsible for the majority of the vascular plant diversity of forest ecosystems. The richness and composition of understory communities are closely related to the tree layer diversity, structure and composition. The aim of this study was to examine the understory diversity of Anatolian black pine (Pinus nigra Arnold subsp. pallasiana (Lamb.) Holmboe)-dominated forests on the Kazda?? Mountains of West Turkey. To describe the overstory structure and composition in a numerically and quantitatively well-defined manner, cumulative abundance profiles (CAPs) of the tree species were used. The resemblance of the sampling plots was classified into five stand types assessing the CAP through the Fuzzy C-Means clustering method. A permutational multivariate analysis of variance (PERMANOVA) was performed to test the variance of the community ecological distance between the five stand types, and the results showed significant differences in these clusters. Many shade-tolerant plants were associated with the mixed stands of Anatolian black pine–Kazda?? fir. The composition of the herb and shrub layer could not be explained by the environmental variables but by differences in the overstory structure of the stands. Pure or nearly pure Anatolian Black pine stands were more diverse than mixed oak–Anatolian black pine and Kazda?? fir–Anatolian black pine stands. However, although dense and young pure Anatolian black pine stands had the most diverse plant species in the shrub layer, they were ranked third in terms of the herb layer diversity. The Anatolian black pine–Kazda?? fir mixed stands had the lowest herb and shrub layer diversity. These results allow us to comprehend the relationship between the overstory structure and composition, and the understory diversity. Understanding this relationship is important for the conservation of understory plant diversity in the management of forest ecosystems.     

Forest succession over a 20-year period following clearcutting in balsam fir-yellow birch ecosystems of eastern Québec,Canada

Vegetation development over a 20-year period following clearcutting in balsam fir (Abies balsamea (L.) Mill.)-yellow birch (Betula alleghaniensis Britt.) ecosystems was examined in a study area located in eastern Québec, Canada. Vegetation, physiographic and soil data were collected in 10 mature ecosystems and in 30 ecosystems harvested 5 years ago (10), 10 years ago (10), or 20 years ago (10). The 40 ecosystems had similar physiographic and soil characteristics. They were typically located on mesic sites situated on ground moraines thicker than 50 cm. Following harvesting, sites were invaded by competing species. Mountain maple (Acer spicatum Lamb.) was the most important competing species. Twenty years after logging, it fully occupied the sites with 7040 stems ha⁻¹ (diameter at breast height ≥ 1 cm). Its regeneration stocking reached 88% with a density of 22775 stems ha⁻¹. Wild red raspberry (Rubus idaeus L. var. strigosus (Michx.)) and fireweed (Epilobium angustifolium L.) were abundant during a 10-year period after logging, but disappeared almost completely afterwards. The abundance of competing species has considerably reduced site production for a period of 20 years and will probably continue to do so for 20 to 30 more years. The proportion of commercial deciduous species increased from 36% of the total number of stems (diameter at breast height ≥ 1 cm) in mature stands to 89% in stands harvested 20 years ago. Balsam fir and white spruce (Picea glauca (Moench) Voss) advanced regeneration was considerably reduced. Stocking of these species went down from 76% in mature stands to only 27% in 20-year-old stands. As a result, it is unlikely that the harvested areas will naturally evolve toward the original climax balsam fir-yellow birch forest type in the foreseeable future.     

Modelling primary branch frequency and size for five conifer species in Maine,USA

Quantitative models of crown structure have been developed for several conifer species, but these studies have rarely simultaneously fit the models across multiple species. This study used extensive crown structure data for the five primary conifer species in Maine to test for species differences in maximum branch diameter profile, branch density, and relative branch diameter distribution. The species included balsam fir [Abies balsamea (L.) Mill], northern white-cedar [Thuja occidentalis (L.)], eastern hemlock [Tsuga canadensis (L.) Carr.], eastern white pine [Pinus strobus (L.)], and red spruce [Picea rubens (Sarg.)]. After accounting for key covariates, significant species differences were found in all crown structural attributes examined in this study. Profiles for the mean tree indicated that northern white-cedar had the smallest maximum branch diameters throughout the crown and white pine had the largest, except near the base of the crown where the species switched in rank. The density of live branches in a crown had the widest range of variation of the examined crown structural attributes. Red spruce had a significantly higher density of primary branches than the other conifers, particularly in the upper crown. The relative branch diameter distribution indicated that balsam fir had a distribution more skewed towards larger relative branch sizes, while eastern hemlock and red spruce had distributions shifted towards smaller relative branches. This study highlights the range of variability in key crown structural attributes due to inherent species differences, but indicates that models fit across multiple species can perform quite well as the amount of explained variation was relatively high.     

Development and activity of early saproxylic fungal communities in harvested and unmanaged boreal mixedwood stands

Limited scientific information is currently available regarding saproxylic fungal communities in the boreal forest of North America. We aimed to characterize the community development, richness and activity of saproxylic fungi on fresh wood in harvested and unmanaged boreal mixedwood stands of northwestern Québec (Canada). Fresh wood blocks (n = 480) of balsam fir (Abies balsamea (L.) Mill.) and trembling aspen (Populus tremuloides Michx.) were placed on the forest floor in a range of stand conditions (n = 24). Blocks were harvested every 6 months for up to 30 months and characterized for species composition and richness (PCR–DGGE, DNA sequencing), respiration, wood density and lignin and cellulose content. Colonization by a wide range of functional groups proceeded rapidly under different stand conditions. We detected a total of 35 different fungal operational taxonomic units, with the highest species richness at the wood block level being observed within the first 12 months. No differences in community composition were found between wood host species or among stand conditions. However, the variability in fungal communities among blocks (β diversity) was lower on trembling aspen wood compared with balsam fir and decreased over time on trembling aspen wood. Also, fungal activity (respiration and wood decomposition) increased on trembling aspen wood blocks and species richness decreased on balsam fir wood over time in partial-cut sites. The overlap in tree composition among stands, the high volume of logs and the recent management history of these stands may have contributed to the similarity of the saproxylic fungal community among stand types and disturbances.     

Establishment of the Second Rotation in the Jutland Heath Plantations

The paper describes briefly the silvicultural methods used toregenerate stands of pure Norway spruce (Picea abies Karst.)or Norway spruce mixed with a small proportion of Silver fir(Abies alba Mill.) on the poor heath soils of Jutland. Regenerationafter clear felling, uniform shelterwood, and shelterwood stripfelling is described. The last method has advantages over theother two.     

Species differences in total and vertical distribution of branch- and tree-level leaf area for the five primary conifer species in Maine, USA

Vertical distribution of leaf area largely governs both tree structure and function. Models of this important tree attribute have been constructed for several commercially important conifers. However, a limited number of studies have compared alternative modeling techniques and inherent species differences. This study used several existing datasets for the five primary conifer species in Maine, namely balsam fir [Abies balsamea (L.) Mill.], northern white-cedar [Thuja occidentalis (L.)], eastern hemlock [Tsuga canadensis (L.) Carr.], eastern white pine [Pinus strobus (L.)], and red spruce [Picea rubens (Sarg.)] to examine species variation in total and vertical distribution of projected leaf area at the individual branch- and tree-levels. In addition, multiple methods for modeling the vertical distribution of leaf area were examined across the species. For a given branch diameter and location within the crown, eastern hemlock branches held the greatest amount of leaf area, followed by balsam fir, northern white-cedar, white pine, and red spruce. At the tree-level, eastern white pine held the greatest amount of leaf area followed by eastern hemlock, balsam fir, red spruce, and northern white-cedar for a given tree size. Across species, the two-parameter, right-truncated Weibull distribution performed the best for predicting vertical distribution of leaf area when compared to the four-parameter beta and Johnson's S_B distributions (reduction of root mean square error of 1.7–21.1%). Northern white-cedar had a relative distribution of leaf area distinctly different than other species in this study with a mode shifted towards the upper crown. In contrast to red spruce and white pine, the mode of the relative distribution of leaf area for balsam fir and eastern hemlock occurred lower in the crown. Results of this study suggest that differences in total and vertical distribution of leaf area exist between species, but significant amounts of their variation are largely accounted for by bole and crown size.     

Effects of root trenching of overstorey Norway spruce (Piceaabies) on growth and biomass of underplanted beech (Fagussylvatica) and Douglas fir (Pseudotsugamenziesii) saplings

In Central Europe, the conversion of pure Norway spruce stands (Picea abies [L.] Karst.) into mixed stands with beech (Fagus silvatica L.) and other species like e.g. Douglas fir (Pseudotsuga menziesii [Mirb.] Franco) is accomplished mainly by underplanting of seedlings beneath the canopy of overstorey spruce trees after partial cutting treatments what means exposure to shade and below-ground root competition by the overstorey to the seedlings. Particularly about the second factor, our knowledge is limited. Therefore, we carried out a below-ground competition exclusion experiment by root trenching and investigated the effects on soil resources, growth, and biomass partitioning of underplanted beech and Douglas fir saplings under target diameter and strip cutting treatments. The exclusion of overstorey root competition by trenching increased the soil water potential in the second year that had a fairly dry growing season and led to significantly higher foliar concentrations of most nutrients, particularly in Douglas fir, indicating an amended nutrient supply. Both improvements were accompanied by an increase in length and diameter increment of the underplanted saplings, appearing in both species only after having surpassed a species-specific threshold light value (Douglas fir 16% of above canopy radiation, beech 22%). We also found significant interactions between trenching and light for specific fine root length and further biomass and morphological parameters. Judged by the much steeper increase in height and diameter growth with increasing light after release from below-ground competition, Douglas fir saplings appeared to be more sensitive to root competition than beech saplings what conforms to older findings for beech. According to our results, a strip cutting seems to be more appropriate than a target diameter cutting treatment to replace a pure spruce stand by a mixed stand with beech and Douglas fir.     

Soil solution,foliar concentrations and tree growth response to 3-year of ammonium-nitrate addition in two boreal forests of Québec,Canada

Ammonium nitrate (NH₄NO₃) was applied monthly (from June to October) for 3 years in a balsam fir (Abies balsamea (Linné) Miller) and a black spruce (Picea mariana (Mill.) BSP) boreal forest in Québec (Canada). The design was composed of nine experimental units of 10 m × 10 m for each site. Application rates were 3 and 10 times the atmospheric N deposition measured at each site which was 6 and 3 kg ha⁻¹ year⁻¹ for the fir and the spruce sites, respectively. Soil solution composition (30 and 60 cm), tree growth, and foliar concentrations were analysed. The inorganic N in the soil solution of the control plots of both sites was low, particularly at the spruce site indicating that these forests are actively accumulating the atmospheric deposited N. Nitrogen additions regularly caused sudden and large inorganic N increases in the soil solution at both sites, both treatments and both sampling depths. However, these increases were transitory in nature and no persistent changes in inorganic N were observed. It was estimated that more than 95% of the added N was retained above the rooting zone at both sites. Nitrogen addition increased N, Ca, Mg and Mn foliar concentrations at the black spruce site but had no effects at the balsam fir site. After 3 years of N application, tree growth was similar in the control and the treated plots at both sites. Our results show that slow growing black spruce boreal forests with low ambient N deposition are responsive (in term of foliar N, Ca, Mg and Mn concentrations) to even small increases in N inputs, compared to higher growth balsam fir boreal forests with higher N deposition.     

Sustainability in multi-aged stands: an analysis of long-term plenter systems

Long-term research plots in multi-aged stands managed with theplenter system were assessed to evaluate sustainability of theplenter system in Central Europe. Plots primarily consistedof Norway spruce (Picea abies (L.) Karst., silver fir (Abiesalba Mill.) or European beech (Fagus sylvatica L.) and weremeasured for seven to 16 measurement intervals over 60–91years. Sustainability was assessed with four types of criteria:stand density, tree species diversity, basal area increment,and stand structure. Comparable even-aged stands were also analysedto compare and evaluate the performance of the measures of sustainability.Measures of species diversity, increment and stand structuraldiversity generally experienced increasing trends over timein these even-aged stands. Basal area generally increased andtrees ha^-1 decreased in multi-aged stands following similarpatterns as in even-aged stands. These results suggest thatthe plenter system is still evolving and is not the model ofsustainability often assumed. Many of the measures used havepotential as indicators of sustainability in multi-aged stands.     

Lumbricid associations on a former open clay pit after recultivation with different tree species

The earthworm fauna was recorded from a former open clay pit five and seven years after the area had been recultivated with various tree species. The highest abundances (200–245 specimens/m²) and biomasses (46.8 to 48.4 g/m²) were found in the following stand types: mixed woodland of balsam poplar (various sorts) and grey alder (Alnus incana (L.)Moench), mixed woodland of balsam poplar (Andoscoggin) and black alder (Alnus glutinosa (L.)Gaertn.), and a pure stand of black alder. Clearly lower values were found in a plot with common oaks (Quercus robur L.) under a dense shelterwood of naturally regenerated willows (Salix spec.), and a plot exclusively stocked with naturally regenerated willows. The rapid resettlement of the backfilled, compacted clay soil is above all explained by the high pH-values found in the surface soil. The differences between the studied plots regarding total abundance and biomass might be explained by the different qualities and amounts of litter. The highest species diversity — expressed by the Shannon-index — and the highest proportion of endogeic species, particularlyAporrectodea caliginosa Savigny 1826, were calculated for the two stands with a mixture of alder and balsam poplar. This result could have been caused by the lack of parent soil bed and the particularly high pH-value of the soils found there.