Fir Regeneration Research Articles

INFLUENCES OF SECONDARY DISTURBANCES ON LODGEPOLE PINE STAND DEVELOPMENT IN ROCKY MOUNTAIN NATIONAL PARK

Although high-severity fire is the primary type of disturbance shaping the structure of lodgepole pine (Pinus contorta) stands in the southern Rocky Mountains, many post-fire stands are also affected by blowdown, low-severity surface fires, and/or outbreaks of mountain pine beetle (MPB; Dendroctonus ponderosae). The ecological effects of these secondary disturbances are poorly understood but are potentially important in the context of managing for ecological restoration and fire hazard mitigation. We investigated the effects of blowdown, surface fires, and MPB outbreaks on demographic processes in post-fire lodgepole pine stands in Rocky Mountain National Park, Colorado, USA. We used dendroecological methods to reconstruct stand characteristics prior to and following secondary disturbances for paired stands with and without secondary disturbances. Surface fire events do not kill canopy trees or trigger pulses of recruitment and as such do not have detectable influences on stand development. In contrast, both MPB and blowdown kill canopy trees and trigger pulses of tree regeneration of lodgepole pine and subalpine fir (Abies lasiocarpa). The amount and species composition of post-disturbance regeneration is dependent on the severity of the disturbance and on the time since stand initiation. Secondary disturbances of higher severity (i.e., killing >50% of the canopy trees) that occur in younger post-fire stands favor new establishment of lodgepole pine. In contrast, secondary disturbances of lower severity in older stands (>250 years) trigger a pulse of establishment of subalpine fir. The results of this study demonstrate that the high tree densities characteristic of lodgepole pine stands in the southern Rockies (southern Wyoming to northern New Mexico) are the result of dense regeneration following stand-replacing fires and that surface fires had little or no thinning effect on tree densities. Thus, current high stand densities in the study area are not the result of suppression of surface fires. Moreover, the strong pulses of regeneration following forest thinning by MPB and blowdowns imply that, depending on the degree of thinning, thinning prescriptions to reduce fuels in the lodgepole pine forest type may have the unintended consequence of increasing ladder fuels 15-20 years following treatments.

Browsing of tree regeneration by white-tailed deer in large clearcuts on Anticosti Island, Quebec

Browsing by the substantial population of white-tailed deer ( Odocoileus virginianus Zimmermann) on Anticosti Island hampers the regeneration of balsam fir ( Abies balsamea (L.) Mill.), which is both the deer's preferred food and shelter. The island's original fir stands have gradually been replaced by stands of white spruce ( Picea glauca (Moench) Voss), as this species is rarely browsed by the deer. This project assesses the impact on the regeneration of balsam fir and companion species by large clearcuts performed using cutting with protection of regeneration and soils (CPRS). To this end, fenced-off areas adjacent to unfenced areas were established in 1995 and 1996 in large CPRS clearcuts. The results show that the distance from forest edge does not influence the stocking, number and height of seedlings, while browsing does reduce these variables in the case of fir and paper birch ( Betula papyrifera Marsh.). However, stocking, number and height of white spruce seedlings were unaffected by both deer browsing and distance from forest edge. Woody debris seemed to protect balsam fir seedlings from browsing 8 years after cutting, but this protection should likely stop when seedlings will outgrow woody debris. It thus appears that large CPRS clearcuts will not permit the regeneration of balsam fir on a level sufficient for re-establishing fir stands on Anticosti Island.

Winter Forage Selection in White‐Tailed Deer at High Density: Balsam Fir is the Best of a Bad Choice

Abstract: We assessed winter forage selection by white‐tailed deer (Odocoileus virginianus) on Anticosti Island, Quebec, Canada, using cafeteria‐feeding trials. Winter habitat on Anticosti is degraded and free‐ranging deer at high densities consume 70% balsam fir (Abies balsamea) and 20% white spruce (Picea glauca), even though spruce is much more available than fir. Deer ate 89.9% balsam fir and 10.1% white spruce when the availability of both trees was equal. Deer did not eat shredded twigs more than intact twigs. Fiber content and condensed tannins were greater in white spruce than in balsam fir. Deer preference for fir was not based on texture but, more likely, on plant constituents, so we concluded that deer will nearly eliminate fir before they use any significant amount of white spruce. Management actions, therefore, need to be undertaken to enhance balsam fir regeneration.

Density‐related effects of deer browsing on the regeneration dynamics of boreal forests

SummaryThe density of large herbivores is a major driver of forest ecosystem structure and function in conjunction with episodic disturbances, especially in forests with a regeneration strategy based on shade‐tolerant seedlings capable of re‐establishing canopy dominance (advance regeneration). Yet, uncertainty about the relationships between forest regeneration, herbivore density and other disturbances makes it difficult to set population goals. Using an innovative controlled browsing experiment, we investigated the relationships between the regeneration dynamics of balsam firAbies balsamea, the density of white‐tailed deerOdocoileus virginianusand timber harvesting.We hypothesize that advance tree regeneration either: (i) recovers approximately linearly as deer density is reduced; (ii) recovers exponentially; or (iii) does not recover because factors other than browsing control advance regeneration. We tested these alternatives through manipulation of deer densities (0, 7·5, 15 deer km−2andin situlocal densities) and forest cover (clearcut and uncut forest).Balsam fir seedling mortality decreased exponentially with decreasing deer density in clearcut and approximately linearly in uncut forest. Independently of deer density, the recruitment of seedlings in clearcut dropped from 56 ± 5% to 7 ± 1% within 3 years.Seedling growth increased exponentially with decreasing deer density in clearcut whereas no height growth was observed in uncut forest.Overall, the abundance of fir saplings recovered exponentially in clearcut but remained low and independent of deer density in uncut forest. The abundance of sprucePiceaspp. saplings was unrelated to deer density and increased with time.Synthesis and applications. Forest disturbance from selective browsing at high deer densities over an extended period of time leads to recruitment failure following a canopy disturbance such as a clearcut. Indirect competitive advantage given to species resistant to browsing can shift forest composition. Nonlinear relationships between fir regeneration and deer densities imply that the level of culling required to reach herbivore densities compatible with natural regeneration of native forest is larger than expected if tree regeneration was proportional to deer density. In the boreal forest of Anticosti Island, local densities < 15 deer km−2achieved within 3 years following clearcut are compatible with the maintenance of native forest.

Factors controlling the regeneration process in unevenly aged silver fir forests: inferences from the spatial pattern of trees

The main objective of this study was to prove the relationship between the spatial pattern of trees and distribution of advanced regeneration in structured Abies alba Mill. forests in the Western Carpathians (of southern Poland). In 13 sample plots (0.45–1.00 ha in size), the locations of all live trees above 15 cm in d<sub>1.3 </sub>and all stumps of canopy trees (above 50 cm in d<sub>1.3</sub>) were determined. In addition, in all plots the coordinates of all live and dead pole-stage trees (5–15 cm in d<sub>1.3</sub>), in seven plots the coordinates of all live and dead younger saplings (0.5–1.3 m in height), and in eight plots the coordinates of all live and dead older saplings (above 1.3 m in height and below 5 cm in d<sub>1.3</sub>) were registered. The univariate and bivariate Ripley’s K-function was applied to test spatial independence of the patterns of trees representing different size categories. In each of the stands, younger and older saplings and pole-stage trees showed an aggregated pattern. The strongest attraction between trees of these size categories was detected at the scale 6, 5 and 10 m, respectively. At the scale below 10 m, a positive spatial correlation was frequently found between large firs and pole-stage trees and saplings. A spatial repulsion between advanced fir regeneration and trees of the middle stand layer was negligible or observable only in a relatively large scale above 15 m. The patterns of saplings and trees of the lower stand layer appeared to be spatially independent in most of the stands being studied. These results suggest that in unevenly aged fir forests, a stable mechanism is generating the aggregated patterns of regeneration functions and the factors involved are spatially linked with the distribution of large firs. Therefore, a hypothesis is advanced that the spatial pattern of regeneration in such forests is controlled by edaphic factors – in particular, the humus form – and that light conditions play only a secondary role.

Dinamiche evolutive di post-selvicoltura nella foresta di Vallombrosa

Abstract: The present study aims to highlight the successional patterns of forest stands showing a simplified structure and in which the silvicultural practices have been neglected along. Surveys were carried out in the Tuscan Apennine stands of Vallombrosa (3 pure silver fir stands, 1 pure chestnut old coppice, 1 pure douglas fir stand and 1 mixed silver fir-Norway spruce stand), where records on the stand dynamics of the last forty years are available (1966, 1987, 2004). The changes in structure are synthetically expressed by means of indexes (regeneration index, both structural and floristic diversity indexes). In three areas the growth pattern of silver fir regeneration was studied: the dendrochronological analysis showed different growth rates according to the different canopy cover degree. As for management aspects, according to the results of the present research, is emphasised that the canopy reduction is the prerequisite for a silviculture style aiming to enhance the system diversity. Gradual openings of the canopy, as the ones following selection or shelterwood systems, basing on long regeneration time span, are suitable to enhance the re-naturalisation both of silver fir stands (e.g., increasing the amount of broadleaves in the understory) and chestnut old coppices (e.g., favouring the coming of silver fir in the understory). Because the undisturbed conifer stands dynamics following the abandonment of forestry practice results very often uncertain as trend and direction, it appears important to follow up the process by mean of close-to-nature silviculture interventions. In this sense, the paper finally outlines the necessity to face the interactions between forest regeneration and wild ungulate populations, which currently represents one of the most dramatic problems of sustainable management.

Étude rétrospective de l'accroissement en diamètre du sapin baumier (Abies balsamea (L.) Mill.) et de l'épinette rouge (Picea rubens Sarg.) en peuplements mixtes après une coupe a diamètre limite

Diameter growth at breast height of 341 balsam fir and red spruce stems has been reproduced over a time lapse of 50 years following a diameter limit cutting. The available information has been analyzed with a statistical model in which the effects of time, species (two levels), ecological type (three levels) and diameter at harvesting have been tested. Results indicate that balsam fir saplings have higher diameter growths than red spruce saplings, but only in the case of better ecological types. The differences between both species are smaller for stems having a merchantable diameter (dbh > 9.0 cm) at harvesting time. On poor ecological station, red spruce diameter growth is more important than for balsam fir and this, whatever the diameter at harvesting time. On the other hand, as indicated by this analysis, stem diameter at the time of silvicultural treatment constitutes a significant variable in the prediction of diameter growth for red spruce stems, while the effect of this variable is less identifiable for balsam fir. Even if significant, the growth differences between the two species are small. The competition created by the balsam fir regeneration on red spruce saplings is definitely not the cause of the depletion of red spruce in second growth stands.. Key words: red spruce (Picea rubens Sarg.), balsam fir (Abies balsamea (L.) Mill.), diameter growth, partial cut, mixed stands, linear model, mixed model

Is browsing the major factor of silver fir decline in the Vosges Mountains of France?

For many years, browsing wild ungulates have been considered the major cause for the decline of silver fir ( Abies alba) in Europe. To better understand the dynamics of silver fir–beech forests hosting important deer populations, we studied forest renewal using a synchronistic approach, i.e. by comparing similar stands of different ages. Regeneration in a series of forests, where seedlings (<150 cm) were submitted to an increasing browsing pressure, was examined initially. We then analysed young stands (>2 m), which have grown in similar ecological conditions and also under increasing browsing. Published results on regeneration have identified three key factors as modulators of the effects of deer browsing on the composition of regeneration: understory abundance, stand composition and orientation to sun. This paper deals with the second part of the study. It examines the influence, over time, of the three environmental characteristics, identified at regeneration stage, by analysing the composition and the structure of young stands grown under comparable conditions. A total of 152 plots of 150 m 2 each were selected, spread over 30 km 2 of an ancient game reserve and core analysis was used to identify whether trees were under 150 cm when browsing became noticeable. Our results confirmed the critical role of stand composition, orientation to sun and understory—the latter being far predominant. Indeed, previous stand composition (i.e. seed trees at the time of regeneration) and orientation to sun did not explain current young stand composition alone, but when a south-exposed slope was previously occupied by mature spruce, then young spruce trees were frequent. Understory clearly played a positive role in the conservation of fir, despite increased browsing by deer. In fact, fir was abundant in the young stands when understory above seedlings was important at the time of regeneration, but when understory was poor, spruce became the dominant species and fir was seldom observed. Overall, silver fir was often the dominant species among young stands, despite a progressive increase in spruce numbers. The dominance of fir may be explained by the particular sylvicultural history of the studied forests. However, in the future, the expansion of spruce, favoured by deer foraging on fir and by even-aged sylviculture, may lead to localized failure of fir regeneration. To promote silver fir–beech forest renewal, forestry practices should change towards a system more closely resembling natural forest dynamics.

Microsite patterns of conifer seedling establishment and growth in a mixed stand in the southern Alps

In many forests of the Alps, permanent forest cover and, therefore, its continuous renewal is the main silvicultural goal. Regenerating these forests must be based on a sound understanding of the ecology of the tree species in question. The regeneration of silver fir ( Abies alba Mill.) and Norway spruce ( Picea abies (L.) Karst.) in the upper montane zone of the southern central Alps has so far received little attention. The aim of this study was, therefore, to characterize the ecological niche for the establishment and growth of silver fir and Norway spruce seedlings in this zone. The study was conducted as a case study on a plot of 1.5 ha in the upper montane zone of southern Switzerland, at an altitude of 1380 m. The basal area of the mixed Norway spruce–silver fir stand was 43.7 m 2 ha −1. Seedlings were censused on 375 plots of 1.0 m 2 area. Seedling density was 1.30 ± 4.25 m −2 (mean ± standard deviation) for Norway spruce and 0.87 ± 1.50 m −2 for silver fir. Logistic regression models were used to test the effect of microsite characteristics on seedling occurrence, and general linear models for effects on seedling height growth and biomass increment. Most seedlings received less than 10% light (photosynthetic photon flux density) as compared to values in the open. Silver fir occurrence was positively related to microsites at the edge of canopy trees, but unrelated to ground cover type, light and micro-relief. Norway spruce occurrence was only, and positively, related to the presence of mosses. Height growth and biomass increment of seedlings of both species were only loosely correlated with microsite conditions. Seedlings without canopy cover grew faster than those under canopy cover, probably as a result of light and moisture limitations under the canopy of adult trees. Diffuse radiation was positively correlated with average annual biomass increment of silver fir, but not of Norway spruce seedlings. In general, the results suggest that silver fir seedlings have less specific microsite requirements than Norway spruce seedlings in terms of ground cover. They are also more shade tolerant, and therefore, grow faster than Norway spruce in low-light environments of the upper montane zone of the southern Alps. While the microsite concept can be helpful in designing silvicultural operations, it has limitations when only patch characteristics that are easy to assess are used, and others neglected. Finally, our study suggests that counting the number of green shoots is a promising method to quickly and non-destructively estimate the biomass of a great number of small seedlings.

Spatial distribution of regeneration in West-Carpathian uneven-aged silver fir forests

The objective of our study was to examine whether distribution of regeneration in uneven-aged fir (Abies alba Mill.) forests is related to the spatial pattern of trees. In 12 sample plots of size 0.45–1.00 ha (in total 8.65 ha, with stand basal areas ranging from 27.6 m2 ha−1 to 39.5 m2 ha−1), all live and dead trees above 5 cm in d1.3 were mapped and their diameters measured. In eight plots, all live and dead fir saplings were mapped. In three plots, the number of live fir saplings and seedlings was registered on small systematically distributed circular plots. The values of an analytically developed index of stand influence were compared in patches occupied and unoccupied by live or dead fir regeneration. Contrary to preliminary assumptions, only in a few cases did saplings and trees 5–15 cm in d1.3 appear more often in gaps and looser stand patches. Rather, in many plots, the opposite tendency was observed. The seedling density showed a weak but positive correlation with the index of influence. If the spatial pattern of regeneration reflects the spatially varying mortality of juvenile trees, then no evidence was found that stand competition was the most important factor inducing this mortality. On the contrary, on the basis of the results obtained, we can presume that the survival rate of juvenile firs was higher in patches with a relatively higher local basal area. Thus, it was hypothesised that, first, dispersion of regeneration in uneven-aged fir forests is controlled by easy-to-change edaphic factors such as humus form and acidity of the upper soil horizons, and second, that these soil features are linked with the spatial pattern of trees.

The influence of the spatial pattern of trees on forest floor vegetation and silver fir ( Abies alba Mill.) regeneration in uneven-aged forests

In the Western Carpathians (of southern Poland), in three representative multilayered fir stands, all trees above 6.9 cm in d 1.3 were mapped. Subsequently, forest floor vegetation cover, vascular plant species, and fir seedlings (below 0.5 m in height) were systematically sampled on small circular plots in a 5 m × 5 m grid. On the basis of location in the stand and indicator values of plant species registered within the plot, an index of influence and a mean indicator value of soil moisture, soil trophy, and soil pH was assigned to every plot. The mean values of these variables were compared in plots with abundant and scarce fir regeneration. Spatial correlation methods were used to test the relationships between the tree pattern and fir seedling density, the vegetation cover, and the species composition of the forest floor. In the studied stands, despite relatively homogeneous spatial structure, both species composition of the forest floor vegetation and vegetation cover, as well as fir seedling density, exhibited a patchy spatial variation. Patches with a higher proportion of larger trees were characterised by less vegetation cover, more frequent occurrence of plant species associated with mesic sites, and more abundant fir regeneration. In gaps, canopy openings, and fragments with relatively small trees, fir regeneration was frequently absent. Occurrence of extremely dense forest patches, creating very unfavourable niches for plants in general, and competition of the forest floor vegetation could be acknowledged as the prime reasons for the lack of fir regeneration only in 30–50% of the area of the stands. It is suggested that adequately explaining the spatial variation of regeneration occurrence would require the inclusion of a complex of factors that potentially limit the survival of juvenile seedlings in fertile microhabitats. If occurrence of fir regeneration on fertile sites is controlled in larger measure by factors associated with edaphic variability than by light conditions, then cuttings aimed at prompting regeneration may be successful only where a regeneration bank has earlier been established. Otherwise, such removal of trees may cause an increase in percent of coverage by forest floor vegetation and, through unfavourable eutrophisation of initially acidified microhabitats, additionally hinder the establishment of fir seedlings.

Dynamics of Norway spruce and silver fir natural regeneration in a mixed stand under uneven-aged management

In a 0.75-ha plot in a Norway spruce (Picea abies Karst.) – silver fir (Abies alba Miller) stand in Comelico (Italian eastern Alps), we analysed (i) the distribution and growth of natural regeneration of Norway spruce and silver fir as affected by stand structure and (ii) the age structure of all saplings between 0.2 and 10 m in height in a 30-year-old gap. In both species, most natural regeneration was clumped and located at the margin of the gaps; however, fir saplings were more represented in understorey environments and less represented in gaps as compared with spruce. Age structure of natural regeneration in the selected gap revealed that the majority (75%) of saplings appeared after the formation of the gap; however, for regeneration taller than 2 m (which has a better chance of reaching the uppermost canopy layer), saplings already present at gap formation predominated. We conclude that (i) gap edges represent a preferential regeneration niche in this forest and (ii) saplings established before gap formation can play an important role in gap refilling. These results provide useful information to ensure, through silvicultural practices, favourable conditions for the temporal and spatial continuity of the regeneration process.

Light and temperature differentially colimit subalpine fir and Engelmann spruce seedling growth in partial-cut subalpine forests

We compared the relative impacts of light, soil N, and soil temperature on Engelmann spruce (Picea engelman nii Parry ex Engelm.) and subalpine fir (Abies lasiocarpa (Hook.) Nutt.) seedling growth by quantifying (i) microsite environment-growth relationships for N-fertilized and unfertilized planted seedlings in shelterwood, patch cut, and clearcut harvest treatments and (ii) growth, photosynthesis, and biomass allocation for greenhouse-grown seedlings at 5, 10, and 15 °C soil temperatures. Fertilization did not affect seedling growth. Furthermore, soil N availability did not vary among harvest treatments. In contrast, clearcut compared with shelterwood seedlings had greater mass (fivefold), light availability (twofold), and soil temperatures (1.6 °C). Across harvest treatments, spruce and fir mass increased linearly to 100% open-sky light (R2 = 0.51 and 0.57, respectively), and temperature and light combined explained more variation in mass than light alone (adjusted R2 = 0.58 for both species). Spruce growth was more sensitive to temperature than fir in both field and greenhouse experiments. Diminished growth at low soil temperature was associated with lower photosynthesis and not lower leaf fraction. Thus, soil temperature and light colimit seedling growth in subalpine forests, but responses were species-specific and consistent with microenvironment differences in spruce and fir regeneration niches.

Aboveground growth responses of understory Abies lasiocarpa saplings to different release cuts

A white birch (Betula papyrifera Marsh.) overstory of a 30+ year old stand was thinned or completely removed, releasing an advance regeneration of subalpine fir (Abies lasiocarpa (Hook.) Nutt.). The overstory was clear-cut (T0), thinned to 600 (T600) or to 1200 (T1200) stems/ha, or left uncut (control). Three years after release, understory responses were best demonstrated by decreasing specific leaf area with increasing release level and by changes to height and radial growth increments. Clear-cutting the overstory stalled the height growth in fir for two seasons and radial growth at the tree base for one season. Compared with the control, the 3-year height increment was proportionally greatest in intermediate trees of T600, and this treatment produced the overall best response in height growth. Complete birch removal produced the best radial growth response despite the initial growth check. However, no release treatment significantly affected the whole tree variables (aboveground biomass, height, diameter at breast height (DBH), live crown ratio) within the studied time frame. Shoot silhouette ratios were lowest in the completely released understory trees, while they were similar to those of the controls in all partial-release treatments. Tree sturdiness (height/DBH ratio) was 80–90 in most treatments except T0, where it declined to below 80. Despite this improvement, large trees in T0 have been damaged by wind and snow.

Ungulate browsing on silver fir ( Abies alba) in the Swiss Alps: beliefs in search of supporting data

European silver fir ( Abies alba Mill.) is the most heavily browsed of the commercially important tree species in montane forests of central and southeastern Europe. There are widespread reports that, for decades, fir regeneration has been poor or has even failed completely. Almost unanimously, browsing ungulates are considered the major cause. We review the scientific evidence for the role of ungulate herbivory in silver fir population dynamics, and use silver fir as a model species to highlight shortcomings in understanding and handling of the problem, with an emphasis on the Swiss situation. (1) Abundance and distribution of mature silver fir today reflect mainly a variable history of the silvicultural value of the species, and do not necessarily provide a standard for target values in today’s close-to-nature silviculture. (2) Evidence for the strong impact of ungulate herbivory on silver fir is overwhelming but from a scientific view, it is largely circumstantial, and a quantitative understanding of how ungulates drive silver fir dynamics is lacking. (3) Browsing herbivores mainly interfere with silver fir development in the sapling stage, but impacts are spatially and temporally variable, and often little related to the size of the herbivore populations. Browsing is only one of a complicated interplay of factors affecting seedling establishment and subsequent growth and survival. Sapling mortality due to browsing has hardly ever been directly measured, let alone been considered in proportion to later mortality caused by inter-tree competition. (4) Most forestry services in central Europe run extensive survey schemes of browsing intensities, but in general, conclusions of ‘insufficient regeneration’ are unwarranted given the limited predictive value of the data for judging long-term stand dynamics. (5) Ultimately, only a sound understanding of tree population dynamics will help to solve this ‘forest-wildlife conflict’, but for the time being, it would help if foresters were more open to the idea that silver fir regeneration may be a highly variable and irregular process in both time and space. If silver fir is dependent on rare ‘windows of opportunity’, wildlife management would also have to abandon the view that strong fluctuations in ungulate populations are to be prevented.

Low-molecular-weight organic acids and hormone-like activity of dissolved organic matter in two forest soils in N Italy.

Concentrations of aliphatic acids, phenolic acid, and inorganic nutrients, as well as hormone-like activity, were determined in soil dissolved organic matter (DOM) from two forest sites in N Italy showing differing degrees of silver fir regeneration. In the site where silver fir recruitment was abundant, humification processes prevailed, and the soil DOM had a high content in aliphatic and phenolic acids. This enhanced the hormone-like activity in the soil, which could in turn promote growth of silver fir seedlings. In the site with poor fir recruitment, the soil DOM underwent rapid mineralization and was richer in inorganic nutrients, but had lower concentrations of aliphatic and phenolic acids, and lower hormone-like activity.

Reply - Effects of adventitious roots on age determination in balsam fir regeneration

In many Canadian boreal forests, balsam fir (Abies balsamea (L.) Mill.) seedlings established under closed canopy generally develop adventitious roots. Adventitious roots induce the formation of a reverse taper, i.e., a reduction of the diameter and of the number of growth rings towards the true collar (hypocotyl region). Consequently, ring count at any level of the trunk underestimates the true age of firs, and we recommend a reassessment of balsam fir dynamics inferred from studies based on ages estimated by ring count. Recently, Kneeshaw and Claveau (D.D. Kneeshaw and Y. Claveau. 2001. Can. J. For. Res. 31: 1292-1295) presented data from a subsample of fir seedlings to demonstrate that ring count is an accurate aging technique for most fir regeneration. A careful examination of the methodology, data, and samples presented suggests that true collars were not precisely located. We also present data collected on seedlings sampled in the same study area as Kneeshaw and Claveau. Most of the seedlings (57 of 60 seedlings, &lt;50 cm in height) had adventitious roots, and ring count was not an appropriate aging method. According to our study, Kneeshaw and Claveau either did not locate the true collar or presented atypical balsam fir seedlings.

Regeneration dynamics in a Norway spruce plantation on a silver fir-beech forest site in the Slovenian Alps

Conversion of Norway spruce ( Picea abies (L.) Karst.) plantations is a great challenge for silviculture in Europe today. While complex problems with these stands are widely recognised, methods to regenerate or convert them to mixed stands are not yet well established. The purpose of this study was to determine favourable combinations of site factors (diffuse solar radiation (DIFF) and direct solar radiation (DIR), forest ground vegetation cover, thickness of humus horizons, browsing) for development of tree regeneration within gaps of different size and age, located in a Norway spruce plantation on a silver fir ( Abies alba Mill.) and common beech ( Fagus silvatica L.) forest site. Fifteen fenced and fifteen unfenced gaps with nine plots each were placed on the north slope of Mount Krasica, in the mountain vegetation belt, on limestone parent material. From 1993 to 1998 woody seedlings and saplings were observed. A successful development of Norway spruce, sycamore ( Acer pseudoplatanus L.) and other frequently seed-bearing broad leaves was determined for the first years. Further development of seedlings was hindered by dense forest ground vegetation and browsing impact. Beech and silver fir regeneration was insufficient due to a lack of seed-bearing trees. On the basis of direct and DIFF radiation four groups of microsites were separated. This satisfactorily explained the differences in regeneration patterns among tree species. Norway spruce seedlings were most frequent in the group with high levels of diffuse and low levels of DIR, while sycamore saplings were most frequent in the group with high levels of both radiation components. Results obtained suggest that natural regeneration success and composition can be successfully influenced by managing the incidence of radiation in context with gap geometry (shape, size and orientation).

Comparison of the two main types of selection forests in Slovenia: distribution, site conditions, stand structure, regeneration and management

Summary Selection forests cover 4 per cent of the total forest area in Slovenia. There are two main types ‐ European silver fir‐beech forests on calcareous substrates (FB type), and Norway spruce‐silver fir forests on acidic substrates (SF type). Using data from forest inventory and research plots, the history, distribution, stand structure, tree species composition and regeneration of these two types is analysed and compared. The FB type is characterized by a relatively stable stand structure, with the diameter distribution having changed only slightly during the last century. The proportion of large diameter trees is much greater, growing stock volume is higher, and beech is more abundant. The SF selection forests have been subject to greater human influence. Nevertheless, during the last century, growing stock volume has increased, leading to a significant surplus of medium- and large-diameter trees. The proportion of conifers is typically high in both types, exceeding 50 per cent of the growing stock volume. In both types, the proportion of Norway spruce has significantly increased during the last century. Simultaneously, the proportion of silver fir has decreased due to the decline of fir, silvicultural measures and deer browsing. Natural regeneration is successful in both types, though the composition differs and silver fir regeneration is scarce in the FB type. Selection forests are dynamic, so their management needs to be adaptive.

Pathogens and insects in a pristine forest ecosystem: the Sierra San Pedro Martir, Baja, Mexico

We determined the incidence of pathogens and insects across mixed-conifer stands in the Sierra San Pedro Martir (SSPM) of northern Baja, Mexico, to assess the role of pests in a pristine forest ecosystem. We also determined the spatial distribution of the two most common pests, mistletoe, Phoradendron pauciflorum Torrey, and the fir engraver, Scolytus ventralis LeConte, of white fir (Abies concolor (Gord. &amp; Glend.) Lindl.) across a 25-ha grid to assess spread and what host and pest variables were related. In these open parklike stands the mean tree density was 160 trees/ha, of which 58% were trees &gt;20 cm diameter at breast height (DBH). In these low-density, mixed-aged stands we found that mixed-conifer species were well represented with no one species being completely dominant. Percent cumulative mortality for the SSPM was 12.7%, ranging from 2 to 24%, with the greatest amount of mortality occurring in the larger size classes, trees [Formula: see text]50 cm DBH. Multiple linear regression analysis showed that 78% of the mortality we observed was explained by pathogens and bark beetles (r2 = 0.78, P = 0.0001, F = 84). Mean pest incidence for Jeffrey pine (Pinus jeffreyi Grev. &amp; Balf. in A. Murray), white fir, and sugar pine (Pinus lambertiana Dougl.) was 21, 88, and 2%, respectively. We found a number of relationships among host and pest variables, as well as a pathogen– insect interaction, and across the SSPM we found that nonhost species may be interfering in certain host–pest interactions. Spatial patterns from the 25-ha grid survey revealed that both P. pauciflorum and S. ventralis incidence were widespread. Phoradendron pauciflorum showed no spatial structure across the 25 ha but S. ventralis showed some degree of spatial structuring across the survey area. We also found that mistletoe severity was negatively correlated with regeneration of white fir. In pristine forests, pathogens and insects influence mortality and regeneration success, affecting stand structure and composition.