Does tree seedling growth and survival require weeding of Himalayan balsam (Impatiens glandulifera)?

The effect of Himalayan balsam (Impatiens glandulifera) on survival and growth of naturally regenerated silver birch (Betula pendula) and planted Norway spruce (Picea abies) and silver fir (Abies alba) seedlings was studied in a weeding experiment over 3 years. Three different treatments were applied: control, mowing, and hand weeding by pulling out the entire plant. There were no consistent treatment effects on height and diameter of the tree seedlings. The coverage of Rubus fruticosus had a negative impact on diameter increment of Norway spruce and silver fir. As opposed to growth, treatment effects on seedling survival could be found for planted Norway spruce and silver fir. However, it is very likely that these effects, namely higher seedling survival after mowing, have to be attributed to the control of bramble (Rubus fruticosus) rather than to that of Himalayan balsam. It is concluded that Himalayan balsam is not able to seriously affect the growth of already established seedlings.     

Survival and competitiveness of Quercus rubra regeneration associated with planting stocktype and harvest opening intensity

Successful regeneration of northern red oak (Quercus rubra L.) on productive sites is problematic in eastern North American forests. Natural and artificial regeneration often cannot compete with fast-growing, shade intolerant species such as yellow-poplar (Liriodendron tulipifera L.). This study examines 5-year survival, growth, and competitive ability of planted northern red oak seedlings in various group selection harvest sizes in south-central Indiana, USA. Seedling stocktypes consisted of high (BHD; 75 seedlings m^?2) and low (BLD; 21 seedlings m^?2) nursery-bed-density bareroot seedlings, and small (CS; 11.4 L) and large (CL; 18.9 L) container seedlings. Group selection openings included large (0.400 ha), medium (0.100 ha), and small (0.024 ha) circular gaps in four stands. Larger stocktypes and gap sizes improved seedling height, diameter, and growth; ANOVA indicated only gap size was significant for seedling survival. Logistic regression showed survival was positively correlated to diameter at year 1, and aspect, gap size, and stocktype were significant predictors of survival. Our data indicated no differences in density of natural regeneration among gap sizes, although trends suggest greater numbers of bigger competitors in larger gaps sizes. Yellow-poplar regeneration was the tallest competitor of more than 50% of all northern red oak seedlings. Competitive status of seedlings after 5 years differed only by stocktype, with large container stock in a better competitive position than bareroot stock. However, less than 20% of seedlings in all stocktypes in each gap treatment were considered competitive (i.e., ≥80% of the height of tallest competitor) against their tallest competitor. The use of larger planting stock may offer greater opportunities for successfully regenerating northern red oak seedlings on productive sites but likely would have to be accompanied by treatments to reduce woody competition.     

Weed control increases nitrogen retranslocation and growth of white spruce seedlings on a reclaimed oil sands soil

Early establishment of seedlings in reclaimed oil sand areas is often limited by low nutrient and water availability due to factors such as strong understory vegetation competition. Management practices such as nursery fertilization and field weed control could help early establishment of planted seedlings and reclamation success. We investigated the effect of nursery nutrient loading and field weed control on the growth, nitrogen (N) retranslocation within seedling components, and plant N uptake from the soil for white spruce (Picea glauca [Moench] Voss) seedlings planted on a highly competitive reclaimed oil sands site for two years. Exponential fertilization during nursery production increased the root biomass but not the nutrient reserve in the seedling. In the field experiment, on average across the treatments, 78 and 49% of the total N demand of new tissue growth in the first and second year were met by N retranslocation, respectively. Though exponential fertilization did not affect N retranslocation, it increased the percent height and root collar diameter growth. Weed control increased not only the growth of seedlings by increasing soil N availability, but also N retranslocation within the seedlings in the second year after outplanting. We conclude that vegetation management by weed control is feasible in improving the early growth of white spruce seedlings planted on reclaimed soils and facilitate tree establishment in the oil sands region. Optimization of the nursery exponential N fertilization regime for white spruce may further help with early revegetation of reclaimed oil sands sites.     

Effects of seed size on seedling attributes in Sitka spruce

No statistically-significant effects of size (small and large) of wind-pollinated seeds from 18 seed-orchard clones could be found in the attributes of 8-month-old seedlings of Sitka spruce (Picea sitchensis (Bong.) Carr.). Clonal variations in seedling attributes was highly significant (P < 0.01), but these variations were within regional specifications for operationally-produced nursery stock.     

Why do large,nitrogen rich seedlings better resist stressful transplanting conditions? A physiological analysis in two functionally contrasting Mediterranean forest species

We analysed the physiological bases that explain why large and high nitrogen (N) concentration seedlings frequently have improved survival and growth relative to small seedlings in Mediterranean woodland plantations. Large seedlings of Aleppo pine (Pinus halepensis Mill.) and holm oak (Quercus ilex L.) with high N concentration (L+), and small seedlings with either high (S+) or low (S−) N concentration, were planted on two sites of different weed competition intensity that created contrasting stress conditions. Seedling survival, growth, gas exchange, N remobilization (N_R) and uptake (N_U), and water potential were assessed through the first growing season. Weeds reduced survival and growth, but seedling response to weed competition varied among phenotypes and between species. At the end of the first growing season, L+ Aleppo pine seedlings had higher survival than both small seedling types in presence of weeds but no differences were observed in absence of weeds. Mortality differences among phenotypes occurred in spring but not in summer. L+ Aleppo pines grew more than small Aleppo pines independently of weed competition. No holm oak seedling type survived in presence of weeds and no mortality differences among phenotypes where observed in absence of weeds, although L+ holm oak seedlings grew more than small seedlings. Mortality and growth differences in Aleppo pine were linked to marked physiological differences among phenotypes while physiological differences were small among holm oak phenotypes. L+ Aleppo pines had greater root growth, gas exchange, N_R, and N_U than small seedlings, irrespective of their N concentration. Seedling size in Aleppo pine had a greater role in the performance of transplanted seedlings than N concentration. The functional differences among oak phenotypes were small whereas they were large in pine seedlings, which led to smaller differences in transplanting performance in holm oak than in pine. This suggests that the nursery seedling quality improvement for planting in dry sites could depend on the species-specific phenotypic plasticity and functional strategy. Improved transplanting performance in large Aleppo pine seedlings relative to small seedlings was linked to greater gas exchange, root growth and N cycling.     

A dwarf bamboo (<Emphasis Type="Italic">Pleioblastus chino</Emphasis>) and winter browsing by Japanese hare (<Emphasis Type="Italic">Lepus brachyurus</Emphasis>) combine to limit establishment of transplanted native tree seedlings in an abandoned agricultural field

Natural forest recovery on abandoned farmland is hindered by a variety of factors and active restoration plays an important role when quick afforestation is desired. We investigated seedling survival of four transplanted native tree species (Quercus myrsinifolia, Quercus serrata, Aphananthe aspera, and Rhus sylvestris) by experimentally manipulating the vegetation cover, which was mainly dominated by dwarf bamboo (Pleioblastus chino), and herbivore access to the planting sites on farmland that had been abandoned for 15 years at the start of the study. Few transplanted seedlings of any species survived under intact vegetation cover, irrespective of herbivore presence. In gaps in the vegetation cover, winter browsing by Japanese hare (Lepus brachyurus) damaged all species. However, lower browsing frequency and higher resprouting ability after grazing of the seedlings enabled both Quercus species to survive better than the other species. These results indicate that dwarf bamboo and the hare jointly limit the establishment of native trees in old fields. If active afforestation by transplanting seedlings at sites dominated by dwarf bamboo is planned, a combination of vegetation removal, selection of suitable species, and temporary seedling protection will be most effective.     

Performance of loblolly pine (Pinus taeda L.) seedlings and micropropagated plantlets on an east Texas site: II. Water relations

Loblolly pine (Pinus taeda L.) seedlings and plantlets, produced from drought resistant genetic families were planted in east Texas and their relative water relations compared through the first two, sixth and seventh growing seasons. Stock type (seedling or plantlet) had a larger influence on water relations than did family source in the early years. Seedlings exhibited more of those characteristics generally considered to benefit survival under harsh environments. The principal difference between stock types was the degree of progressive decrease in predawn water potential (Ψ_pre) through the growing season. On average and across families, Ψ_pre decreased through the first growing season by 32 and 17% for plantlets and seedlings, respectively.Complete stomatal closure was never observed for any genetic source or stock type even when water potential was below −2.0 MPa. However, seedlings exhibited more stomatal regulation by lowering their stomatal conductance when water deficit was encountered, and increasing it during periods of favorable soil moisture availability. Predawn water potential was never below −0.9 MPa for any tree in either of the two first growing seasons. Although significant differences between seedling and plantlet performance were observed, their magnitude was small and diminished in the later years (sixth and seventh growing seasons). We conclude that plantlets need further development to be considered as a viable regeneration source for loblolly pine plantations on sites where summer drought is common.     

Seedling emergence in uneven-aged Norway spruce stands in Finland

The emergence of Norway spruce seedlings on different types of germination sites in uneven-aged Norway spruce dominated stands four years after selection harvesting was studied. The data were collected from 20 stands in southern Finland. In each stand, ground cover was measured from a set of 64 one square metre subplots on a permanent experimental plot of 1600?m². Correlation analysis, direct comparison of subplots with and without seedlings and mixed-effects models were used to estimate the influence of ground and tree cover on seedling occurrence. Grass cover, dwarf shrub cover, cover of certain moss species and close vicinity of trees decreased the occurrence probability and number of seedlings, while greater stand and local basal area around the subplots increased the seedling number. The cover of vegetation free surfaces, usually considered as good germination sites, was rather low. Variation in seedling emergence between plots was high. We concluded that spruce regeneration was slightly more abundant in stands with greater overall stand density and local density within a stand in postharvest conditions.     

Stand and landscape level effects of a major outbreak of spruce beetles on forest vegetation in the Copper River Basin,Alaska

From 1989 to 2003, a widespread outbreak of spruce beetles (Dendroctonus rufipennis) in the Copper River Basin, Alaska, infested over 275,000 ha of forests in the region. During 1997 and 1998, we measured forest vegetation structure and composition on one hundred and thirty-six 20-m × 20-m plots to assess both the immediate stand and landscape level effects of the spruce beetle infestation. A photo-interpreted vegetation and infestation map was produced using color-infrared aerial photography at a scale of 1:40,000. We used linear regression to quantify the effects of the outbreak on forest structure and composition. White spruce (Picea glauca) canopy cover and basal area of medium-to-large trees [≥15 cm diameter-at-breast height (1.3 m, dbh)] were reduced linearly as the number of trees attacked by spruce beetles increased. Black spruce (Picea mariana) and small diameter white spruce (<15 cm dbh) were infrequently attacked and killed by spruce beetles. This selective attack of mature white spruce reduced structural complexity of stands to earlier stages of succession and caused mixed tree species stands to lose their white spruce and become more homogeneous in overstory composition. Using the resulting regressions, we developed a transition matrix to describe changes in vegetation types under varying levels of spruce beetle infestations, and applied the model to the vegetation map. Prior to the outbreak, our study area was composed primarily of stands of mixed white and black spruce (29% of area) and pure white spruce (25%). However, the selective attack on white spruce caused many of these stands to transition to black spruce dominated stands (73% increase in area) or shrublands (26% increase in area). The post-infestation landscape was thereby composed of more even distributions of shrubland and white, black, and mixed spruce communities (17–22% of study area). Changes in the cover and composition of understory vegetation were less evident in this study. However, stands with the highest mortality due to spruce beetles had the lowest densities of white spruce seedlings suggesting a longer forest regeneration time without an increase in seedling germination, growth, or survival.     

Eight-year performance of bareroot Douglas-fir and bareroot and plug western larch Seedlings following herbicide applications,northeast Oregon,USA

Plantation success in northeastern Oregon can be limited by poor survival for western larch (Larix occidentalis Nutt.) and Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco var. glauca (Beissn.) Franco) seedlings. Vegetation management treatments may increase soil moisture availability during the dry summer months, thereby increasing the probability of seedling survival. Chemical site preparation treatments were applied in spring 2007, summer 2007, and spring 2008 to determine if such treatments would improve survival and growth of bareroot Douglas-fir and bareroot and plug western larch seedlings on three sites near Elgin, Oregon. Although some herbicide treatments significantly increased survival, results were not consistent among sites. Overall, Douglas-fir had greater survival after 7–8 years than larch seedlings. Seedling size 7–8 years after planting was also highly variable among sites and treatments with larch seedlings being taller and larger than Douglas-fir seedlings, on the average. Size for all stock types was negatively correlated with vegetative cover and positively correlated with first-year soil moisture. Macro- and microclimatic conditions, including topography and soil depth, were likely contributors to differences in survival and growth.     

Dynamics of seedling establishment and survival in uneven-aged boreal forests

The aim of this study was to describe the dynamics of seedling establishment and development in spruce-dominated uneven-aged boreal forests. The study was based on empirical data from 15 stands with permanent plots, which had been intensively monitored for 10 years in southern Finland. All trees (height > 1.3 m) were measured every fifth year. Regeneration was measured on 64 permanent sample plots (4 m²) in each stand. The establishment of first-year seedlings was analysed on a yearly basis. The survival and development of older Norway spruce (Picea abies (L.) H. Karst.) seedlings were analysed based on observations made every five years. The establishment of spruce seedlings was closely correlated with the abundance of seed crops. Seedling cohorts originating from abundant seed crops were clearly detectable in the development of seedling height distributions over time. It took about 15 years for spruce seedlings to reach a height level of 15-30 cm. Local basal area had hardly any effect on the emergence or survival of small spruce seedlings, while the number of higher spruce seedlings decreased with increasing local basal area.     

The effect of herbivory on seedling survival of the invasive exotic species Pinus radiata and Eucalyptus globulus in a Mediterranean ecosystem of Central Chile

Herbivory may be an important factor affecting seedling survival of exotic species invading new habitats. We evaluated the effect of vertebrate herbivory on the seedling survival of two widely planted and invasive tree species (Pinus radiata and Eucalyptus globulus), in a Mediterranean-type ecosystem of central Chile. An important role of herbivory on seedling survival of these two species in their introduced ranges has previously been documented. However, this has mainly been evaluated in forest plantations where habitat and vegetation conditions differ from wild habitats in which invasion occurs. We planted seedlings with and without protection against vertebrate herbivores in different aspects (a mesic south-facing slope and a xeric north-facing slope) and vegetation cover (open sites and sites with patchy tree cover). We found that regardless of aspect or vegetation cover, herbivory, in this case mainly caused by exotic vertebrates, significantly and negatively affected seedling survival of both species. However, while the effect of herbivory on P. radiata was significant in every vegetation and habitat condition, for E. globulus, the effect of herbivory was significant only for open sites in the mesic habitat. These results suggest that, as observed in forestry plantations, vertebrate herbivory may constrain seedling establishment of these two exotic trees and potentially impede the invasion. However, the importance of herbivory in controlling exotic species may vary depending on the vegetation and habitat conditions in some species such as E. globulus.     

Establishment and growth of white spruce on a boreal forest floodplain: Interactions between microclimate and mammalian herbivory

White spruce (Picea glauca (Moench) Voss) is a dominant species in late-successional ecosystems along the Tanana River, interior Alaska, and the most important commercial timber species in these boreal floodplain forests. Whereas white spruce commonly seed in on young terraces in early primary succession, the species does not become a conspicuous component of the vegetation until after 60–80 years. To address what abiotic and/or biotic factors may explain the paucity of spruce in earlier stages of succession, we examined germination and growth of planted white spruce seedlings across an environmental gradient that included variation in soil physico-chemical properties in the presence and absence of mammal browsing. The effect of browsing pressure over the first four years after planting was most noticeable on the older terraces. Likewise, direct effects of hare browsing on spruce seedling mortality were only manifested at the oldest sites. Spruce germination and survival was inversely proportional to soil cation concentrations, which was largely controlled by temperature-driven evapotranspiration. High light intensities and high air temperatures significantly reduced seedling growth, whereas variation in soil moisture only explained a significant amount of variation in seedling survival. Temperatures within the needle clusters on terminal shoots reached values that adversely affect photosynthesis (>32 °C) on multiple occasions over the growing season. We conclude that the direct (temperature) and indirect (soil chemistry) effects of high insolation are major factors constraining spruce performance on early successional terraces, and that these effects can be significantly exacerbated by mammal browsing on associated deciduous vegetation.     

Dynamics and determinants of Quercus alba seedling success following savanna encroachment and restoration

The scattered tree layer that defines savannas is important for structuring the understory community and determining patterns of overstory recruitment. However, encroachment by woody plants has altered overstory tree densities and regeneration dynamics. We characterized seedling success of the savanna-forming species Quercus alba within Midwestern (USA) oak savannas that had been degraded by encroachment (control; n = 4) or experimentally restored by removal of encroaching woody vegetation (treatment; n = 4). In early 2004, 981 seedlings were transplanted along transects radiating from tree boles of overstory Q. alba trees to inter-canopy gaps and monitored for three growing seasons. Seedlings in restored sites had greater survival (>2×), height growth (by >50%), and basal diameter growth (by >20%). In general, seedling survival and growth parameters increased with distance from overstory trees and were greatest in inter-canopy gaps of restored sites. By the final growing season (2006), the seedling survival-by-distance from tree correlation was stronger in control (r² = 0.25) than treatment sites (r² = 0.18), due to relatively uniform (and greater) survival at all distances from trees in treatment sites. In 2006, growth parameters (seedling height, diameter, Δ height, Δ diameter, and # leaves) were significantly (and more strongly) positively correlated with distance from trees in treatment sites. However, seedling herbivory was also greater after treatment and increased with distance from overstory trees. To understand seedling/microenvironment relationships, we created logistic (survival) and linear regression models (Δ height, Δ basal diameter, # leaves in 2006). Control seedling models had consistently greater predictive power and included more variables, suggesting that savanna restoration may decouple seedlings from their microenvironments, potentially by decreasing competition for limiting resources. Encroachment of the savannas in this study is limiting regeneration of Q. alba, suggesting substantially altered regeneration dynamics from those under which these savannas originally formed. Initial responses from our test of restoration, however, were promising and mechanical encroachment removal may be a means to promote overstory regeneration of this species. Finally, the savannas in this study appear inherently unstable and a scattered canopy tree configuration is unlikely to persist without regular disturbance, even in the restoration sites. Repeated mechanical thinning treatments with selected retention of recruiting Q. alba individuals or reintroduction of understory fire or grazing animals may be potential mechanisms for promoting long-term persistence of savannas at these sites.     

Influences of gap position, vegetation management and herbivore control on survival and growth of white spruce (Picea glauca (Moench) Voss) seedlings

The boreal mixedwood forest type of the Canadian interior boreal is largely comprised of two dominant tree species: white spruce and trembling aspen (Picea glauca and Populus tremuloides). This forest type is expansive, providing important ecosystem services and economic production, yet such mixtures are difficult to establish after harvests. While aspen resprouts and grows vigorously following disturbance, spruce growth is relatively slow and is often limited by intense competition from associated vegetation, including aspen. To improve management, it is important to understand how environmental and vegetative conditions vary in relation to the competitive-facilitative relationship of spruce-aspen mixtures. In this study white spruce was planted across large canopy openings to determine whether survival and height growth is influenced by position within gap and by differing levels of competing vegetation control of aspen and understory plants. In addition, we addressed the issue of herbivory, which can pose a significant threat to planted spruce seedlings. Within each of four sites, linear gaps were created and five gap positions were recognized spanning the southern and northern forest understories, and southern, center and northern positions within each opening. Three different levels of vegetation management were implemented: a brush saw treatment in which all vegetation was cut to ground level, a mixing treatment in which all vegetation and rootstock was ground up, and a control with no vegetation management. The three herbivory treatments excluded large ungulates, small herbivores (rabbits, hares) or had no herbivore exclusion. Growth and survival of white spruce seedlings were measured for four years (1997-2000). Understory survival was significantly lower than within the gap, with the sheltered southern edge position providing the best initial environmental conditions and or ameliorative cover for spruce establishment. However, after four years the shelter effect starts to be inhibitive relative to center and northern gap positions, suggesting the removal of the canopy is necessary before spruce productivity declines. The optimal vegetation management treatment also changed over the study period. The most intensive treatment (mixing) initially showed a negative influence on survival and growth, but by year four, survival converged to approximately 75% for all treatments, and the mixing treatment produced the best height growth. The growth advantage became most evident in the center gap positions, which initially lagged the brushsaw and control treatments. Lastly, some growth losses from herbivory must be expected in boreal mixedwoods, although not enough to merit control. Results have implications for the timing and intensity of silvicultural treatments for harvesting and planting.     

Influence of woody and herbaceous competition on microclimate and growth of eastern white pine (Pinus strobus L.) seedlings planted in a central Ontario clearcut

The influence of woody and herbaceous plant competition, either alone or in combination, on microclimate and growth of planted eastern white pine (Pinus strobus L.) seedlings was examined over four consecutive growing seasons in a central Ontario clearcut. Treatments that manipulated the comparative abundance of these two plant functional groups significantly affected light availability, soil moisture, and air and soil temperature regimes. These microclimate alterations, coupled with the relative competitiveness of herbaceous and woody vegetation, corresponded to temporal changes in vegetation cover and dominance. The more rapid colonization and growth of the herbaceous plant community, dominated by bracken fern (Pteridium aquilinum) and ericaceous shrubs (Kalmia sp., Vaccinium sp.), resulted in this form of vegetation being a comparatively important early competitor for soil moisture. As the woody plant community, dominated by naturally regenerated trembling aspen (Populus tremuloides Michx.), grew in height and leaf area, it became a comparatively strong competitor for both light and soil moisture. For all vegetation treatments combined, white pine seedling growth responses were strongly correlated with total cover of competing vegetation and its relative influence on above- and belowground microclimatic variables. Higher total cover of competing vegetation was generally associated with lower light and soil moisture availability and cooler soil temperatures. Multiple regression analyses indicated that pine seedling relative height growth increased with soil moisture content and growing season soil heat sum, while seedling relative diameter and relative volume growth increased with light availability.     

Effects of Douglas-fir 2+0 seedling morphology on field performance

The relationships between field performance of Douglas-fir (Pseudotsuga menziesii) 2+0 seedlings and their initial diameter and root mass were evaluated on five sites in Oregon in the early 1980s to identify opportunities for improving seedling grading prior to planting. Survival and height 3–5 years after planting were positively related to seedling size at the time of planting. On all sites, survival nearly doubled from the smallest to largest diameter classes. Root mass had a similar relationship to survival on sites with environmental stress. Increasing root size class increased survival more for the small diameter classes than for the larger diameter clases. On the other hand, increasing root size class increased total height more for the large diameter class than the smaller ones. Although height was not as strongly affected as survival on several sites, height differences among initial seedling diameter classes were still significant and increasing after five years. Root class effects on height were less important than diameter class effects.     

White spruce recruitment distances relative to lodgepole pine in southern Yukon,Canada

Eleven seral, postfire forest stands in southern Yukon (Canada) were sampled to determine where western white spruce (Picea albertiana ssp. albertiana) seedlings occurred with respect to distance to the nearest lodgepole pine (Pinus contorta var. latifolia) tree. Seedling-to-nearest tree distances were assessed at 10-cm increments up to 220?cm. On average, seedlings occurred 54?cm from the nearest pine (n?=?490), but peak frequencies were 20–50?cm away, compared to a potential separation distance of 103?cm. Greatest average seedling density occurred 10–20?cm from pine (0.81?m^?2), with values between 10 and 120?cm decreasing logarithmatically with increasing distance from pine (r?=?0.994, p?n?=?11). Spruce seedling densities were <0.02?m^?2 beyond 120?cm. The differences in frequency, which represented moderately strong aggregation (Clark-Evans Index 0.34–0.52), and density suggest greater spruce recruitment near lodgepole pine was facilitated by more favorable ecological conditions than further away, for example, greater nutrient availability. The bias in seedling-to-nearest tree distances occurred regardless of stand age (57–165 years), pine density (1599–5935 stems?ha^?1), or understory vegetation type, although the bias may be weakened by the abundant presence of feathermosses (Hylocomium splendens) on the forest floor.     

Vegetation change and forest regeneration on the Kenai Peninsula,Alaska following a spruce beetle outbreak, 1987–2000

Forests of the Kenai Peninsula, Alaska experienced widespread spruce (Picea spp.) mortality during a massive spruce beetle (Dendroctonus rufipennis) infestation over a 15-year period. In 1987, and again in 2000, the U.S. Forest Service, Pacific Northwest Research Station, Forest Inventory and Analysis Program conducted initial and remeasurement inventories of forest vegetation to assess the broad-scale impacts of this infestation. Analysis of vegetation composition was conducted with indirect gradient analysis using nonmetric multidimensional scaling to determine the overall pattern of vegetation change resulting from the infestation and to evaluate the effect of vegetation change on forest regeneration. For the latter we specifically assessed the impact of the grass bluejoint (Calamagrostis canadensis) on white spruce (Picea glauca) and paper birch (Betula papyrifera) regeneration. Changes in vegetation composition varied both in magnitude and direction among geographic regions of the Kenai Peninsula. Forests of the southern Kenai Lowland showed the most marked change in composition indicated by relatively large distances between 1987 and 2000 measurements in ordination space. Specific changes included high white spruce mortality (87% reduction in basal area of white spruce >12.7 cm diameter-at-breast height (dbh)) and increased cover of early successional species such as bluejoint and fireweed (Chamerion angustifolium). Forests of the Kenai Mountains showed a different directional change in composition characterized by moderate white spruce mortality (46% reduction) and increased cover of late-successional mountain hemlock (Tsuga mertensiana). Forests of the Gulf Coast and northern Kenai Lowland had lower levels of spruce mortality (22% reduction of Sitka spruce (Picea sitchensis) and 28% reduction of white spruce, respectively) and did not show consistent directional changes in vegetation composition. Bluejoint increased by ≥10% in cover on 12 of 33 vegetation plots on the southern Kenai Lowland but did not increase by these amounts on the 82 plots sampled elsewhere on the Kenai Peninsula. Across the Kenai Lowland, however, regeneration of white spruce and paper birch did not change in response to the outbreak or related increases in bluejoint cover from 1987 to 2000. Although some infested areas will be slow to reforest owing to few trees and no seedlings, we found no evidence of widespread reductions in regeneration following the massive spruce beetle infestation.     

Morphological characteristics associated with tolerance to competition from herbaceous vegetation for seedlings of jack pine,black spruce,and white pine

Tolerance of bareroot and container-grown seedlings of black spruce (Picea mariana (Mill.) B.S.P.), jack pine (Pinus banksiana Lamb.), and eastern white pine (Pinus strobus L.) to competition from herbaceous vegetation was examined in the first five years after planting on a site in the Great Lakes/St. Lawrence forest of Ontario, Canada. Shoot and root morphological characteristics of various stocktypes were measured before planting and correlated with 5-year survival and growth following control and no control of herbaceous vegetation. For black spruce and jack pine, medium-sized bareroot stocktypes had greater relative 5-year stem volume growth in the presence of herbaceous vegetation than did container stock of either species or large bareroot stock of spruce. Relative volume growth was measured as the ratio of the cumulative stem volume increment in the presence of vegetation (Veg) to that in the absence of vegetation (NoVeg), i.e., the Veg:NoVeg ratio. In white pine, the Veg:NoVeg ratio of volume increment of medium container and large bareroot stocktypes exceeded that of small container and medium bareroot stocktypes. In jack pine, root collar diameter at planting and number of first-order lateral roots were positively correlated with 5-year Veg:NoVeg ratio of volume increment. In white pine, the Veg:NoVeg ratio was also positively correlated with root collar diameter at planting and with root volume. In black spruce, the ratio was not related to pre-plant morphology. Thus, for white pine and jack pine, certain pre-plant morphological features may be useful in forecasting the relative ability of different stocktypes to grow under herbaceous competition conditions in the field.