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.     

Ash-fertilization improves germination and early establishment of birch (Betula pubescens Ehrh.) seedlings on a cut-away peatland

Common objectives of afforestation of cut-away peatlands are the diminution of nutrition loads and the production of energy wood in an efficient and economic way. We studied the effect of fertilization and afforestation methods on the early establishment of downy birch (Betula pubescens Ehrh.) seedlings on a cut-away peatland. Six treatments of peat-ash, wood-ash, biotite, or PK-fertilizer were replicated in three blocks in different mixtures corresponding to 50 kg/ha of phosphorous. Birch seeds were sown in randomized halves of split plots, while other halves were naturally afforested. Natural afforestation was equal to sowing in terms of seedling amounts due to closeness of surrounding birch stands with abundant seed crops. After the first growing season the greatest quantities and dominant heights of birch seedlings appeared on the ash-fertilized plots, whereas on the unfertilized areas both the establishment and growth of seedlings was very poor. On the other hand, the quantity of Scots pine (Pinus sylvestris L.) seedlings was more than three times higher on the unfertilized areas compared to the ash-fertilized areas. The differences between the fertilized and the unfertilized areas accentuated during the four observation years. Our results support regular use of ash-fertilizers for the afforestation of cut-away peatlands instead of the ash being deposited as a waste in landfills.     

Long-term dynamics of a mixed conifer stand in Slovenia managed with a farmer selection system

The single-tree selection system is an important option for management of Norway spruce (Picea abies (L.) Karst.) and silver fir (Abies alba Mill.) forests because it provides continuous cover, requires low investments for tending, and promotes natural regeneration as well as high stand resistance and elasticity. It is often regarded as a very conservative system that usually results in only minor spatiotemporal changes in forest structure and composition. We studied management history, structural changes, regeneration dynamics, and light climate of a traditional single-tree farmer selection silver fir-Norway spruce forest (site typology Bazzanio-Abietetum). Stand structure was analyzed on five 0.25 ha permanent plots in 1994, 2001, and 2008. Regeneration density and height growth, forest floor vegetation, and light climate were also assessed on 1.5 × 1.5 m regeneration subplots in 2001 and 2008. Tree cores extracted from dominant trees from both species in two plots were used for reconstructing stand history and age structure of the canopy layer. We documented the forest response to three types of selection management regimes: excessive, normal, and conservative. Excessive management with harvest intensity significantly above the increment was documented until the late 1950s, including two peaks of heavy fellings (diameter limit cut) in the 1880s and 1930s, which favoured establishment of Norway spruce and released regeneration. The period that followed was characterized by normal selection management, but was nevertheless marked by a decline of silver fir as a result of air pollution and several droughts. This led to sanitary fellings that were carried out from the late 1970s to the early 1990s. In the last two decades conservative management followed, which led to suppression and decline of regeneration, especially of Norway spruce, and loss of selection structure. Although we recorded lower regeneration potential of silver fir compared with Norway spruce within the seedling category, silver fir outcompeted Norway spruce within the small-sized tree category (1 cm < dbh ? 10 cm) because of its superior height growth in low light levels (diffuse light <6%) and occupied a greater share of the canopy. Nevertheless, we anticipate that over the long-term the low light regime will also cause regeneration decline of silver fir and broadleaves. Our research revealed significant structural changes in a single-tree farmer selection forest during the last 150 years. These were a result of variable management regime and environment. A farmer single-tree selection system could better mimic the natural disturbance regime if spatiotemporal combinations of diverse felling regimes would be used.     

Influence of local stand basal area on density and growth of regeneration in uneven‐aged Picea abies stands

In single‐tree selection, trees removed by harvest or lost through mortality are replaced by ingrowth from the seedling/sapling bank. Because the level of ingrowth is governed not only by the recruitment rate of new seedlings, but also by mortality and growth rates within the seedling/sapling stratum, knowledge of how these processes are related to the tree stratum is important for successful application of single‐tree selection. Therefore, Norway spruce (Picea abies (L.) Karst.) regeneration (0.1 m ≤ height ≤ 2.0 m) was measured on seventy 100 m² circular subplots at each of two sites in central and northern Sweden. Both sites had previously been selectively logged, but the time elapsed since the last harvest was at least 30 yrs. Basal area of trees of at least 2 m height within three different radii from the subplot centres was measured. Measurements on regeneration included height and leader length. Influence of local stand basal area on density and growth of regeneration was analysed by ordinary least‐squares linear regression for each of four height intervals. Regeneration was significantly aggregated at both sites, but number of Norway spruce seedlings and saplings per circular subplot was not correlated to local stand basal area. Out of 36 regressions, only eight showed a significantly (p < 0.05) negative correlation between seedling and sapling height growth and local stand basal area. In five of these cases, removal of one point (subplot) made p > 0.05. The results suggest that density and growth of Norway spruce regeneration in selectively logged uneven‐aged Norway spruce stands is affected more by ground conditions than by local stand basal area.     

Altitudinal genetic variation in Pinus hartwegii Lindl. I: Height growth,shoot phenology,and frost damage in seedlings

The altitudinal pattern of genetic variation in Pinus hartwegii Lindl. populations was explored for seedling height growth, frost damage, grass-stage, and phenological stage of the terminal shoot. A provenance test was conducted with open-pollinated seed from 13 populations collected along an altitudinal transect (3000–3600 m) at the National Park Pico de Tancítaro, Michoacán, center-west Mexico. Height growth of seedlings in a nursery was assessed at seven and 18 months of age. Frost damage at −15 °C was evaluated in laboratory at 18 months of age; proportion of plants that had left grass-stage and stage of shoot development was assessed at the age of 22 months. Significant differences among provenances (P < 0.0001) were detected for all of the evaluated characters. The variation among populations was structured as a moderate altitudinal cline, with populations from lower altitudes showing larger height growth in seedlings, larger proportion of frost damages, fewer seedlings in grass-stage and more seedlings with developed shoot, whereas in populations from higher altitudes, seedlings exhibiting shorter plant height, lower percentages of frost damage, more seedlings with unbroken grass-stage, and fewer seedlings with advanced shoot development were displayed. Options for seed and seedling movement along the altitudinal gradient are discussed under the scope of reforestation, aiming at ecological restoration, conservation of forest genetic resources, and assisted migration considering global warming. We suggest delineation of two altitudinal seed zones (Zone I: 3000–3350 m; Zone II: 3350–3700 m).     

Seed and microsite limitation for seedling recruitment of <Emphasis Type="Italic">Quercus wutaishanica</Emphasis> on Mt. Ziwuling,Loess Plateau,China

The relative influence of seed and microsite availability in the seedling emergence and recruitment of Liaodong oak (Quercus wutaishanica), which dominates the native hardwood forest in Loess Plateau, was examined by seed sowing experiments. Experiments were performed in 216 plots (30 × 30 cm), located in three typical stands (Pinus tabulaeformis plantation, Liaodong oak forest and grassland, 72 plots per stand). A seed augmentation experiment was performed in an oak forest and a conifer plantation, and a seed introduction experiment was carried out in a grassland. Three main factors were considered: seed addition, disturbance and shrub cover. The seedling number and growth in every plot were recorded continuously over 3 years. GLM multivariate was used to analyze the relationships between seedling emergence/recruitment and the explanatory variables in every stand. The results showed that seed addition in undisturbed or disturbed plots always caused significantly increased seedling emergence and recruitment in oak and conifer forests. It demonstrated that the recruitment of Liaodong oak was limited by seed and microsite availability under closed forest, and litter is one of the factors leading to microsite limitation. However, in the grassland, no treatments improved recruitment, indicating that the grassland was not suitable for seedling recruitment because of intense light and soil drought. In the conifer forest, more recruited seedlings, and lower herbivory on seedling leaves, as well as thicker stem basal diameters, indicated that the P. tabulaeformis plantation was safer for Liaodong oak seedling establishment. Unexpectedly, shrub cover did not affect the recruitment of Liaodong oak in the three stands.     

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.     

Corrigendum to: Growth of white spruce underplanted beneath spaced and unspaced aspen stands in northeastern B.C.—10 year results

Establishing white spruce (Picea glauca (Moench) Voss) by planting it under established aspen (Populus tremuloides Michx.), stands has substantial potential as a technique for regenerating boreal mixedwood stands. The presence of an aspen overstory serves to ameliorate frost and winter injury problems and suppresses understory vegetation that may compete with white spruce. In this study we examine the growth of white spruce during the first 10 years after being planted underneath a 39-year-old stand of trembling aspen following thinning and fertilization. Results indicate successful establishment and reasonable growth rates of white spruce planted under thinned and unthinned aspen stands, even with aspen basal area of 51 m² ha⁻¹. Thinning of overstory aspen to 1000 or 2000 stems ha⁻¹ did not increase light reaching seedlings, but did result in improvements in light above the shrub layer and in diameter and height growth of the underplanted seedlings. However, these increases in growth of underplanted spruce may not justify the expense of thinnings. Fertilization of these stands prior to planting had no effect on spruce growth. Growth of spruce underplanted at this site near Fort Nelson was similar to that at two other stands near Dawson Creek, B.C.     

Establishment and growth of oak (Quercus alba, Quercus prinus) seedlings in burned and fire-excluded upland forests on the Cumberland Plateau

Recurrent problems with regeneration of oaks (Quercus spp.) have been documented across a wide range of ecosystems. In oak-dominated forests of the central and Appalachian hardwood regions of the United States, a lack of competitive oak regeneration has been tied, in part, to fire suppression in these landscapes, and managers throughout the region are using prescribed fire to address this concern. To examine fire effects on oak regeneration, researchers have generally relied on inventories or population studies of existing seedlings. These studies are valuable but do not permit examination of the role of fire in enhancing the establishment and growth of new oak seedlings stemming from oak mast events. In this study, white (Quercus alba) and chestnut oak (Quercus prinus) acorn mast crops serendipitously occurred in year three (fall 2005) of a landscape-scale prescribed fire experiment. We examined establishment, survival, height and diameter of new seedlings on sites on the Cumberland Plateau in eastern Kentucky. Treatments were fire exclusion, a single prescribed fire (1x-burn; 2003), and repeated prescribed fire (3x-burn; 2003, 2004, and after acorn drop in 2006), all conducted in late spring. Initial densities of newly established chestnut and white oak seedlings were statistically similar across treatments (P = 0.42), despite fires on the 3x-burn site having occurred after acorns were on the ground. Oak seedling density was significantly predicted by oak basal area on all sites (R² = 0.12–0.46), except for chestnut oak on fire-excluded sites (R² = 0.04). Litter depth was less on 3x-burn sites compared to 1x-burn and fire-excluded sites, whereas canopy openness was greater on both burn treatments compared to fire-excluded sites. Seedling mortality was generally higher on fire-excluded sites compared to burn sites, especially for white oak. Oak seedling mortality in the first two growing seasons was significantly predicted by initial litter depth and open sky, with greater litter depth and lower percent open sky leading to higher mortality. In the third growing season none of the measured variables predicted chestnut oak seedling survival; for white oak, percent open sky remained a significant predictor of mortality. Initially, seedlings on the fire-excluded sites had similar height but smaller diameter; after three growing seasons there were few differences in seedling height or diameter among treatments. Our findings suggest a potential role for prescribed fire in establishing forest floor and light conditions that may enhance the success of new oak germinants, although different responses among species may suggest the need to target management for individual oak species.     

Overstorey density influence on the height of Picea abies regeneration in northern Sweden

The study aimed specifically at investigating if canopy opennesswas a better predictor of the height growth of Norway spruce(Picea abies (L.) Karst.) advance regeneration than overstoreybasal area or overstorey standing volume. In 1990, a field experimentwith 3 x 2 factorial design and two replications (blocks) wasestablished in an uneven-aged Norway spruce forest. Plots hada net plot area of 30 x 30 m, each with a 10-m-wide treatedbuffer zone. Three overstorey density levels retained approximately15, 40 and 70 per cent of the pre-harvest overstorey standingvolume and were allotted to the plots. Two types of thinningthat harvested smaller trees or harvested larger trees wererandomly allocated to each pair of overstorey density plots.In mid-June 2000, canopy openness was estimated from hemisphericalphotographs taken at five marked points in the centre of eachof the plots at 0.9 m from ground to the top of the ‘fish-eye’camera lens. Regression results showed that canopy opennesswas a better predictor of height increments of spruce seedlings(0.1< height < 0.5 m), saplings (0.5 height < 2.0m), and small trees (height 2.0 m, diameter at 1.3 m height< 5 cm) than with overstorey basal area (m² ha^–1) oroverstorey standing volume (m³ ha^–1). The height incrementof the spruce advance regeneration was not significantly correlatedto stand basal area or to standing volume. Overstorey basalarea in the net plots was significantly negative (P 0.05) withmean canopy openness estimates, and the r² value was 0.40. Resultsindicated that basal area was not linearly related to canopyopenness as it increased, which might explain the lack of predictivepower of retained basal area on spruce regeneration height indense stands in boreal Sweden.     

Growth of white spruce underplanted beneath spaced and unspaced aspen stands in northeastern B.C.—10 year results

Establishing white spruce (Picea glauca (Moench) Voss) by planting it under established aspen (Populus tremuloides Michx.), stands has substantial potential as a technique for regenerating boreal mixedwood stands. The presence of an aspen overstory serves to ameliorate frost and winter injury problems and suppresses understory vegetation that may compete with white spruce. In this study we examine the growth of white spruce during the first 10 years after being planted underneath a 39 year-old stand of trembling aspen following thinning and fertilization. Results indicate successful establishment and reasonable growth rates of white spruce planted under thinned and unthinned aspen stands, even with aspen basal area of 51 m² ha⁻¹. Thinning of overstory aspen to 1000 or 2000 stems ha⁻¹ did not increase light reaching seedlings, but did result in improvements in light above the shrub layer and in diameter and height growth of the underplanted seedlings. However, these increases in growth of underplanted spruce may not justify the expense of thinnings. Fertilization of these stands prior to planting had no effect on spruce growth. Growth of spruce underplanted at this site near Fort Nelson was similar to that at two other stands near Dawson Creek, B.C.     

The effect of scalping on seedling establishment after seed tree cutting of Scots pine stands in drained peatlands in northern Finland

We studied the establishment of natural seedlings after seed tree cutting and scalping in two drained Scots pine peatland stands in northern Finland (Simo and Sievi). Approximately, 50?ha^?1 of Scots pine stems were retained on both sites. During the six subsequent years, five seedling surveys were conducted. The effect of site preparation was analysed using generalized linear mixed models (GLMM). The mean density of pine seedlings increased more quickly in the scalped plots and was ca. 1.1?m^?2 after six years compared to 0.87?m^?2 in the non-scalped plots, on average. Scalping increased the number of pine seedlings 2-fold compared to that in non-treated plots in Simo, however, in Sievi non-treated plots had 30% higher pine seedling density after six years. Downy birch seedling density was 9–10-fold compared to that of non-treated plots in both sites. In terms of seedling density, seed tree cutting led to satisfactory pine regeneration after just two growing seasons in drained pine peatlands, even without scalping. Scalping significantly increased the number of pine seedlings, but it also enhanced the germination of birch seedlings strongly.     

Stand characteristics and downed woody debris accumulations associated with a mountain pine beetle (Dendroctonus ponderosae Hopkins) outbreak in Colorado

Lodgepole pine (Pinus contorta Dougl. ex Loud.)-dominated ecosystems in north-central Colorado are undergoing rapid and drastic changes associated with overstory tree mortality from a current mountain pine beetle (Dendroctonus ponderosae Hopkins) outbreak. To characterize stand characteristics and downed woody debris loads during the first 7 years of the outbreak, 221 plots (0.02 ha) were randomly established in infested and uninfested stands distributed across the Arapaho National Forest, Colorado. Mountain pine beetle initially attacked stands with higher lodgepole pine basal area, and lower density and basal area of Engelmann spruce (Picea engelmannii [Parry]), and subalpine fir (Abies lasiocarpa (Hook.) Nutt. var. lasiocarpa) compared to uninfested plots. Mountain pine beetle-affected stands had reduced total and lodgepole pine stocking and quadratic mean diameter. The density and basal area of live overstory lodgepole declined by 62% and 71% in infested plots, respectively. The mean diameter of live lodgepole pine was 53% lower than pre-outbreak in infested plots. Downed woody debris loads did not differ between uninfested plots and plots currently infested at the time of sampling to 3 or 4–7 years after initial infestation, but the projected downed coarse wood accumulations when 80% of the mountain pine beetle-killed trees fall indicated a fourfold increase. Depth of the litter layer and maximum height of grass and herbaceous vegetation were greater 4–7 years after initial infestation compared to uninfested plots, though understory plant percent cover was not different. Seedling and sapling density of all species combined was higher in uninfested plots but there was no difference between infested and uninfested plots for lodgepole pine alone. For trees ≥2.5 cm in diameter at breast height, the density of live lodgepole pine trees in mountain pine beetle-affected stands was higher than Engelmann spruce, subalpine fir, and aspen, (Populus tremuloides Michx.), in diameter classes comprised of trees from 2.5 cm to 30 cm in diameter, suggesting that lodgepole pine will remain as a dominant overstory tree after the bark beetle outbreak.     

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 m² ha⁻¹. Seedlings were censused on 375 plots of 1.0 m² 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.     

Restoring longleaf pine (Pinus palustris Mill.) in loblolly pine (Pinus taeda L.) stands: Effects of restoration treatments on natural loblolly pine regeneration

Historical land use and management practices in the southeastern United States have resulted in the dominance of loblolly pine (Pinus taeda L.) on many upland sites that historically were occupied by longleaf pine (Pinus palustris Mill.). There is currently much interest in restoring high quality longleaf pine habitats to such areas, but managers may also desire the retention of some existing canopy trees to meet current conservation objectives. However, fast-growing natural loblolly pine regeneration may threaten the success of artificially regenerated longleaf pine seedlings. We evaluated the establishment and growth of natural loblolly pine regeneration following different levels of timber harvest using single-tree selection (Control (uncut, residual basal area ∼16 m²/ha), MedBA (residual basal area of ∼9 m²/ha), LowBA (residual basal area of ∼6 m²/ha), and Clearcut (complete canopy removal)) and to different positions within canopy gaps (approximately 2800 m²) created by patch cutting at two ecologically distinct sites within the longleaf pine range: Fort Benning, GA in the Middle Coastal Plain and Camp Lejeune, NC in the Lower Coastal Plain. The density of loblolly pine seedlings was much higher at Camp Lejeune than at Fort Benning at the end of the first growing season after harvesting. Following two growing seasons, there were no significant effects of canopy density or gap position on the density of loblolly pine seedlings at either site, but loblolly pine seedlings were taller on treatments with greater canopy removal. Prescribed fires applied following the second growing season killed 70.6% of loblolly pine seedlings at Fort Benning and 64.3% of seedlings at Camp Lejeune. Loblolly pine seedlings were generally less than 2 m tall, and completeness of the prescribed burns appeared more important for determining seedling survival than seedling size. Silvicultural treatments that include canopy removal, such as patch cutting or clearcuts, will increase loblolly pine seedling growth and shorten the window of opportunity for control with prescribed fire. Therefore, application of prescribed fire every 2-3 years will be critical for control of loblolly pine regeneration during restoration of longleaf pine in existing loblolly pine stands.     

Logging residue removal after thinning in Nordic boreal forests: Long-term impact on tree growth

The aim of this study was to determine the effect of whole-tree harvesting (WTH) on the growth of Scots pine (Pinus sylvestris L.) and Norway spruce (Picea abies (L.) Karst.) as compared to conventional stem harvesting (CH) over 10 and 20 years. Compensatory (WTH + CoF) and normal nitrogen-based (CH + F or WTH + F) fertilisation were also studied. A series of 22 field experiments were established during 1977-1987, representing a range of site types and climatic conditions in Finland, Norway and Sweden. The treatments were performed at the time of establishment and were repeated after 10-13 years at 11 experimental sites. Seven experiments were followed for 25 years.Volume increment was on average significantly lower after WTH than after CH in both 10-year periods in the spruce stands. In the pine stands thinned only once, the WTH induced growth reduction was significant during the second 10-year period, indicating a long-term response.Volume increment of pine stands was 4 and 8% and that of spruce stands 5 and 13% lower on the WTH plots than on CH during the first and the second 10-year period, respectively. For the second 10-year period the relative volume increment of the whole-tree harvested plots tended to be negatively correlated with the amount of logging residue. Accordingly, the relative volume increment decreased more, the more logging residue was harvested, stressing the importance of developing methods for leaving the nutrient-rich needles on site.If nutrient (N, P, K) losses with the removed logging residues were compensated with fertiliser (WTH + CoF), the volume increment was equal to that in the CH plots. Nitrogen (150-180 kg ha⁻¹) or N + P fertilisation increased tree growth in all experiments except in one very productive spruce stand. Pine stands fertilised only once had a normal positive growth response during the first 10-year period, on average 13 m³ ha⁻¹, followed by a negative response of 5 m³ ha⁻¹ during the second 10-year period. The fertilisation effect of WTH + F and WTH + CoF on basal area increment was both smaller and shorter than with CH + F.     

Silvicultural options to promote seedling establishment on Kalmia–Vaccinium-dominated sites

Seedling growth is often hampered on sites dominated by Kalmia angustifolia. In June 2000, a trial was established on a clear-cut site in Quebec, Canada, with a high cover of Kalmia and Vaccinium species. The objectives were to evaluate how soil scarification and fertilization at the time of planting influence early growth and establishment of black spruce [Picea mariana (Mill.) BSP] and jack pine (Pinus banksiana Lamb.) seedlings. During the first 2 years, scarification reduced Kalmia cover three-fold and doubled the distance from seedlings to the nearest Kalmia stem. Scarification did not increase soil-extractable NH₄-N concentration, and reduced soil potassium, calcium and magnesium. Scarification had no effect on seedling water stress. Seedling growth improved and foliar nutrient concentrations were generally higher in scarified plots than in unscarified control plots. No differences were observed between single- and double-pass scarification for any variables except for ground-level stem diameter of seedlings, which was greater with double-pass scarification (12.1 vs 13.1 mm). Spot fertilization increased seedling growth and foliar nitrogen concentrations. Jack pine growth was greater than black spruce growth, an effect enhanced when seedlings were fertilized.     

Polylepis australis’ regeneration niche in relation to seed dispersal,site characteristics and livestock density

Establishment of Polylepis forests endemic to the mountains of South America may be affected by seed dispersal, site characteristics and livestock density. Polylepis australis (“tabaquillo”) grows in the high mountains of central Argentina, where we set up 76 square study plots of 900 m². To determine dispersal distance, we distributed 6 seed traps per plot in and around 20 plots. To determine the best site characteristics and livestock stoking rates, at two river basins differing in historic stocking rates, we analyzed the presence of seedlings in 56 plots and recorded topography, vegetation types and indicators of livestock activity. We also measured microsite characteristics in a sample of 32 comparable pairs of 1 m² quadrats, with and without seedlings. Maximum recorded dispersal distance of P. australis seeds was 6 m, and seedlings were found no more than 10 m from seed trees. The numbers of seedlings and seed trees were 3.5 and 4 times higher, respectively, in the basin with less livestock. At the 900 m² plot scale, a Poisson regression indicated a positive relationship between seedling number and P. australis canopy cover. At the quadrat scale (1 m²), seedlings were found in quadrats with significantly lower evidence of soil erosion than comparison quadrats without seedlings. We conclude that the main limitations to recruitment are short seed dispersal distances, lack of seed trees and extreme soil erosion. Management should therefore aim at preserving seed trees and reducing livestock density to prevent erosion.     

Effects of fertilization and irrigation on American sycamore and black locust planted on a reclaimed surface mine in Appalachia

Short rotation woody biofuel plantations on reclaimed surface mines in Appalachia can diversify domestic energy supplies and facilitate the reforestation of these disturbed lands. This study examined growth, survival, biomass accumulation and allocation, and nitrogen concentrations following two growing seasons in American sycamore (Platanus occidentalis L.) and black locust (Robinia pseudoacacia L.) seedlings receiving irrigation, granular fertilization, and irrigation + fertilization compared with untreated controls. Fertilization increased basal diameter, height, and stem mass of American sycamore following two growing seasons. Increased stem production was attributed to accelerated development and not shifts in biomass allocation due to treatment. Irrigation and irrigation + fertilization treatments did not enhance growth or biomass accumulation of American sycamore. Similarly, black locust basal diameter, height, and stem mass did not differ among the treatments. Browse surveys showed that more than 76% of black locust seedlings experienced arrested or retrogressed growth due to browse; less than 3% of American sycamores were browsed. This intensive browse by ungulates, likely including reintroduced elk, may have affected growth differences among species and confounded the effects of treatments on black locust. Survival was unaffected by treatment in both species, but mean survival was greatest in American sycamore (80%) compared to black locust (58%). Per tree total nitrogen uptake was highest in fertilized American sycamore (7.9 g) and lowest in irrigated American sycamore (0.9 g). The results of our study suggest that granular fertilizer applications can accelerate seedling growth on reclaimed surface mines in the Appalachian region.