bluuebunny/crossref_metadata_2025 huggingface dataset:
Introduction and overview of a study dealing with the role of salt-affected soils in primary succession on the Tanana River floodplain, interior Alaska
Authors: Cleve K. Van , Viereck L.A. , Marion G.M.
Published: July 2007

This paper provides an overview of the environmental setting, rationale, and organization of a multidisciplinary research program designed to examine the role of salt-affected soils in primary succession on the Tanana River floodplain of interior Alaska. The papers included in this series report results of studies designed to examine the controls of salt-affected soil formation and vegetation development and their interaction in this fluvial environment. The association of pedogenic salts and forests is largely restricted to northern latitudes where both low precipitation and moderate potential evapotranspiration occur simultaneously. In contrast with upland secondary-successional sites, where fire is the principal determinant of forest type distribution and successional change, ecosystem processes on the floodplain are determined by the fluvial nature of the environment. Consequently, the research presented an opportunity to evaluate some of the markedly contrasting controls of development that exist between forests in the two topographic locations. This study makes a substantial contribution to our understanding of how soil and vegetation interact on interior Alaskan floodplains to give rise to productive, commercially valuable forests.
An overview of the vegetation and soils of the floodplain ecosystems of the Tanana River, interior Alaska
Authors: Viereck L.A. , Dyrness C.T. , Foote M.J.
Published: July 2007

The soils and vegetation of 12 stages of forest succession on the floodplain of the Tanana River are described. Succession begins with the invasion of newly deposited alluvium by willows (Salix spp.) and develops through a willow–alder (Alnustenuifolia Nutt.) stage to forest stands of balsam poplar (Populusbalsamifera L.), followed by white spruce (Piceaglauca (Moench) Voss), and finally black spruce (Piceamariana (Mill.) B.S.P.). The principal changes in substrate characteristics during the successional sequence are (i) change from sand to silt loam, (ii) increase in terrace height and distance from the water table, (iii) development of a forest floor, first of leaf litter and then live and dead feather mosses, (iv) burial of organic layers by flooding, and (v) the development of permafrost as soils are insulated by a thick organic layer. Soils and vegetation of six stands occurring in three successional stages used in the salt-affected soils study are described in detail: open willow stands (stage III), balsam poplar–alder stands (stage VI), and a mature white spruce stand (stage VIII). There is a general progression of plant species resulting from the modification of the environment by the developing vegetation and changes in soil characteristics. Life history and stochastic events are important in the early stages of succession, and biological controls such as facilitation and competition become more important in middle and late stages of succession.
Selection of site trees: the combined method and its application
Authors: Zeide Boris , Zakrzewski W.T.
Published: July 2007

A new method is proposed for the selection of site trees. It is a combination of the two oldest and best-known methods: the fixed number and the fixed proportion methods. The fact that both methods have survived the trial of time suggests that neither is superior. The presented analysis shows that both methods are biased and that the biases are of opposite sign. Therefore, their estimates, when taken together, could produce an accurate site index. Weights needed to generate an unbiased estimate were calculated using permanent plots established in jack pine (Pinusbanksiana Lamb.) stands in Ontario. For this species, weights were found to be constant and almost equal. In general, it is likely that weights vary with species tolerance. A practical guide to applications of the combined method for the construction of site index curves, estimation of site index, and preparation of yield tables is provided.
A topographic index to quantify the effect of mesoscale landform on site productivity
Authors: McNab W. Henry
Published: July 2007

Landform is related to environmental factors that affect site productivity in mountainous areas. I devised a simple index of landform and tested this index as a predictor of site index in the Blue Ridge physiographic province. The landform index is the mean of eight slope gradients from plot center to skyline. A preliminary test indicated that the index was significantly associated with slope position and three classes of landform (ridge, slope, and cove). In a test with data from four locations, site index of yellow-poplar (Liriodendrontulipifera L.) was significantly correlated with landform index for each location (r = 0.45–0.65). Landform index and two other topographic variables together accounted for 31 percent of the variation in yellow-poplar site index throughout the Blue Ridge province. Landform index is a conveniently measured site variable that may be useful in various forestry-related applications, including multivariate analysis of the distribution and composition of forest vegetation.
Chlorophyll–nutrient relationships identify nutritionally caused decline in Piceaabies stands
Authors: Oren R. , Werk K.S. , Buchmann N. , Zimmermann R.
Published: July 2007

Increasing needle chlorosis at a declining Piceaabies (L.) Karst. site in northeast Bavaria, Germany, as well as in other declining P. abies stands in southern Germany, was associated with a decrease in the concentrations of both chlorophyll a and b, and, to a lesser extent, of carotenoids. Needle chlorosis related more to a decrease in the chlorophyll concentration than to a decrease in the ratio of total chlorophyll to carotenoids. In forests growing on relatively acidified soils, concentrations of both chlorophyll a and b, and of carotenoids in chlorotic needles were related only to foliar magnesium concentration. In forests growing on more alkaline soils, chlorophyll concentration increased with potassium and phosphorus concentrations and decreased with calcium and magnesium concentrations. Green needles from a declining site in northeast Bavaria were also compared with those from a nearby healthy site. The chlorophyll concentrations in needles increased more at the healthy site than at the declining site during the growing season and with increasing needle age as predicted by a nutritional disharmony model. The use of foliar chlorophyll and nutrient analyses of needles representing a range in severity of chlorosis is proposed as a quick method of identifying the soil processes which, in some areas, cause forest decline.
Bud development in coastal Douglas-fir seedlings under controlled-environment conditions
Authors: MacDonald Joanne E. , Owens John N.
Published: July 2007

Bud development under controlled-environment conditions in coastal Douglas-fir (Pseudotsugamenziesii var. menziesii (Mirb.) Franco) seedlings was investigated. In eight dormancy induction treatments, type of short, day, temperature, and moisture varied. Photoperiod was decreased to 8 h either abruptly (abrupt short day) or gradually (gradual short day). Temperature was either constant at a high temperature or gradually decreased to a low temperature. Moisture was controlled either to result in no moisture stress or to cause moisture stress. Once a dormancy induction signal was perceived by seedlings, neoformed-leaf initiation stopped and bud development began. Bud development involved two stages of primordial initiation (bud scale and leaf) separated by a transitional phase. The change from neoformed-leaf to bud-scale initiation was faster, fewer bud scales were initiated, and the development of the bud-scale complex was faster under abrupt short day than under gradual short day. The transitional phase was shorter and hence leaf initiation began earlier under abrupt short day than under gradual short day and under no moisture stress than under moisture stress. More leaf primordia were initiated under abrupt short day than under gradual short day and under no moisture stress than under moisture stress. The bud-scale receptacle was concave under abrupt short day and convex under gradual short day. Crown height was greater under abrupt short day than under gradual short day.
Wildfires in the southern Canadian Rocky Mountains and their relationship to mid-tropospheric anomalies
Authors: Johnson E.A. , Wowchuk D.R.
Published: July 2007

In this paper we present evidence for a large-scale (synoptic-scale) meteorological mechanism controlling the fire frequency in the southern Canadian Rocky Mountains. This large-scale control may explain the similarity in average fire frequencies and timing of change in average fire frequencies for the southern Canadian Rocky Mountains. Over the last 86 years the size distribution of fires (annual area burned) in the southern Canadian Rockies was distinctly bimodal, with a separation between small- and large-fire years at approximately 10–25 ha annual area burned. During the last 35 years, large-fire years had significantly lower fuel moisture conditions and many mid-tropospheric surface-blocking events (high-pressure upper level ridges) during July and August (the period of greatest fire activity). Small-fire years in this period exhibited significantly higher fuel moisture conditions and fewer persistent mid-tropospheric surface-blocking events during July and August. Mid-tropospheric surface-blocking events during large-fire years were teleconnected (spatially and temporally correlated in 50 kPa heights) to upper level troughs in the North Pacific and eastern North America. This relationship takes the form of the positive mode of the Pacific North America pattern.
Relationships between foliar number and the cross-sectional areas of sapwood and annual rings in red oak (Quercusrubra) crowns
Authors: White D. Andrew
Published: July 2007

Correlations and functional relationships of sapwood and annual ring cross-sectional areas versus the number of leaves supported inside the live crowns of red oak (Quercusrubra L.) were found, based on analyses of six 20- to 25-year-old oaks from monocultures in southern Ontario. Differences in numbers of leaves supported across intervals inside the crowns were compared, using correlation analyses, with the corresponding differences in conductive sapwood (outer two annual rings) cross-sectional areas, and the current and previous year's annual ring's cross-sectional areas. These analyses showed that the current year's annual ring area had a lower correlation with number of current leaves supported (R = 0.918, P < 0.0001) than did the previous year's annual ring area (R = 0.953, P < 0.0001) or the conductive sapwood area (R = 0.939, P < 0.0001). Functional relationships between foliar numbers supported and sapwood and annual ring cross-sectional areas inside the live crowns were found with regression analysis. The previous year's ring area (PRA) had a more linear relationship to leaf counts (FQ) than did conductive sapwood area and current annual ring area. FQ = 815.6 leaves/cm2 × PRA1.14 − 137.9. The close relationship between current foliage and previous annual ring area may reflect a developmental link between foliar primordia, which will become the following year's foliage, and the cross-sectional area of the supporting xylem.
Microbial biomass and activity in the humus layer following burning: short-term effects of two different fires
Authors: Pietikäinen Janna , Fritze Hannu
Published: July 2007

During a 3-year study, soil microbial biomass C and N, length of the fungal hyphae, soil respiration, and the percent mass loss of needle litter were recorded in coniferous forest soil humus layers following a prescribed burning (PB) treatment or a forest fire simulation (FF) treatment (five plots per treatment). Unburned humus from adjacent plots served as controls (PC and FC, respectively). Prescribed burning was more intensive than the forest fire, and this was reflected in all the measurements taken. The amounts of microbial biomass C and N, length of fungal hyphae, and soil respiration in the PB area did not recover to their controls levels, whereas unchanged microbial biomass N and recovery of the length of the fungal hyphae to control levels were observed in the FF area. The mean microbial C/N ratio was approximately 7 in all the areas, which reflected the C/N ratio of the soil microbial community. Deviation from this mean value, as observed during the first three samplings from the PB area (3, 18, and 35 days after fire treatment), suggested a change in the composition of the microbial community. Of the two treated areas, the decrease in soil respiration (laboratory measurements) was much more pronounced in the PB area. However, when the humus samples from both areas were adjusted to 60% water holding capacity, no differences in respiration capacity were observed. The drier humus, due to higher soil temperatures, of the PB area is a likely explanation for the low soil respiration. Lower soil respiration was not reflected in lower litter decomposition rates of the PB area, since there was a significantly higher needle litter mass loss during the first year in the PB area followed by a decline to the control level during the second year. Consistently higher mass losses were recorded in the FC area than in the FF area.
Dead bole mass and nutrients remaining 23 years after clear-felling of a northern hardwood forest
Authors: Arthur M.A. , Tritton L.M. , Fahey T.J.
Published: July 2007

Dead bole mass and nutrients were measured in a northern hardwood forest watershed at the Hubbard Brook Experimental Forest, New Hampshire, 23 years after all of the trees were felled and left in place. The experimental treatment of this watershed provided a unique opportunity to study large woody decay in a northern hardwood forest ecosystem with a well-documented disturbance history. We classified dead boles along line transects into four decay classes based on objective criteria, including bole shape and degree of fragmentation. Subsamples were returned to the laboratory for measurements of wood density and root ingrowth, species identification, and nutrient analysis. In 23 years, mass of dead boles (not including stumps) declined by approximately 90%, from 116.5 to 12.7 Mg•ha−1, and had an exponential decay rate constant, k, of 0.096 year-1. Significant differences in deadwood density were found among decay classes. The density of hardwood species declined approximately 50% by decay class 1, and softwood density declined 17% by decay class 1. Rates of decay appeared to be different among species, with maple and beech decomposing more quickly than birch and ash. Differences in concentrations of some nutrients were highly significant among decay classes (P and Ca) and among species (K, P, and Mg). Net release of nutrients ranged from 31% (N) to 93% (K). Root proliferation was highly correlated with decay class of dead boles. Highly decayed boles had much higher root biomass, but the total fine-root mass associated with deadwood was very low (2.1 g•m−2) compared with fine-root mass measured in forest floor (314 g•m−2). Our study demonstrates that decay of boles in this northern hardwood forest was rapid relative to conifer forests, and that decaying boles were not a site of significant nutrient accumulation or an important medium for tree roots.
Small-scale disturbance in a northern hardwoods forest: effects on tree species abundance and distribution
Authors: McClure Jan W. , Lee Thomas D.
Published: July 2007

Sampling of 24-, 34-, and 44-year-old patch cuts (324–2400 m2) in the Bartlett Experimental Forest, New Hampshire, was undertaken to assess the effect of gap size and location within a gap on tree species abundance (relative basal area and relative density). Shade-tolerant species, especially eastern hemlock (Tsugacanadensis (L.) Carr.) and American beech (Fagusgrandifolia Ehrh.), were relatively more abundant in small gaps and gap edges and generally decreased with increasing gap size. Shade-intolerant species, including paper birch (Betulapapyrifera Marsh.) and pin cherry (Prunuspensylvanica L.f.), were relatively more abundant in large gaps and gap centers and increased with increasing gap size. Intermediately shade-tolerant species, especially yellow birch (Betulaalleghaniensis Britt.) and red maple (Acerrubrum L.), were relatively more abundant in gap centers. Striped maple (Acerpensylvanicum L.) was relatively more abundant in gap edges. Many of these relationships were complex due to interactions with gap age and slope. Sugar maple (Acersaccharum Marsh.) relative abundance was not associated with gap size or location within a gap. Analyses isolating irradiance as a factor influencing species composition were inconclusive. Instead, other effects of gap disturbance and characteristics associated with different locations in the gap, such as soil conditions and root competition, may play an important role in the gap dynamics of this northern hardwoods forest. Gap age had a strong effect on species relative abundances and these patterns reflected typical successional sequences in northern hardwood forests. The gap disturbances increased species richness and diversity in this forest. Gaps contained species not present in the old-growth forest, and the species compositional variations among different gap sizes suggest that a forest with a range of gap sizes will have high diversity. Competitive exclusion appeared to be prevented by the gap disturbances, a likely consequence of the release of previously unavailable resources.
Effects of sclerophyllous shrub competition on root and shoot development and biomass partitioning of Douglas-fir seedlings
Authors: Tesch Steven D. , Korpela Ed J. , Hobbs Stephen D.
Published: July 2007

Effects of sclerophyllous shrub sprout competition on the morphological development of 1 + 0 containerized Douglas-fir (Pseudotsugamenziesii (Mirb.) Franco) seedlings were monitored above- and below-ground for 5 years after planting. Seedlings were planted among dead shrub sprouts 0.25 m in height (treatment C1), stumps of mature shrubs slashed just before planting (treatment C2), and shrub sprouts 0.5 m in height (treatment C3). In treatments C2 and C3, stumps sprouted quickly and sprouts grew vigorously, whereas C1 seedlings grew initially without competition. Above- and below-ground growth were reduced substantially and similarly by increasing competition. Root and shoot biomass of C1 seedlings were approximately 9–10 times and 22–25 times larger than that of C2 and C3 seedlings, respectively. During the first growing season, root biomass of seedlings in all three treatments increased relatively more than did shoot biomass. This growth pattern was reversed during subsequent seasons, and over the 5-year period resulted in greater growth in shoot biomass than in root biomass. Both shoot/root and height/diameter ratios increased over time in C2 and C3 seedlings. In contrast, the shoot/root ratio increased and the height/diameter ratio decreased in C1 seedlings. Allometric regression analyses showed no significant difference in biomass allocation to shoot and root among treatments over time.
Wood production and latewood percentage of Douglas-fir from different stands and vitality classes
Authors: Kort Ingrid de
Published: July 2007

Trunk wood production and amount of latewood of 171 Douglas-firs (Pseudotsugamenziesii (Mirb.) Franco) belonging to different vitality classes are analysed. The trees originated from 10 stands in the Netherlands varying in age from 25 to 70 years. Wood production is expressed as radial and volume increment over the last 15 years before sampling. The trees of 25–35 years old showed a better average vitality (less needle loss) than the older trees, and had a higher radial increment. Percentage of needle loss at the time of sampling was significantly and negatively correlated with radial and volume increment. The average latewood percentage over the last 15 years was the lowest in non vital trees. In non vital trees the wood-biomass production over the last 15 years was only ~30% of that in more vital trees. For the Netherlands as a whole the radial and volume increment in the last 15 years are estimated to be ~20% and ~4% lower, respectively, than they hypothetically would have been if all Douglas-firs belonged to the vitality classes 0 and 1. Total biomass production by Douglas-fir stands in the Netherlands is not greatly reduced by the small decrease in density in nonvital trees and is approximately 4% lower than if all trees were vital or slightly less vital.
Recovery of Douglas-fir seedlings and saplings wounded during overstory removal
Authors: Tesch Steven D. , Baker-Katz Kathryn , Korpela Ed J. , Mann John W.
Published: July 2007

Damaged and undamaged Douglas-fir (Pseudotsugamenziesii (Mirb.) Franco) seedlings and saplings, ranging in height from 15 to 450 cm, were monitored for 6 years after overstory removal to evaluate recovery from an assortment of logging wounds. Mortality (26%) was concentrated in seedlings less than 75 cm tall and was not related to damage. Surviving trees recovered from most wounds within the 6-year period. In most cases, lateral branches turned up to replace broken terminal leaders or stems; bole wounds healed over; and trees that had been pushed over returned to an upright position. A combination of a bole wound and being pushed to the ground resulted in the poorest recovery, especially for larger trees. With discriminant analysis, initial crown ratio alone enabled correct reclassification of sample trees as crop trees from 64 to 71% of the time; small trees were the most difficult to classify correctly. The addition of preharvest height growth and percentage of bole girdled variables improved the reclassification slightly. Across all three size classes analyzed, damaged trees with initial crown ratios of at least 0.66 were classified as crop trees a minimum of 75% of the time after 6 years. Significant height growth reductions were found only for damaged trees taller than 150 cm.
Nitrification and denitrification in a white spruce forest in southwest Alberta, Canada
Authors: Blew R.D. , Parkinson D.
Published: July 2007

Nitrification and denitrification were measured in a 120-year-old Piceaglauca (Moench) Voss forest in southwestern Alberta. Nitrifying activity could not be detected using short-term incubations of F–H and upper mineral soil horizons. Long-term incubations for nitrifying potential indicated that nitrifying organisms were present. The results suggest that the population of nitrifying organisms must have been small, their activity was limited, or the microhabitat necessary for their activity was not adequately simulated by the soil slurries in the short-term incubations. Low rates of denitrification were detected but probably did not represent a substantial loss of N from the soil–plant system. Low rates of denitrification may have been due to a lack of substrate (NO3−), reflecting the low rates of nitrification.
Using infrared thermography to assess viability of Pinussylvestris and Piceaabies seedlings before planting
Authors: Egnell Gustaf , Örlander Göran
Published: July 2007

One-year-old Scots pine (Pinussylvestris L.) and 2-year-old Norway spruce (Piceaabies (L.) Karst.) seedlings were lifted and stored under an array of conditions to test infrared thermography as a means of determining seedling viability. After winter storage, temperature was measured on each seedling with an infrared thermovision scanner (3–5 μm) in an environment favoring transpiration (vapor pressure deficit of the ambient air 1.6–2.9 kPa, photosynthetic photon flux density 1500 μmol•m−2•s−1). Thereafter the seedlings were planted in the field. Visual signs of damage were assessed and annual height increments were measured after one and two growing seasons. Significant positive correlations were found between seedling temperature and degree of damage. The warmest seedlings had a lower survival rate as a group when compared with the remaining seedlings. There were significant negative correlations between seedling temperature and annual height increment in the first growing season.
Evaluation of a soft-copy photogrammetry system for tree-plot measurements
Authors: Gagnon P.A. , Agnard J.P. , Nolette C.
Published: July 2007

This article describes and evaluates the application of a soft-copy photogrammetry system to large-scale forest inventories. A specially designed software, developed by the authors, has been investigated in terms of accuracy and general operability. Tests based on 1:1100 color aerial photographs, taken with a 10-m cross-boom system and digitized at resolutions of 300, 450, and 600 dots per inch, confirmed the expected tree-height accuracies of 48, 32, and 24 cm, respectively. This indicates that a photographic scale of 1:800 and a scanning resolution of 800 dots per inch could produce a tree-height precision of the order of 10 cm. The tests have shown that model orientation takes about 15 min; for a tree plot of 24 trees, measurements (height and crown diameter) and observations (species and condition) also take about 15 min. As the important problem of positioning a helicopter over a tree plot has now been solved using global positioning system receivers, the results and information presented in this paper indicate that the existing technology can provide a rigorous and operational photogrammetric system for large-scale forest inventories and regeneration monitoring.
Responses of western hemlock, Pacific silver fir, and western red cedar plantations on northern Vancouver Island to applications of sewage sludge and inorganic fertilizer
Authors: Weetman G.F. , McDonald M.A. , Prescott C.E. , Kimmins J.P.
Published: July 2007

A field experiment was designed to determine whether or not municipal sewage sludge would be effective for fertilization for chlorotic and checked plantations of western hemlock (Tsugaheterophylla (Raf.) Sarg.), Pacific silver fir (Abiesamabilis (Dougl.) Forbes), and western red cedar (Thujaplicata Donn ex. D. Don) already shown to be responsive to conventional nitrogen and phosphorus fertilization. Sewage sludge was applied at an estimated rate of 500 kg N/ha and 133 kg P/ha and ammonium nitrate and triple superphosphate were applied at 225 kg N/ha and 75 kg P/ha to plots planted 8 years earlier on a cutover of old-growth cedar–hemlock forest. Current-year leader growth and foliar vector analyses showed that the trees responded to both treatments during the first growing season with a doubling or tripling of growth rates and improved nutrition. The apparent problem of insufficient sulphur following nitrogen and phosphorus fertilization was not seen in trees treated with sludge. There were no apparent problems in micronutrient supply in these plantations. The extensive area of checked plantations on northern Vancouver Island present an opportunity for the disposal of sewage sludge.
Aboveground dry matter partitioning, size variation, and competitive processes within second-growth black spruce stands
Authors: Newton P.F. , Jolliffe P.A.
Published: July 2007

Three density-stressed black spruce (Piceamariana (Mill.) B.S.P.) populations that naturally regenerated following harvesting in 1970 were selected for study within central insular Newfoundland. Employing historical tree and stand reconstruction techniques, bark, stem, branch, foliage, and total mass distributions were estimated by age-class. Regression analysis was used to assess the effect of density stress on distributional indices, and stepwise multivariate analysis of variance was used to investigate dry matter partitioning patterns. Bark and foliar mass proportions increased with increasing density stress, whereas stem and branch mass proportions declined. Among components, decreased stem proportions best expressed the effects of increasing density stress on dry matter partitioning. Asymmetry within the mass frequency distributions for bark, branch, and foliar components shifted from negative skewness at low relative densities to positive values at high relative densities. Inequality (mass concentration) within the stem mass frequency distributions remained constant, whereas inequality within the bark mass frequency distribution declined in direct proportion to increasing density stress. Inequality within both the branch and foliar mass distributions had curvilinear relationships with increasing density stress: inequality increased from low to intermediate levels of density stress, but declined thereafter. Specific leaf areas did not differ among trees of varying size, suggesting that competition for light may not have been of consequence within the sampled stands. The results are consistent with a resource depletion competitive process, implying that competition within the dense second-growth black spruce stands may have been principally for belowground resources.
Effects of clumping on estimates of stand leaf area index using the LI-COR LAI-2000
Authors: Smith N. J. , Chen J. M. , Black T. A.
Published: July 2007

Eighteen natural second-growth stands of Douglas-fir (Pseudotsugamenziesii (Mirb.) Franco) from a wide range of stand densities and stocking levels were measured for stand leaf area index (LAI) from allometric relationships (direct LAI) and the LI-COR LAI-2000 plant canopy analyzer (indirect LAI). LAI was based on one-half total leaf area (m2) per square metre of ground surface area, normal to any slope. The LAI-2000 underestimated direct LAI by 62%. The underestimate of LAI was due to the confinement of needles within branches (74%) and nonrandom branch distribution (26%). In effect, the branches behaved like big leaves. The LAI-2000 can be used to estimate LAI across a variety of stand density and stocking levels by using a single stand clumping factor of 2.63.
Status of biological control in vegetation management in forestry
Authors: Markin George P. , Gardner Donald E.
Published: July 2007

Biological control traditionally depends upon importing the natural enemies of introduced weeds. Since vegetation management in forestry has primarily been aimed at protecting economic species of trees from competition from other native plants, biological control has been of little use in forestry. An alternative approach to controlling unwanted native plants, supplementing their existing complex of natural enemies with introduced insects found attacking closely related plants, is being used on rangeland, but is not recommended for forestry. New agents will not remain restricted to the location where they are released, but will spread and would eventually affect the target plant throughout its entire range, including areas where it might be desirable. A more promising alternative is manipulating one or more insects or diseases that already attack the undesirable plants. Many plant pathogens naturally associated with a particular plant species are highly virulent and specific to only the target plant. Mass producing these pathogens and applying them with conventional spray systems is being used in agriculture and is being considered for forestry. Other methods of manipulation, such as mass rearing insects and releasing them to attack the undesirable plant or manipulating populations of the insect predators that naturally suppress phytophagous insects of a target plant, are discussed.
Interference interactions in experimental pine–hardwood stands
Authors: Fredericksen Todd S. , Zedaker Shepard M. , Smith David W. , Seiler John R. , Kreh Richard E.
Published: July 2007

A replacement series field experiment was established in 1989 in the Piedmont physiographic province of Virginia with loblolly pine (Pinustaeda L.), red maple (Acerrubrum L.), and black locust (Robiniapseudoacacia L.) to quantify the effects of interference and elucidate its mechanisms. Stands were planted with and without herbaceous vegetation. After three growing seasons, interference among pine, hardwood species, and herbaceous vegetation significantly affected growth and yield. While herbaceous vegetation significantly affected all stands, it reduced the yield of hardwood species more than of loblolly pine. Loblolly pine appeared to ameliorate the effect of herbaceous vegetation on hardwoods in some stands. Based on relative yield totals, interference relationships between pine and hardwood species were neutral in all replacement series except for the loblolly pine–black locust series with herbaceous vegetation, where a mutualistic relationship was evident on poorer sites of the study. Pine appeared to compete effectively with hardwoods through efficient use of soil moisture and nitrogen, although pines had lower root/shoot ratios. Pine also had the greatest amount of leaf area of all species. Black locust reduced light availability to pine in some stands, but may have provided some nutritional benefits. Black locust and red maple appeared to increase allocation to roots in herbaceous vegetation, especially in pure stands. Root/shoot ratio, water-use efficiency, and leaf area were the measured variables most closely correlated with tree yield.
Competitive responses of loblolly pine to gradients in loblolly pine, sweetgum, and broomsedge densities
Authors: Perry M. A. , Mitchell R. J. , Zutter B. R. , Glover G. R. , Gjerstad D. H.
Published: July 2007

A factorial combination of 0, 1, 2, and 4 loblolly pine (Pinustaeda L.) seedlings and sweetgum (Liquidambarstyraciflua L.) sprouts, and 0, 4, and 16 broomsedge (Andropogonvirginicus L.) seedlings per square metre were used to determine the nature of pine response to competition (competitive response) from multiple life forms during the first season after outplanting. Following adjustment for effects of seedling size and site heterogeneity (soil organic matter), polynomial regression was used to describe pine competitive responses. Patterns in competitive responses varied with time and were dependent upon the particular response variable of interest. Pine response in terms of volume was similar to that for diameter. By early May, pine diameter decreased linearly with increasing sweetgum density but was unrelated to either broomsedge or pine density. Approximately 1 month later, pine diameter response to competition was more complex, being curvilinearly related to both sweetgum and broomsedge density, as well as their interaction. Intraspecific competition effects on diameter response were not detected until mid-September. Height response differed substantively from diameter or volume response. In general, height tended to be less responsive to interspecific competition, although intraspecific competition was more readily detected. Furthermore, pine height response to competition tended to be linear rather than curvilinear, as observed for both diameter and volume. The biologically based reciprocal yield equation produced similar trends in competitive pine volume response, as noted with the polynomial regression equations (i.e., sweetgum and broomsedge density as well as their interaction strongly influenced the inverse of pine stem volume). Removing variation in organic matter and initial seedling size resulted in a considerable increase in the amount of variation in final size accounted for by competition. The reciprocal yield equation was also used with crown area rather than density to account for size differences among competitors. Analyzed in this manner, only main effects of sweetgum and broomsedge significantly influenced reciprocal yield; however, considerably less variation in response was accounted for using crown area than using density.
Factors related to seedling growth in a boreal Scots pine stand: a spatial analysis of a vegetation–soil system
Authors: Kuuluvainen Timo , Hokkanen Timo J. , Järvinen Erkki , Pukkala Timo
Published: July 2007

The spatial structure of vegetation and soil properties of a patchy Scots pine (Pinussylvestris L.) forest of 1 ha was described and examined in relation to the height growth of pine seedlings in the understory. Measured ecosystem properties included the distribution and sizes of canopy trees, within-stand radiation regime, composition of understory vegetation, and topsoil and mineral soil properties. The joint distance dependent effects of large trees were described as the influence potential, derived from the ecological field theory approach. The variation in understory vegetation and soil characteristics was described as score values, derived from multivariate analyses, summarizing the variation of multiple measured variables; factor analysis was used for topsoil and mineral soil properties and canonical correspondence analysis was used for understory species composition. The spatial variation of variables was examined and mapped using geostatistical techniques. The influence potential of canopy trees, as determined by their size and spatial distribution, correlated most strongly with seedling growth, so that the height growth of seedlings was retarded in the vicinity of trees. Correlations suggest that canopy trees also affected seedlings indirectly through their dominating effect on the properties of understory vegetation and humus layer. The mineral soil nutrient content showed a weak positive correlation with seedling height growth. All the factors related to seedling growth showed substantial small-scale variation across the 1-ha study site. The analysis suggests that the variation in seedling height growth in the understory of the studied Scots pine stand is largely caused by the spatial heterogeneity of both above- and below-ground factors and by the joint effect of their complex interaction.
Simulation of salmonberry and thimbleberry population establishment and growth
Authors: Maxwell Bruce D. , Zasada John C. , Radosevich Steven R.
Published: July 2007

A salmonberry (Rubusspectabilis Pursh) and thimbleberry (Rubusparviflorus Nutt.) population simulation model was developed and compared with field observations for verification and validation. The species-specific influence of different phenological stages (early spring bud break, early summer fruit set, and fall senescence), different environments (at different sites), and intraspecific density on demographic processes was incorporated into the model. The model predicts the number of individuals in different life-history stages at three phenological stages during a growing season. Simulations were most accurate when compared with low genet density planted populations. Salmonberry populations on a moist site were most accurately simulated. Thimbleberry simulation accuracy was reduced by poor prediction of sprout densities. Salmonberry and thimbleberry population response to an application of glyphosate was simulated and compared with observed canopy cover for 3 years following application. The simulated response was accurate for the 1st year following application, but did not account for continued canopy cover in the observed populations. Salmonberry canopy cover and mean ramet height in response to manual cutting at three phenological stages was also simulated. The model simulations indicated that the most prolonged reduction in salmonberry cover followed cutting at the reproductive stage of growth.
Site preparation burning to improve southern Appalachian pine-hardwood stands: nitrogen responses in soil, soil water, and streams
Authors: Knoepp Jennifer D. , Swank Wayne T.
Published: July 2007

Three paired watersheds treated with a fell and burn prescription were studied to determine the effects on soil, soil water, and stream water. Soil nitrification and mineralization were measured by in situ closed-core incubation. Soil water was collected with porous cup lysimeters placed at 30 and 60 cm depths, and water samples were collected from streams draining control and burned areas on one of the three sites. All data were collected for 6 months prior to and 12 months after treatment. Soil ammonium (NH4+) content increased significantly in all three sites after burning, but the magnitude differed greatly among sites. However, there was no change in soil nitrate (NO3−) content. In situ measurements of net mineralization showed increased rates with increasing burn severity. Net nitrification displayed no treatment response. Slight and nonsignificant increases in soil water NO3− concentration occurred after burning in two of the three sites. Stream water NO3− concentrations increased in the one stream sampled. Thus, while prescribed burning increased available soil N, there was little change in N transformation rates or movement of dissolved inorganic N off site during the first year after burning.
Short-term changes in vegetation after the silvicultural spraying of glyphosate herbicide onto regenerating clearcuts in Nova Scotia, Canada
Authors: Freedman B. , Morash R. , MacKinnon D.
Published: July 2007

Glyphosate herbicide was applied by helicopter to release small conifer plants from the effects of competition with silvicultural "weeds" on regenerating clearcuts at four study sites. Prior to clear-cutting the study sites were (i) a mixed conifer-hardwood stand in which the regeneration was dominated by red maple (Acerrubrum L.), raspberries, and dicotyledonous herbs; (ii) a conifer stand, with regeneration dominated by heath shrubs, bracken, and birches; (iii) an old-field stand of white spruce (Piceaglauca (Moench) Voss), with regeneration dominated by alder, Asteraceae, and graminoids; and (iv) a mixed conifer–hardwood stand, with regeneration dominated by red maple, raspberries, Asteraceae, and graminoids. The study design included spray and reference (unsprayed) plots at each study site, and prespray surveys of vegetation in permanent plots, followed by as many as 6 years of measurement of regeneration after herbicide treatment. Aerial glyphosate treatment caused large decreases in the abundance of vegetation, especially of pteridophytes and herbaceous and woody angiosperms. There was a substantial recovery of some plant taxa by the end of the first and second postspray growing seasons, especially raspberry and various herbaceous angiosperms. By the end of the study period, no plant taxa had been eliminated, but there were substantial changes in relative abundance. In particular, conifers had a relatively greater abundance on sprayed plots than on unsprayed plots, suggesting that sprayed clearcuts will more rapidly develop into conifer-dominated stands.
Persistence and nontarget effects of Bacillusthuringiensis in soil: a review
Authors: Addison J.A.
Published: July 2007

This review presents information on the occurrence, persistence and nontarget effects of Bacillusthuringiensis Berliner (B.t.) in soil, with particular emphasis on forest ecosystems. Both field and laboratory studies have confirmed that B.t. is able to survive for several years after spraying, but studies on long-term persistence and possible accumulation of spores in soils are inadequate. The ecological role of B.t. in the soil ecosystem is poorly understood; we do not even know where and under what conditions B.t. multiplies in nature. Information on the effects of B.t. on soil microflora is contradictory, with studies variously suggesting that B.t. caused an increase, a decrease, or did not affect indigenous bacterial populations. Toxicity of B.t. to species of several invertebrate taxa (Acarina, Nematoda, Collembola, Annelida, Hymenoptera) inhabiting the soil has been demonstrated, but only rarely is it possible to relate dosage information to field situations, and in many cases the B.t. subspecies tested are not currently used for pest control in North America. There is an urgent need for further research to elucidate the relationships between B.t. and the natural soil microflora and fauna.
Uprooting in boreal spruce forests: long-term variation in disturbance rate
Authors: Jonsson Bengt Gunnar , Dynesius Mats
Published: July 2007

Uprooted trees provide many kinds of exposed and colonizable substrates and may mediate coexistence of plant species. Here we present, for the first time, the temporal forest floor disturbance pattern caused by uprooted trees over a long period of time (120 years). There was a significant correlation between the frequency of high winds and number of uprooted trees, and the fall direction was closely related to the main direction of high winds. The temporal distribution was strongly aggregated, with many uprootings in the 1890s and the 1970s, resulting in large variations in disturbance rate between different decades. This implies periods with low availability of exposed soil. To interpret traits among species dependent on the disturbance as adaptations to some mean rate may thus be strongly misleading. However, the occurrence and importance of such bottleneck periods is hard to evaluate, as studies of the process of uprooting have only documented numbers and rates of uprooted trees and not the availability of exposed soil. We recommend more retrospective studies to evaluate long-term variation in disturbance regime parameters and studies on the temporal availability of exposed and colonizable soil.
Comparing natural and planted black spruce seedlings. I. Water relations and growth
Authors: Bernier Pierre Y.
Published: July 2007

Container-grown black spruce (Piceamariana (Mill.) B.S.P.) seedlings were planted during 2 consecutive years alongside natural black spruce seedlings of similar initial height on an upland boreal forest clearcut. Acclimation of the planted seedlings to site conditions was followed by comparing needle conductance, shoot water potential, and growth of the planted seedlings to values obtained on the natural seedlings. Relative growth rates of the newly planted seedlings were significantly lower than those of the natural seedlings, but the difference was smaller during their second season in the field. Predawn and midday shoot water potential as well as midday needle conductance showed significant but relatively small differences between planted and natural seedlings during both years. On any given date of measurement, no clear relation could be found between water status and growth in planted seedlings. Seasonal midday averages of shoot water potential, needle conductance, and soil–plant resistance to water movement were related to the relative growth rates of all seedling types over the course of the two growing seasons. Seasonal averages of midday shoot water potential appeared to best reflect the acclimation of the planted seedlings to site conditions.
The gravitational forces generated by dropping plants and the response of Sitka spruce seedlings to dropping
Authors: McKay H.M. , Gardiner B.A. , Mason W.L. , Nelson D.G. , Hollingsworth M.K.
Published: July 2007

Two-year-old Sitka spruce (Piceasitchensis (Bong.) Carr.) seedlings were lifted from the nursery at different times of the year and subjected to known forces by dropping bags of plants from a height of 10, 100, or 300 cm onto a concrete floor for a varying number of times (0 to 135). The response of the seedlings to dropping was assessed by their growth and survival in field experiments, root growth potential, root electrolyte leakage, and triphenyl tetrazolium chloride reduction. The forces were measured by attaching an accelerometer linked to an oscilloscope to the root collar of trees in the centre of each bag. Typically the forces generated by a 10-cm drop were about 11 g, while those generated by a 300-cm drop were about 140 g. All seedlings lifted in mid-February and mid-March survived one growing season in a cultivated, weed-free nursery soil, but height growth was significantly reduced by 300-cm drops. The survival of seedlings lifted in August was reduced by 5 and 15 drops particularly from 300 cm. Root growth potential was decreased while electrolyte leakage and triphenyl tetrazolium chloride reduction activity of the fine roots 2 days after dropping were increased by dropping. Growth and physiological differences associated with dropping were more closely and frequently correlated with the maximum force exerted than to the mean or the total force.