Northern Conifer Research Articles

Effect of Nitrogen Supply and Irradiance on Seedling Survival and Biomass in Two Evergreen, Ericaceous Species

Ericaceous species are important competitors in many northern conifer plantations. Nitrogen (N) fertilization of forests can reduce the cover of ericaceous species, but whether this is a direct effect of N or an indirect effect of increased shade from fertilized trees is debated. To address this question, the growth and photosynthetic characteristics of two evergreen ericaceous species were studied in response to N fertilization and irradiance in a controlled environment. Salal (Gaultheria shallon Pursch) seedlings were grown with 10, 100 or 250 mg l−1 N [+ phosphorus (P) and potassium (K)] under 0% or 60% shade. Evergreen huckleberry (Vaccinium ovatum Pursch) seedlings were grown with 10 or 250 mg l−1 N (+PK), and with 250 mg l−1 N+K only under 0 or 50% shade. Salal survival decreased with increasing N supply, but shoot biomass was greatest in the 100 mg l−1N treatment. Shade had no effect on salal survival, but shoot biomass was greater in shade. Survival of evergreen huckleberry grown in sun decreased with increasing N supply (+PK); however, survival of shaded plants was unaffected by N supply. Biomass of evergreen huckleberry shoots was greatest with 250 mg l−1 N (+PK) and was unaffected by irradiance. Shoot:root ratios increased with N supply and shade in both species. Rates of net photosynthesis in salal were unaffected by N treatment, and were higher in shaded plants. Chlorophyll concentrations in evergreen huckleberry increased with N supply, and were greatest in shade plants. It is suggested that fertilization of these ericaceous species with high levels of N reduces root growth which increases plant mortality under water stress. Shoot growth of plants surviving this stress is improved by fertilization.

Does current summer temperature contribute to the final shoot length on Pinus sylvestris? A case study at the northern conifer timberline

Scots pine (Pinus sylvestris L.) in its natural distribution range is typically classified as a monocyclic species with its predetermined apical growth. It was confirmed by the material sampled in a 50-year-old Scots pine stand from near the northern conifer timberline at Kaamanen, northern Finland that the main controller of the height increment is the mean July temperature of the previous year. Mean monthly temperatures of the current growing season did not correlate significantly with the annual height increment, neither did they improve the fit of the transfer function models predicting annual height increment. This suggests that at least in the northernmost conditions, where the summer is the shortest, the final length of the annual shoot of Scots pine is determined by the summer temperature of the previous year rather than the current year in normal, undisturbed conditions.

Silviculture affects composition, growth, and yield in mixed northern conifers: 40-year results from the Penobscot Experimental Forest

This long-term experiment in Maine, U.S.A., was designed to provide information on the best silvicultural practices for managing stands of mixed northern conifers in northeastern U.S.A. We evaluated growth and yield and changes in species composition, quality, and structure during the first 40 years of the experiment. Replicated treatments include the selection system, uniform shelterwood, unregulated harvesting, and diameter-limit cutting. The new cohort established under three-stage shelterwood was subsequently left untreated or precommercially thinned. Between-treatment differences in net volume growth were not significant (α = 0.10), though gross volume growth differed significantly for managed vs. unmanaged, selection vs. shelterwood, and shelterwood vs. diameter-limit treatments. A three-stage shelterwood method with precommercial thinning 10 years following final overstory removal resulted in good control of hardwoods and hemlock and a dramatic increase in spruce and fir. The selection system on a 5-year cutting cycle resulted in increased hemlock, spruce, and fir, with a decrease in hardwood species. If the primary goal were production, even-aged management would most likely be preferred. We recommend a two-stage shelterwood method as applied in this experiment with some modification to improve species composition and stand quality. Stand quality (proportion of stand volume in cull trees) and species composition was influenced by treatment.

Red squirrels and predation risk to bird nests in northern forests

Red squirrels (Tamiasciurus hudsonicus) are important predators on bird nests in northern conifer forests, and previous work has shown that nest density of understory birds is low in these forests compared with deciduous forest. Here, we examine the relationships between the risk of squirrel predation and nest distribution at a smaller, within-habitat scale using both experimental and comparative studies. Female squirrels depredated experimental nests more quickly than males in interior forests near the Yukon – British Columbia border, but after 2 weeks, there was no difference in the percentage of nests depredated by males and females. The density of squirrels and the risk of experimental nest predation increased but the index of natural nest density did not decrease with the density of cone-bearing Sitka spruce (Picea sitchensis) trees in coastal conifer forests of Southeast Alaska. Experimental nests in successional deciduous stands had high risks of predation, in part because squirrels occupied small stands of colonizing spruces in the deciduous matrix and foraged widely in the deciduous stands. In the experimental study site, natural nests occurred at similar densities both next to and away from squirrel-occupied spruce stands, but in other areas, there was a "halo" of low nest density in deciduous vegetation next to spruce stands. Overall, there was little evidence that, within habitats, birds chose nest sites that minimized the risk of squirrel predation.

Differential impacts of long-term (CO2) and O3 exposure on growth of northern conifer and deciduous tree species

The long-term effects of elevated CO2 and CO2+O3 concentrations on the growth allocation in northern provenances of Norway spruce [Picea abies (L.) Karst.], Scots pine [Pinus sylvestris (L.)] and pubescent birch clones (Betula pubescens Ehrh.) were examined in open-top chambers after a 4-year-long experiment. The total biomass responses of the tree seedlings to increased CO2 and CO2+O3 concentrations were not statistically significant and varied between the provenances and species. The seedlings of northern origin were the least sensitive in their response to treatments. The total biomass of the Norway spruce seedlings slightly decreased in response to CO2 in three provenances. Scots pine from the local provenance had a slight biomass increase after elevated CO2+O3 treatment. The slower-growing birch clone seemed to benefit from elevated CO2, whereas in the faster-growing clone, reductions in biomass accumulation were seen. The combined CO2+O3 treatment reduced the positive effects of elevated CO2, especially in the slower-growing birches. Observations of significant effects were limited to a few parameters. Carbon dioxide treatment decreased needle dry weight of Norway spruce in one northern provenance. The needle and wood dry weight increased (CO2 + O3) in local Scots pine. Significant birch response was limited to increased fine root density (O3 + CO2) in the inland clone. The diverse effects of elevated CO2 and CO2 +O3 on seedling growth and biomass provide evidence that exposure of northern trees to the enhanced variable CO2 and O3 concentrations of the future will have varied effects on the growth of these species. The direction and magnitude of those effects will differ depending on species and origins.

Influence of age on growth efficiency of Tsuga canadensis and Picea rubens trees in mixed-species, multiaged northern conifer stands

Well-known patterns in the fundamental relationship between tree-level stemwood volume increment (VINC) and projected leaf area (PLA) are examined and quantified for Tsuga canadensis (L.) Carrière (eastern hemlock) and Picea rubens Sarg. (red spruce) growing in managed, mixed-species, multiaged stands in east-central Maine, U.S.A. Both species follow a sigmoid pattern, suggesting a peak growth efficiency (GE, stemwood volume growth per unit of PLA) in mid- to upper-canopy trees with PLAs of less than half that of the largest trees sampled. Tree age negatively influenced the VINC–PLA relationship in the expected manner: at a given PLA, older trees produce less stemwood than younger ones. The combined effect of leaf area and age is accurately modeled with a Weibull-like function in which the asymptote is an index of tree maturity defined as tree age relative to an estimated maximum for the species. Although previous studies have independently documented both the sigmoid relationship between VINC and PLA and the negative effect of age, their conclusions have been confounded by the strong correlation between age and mean tree PLA. This study addresses both issues simultaneously, and is the first to demonstrate a decline in GE with age independent from the effect of increasing PLA.

Field Note—Timber Marking Costs in Spruce-Fir: Experience on the Penobscot Experimental Forest

Abstract In the application of partial harvests, time needs to be allocated to marking trees to be cut. On the Penobscot Experimental Forest located in Maine, eight major experimental treatments have been applied to northern conifer stands for more than 40 yr. Data recorded at the time of marking were used to estimate the time required to mark trees for harvest. A simple linear regression equation is presented that estimates labor hours per acre marked from data on volume marked per acre.

An integrated GIS and modeling approach for assessing the transient response of forests of the southern Great Lakes region to a doubled CO 2 climate

This research examines the effects of climate change on the species composition of forests in the southern Great Lakes region in USA (Illinois, Indiana, and Ohio) by simultaneously addressing five key components necessary for realistic predictions of future forest composition. We simulated transient (1), species-level (2), forest response to climate change at a spatial scale that accounted for competitive effects (3), and regional site diversity (4), in the spatial configuration of forests within the regional landuse matrix (5). The JABOWA-II forest growth model was used to provide species-specific responses of 45 tree species to site conditions (e.g. climatic, edaphic) while accounting for competition for limited resources (e.g. light, nutrients, water). Forest growth was simulated annually from 1981 to 2060 in 0.01 ha plots, each representing a unique 4 km 2 area (site) in the region with 30% or more forest cover (16,431 unique sites). Geo-spatial input data included land use (Land Use/Land Cover Data), community-level tree species composition (Eastwide Forest Inventory Database), site conditions (State Soils Geographic Data Base, Digital Elevation Model), baseline climate (1951–1980 normals from National Oceanic and Atmospheric Administration weather stations), and general circulation model output for generating the changed climate scenario (2×CO 2 equilibrium run, Oregon State University model). The equilibrium run output, which predicted temperature increases ranging from 3.11 to 3.67 °C and precipitation increases from 2 to 14% over the study area, was applied linearly to the baseline climate over an 80-year modeling period. Results from forty iterations of simulated forest growth under each climate scenario (baseline and changed) were compiled at 10-year intervals as total basal area for each species. These plot results were scaled to the appropriate site according to the amount of forest cover in the 4 km 2 areas. Dominance-weighted population centroids were calculated for the regional distribution of each species for both climate scenarios at the years 1981 and 2060. Relative to forest conditions at 2060 after growth under baseline climate, the climate change scenario caused a decrease in total basal area of Northern Conifers (−99.9%) and Northern Deciduous (−99.4%) species and only a slight increase in Intermediate (+1.23%) and Southern species (+0.3%). Direction of population centroid shifts for these four species groups primarily were northeast. Our results for the northern species groups were consistent with previous studies. Possibly, our most important results were the minor differences in relative response for Intermediate and Southern species at the group level.

Winter Photosynthesis in Red Spruce (Picea rubens Sarg.): Limitations, Potential Benefits, and Risks

Numerous cold-induced changes in physiology limit the capacity of northern conifers to photosynthesize during winter. Studies of red spruce (Picea rubens Sarg.) have shown that rates of field photosynthesis (Pfield) and laboratory measurements of photosynthetic capacity (Pmax) generally parallel seasonal ambient temperature trends; carbon exchange decreases in the fall, remains negative or close to zero for much of the winter, and increases in the spring. However, increases in Pfield, Pmax, and foliar carbohydrate concentrations can occur during winter thaws. Thaw-induced increases in photosynthesis are probably not the result of increased stomatal conductance, but may result from other changes in physiology associated with thaw-induced improvements in water relations. In addition to increased photosynthesis, red spruce also decrease in cold hardiness during thaws. The cooccurrence of thaw-induced changes in photosynthesis and cold hardiness raises questions regarding their adaptive significance, particularly in the context of potential climate change. Red spruce may face a tradeoff between potentially beneficial increases in carbon capture and potentially detrimental reductions in cold tolerance. The physiological consequence(s) of this tradeoff may depend on the number and duration of thaws, as well as ambient temperature trends following thaw. Pollution-induced reductions in cold tolerance, and the low genetic variability of red spruce, may also influence the net outcome of thaw-induced changes in physiology.

Winter Photosynthesis in Red Spruce (Picea rubens Sarg.): Limitations, Potential Benefits, and Risks

Numerous cold-induced changes in physiology limit the capacity of northern conifers to photosynthesize during winter. Studies of red spruce (Picea rubens Sarg.) have shown that rates of field photosynthesis (Pfield) and laboratory measurements of photosynthetic capacity (Pmax) generally parallel seasonal ambient temperature trends; carbon exchange decreases in the fall, remains negative or close to zero for much of the winter, and increases in the spring. However, increases in Pfield, Pmax, and foliar carbohydrate concentrations can occur during winter thaws. Thaw-induced increases in photosynthesis are probably not the result of increased stomatal conductance, but may result from other changes in physiology associated with thaw-induced improvements in water relations. In addition to increased photosynthesis, red spruce also decrease in cold hardiness during thaws. The cooccurrence of thaw-induced changes in photosynthesis and cold hardiness raises questions regarding their adaptive significance, particularly in the context of potential climate change. Red spruce may face a tradeoff between potentially beneficial increases in carbon capture and potentially detrimental reductions in cold tolerance. The physiological consequence(s) of this tradeoff may depend on the number and duration of thaws, as well as ambient temperature trends following thaw. Pollution-induced reductions in cold tolerance, and the low genetic variability of red spruce, may also influence the net outcome of thaw-induced changes in physiology.

Precommercial thinning in a northern conifer stand: 18-year results

Four levels of precommercial thinning were applied with and without fertilization in a young, even-aged stand of northern conifers in east-central Maine. After 18 years, precommercial thinning resulted in longer and wider crowns and greater survival, growth, and yield of selected crop trees compared to untreated controls. Growth and yield were greater with uniform spacing at approximately 2.4 × 2.4 m and 1.5-m row thinning with crop-tree release in residual strips than with row thinning without crop-tree release. Control of stand species composition was greatest with uniform spacing. Fertilization had no significant effect.

Critical period of interspecific competition for northern conifers associated with herbaceous vegetation

Using critical-period analysis, we examined the temporal effects of interspecific competition from herbaceous vegetation on seedlings of jack pine (Pinus banksiana Lamb.), red pine (Pinus resinosa Ait.), eastern white pine (Pinus strobus L.), and black spruce (Picea mariana (Mill.) BSP) during the first 5 years after planting. The critical period is the time period during stand development when interspecific competition reduces tree growth. We found both similarities and differences in responses among tree species. Gains in stem volume index associated with increasing duration of vegetation control (expressed by weed-free curves) differed among species. In contrast, declines in stem volume index with increasing duration of competition after planting (expressed by weed-infested curves) were equal among species. Critical periods for stem volume index were shorter for shade-intolerant jack and red pine (1 and 2 years after planting) than for more shade-tolerant white pine and black spruce (1-3 years for spruce and 1-4 years for white pine). Intolerant species had greater absolute stem volume growth, but smaller relative declines from continuous association with herbaceous vegetation (85, 81, 78, and 67% for white pine, black spruce, red pine, and jack pine, respectively). Herbaceous vegetation did not affect survival and had a variable influence on height growth of all species.

Allometric crown relations in three northern Idaho conifer species

Allometric crown relations in three northern Idaho conifer species

Critical period of interspecific competition for northern conifers associated with herbaceous vegetation

Critical period of interspecific competition for northern conifers associated with herbaceous vegetation

Armillaria Root Disease Inoculum Remaining in Young Ontario Conifer Plantations Following Root Raking or Madge Rotoclearing

Abstract Armillaria ostoyae causes a destructive root disease in northern conifers. Most infections result from root invasions by rhizomorphs growing through the soil from previously colonized stump and woody root debris. Armillaria longevity in woody debris is related to the colonized volume. Stump and root removal by root raking alone often does not satisfactorily reduce subsequent root disease mortality. This investigation characterized residual woody debris volumes in three conifer seed orchards in northern Ontario. Site preparation for stump and root removal in two of the orchards consisted of root raking alone, vs. Madge Rotoclear™ treatment ("rotoclearing") in the third orchard. Fallow periods between site preparation and planting were 1, 5, and 8 yr in the three orchards, respectively. Mortality related to colonized residual woody debris is continuing in the raked orchards, but appears to have ended in the rotocleared orchard. Root systems of 32 orchard trees recently killed by Armillaria root disease and 9 apparently healthy (otherwise comparable) trees were excavated. Regardless of site preparation method, Armillaria-killed trees were associated with greater total volumes of residual woody debris (comprising larger pieces on average) than were healthy trees. Also, healthy trees in the rotocleared orchard were associated with smaller debris pieces on average than were healthy trees in the root-raked orchard. Size of individual woody debris pieces which contained viable A. ostoyae was highly variable. Even small pieces of colonized debris close to a root crown were apparently capable of causing lethal infection. Nevertheless, compared to root raking, rotoclearing apparently breaks A. ostoyae-colonized woody debris into smaller pieces resulting in more rapid displacement of A. ostoyae. We conclude that rotoclearing followed by a fallow period of 8 yr before planting merits consideration as an inoculum reduction treatment for site preparation. A 10 yr fallow period might have prevented nearly all root disease mortality under the conditions of this study. North. J. Appl. For. 15(4):191-196.

Influence of White Pine on Structure and Yields of Mixed Northern Conifer Forests

The presence of white pine (Pinus strobusL.). influenced the structure and yields of mixed-species, multi-cohort, northern conifer stands in Maine. In each of the five stands studied, mean plot volumes were consistently higher where white pine grew with more shade tolerant conifers, than in plots without the additional pine component. However, considerable variability in stand structures among plots resulted in no significant differences in volumes within stands. When plot volumes from the five stands were combined, the larger sample size resulted in the mean volume of pine plots being significantly higher (P < 0.02) than those that had none (355.30 ± 25.24 m3/ha vs. 275.06 ±16.98 m-Vha). Generally, pine's presence enhanced plot volumes but had a negative effect on spruce and hemlock volumes. Whether or not pine was present, plot volumes were greatly affected by variability in age structures. Plots with a representation of two or three cohorts had higher volumes than plots with a single cohort.

Balance and Sustainability in Multiaged Stands: A Northern Conifer Case Study

Abstract Classical silvicultural concepts of balance and sustainability in selection stands are examined using a 40-year case study in a mixed hemlock-spruce-fir stand. Although the stand initially conformed well to the target structure, deficits of poletimber and surpluses of sawtimber have since developed. Viewing stand structure in terms of area occupied by 10-year age classes, in addition to the diameter distribution, reveals important structural and species imbalances and suggests future management directions.

Coastal Massachusetts pond development: edaphic, climatic, and sea level impacts since deglaciation

Kettle ponds in the Cape Cod National Seashore in southeastern Massachusetts differ in their evolution due to depth of the original ice block, the clay content of outwash in their drainage basins, and their siting in relation to geomorphic changes caused by sea-level rise, barrier beach formation, and saltmarsh development. Stratigraphic records of microfossil, carbon isotope, and sediment changes also document late-glacial and Holocene climatic changes. The ponds are separated into 3 groups, each of which follow different development scenarios. Group I ponds date from the late-glacial. They formed in clay-rich outwash, have perched aquifers and continuous lake sediment deposition. The earliest pollen and macrofossil assemblages in Group I pond sediments suggest tundra and spruce-willow parklands before 12 000 yr B.P., boreal forest between 12 000 and 10 500 yr B.P., bog/heath initiation and expansion during the Younger Dryas between 11 000 and 10 000 yr B.P., northern conifer forest between 10 500 and 9500 yr B.P., and establishment of the Cape oak and pitch pine barrens vegetation after 9500 yr B.P. Sedimentation rate changes suggest lowered freshwater levels between 9000 and 5000 yr B.P. caused by decreased precipitation on the Atlantic Coastal Plain. Lake sediment deposition began in the middle Holocene in Group II ponds which formed in clay-poor outwash. These ponds date from about 6000-5000 yr B.P. In these ponds sediment deposition began as sea level rose and the freshwater lens intersected the dry basins. The basal radiocarbon dates of these ponds and stable carbon isotope analyses of the pond sediments suggest a sea-level curve for Cape Cod Bay. Holocene topographic changes in upland and the landscape surrounding the ponds is reconstructed for this coastal area. Group III ponds in the late Holocene landscape of the Provincelands dunes originated as interdunal bogs about 1000 yr B.P. and became ponds more recently as water-levels increased. Peat formation in the Provincelands reflects climatic changes evident on both sides of the Atlantic region.

The effects of initial spacing on growth and crown development for planted northern conifers: 37-year results

A spacing trial was established near Thunder Bay, Ontario in 1950. This trial consisted of black spruce (Picea mariana (Mill.) B.S.P.), white spruce (Picea glauca (Moench) Voss.), and red pine (Pinus resinosa Ait.) each established at three different spacings: 1.8 m, 2.7 m, and 3.6 m. This study examines the differences in growth and crown development as attributed to initial spacing, after 37 years. In addition, a benefit/cost analysis was performed to evaluate the economic efficiency of the various species/spacing combinations. Diameter at breast height, live crown length, and crown width, all exhibited significant (P &lt; 0.001) increases as initial spacing increased, irrespective of species, but, height demonstrated a decreasing trend (P &lt; 0.020). Gross total and merchantable stem volume per tree increased for all species as initial spacing increased; however, volume production per unit area decreased significantly for all species as spacing increased. The shift to higher-valued products from the wider-spaced plantations appeared to provide the best economic return. As a result of both greater merchantable volumes and greater percentages of these volumes available as a higher-valued product, benefit/cost ratios for red pine (0.995 to 1.337) were greater than those for the spruces (0.595 to 0.866). Although red pine currently represents less than 4% of Ontario's total regeneration effort, the results from this study suggest it deserves further consideration on some boreal sites. Key words: spacing trial, plantation growth, crown development, black spruce, white spruce, red pine, benefit/cost ratio

Elemental dynamics in forested bogs in northern Minnesota

Dynamics of nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), and magnesium (Mg) were determined for three perched bogs, formed by lake filling, and three raised bogs, formed by landscape swamping. N and K concentrations were higher in the undergrowth of perched bogs, and Ca and Mg concentrations were higher in subsurface anaerobic peat of raised bogs. Elemental pools in vegetation were in the order N &gt; Ca &gt; K &gt; Mg &gt; P; in surface peat, N &gt; Ca &gt; Mg &gt; P = K. Differences in elemental mass between the bog types were closely related to biomass differences. The atmosphere potentially supplied from 3% of annual plant uptake of K to 20% of Mg; this fraction was inversely related to uptake as a proportion of the surface peat. Vegetation on raised bogs had a greater proportion of uptake from the atmosphere (15 vs. 12%), a faster rate of elemental turnover (3.8 vs. 4.8 years), and lower net primary productivity (NPP) than on perched bogs, all indicative of a lower nutrient status. The annual mineralization rate of the surface peat for both bog types was estimated at 1.5% year−1; NPP predicted from N mineralized at this rate agrees well with observations. The better nutritional status of perched bogs may be related to landscape position, with potential inputs via runoff from adjacent uplands. The nutrient capital in both bog vegetation and substrate was similar to that in upland northern conifer forests. Key words: acrotelm, ombrotrophic, raised bogs, nutrients, peatlands, nutrient cycling.