White Spruce Stands Research Articles

Early vegetation control for the regeneration of a single-cohort, intimate mixture of white spruce and trembling aspen on upland boreal sites

In Canada’s boreal forest region, there is increasing demand for practical regeneration strategies that will recreate mixed stands of white spruce ( Picea glauca (Moench) Voss) and trembling aspen ( Populus tremuloides Michx.). In 2002, we implemented an experiment in both west-central Alberta and northeastern Ontario to better understand the effects of herbaceous and woody vegetation control on crop tree survival and growth, within the context of prescription development for the regeneration of a single-cohort, intimate mixture of spruce and aspen. After five growing seasons, good spruce growth, health, and survival were observed with 2 m radial treatments consisting of herbaceous and woody (i.e., complete) vegetation control centred on trees planted at 5 m spacing. These spruce were 4%–64% taller and 68%–178% larger in stem diameter than untended trees, leading to 167%–1166% gains in stem volume, and were at least equivalent to the same stock grown at 2.5 m spacing and provided with complete, continuous relief from competition. Removing only the woody vegetation within treated radii stimulated herbaceous competition, resulting in reduced survival and growth of spruce and reduced height of surrounding aspen. Early results suggest that spot treatments that provide 2–4 years of relief from herbaceous and woody competition may offer a practical strategy for growing spruce with aspen.

Growth responses of three coexisting conifer species to climate across wide geographic and climate ranges in Yukon and British Columbia

This work aimed to compare radial growth–climate relationships among three coexisting coniferous tree species across a wide geographic and climate range from southern British Columbia (BC) to central Yukon, Canada. Tree-ring data were collected from 20 mature stands of white spruce (Picea glauca), lodgepole pine (Pinus contorta var. latifolia), and subalpine fir (Abies lasiocarpa). Linear relationships between annual growth variation and monthly and seasonal climate were quantified with correlation and regression analyses, and variation in climate–growth responses over a climatic gradient were quantified by regressing growth responses against local mean climatic conditions. Temperatures had more consistent and stronger correlations with growth for all three species than precipitation, but growth–climate responses varied among species and among sites. In particular, pine and fir populations showed different responses between BC and Yukon, whereas spruce showed a more consistent response across the study domain. Results indicate that (1) the response and sensitivity of trees to seasonal climate variables vary among species and sites and (2) winter temperatures prior to growth may have significant impacts on pine and fir growth at some sites. The capacity to adapt to climate change will likely vary among the study species and across climatic gradients, which will have implications for the future management of mixed-species forests in Yukon and BC.

A Survey of Lichens and Bryophytes in White Spruce, <em>Picea glauca</em>, Tree Islands on a Calcareous Beach Ridge in Northeastern Manitoba

Studies on the diversity of lichens and bryophytes in northern ecosystems have focused on open tundra and boreal forests. Krummholz tree islands have received little attention. This study examined species’ diversity of lichens and bryophytes among islands of White Spruce trees in northern Manitoba. Thirty-three species were found in the tree islands with 11 additional species forming the understorey layer. The trees were dominated by epiphytic lichens and the understorey was dominated by pleurocarpous mosses. The most common lichens were widespread species. Rare lichens in the study area included Protopannaria pezizoides and Alectoria nigricans growing in the shaded interior of the tree islands. The age and density of the tree islands may produce habitat conditions different from those in mature White Spruce boreal forests. Comparative studies between White Spruce krummholz and other White Spruce stands are needed.

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

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

No Evidence of an Impact on the Rhizosphere Diazotroph Community by the Expression of Bacillus thuringiensis Cry1Ab Toxin by Bt White Spruce

Nitrogen fixation is one of the most important roles played by soil bacterial communities, as fixation supplies nitrogen to many ecosystems which are often N limited. As impacts on this functional group of bacteria might harm the ecosystem's health and reduce productivity, monitoring that particular group is important. Recently, a field trial with Bt white spruce, which constitutively expresses the Cry1Ab insecticidal toxin of Bacillus thuringiensis, was established. The Bt white spruce was shown to be resistant to spruce budworm. We investigated the possible impact of these genetically modified trees on soil nitrogen-fixing bacterial communities. The trial consisted of untransformed controls, GUS white spruce (transformed with the beta-glucuronidase gene), and Bt/GUS white spruce (which constitutively expresses both the Cry1Ab toxin and beta-glucuronidase) in a random design. Four years after planting, soil samples from the control and the two treatments from plantation as well as from two natural stands of white spruce were collected. Diazotroph diversity was assessed by extracting soil genomic DNA and amplifying a region of the nitrogenase reductase (nifH) gene, followed by cloning and sequencing. Analysis revealed that nitrogen-fixing communities did not differ significantly among the untransformed control, GUS white spruce, and Bt/GUS white spruce. Nevertheless, differences in diazotroph diversity were observed between white spruce trees from the plantation site and those from two natural stands, one of which grew only a few meters away from the plantation. We therefore conclude, in the absence of evidence that the presence of the B. thuringiensis cry1Ab gene had an effect on diazotroph communities, that either site and/or field preparation prior to planting seems to be more important in determining diazotroph community structure than the presence of Bt white spruce.

Importance of balsam fir as winter forage for white-tailed deer at the northeastern limit of their distribution range

Interspersion of dense coniferous stands that offer cover and more open mixedwood stands providing food resources has been recommended for the management of white-tailed deer (Odocoileus virginianus) wintering yards in northeastern North America. On Anticosti Island, at the northeastern limit of this deer's distribution range, previous studies have shown continuous decline of deciduous browse. As native balsam fir (Abies balsamea) stands progressively shift to white spruce (Picea glauca), the persistence of the deer population will increasingly depends on its capacity to use white spruce stands. To provide insights into deer responses to long-term changes in their habitat, we investigated resource use along a gradient of expected habitat quality for deer. Stand use increased with the proportion of balsam fir, reaching an asymptote when > 40% of the stand's basal area was composed of fir. Stand use does not appear to be related to snow interception since sinking depth was lower in white spruce forests. Deer using white spruce stands mainly consumed balsam fir (72%), whereas spruce represented only 17% of their diet. The consumption of arboreal lichens increased from 6% in January to 21% in March. The observed patterns of habitat use and the composition of the winter diet confirm the dependence of deer on balsam fir in winter and give additional support to the hypothesis that litterfall from balsam fir provides an alternate food source sustaining high deer density in a boreal forest without predators.

The Effects of Decreasing Winter Diet Quality on Foraging Behavior and Life-History Traits of White-Tailed Deer Fawns

Many high-density populations of wild ungulates have exerted strong negative impacts on their habitat. A decrease in forage quantity and quality may affect individual growth, fecundity, and survival, especially under harsh winter conditions. On Anticosti Island, Québec, Canada, browsing by introduced white-tailed deer (Odocoileus virginianus) negatively affected boreal forest composition. Since the preferred contemporary winter forage of deer, balsam fir (Abies balsamea), has been almost completely extirpated from the island at browse height, deer are forced to increase the proportion of normally avoided forage, such as white spruce (Picea glauca), in their winter diet. We predicted that an increase in the proportion of white spruce in the diet would have detrimental effects on deer body condition and would affect their behavior and life history traits. We experimentally simulated a deterioration of winter forage quality in semi-natural enclosures by increasing the proportion of white spruce in the diet and examined the effects of winter diet quality on 1) forage intake, 2) body condition loss, 3) activity budget, and 4) survival of white-tailed deer fawns. Fawns fed the poor-quality diet maintained a higher forage intake rate throughout the winter than fawns fed the control diet, suggesting a compensatory response to the decrease of forage quality by consuming more forage during winter. Body mass decreased over the winter, but we did not observe any significant effects of diet quality on body mass loss. Diet quality did not influence the activity budget of fawns, but deer decreased activity in cold weather. The main determinant of overwinter survival was individual body mass in early winter. Our study suggests that deer have adapted to the extreme conditions encountered on Anticosti (i.e., harsh and long winters, low-quality browse, and a high-density population). Even though white spruce stands are gradually replacing balsam fir stands, our results suggest that deer on Anticosti could maintain a high-density population by increasing the amount of white spruce in their diet. However, future studies are necessary to address the long-term effects of a diet dominated by white spruce on deer body condition, survival, and reproduction under natural conditions.

Contribution of winter processes to soil nitrogen flux in taiga forest ecosystems

We measured annual net nitrogen (N) mineralization, nitrification, and amino acid pro- duction in situ across a primary successional sequence in interior Alaska, USA. Net N miner- alization per gram dry soil increased across the successional sequence, but with a sharp decline in the oldest stage (black spruce). Net N minerali- zation expressed per gram soil organic matter exhibited the opposite pattern, suggesting that soil organic matter quality decreases significantly across succession. Net N mineralization rates during the growing season from green-up (early May) through freeze-up (late September-early October) accounted for approximately 60% of the annual inorganic N flux, whereas the remaining N was released during the apparent dormant season. Nitrogen release during winter occurred primarily during October-January with only negligible N mineralization during early spring in stands of willow, alder, balsam poplar and white spruce. By contrast, black spruce stands exhibited substantial mineralization after snow melt during early spring. The high rates of N mineralization in late autumn through early winter coincide with high turnover of fine root biomass in these stands, suggesting that labile substrate production, rather than temperature, is a major controlling factor over N release in these ecosystems. We suggest that the convention of restricting measurements of soil processes to the growing season greatly underestimate annual flux rates of inorganic nitrogen in these high-latitude ecosystems.

Tree bole mineralization rates of four species of the Canadian eastern boreal forest: implications for nutrient dynamics following stand-replacing disturbances

To assess nutrient dynamics in decomposing logs of trembling aspen (Populus tremuloides Michx.), white birch (Betula papyrifera Marsh.), white spruce (Picea glauca (Moench) Voss), and jack pine (Pinus banksiana Lamb.), we monitored mass losses and changes in N and P contents in dead boles from a chronosequence of sites following stand-replacing disturbances. To assess the importance of wood decomposition to nutrient cycling, we compared net estimates of nutrient release from logs with net nutrient immobilization in live-tree biomass of stands as a function of time since disturbance. Mineralization rates were 0.060, 0.053, 0.038, and 0.020·year–1 for trembling aspen, white birch, white spruce, and jack pine logs, respectively. Trembling aspen boles released large quantities of N and P during the first year of decomposition (51 kg·ha–1 of N and 7 kg·ha–1 of P, assuming a bole volume of 150 m3·ha–1). White birch boles acted initially as a nutrient sink and delayed the release of immobilized nutrients until a period when the stand's net nutrient immobilization rates were highest. Jack pine boles appeared to be intermediate in terms of their contribution as a sink or a source of nutrients but, in mature stands, provided up to 40% of N and 26% of P immobilized annually in tree biomass. As pure stands of white spruce are rare in boreal Quebec, information on nutrient accumulation in white spruce stands was not available.

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

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

Genetic diversity and population structure of boreal white spruce (Picea glauca) in pristine conifer-dominated and mixedwood forest stands

White spruce ( Picea glauca (Moench) Voss) is a characteristic primary species of the Canadian boreal forest region, where it occurs in conifer-dominated and mixedwood forest types. Genetic diversity and population structure of white spruce may differ between the conifer-dominated and mixedwood forest types owing to the inherent differences in stand structure and dynamics. The objective of our study was to determine genetic diversity and population structure of pristine white spruce stands as they occur in conifer-dominated and mixedwood forest types at the EMEND (Ecosystem Management Emulating Natural Disturbance) study sites in northern Alberta. Nuclear microsatellite DNA markers were used to examine genetic diversity and population structure of 16 pristine natural old-growth (≥100 years) white spruce stands (subpopulations) of fire origin; 8 from conifer-dominated and 8 from neighboring mixedwood forest types. High levels of genetic diversity were observed, as expected. The genetic diversity and genetic constitution of white spruce were similar between the conifer-dominated and mixedwood forest types. Most of the genetic variation resided within subpopulations, with only about 2% genetic differentiation detected among 16 subpopulations as well as among 8 subpopulations within the same forest type. The mean genetic distances among subpopulations within and between the forest types were similar. Our study suggests that white spruce genetic resources are similar in the conifer-dominated and mixedwood forest types located in the EMEND study area in northern Alberta, and it provides the benchmarks for determining and monitoring the genetic diversity impacts of forest harvesting and forest fires.

Tree-ring Analysis of Five Picea Glauca- Dominated Sites from the Interior Boreal Forest in the Shakwak Trench, Yukon Territory, Canada

Five tree-ring chronologies were developed from low-elevation stands of white spruce (Picea glauca [Moench] Voss) situated in the interior boreal forest of the Shakwak Trench, Yukon Territory. The objective of this study was to investigate the climate impacts on tree growth using trees from within plots located in an interior boreal forest. The five chronologies depict similar trends in tree-ring width, suggesting a significant climatic influence on tree growth. Although the variability and sensitivity of these chronologies is lower than that of treeline sites, low-frequency ring-width variability is remarkably coherent among all the sites used in this study. The relationship between the chronologies and the regional climate data demonstrates that precipitation is more highly correlated with tree-ring width than temperature. This study demonstrates the importance of climate influences on tree growth within sites located in the interior of the boreal forest.

The Influence of Forest and Stand Conditions on Spruce Budworm Defoliation in New Brunswick, Canada

Abstract The species composition of stands and surrounding forest have been suggested as important factors influencing the amount of spruce budworm (Choristoneura fumiferana [Clem.]) defoliation and, consequently, budworm-induced growth loss and mortality. We measured spruce budworm defoliation from 1989–1993 in 40 spruce (Picea sp.) and balsam fir (Abies balsamea [L.] Mill.) stands in north-central New Brunswick, Canada, and evaluated the influence of surrounding forest type (softwood, mixedwood), species group (balsam fir, spruce), and site quality (wet/nutrient poor, moist/nutrient rich) on defoliation. Surrounding forest type had a significant effect on the amount of defoliation in white spruce (Picea glauca [Moench] Voss) stands; stands in softwood forests sustained 11% more (P = 0.0485) defoliation than those in mixedwood. There was evidence that hardwood species have to be within, rather than surrounding, a spruce-fir stand to significantly influence defoliation. Site quality had a significant effect (P = 0.0039) on balsam fir defoliation, with stands on moist/rich sites sustaining 19% more defoliation than those on wet/poor sites. In softwood forest, white spruce stands sustained an average of 16% more defoliation than red-black spruce (Picea rubens Sarg.-Picea mariana [Mill.] B.S.P.) stands.

Old-growth forests in the temperate deciduous zone of Quebec: Identification and evaluation for conservation and research purposes

The Quebec Department of Natural Resources (Ministère des ressources naturelles du Québec) is working to identify and protect old-growth forests in the deciduous forest zone of the province. A total of 88 sites was visited and a multivariate analysis of the main attributes of old growth allowed the development of quantitative definitions and criteria for identifying old-growth sugar maple (Acer saccharum), eastern hemlock (Tsuga canadensis), eastern white pine (Pinus strobus), eastern white-cedar (Thuja occidentalis), and red spruce (Picea rubens) stands. Life expectancy of various species according to environment was determined through a statistical analysis of 21 500 study trees taken from the province's forest inventory. Four different identification criteria for old-growth forests were developed that include a number of indicators for old growth. Along with advanced age of forest cover, the criteria that best reflected the nature of old-growth forests were the presence of large dead trees, low cutting intensity, and the importance of shade-tolerant species. Old-growth forests identified during this validation work occupy roughly 60 km2 in Quebec's deciduous forest zone. Among other things, old-growth sugar maple stands of over 400 years old were discovered, containing stems with a diameter at breast height of 140 cm and a height of over 38 m. The very great potential of many of these exceptional forests for scientific research and biodiversity conservation is illustrated by the work carried out in the Boisé des Muir. Despite its small size, this sugar maple stand, which is over 300 years old, has advanced knowledge in fields as varied as forest dynamics, biodiversity, and climate studies, and has also served as a control site for various scientific studies. Key words: old-growth forests, definitions, criteria, indicators, inventory, Quebec, conservation, scientific value

Environmental controls on soil CO2 flux following fire in black spruce, white spruce, and aspen stands of interior Alaska

Boreal forests contain large amounts of stored soil carbon and are susceptible to periodic disturbance by wildfire. This study evaluates the relationship between post-fire changes in soil temperature, moisture, and CO2 exchange in paired burned and control stands of three Alaskan forest systems: Picea mariana (Mill.) BSP, Picea glauca (Moench) Voss, and Populus tremuloides Michx. In these systems, the environmental factor that most directly controlled rates of carbon exchange varied depending upon burn status and soil drainage. In mature unburned stands, CO2 flux was highly correlated with seasonal patterns of soil temperature. Following fire, these soils became significantly warmer, and carbon exchange became more sensitive to fluctuations in surface moisture conditions. The effect of fire on soil climate was most pronounced in the P. mariana stands, which experienced a mean seasonal temperature increase of 5–8°C in the upper 1 m of the soil profile, a 200% increase in the rate of active layer thaw, and a reduction in mean surface moisture potential. Evidence from soil CO2 profiles suggests that these environmental changes may have resulted in enhanced decomposition of carbon previously immobilized by permafrost, potentially transforming a landscape that was once a net sink for carbon into a carbon source.

Simulating the effects of climate change on the carbon balance of North American high-latitude forests.

The large magnitude of predicted warming at high latitudes and the potential feedback of ecosystems to atmospheric CO2 concentrations make it important to quantify both warming and its effects on high-latitude carbon balance. We analysed long-term, daily surface meteorological records for 13 sites in Alaska and north-western Canada and an 82-y record of river ice breakup date for the Tanana River in interior Alaska. We found increases in winter and spring temperature extrema for all sites, with the greatest increases in spring minimum temperature, average 0.47 °C per 10 y, and a 0.7-day per 10 y advance in ice breakup on the Tanana River. We used the climate records to drive an ecosystem process model, BIOME_BGC, to simulate the effects of climate change on the carbon and water balances of boreal forest ecosystems. The growing season has lengthened by an average of 2.6 days per 10 y with an advance in average leaf onset date of 1.10 days per 10 y. This advance in the start of the active growing season correlates positively with progressively earlier ice breakup on the Tanana River in interior Alaska. The advance in the start of the growing season resulted in a 20% increase in net primary production for both aspen (Populus tremuloides) and white spruce (Picea glauca) stands. Aspen had a greater mean increase in maintenance respiration than spruce, whereas spruce had a greater mean increase in evapotranspiration. Average decomposition rates also increased for both species. Both net primary production and decomposition are enhanced in our simulations, suggesting that productive forest types may not experience a significant shift in net carbon flux as a result of climate warming.

Reduced growth of Alaskan white spruce in the twentieth century from temperature-induced drought stress.

The extension of growing season at high northern latitudes seems increasingly clear from satellite observations of vegetation extent and duration. This extension is also thought to explain the observed increase in amplitude of seasonal variations in atmospheric CO2 concentration. Increased plant respiration and photosynthesis both correlate well with increases in temperature this century and are therefore the most probable link between the vegetation and CO2 observations. From these observations, it has been suggested that increases in temperature have stimulated carbon uptake in high latitudes and for the boreal forest system as a whole. Here we present multi-proxy tree-ring data (ring width, maximum late-wood density and carbon-isotope composition) from 20 productive stands of white spruce in the interior of Alaska. The tree-ring records show a strong and consistent relationship over the past 90 years and indicate that, in contrast with earlier predictions, radial growth has decreased with increasing temperature. Our data show that temperature-induced drought stress has disproportionately affected the most rapidly growing white spruce, suggesting that, under recent climate warming, drought may have been an important factor limiting carbon uptake in a large portion of the North American boreal forest. If this limitation in growth due to drought stress is sustained, the future capacity of northern latitudes to sequester carbon may be less than currently expected.

Criteria for estimating old growth in boreal mixedwoods from standard timber inventory data

This paper quantifies the amount of old growth forest in a boreal mixedwood landscape using the profile of tree sizes within stands. In the boreal mixedwood, successional trajectories exhibit significant variability, thereby making classification systems based on age or seral stage difficult to apply. Furthermore, a lack of extensive datasets on forest structure prevents comprehensive, multivariate classification of stands. Alternatively, we designated old growth status using the proportion (≥15%) of large trees (≥40 cm DBH) and the subcanopy/canopy tree ratios (>1.5). With these riteria, approximately 11.4% of the boreal mixedwood landbase within northeastern Alberta has an old growth structure. Proportionally, more old growth structure was found in aspen and white spruce mixedwood types, with lesser proportions in pure aspen and white spruce stands. Sensitivity analysis revealed that the tree size criteria was the most important driving variable in determining the amount of old growth.

Predation in heterogeneous forests: A comparison at natural and anthropogenic edges

The boreal mixed-wood forest is a naturally heterogenous system that has an extensive amount of forest edge. Recent increases in timber harvesting as well as oil and gas exploration have imposed an abundance of anthropogenic forest edges across this landscape. Because past research has indicated that songbirds nesting near forest edges can suffer increased nest predation, we conducted an artificial nest experiment to compare predation pressure on songbird populations along natural and anthropogenic edges. Artificial nests were placed in shrubs and on the ground in aspen stands adjacent to: (i) white spruce stands, (ii) clearcuts, (iii) seismic lines, and, (iv) in the interior of aspen stands. In 1995, predation on shrub nests was higher at aspen/seismic line edges, whereas in 1996 it was higher at aspen/white spruce edges. In both years, predation on ground nests was not significantly different among sites. We also examined vegetation at the nest, stand, and landscape scale to determine if these factors affected the probability of predation. Vegetation was not a strong or consistent predictor of predation events at these scales. Predation tended to be higher where there was preferred habitat for nest predators such as red squirrels (Tamiasciurus hudsonius). We encountered a large degree of temporal and spatial variation with this study and we emphasize the importance of long-term studies to separate true effects from stochastic processes. In the short term, the creation of anthropogenic edges in the boreal mixed-wood forest does not appear to cause any relative increase in predator pressure on artificial nests when compared with natural edges or the forest interior.

Regeneration in Unmanaged Conifer Plantations, Upstate New York

This study addresses the secondary succession of abandoned Pinus resinosa (red pine) and Picea glauca (white spruce) plantations in upstate New York. Both red pine and white spruce are not regenerating in the unmanaged plantations. Successful regeneration of hardwood tree species in the white spruce plantations occurred only within the 25-30 years following plant? ing. Higher light levels in the red pine stands have led to a greater degree of subsequent hardwood invasion than in the white spruce stands. The impact of abandoned conifer plantations will have long-term effects, altering the forest species composition for several hundred years. However, the plantations will eventually return to a natural forest composition, and expansion of planted conifers into adjacent undisturbed forests is unlikely.