Clear-cut Forest Sites Research Articles

DNA-Metabarcoding of Belowground Fungal Communities in Bare-Root Forest Nurseries: Focus on Different Tree Species.

The production of tree seedlings in forest nurseries and their use in the replanting of clear-cut forest sites is a common practice in the temperate and boreal forests of Europe. Although conifers dominate on replanted sites, in recent years, deciduous tree species have received more attention due to their often-higher resilience to abiotic and biotic stress factors. The aim of the present study was to assess the belowground fungal communities of bare-root cultivated seedlings of Alnus glutinosa, Betula pendula, Pinus sylvestris, Picea abies and Quercus robur in order to gain a better understanding of the associated fungi and oomycetes, and their potential effects on the seedling performance in forest nurseries and after outplanting. The study sites were at the seven largest bare-root forest nurseries in Lithuania. The sampling included the roots and adjacent soil of 2–3 year old healthy-looking seedlings. Following the isolation of the DNA from the individual root and soil samples, these were amplified using ITS rRNA as a marker, and subjected to high-throughput PacBio sequencing. The results showed the presence of 161,302 high-quality sequences, representing 2003 fungal and oomycete taxa. The most common fungi were Malassezia restricta (6.7% of all of the high-quality sequences), Wilcoxina mikolae (5.0%), Pustularia sp. 3993_4 (4.6%), and Fusarium oxysporum (3.5%). The most common oomycetes were Pythium ultimum var. ultimum (0.6%), Pythium heterothallicum (0.3%), Pythium spiculum (0.3%), and Pythium sylvaticum (0.2%). The coniferous tree species (P. abies and P. sylvestris) generally showed a higher richness of fungal taxa and a rather distinct fungal community composition compared to the deciduous tree species (A. glutinosa, B. pendula, and Q. robur). The results demonstrated that the seedling roots and the rhizosphere soil in forest nurseries support a high richness of fungal taxa. The seedling roots were primarily inhabited by saprotrophic and mycorrhizal fungi, while fungal pathogens and oomycetes were less abundant, showing that the cultivation practices used in forest nurseries secured both the production of high-quality planting stock and disease control.

Growth and genotype × environment interactions in Betula pendula: can tree genetic variation be maintained by small-scale forest ground heterogeneity?

Forest ground heterogeneity can affect interactions among tree species and control the assembly of local forest communities. Less is known of the effects of spatial heterogeneity on the maintenance of tree genetic variation through small-scale geno- type 9 environment (G 9 E) interactions. We measured growth variation within and among 17 Betula pendula genotypes, planted in a clear-cut forest site through the summers 2009-2011. We assessed the spatial heterogeneity at two scales: among forest stands having history of the same or different tree species combinations (treated as replicate blocks), and along a gradient of within-block forest density, revealed by the stump density. To add a temporal perspective, we distinguished between old (cut 50 years earlier) and new stumps (cut one year earlier). The broad-sense heritabilities for growth were 0.093-0.055 and the coefficients of genotypic variation 0.37-0.21 in 2009-2011. The growth difference among the genotypes was 3.5-5.5 fold, significant in all years, and the rank of genotype means correlated positively between the years. The most favourable block had 106 % higher growth than the least favourable block and the amount of total variation explained by block increased from 0.4 % in 2009 to 6.9 % in 2011. Geno- type 9 block interaction was marginally significant in 2009, but not later. Similarly, the response of growth to old stump density in sapling vicinity varied among the genotypes in 2009, but not later. In 2010 and 2011, the mean growth increased by 50-91 % along the old stump density gradient. Our results suggest that despite creating significant variation in sapling growth the small-scale forest ground heterogeneity, which reflects the recent forest history, may not significantly contribute to the maintenance of genetic variation in B. pendula populations.

Hybrid poplar yields in Québec: Implications for a sustainable forest zoning management system

In the province of Québec, approximately 12 000 ha of fast-growing poplar plantations are managed by industrials, while small private landowners have planted only 1000 ha. Most of these poplar plantations are established on clearcut forest sites (approx. 11 000 ha). What are the yields of these hybrid poplar plantations? In this article, available yield data are presented and discussed in the context of a sustainable forest zoning management system. In southern Québec, three factors are highly correlated to yield for clones of various parentages: NO3supply rate in riparian soils, elevation (or climate) and soil P availability in abandoned farmland soils. Many Québec forest sites, particularly in the boreal shield ecozone, have acidic soils and harsh climate, with low mineralization rates. They generally cannot fulfill the very high nutrient requirements of hybrid poplars. Within a forest zoning management system, hybrid poplar plantations and agroforestry should be located in priority in southern Québec landscapes, with low remaining natural forest cover, and where intensive agriculture is the dominant land-use. This strategy will increase biodiversity and the provision of ecosystem services. Elsewhere, intensive trembling aspen regeneration silviculture could be a sustainable alternative to forest conversion into hybrid poplar plantations.

Effects of controlled forest burning and intensity of timber harvesting on the occurrence of pine weevils, Hylobius spp., in regeneration areas

Recently introduced modifications to timber harvesting, such as leaving retention trees and applying prescribed burning, are likely to have an influence on the occurrence of pests affecting regeneration, such as pine weevils ( Hylobius spp.). We analyze here the occurrence of pine weevils in regeneration areas representing different harvesting methods. Pine weevils were monitored during three summers using flight intercept and pitfall traps placed on clear-cut sites, sites with 10 or 50 m 3 timber ha −1 and uncut forest sites, totalling 24 in all. A half of the sites were treated with prescribed burning. Burning and the use of retention trees increased the catches of Hylobius abietis but not of H. pinastri. Pitfall trap catches suggested 10–24 times higher population density of H. abietis on logged clear-cut sites than in undisturbed forests. Catches on burned and clear-cut forest sites were 35–55 times higher than in undisturbed forests. Flight intercept trap catches suggested that the migration of flying weevils to freshly treated sites (logging or prescribed burning or both) continued after the early summer swarming period, which differs from previous results. The groups of retention trees attracted both flying and walking H. abietis individuals. These results indicate that retention trees may provide an alternative food source for weevils and may consequently reduce the harmful impacts that weevils have on pine seedlings.

Soil N and C transformations in two forest clear-cuts during three years after mounding and inverting

Transformations of nitrogen and carbon in the humus layer were studied in central Finland on two clear-cut forest sites for 3 yr after spot mounding and inverting together with an untreated control. In laboratory-incubation experiments, samples from the humus layer were measured for rates of C mineralization, net N mineralization and net nitrification, and the amounts of C and N in the microbial biomass were determined. Soil solutions were collected for 4 yr with suction lysimeters. Overall, site preparation did not affect the rate of net N mineralization significantly (per kg organic matter). In the first growing season, however, the mean rate of net N mineralization was higher in both site preparation treatments than in the untreated control. At first, net nitrification was negligible in all treatments, but in the second year it increased in both site preparation treatments. On the other site, C mineralization was lowest with inverting, but the amounts of microbial C and N were highest. This indicates a shortage of easily mineralizable C sources in inverted spots. In the soil solution collected below the humus layer, increased concentrations of NO3-N and total N were found in both site-preparation treatments but, during the fourth year, overall concentrations of N had declined. Key words: Boreal forest, clear-cut, N transformations, site preparation, soil solution

Nutrient‐Release Rates of Controlled‐Release Fertilizers in Forest Soil

Nutrient‐release rates of controlled‐release fertilizer (CRF) with four different labeled release periods were evaluated. Samples (30 g) sealed with nylon mesh were buried at a clearcut forest site (Price soil series) in western Oregon, USA, in February 2000 and excavated every 7 weeks for 14 months to determine residual weight and composition. Cool, dry soil conditions apparently prolonged nutrient release beyond labeled rates; the fertilizer with the shortest release period (3–4 months) released approximately 72% of the fertilizer (by weight), whereas that with the longest release period (8–9 months) released 48%. Release varied among individual nutrients [nitrate (NO3)>ammonia (NH3)>potassium (K)>sulfur (S)>magnesium (Mg)>phosphorus (P)]. Minimal changes in micronutrient [iron (Fe), manganese (Mn), zinc (Zn), and molybdenum (Mo)] contents were attributed to the formation of insoluble compounds with P. Variable release among individual nutrients demonstrates a limitation toward delivering a full range of nutrients and suggests that further refinement of CRF technology is needed to optimize nutrient availability under realistic field conditions.

Root growth and nutrient uptake of Norway spruce container seedlings planted in mounded boreal forest soil

The effects of mounding on root and shoot growth and nutrient uptake in 1- and 2-year-old Norway spruce ( Picea abies (L.) Karst.) container seedlings were studied for 2 years after planting at a clear-cut forest site in Finland. Three different mounding treatments (spot mounding with and without mixing, and inverting) were compared with two unscarified treatments with or without a cardboard mulch. All of the mounding treatments that were used enhanced both the root and the shoot growth and also the nutrient uptake of the 1- and 2-year-old seedlings compared with the unscarified treatments. The foliar nitrogen concentration increased after planting, but the concentrations of other nutrients decreased. In particular, foliar boron decreased to a level of deficiency. The biomass growth of roots and shoots was greater in 2-year old than in 1-year-old seedlings. The results suggest that larger 2-year-old seedlings can utilize improved soil conditions after mounding slightly better than 1-year-old seedlings.

Molecular characterization of airborne fungal spores in boreal forests of contrasting human disturbance

In this study we present a new approach to characterize fungal diversity with DNA sequencing of mycelium grown from trapped airborne spores. Fungal spores were extracted systematically from air in three boreal forest sites (clear-cut, young and old-growth forests) using an air sampling device. Internal transcribed spacer (ITS) sequences from the nuclear ribosomal DNA (nrDNA) were generated, and the sequences most likely taxon affinities were established through DNA homology searches. Phylogenetic analyses were used to classify similar sequences into operational taxonomic units (OTUs). The analyses indicated that a total of 84 different OTUs had been sampled, 24 basidiomycetes and 60 ascomycetes. OTUs belonging to the ascomycete orders Helotiales and Pleosporales were most frequent (31 and 18 respectively). A total of 54, 29 and 33 OTUs were sampled, respectively, in the old-growth, young and clear-cut forest sites. Although heavy generalization should be avoided due to few replicates, the results could indicate that old-growth boreal forests have significantly higher airborne fungal species richness than recently managed forests. The study shows that the spore-trapping approach has a great potential for targeting and studying anonymous fungi.

Molecular characterization of airborne fungal spores in boreal forests of contrasting human disturbance

In this study we present a new approach to characterize fungal diversity with DNA sequencing of mycelium grown from trapped airborne spores. Fungal spores were extracted systematically from air in three boreal forest sites (clear-cut, young and old-growth forests) using an air sampling device. Internal transcribed spacer (ITS) sequences from the nuclear ribosomal DNA (nrDNA) were generated, and the sequences most likely taxon affinities were established through DNA homology searches. Phylogenetic analyses were used to classify similar sequences into operational taxonomic units (OTUs). The analyses indicated that a total of 84 different OTUs had been sampled, 24 basidiomycetes and 60 ascomycetes. OTUs belonging to the ascomycete orders Helotiales and Pleosporales were most frequent (31 and 18 respectively). A total of 54, 29 and 33 OTUs were sampled, respectively, in the old-growth, young and clear-cut forest sites. Although heavy generalization should be avoided due to few replicates, the results could indicate that old-growth boreal forests have significantly higher airborne fungal species richness than recently managed forests. The study shows that the spore-trapping approach has a great potential for targeting and studying anonymous fungi.

Effects of Mounding on Damage by the European Pine Weevil in Planted Norway Spruce Seedlings

Abstract The European pine weevil (Hylobius abietis L.) is not found in northern America so far but is the major pest in conifer reforestation in northern Europe. The effects of mounding on pine-weevil damage and growth in planted Norway spruce (Picea abies (L.) Karst.) seedlings were studied on two clearcut forest sites in Finland. Three different mounding treatments (spot mounding with or without mixing and inverting) were compared to three unscarified treatments with or without vegetation control (mulch or herbicide). Mounding significantly decreased pine-weevil damage, mortality, and growth losses of planted Norway spruce seedlings even if insecticide was used before planting. Seedling growth and survival were poorest with the heaviest feeding by the pine weevil. After the first growing season, the proportion of gnawed seedlings was higher on unscarified spots (76% gnawed), whereas seedlings on mounded spots had hardly any feeding (1%). Seedling mortality was lower on mounded (1%) than on unscarified spots, where it was higher in 1-year-old (27%) than 2-year-old seedlings (10%). After the second growing season, mortality and proportion of gnawed seedlings increased on both mounded and unscarified spots. The study indicates that mounding can provide an effective method of decreasing pine-weevil damage and improving plantation success.North. J. Appl. For. 22(3):154 –161.

Prescribed fire-induced changes in properties of sub-boreal forest soils

Pile and windrow burning of logging slash are important silvicultural practices in sub-boreal forests, yet, little is known about their effects on soil properties. We investigated the physical, chemical, and mineralogical properties of soils collected 2 years after prescribed pile and windrow burning treatments of clearcut forest site in the central interior of British Columbia. We also used scanning electron microscopy to investigate the effects of fire on soil morphology, particularly, soil aggregate and sand fraction. We observed higher soil pH, exchangeable Ca, Mg, K and Na and base saturation in burnt plots compared to unburnt plots. The concentrations of total and available N were similar in all treatments. In general, pile burning had more significant effects on soil properties than windrow burning. Pile and windrow burning reduced the amount of 2:1 expanding clays (vermiculite) but not kaolinite in the clay fractions of Ae and Bm horizons indicating that the temperature <500 °C. Prescribed burns may also have caused the cracks in sand-sized amphibole, perhaps reducing their sizes into silt fraction and finer. The prescribed burns may also be responsible for the cracking patterns observed in soil aggregates and sand fraction potentially contributing to increased weathering rates.

Effect of Site Preparation and Reforestation Method on Survival and Height Growth of Scots Pine

The influence of site preparation and reforestation method on the performance of Scots pine (Pinus sylvestris L.) was followed during 16 growing seasons in northern Finland using a split-plot design in randomized blocks. The site-preparation methods were prescribed burning (BURN), patch scarification (PATCH), disk trenching (DISK) and ploughing (PLOU). The reforestation methods were sowing (SOW) and planting with containerized seedlings (CON) and bare-rooted transplants (BARE). The reforestation was repeated in three successive years. A total of 72000 reforestation spots was sown or planted on the 288 plots using the reforestation density of 2500 spots ha –1. Four of the eight clear-cut forest sites were dryish pine-dominated sites and four were moist, formerly Norway spruce-dominated sites. After 16 growing seasons, average survival was 49% on the pine sites and 33% on the spruce sites. Site preparation significantly affected survival on the spruce sites (PLOU 44%>DISK 23%) but not on the pine sites. The reforestation method had a significant effect only on the pine sites (CON 58%)>SOW 36%). The effect of site preparation on mean height was significant on the pine (BURN 271 cm>DISK 222 cm) and spruce sites (PLOU 269, BURN 256 cm>DISK 212 cm). The differences between the reforestation methods were highly significant on the pine (BARE 295 cm>CON 261 cm>SOW 186 cm) and spruce sites (BARE 309 cm>CON 255 cm>SOW 171 cm). The results of this study indicate that different site-preparation methods can be used successfully in Scots pine reforestation on dryish, formerly pine-dominated sites in northern Finland. Intensive site-preparation methods, such as ploughing or mounding, are needed if Scots pine is to be established on moist, formerly spruce-dominated sites. However, the low survival and wide variation in survival indicated that there is a high risk of failure on such sites.

Effect of Site Preparation and Reforestation Method on Survival and Height Growth of Scots Pine

Abstract The influence of site preparation and reforestation method on the performance of Scots pine (Pinus sylvestris L.) was followed during 16 growing seasons in northern Finland using a split-plot design in randomized blocks. The site-preparation methods were prescribed burning (BURN), patch scarification (PATCH), disk trenching (DISK) and ploughing (PLOU). The reforestation methods were sowing (SOW) and planting with containerized seedlings (CON) and bare-rooted transplants (BARE). The reforestation was repeated in three successive years. A total of 72000 reforestation spots was sown or planted on the 288 plots using the reforestation density of 2500 spots ha –1. Four of the eight clear-cut forest sites were dryish pine-dominated sites and four were moist, formerly Norway spruce-dominated sites. After 16 growing seasons, average survival was 49% on the pine sites and 33% on the spruce sites. Site preparation significantly affected survival on the spruce sites (PLOU 44%>DISK 23%) but not on the pine sites. The reforestation method had a significant effect only on the pine sites (CON 58%)>SOW 36%). The effect of site preparation on mean height was significant on the pine (BURN 271 cm>DISK 222 cm) and spruce sites (PLOU 269, BURN 256 cm>DISK 212 cm). The differences between the reforestation methods were highly significant on the pine (BARE 295 cm>CON 261 cm>SOW 186 cm) and spruce sites (BARE 309 cm>CON 255 cm>SOW 171 cm). The results of this study indicate that different site-preparation methods can be used successfully in Scots pine reforestation on dryish, formerly pine-dominated sites in northern Finland. Intensive site-preparation methods, such as ploughing or mounding, are needed if Scots pine is to be established on moist, formerly spruce-dominated sites. However, the low survival and wide variation in survival indicated that there is a high risk of failure on such sites.

Site preparation, fertilization, and 10-year yields of hybrid poplar on a clearcut forest site in eastern Maine, USA

Cuttings of two similar hybrid poplar clones were planted on a drum-chopped, chip-harvested clearcut in eastern Maine. The site had never been previously cleared for agriculture. The coarse loamy glacial till soils were acid (pH < 5.0) and moist—moderately well—to somewhat poorly drained. Control, lime (L), L nitrogen (N), L phosphorus (P), LNP, and LNP potassium (K) treatments were established. Competing woody vegetation was mowed once per year for the first three years on half the area. Each mowed treatment produced significantly greater hybrid poplar biomass than the corresponding unmowed treatment. After 10 years, the mowed+LNPK treatment attained the greatest total biomass, 45 Mgha-1, while the unmowed control attained the least, 2 Mgha-1. On mowed plots, L produced 4 times the biomass of control: 32 vs 8 Mgha-1. Unmowed plots with L and N produced about as much hybrid poplar biomass as the mowed control (8 Mgha-1). Mowing and L each improved survival as well as growth.

Response on the ground of bark beetle and weevil species colonizing conifer stumps and roots to terpenes and ethanol

Responses of threeHylastes species,Dryocoetes autographus, and twoHylobius species to terpenes and ethanol were studied in field experiments on clear-cut forest sites in Sweden using baited ground traps.α-Pinene alone did not attract any of the six species. A terpene blend (spruce turpentine consisting mainly ofα-pinene,β-pinene, and 3-carene) attractedHylastes cunicularius, H. brunneus, andHylobius abietis in some experiments, but not in others. The attractiveness of ethanol also varied; the only species consistently attracted wasH. abietis. Baits containing both terpenes and ethanol, particularly the combination of spruce turpentine and ethanol, were attractive to all species exceptHylobius pinastri. InH. abietis, the terpene plus ethanol/ ethanol catch ratios increased during early summer. Seasonal differences in catch levels were observed inH. cunicularius andH. abietis. The addition ofα-pinene reduced the attractiveness of the combination of spruce turpentine and ethanol toH. cunicularius, H. opacus, andD. autographus. The differences in response to the volatiles between species are probably related to differences in reproductive behavior and host preferences.

Implications of physiological responses to chronic air pollution for forest decline in the southeastern United States

The effects of acidic precipitation and ozone on physiological processes in loblolly pine (Pinus taeda L.) were assessed over time to determine dose-response relationships of cumulative exposure to varying levels of ozone and acid rain in combination. Seedlings of known provenance were grown in open-top field chambers in a clear-cut forest site in Duke Forest in the Piedmont of North Carolina and were exposed to pH 5.2 or 3.5 precipitation and several proportional ozone treatments (0.5-3.0x ambient ozone). No direct effects of acid precipitation on gas exchange and carbon fixation were found. Elevated ozone exposures had strong negative effects on needle abscission and net photosynthesis. Exposure-response relationships for photosynthesis indicated that a threshold level of approximately 100 ppm·h of cumulative ozone exposure (12-h summation) had to be reached before significant inhibition occurred. Results suggest that chronic pollutant exposure over the growing season has direct negative effects on carbon fixation in loblolly pine that can significantly reduce long-term growth potential. Current ambient ozone levels in the southeastern United States could be responsible for an approximate 19% reduction in instantaneous carbon fixation rates in loblolly pine by the end of one growing season. An 80 to 90% decrease in net photosynthesis was found at 2.25 and 3.0x ambient ozone concentrations, levels often found in major cities and surrounding areas in the South.

IMPLICATIONS OF PHYSIOLOGICAL RESPONSES TO CHRONIC AIR POLLUTION FOR FOREST DECLINE IN THE SOUTHEASTERN UNITED STATES

The effects of acidic precipitation and ozone on physiological processes in loblolly pine (Pinus taeda L.) were assessed over time to determine dose-response relationships of cumulative exposure to varying levels of ozone and acid rain in combination. Seedlings of known provenance were grown in open-top field chambers in a clear-cut forest site in Duke Forest in the Piedmont of North Carolina and were exposed to pH 5.2 or 3.5 precipitation and several proportional ozone treatments (0.5-3.0x ambient ozone). No direct effects of acid precipitation on gas exchange and carbon fixation were found. Elevated ozone exposures had strong negative effects on needle abscission and net photosynthesis. Exposure-response relationships for photosynthesis indicated that a threshold level of approximately 100 ppm·h of cumulative ozone exposure (12-h summation) had to be reached before significant inhibition occurred. Results suggest that chronic pollutant exposure over the growing season has direct negative effects on carbon fixation in loblolly pine that can significantly reduce long-term growth potential. Current ambient ozone levels in the southeastern United States could be responsible for an approximate 19% reduction in instantaneous carbon fixation rates in loblolly pine by the end of one growing season. An 80 to 90% decrease in net photosynthesis was found at 2.25 and 3.0x ambient ozone concentrations, levels often found in major cities and surrounding areas in the South.

Use of the Priestley-Taylor evaporation equation for soil water limited conditions in a small forest clearcut

The Priestley-Taylor equation, a simplification of the Penman equation, was used to allow calculations of evapotranspiration under conditions where soil water supply limits evapotranspiration. The Priestley-Taylor coefficient, α, was calculated to incorporate an exponential decrease in evapotranspiration as soil water content decreases. The method is appropriate for use when detailed meteorological measurements are not available. The data required to determine the parameter for the α coefficient are net radiation, soil heat flux, average air temperature, and soil water content. These values can be obtained from measurements or models. The dataset used in this report pertains to a partially vegetated clearcut forest site in southwest Oregon with soil depths ranging from 0.48 to 0.70 m and weathered bedrock below that. Evapotranspiration was estimated using the Bowen ratio method, and the calculated Priestley-Taylor coefficient was fitted to these estimates by nonlinear regression. The calculated Priestley-Taylor coefficient (α′) was found to be approximately 0.9 when the soil was near field capacity (0.225 cm 3 cm −3). It was not until soil water content was less than 0.14 cm 3 cm −3 that soil water supply limited evapotranspiration. The soil reached a final residual water content near 0.05 cm 3 cm −3 at the end of the growing season.

Early growth of planted western hemlock in relation to stock type and controlled-release fertilizer application

Four types of western hemlock (Tsugaheterophylla (Raf.) Sarg.) nursery stock, differing in size, morphology, and root growth capacity were planted on a clear-cut forest site on Vancouver Island, British Columbia. The stock types were: (i) 1-year-old, plug-rooted seedlings raised in 36-cm3 containers; (ii) as (i) but transplanted to a bareroot nursery for 1 year; (iii) 1-year-old, bareroot seedlings raised in 1000-cm3 containers; (iv) as (iii) but raised in containers coated on the inside with copper paint to inhibit lateral root elongation upon contact with the container wall. Survival and growth of seedlings with and without fertilization at planting with 50 g of a slow-release (Nutricote®, 12-month release at 25 °C) N–P–K fertilizer were observed for 3 years. Neither stock type nor fertilizer had a statistically significant (P &lt; 0.05) effect on seedling survival. At planting, plug seedlings were significantly (P &lt; 0.01) shorter and smaller in stem volume than the other stock types. These differences were no longer evident by the end of the third growing season because of more rapid growth by the plug stock. The largest differences between the plugs and the other stock types in height and diameter relative growth rates occurred during the first growing season. Fertilization significantly (P &lt; 0.01) increased height and stem volume relative growth rates of all stock types during the first growing season. During the third growing season fertilization had a significant (P &lt; 0.01) negative effect on height, and diameter and stem volume relative growth rates of all stock types, but not on absolute rates. At the end of three growing seasons, fertilized trees remained significantly (P &lt; 0.01) larger in all stock types than in the controls.

Planting stress in newly planted jack pine and white spruce. 1. Factors influencing water uptake.

Bareroot jack pine (Pinus banksiana Lamb.) seedlings (2 + 0) and bareroot white spruce (Picea glauca (Moench) Voss) transplants (1 1/2 + 1 1/2) were taken from cold storage and planted on a clearcut forest site in northeastern Ontario on several dates between May 6 and June 5 during which period soil temperature at 15 cm depth increased from 0 to 18 degrees C. Additional cold-stored trees were transferred to a greenhouse where they were grown in pots for 0, 7 or 28 days and then placed with their roots in aerated water maintained at one of a range of constant temperatures between 0 and 22 degrees C. In both species, daytime xylem pressure potentials (Psi(x)) and needle conductances (g(wv)) decreased with decreasing soil or water temperature. At all root temperatures, g(wv) was lower, and Psi(x) higher, in jack pine than in white spruce. After 28 days in the greenhouse, g(wv) of jack pine seedlings, and Psi(x) of white spruce, was higher than in plants just removed from cold storage. In both species, water-flow resistance through the soil-plant-atmosphere continuum (RSPAC) increased as root temperature decreased. At all root temperatures, RSPAC was higher in plants just removed from cold storage than in plants grown in the greenhouse for 28 days, during which time many new unsuberized roots were formed. At root temperatures above 10 degrees C, RSPAC of both species was higher in trees newly planted in mineral soil than in trees with roots in aerated water; presumably because the roots of planted trees had limited hydraulic contact with the soil. On the day following removal from cold storage, relative plant water flow resistance increased, in both species, more rapidly with declining root temperature than could be accounted for by the change with temperature in the viscosity of water, thus indicating an effect of temperature on root permeability. The same effect was evident in jack pine seedlings, but not white spruce transplants, that had been grown for 28 days in the greenhouse after removal from cold storage.