Canadian Journal of Forest Research

Seedlings from three conifer species (Pinus contorta Doug. ex Loud. var. latifolia Englem., Picea glauca (Moench) Voss, and Picea mariana (Mill.) BSP) were planted on two clear-cut sites in Alberta, Canada, after inoculation in the nursery with strains of six different ectomycorrhizal species (Hebeloma longicaudum, Laccaria bicolor,Paxillus involutus,Pisolithus tinctorius,Rhizopogon vinicolor, and Suillus tomentosus). Five and 6 years after planting, morphological characterization and molecular typing techniques (internal transcribed spacer – restriction fragment length polymorphism (ITS-RFLP) and simple sequence repeat (SSR) markers) were used to identify the ectomycorrhizal fungal communities and to assess the occurrence of the inoculated ectomycorrhizal fungi on host roots. Ectomy corrhi zae recovered from the roots of the planted trees on each of the two sites showed little diversity, with a total of 16 and 19 ITS-RFLP patterns corresponding to 11 and 13 ectomycorrhizal taxa, respectively. The most abundant ectomycorrhizal fungi found on colonized roots were ascomycetes and the widespread basidiomycete Amphinema byssoides. Amongst the six introduced fungal strains, only L. bicolor UAMH 8232 was detected on one site after 5 and 6 years, as determined using six SSR markers. Although not detected after 5 years, some of the introduced strains might have had a positive effect on the early growth of the trees before their replacement by competing species, because significant differences in plot volume index were detected between inoculation and control treatments.

The effects of ontogeny and soil nutrient supply on aboveground biomass accumulation, allocation, and stemwood growth efficiency of loblolly (Pinus taeda L.) and slash pine (Pinus elliottii Engelm. var. elliottii) were investigated in north-central Florida over 16 years using a 2 × 2 × 2 factorial experiment (species, fertilization, weed control). Aboveground biomass growth responses to the combined fertilizer and weed control treatments (FW) averaged ~2- and 2.8-fold for slash and loblolly pine, respectively. In the same treatment, annual needlefall (NF) production for slash pine approached a "steady state" of 6 Mg·ha^-1 at ages 8-14 years, while loblolly pine NF production peaked at 7 Mg·ha^-1 at age 10 years, and then declined 17% following curtailment of the fertilizer treatment. Periodic stemwood biomass increment (PAI) for the FW treatment for both species culminated at about 15 Mg·ha^-1·year^-1 at age 8 years and then declined rapidly (~275%) to <4 Mg·ha^-1·year^-1 at 15 years; reductions for the untreated control were considerably slower. The progressive decline in PAI following peak leaf area development was closely associated with a decrease in stemwood production per unit leaf area (growth efficiency). A unit increase in leaf area index in the 7- to 9-year-old stands produced about 3.0 and 3.1 times more stemwood biomass per year than in the 14- to 16-year-old stands for loblolly and slash pine, respectively.

Levels of nitrogen in foliage associated with optimum growth of pine were determined in two hydroponic experiments in the glasshouse and two forest fertilizer experiments each designed to cover the full response range for Pinusnigra var. maritima (Ait.) Melv. During the years prior to canopy closure optimum nitrogen concentrations declined with the logarithm of tree weight, falling from 3.3% in very young seedlings to 1.5% in forest trees of 2.0–2.5 m in height. After canopy closure the level increased to about 2.0%. At all stages the concentrations associated with maximum height growth were less than those for maximum volume, weight, or diameter increment. The relationships in the forest experiments, which are on sand dunes in the north of Scotland, could be improved by including factors of rainfall during the previous August and September and of temperature in June of the same year, but this did not alter the optima. It is concluded that for diagnostic purposes critical foliar nitrogen levels must be qualified by the age or developmental stage of the trees.

The effects of slash and litter management practices on soil water and temperature, fluxes of mineral N, needle water potential, and tree nutrition and growth were studied in a young Pinusradiata D. Don plantation growing on a sandy Podzol in southeastern Australia. Treatments were slash and litter retained (SL), litter only retained (L), litter ploughed (LP), and slash and litter removed (SLR). Soils without slash or litter cover (LP and SLR) were up to 4 °C warmer on average than soils overlaid by slash or litter and were subjected to greater extremes of temperature. Treatments had relatively little effect on soil water content and needle water potential in trees. Carbon in surface soil increased from 1.14 to 1.83% after incorporation of litter by ploughing, but decreased to 1.37% during the next 40 months. Smaller but significant decreases in C also occurred in other treatments. LP and SLR led to the highest rates of N mineralization in the 1st year. During the first 3 years after clear-felling, rates of N mineralization increased in SL, L, and LP but decreased in SLR. During the 4th year, rates of N mineralization were low (20–30 kg N•ha⁻¹•year⁻¹) in all treatments. Over 4 years, 211, 170, 210, and 147 kg N•ha⁻¹ were mineralized in treatments SL, L, LP, and SLR, respectively. Rates of mineralization and leaching were strongly correlated (R² = 0.82) and leaching below 30 cm accounted for 75–85% of N mineralized irrespective of treatment. Incorporation of litter by ploughing doubled concentrations of mineral N during the first summer after planting and increased early tree growth. However, rates of N mineralization in the slash and litter treatments, which were high compared with potential rates of uptake, were weakly correlated with tree growth. Factors controlling N supply were of little consequence for tree growth during this early phase of plantation establishment.

A field study examined the effects of competing vegetation on the moisture and nutrient status of 5-year-old loblolly pines (Pinustaeda L.). Similar experiments were conducted on a Piedmont site and a Coastal Plain site using individual pines as experimental units. Predawn measurements of xylem pressure potential were made using detached needle fascicles, and nutrient concentrations in soil and foliage samples were determined monthly. This study was conducted during the 3rd year of a relatively dry 3-year period. On the Piedmont site, elimination of all competing vegetation within 1.5 m of the pines significantly lowered moisture stress when compared with the no-elimination treatment; on the Coastal Plainee site, differences were significant on only half of the assay dates. Removing only arborescent vegetation on the Piedmont site reduced pine water stress one-half as much as removing all vegetation, but on the Coastal Plain site this reduction was about two-thirds of that found following removal of all vegetation. As drought length increased, stress increased, regardless of treatment. Higher levels of competing vegetation significantly reduced available potassium, calcium, magnesium, and manganese concentrations in the loamy sand of the Coastal Plain site, but only potassium was reduced on the Piedmont. None of the treatments significantly affected foliar nutrients at either site.

Herbaceous weed control studies installed by the Auburn University Silvicultural Herbicide Cooperative to examine response to methods and duration of herbaceous weed control in eight loblolly pine (Pinustaeda L.) plantations were analyzed to determine stand response through age 9. Studies were designed to compare weed control treatments with an untreated check, weed control methods (band vs. broadcast), and weed control duration (first year vs. first 2 years). Pine growth was increased by weed control on all sites. Growth was increased by an additional year of weed control (duration) on about one-half of the sites, but did not differ between band and broadcast treatments (method). Age 9 volume response above the check averaged 27.3 m³/ha for first-year weed control and 42.9 m³/ha for the first 2 years of weed control. Individual-tree height growth between ages 7 and 9 did not differ by treatment at most sites, but stand volume growth was higher with weed control at six of the eight sites. Uniformity of individual tree size, as represented by the standard deviation of DBH adjusted for dominant height, was more dependent on survival, hardwood encroachment, and level of fusiform rust stem infection, which varied by treatment and site, than on the result of herbaceous weed control per se. Growth projections made with the least intensive weed control treatment at each site indicated that on average, merchantable volume at age 22 with weed control will equal that of an age 25 stand without weed control. Largest gains were on sites where weed control increased survival.

We examined the importance of intermediate-sized gaps and a dense shrub layer on tree seedling recruitment in a southern Appalachian deciduous forest. We created 12 canopy gaps under two contrasting understory conditions: 6 gaps were dominated by the dense, shade-producing shrub, Rhododendron maximum L., while the remaining gaps were relatively open. Density of first-year and >first-year seedlings was monitored for 5 years in transects extending from adjacent undisturbed forest through the experimental gaps. We concurrently measured the understory light environment, soil moisture, litter biomass, and seed rain. Neither species diversity nor richness consistently increased following gap formation. Acer rubrum L. responded consistently to canopy gaps with increased seedling densities while most other species, including both shade-tolerant and shade-intolerant species, did not. Seedling densities were especially low and unresponsive to gap formation in areas dominated by R. maximum. Understory light levels were consistently low beneath R. maximum and did not increase with canopy gap formation. Our results suggest that dense shrub cover can neutralize recruitment opportunities in canopy gaps, that seed rain often limits recruitment in gaps, and that canopy gaps that are larger or include understory disturbance are needed to maintain diversity in these forests.

A new breeding zone delineation scheme identifies for a given number of zones the zone-boundary placement that minimizes regional maladaptation in breeding programs. First, an adaptive map is created by using conventional genetic test data. Then, the large array of predicted adaptive values is subjected to cluster analysis, which assigns each grid cell of the region to one of a predetermined number of clusters (breeding zones) such that the sum of the squared distances between each cell's adaptive value and its cluster mean is minimized. This approach minimizes the average adaptive distance between the origin of a breeding program's selected trees and planting locations throughout the region of focus. The procedure is illustrated by the use of adaptive values of 69 interior spruce (Picea engelmannii Parry ex Engelm. × Picea glauca (Moench) Voss) open-pollinated families (sources) from southeast British Columbia, Canada. Adaptive values of each 1.5 km × 1.5 km grid cell in the 80 000-km² region were predicted using a geneco logical model (R² = 0.64), and the values were subjected to cluster analysis to identify breeding zone boundaries that were then mapped using a geographic information system. Regardless of the number of zones created, a regional maladaptation index was consistently smaller when zones were devised with area-based cluster (ABC) analysis than when zones were created by dividing the region into bands of equal elevational or adaptive-value widths. Application of the ABC procedure should assist in identifying the optimum breeding-zone alignment for a given number of zones.

The relationships among stand structure, Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) branch characteristics, and red alder (Alnus rubra (Bong.)) stem form attributes were explored for 10- to 15-year-old trees growing in mixed Douglas-fir – red alder plantations. Treatments included a range of species proportions, and red alder was either planted simultaneously with Douglas-fir or after 5 years. Both replacement effects (total stand density held constant) and additive effects (stand density doubled) of competition were considered. When the two species were planted simultaneously and red alder proportion was low, red alder trees had low crown bases and much stem defect (lean, sweep, and multiple stems). Douglas-fir grew slowly when the two species were planted simultaneously. When red alder planting was delayed, species proportion did not affect red alder stem form, and height to the base of the Douglas-fir live crown decreased with increasing red alder proportion. Doubling Douglas-fir density increased the height to the base of the Douglas-fir live crown; however, doubling stand density by adding red alder did not affect Douglas-fir crown height. Douglas-fir lumber coming from mixed stands may be inferior because of the changes in knot characteristics associated with these different patterns of crown recession. In stands with a low proportion of red alder, red alder product recovery may be compromised because of the stem defects described above.

The effects of nitrogen fertilization on foliage nitrogen concentration, rates of photosynthesis, and stem diameter growth were studied for Douglas-fir (Pseudotsugamenziesii (Mirb.) Franco) trees, with a range of fertilizer applications from 0 to 896 kg N/ha. Ammonium nitrate (AN) and urea were compared as nitrogen sources. AN provided for a higher foliage nitrogen concentration and better growth the 1st year, but there was no source effect thereafter. A significant relationship was obtained between foliage nitrogen concentration and rate of photosynthesis, with an optimum rate at 1.74% foliar nitrogen and with no effect of nitrogen source. Stem diameter growth was increased at all fertilization rates, although no effect of the two lowest rates of fertilization (112 and 224 kg N/ha) was found on foliar nitrogen concentration.