bluuebunny/crossref_metadata_2025 huggingface dataset:
Effects of pollen tube number and archegonium number on reproduction in Douglas-fir: significance for seed orchard management
Authors: Crook Reed W. , Friedman William E.
Published: January 2008

Analyses of the relationships between pollen tube number and fertilization number and between archegonium number and fertilization number in Douglas-fir (Pseudotsugamenziesii (Mirb.) Franco) indicate strong trends toward higher levels of simple polyembryony as both pollen tube number and archegonial number increase on a per-seed basis. These relationships have a significant bearing on the management of conifer seed orchards. Simple polyembryony has been proposed to be an effective means of increasing competition on a per-seed basis in conifers and, potentially, the overall fitness of progeny. In conifers, supplemental mass pollination has the direct effect of increasing the number of pollen tubes per ovule. Clonal variation in average number of archegonia per ovule is also likely to exist among conifers. We propose that when used together, supplemental mass pollination and selection of clones with high archegonial averages may enhance the fitness of seed orchard progeny.
Indice de maturité et conservation en fonction de la période de récolte des semences d'épinette blanche du Québec
Authors: Mercier Stéphan , Langlois Charles-Gilles
Published: January 2008

White spruce cones were harvested weekly to identify the period of maturity of seed and verify the efficiency of some indicators of maturity. The cones were collected in five stations distributed all over Quebec. The results show that the seeds reached maturity about 1 or 2 weeks before scattering. It seems preferable to collect them at this time because their germination rate is better and they maintain good viability after 15 months of stocking. The seed maturity of white spruce in Quebec may be determined by one of the following indices: the embryo reaches 90% of embryo cavity length, cone moisture is 63%, cone specific gravity is 0.99 g/L, or about 80% of cones float in a solution of methanol (d = 0.93 g/L). These indicators have shown that the northernmost station, Les Escoumins, scattered immature seeds. On the other end, the germination rate of seeds present into opened cones drop gradually. However, we did not notice any significant difference between the germination rate of scattered seeds and that of seeds left in opened cones. The effect of seed sorting on the results is also discussed.
Comparaison de la croissance de marcottes d'épinette noire (Piceamariana) adultes après coupe à celle d'individus issus de graines après feu
Authors: Lussier Jean-Martin , Morin Hubert , Gagnon Réjean
Published: January 2008

Analysis was performed on 112 stems of black spruce (Piceamariana (Mill.) BSP) from the Réserve faunique des Laurentides to compare the growth in height, DBH, and volume of layers released by clear-cutting to the growth of individuals of comparable age originating from seeds after fire. The sampled stands originated from fires and clear-cuttings that occurred between 1894 and 1941. Stem analysis also permitted the calculation of specific volume increment, which corresponds to the annual volume increment divided by the surface of the cambium. Results show that height, DBH, and volume measured 60 years after clear-cutting were better correlated to the height of the advanced growth at the moment of release (Ho) than to the number of years of suppression. The mean annual increments in height and DBH of released layers were positively related to height at the year of logging when the height was less than 2 m. When layers were taller, mean annual increments in height and DBH were negatively related to initial height. These relationships were however variable, since for two-thirds of the stand's life, the periodic annual increments in height and diameter did not differ significantly (α = 0.05) between small (Ho < 1 m ), medium (1 m ≤ Ho ≤ 2 m), and large second-growth spruces (Ho > 2 m). The superiority of taller layers is consequently due to greater heights before release. Volume growth rate of layers was positively related to initial height until approximately 60 years after clear-cutting. However, no differences in specific volume increment could be associated with initial height. Therefore, the relationship between initial height and volume increment can be attributed to the difference of cambial area between small, medium, and large second-growth spruces. Black spruce originating from seeds had greater height, DBH, and specific volume increments than second-growth trees, until about 50 years after stand origin. Thereafter, growth rates are comparable. Consequently, after 40 years, stands originating from seeds are comparable in height, volume, and DBH to layers that reached between 1 and 2 m in height after clear-cutting. Neither drainage class nor point density had a significant effect on the sampled black spruces. Stem analysis also revealed an important growth reduction that can be associated with the last spruce budworm (Choristoneurafumiferana Clem.) outbreak in the Réserve faunique des Laurentides. We can deduce from the results of this study that the performance of second-growth stands compared with fire-origin stands will mainly depend on the density of the advanced growth and its height structure.
Geomorphic influences on ground-flora and overstory composition in upland forests of northwestern lower Michigan
Authors: Host George E. , Pregitzer Kurt S.
Published: January 2008

Ground-flora and overstory composition and abundance patterns in 76 upland forest stands were related to the glacial geomorphology of a five-county area in northwestern lower Michigan. Nine classes of landforms were identified based on parent material and surface configuration. Chi-squared analyses of standardized residuals indicated that spatial distribution patterns of the ground flora were significantly associated with glacial landform. Detrended correspondence analyses showed that specific overstory–ground flora assemblages recur in characteristic landscape positions. The Interlobate Moraine, a predominant landform in the northeastern portion of the study area, was characterized by a northern hardwood canopy, primarily sugar maple (Acersaccharum Marsh.), basswood (Tiliaamericana L.), and red oak (Quercusrubra L.), with herbaceous annuals, perennials, and ephemerals forming the ground flora. Other morainal and glaciofluvial landforms supported oak (Quercus spp.) overstories with a woody ericaceous or graminoid ground flora. Ground-flora and overstory composition were highly correlated, indicating that they respond similarly to variation in environmental and historical factors. Moisture availability, as evidenced by soil texture and the presence of subsurface textural discontinuities, appeared to be a predominant factor influencing species distribution patterns. Since moisture availability and related nutrient dynamics are functions of depositional and postglacial history, regional-scale geomorphic patterns constrain forest composition in a probabilistic manner.
Le système radiculaire dans les érablières du Québec. I. Nouvelle méthode d'estimation du volume et de la masse des radicelles
Authors: Pagé Fernand , Badibanga Bady , Sauvesty Annie , Ansseau Colette
Published: January 2008

A method for rapidly estimating the rootlet volume and mass in sugar maple groves was developed in relation with the rootlet size. Soil samples were obtained with corers and cut in 2-cm thick slices. The number of rootlets of diameter classes <0.3, 0.3–0.5, 0.5–0.8, and 0.8–1.0 mm were determined under microscope (× 150) on the upper surface of slices. Rootlet surface for each class was measured on thin sections of soil, with an optic microscope connected to a digitalizing board. Mean rootlet surface [Formula: see text] showed a small standard deviation within each diameter class. The rootlet surface (S) on a surface of soil St can be estimated as [Formula: see text], where N is the number of rootlets observed in nc fields of observation, each field having a surface So. If two soil slices are located at depths h1 and h2, respectively, and if the rootlet surfaces of those slices are S1 and S2, the rootlet volume V of the first slice corresponds approximately to the volume of a truncated cone, and can be calculated as V = [S1 + S2 + (S1S2)0,5] (h2–h1)/3. The rootlet density (g•cm−3 of root) was also determined for each diameter class. The standard deviation from [Formula: see text], the mean density for each diameter class was small. Thus, the rootlet mass M was determined as [Formula: see text]. Estimated and real rootlet volume and mass values were compared. A difference of about 10% was found between estimated and real values.
A dynamic programming algorithm for optimization of uneven-aged forest stands
Authors: Anderson David J. , Bare B. Bruce
Published: January 2008

A deterministic dynamic programming formulation of the transition uneven-aged stand management problem is presented. Using a previously published northern hardwoods growth model, a forward recursive, discrete, two-state problem that maximizes the net present value of harvested trees at each stage is developed. State variables represent the total number of trees and the total basal area per acre. A neighborhood storage concept previously published is used to reduce the number of states considered at each stage. Two harvest allocation rules are used to assign the harvested basal area to individual diameter classes. Terminal end point conditions and stage to stage sustainability are not required. Results from four base runs of the model are presented and compared with previously published results. Each run produces significantly different optimal paths, with one showing a higher net present value than any previously published. Sensitivity runs illustrate the impact of changes in interest rates, width of neighborhood storage class, and initial conditions. Dynamic programming offers promise for analyzing uneven-aged stand management problems.
Decomposition rates of Scots pine needle litter related to site properties, litter quality, and climate
Authors: Johansson Maj-Britt
Published: January 2008

Decomposition of Scots pine (Pinussylvestris L.) needle litter was studied at 14 sites along a climatic transect through Sweden. The forests encompassed a wide range of the variability in site properties found in the country. The mass loss pattern of litter differed considerably among sites. Mass losses obtained during the 1st year of decomposition varied from 11.1 to 43.7% among sites and showed positive linear correlations with climatic factors as well as site productivity indices. After 2 years, about 60% of the litter mass was decomposed at the majority of sites in the middle and southern parts of the country. Mass losses ranged from 20 to 50% in northern Sweden. During later stages of decomposition, mass losses seemed to be highly dependent on the organic–chemical composition of the litter. For accumulated mass losses up to 65%, the annual mass loss of litter was described as a function of the holocellulose to lignocellulose ratio of the litter. For litter mass losses exceeding 65%, a significant linear relation between litter calcium content and mass loss rate was found. Significant linear relations were also obtained between annual lignin loss and litter calcium content.
Un modèle hyperbolique pour l'ajustement de faisceaux de courbes hauteur–diamètre
Authors: Dhôte Jean-François , Hercé Éric de
Published: January 2008

A hyperbolic model is proposed for the construction of sets of height–diameter curves in even-aged stands. On the basis of 86 samples from pure stands of beech (Fagussilvatica L.) and oak (Quercuspetraea (Matt.) Liebl), this model fitted adequately the geometry of data sets. The qualitative behaviour is correct over the whole range of the independent variable. Each parameter characterizes a significant geometric feature of the curve. The three parameters correspond to the asymptote, the slope at the origin, and the curve shape (curvature). The latter two are fairly stable over a large range of age (30–150 years) and stand density. A fitting procedure is proposed, through step-by-step reductions of the model, to overcome the limitations of poorly conditioned samples; only the asymptote, which is very close to top height, is to be estimated from each data set. The time series of estimates exhibit satisfactory evolutions for a large age interval. We interpret the shape of curve sets as the consequence of dominance on height and diameter growth in hierarchized stands.
Root distribution of 12-year-old forests at rocky sites in southwestern Oregon: effects of rock physical properties
Authors: Zwieniecki Maciej A. , Newton Michael
Published: January 2008

Distribution of root length density (in terms of centimetres of fine and large roots per cubic centimetre of soil and bedrock) was analyzed at harsh forest sites supporting 12-year-old stands of pure whiteleaf manzanita (Arctostaphylosviscida Parry), pure ponderosa pine (Pinusponderosa Dougl. ex Laws.), or mixtures of Pacific madrone (Arbutusmenziesii Pursh) and Douglas-fir (Pseudotsugamenziesii (Mirb.) Franco) in southwest Oregon. On such sites, soil (usually <50 cm deep) dries below the wilting point of plants before the middle of the growing season. The bedrock contains enough water to support a dense stand of woody plants. The study shows that about one quarter to one third of the total root length is located in the rock layer. Stepwise procedures were applied to find the best fitting multiple-regression model for relating root length density to depth, bulk density of the soil and rock, and the space penetrable by roots (SPR). Linear expressions of SPR and depth were found to be the only significant explanatory variables. Bulk density had very limited explanatory power, reflecting the high general density of the bedrock containing the water but lower density of the fine material in minuscule fissures in which roots were found.
Dependence of Laccariabicolor basidiome development on current photosynthesis of Pinusstrobus seedlings
Authors: Lamhamedi M.S. , Godbout C. , Fortin J.A.
Published: January 2008

Development of the Laccariabicolor (Maire) Orton basidiome in association with container-grown Pinusstrobus L. seedlings was influenced by photosynthetic photon flux densities (PPFD). Three growth patterns were observed. At a PPFD of 330 μmol•m−2•s−1, basidiome growth was rapid, and complete development was achieved after 16 days. At a very low PPFD (20 μmol•m−2•s−1), the basidiome development ceased, although some residual growth was observed for a few days. At an intermediate PPFD (50 and 90 μmol•m−2•s−1), basidiome growth was less rapid than that observed at 330 μmol•m−2•s−1. Significant differences in the net photosynthesis of the host plant resulted in corresponding changes in basidiome biomass. The effect of basidiome removal on the photosynthetic response of the host plant was evaluated at three stages of basidiome development (2- to 4-, 6- to 8-, and 10- to 15-mm pileus diameter). At each developmental stage, removal of the basidiome induced a very rapid decrease in both net photosynthesis and stomatal conductance of the host plant. This decrease in net photosynthesis indicates that the growth and development of the basidiome are dependent on the host plant's current rate of net photosynthesis.
Climate and the southern limit of the western Canadian boreal forest
Authors: Hogg Edward H. (Ted)
Published: January 2008

Four species of boreal forest conifers share a similar southern limit of natural distribution in the three Prairie Provinces of western Canada. The southern boundaries of boreal forest and aspen parkland were compared with geographic patterns of several climate variables to provide a preliminary assessment of how global climate change could affect forest distribution in the future. Forest zonation corresponded most closely with climatic moisture regimes (annual precipitation minus potential evaporation). In contrast, thermal characteristics of climate (mean July and annual temperature, growing degree-days) showed an inconsistent relationship with forest zonation. It is postulated that moisture limitations prevent conifer regeneration south of the present limit of natural distribution. Alternatively, the more arid climates south of the boreal forest may have promoted higher fire frequencies historically, thus preventing conifers from achieving sufficient longevity to regenerate. The driest areas of boreal forest in the region occur at low elevations in west-central Manitoba, throughout Saskatchewan and Alberta, and the southwestern Mackenzie District, Northwest Territories; these areas may be most vulnerable to increased climatic dryness. Climatically induced losses of forest cover from these low-elevation areas could eventually lead to the fragmentation of the boreal forest in western Canada.
Foliar ozone injury and radial growth of ponderosa pine
Authors: Temple Patrick J. , Miller Paul R.
Published: January 2008

Foliar injury symptoms and stem diameter growth were measured on well-watered and drought-stressed ponderosa pine (Pinusponderosa Dougl. ex Laws.) seedlings at the end of each of 3 years of exposure to three levels of ozone: charcoal-filtered air, nonfiltered air, and nonfiltered air plus 1.5 times ambient ozone. Ozone-injury indices were constructed by adding percent chlorotic mottle and percent necrosis for each needle age-class. Percent necrosis was weighted from 1 to 5 times to construct different indices. Seedlings grown in nonfiltered air plus 1.5 times ambient ozone developed severe foliar injury after 2 years of exposure and were the only seedlings with significant reductions in radial growth after three seasons of exposure to a mean seasonal ozone concentration of 88 ppb. Foliage that had developed >30% chlorotic mottle by September of the 2nd year had abscised by September of the following year. Reduction in radial growth was significantly correlated with amount of foliar injury in well-watered trees, and the best-fit regression equation occurred when percent necrosis was weighted by a factor of 4. Regressions between foliar-injury indices and radial growth in drought-stressed trees were not significant, nor were regressions between radial growth and foliar injury among well-watered trees with only 1 year of premature needle abscission. The low R2 (0.30) between foliar injury and radial growth in well-watered trees and the lack of a significant regression in drought-stressed trees suggest that detection of reductions in stem diameter growth of ponderosa pine in the field in response to ozone injury could be difficult, except for severely injured trees with fewer than 2 years of foliar retention.
Tree form and taper variation over time for interior lodgepole pine
Authors: Muhairwe Charles K.
Published: January 2008

Changes in tree form and taper over time, as affected by changes in tree, stand, and site factors for interior lodgepole pine (Pinuscontorta var. latifolia Engelm.) were investigated using detailed stem analysis data from interior British Columbia. It was found that tree shape and taper change along the stem at one time and over time with changes in tree and stand factors, particularly the diameter at breast height to total tree height ratio, crown length, and crown ratio, and with predicted quadratic mean diameter at age 50 years, a stand density measure. At young ages, the trees were parabolic in shape from ground to top. However, as they increased in size over time, different portions of the stem took different shapes because of unequal growth in diameter along the stem. Changes in tree shape and taper over time were closely related to the crown size, which is related to stand density.
Effects of defoliation, nitrogen nutrition, and temperature on leafing and root carbohydrates of birch seedlings
Authors: Raitio H. , Paukkonen K. , Kauppi A.
Published: January 2008

Difficulties were observed in the leafing of mature birch, alder, and willow species in southern Finland in the spring 1989, especially at lush growing sites. The suspected reason was freezing of the buds in the preceding autumn caused by disturbed bud dormancy. The hypothesis was tested experimentally with 1-year-old Betulapendula Roth seedlings, investigating the effects of partial defoliation, nitrogen nutrition, and temperature. Defoliation clearly weakened both the growth and overwintering of the seedlings, altered the carbohydrate relations in their roots, and markedly delayed leafing in the spring. The earlier in the summer the defoliation was performed, the more conspicuous were its effects, which were also emphasized by the fertilization. A short greenhouse treatment in autumn had no significant effect, however, and it is thought that the partial death of the defoliated top shoots may have been caused by frost drying. The main reason for the late leafing seems to be the delayed development of the buds as a consequence of early defoliation. On the other hand, the growth-promoting effect of nitrogen fertilization and the premature branching of the buds evidently disturbed the carbohydrate balance in the roots and thus the development of the whole seedlings.
Effects of climate on radial growth of subalpine conifers in the North Cascade Mountains
Authors: Peterson David W. , Peterson David L.
Published: January 2008

Dendroecological techniques were used to study the influence of climate on the growth of subalpine fir (Abieslasiocarpa (Hook.) Nutt.), Engelmann spruce (Piceaengelmannii Parry), and subalpine larch (Larixlyallii Parl.) in the North Cascade Mountains of Washington state. Study sites were selected on different topographic features at three points along an elevation gradient (ridgetop, valley slope, and valley floor) to characterize site influences on growth response to climate. Mixed species stands were sampled to identify possible differences in species response to climate on a common site. Species differences account for most of the variability in radial growth patterns and response to climate. The greatest differences are between subalpine fir and subalpine larch, while the greatest similarities are between subalpine fir and Engelmann spruce. After species, aspect is the most significant factor affecting growth response to climate. Spring snowpack and summer temperature are the primary climatic factors influencing growth. Spring snowpack is negatively correlated with growth for all three species, but the relationship is strongest for subalpine fir and weakest for subalpine larch. Subalpine larch growth is positively correlated with June temperature. Subalpine fir growth is positively correlated with July–August temperature. Engelmann spruce growth is positively correlated with June–August temperature, but unusually warm July–August temperatures are associated with reduced growth the following year. The response of subalpine forests in the North Cascades to future climate change will depend on winter snowpack accumulations and spring snowmelt rates. Earlier meltouts and warmer summers would benefit growth on north aspect sites, but could also increase the frequency and severity of summer drought conditions on ridges and south-aspect sites, where summer soil moisture may already be limiting.
Movement and characteristics of stream-borne coarse woody debris in adjacent burned and undisturbed watersheds in Wyoming
Authors: Young Michael K.
Published: January 2008

Following fire, changes in streamflow and bank stability in burned watersheds can mobilize coarse woody debris. In 1990 and 1991, I measured characteristics of coarse woody debris and standing riparian trees and snags in Jones Creek, a watershed burned in 1988, and in Crow Creek, an unburned watershed. The mean diameter of riparian trees along Jones Creek was less than that of trees along Crow Creek, but the coarse woody debris in Jones Creek was greater in mean diameter. Tagged debris in Jones Creek was three times as likely to move, and moved over four times as far as such debris in Crow Creek. In Jones Creek, the probability of movement was higher for tagged pieces that were in contact with the stream surface. Larger pieces tended to be more stable in both streams. It appears that increased flows and decreased bank stability following fire increased the transport of coarse woody debris in the burned watershed. Overall, debris transport in Rocky Mountain streams may be of greater significance than previously recognized.
Scleroderris canker on lodgepole pine introduced in northern Sweden
Authors: Karlman Margareta , Hansson Per , Witzell Jesper
Published: January 2008

From 1987–1991, conditions in 110 conventional plantings of introduced lodgepole pine (Pinuscontorta Dougl. ex Loud.) were investigated in northern Sweden. Severe damage by Scleroderris canker, caused by the fungus Gremmeniellaabietina (Lagerb.) Morelet, was recorded at high elevations in 1987. Damage was related to a period with extreme weather conditions. The disease was initially severe in low lying areas, from where it quickly spread throughout the plantations during 1988. Temperatures above average during 1988–1990 favoured tree vigour, which in turn slowed the spread of the disease. The frequency of stem cankers increased in seriously infected areas during 1989, and new severe damage was recorded locally in 1990 and in 1992. A strong correlation was found between disease severity and the temperature sum at the site. Lodgepole pine planted on spruce sites was often severely affected. A negative correlation was found between the frequency of G. abietina and the abundance of birch thicket. In large areas in northern Sweden with a more favourable climate, lodgepole pine plantations were healthy and productive up to 1991. However, instability, leading to increased susceptibility to disease, has become a problem of great concern in some of these areas during the 1990s.
Mortality among hybrid poplar clones in a stool bed following leaf rust caused by Melampsoramedusae f.sp. deltoidae
Authors: Newcombe G. , Chastagner G.A. , Schuette W. , Stanton B.J.
Published: January 2008

Melampsoramedusae Thuem. f.sp. deltoidae was found to be the primary cause of leaf rust in a stool bed, in Westport, Oregon, on 41 hybrid poplar clones. Each clone was represented by approximately 1000 ramets planted in a block in spring of 1992. Rust severity was rated, using the Schreiner scale (0–100), on three dates in the fall of 1992: August 28, September 18, and October 28, 1992. Of the 41 clones, 1, 12, and 21 scored 100 (i.e., maximal rust) on the three rating dates, respectively. Percent mortality the following spring was estimated for each clone on May 19. Correlation coefficients for rust severity versus mortality on the three rating dates were 0.89 (p < 0.0001), 0.85 (p < 0.0001), and 0.63 (p < 0.0001), respectively. Thus, rust severity and subsequent mortality were highly correlated, especially on the first rating date characterized by maximal infection of the most susceptible clone.
Effects of simulated moose browsing on growth, mortality, and fecundity in Scots pine: relations to plant productivity
Authors: Edenius Lars , Danell Kjell , Nyquist Hans
Published: January 2008

Current theory on plant–animal interactions predicts that the outcome of herbivory on plant performance will be dependent on plant productivity. Thus, slow-growing plants should be less able to compensate for biomass losses than fast-growing plants, and therefore be more susceptible to herbivory if attacked. We simulated winter browsing by moose (Alcesalces (L.)) on Scots pine (Pinussylvestris L.) along a gradient of plant productivity and addressed the following questions: (1) Does herbivory affect growth independently of plant productivity? (2) Is herbivory a more important mortality factor for slow-growing than for fast-growing plants? (3) Is there any effect of herbivory on fecundity, and is it related to plant productivity? Two clipping regimes simulated different intensities of moose winter browsing. Mortality was followed annually, and after 4 years we measured tree growth and fecundity on control as well as on treatment pines. The effect of clipping on growth was related with both clipping intensity and plant productivity. In the light-clipping treatment mortality was restricted to the slow-growing pines, in contrast with the severe treatment, where it occurred across the whole range of plant growth. Moreover, in the light-clipping treatment most mortality occurred within 1 year after treatment, whereas tree death occurred over 2 or more years in the severe treatment. We found no effect of age on mortality within growth-rate classes. The proportion of trees with cones increased with growth rate for control trees but not for treated trees, indicating that herbivory more strongly affects fecundity on fast-growing than on slow-growing trees. Our results confirm the hypothesis that herbivory affects plant performance differently across a gradient of plant productivity. We suggest that mammalian herbivores can increase mortality of plant genets after the seedling stage primarily in stands on low-productivity sites, especially in combination with a high density of the herbivore.
The effect of advance regeneration height on future yield of black spruce stands
Authors: Pothier David , Doucet René , Boily Jocelyn
Published: January 2008

The advance regeneration often present following clear-cutting in black spruce (Piceamariana (Mill.) B.S.P.) stands is generally composed of individuals of various heights. This initial height difference is hypothesized to affect the yield of the future stand. Height of the advance regeneration at time of release was determined on several black spruce trees within 33 stands distributed across the boreal forest of the province of Quebec, Canada. From these data, a regeneration structure index was developed and used to explain a part of the variation in subsequent stand yield. Dominant trees of stands developing for 38 to 65 years since clear-cutting generally originated from the tallest advance regeneration at time of release. Stands with the tallest regeneration at time of release produced the largest yields for a given site quality and number of years since harvesting. A 3-m increase in advance-regeneration height resulted in a similar yield gain as a 3-m increase in site index. Site indices calculated from age-height relationships of dominant trees originating from tall advance regeneration were less than those calculated from trees that have undergone a relatively short period of suppression. These results suggest that traditional management tools developed for fire-origin black spruce stands, i.e., stands mainly composed of seed-origin trees established after perturbation, should be adjusted for clearcut-origin stands that largely develop from advance regeneration.
Responses of black spruce seedlings to simulated present versus future seedbed environments
Authors: Wang Zhang Ming , Lechowicz Martin J. , Potvin Catherine
Published: January 2008

We investigated the effects of nitrogen availability and present versus future atmospheric environments (i.e., climate) on the seedling performance of 16 open-pollinated maternal families of Piceamariana (Mill.) B.S.P. over two simulated growing seasons. Diurnal and seasonal patterns of temperature, relative humidity, photoperiod, and light intensity were simulated. The simulated future climate included both elevated CO2 and seasonally appropriate increases in mean monthly temperatures. Compared with the present, the future climate increased seedling survival, total and root dry mass, rate of winter bud development, net photosynthetic rate, and water and nitrogen use efficiencies; decreased needle nitrogen content; and altered biomass allocation patterns. Greater nitrogen availability greatly improved seedling performance and changed biomass allocation patterns. Climate and nitrogen level interacted synergistically to promote seedling growth (branch number and root dry mass), survival, and bud development. The future climate increased seedling survival, rate of bud development, and nitrogen use efficiency much more in the low than in the high nitrogen regime. Seedling performance in the second season was dependent on initial seed mass, but less than in the 1st year. Some of the differences among the families and in their interactions with the climate and (or) nitrogen fertilization suggest that families selected for rapid growth under present conditions may not do well in the future, at least in terms of early establishment. Forest managers and tree breeders should take this possibility into consideration in their tree improvement and reforestation programs.
Effects of soil freezing stress on sap flow and sugar content of mature sugar maples (Acersaccharum)
Authors: Robitaille Gilles , Boutin Robert , Lachance Denis
Published: January 2008

Mature dominant and codominant sugar maples (Acersaccharum Marsh.) at the Duchesnay Experimental Forest (Quebec, Canada) were subjected to deep soil freezing (DF), superficial freezing (SF), and superficial freezing with drought (SFD) during the 1990–1991 and 1991–1992 seasons. Soil temperatures below the DF trees reached lows of −6 °C at 20 cm depth and were significantly lower than the controls. Compared with the controls, unfrozen soil water content was lower (10%, v/v) below the DF trees. During the dry summer of 1991, soil water content remained high below the DF trees at 30% (v/v); controls reached 10% (v/v). Deep frost treated trees had significantly lower sap flow rates, total sap volume, and less total sugar per tree than other treatments for at least 2 years after treatment. These lower values were likely related to the condition of the DF trees (increased canopy transparency; branch dieback). Percent sugar was significantly higher in the DF trees in 1992. Drought did not seem to have a significant effect on sap flow rate as values obtained for 1991 to 1993 followed the same pattern as that for the control trees. Sap in SF trees tended to flow more than in control trees in 1991. Sap in DF-treated trees that did not show visual symptoms of dieback had a lower flow rate than control trees. Soil freezing, which is concomitant with severe reductions in soil water availability, had a negative effect on spring sap flow. A sufficient source of soil water at the moment of stem recharge seems to be critical during the conditioning period to maintain stem pressure and sap flow.
Increased soil nitrate losses under mature sugar maple trees affected by experimentally induced deep frost
Authors: Boutin Robert , Robitaille Gilles
Published: January 2008

This work reports and discusses data gathered during soil solution monitoring that was part of an experiment conducted in the Duchesnay Experimental Forest (Quebec, Canada) to study the effects of induced deep frost, superficial frost, and superficial frost plus drought on mature sugar maple trees (Acersaccharum Marsh.). Frost treatment was applied by preventing snow from accumulating under the canopy. Soil solution chemistry was modified when mature sugar maple trees declined after exposure to a severe deep frost. The first vegetation period after treatment showed that losses of NO3− below the rooting zone were greatly increased under affected trees. The leaching rate of NO3− and basic cations was directly related to the level of change in canopy dieback and transparency. A mean NO3− concentration of 630 μmolc•L−1 (53 times the controls; max. 4500 μmolc•L−1) was measured in soil solution under the deep frost treated trees. The leaching rate of K+ (18×, relative to the control) and Mn2+ (11×) was higher than that of Mg2+ (5×) and Ca2+ (2.6×). Acidification of the soil solution (50% more H+) as a result of intense nitrification caused an increase in aluminum concentration (5×) and a decrease in SO42−. The acidification during the year after treatment was equivalent to decades of atmospheric acid deposition. The seasonal mean of SO42− did not differ between treatments, but there was evidence of a significant correlation between pH and SO42− in soil solution. Concentration of NH4+ was also enhanced but to a lesser degree (10×) than that of NO3−. Specific conductivity was a good predictor of NO3−, Ca2+, Mg2+, and total Al in soil solution. The ion balance shifted from an anion deficit to a strong cation deficit when NO3− concentrations were high. Superficial frost with or without induced summer drought did not cause any significant change in soil solution chemistry compared with the controls. These results indicated the necessity to consider perturbations induced by extreme climate conditions, like deep soil frost, for the interpretation of soil solution chemistry data in the context of acid deposition studies and forest health.
Physiographic analysis of witness-tree distribution (1765–1798) and present forest cover through north central Pennsylvania
Authors: Abrams Marc D. , Ruffner Charles M.
Published: January 2008

This study analyzed witness-tree data recorded from 1765 to 1798 with respect to landform in four major physiographic provinces represented through north central Pennsylvania. These data were also compared with present-day forest composition to evaluate broad changes that occurred 200 years after European settlement. In the Allegheny High Plateau, Tsugacanadensis (L.) Carr. represented 40–47% of witness trees in mountain coves and stream valleys, but only 9% on plateau tops, which comprised 45% Fagusgrandifolia Ehrh. Pinusstrobus L. represented ≤4% frequency across all landforms. The original forests of the Allegheny Mountains were dominated by mixed Quercus, Acer, Castaneadentata (Marsh.) Borkh., and Pinus and had significant T. canadensis only in stream valleys. The presettlement forests of the Allegheny Front and the Ridge and Valley provinces had a similar mix of Quercus, Pinus, Castanea, and Carya, with increased P. strobus on the more mesic sites and Pinusrigida Mill, on the xeric ridges. Comparisons of presettlement with present-day forest composition indicate a dramatic reduction of T. canadensis (32% to 4%) and F. grandifolia (33% to 12%) in the High Plateau and increases in Acer (11% to 37%), Quercusrubra L. (0% to 10%), Prunusserotina Ehrh. (1% to 6%), and Betula (5% to 10%). Other units exhibited reductions in P. strobus, P. rigida, Quercusalba L., and Carya spp. and increases in Quercusprinus L., Q. rubra, Acerrubrum L., and P. serotina. Castaneadentata had its greatest abundance on higher elevation sites in each physiographic unit, and the elimination of this species this century apparently facilitated the increase in Q. prinus and Q. rubra on ridge sites. South of the Allegheny Plateau, increases in A. rubrum, P. serotina, and other mixed-mesophytic species may be in response to fire exclusion this century. The results of this study indicate the importance of landform and physiography on presettlement forest composition as well as the dramatic changes that have occurred as a result of altered disturbance regimes following European settlement.
A portable system to quantify seedling damage using stress-induced volatile emissions
Authors: Templeton C.W.G. , Colombo S.J.
Published: January 2008

This paper describes a portable gas analysis system that was used to quantify stress-induced ethanol in black spruce (Piceamariana (Mill.) B.S.R). Operationally fall-lifted black spruce seedlings, packaged in polyethylene-lined kraft bags, were placed in a greenhouse to simulate conditions in the field, where stock may be exposed to elevated temperatures. The maximum temperature in the greenhouse was 36 °C, and the duration of heat treatment exposure ranged from 3 h to 7 days. After exposure to the heat stress event, the ethanol concentration in the bags of seedlings was measured using a portable gas analysis system. A sample of 20 seedlings were then potted and placed in a controlled-environment room for a 14-day growth period. At the conclusion of the growth period the seedlings were removed from the pots and the number of white roots >1 cm were counted. The terminal buds were dissected to determine viability, and the degree of foliage browning was estimated. The experiment was repeated four times. Ethanol concentration was significantly correlated with subsequent root growth potential, foliage viability, and terminal bud viability.
VANISHING RESULTS FOR L2-BETTI NUMBERS AND L2-EULER CHARACTERISTICS AND THEIR APPLICATIONS
Authors: JO JANG HYUN
Published: January 2008

A CW-complex X is called a [G,m]-complex if X is an m-dimensional complex with π1(X) ≅ G and the universal cover [Formula: see text] is (m - 1)-connected. We show that if G has an infinite amenable normal subgroup, then the asphericity of a [G,m]-complex X is equivalent to the vanishing of L2-Euler characteristic of [Formula: see text]. This result corresponds to a generalization and a variation of earlier several works. Also, we show that the L2-Betti numbers of a group which belongs to the class of groups K𝔉 eventually vanish. As a byproduct, we give an example of a group which belongs to the class of groups H𝔉 but does not belong to the class of groups K𝔉.
$\widetilde{{\rm SL}(2, \mathbb{R})}$-HOMOGENEOUS VECTOR BUNDLES
Authors: BISWAS INDRANIL , MISRA GADADHAR
Published: January 2008

We describe all the holomorphic Hermitian vector bundles (E, h) over the upper half plane in ℂ with the property that (f* E, f* h) is holomorphically isometric to (E, h) for any holomorphic automorphism f of the upper half plane. We give an explicit construction of all such holomorphic Hermitian vector bundles using some linear algebraic data.
CUNTZ–PIMSNER C*-ALGEBRAS ASSOCIATED WITH SUBSHIFTS
Authors: CARLSEN TOKE MEIER
Published: January 2008

By using C*-correspondences and Cuntz–Pimsner algebras, we associate to every subshift (also called a shift space) 𝖷 a C*-algebra [Formula: see text], which is a generalization of the Cuntz–Krieger algebras. We show that [Formula: see text] is the universal C*-algebra generated by partial isometries satisfying relations given by 𝖷. We also show that [Formula: see text] is a one-sided conjugacy invariant of 𝖷.
FROM NONRESONANT TO RESONANCE-ENHANCED THz GENERATION
Authors: MU XIAODONG , DING YUJIE J. , ZOTOVA IOULIA B.
Published: January 2008

We have reviewed mechanisms for the efficient conversion of the broadband terahertz (THz) pulses from ultrafast laser pulses propagating in semiconductor electro-optic materials. By measuring the behaviors of the THz output versus the pump beam in terms of incident angle, polarization, and azimuthal angle, we have demonstrated that we can precisely determine the contributions made by optical rectification and photocurrent surge. When a material is pumped below its bandgap, optical rectification is always the mechanism for the THz generation. Above the bandgap, however, these two mechanisms often compete with each other, depending on the material characteristics and pump intensity. At a sufficiently high pump intensity, optical rectification usually becomes the dominant mechanism for a second-order nonlinear material. Our analysis indicates that second-order nonlinear coefficients can be resonantly enhanced when a material is pumped above its bandgap. In such a case, the THz output power and normalized conversion efficiency can be greatly enhanced. We have also analyzed how the THz generation is affected by some competing processes such as two-photon absorption.
OBSERVATION OF ONE- AND TWO-DIMENSIONAL DISCRETE SURFACE SPATIAL SOLITONS
Authors: SUNTSOV S. , MAKRIS K. G. , SIVILOGLOU G. A. , IWANOW R. , SCHIEK R. , CHRISTODOULIDES D. N. , STEGEMAN G. I. , MORANDOTTI R. , YANG H. , SALAMO G. , VOLATIER M. , AIMEZ V. , ARÈS R. , SOREL M. , MIN Y. , SOHLER W. , WANG XIAOSHENG , BEZRYADINA ANNA , CHEN ZHIGANG
Published: January 2008

The recent theoretical predictions and experimental observations of discrete surface solitons propagating along the interface between a one- or two-dimensional continuous medium and a one- or two-dimensional waveguide array are reviewed. These discrete solitons were found in second order (periodically poled lithium niobate) and third order nonlinear media, including AlGaAs, photorefractive media and glass, respectively.
THIRD-ORDER NONLINEAR OPTIC AND OPTICAL LIMITING PROPERTIES OF A MN(III) TRANSITION METAL COMPLEX
Authors: KARAKAS ASLI , ELMALI AYHAN , YAHSI YASEMIN , KARA HULYA
Published: January 2008

N,N′-bis(5-bromosalicylidene)propane-1,2-diamine-O,O′,N,N′)-manganese(III) chloride transition metal complex has been synthesized and characterized by elemental analysis and UV-vis spectroscopy. Its crystal structure has been determined using X-ray diffraction analysis. To provide an insight into the optical limiting (OL) behavior of the title compound, the third-order nonlinear optical (NLO) properties, one-photon absorption (OPA) and two-photon absorption (TPA) characterizations have been theoretically investigated by means of the time-dependent Hartree–Fock (TDHF), AM1 and configuration interaction (CI) methods, respectively. According to ab initio calculation results, the examined molecule exhibits second hyperpolarizabilities (γ) with non-zero values at the positions of TPA peaks, implying microscopic third-order optical nonlinearity. The maximum OPA wavelengths recorded by linear optical experiment and quantum mechanical computations are estimated in the UV region to be shorter than 400 nm, showing good optical transparency to the visible light. The TPA cross-sections (δ(ω)) at [Formula: see text] values indicate that the synthesized compound might possess OL phenomena, which are in accord with the experimental observations on the manganese complexes in the literature.
THE STUDY OF Pd SCHOTTKY CONTACT ON POROUS GaN FOR UV METAL–SEMICONDUCTOR–METAL (MSM) PHOTODETECTORS
Authors: CHUAH L. S. , HASSAN Z. , ABU HASSAN H.
Published: January 2008

High quality unintentionally doped n-type GaN layers were grown on Si (111) substrate using AlN (about 200 nm) as buffer layer by radio frequency (RF) nitrogen plasma-assisted molecular beam epitaxy (MBE). This paper presents the structural and optical studies of porous GaN sample compared to the corresponding as-grown GaN. Metal–semiconductor–metal (MSM) photodiode was fabricated on the samples. For as-grown GaN-based MSM, the detector shows a sharp cut-off wavelength at 362 nm, with a maximum responsivity of 0.254 A/W achieved at 360 nm. For porous GaN MSM detector, a sharp cut-off wavelength at 360 nm with a maximum responsivity of 0.655 A/W was achieved at 359 nm. Both the detectors show a little decrease in responsivity in the UV spectral region. The MSM photodiode based on porous GaN shows enhanced (2×) magnitude of responsivity relative to the as-grown GaN MSM photodiode. Enhancement of responsivity can be attributed to the relaxation of tensile stress and reduction of surface pit density in the porous sample.
DESIGN AND TRANSMISSION-REFLECTION PROPERTIES OF LIQUID CRYSTALLINE OPTICAL METAMATERIALS WITH LARGE BIREFRINGENCE AND SUB-UNITY OR NEGATIVE-REFRACTIVE INDEX
Authors: DIAZ A. , PARK J. H. , KHOO I. C.
Published: January 2008

The dispersion of nanoparticles in a nematic liquid crystal host medium provides an efficient way of designing tunable optical metamaterials that respond from the visible to the Terahertz and microwave regime. As studied in this article, these systems exhibit much larger birefringence than the nematic host and possess sub-unity, zero, and even negative refractive indices with unique reflection and transmission properties. These tunable optical metamaterials will enable a wide range of application possibilities in next-generation reflective, transmissive, modulation and switching elements and devices.