Conifer Stem Research Articles

Leaf phenology and paleoclimatic and paleoenvironmental insights derived from Yiwupitys elegans of the Yiwu Jurassic Forest, Xinjiang, China

Many permineralized conifer stems and trunks have been documented from the Jurassic strata of the Xinjiang Uygur Autonomous Region (Xinjiang), Northwest China. Xylem anatomical studies have showed that these stems and trunks belonged to a diverse range of plants. However, the leaf phenology and the paleoclimatic and paleoenvironmental significance of these fossil plants have rarely been studied. We quantitatively analyzed the anatomical characteristics of a permineralized conifer stem—Yiwupitys elegans Gou et Feng 2023—from the Middle Jurassic Xishanyao Formation in northeastern Xinjiang, which has distinct and wide growth rings in the secondary xylem. Analyses of the Mean Sensitivity and Ring Markedness Index of the growth rings suggest that a stable paleoclimate with regular seasonal fructifications likely prevailed during the Middle Jurassic in this area. The statistical analyses of cell diameters and anatomical features of leaf traces in six successive growth rings indicate that this fossil plant was deciduous. Our study elucidates the ecophysiological characteristics of a Middle Jurassic conifer plant and provides new insights into the corresponding paleoclimate and paleoenvironment based on quantitative cellular analysis of the fossil stem.

DEVELOPMENT OF MYCROCRYSTALLINE CELLULOSE ORIGINATE FROM SAGO (METROXYLON SAGU) STEM BARK BY HYDROLISIS METHODE USING NITRIC ACID

Objective: Microcrystalline cellulose (MCC) is an essential excipient in tablet formulation. Mostly MCC was obtained from wooden conifer stem fiber, therefore environment issues had been came up. Alternative sources for MCC which offer friendly conifer wood need to be explored. This study aimed to isolate and determine the characteristics of MCC originated from Sago (Metroxylon sago Rottb.) stem fibers as an promising alternative of MCC. Methods: MCC was prepared through pre-hydrolysis using an acetic acid solution, alkali heating using NaOH solution, and acid hydrolysis using nitric acid 0.3 N using three variations of heating temperature, namely 90, 95 and 100 °C. The characterization carried out were pharmaceutical grade, powder properties, FTIR analysis and powder morphology by SEM. Results: The yields obtained were 66.02; 65.53 and 65.08%, respectively. The characteristics of the MCC sample based on pharmaceutical grade quality were white to yellowish white powder, odorless, tasteless, insoluble in: ether, 96% alcohol, HCl 2N and NaOH 1N. The pH of the MCC suspension were 5.07-5.12, while moisture content were 3.67-4.17%, with loss on drying value as much as 0.37-0.4%, and ash content 1-2.17%. The value of permanganate number were 0.09-0.11, Hausner factor was between 1.05-1.25, and angle of repose were between 11.4-24.8°. Conclusion: Based on the results, it can be concluded that Sago is potent natural resource for MCC. The resulting MCC revealed physicochemical and characteristic of MCC, which almost similar to Avicel PH 102 as standard.

In search of lost time: tracing the fossil diversity of Podocarpaceae through the ages

Abstract The Podocarpaceae are a morphologically diverse conifer family that have a cryptic fossil record reported since the Permian. We reviewed the fossil record of Podocarpaceae, tested the affinities of its oldest records using phylogenetic analyses, compiled macrofossil occurrence records, and investigated the diversity, distribution, and morphology of Podocarpaceae through time. We found that Permian, Triassic, and some Jurassic fossils referred to Podocarpaceae should not be placed in the family. Our total-evidence phylogenetic analyses, which sampled all major conifer lineages, recovered the Triassic Rissikia and the Jurassic Nothodacrium as stem-group conifers and the Jurassic Mataia as part of the Araucariales stem group. We further discuss the phylogenetic position of the Mesozoic enigmatic conifers Pararaucaria (Cheirolepidiaceae) and Telemachus (Voltziales), which were recovered most frequently in the conifer stem group. We conclude that the earliest reliable Podocarpaceae occurrences are from the Jurassic of both hemispheres and have scale-like leaves. Most extant genera appear in the fossil record between the Late Cretaceous and the Early Cenozoic. Many extant leaf morphologies appear in the Early Cretaceous, coeval with angiosperm diversification, consistent with the hypothesis that expanded leaves in Podocarpaceae are adaptive responses for light harvesting in angiosperm-dominated environments today.

A new conifer stem, Ductoagathoxylon tsaaganensis, from the Upper Permian of the South Gobi Basin, Mongolia and its palaeoclimatic and palaeoecological implications

Permineralised stems of Ductoagathoxylon tsaaganensis Cai, Zhang et Feng sp. nov. are described from the Upper Permian strata of the Tsaagan Tolgoy section, South Gobi Basin, Mongolia. The stems were preserved with pith and primary and secondary xylems. The pith is solid, heterocellular, and characterised by regularly arranged clusters of secretory cells at the periphery. The primary xylem is the endarch and mesarch. The tracheid walls exhibited annular, helical, and scalariform thickening from the protoxylem to metaxylem. The secondary xylem is of the Agathoxylon-type and is composed of tracheids and parenchymatous rays. The growth rings of the stems were distinct, with broad earlywood and narrow latewood. Radial tracheid pits in the secondary xylem are contiguous and alternately arranged, uni- or biseriate in the latewood, and bi- to tetraseriate in the earlywood. Rays are uniseriate and 1–7 (mostly 2–4) cells high. Each cross-field possessed 1–19 (mostly 3–9) cupressoid pits. Quantitative analysis of the growth rings indicated that the plant was likely a deciduous conifer that lived in a seasonal, temperate, and wet climate. However, a growth interruption with inflated cells was present in the secondary xylem, indicating that the tree had survived climatic damage, probably an early spring cooling event. Fungal remains, including hyphae and spores, and evident white-rot patterns in the stems revealed a common occurrence of fungal infections in the ecosystem. Our study sheds new light on the plant diversity and climatic and ecological features of the Angara flora during the Late Permian in the South Gobi Basin.

Leaf phenology, paleoclimatic and paleoenvironmental insights derived from an Agathoxylon stem from the Middle Jurassic of Xinjiang, Northwest China

Fossil wood serves as a natural data source for deciphering plant physiological features and paleoclimatic and paleoenvironmental conditions experienced during its lifespan. Although permineralized conifer wood commonly occurs in the Jurassic of Xinjiang Uygur Autonomous Region (Xinjiang), Northwest China, their physiological features and paleoclimatic and paleoenvironmental significance have been rarely studied. Here, we quantitatively analyzed the anatomical characteristics of a permineralized conifer stem (Agathoxylon sp.) from the Middle Jurassic Xishanyao Formation in Naomaohu Town of Yiwu County, Hami City, Xinjiang. The fossil stem is only preserved with secondary xylem. The secondary xylem is pycnoxylic and exclusively composed of tracheids and parenchymatous rays. Tracheids have mostly uniseriate or biseriate, partially triseriate or tetraseriate, alternately or sub-oppositely arranged bordered pits on their radial walls. Rays are mostly uniseriate, partially biseriate, and are up to 27 cells high. There are 4 to 11 cupressoid pits in each cross field, arranged in the araucarioid type. Growth rings are distinct and wide. The mean sensitivity and ring markedness index analyses of growth rings suggest that a stable paleoclimate with regular seasonal fructifications could have prevailed in the Santanghu Basin during the Middle Jurassic. Statistical analyses of cell diameters in 11 successive growth rings indicate that this fossil plant was deciduous. Our study sheds new light on leaf phenology and paleoclimatic and paleoenvironmental conditions of Middle Jurassic conifer plants.

Effects of forest characteristics on ruffed grouse nesting ecology in central Maine, USA

Effective wildlife management requires a broad understanding of how forest structure and composition influence habitat use and vital rates during all aspects of species' life-cycles, however habitat characteristics may have variable importance during different life phases. Even though the ruffed grouse Bonasa umbellus is a popular game bird that has long been a focal species for management, a greater understanding of the links between forest characteristics and components of ruffed grouse reproduction would enhance managers' ability to promote the species. We monitored 45 nests belonging to 37 females during 2015–2017 in central Maine, USA, and evaluated the influence of forest characteristics on nest-site selection, nest survival and female survival while nesting. Ruffed grouse females selected nest sites with greater horizontal visual obstruction (β = 0.16 ± 0.06 85% CI) than found at other sites that were locally available to them, however this characteristic did not appear to improve nest survival or female survival while nesting. Cumulative nest success was 42.8% and daily nest survival was reduced when coarse woody debris (CWD) was present at nest sites (β = –0.41 ± 0.33 85% CI), but we found no evidence that other habitat characteristics or features of nests themselves were related to nest survival. However, reduced female survival while nesting was associated with presence of CWD (β = –1.27 ± 0.91 85% CI), greater tree basal area (β = –0.96 ± 0.81 85% CI) and greater conifer stem density (β = –0.45 ± 0.28 85% CI) at nest sites; females had a 74.4% chance of survival during the length of time required to successfully nest. Our results demonstrate the importance of forest characteristics on multiple components of species' nesting ecology, and we provided management suggestions to promote attractive ruffed grouse nesting habitat while potentially mitigating sources of nesting failure.

Spatial patterns of precipitation-induced moisture availability and their effects on the divergence of conifer stem growth in the western and eastern parts of China’s semi-arid region

Conifer forests in semi-arid regions are fragile and sensitive to climate change. As the climate changes, more frequent drought and higher temperatures may reduce conifer stem growth in these regions, but moistening and lengthening of the growing season may improve tree growth conditions. The relative influences of specific climate parameters on conifer stem growth, however, remain poorly quantified in Asian regions. We analyzed conifer stem growth responses to climate in the semi-arid region of China. Our analyses show a wetting trend since 1960 in the western part of this region, versus a drying trend in the east. We used tree-ring width data from a network of 33 forests as inputs for the process-based Vaganov–Shashkin-Lite growth model to assess how moisture patterns have affected tree growth in this region, and then used the resulting model to predict changes in tree growth during the 21st century. Tree-ring growth in our study region is mainly controlled by precipitation and soil moisture, and shows significant impacts of antecedent moisture conditions (the “water memory effect”). However, the contribution of soil moisture to tree growth was stronger in the eastern vs. western sub-regions (77% vs. 69%). Pointer-year analysis showed significantly stronger growth responses to soil moisture in the early growing season (April to June) in positive pointer years in the eastern sub-region, but showed no difference in the western sub-region. These results indicate that tree-ring growth in the eastern sub-region is more vulnerable to moisture availability. Our simulations suggest that tree growth will increase slightly under the RCP 4.5 and RCP 8.5 scenarios in both sub-regions, possibly due to the prolongation of the growing season caused by climate warming.

Multitrophic interactions in a geothermal setting: Arthropod borings, actinomycetes, fungi and fungal-like microorganisms in a decomposing conifer wood from the Jurassic of Patagonia

A permineralized araucarioid conifer stem, preserved in state of partial decay, is described from the Middle to Late Jurassic Chon-Aike Formation (Bahía Laura Group) at Laguna Flecha Negra, in the Deseado Massif, Santa Cruz Province, Argentina. The tree-stem, which comprises periderm to the secondary xylem, shows evidence of interactions with xylophagous borers, fungi, actinomycetes and other fungal-like microorganisms. In the secondary phloem, it displays rows of traumatic resin ducts, which host abundant mycelium comprising very thin hyphae differentiated into spore-producing structures comparable to actinomycete bacteria and spherical fungal-like resting structures. In the cortical and phloem regions, there are cell groups with structural changes, which appear variably degraded by fungi. The secondary xylem displays decay of cellulose and lignified components, at various spatial scales, comparable with fungal decay patterns in modern wood. Further septate fungal filaments, sometimes bearing clamp connections are associated with decayed regions. The degraded secondary xylem shows circular to oval borings filled with frass containing degraded tracheids, comparable to those bored by different wood boring beetles. Development of traumatic resin ducts in the phloem could have been triggered by penetration of the living stem by these xylophagous arthropods. The association of the different components present suggests pathogenic and saprotrophic interactions promoting decomposition of the stem, and represents a rarely-documented example of multitrophic biological interactions involving several different biological groups in Jurassic terrestrial paleoecosystems.

Cyclic Variation of Residual (CO2 + H2O) and Total Pressure in Conifer Stem and Woody Root Tree Rings

Cyclic Variation of Residual (CO2 + H2O) and Total Pressure in Conifer Stem and Woody Root Tree Rings

Variation in reproductive potential across a multi-species treeline

ABSTRACT Cone and seed production at the forest-tundra ecotone, or treeline, depend on species-specific tolerances to limiting abiotic and biotic factors. As range expansion via seed dispersal is needed to keep pace with climate change, reproductive limitations act as a bottleneck for treeline advance. The treeline in the Mealy Mountains, central Labrador, was comprised of four codominant species: black spruce (Picea mariana [Mill.] B.S.P.), white spruce (Picea glauca [Moench] Voss), eastern larch (Larix laricina [Du Roi] K. Koch), and balsam fir (Abies balsamea [L.] Mill.). Conifer stem surveys from three treeline zones (forest, forest-tundra transition, krummholz) were used to assess patterns of altitudinal distributions, tree densities, and cone production to provide insight into overall reproductive potential. The altitudinal limit of the spruce species was 39 m a.s.l. higher than the altitudinal limit of black spruce cone production. Black spruce had the highest densities of cone-bearing trees across treeline with eastern larch values being comparable in the forest-tundra transition zone, although overall cone production was low and highly variable in all species. Compared to the other treeline species, black spruce has the greatest reproductive potential for upslope advance.

Quality of Feedstock Produced from Sorted Forest Residues

Emerging biomass conversion technologies, such as small scale mobile biochar or pyrolysis/torrefaction machines, aim to use forest residues left after extracting merchantable timber from timber harvest or fuel reduction thinning operations. The residues generated from these operations typically produce low quality feedstock which may not be suitable for new biomass conversion technologies. In an effort to increase feedstock quality, our study separated sub-merchantable trees and tops from piled limbs during the timber harvest. A portion of the separated material was further processed to remove limbs to create five material types: processed and unprocessed, conifer and hardwood stem wood, and slash (stems, limbs and chunks). These materials were comminuted with a disc-chipper or a grinder. The quality of the feedstock produced was characterized by moisture content, particle-size distribution, bulk density, and ash content. Moisture content of sample collected ranged from 19 to 29%. The mean geometric lengths for unprocessed hardwood, unprocessed conifer, processed hardwood, processed conifer, and slash were 20.60, 18.27, 18.16, 17.41, and 47.47 mm, respectively. The bulk density of the five material types ranged from 137.20 – 322 kg/m 3 . The least amount of ash were observed in processed conifer samples (0.27%) and greatest in ground slash (1.5%). The results showed that a high quality feedstock can be produced by separating stem wood from other residues during a harvest.

Florida Turkey Nest Site Selection and Success

Changing landscapes and land-use practices are altering habitat for Florida wild turkeys (Meleagris gallopavo osceola). However, an understanding of habitat determinants of nest success is lacking for this unique turkey subspecies, potentially limiting conservation success. We examined female wild turkey nest site selection and nest success at microhabitat and patch levels using logistic regression in an Information-Theoretical framework in Florida, 2008-2010. We captured and radio-equipped adult female turkeys, and followed birds to nests. Nests were monitored to document success, and habitat was measured at multiple levels at nest and random sites. Females selected nest sites in dense vegetation (i.e., increased saw palmetto cover [Serenoa repens] and higher palm stem densities) that may have provided lateral and vertical cover for concealment at the microhabitat level (i.e., area within 7 m of the nest), while selecting for a more open habitat (i.e., decreasing hardwood and conifer stem densities) at the patch level (i.e., area within 28 m of the nest). Similarly, successful nests were in more dense vegetation at the nest site (i.e., increased saw palmetto cover) in an otherwise more open habitat (i.e., lower basal area) than unsuccessful nests. Habitat management that creates patches of dense shrub vegetation such as saw palmetto within an open landscape may be best for Florida wild turkey nesting habitat and success.

Climatic drivers of hourly to yearly tree radius variations along a 6 °C natural warming gradient

Climate affects the timing, rate and dynamics of tree growth, over time scales ranging from seconds to centuries. Monitoring how a tree's stem radius varies over these time scales can provide insight into intra-annual stem dynamics and improve our understanding of climate impacts on tree physiology and growth processes. Here, we quantify the response of radial conifer stem size to environmental fluctuations via a novel assessment of tree circadian cycles. We analyze four years of sub-hourly data collected from 56 larch and spruce trees growing along a natural temperature gradient of ∼6°C in the central Swiss Alps. During the growing season, tree stem diameters were greatest at mid-morning and smallest in the late evening, reflecting the daily cycle of water uptake and loss. Along the gradient, amplitudes calculated from the stem radius cycle were ∼50% smaller at the upper site (∼2200m a.s.l.) relative to the lower site (∼800m a.s.l.). We show changes in precipitation, temperature and cloud cover have a substantial effect on typical growing season diurnal cycles; amplitudes were nine times smaller on rainy days (>10mm), and daily amplitudes are approximately 40% larger when the mean daily temperature is 15–20°C than when it is 5–10°C. We find that over the growing season in the sub-alpine forests, spruce show greater daily stem water movement than larch. However, under projected future warming, larch could experience up to 50% greater stem water use, which may severely affect future growth on already dry sites. Our data further indicate that because of the confounding influences of radial growth and short-term water dynamics on stem size, conventional methodology probably overstates the effect of water-linked meteorological variables (i.e. precipitation and relative humidity) on intra-annual tree growth. We suggest future studies use intra-seasonal measurements of cell development and consider whether climatic factors produce reversible changes in stem diameter. These study design elements may help researchers more accurately quantify and attribute changes in forest productivity in response to future warming.

Additives in wood pellet produciton - A pilot-scale study of binding agent usage

Finland currently has tremendous enthusiasm to increase decentralised pellet production alongside of large-scale factories. The aim of research is to promote the development of eco-/cost-efficient Nordic wood-based pellet production by means of multidisciplinary research. Using Finnish conifer stem wood (bark-free Scotch pine sawdust and shavings) as a model raw material, the total functionality of a pilot-scale pellet facility combined with an extensive chemical toolbox was tested in this study to promote future development of eco- and cost-efficient wood-based pellet production in both quantitative and qualitative senses. Lignosulphonate, residual potato flour, and potato peel residue were used as adhesive binding agents. A pilot-scale pellet facility was equipped with a data logger for temperature and power measurements. The chemical toolbox included also novel specific staining and optical microscope methods and respirometric BOD Oxitop measurements. The results showed that adhesive binding agents increased the quality of pellets and changed inorganic characteristics, but did not have a significant effect on their calorimetric heat values. Lignosulphonate even increased the rate of production. Valuable information about both the pelletizing process and pellets is necessary in the future when developing good-quality pellets, a prime biofuel, from low-value and/or moist biomass that has undergone a cost-efficient drying process.

Laser microdissection of conifer stem tissues: Isolation and analysis of high quality RNA, terpene synthase enzyme activity and terpenoid metabolites from resin ducts and cambial zone tissue of white spruce (Picea glauca)

BackgroundLaser microdissection (LMD) has been established for isolation of individual tissue types from herbaceous plants. However, there are few reports of cell- and tissue-specific analysis in woody perennials. While microdissected tissues are commonly analyzed for gene expression, reports of protein, enzyme activity and metabolite analysis are limited due in part to an inability to amplify these molecules. Conifer stem tissues are organized in regular patterns with xylem, phloem and cortex development controlled by the activity of the cambial zone (CZ). Defense responses of conifer stems against insects and pathogens involve increased accumulation of terpenoids in cortical resin ducts (CRDs) and de novo formation of traumatic resin ducts from CZ initials. These tissues are difficult to isolate for tissue-specific molecular and biochemical characterization and are thus good targets for application of LMD.ResultsWe describe robust methods for isolation of individual tissue-types from white spruce (Picea glauca) stems for analysis of RNA, enzyme activity and metabolites. A tangential cryosectioning approach was important for obtaining large quantities of CRD and CZ tissues using LMD. We report differential expression of genes involved in terpenoid metabolism between CRD and CZ tissues and in response to methyl jasmonate (MeJA). Transcript levels of β-pinene synthase and levopimaradiene/abietadiene synthase were constitutively higher in CRDs, but induction was stronger in CZ in response to MeJA. 3-Carene synthase was more strongly induced in CRDs compared to CZ. A differential induction pattern was observed for 1-deoxyxyulose-5-phosphate synthase, which was up-regulated in CRDs and down-regulated in CZ. We identified terpene synthase enzyme activity in CZ protein extracts and terpenoid metabolites in both CRD and CZ tissues.ConclusionsMethods are described that allow for analysis of RNA, enzyme activity and terpenoid metabolites in individual tissues isolated by LMD from woody conifer stems. Patterns of gene expression are demonstrated in specific tissues that may be masked in analysis of heterogenous samples. Combined analysis of transcripts, proteins and metabolites of individual tissues will facilitate future characterization of complex processes of woody plant development, including periodic stem growth and dormancy, cell specialization, and defense and may be applied widely to other plant species.

Conifer stem growth at the altitudinal treeline in response to four years of CO2 enrichment

AbstractNorthern latitude and upper altitude climatic treelines have received increasing attention given their potential sensitivity to atmospheric and climate change. While greater radial stem growth at treeline sites in recent decades has been attributed largely to increasing temperature, rising atmospheric CO2 concentration may also be contributing to this growth stimulation. Tree ring increments of mature Larix decidua and Pinus uncinata were measured over 4 years in a free air CO2 enrichment experiment at treeline in the Swiss Central Alps (2180 m a.s.l.). In addition, a one‐time defoliation treatment in the second year (2002) of the experiment was used to simulate one of the common natural insect outbreak events. In response to elevated atmospheric CO2, Larix showed a cumulative 4‐year growth response of+41%, with particularly strong responses in the third and fourth year. This increase in radial stem wood growth was the result of more latewood production, in particular, the formation of larger tracheids, rather than a greater number of cells. In contrast, Pinus showed no change in ring width to elevated [CO2], neither in each of the treatment years, nor in the cumulative response over 4 years, although an increase in tracheid size was observed in the third year. Defoliation led to a pronounced decrease in annual ring width of both species, marked in particular by less latewood production, in the treatment, as well as subsequent years. There was no significant interaction between defoliation and CO2 enrichment. Although Pinus showed no growth response to CO2, the positive growth response observed in Larix after 4 years of CO2 enrichment implies that the sensitivity of treeline trees to global change may not be purely temperature driven. We conclude that the open sparse canopy in the treeline ecotone favours the indeterminate growth strategy of the early successional Larix when neither weather nor carbon are limiting, whereas the later successional Pinus does not show any indication of more vigorous growth under future higher atmospheric CO2 concentrations.

Methyl jasmonate-induced ethylene production is responsible for conifer phloem defense responses and reprogramming of stem cambial zone for traumatic resin duct formation.

Conifer stem pest resistance includes constitutive defenses that discourage invasion and inducible defenses, including phenolic and terpenoid resin synthesis. Recently, methyl jasmonate (MJ) was shown to induce conifer resin and phenolic defenses; however, it is not known if MJ is the direct effector or if there is a downstream signal. Exogenous applications of MJ, methyl salicylate, and ethylene were used to assess inducible defense signaling mechanisms in conifer stems. MJ and ethylene but not methyl salicylate caused enhanced phenolic synthesis in polyphenolic parenchyma cells, early sclereid lignification, and reprogramming of the cambial zone to form traumatic resin ducts in Pseudotsuga menziesii and Sequoiadendron giganteum. Similar responses in internodes above and below treated internodes indicate transport of a signal giving a systemic response. Studies focusing on P. menziesii showed MJ induced ethylene production earlier and 77-fold higher than wounding. Ethylene production was also induced in internodes above the MJ-treated internode. Pretreatment of P. menziesii stems with the ethylene response inhibitor 1-methylcyclopropene inhibited MJ and wound responses. Wounding increased 1-aminocyclopropane-1-carboxylic acid (ACC) oxidase protein, but MJ treatment produced a higher and more rapid ACC oxidase increase. ACC oxidase was most abundant in ray parenchyma cells, followed by cambial zone cells and resin duct epithelia. The data show these MJ-induced defense responses are mediated by ethylene. The cambial zone xylem mother cells are reprogrammed to differentiate into resin-secreting epithelial cells by an MJ-induced ethylene burst, whereas polyphenolic parenchyma cells are activated to increase polyphenol production. The results also indicate a central role of ray parenchyma in ethylene-induced defense.

Seven decades of stand development in mixed and pure stands of conifers and nitrogen-fixing red alder

Early insights on the effects of N2-fixing red alder (Alnus rubra Bong.) on conifer forests came largely from two case studies dating from the 1920s at Wind River, Washington (low soil N), and Cascade Head, Oregon (high soil N). These classic experiments were remeasured after 70 years of stand development. The pure conifer stand at Wind River showed near-zero net increment in stem mass for the past 20 years, with stem mass remaining near 120 Mg/ha. Conifer stem mass in the mixed stand continued to increase at 4.5 Mg·ha–1·year–1, reaching 230 Mg/ha at age 72. The alder mass declined over this period from about 70 Mg/ha near age 50 to just 10 Mg/ha at age 72 as a result of increasing dominance of tall Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) trees. The pure conifer plot at Cascade Head reached a stem mass of 600 Mg/ha at age 74 years compared with 312 Mg/ha in the mixed stand (conifers, 200 Mg/ha; alder, 112 Mg/ha) and 173 Mg/ha in the pure alder plot. The long-term impacts of alder appeared to remain very strong after seven decades, greatly increasing ecosystem productivity at the N-poor Wind River site and reducing productivity at the N-rich Cascade Head site.

Relative competitiveness of nine early-successional boreal forest species associated with planted jack pine and black spruce seedlings

Differences in yield-density models derived from an additive experimental design were used to compare the relative competitiveness of nine early-successional boreal forest plants (aster, grass, fireweed, fern, raspberry, willow, alder, birch, and aspen) on jack pine (Pinus banksiana Lamb.) and black spruce (Picea mariana (Mill.) BSP). A randomized complete block split-split-plot design with three replications blocked on soil type was used. Initial density gradients were 0-4 plants/m2 for woody and 0-8 plants/m2 for herbaceous species. An a priori analytical approach that compared a full model (using linear regression analysis of 4th-year stem diameter of conifers under increasing cover and height of competitors) to various reduced models was used to assess competition. Increasing cover and (or) height of all competitors (except fern) significantly (P < 0.05) decreased conifer stem diameter. The final regression model (based on visual estimates of cover and differences in initial conifer size) accounted for 89% of the variation in stem diameter. During the years studied, both conifers responded similarly to competition, and herbaceous species were on average 28.9% more competitive than woody species. Under different growing conditions (e.g., a natural forest) the relative competitiveness of herbaceous and woody species may vary from these results.

Relative competitiveness of nine early-successional boreal forest species associated with planted jack pine and black spruce seedlings

Differences in yield-density models derived from an additive experimental design were used to compare the relative competitiveness of nine early-successional boreal forest plants (aster, grass, fireweed, fern, raspberry, willow, alder, birch, and aspen) on jack pine (Pinus banksiana Lamb.) and black spruce (Picea mariana (Mill.) BSP). A randomized complete block split-split-plot design with three replications blocked on soil type was used. Initial density gradients were 0-4 plants/m2 for woody and 0-8 plants/m2 for herbaceous species. An a priori analytical approach that compared a full model (using linear regression analysis of 4th-year stem diameter of conifers under increasing cover and height of competitors) to various reduced models was used to assess competition. Increasing cover and (or) height of all competitors (except fern) significantly (P < 0.05) decreased conifer stem diameter. The final regression model (based on visual estimates of cover and differences in initial conifer size) accounted fo...