Old-growth Pseudotsuga Menziesii Research Articles

Crown closure affects endophytic leaf mycobiome compositional dynamics over time in Pseudotsuga menziesii var. menziesii

Old-growth Pseudotsuga menziesii var. menziesii forests produce complex environmental and spatial gradients along which biota assemble. Given this, it has been proposed that changes in the crown microenvironment are associated with different community assembly outcomes for needle fungi. Using high-throughput sequencing, the endophytic mycobiomes of needles were characterized for increasing ages of needles sampled along the boles of eight coastal Douglas-fir trees. Leveraging airborne light detection and ranging (LiDAR) data to create three-dimensional “point cloud” representations of tree crowns revealed that crown closure accounted for more fungal compositional variation than height in crown, and fungal richness and diversity were positively correlated with increasing crown closure. Supplementing the point clouds of each climbed tree with clouds from >5,000 randomly selected trees in the study area showed that fungal communities from closed portions of the crown were increasingly structured with needle age. These findings highlight the importance of the crown microenvironment in the development of foliar fungal communities for a foundation tree species.

Two-criteria model assessment shows that foliage maintenance in old-growth Pseudotsuga menziesii requires both delayed and sequential reiteration

Functional structural models (FSMs) are valuable tools to explore relationships between plant form and function, yet they lack rigorous methods for development and assessment. We use multi-criteria assessment of an architectural FSM to show that both traumatic sequential and adaptive delayed reiteration (ADR) are necessary components of foliage maintenance in branches of old-growth Pseudotsuga menziesii. ADR has previously been established as a process that maintains foliage in old-growth P. menziesii. We use a simulation model of branch development in the species to evaluate morphogenesis in the context of this ADR. The structure of the model is a theoretical representation of how P. menziesii branch morphology develops throughout the branch lifespan, and this model structure is assessed with two criteria that are optimized simultaneously; the criteria measure foliage demography by the number of foliated shoots, and how those foliated shoots are organized into independent clusters. Assessment results indicated that improvements in model structure were required. Anomalous parameter vectors from the assessment search uncovered an inadequacy in the process of foliage maintenance, and the model was modified to include traumatic sequential reiteration in addition to ADR. The modes of the resulting parameter distributions were consistent with empirical observations. We discuss why the assessment of FSMs is an essential procedure that requires multiple criteria.

Model analysis of the importance of reiteration for branch longevity inPseudotsuga menziesiicompared withAbies grandis

Reiteration is an important process in the maintenance of tree crowns and in plant longevity. We use a geometric simulation model of branch growth to explore differences in longevity between old-growth Pseudotsuga menziesii (Mirb.) Franco and Abies grandis (D. Don ex Lamb.) Lindl. branches. Reiteration is defined through rules that reflect apical dominance relationships, and these rules are used to define shoot cluster units (SCU) on P. menziesii branches. Reiteration through epicormic production dominates growth in simulated P. menziesii branches and is shown to be a major factor that differentiates growth between P. menziesii and A. grandis. Branch growth is shown to be highly sensitive to rules for bifurcation and capacity for reiteration. The rules employed in the model that define epicormic initiation and SCU independence reveal possible physiological mechanisms through which reiteration occurs in P. menziesii. A simple morphological rule fails to simulate branch growth adequately, whereas a physiological rule through epicormic initiation after release from inhibition of a lateral axis yields realistic simulated branches. Branch growth is best simulated through a combination of physiological controls and morphological rules.Key words: reiteration, old growth, architecture, branch modeling, longevity.

Large wood recruitment and redistribution in headwater streams in the southern Oregon Coast Range, U.S.A.

Large wood recruitment and redistribution mechanisms were investigated in a 3.9 km2 basin with an old-growth Pseudotsuga menziesii (Mirb.) Franco and Tsuga heterophylla (Raf.) Sarg. forest, located in the southern Coast Range of Oregon. Stream size and topographic setting strongly influenced processes that delivered wood to the channel network. In small colluvial channels draining steep hillslopes, processes associated with slope instability dominated large wood recruitment. In the larger alluvial channel, windthrow was the dominant recruitment process from the local riparian area. Consequently, colluvial channels received wood from further upslope than the alluvial channel. Input and redistribution processes influenced piece location relative to the direction of flow and thus, affected the functional role of wood. Wood recruited directly from local hillslopes and riparian areas was typically positioned adjacent to the channel or spanned its full width, and trapped sediment and wood in transport. In contrast, wood that had been fluvially redistributed was commonly located in mid-channel positions and was associated with scouring of the streambed and banks. Debris flows were a unique mechanism for creating large accumulations of wood in small streams that lacked the capacity for abundant fluvial transport of wood, and for transporting wood that was longer than the bank-full width of the channel.

Diffusion and seasonal dynamics of O2 in woody debris from the Pacific Northwest, USA

O2 is an important regulator of physiological processes involved in the decomposition of woody debris, yet O2 levels and diffusion rates within decomposing logs are largely unknown. We examined how O2 diffusion rates in decayed and sound wood varied with moisture and density, and we compared predicted with observed seasonal changes in oxygen concentration in logs in a Pacific Northwest old-growth Pseudotsuga menziesii forest. In the laboratory, the oxygen diffusion coefficient (DO2) was determined in the longitudinal and radial (or tangential) directions on wood cores of varying moisture content and density. In the field, O2 was measured in tubes inserted to three radial depths (2, 6 and 15 cm) within logs of two species (Pseudotsuga menziesii and Tsuga heterophylla) and five decay classes (where class 5 = most decayed). In both the radial and longitudinal directions, DO2 increased exponentially as the air filled pore space (AFPS) increased and as density decreased. In the field, mean O2 concentrations in logs were not significantly different between species. Mean O2 concentrations were significantly lower in the least decayed logs as compared to the most decayed logs. Mean O2 concentrations decreased with radial depth only in decay class two logs. Seasonal O2 levels did not consistently vary with log moisture, respiration, or air temperature. The comparison of the results from a model that assumes oxygen diffuses only in the radial direction to field data indicates that laboratory measurements of oxygen diffusion may underestimate field oxygen concentrations. Cracks, insect galleries and other passages in decayed logs, and longitudinal oxygen diffusion may account for this discrepancy. In the field, log oxygen concentrations were rarely as low as 2%, indicating anaerobic conditions may not be as common in logs as we previously thought. Oxygen limitations on decomposition may occur in relatively sound and/or water soaked wood, but probably not in decayed logs in a terrestrial setting.

Height growth and vertical development of an old-growthPseudotsuga-Tsugaforest in southwestern Washington State, U.S.A.

A detailed analysis of diameter-height relationships was applied to an old-growth Pseudotsuga menziesii (Mirb.) Franco var. menziesii - Tsuga heterophylla (Raf.) Sarg. forest in southwestern Washington State, U.S.A., to predict future development of vertical stratification among tree species. Differences among species in relative abundance and size structure resulted in diameter-height regressions of varying certainty and stability. Damage and shading had negative impacts on predicted heights and estimates of maximum attainable height (Hmax) in all species. However, species varied as to the main causes and size dependency of damage in relation to tree height. Current height-growth rates of the upper canopy species declined with increasing tree height, reaching minimum values near the predicted Hmax. The future development of the forest canopy would involve a slow invasion of the upper canopy by Tsuga heterophylla and Thuja plicata Donn ex D. Don, as P. menziesii are near their maximum attainable height, and Abies amabilis Dougl. ex Forbes and Taxus brevifolia Nutt. are restricted to the middle to lower canopy. However, if current height-growth rates continue, P. menziesii should maintain its dominant status in the upper canopy for at least another century.

Height growth and vertical development of an old-growth <i>Pseudotsuga</i>-<i>Tsuga</i> forest in southwestern Washington State, U.S.A.

A detailed analysis of diameter-height relationships was applied to an old-growth Pseudotsuga menziesii (Mirb.) Franco var. menziesii - Tsuga heterophylla (Raf.) Sarg. forest in southwestern Washington State, U.S.A., to pre- dict future development of vertical stratification among tree species. Differences among species in relative abundance and size structure resulted in diameter-height regressions of varying certainty and stability. Damage and shading had negative impacts on predicted heights and estimates of maximum attainable height (Hmax) in all species. However, spe- cies varied as to the main causes and size dependency of damage in relation to tree height. Current height-growth rates of the upper canopy species declined with increasing tree height, reaching minimum values near the predicted Hmax. The future development of the forest canopy would involve a slow invasion of the upper canopy by Tsuga heterophylla and Thuja plicata Donn ex D. Don, as P. menziesii are near their maximum attainable height, and Abies amabilis Dougl. ex Forbes and Taxus brevifolia Nutt. are restricted to the middle to lower canopy. However, if current height- growth rates continue, P. menziesii should maintain its dominant status in the upper canopy for at least another century.

Crown structure and the distribution of epiphyte functional group biomass in old-growth Pseudotsuga menziesii trees

Epiphyte functional groups (alectorioid lichens, cyanolichens, other lichens, and bryophytes) were sampled in nine old-growth, canopy-emergent, Pseudotsuga menziesii trees along a riparian corridor in the Wind River Experimental Forest, Washington State, U.S.A., with the objective of determining epiphyte abundance and its relationship to crown structure. An additional objective was to develop a sampling design that reasonably captured the variation in epiphyte distribution so that total biomass could be estimated for an individual large tree, a design efficient enough to make description economically and logistically possible. Trees ranged in height from 51 to 66 meters and averaged 83 live and 79 dead limbs in a crown length of 40 meters. Diameter at breast height was a useful estimator of tree crown structural complexity. Epiphytes averaged 27.1 kg/tree, with alectorioid lichens (19.3 kg/tree) dominating the assemblages, followed by other lichens (3.3 kg/tree), bryophytes (2.6 kg/tree) and cyanolichens (1.9 kg/tree). The foliage region had the highest biomass of lichens (16.4 kg/tree), followed by the branches (8 kg/tree) and trunk (2.6 kg/tree). Alectorioid lichens predominated in the upper, middle and outer portions of the tree crown, whereas the lower and inner portion of the tree crowns had more equal distributions of all four functional groups. Relative height and limb size were the most significant structural attributes influencing epiphyte distribution. Limb size had a particularly strong effect on the distribution of bryophytes regardless of height. In old, canopy-emergent P. menziesii, the crown structural variables which determine epiphyte distribution and abundance are height, crown length, trunk surface area and exposure, distribution and abundance of small, medium and large branches, and distribution and exposure of foliated branches.

The canopy water relations of old-growth Douglas-fir trees

We investigated whole tree water relations in 56–65 m tall, old-growth Pseudotsuga menziesii trees within the Wind River Canopy Crane site, Carson, Washington, USA. We measured at predawn and solar noon the vertical gradients in xylem pressure potential using a pressure chamber. On an Abies amabilis sapling located in the understory at the base of one of the study trees, predawn and solar noon xylem pressure potentials were also measured. Xylem pressure potential data were measured from late June through early September 1996 on foliage sampled from 1 to 64.5 m. Over this height gradient, predawn water potentials ranged from –0.23 to –1.10 MPa. Solar noon values showed an even greater range (from –0.44 to –2.51 MPa). At predawn, the water potential gradient approached the theoretical hydrostatic gradient (–0.0105 vs –0.010 MPa m–1). The gradient at solar noon was steeper (–0.0331 MPa m–1). Instantaneous stomatal conductances were not greatly different between young, sapling-sized and old-growth trees [0.094±0.033 (SD) vs 0.086±0.045 cm s–1, respectively]. Stomata of both size classes of trees appeared very sensitive to increasing vapor pressure deficits. A comparison of stable carbon isotope values from the old-growth and sapling-sized trees indicated lower stomatal conductances in the old-growth. This study provides sound documentation regarding the utility of the cohesion theory in the interpretation of water potential gradients. This study also emphasizes inherent differences between sapling-sized and tall, old-growth trees.

Buried propagules in an old-growth forest and their response to experimental disturbances

Soil blocks collected from an old-growth Pseudotsuga menziesii forest were subjected to three types of disturbances (shade removal, surface burning, and soil churning) in a factorial experiment. Most émergents (88%) were vegetative sprouts. Total emergence and emergence of vegetative sprouts were significantly higher in the undisturbed (control) treatment than in any other treatment. As intensity of disturbance (measured by the number of disturbance factors applied) increased, the number of emergents declined. Exposure to sun caused a significant decline in emergence of each of the six most abundant species; the effects of burning and churning varied by species. Burning decreased the emergence of species with shallow regenerating structures. None of the experimental treatments significantly affected seedling emergence. Density of émergents (both seedlings and vegetative sprouts) was higher under greenhouse condition (411.7/m2) than in the experimental treatments (94.6/m2), indicating that greenhouse emergence is more suitable for quantifying the buried propagule bank. Key words: seed bank, propagules, old-growth forest, disturbance, fire.

Forest development in canopy openings in old-growth Pseudotsuga forests of the western Cascade Range, Oregon

Size and age structure, and spatial pattern analysis were used to study the population dynamics of old-growth Pseudotsugamenziesii (Mirb.) Franco forests of the western Cascade Range, Oregon, U.S.A. Tree population structures confirmed that in the absence of fire, Pseudotsuga was replaced by Tsugaheterophylla (Raf.) Sarg. and (or) Abiesamabilis (Dougl.) Forbes. Regeneration patterns of these species reflected establishment in canopy openings or under Pseudotsuga, but not under Tsuga. Abiesamabilis occurred more frequently as seedlings and saplings in openings than did Tsuga because of favourable aspects of its life history. The composition and structure of the pioneer forest developing after fire was a determinant of subsequent regeneration. If Pseudotsuga dominated, Tsuga and Abies invaded the stand at an early stage. Regeneration in stands where Tsuga was a large component, however, was limited by dense canopies and the occurrence of canopy openings. These patterns demonstrate the importance of small-scale disturbances such as tree falls in the dynamics of Pacific Northwest conifer forests.

Nitrogen fixation and acetylene reduction in decaying conifer boles: effects of incubation time, aeration, and moisture content

Free-living microaerophiles fixed 15N2 and reduced acetylene in fallen tree boles at two old-growth Pseudotsugamenziesii stands in western Oregon. Acetylene reduction was most rapid under an atmosphere of 2–10% O2, whereas under prolonged anaerobic conditions it was at or below detection limits. Acetylene reduction rates increased up to fourfold during long-term incubations in acetylene (> 12 h). Ratios of acetylene reduction to N2 fixation frequently exceeded 6.0 during such long-term incubations but averaged 3.5 when samples were incubated < 7 h; consequently, long-term incubation of low-activity material in acetylene should be avoided. A preliminary survey indicated that N2 fixation by free-living organisms in fallen boles was less than other potential N inputs to fallen boles and to the forest ecosystem.