Author: David D. Marshall
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ISBN:
Category : Douglas fir
Languages : en
Pages : 378
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The Levels-of-Growing-Stock Studies in Douglas-fir is a regional cooperative to investigate the effects of levels of growing stock on young stand growth. The Hoskins installation, in western Oregon, was established in a dense, high site natural stand at total age 20 years. The initial thinning resulted in an immediate 131 percent increase in diameter growth. Subsequent crown type thinning treatments retained eight different, predetermined percentages of the gross basal area growth on the control plots. At age 45, diameter growth remains strong on the heavily thinned treatments, but decreases with increased growing stock. Gross volume growth increased with growing stock, while gross basal area growth was much less influenced by growing stock. Volume growth was strongly related to density because of the rapid height growth of this young stand. Heavy thinnings reduced volume production because of the depletion of growing stock. Total volume production was only slightly reduced on the light thinnings, whereas merchantable volume was greater than the unthinned control. Mortality was heavy on the control, but negligible on the treated plots. Heavy mortality in the last period, reduced net volume growth on the control to less than the treatments. Periodic annual increment (PAI) for cubic foot volume appear to have culminated for the treatments, although they are nearly twice the mean annual increments on the thinned plots. Board foot volume PAI does not appear to have culminated for any of the treatments. The diameter growth of individual trees was particularly influenced by the amount of density in trees larger than any given tree. Density had only a minor effect on height growth. Trees in lower densities had longer crowns and greater taper. Results from simulations of alternative thinning regimes show the desirability of early thinnings. Compared to thinning from below, crown thinning appeared to give the greatest release to the residual stand and produce high volume growth. Management must consider the trade-off s between greater diameter growth at low densities and greater volume growth at high densities.
Author: John Duff Bailey
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ISBN:
Category : Douglas fir
Languages : en
Pages : 252
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This research examined thinning effects on stand structure and species composition in 50- to 120-year-old Douglas-fir forests. Thirty-two paired stands (thinned and unthinned) were measured throughout western Oregon, as were 20 old-growth stands for comparison. Thinnings occurred 10 to 24 years previously and ranged in intensity from 8 to 60% volume removal. Overstory and intermediate tree characteristics, conifer and hardwood regeneration, and shrub/herbaceous species composition and cover were recorded. From this, I assessed whether thinning young stands promoted vegetation structure and composition associated with old-growth stands. Overstory trees in thinned stands had diameters, live crown ratios, crown radii, and radial growth rates greater than those in unthinned stands, and equal to or approaching those found in old-growth stands. Stand volume production was neither affected by earlier clearcut harvesting nor by thinning. Intermediate trees in thinned stands, like old-growth stands, were typically young saplings with radial growth rates and live crown ratios greater than those in unthinned stands (typically suppressed members of the original cohort). Living intermediate structure (multi-storied canopies) was common to thinned and old-growth stands. Given such overstory and intermediate tree responses, canopy leaf area in stands thinned>20 years previously was greater than in unthinned stands. Conifer regeneration density, frequency and growth rates were greater in thinned stands than in old-growth and unthinned stands. Densities and frequencies of tall shrubs were similar in thinned and old-growth stands, and greater than unthinned stands. Low shrub and herbaceous cover were 33% and 25% greater, respectively, in thinned than other stand types. Herbaceous species frequency and richness were similarly stimulated. Low shrub composition was altered by thinning (unthinned and old-growth stands did not ordinate differently). However, herbaceous species composition was similar across all stand types and showed more variability among sites than among stand types. Thinning appeared to create old-growth-type structure by stimulating overstory and intermediate tree crowns and growth rates, tall shrub densities and conifer regeneration. Though low shrub and herbaceous species cover and frequency were greatest in thinned stands, composition was not affected by thinning, nor by clearcut harvesting 50 to 120 years ago or other differences in stand origin.
Author: Richard L. Williamson
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ISBN:
Category : Douglas fir
Languages : en
Pages : 24
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Author:
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ISBN:
Category : Biodiversity
Languages : en
Pages : 92
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Author: Richard L. Williamson
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Category : Douglas fir
Languages : en
Pages : 20
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Author: Eric K. Zenner
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ISBN:
Category : Douglas fir
Languages : en
Pages : 116
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The purpose of this study was to assess how growth of young to mature Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) and western hemlock (Tsuga heterophylla (Raf.) Sar.) in mixed stands was influenced by the presence of residual trees. Fourteen paired plots with and without residual trees were examined in a retrospective study on the Willamette National Forest, Oregon. Growth was analyzed at the stand level, and at the individual tree level, contrasting growth behavior of Douglas-fir and western hemlock. Stands were generally highly stocked with relative densities between 0.38 and 1.05 and age ranged between 55 and 121 years. Results indicate that both understory and residual tree densities had a major influence on average tree size and growth and yield of the young cohort. At the stand level, residual trees and high understory densities reduced volume, basal area, and the mean squared diameter of the young cohort, while understory mortality increased. The influence of residual tree density on total understory and Douglas-fir volume and basal area was best fit by a negative logarithmic function. After accounting for understory density effects, the decrease of understory volume and basal area per individual residual tree decreased with increasing residual tree density. With 5 to 50 residual trees/ha, total understory volume reduction was 22 and 45%, respectively, averaging 2.4 and 1.5% per residual tree, respectively. In mixed stands, Douglas-fir volume and basal area declined more rapidly than the volume and basal area of the entire young cohort, when residual tree density exceeded 15 trees/ha. This was probably due to the relative shade-intolerance of Douglas-fir. Douglas-fir volume and basal area on southerly aspects was more than double the values on northerly aspects. Examination of quadratic mean diameters and radial growth rates by crown class revealed that the average size and growth rates of dominant Douglas-fir were not reduced by residual trees. However, the number and basal area of understory trees, particularly dominant and codominant Douglas-fir, declined with increasing residual tree densities. Understory volume was highest in stands that had lowest understory densities. High understory stocking levels were associated with reduced growth and high mortality rates of the young cohort, suggesting stands were undergoing self-thinning. At the individual tree level, basal area growth and diameter growth of trees increased with increasing size and dominance. The marginal effect of residual trees declined with increasing numbers of residual trees per hectare. No residual tree effects on heights of dominant Douglas-fir was found, perhaps because the few dominant Douglas-firs may have been located sufficiently far from residual trees to minimize interaction. Due to high stocking levels in the young cohort, results from this study only apply to stands with relative densities above 0.38. In addition, leave-trees in managed stands may be younger, smaller, and may have different growth rates from residual trees in this study, thus affecting the young cohort differently. Finally, due to the observational nature of this study, cause-and-effect relationships cannot be established. However, since understory volume was highest in stands with low understory densities, understory density management may reduce growth.
Author: Christopher D. Dowling
Publisher:
ISBN:
Category : Douglas fir
Languages : en
Pages : 258
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Ages, diameter growth, density, tree size, and species were studied in old-growth, plantation, and young natural Douglas-fir stands in three areas in western Oregon: the western and eastern Coast Range and the western Cascades. The purpose was to compare the development of these three stand types and to determine whether plantations and young natural stands would develop old-growth structures and characteristics. The Douglas-fir age ranges in plantations (8 to 15 yr) were much narrower and than the ranges of tree ages found in the young natural (21 to 102 yr) and in the old-growth stands (300 to 354 yr). This wide range of tree ages, along with diameter growth rates and tree and stand structural characteristics, supported the hypothesis that old-growth developed at low initial stand densities. These low initial stand densities, probably the result of prolonged stand establishment, likely enabled height and crown size advantages among old and younger trees. Dominant and large codominant trees maintained live crown ratios and sustained diameter growth resulting in large stable trees indicated by low height-to-diameter ratios. The mean diameters of the dominant trees in the old-growth and the dominant trees in the young natural stands were not significantly different at age 40 and 100, indicating the young natural stands appear to be growing at the same rates as the old-growth in its first 100 years. The mean dominant diameters in the plantations and old-growth at age 40 and 100 were significantly different, indicating the plantations are growing and developing differently than young natural and old-growth forests. Plantations had grown rapidly for the first 20 to 30 years, and computer simulation indicated that a significant rapid decline in radial growth would occur between ages 30 and 55. Simulations also indicate that during this period, the mean diameters of the dominant plantation trees would fall below those of the old-growth in two of the three stands by age 85. Pre-commercial thinning 20 to 25 years ago in the plantations has helped sustain high early growth rates for a longer period of time than would have occurred if thinning had not been performed. Additional thinning in the future is likely needed to maintain rapid current rates. When simulated to age 250 both the young natural stands and the plantations maintained higher densities of smaller diameter trees than the old-growth stands. This simulation result indicates the possible inability of these stands to self-thin to the densities found in old-growth stands without some sort of density-reducing disturbance. The broad range of tree ages in the old-growth stands suggests that stand disturbances are a normal part of old-growth development on these sites. Five different plantation thinning options were also simulated to age 250, including additional options with thinning of understory trees and ingrowth. The projections indicate that when the plantations are left unthinned they would generally develop trees with small live crowns and mean diameters but still produce stable dominant overstory trees (low H:D ratios). Shade tolerant understory trees and ingrowth, such as western hemlock, are a key part of old-growth development. These trees may reduce the rate of growth and alter crown structure of the overstory trees over extended periods of time (200+ years). Additional thinning, possibly in multiple entries, in both the overstory and understory may be necessary for dense plantations to develop the tree size heterogeneity found in local old-growth forests. I also demonstrated a methodology to determine site-specific management targets or goals for creating old-growth structure from plantations. This was performed using past and current forest structure and composition information within a local landscape scale of 500 to 1000 acres, typical of the public land checkerboard ownership pattern. Stand types making up the historical landscape are identified and described retrospectively using historical and current aerial photographs and digital orthophotos, cruise records, previous studies, and sample plots of standing and harvested forests. The degree of detail provided through this methodology will likely help forest managers to define complex late-successional characteristics of stands and landscapes. My results indicate that stand and project area-specific definitions of old-growth and clearly defined goals for young stand management will facilitate development of old forest characteristics.
Author: Steven Lee Garman
Publisher:
ISBN:
Category : Douglas fir
Languages : en
Pages : 64
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The goal of this simulation study was to provide information for defining thinning regimes for young Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) stands in the Central Cascades Adaptive Management Area, located in west-central Oregon. Specifically, this study used the ZELIG. PNW (3.0) gap model to evaluate effects of experimental thinning treatments on the development of late-successional attributes and on extracted merchantable volume. Sixty-four thinning treatments were simulated for four rotation intervals (260, 180, 100, and 80 years) starting with a 40-year-old managed Douglas-fir stand. The amount of time for five late successional attributes to reach defined threshold levels, long-term developmental trends of these attributes, and amount of extracted merchantable volume were recorded for each treatment. Stand conditions of selected treatments were used in a subsequent harvest rotation in which 64 additional experimental thinning treatments were applied and evaluated. A total of 1,744 thinning treatments was evaluated in this study. Results of this study confirm previous recommendations for accelerating development of late-successional attributes in young managed stands. Additionally, results show the potential for a range of thinning treatments to attain late-successional conditions in about the same amount of time, but with different tradeoffs in terms of merchantable volume and long-term stand conditions. In general, heavy thinning of existing stands at ages 40 and 60 years promoted rapid development of large boles, vertical diversity, and tree-species diversity, but provided the least amount of extracted volume and required artificial creation of dead wood. Treatments that retained more than 40 percent of the original overstory and thinned to 99 trees per hectare at age 60 delayed attainment of late-successional conditions by 10 to 30 years but provided 12 to 20 percent more extracted volume, resulted in higher levels of most late-successional attributes at the end of a rotation, and required less artificial creation of dead wood. Treatments providing the fastest development of late-successional conditions in subsequent rotations varied with the amount of canopy cover retained at the end of the first rotation. For stands starting with ÃÃY30 percent canopy cover, delaying the first commercial thin for 40 years promoted the most rapid development of vertical structure and shadetolerant stems. Lower canopy-retention levels required heavy or light thins in subsequent entries, depending on the rotation interval, for rapid development of late-successional attributes.
Author: Liane R. Beggs
Publisher:
ISBN:
Category : Douglas fir
Languages : en
Pages : 190
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Across western Oregon, Washington, and British Columbia, forest management practices over the past century reduced the amount of late-successional forest while simultaneously increasing the amount of young (less than 80 years old), managed Douglas-fir (Pseudotsuga menziesii) dominated forests. Recently, concerns over loss of late-successional habitat pushed management objectives on public lands away from timber production and toward maintenance and restoration of late-successional habitat. In accordance with these new objectives, The Young Stand Thinning and Diversity Study (YSTDS) was developed to test if thinning could accelerate development of latesuccessional habitat in young managed Douglas-fir forests. Though the YSTDS examines several components of forest ecosystems, the goal of this study was to investigate short-term (5-7 years post-treatment) responses of vegetation to thinning treatments and to evaluate this response in relation to long-term objectives of late-successional development. The study is located on the western slope of the central Oregon Cascades. It consists of four replications of four thinning treatments (treatment areas average 30 ha each) in 30-50 year old second-growth Douglas-fir forest stands. Treatments include a control, heavy thin, light thin, and light thin with gaps. Unlike traditional thinning, the thinning treatments in this study sought to maintain and enhance overstory structural diversity by: (1) retaining species other than Douglas-fir, (2) simulating low densities that characterized development of some old-growth stands, and (3) adding canopy gaps to enhance spatial diversity. Following treatment completion, first, third, and fifth-year vegetation responses were measured Results for overstory vegetation indicate that heavy thinning may accelerate development of large trees, one important component of old-growth structure. This was evident by faster growth of the largest trees in the heavy thin than in the control. A heavy thin may also permit more time for understory development than a lighter thin because canopies of heavy thinned stands remained open longer than canopies of light thinned stands. Variation in overstory cover, which may promote heterogeneous understory development, was higher in the treatment that included canopy gaps than in other treatments including the control. Although accelerated development of a multi-layered canopy was not evident in any treatment, retention of non-dominant tree species prevented simplification of vertical canopy structure by retaining layers that are typically removed by a low thinning prescription. In addition, mortality of non-dominant species was not greater in thinned treatments than in the control. In the understory, results suggest that thinning can increase abundance of some vegetative layers without encouraging homogenization of the understory by clonal shrubs or exotic species. The thinnings resulted in initial declines of bryophytes, tall shrubs, and low shrubs followed by subsequent recovery and growth. While herbs displayed little initial response, a release of early-seral species was evident by 5-7 years post-treatment. Initial changes following thinning were likely due to harvesting damage and/or alteration of microclimate while subsequent changes were probably also related to increased resource availability. It is expected that eventually similarities and differences in overstory structure among thinned treatments will be reflected in the understory. For example, variation in canopy cover created by the addition of canopy gaps was already reflected in the understory, as plant assemblages differed across the gradient from gaps to the thinned forest matrix. Hence, although understory vegetation was similar among heavy and light thins in the short-term, early closure of the canopy following a light thin could preclude continuation of late-seral understory development. Finally, the effect of canopy gaps on the understory was more apparent at a within-stand scale than at a stand scale. Had the within-stand scale been ignored, relevant information regarding understory response would have been overlooked. This indicates that spatial scale should be considered when assessing ecological patterns. In conclusion, it is acknowledged that there are drawbacks to thinning (e.g., certain species decline following thinning) It is also acknowledged that the short-term nature of the data permits only speculation regarding long-term succession. While these limitations are recognized, current trends indicate that a moderate to heavy thinning in combination with gap formation can hasten development of late-successional features in thinned stands relative to unthinned stands. Thus, thinning similar to that used in this study can be one useful tool in the management of young Douglas-fir forests.
Author: Pablo Romero Castaño
Publisher:
ISBN:
Category : Douglas fir
Languages : en
Pages : 162
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The search for the stand density that optimizes growth and hence generates the maximum amount of wood is one of the philosopher's stone in modern forestry. Since scientific methods were applied to forestry, numerous generations of foresters have studied the relations between stocking density and growth, obtaining diverse results and structuring acquired knowledge into different principles that continue to be debated by supporters and detractors. Three main principles are: 1) any reduction in stand density entails a decreasing in the growing capacity, 2) growth is constant for a range of stand densities and, 3) progressive reductions in stand density increase growth up to an optimum, after which growth starts decreasing. Thinning is the traditional tool that foresters use to manage stand density. Consequently, most of growth-growing stock relations are based on data from thinning experiments. In addition to the potential effects of thinning on growth of residual trees, the erratic behavior of periodic annual increment routinely found in field studies may be contributed by measurement errors, imputation inaccuracies, variation in initial conditions, imprecise treatment implementation, irregular mortality, or variation in definition of density and stocking. These sources of variation in response to thinning lead to different results and different interpretations of conformity to the principles listed above. The Black Rock Unit of the George T. Gerlinger Experimental Forest in Oregon holds one of the largest and oldest Douglas-fir thinning experiments with the native region of this species. The characteristics of the stand, particularly the age when treatments were carried out and the initial dimensions of the trees, broaden our perspective to the on results from other studies in other areas and in younger stands of both Douglas-fir and other species. Reductions in stand density generally lead to a change in the expected growth of the stand, most typically a reduction in growth more or less commensurate with the reduction in stand density, as further controlled by the initial diameter, height, and crown length of the residual trees. The direct effect of thinning is that portion of the growth response that is systematically related to the type, intensity, and timing of the thinning and that is not explained by the relationship of growth to conventional stand, tree, and site predictor variables in unthinned stands. Accurate forecasting of tree and stand growth after thinning therefore requires quantification of the direct effects of thinning and its change over time since thinning. In an effort to isolate the direct effect of thinning treatments at the stand and tree level, from effects of conventional stand, tree, and site variables, regression techniques were applied to data from a set of thinned and unthinned stands. After an initial period of no response, limited response, or even "shock", thinning increased stand growth inversely proportional to the intensity of treatment (if stands were compared at the same initial conditions). The overall direct effect of thinning was consequently an initial decrease relative to the growth rate of an unthinned stand with the same initial conditions, but then an increase growth after several years. Direct effects at the stand level were the aggregate result of direct effects of thinning on the constituent trees. These tree-level direct effects were more complicated than has previously been assumed in growth models. Trees of different diameter classes (correlated with crown classes) differed in their direct response to thinning. In general, thinning had little direct effect on growth patterns in the largest diameter class (largest 28%), increased the growth performance in mid-sized trees (next largest 22% by diameter), and reduced initially the average growth of smallest trees (smallest 19% by diameter). However, most diameter classes under most thinning intensities recovered quickly after a few years and direct thinning effects led to greater growth that expected for the same initial conditions in unthinned stands. The intensity of thinning increased this positive direct response among all size classes. These results help to understand the factors that control growth in Douglas-fir stands. Likewise, quantification of direct growth effects attributable to thinning add to our knowledge base on tree and stand-level responses to thinning. In regard to the stated growth-growing stock principles, the Black Rock thinning trials seemed to support the principle that stand growth declines in direct proportion to thinning intensity. The eventual growth increase stimulated by the direct thinning effect did not compensate for the reduced growing stock imposed by thinning. Furthermore, little evidence was found for uniform growth across a wide range in initial stand density. Finally, analyses of individual trees and percentiles of the diameter distribution corresponding roughly to crown classes demonstrated that the direct effect of thinning within a stand is not uniform across tree size, implying that stand-level multipliers for the direct thinning effect might gainfully be replaced by a tree-level function of relative tree size as well as thinning intensity and time since thinning.
