Kevin L. O'Hara

Multiaged silviculture : managing for complex forest stand structures

1. Introduction to Multiaged Silviculture 2. History of Multiaged Silviculture 3. Disturbance Dynamics of Multiaged Stands 4. Dynamics of Multiaged Stands 5. Dynamics of Forest Gap and Group Openings 6. Multiaged Management Systems 7. Multiaged Stocking Control 8. Regenerating Multiaged Stands 9. Tending Multiaged Stands 10. Transformations to Multiaged Stand Structures 11. Managing Multiaged Stands for Diverse Objectives 12. Growth Projection in Multiaged Stands 13. Volume and Economic Production of Multiaged Stands 14. Genetics and Multiaged Silviculture 15. Multiaged Structures and Stand Health 16. Social Justifications for Multiaged Silviculture

Masam – a flexible stand density management model for meeting diverse structural objectives in multiaged stands

A flexible approach for density control of multiaged stands (stands with two or more age classes) managed with the single-tree selection system is presented. This density management approach divides stands into components such as age classes, canopy strata, or species, and allocates growing space among components to control stocking. Growing space is represented by leaf area. Users specify a total stand growing space occupancy, the number of desired components, number of trees per component, and the percentage of occupied growing space allocated to each component. A series of equations can be developed and assembled in a simple spreadsheet to design and assess density management alternatives. Organization of these equations is presented as the Multiaged Stocking Assessment Model (MASAM) and is used to design several example prescriptions for several species. Model outputs which aid in implementation of designed prescriptions include stand-level totals for basal area, stand density index, and average annual volume growth for a cutting cycle. Other outputs may include component totals for basal area, stand density index, average tree vigor, and quadratic mean diameter. This approach provides flexibility in designing density management regimes for multiaged stands with a variety of stand structural characteristics including two or more age classes or strata, or stands with a preponderance of large or small trees.

An evaluation of the uniform stress hypothesis based on stem geometry in selected North American conifers

Abstract. The uniform stress hypothesis of stem formation was evaluated by comparing stem taper of Abies balsamea, Abies lasiocarpa, Picea rubens, Pinus contorta, Pinus elliottii, Pinus palustris, Pinus ponderosa, Pinus taeda, and Pseudotsuga menziesii to the taper expected if stems develop to uniformly distribute bending stress. The comparison was conducted by regressing stem diameter at height h (Dh) against bending moment at h (Mh) using the model Dh=φ (Mh)δ where φ and δ are fitted coefficients, and testing for δ=0.333, the hypothesized value. Twelve curves were fitted with the model. Seven of the fitted values of δ were significantly different from 0.333, but eight of the values were within ±10% of 0.333 and eleven values were within ±15% of 0.333. Where the fitted value of δ was >15% of 0.333, residuals were biased with height. Fit by relative height, values of δ were within ±10% of 0.333 for large portions of these stems. While most of the fitted values of δ support the uniform-stress hypothesis, the values of δ for Pseudotsuga menziesii trees clearly did not. Many of the fitted values of φ were inversely related to the modulus of elasticity (E) of green wood reported for these species. With the exception of Pseudotsuga menziesii, growing conditions appeared to account for extraordinary values of φ. Increases in φ with stem height corresponded with reported decreases in E with height. The covariance between φ and E suggests some regulation of bending curvature by adjustments in cross-sectional area. These results suggest that stems taper to maintain a uniform bending curvature and that when E is relatively constant within and among stems, diameter along the stem or across stems can be predicted from bending moment using a simple power function.

BAAD: a biomass and allometry database for woody plants

Understanding how plants are constructed—i.e., how key size dimensions and the amount of mass invested in different tissues varies among individuals—is essential for modeling plant growth, carbon stocks, and energy fluxes in the terrestrial biosphere. Allocation patterns can differ through ontogeny, but also among coexisting species and among species adapted to different environments. While a variety of models dealing with biomass allocation exist, we lack a synthetic understanding of the underlying processes. This is partly due to the lack of suitable data sets for validating and parameterizing models. To that end, we present the Biomass And Allometry Database (BAAD) for woody plants. The BAAD contains 259 634 measurements collected in 176 different studies, from 21 084 individuals across 678 species. Most of these data come from existing publications. However, raw data were rarely made public at the time of publication. Thus, the BAAD contains data from different studies, transformed into standard units and variable names. The transformations were achieved using a common workflow for all raw data files. Other features that distinguish the BAAD are: (i) measurements were for individual plants rather than stand averages; (ii) individuals spanning a range of sizes were measured; (iii) plants from 0.01–100 m in height were included; and (iv) biomass was estimated directly, i.e., not indirectly via allometric equations (except in very large trees where biomass was estimated from detailed sub-sampling). We included both wild and artificially grown plants. The data set contains the following size metrics: total leaf area; area of stem cross-section including sapwood, heartwood, and bark; height of plant and crown base, crown area, and surface area; and the dry mass of leaf, stem, branches, sapwood, heartwood, bark, coarse roots, and fine root tissues. We also report other properties of individuals (age, leaf size, leaf mass per area, wood density, nitrogen content of leaves and wood), as well as information about the growing environment (location, light, experimental treatment, vegetation type) where available. It is our hope that making these data available will improve our ability to understand plant growth, ecosystem dynamics, and carbon cycling in the worlds vegetation.

The ecology and management of moist mixed-conifer forests in eastern Oregon and Washington: a synthesis of the relevant biophysical science and implications for future land management

Land managers in the Pacific Northwest have reported a need for updated scientific information on the ecology and management of mixed-conifer forests east of the Cascade Range in Oregon and Washington. Of particular concern are the moist mixed-conifer forests, which have become drought-stressed and vulnerable to high-severity fire after decades of human disturbances and climate warming. This synthesis responds to this need. We present a compilation of existing research across multiple natural resource issues, including disturbance regimes, the legacy effects of past management actions, wildlife habitat, watershed health, restoration concepts from a landscape perspective, and social and policy concerns. We provide considerations for management, while also emphasizing the importance of local knowledge when applying this information at the local and regional level.

The role of fire in the competitive dynamics of coast redwood forests

Fire is a major component of the disturbance regime and a critical determinant of competitive outcomes in many ecosystems. In forests dominated by coast redwood (Sequoia sempervirens), fire was frequent and ubiquitous prior to European settlement, but fires have been exceedingly small and rare over the last 70–80 years because of aggressive fire prevention and suppression policies. As a result, many aspects of redwood fire ecology remain poorly understood. However, in 2008 a single storm ignited numerous fires throughout the redwood region, providing a rare opportunity to conduct replicated fire effects research. One year post-fire, we investigated competitive dynamics by quantifying bole survival and basal sprouting, for redwood and associated species, at four field sites that spanned much of the latitudinal range of redwood and encompassed (1) second-growth and old-growth stands, (2) burned and unburned areas, and (3) a wide range of fire severities. We employed a mixed effects analytical framework and found that: (1) the probability of bole survival was greater for redwood than for its primary competitor (tanoak; Notholithocarpus densiflorus), (2) this divergence was much more pronounced at higher fire severities, and (3) tanoak exhibited a slight advantage in terms of post-fire basal sprouting, but the dominance of tanoak basal sprouts in burned areas was reduced relative to unburned areas. For many disturbance types in many ecosystems, the empirical data necessary for effective management decisions are lacking, and studies incorporating vegetative tree regeneration are especially scarce. Our work demonstrates the importance of utilizing unique field research opportunities to test current theories, while unequivocally documenting that fires of all severities increased the abundance of redwood relative to tanoak, and that higher severity fires more strongly favored redwood.

Long‐term vegetation changes in a temperate forest impacted by climate change

© 2014 Oakes et al. Pervasive forest mortality is expected to increase in future decades as a result of increasing temperatures. Climate-induced forest dieback can have consequences on ecosystem services, potentially mediated by changes in forest structure and understory community composition that emerge in response to tree death. Although many dieback events around the world have been documented in recent years, yellowcedar (Callitropsis nootkatensis) decline provides an opportunity to study vegetation changes occurring over the past century. Current research identifies climate-related reductions in snow cover as a key driver of this species dieback. To examine the process of forest development post-dieback, we conducted vegetation surveys at 50 plots along the outer coast of southeast Alaska across a chronosequence of mortality. Our main study objectives were to examine changes in seedling and sapling abundance, and community structure of conifer species in the overstory; effects of yellow-cedar mortality on plant diversity and community composition of functional groups in the understory; and volume of key forage species for Sitka black-tailed deer (Odocoileus hemionus sitkensis) managed throughout the region. The probability of yellow-cedar sapling occurrence was reduced across the chronosequence. Yellow-cedar seedling and sapling abundance also decreased. We observed a turnover from yellow-cedar to western hemlock (Tsuga heterophylla) dominated forests. Functional plant diversity increased and the community composition of the understory changed across the chronosequence. Bryophytes became less abundant and grasses more abundant in the early stages of stand development, and shrubs increased in relative abundance in latter stages. Our results demonstrate that yellow-cedar is significantly less likely to regenerate in forests affected by widespread mortality, and a species dieback can dynamically rearrange the plant community over time. These findings emphasize the importance of considering long-term temporal dynamics when assessing the impacts of climate change on biodiversity and ecosystem services, and adapting forest management to a changing climate. Copyright:

Epicormic sprout development in pruned coast redwood: pruning severity, genotype, and sprouting characteristics

Abstract• Young coast redwood (Sequoia sempervirens (D. Don.) Endl.) trees were pruned to various heights to examine the effect of pruning severity on epicormic sprouting. Seven separate stands were used with as many as six treatments per stand in coastal Humboldt County, California, USA.• Epicormic sprout development was affected by pruning severity but primarily at the most severe pruning treatments that removed all but the branches in the top 15% of tree height. Less severe treatments produced sprouts but the number and size of these sprouts were comparable to unpruned trees.• Natural clonal patterns were also used to explore patterns of sprouting between genotypes. Linear mixed-effects models were developed to predict sprouting frequency as a function of pruning severity while accounting for the nested data structure (i.e., stem sections sampled nested within genotypes within treatments within sites).• Comparing variances attributed to each of these random effects indicated that at any level of pruning severity, differences in epicormic sprouting between genotypes and sites expressed soon after pruning had disappeared after six growing seasons. Epicormic branches were more common two years after pruning than six years indicating many branches were dying. Branches were more common in the middle of the pruned bole, possibly because of competition from basal sprouts and the expanding tree crown.Résumé• De jeunes séquoias de Californie (Sequoia sempervirens (D. Don.) Endl.) ont été élagués à différentes hauteurs afin d’examiner l’effet de l’intensité de l’élagage sur les rejets épicormiques. Sept peuplements ont été utilisés avec jusqu’à six traitements par peuplement dans la région côtière du Comté de Humboldt en Californie (USA).• Le développement des rejets épicormiques a été affecté par l’intensité de l’élagage, mais surtout par les traitements les plus sévères qui ont presque supprimé toutes les branches au sommet sur 15 % de la hauteur des arbres. Des traitements moins sévères ont produit des rejets, mais le nombre et la dimension de ces rejets étaient comparables à ceux des arbres non élagués.• Des clones naturels ont également été utilisés pour explorer les modèles de rejet entre génotypes. Des modèles linéaires a effets mixtes ont été développés pour prédire la fréquence des rejets en fonction de l’intensité de l’élagage, en prenant en compte la structure imbriquée des données (c’est-à-dire, les sections du tronc échantillonnées, imbriquées avec les génotypes, les traitements et les stations).• La comparaison des variances attribuées à chacun de ces effets aléatoires a indiqué qu’à tout niveau d’intensité d’élagage, les différences de rejets épicormiques entre les génotypes et les stations exprimées peu de temps après la taille avaient disparu au bout de six saisons de croissance.• Les branches épicormiques ont été plus fréquentes deux ans après l’élagage que six ans plus tard indiquant que de nombreuses branches sont en train de mourir. Les branches ont été plus fréquentes dans le milieu de la partie du tronc élaguée, peut-être en raison de la concurrence des rejets de la base et de l’expansion du houppier.

Diurnal fluctuations of gas exchange and water potential in different stand structures of Pinus ponderosa

Abstract. Leaf-level gas exchange and leaf water potential (Ψleaf) measurements were made over a diurnal time-course in multi-aged and even-aged stand structures of ponderosa pine (Pinusponderosa Dougl. ex Laws.) in central Oregon (June) and western Montana (July) to test for differences in physiological performance due to stand structure. Total site occupancy was similar between the geographic regions as measured by basal area, leaf area index, and stand density index. No differences in net photosynthesis (Anet), stomatal conductance (gs), transpiration (E), instantaneous water use efficiency (WUE) or Ψleaf were observed in June in Oregon. As a whole, even-aged plots appeared to be more water-stressed than multi-aged plots that were able to maintain higher rates of E in July in Montana. There were no differences in WUE between multi-aged and even-aged stand structures in Montana, but because both Anet and E tended to be less in even-aged trees, overall productivity and efficiency of foliage may be less than in multi-aged stand structures. It is concluded that under environmental conditions that are not limited by water, patterns in gas exchange and water use are unaffected by stand structure. The data from this study further suggest that water-limiting conditions found later in the growing season may influence diurnal gas exchange patterns in a way that could result in lower productivity in even-aged stand structures.

Stand Development and Tree Growth Response to Sugar Pine Mortality in Sierran Mixed-Conifer Forests

Abstract Sugar pine (Pinus lambertiana) is a major component of the mixed-conifer forests found in the Sierra Nevada Mountains of California, USA. In the past several decades, sugar pine mortality has increased due to an introduced pathogen, white pine blister rust (caused by Cronartium ribicola). This study described stand development patterns in the mixed-conifer forests and quantified stand and tree growth response to the loss of sugar pine. Stratification patterns tended to follow patterns of shade tolerance with the more shade tolerant species found in lower canopy positions. Growth response was analyzed following the initial entry of blister rust and after more recent sugar pine mortality. Following the initial wave of mortality induced by blister rust, overstory trees and most individual species increased overall basal area growth. Although most species also responded to recent sugar pine mortality (occurring within the past ten years) by increasing basal area growth, the increase was only significant for white fir. Mortality of sugar pine has favored other conifer species, leading to changes in species dominance and negative effects on understory growth of sugar pine; release of these trees could improve overstory recruitment of sugar pine. However, due to the increased growth of white fir, any management strategies aimed at restoring sugar pine must also consider white fir management.