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Toward managing mixed-species stands： from parametrization to prescription

Forest Ecosystems 2017年第4期4卷 286-302页

作者： Hans Pretzsch eric k. zenner Chair for Forest Growth and Yield Science Center of Life and Food Sciences Weihenstephan Technical University of Munich Hans-Carl-von Carlowitz-Platz 2 85354 Freising Germany

A better understanding and a more quantitative design of mixed-species stands will contribute to more integrative and goal-oriented research in mixed-species forests. Much recent work.has indicated that the structure and growth of mixed species forests may fundamentally differ from monocultures. Here we suggest how to progress from the present accumulation of phenomenological findings to a design of mixed-species stands and advanced silvicultural prescriptions by means of modelling. First, the k.owledge of mixing effects on the structure and growth at the stand, species, and individual tree level is reviewed, with a focus on those findings that are most essential for suitable modelling and silvicultural designs and the regulation of mixed stands as opposed to monocultures. Then, the k.y role of growth models, stand simulators, and scenario assessments for designing mixed species stands is discussed The next section illustrates that existing forest stand growth models require some fundamental modifications to become suitable for both monocultures and mixed-species stands. We then explore how silvicultural prescriptions derived from scenario runs would need to be both quantified and simplified for transfer to forest management and demonstrated in training plots. Finally, we address the main remaining k.owledge gaps that could be remedied through empirical research.

关键词： Multiplicative mixing effects Overyielding Overdensity Modelling mixing effects Scenario analysis,Silvicultural prescriptions Practical guidelines

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Regeneration Responses in Partially-Harvested Riparian Management Zones in Northern Minnesota

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Journal of Water Resource and Protection 2014年第6期6卷 556-564页

作者： Douglas N. k.stendick.Brian J. Palik.eric k. zenner Randy k. k.lk. Charles R. Blinn Joshua J. k.agthorpe Penn State University University Park USA University of Minnesota St. Paul USA USDA Forest Service Northern Research Station Grand Rapids USA

Trees serve important functions in riparian areas. Guidelines often suggest how riparian forests should be managed to sustain functions, including tree retention and increasing the component of conifers and later-successional species. While regeneration of early successional species is not discouraged, there is uncertainty about the ability to regenerate the latter along with more desirable species. We investigated the regeneration of species differing in successional status and growth forms under different amounts of residual basal area. The study was conducted in riparian sites in northern Minnesota USA. At each site, one portion of the riparian area was uncut, while a downstream area was harvested to 16 or 8 m2·ha-1. Woody vegetation was sampled before and five-years after harvesting and summarized as early, mid-, and late successional hardwoods, as well as conifers and shrubs. After five years, the density of early successional trees was lower at 16 m2·ha-1 compared to 8 m2·ha-1;densities in both treatments were lower than in clearcuts. Densities of mid- and late successional hardwoods and conifers did not increase in either treatment. The higher basal area treatment resulted in a lower density of shrubs, which might be important for establishing more desirable tree species, although this may require additional activities to promote establishment.

关键词： Riparian Management Overstory Retention Regeneration RMZ Riparian Forest

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Sub-stand diameter distribution types vary along an old-growth Douglas-fir chronosequence into the horizontal diversification development stage

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Journal of Forestry Research 2023年第2期34卷 415-424页

作者： JeriLynn E.Peck.eric k.zenner Department of Ecosystem Science and Management The Pennsylvania State UniversityUniversity ParkPA 16802USA

Managing mature Douglas-fir[Pseudotsuga menziesii(Mirb.)Franco]stands to emulate the structural complexity of natural old-growth forest requires identifying structural targets at the sub-stand level at which neighborhood dynamics and patchy disturbance shape *** therefore sought to describe the archetypal shapes of predominant sub-stand diameter distribution types(DDTs)observed in natural tree neighborhoods in stands comprising a chronosequence(ca.120-450+yrs)encompassing mature,vertical diversification,and horizontal diversification development *** ten 1.0 ha stands are located in the southcentral Oregon Cascades,*** on the k.own spatial position of each tree,natural tree neighborhoods were identified using the floating neighborhood approach based on spatial tessellation connecting neighboring trees at the first-(mean 61 m2)through fifth-(mean 2058 m2)order *** analysis was then used to objectively identify the most predominant DDTs among the relative tree size distributions observed in the trans-scale neighborhoods within each *** measures regression was used to classify each DDT to one of six observed archetypal shapes:negative exponential,unimodal,rotated sigmoid,bimodal,concave,or *** three of the 81 observed DDTs deviated by50%(maximum 83%).Within each stand,five to ten predominant DDTs were observed,which deviated from the stand average by 30-48%and were characterized by two to five different archetypal ***,in some stands the majority of tree neighborhoods were best characterized by a different shape from that assigned at the stand *** from the stand average increased from the youngest stand in the mature development stage through the middle stands in the vertical diversification stage to the oldest stands in the horizontal diversification *** complexity of DDT shapes tended to increas

关键词： Diameter distribution type Floating neighborhood Restoration silviculture Small-scale Structural complexity

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Soil physical properties degrade further on sk.d trails in the year following operations

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Journal of Forestry Research 2018年第1期29卷 93-101页

作者： Ramin Naghdi Ahmad Solgi eric k.zenner Farshad k.ivan Behjou Department of Forestry Faculty of Natural Resources University of Guilan Department of Ecosystem Science and Management Penn State UniversityUniversity Park Faculty of Agricultural Technology and Natural Resources University of Mohaghegh Ardabili

Short-term recovery of soil physical properties on sk.d trails was investigated upon cessation of sk.dding operations and 1 year later. Bulk.density and porosity were assessed at three levels of traffic intensity and two slope gradients. Compared to undisturbed areas, bulk.density increased, total porosity and macroporosity decreased, and microporosity increased in the compacted areas immediately after sk.dding. In all cases, changes were significantly greater when traffic intensity was higher and when slopes were steeper. Surface soil compaction did not show any recovery over the 1-year period, illustrating the persistent effects of compaction on soil structure. In fact, surficial compaction further increased and macroporosity further decreased after 1 year of recovery, compared to immediately after sk.dding. While these changes may reflect inherent small-scale site variability or differences in soil moisture content at times of sampling, direct negative physical impacts on newly exposed soil（such as by raindrops）, in addition to the loss of organic matter after canopy removal and sk.dding, lik.ly delayed any physical recovery, particularly on heavily traffick.d trails on steeper slopes. These results raise serious concerns about longterm resilience to traffic on forest soils and indicate the necessity to properly retire sk.d trails to avoid further soil degradation as trails age.

关键词： Compaction Porosity Recovery Sk.d trail slope Traffic frequency

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