Optimizing any-aged management of mixed-species stands. I. Performance of a coordinate-search process

1990 ◽  
Vol 20 (1) ◽  
pp. 15-25 ◽  
Author(s):  
Robert G. Haight ◽  
Robert A. Monserud
Keyword(s):  
Size Structure ◽  
Timber Harvesting ◽  
Stand Age ◽  
Solution Technique ◽  
Search Process ◽  
Mixed Species ◽  
Wide Diameter ◽  
Single Tree ◽  
Starting Point ◽  
Time Problem

Optimal any-aged management problems for mixed-species stands have been solved for the first time. Problem formulation calls for periodic planting and harvesting controls to be applied without constraints on the stand age or size structure over time; classical definitions of both even- and uneven-aged management are, thus, subsets of this general any-aged management definition. The solution technique is a derivative-free, coordinate-search process called the method of Hooke and Jeeves. The optimizer incorporates without modification the Stand Prognosis Model, a single-tree simulator that is used extensively in the western United States. This paper focuses on sensitivity analysis and performance of the optimizer on problems with both short and long time horizons and with different definitions of the harvest controls. Superior harvest regimes are found by defining harvest controls with relatively wide diameter-class boundaries and with broad species groups. In all cases examined, there is variability in present value and harvest pattern associated with the choice of the starting point for the optimizer. The cause of these multiple optima is a nonconvex and discontinuous response surface produced by the single-tree simulator. This points out the need to examine the results from several random starts before making conclusions about optimal timber harvesting.

How Starting Strategy and Network Structure Shape Problemistic Search: An Examination of Venture Capital Firms

2021 ◽  
pp. 104225872110335
Author(s):  
Jake Duke ◽  
Taha Havakhor ◽  
Rachel Mui ◽  
Owen Parker
Keyword(s):  
Venture Capital ◽  
Network Structure ◽  
Theory Of The Firm ◽  
Behavioral Theory ◽  
Organizational Strategy ◽  
Search Process ◽  
Strategy Research ◽  
Structural Holes ◽  
Starting Point ◽  
Venture Capital Firms

Building on the behavioral theory of the firm, we empirically examine how starting strategies and syndication networks can influence venture capital (VC) firms’ problemistic search. We propose that: (a) depending on a VC’s strategic starting point, that is, the VC’s extent of specialization, the directionality of problemistic search may change to either expanding or contracting search activities; and (b) depending on search direction, structural holes in syndication networks can either impede or facilitate the problemistic search process. In a sample of U.S. VC firms, we find results consistent with our predictions, which have important implications for entrepreneurship and organizational strategy research.

Fifty years of partial harvesting in a mixed mesophytic forest: composition and productivity

2004 ◽  
Vol 34 (5) ◽  
pp. 985-997 ◽  
Author(s):  
Thomas M Schuler
Keyword(s):  
Forest Management ◽  
Sugar Maple ◽  
Acer Rubrum ◽  
Timber Harvesting ◽  
Red Oak ◽  
Northern Red Oak ◽  
Single Tree ◽  
Periodic Growth ◽  
Mesophytic Forest ◽  
Single Tree Selection

Long-term silvicultural trials contribute to sustainable forest management by providing a better scientific understanding of how forest ecosystems respond to periodic timber harvesting. In this study, species composition, diversity, and net periodic growth of tree species in a mixed mesophytic forest in the central Appalachians were evaluated after about a half century of management. Three partial cutting practices on 18 research compartments and on 3 unmanaged reference compartments were evaluated (1951–2001) on 280 ha. Single-tree selection, diameter-limit harvesting, and timber harvesting in 0.162-ha patches were assessed on three northern red oak site index50 (SI) classes: 24, 21, and 18. Shannon–Weiner's diversity index (H′) declined from the first (1951–1959) to last (1987–2001) measurements and was related to both SI (P = 0.004) and treatment (P = 0.009). Sugar maple (Acer saccharum Marsh.) and red maple (Acer rubrum L.) were the two most abundant species in recent years (1987–2001); in contrast, in initial inventories (1951–1959), northern red oak (Quercus rubra L.) and chestnut oak (Quercus prinus L.) were most abundant. Net periodic annual increment (PAI) of merchantable trees (DBH ≥12.7 cm) was related to both SI (P = 0.004) and treatment (P = 0.003). Mean PAI ranged from 4.6 m3·ha–1·year–1 for single-tree selection to 2.5 m3·ha–1·year–1 for unmanaged reference areas across all SI classes. The decline of oak species suggests that only intensive and specific forest management focused on maintaining oak species can obtain historical levels of diversity.

From single-species advice to mixed-species management: taking the next step

2004 ◽  
Vol 61 (8) ◽  
pp. 1398-1409 ◽  
Author(s):  
Morten Vinther ◽  
Stuart A. Reeves ◽  
Kenneth R. Patterson
Keyword(s):  
North Sea ◽  
Fishery Management ◽  
Single Species ◽  
Mixed Species ◽  
The North ◽  
Recent Approach ◽  
Starting Point ◽  
The North Sea ◽  
Management Advice ◽  
Management Priorities

Abstract Fishery management advice has traditionally been given on a stock-by-stock basis. Recent problems in implementing this advice, particularly for the demersal fisheries of the North Sea, have highlighted the limitations of the approach. In the long term, it would be desirable to give advice that accounts for mixed-fishery effects, but in the short term there is a need for approaches to resolve the conflicting management advice for different species within the same fishery, and to generate catch or effort advice that accounts for the mixed-species nature of the fishery. This paper documents a recent approach used to address these problems. The approach takes the single-species advice for each species in the fishery as a starting point, then attempts to resolve it into consistent catch or effort advice using fleet-disaggregated catch forecasts in combination with explicitly stated management priorities for each stock. Results are presented for the groundfish fisheries of the North Sea, and these show that the development of such approaches will also require development of the ways in which catch data are collected and compiled.

scholarly journals Modelling Bark Thickness of Norway Spruce (Picea abies Karst)

2019 ◽  
Vol 10 (2) ◽  
pp. 125-135
Author(s):  
Jusuf Musić ◽  
Velid Halilović ◽  
Jelena Knežević ◽  
Admir Avdagić ◽  
Aida Ibrahimspahić ◽  
...  
Keyword(s):  
Norway Spruce ◽  
Bosnia And Herzegovina ◽  
Timber Harvesting ◽  
Bark Thickness ◽  
Optimal Model ◽  
Breast Height ◽  
Starting Point ◽  
Mean Diameter ◽  
The Mean ◽  
Actual Method

Background and Purpose: Bark thickness and its share in the volume of roundwood are the most important characteristics of the bark, particularly in the process of timber harvesting, and during scaling of processed logs. Therefore it is very important to have at disposal relatively accurate data regarding these characteristics of bark for particular tree species. The main goal of this paper is to investigate the thickness of the bark and its share in the volume of roundwood of Norway spruce. Materials and Methods: The research was carried out in the area of the Canton 10 of the Federation of Bosnia and Herzegovina and it encompassed 393 trees of Norway spruce from 10 cm to 115 cm of thickness at breast height. Measuring of the mean diameter and double thickness of bark was conducted by section method. In total, 4,647 diameters and bark thicknesses were measured in different relative lengths of stems or in average 10.6 measurements per one stem. Results: As an optimal model for the evaluation of double thickness of the bark of Norway spruce depending on mean diameter of roundwood the function with designated determination coefficient of 0.7142 was selected. The obtained results have confirmed the previously defined relations of investigate characteristics, which are as following: a) with the increase of mean diameter of roundwood (section) double bark thickness is increased from 9.26 mm (thickness class 12.5 cm) to 31.65 mm (thickness class 92.5 cm); b) with the increase of mean diameter of roundwood the share of bark in its volume decreased from 14.26% (thickness class 12.5 cm) to 6.73% (thickness class 92.5 cm). Conclusions: By the actual method of estimating bark thickness or the share of bark in the volume of roundwood of Norway spruce in the forestry of the Federation of Bosnia and Herzegovina a significant error was created which increases with the increase of mean diameter. The obtained results point to the necessity of investigation of these bark characteristics in Bosnia and Herzegovina and represent an inevitable starting point for making adequate tables of bark thickness and its percentage share in the volume of roundwood of Norway spruce.

Effect of decision variable definition and data aggregation on a search process applied to a single-tree simulator

2001 ◽  
Vol 31 (6) ◽  
pp. 1057-1066 ◽  
Author(s):  
Peder Wikström
Keyword(s):  
Tabu Search ◽  
Data Aggregation ◽  
Net Present Value ◽  
Planning Horizon ◽  
Solution Technique ◽  
Search Process ◽  
Decision Variable ◽  
Stand Management ◽  
Harvest Timing ◽  
Execution Times

This paper focuses on how computer execution times and net present value (NPV) are affected by different groupings of tree-selection harvest controls, different procedures to determine harvest timing, and tree data aggregation. The problems related to stand management are viewed as a hierarchy, where the main problem is determining harvest periods and the subordinate problem is determining what trees to cut in a given set of harvest periods. The solution technique is a derivative-free search process, and the objective is to maximize the NPV of harvest revenues for a stand over a given planning horizon. The tree-selection harvest controls are based on diameter and species groupings. The procedure to determine harvest timing is based on Tabu search and fixed cutting cycles, respectively. Sensitivity analysis is performed for a selection of stands in southern Sweden, where each stand is represented by a set of inventoried plots. Both even-aged and uneven-aged management are considered. Solutions improved with the number of decision variables. The Tabu search procedure proved very efficient at determining harvest periods for the even-aged problems. For the uneven-aged problems, fixed cutting cycles approximated the harvest timing problem, but at considerably shorter execution times. It is suggested that aggregated data be used for determining harvest timing, after which, using the original nonaggregated data, the tree-selection problem for a given set of harvest periods can be resolved.

scholarly journals Over- and Underyielding in Time and Space in Experiments with Mixed Stands of Scots Pine and Norway Spruce

Forests ◽  
2018 ◽  
Vol 9 (8) ◽  
pp. 495 ◽  
Author(s):  
Lars Drössler ◽  
Eric Agestam ◽  
Kamil Bielak ◽  
Małgorzata Dudzinska ◽  
Julia Koricheva ◽  
...  
Keyword(s):  
Norway Spruce ◽  
Scots Pine ◽  
Tree Species ◽  
Mixed Forest ◽  
Stand Age ◽  
Mixed Species ◽  
Mixed Stands ◽  
Mixing Effect ◽  
Individual Site ◽  
Study Sites

Pine-spruce forests are one of the commonest mixed forest types in Europe and both tree species are very important for wood supply. This study summarized nine European studies with Scots pine and Norway spruce where a mixed-species stand and both monocultures were located in an experimental set-up. Overyielding (where growth of a mixed stand was greater than the average of both monocultures) was relatively common and often ranged between 0% and 30%, but could also be negative at individual study sites. Each individual site demonstrated consistent patterns of the mixing effect over different measurement periods. Transgressive overyielding (where the mixed-species stand was more productive than either of the monocultures) was found at three study sites, while a monoculture was more productive on the other sites. Large variation between study sites indicated that the existing experiments do not fully represent the extensive region where this mixed pine-spruce forest can occur. Pooled increment data displayed a negative influence of latitude and stand age on the mixing effect of those tree species in forests younger than 70 years.

Undergraduate information behaviors in thesis writing: A study using the Information Search Process model

2016 ◽  
Vol 49 (3) ◽  
pp. 256-268 ◽  
Author(s):  
Dan Wu ◽  
Wanyu Dang ◽  
Daqing He ◽  
Renmin Bi
Keyword(s):  
Undergraduate Students ◽  
Information Search ◽  
Information Seeking ◽  
Process Model ◽  
Information Sources ◽  
Writing Process ◽  
Search Process ◽  
Online Information ◽  
Starting Point ◽  
Thesis Writing

The study investigates whether information-seeking behavior models and theories obtained in previous research are applicable to more complex tasks. It also aims to gather students’ opinions on the importance and helpfulness of various traditional and online information sources in their thesis-writing process. This study would help to develop a better understanding of the roles and impacts of these information sources in the current networked academic infrastructure. Inspired by the Information Search Process model, we divided the process into six stages and conducted three separate surveys that covered students’ feelings, thoughts and actions, as well as other important factors that might affect their behaviors in each of the stages. Our study shows that both the feelings and thoughts of students changed during the different stages of the process, and that they were generally consistent with the descriptions in the Information Search Process model. The study indicates that it is beneficial to use the Information Search Process model as the starting point for studying the student thesis-writing processes. As the outcome of the study, we ultimately proposed a multi-stage model for Chinese undergraduate students’ thesis-writing process.

scholarly journals Sustainable management, earthquake disturbances, and transient dynamics: modelling timber harvesting impacts in mixed-species forests

2012 ◽  
Vol 70 (3) ◽  
pp. 287-298 ◽  
Author(s):  
Georges Kunstler ◽  
Robert B. Allen ◽  
David A. Coomes ◽  
Charles D. Canham ◽  
Elaine F. Wright
Keyword(s):  
Sustainable Management ◽  
Timber Harvesting ◽  
Transient Dynamics ◽  
Mixed Species ◽  
Dynamics Modelling

scholarly journals Effects of Forest Fragment Size and Successional Stage on Mixed-Species Bird Flocks in Southeastern Brazil

The Condor ◽  
2000 ◽  
Vol 102 (3) ◽  
pp. 585-594 ◽  
Author(s):  
Marcos Maldonado-Coelho ◽  
Miguel  Marini
Keyword(s):  
Species Richness ◽  
Size Structure ◽  
Fragment Size ◽  
Southeastern Brazil ◽  
Size Analysis ◽  
Forest Fragments ◽  
Forest Fragment ◽  
Mixed Species ◽  
Successional Stage ◽  
Mixed Species Flocks

Abstract We analyzed patterns of species richness, size, structure, and composition of mixed-species flocks in relation to forest fragment size and forest successional stage during dry and rainy seasons, at the state of Minas Gerais, southeastern Brazil. Three forest fragments (1.7, 50, and 200 ha) were used for fragment size analysis, and two fragments (200 and 300 ha) were used for successional stage analysis. Fragment size and season affected flock richness, size, stability, and composition. In the 1.7-ha fragment, flock species richness, size, and stability were significantly different only during the rainy season. Fragment successional stage also influenced flock richness and size, although season did not. Flock composition also had changes related to fragment successional stage. Fragment geometry seems to be an important factor influencing flock structure and composition.

scholarly journals Spacing and Age Effects on Biomass Production in Red Pine Plantations

1982 ◽  
Vol 58 (5) ◽  
pp. 220-224 ◽  
Author(s):  
I. S. Alemdag ◽  
W. M. Stiell
Keyword(s):  
Pinus Resinosa ◽  
Stem Bark ◽  
Red Pine ◽  
Stand Age ◽  
High Survival ◽  
Single Tree ◽  
Breast Height ◽  
Drying Procedures ◽  
Initial Spacing ◽  
Whole Tree

Data and wood samples were collected from 155 trees in 16 high-survival, unthinned plantations of red pine (Pinus resinosa Ait.) near Chalk River, Ontario, aged 27 to 54 years, with initial spacings of from 1.52 × 1.52 m to 4.27 × 4.27 m. Following standard weighing and drying procedures, ovendry mass values of the whole tree and or their individual components were calculated, and regressions developed to relate mass values to stem dimensions of diameter breast height (d) and total height (h), and to determine what effects the initial spacing and stand age had on those relations. Single-tree equations based simply on d and h gave satisfactory mass estimates only for the whole tree and for the component stem bark. For other components the addition of spacing and age showed successive improvements in the estimates over those provided by d2h alone.

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