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  • existence theory  (3)
  • Pseudotsuga menziesii  (2)
  • 1
    Electronic Resource
    Electronic Resource
    Direct impacts of sheep upon Douglas-fir trees in two agrosilvopastoral systems (1992)
    Springer
    Agroforestry systems 19 (1992), S. 223-232 
    Details
    ISSN: 1572-9680
    Keywords: agroforestry ; browsing ; debarking ; sheep ; deer ; Pseudotsuga menziesii
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Livestock may provide important service and production functions in agroforestry systems. However, use of livestock in conifer/improved pasture agrosilvopastoral systems is currently limited by concerns about potential damage to trees by livestock. Effects of sheep grazing on Douglas-fir (Pseudotsuga menziesii) trees in two patterns of sheep/pasture/conifer agroforest (cluster and grid plantations) were studied from 4 years after planting (1983) until the first precommercial thinning at age 10 years (1988). Trees averaged over 1 m in height when grazing began in summer 1983. Some browsing of tree lateral branches by sheep occurred regardless of grazing season in 1983–1985. However, the 2 to 10% of current year's lateral branch growth removed by grazing sheep was too low to impact tree growth. Sheep removed the terminal leaders from only 3 to 9% of trees each year during 1983–1985. Most browsing of terminals occurred in the summer when other forages had become mature and were relatively unpalatable to sheep. Less than 13% of agroforest trees were debarked by sheep each year during 1983–1987. By the end of grazing in 1987, less than 8% of agroforest trees had sustained a level of debarking likely to impact future growth (〉50% of tree circumference debarked). Grazing had no discernible effect upon tree diameter or height in any year (P 〉 0.05). Total tree mortality attributable to sheep grazing during 1983–1987 was only 0.9%, including three trees girdled by sheep and two debarked trees which were subsequently attacked by insects. Overall, grazing had no detrimental impact on timber stand growth or mortality.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00118780
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  • 2
    Electronic Resource
    Electronic Resource
    Productivity of two Douglas fir/subclover/sheep agroforests compared to pasture and forest monocultures (1996)
    Springer
    Agroforestry systems 34 (1996), S. 305-313 
    Details
    ISSN: 1572-9680
    Keywords: spatial pattern ; silvopastoral ; intercropping ; polyculture ; Pseudotsuga menziesii ; Trifolium subterraneum
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Resource sharing between tree and forage plant components in silvopastoral systems includes a complex set of facilitative and competitive interactions. To the extent that facilitation exceeds competition, agroforests are expected to outyield monocultures of their components. Pasture and Douglas fir (Pseudotsuga menziesii) tree production of young agroforests was compared to pasture and forest monocultures under both grid and cluster patterns of tree planting near Corvallis, Oregon, USA, during 1983–1987. The height and diameter growth of forest and agroforest trees was similar, regardless of tree planting pattern. Five-year average annual forage production was 6500, 5800, and 2800 kg ha−1 on pasture, agroforest, and forest plots, respectively. The total cumulative 1982–1987 above-ground phytomass yield of forage plus trees was similar for pasture and conventional grid forest monocultures. The total productivity of agroforests, however, was over 30% greater than either pasture or forest components grown in monoculture. Approximately 1.6 ha (0.96 ha forest + 0.64 ha pasture) of monocultures would be needed to equal the productivity of 1 ha of agroforest.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00046930
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  • 3
    Electronic Resource
    Electronic Resource
    On the existence of catching-up optimal solutions for Lagrange problems defined on unbounded intervals (1986)
    Springer
    Journal of optimization theory and applications 49 (1986), S. 207-225 
    Details
    ISSN: 1573-2878
    Keywords: Optimal control ; existence theory ; catching-up optimal solutions ; infinite-horizon problems
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Abstract In this paper, we are concerned with the question of the existence of optimal solutions for infinite-horizon optimal control problems of Lagrange type. In such problems, the objective or cost functional is described by an improper integral. As dictated by applications arising in mathematical economics, we do nota priori assume that this improper integral converges. This leads us to consider a weaker type of optimality, known as catching-up optimality. The results presented here utilize the classical convexity and seminormality conditions typically imposed in the existence theory for the case of finite intervals. These conditions are significantly weaker than those imposed by other authors; as a consequence, their existence results are contained as special cases of the results presented here. The method of proof utilizes the Carathéodory-Hamilton-Jacobi theory previously developed by the author for infinite-horizon optimal control problems.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00940757
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  • 4
    Electronic Resource
    Electronic Resource
    Existence of finitely optimal solutions for infinite-horizon optimal control problems (1986)
    Springer
    Journal of optimization theory and applications 51 (1986), S. 41-62 
    Details
    ISSN: 1573-2878
    Keywords: Optimal control ; existence theory ; finite optimality ; infinite horizons ; continuous dependence
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Abstract In this paper, we investigate the existence of finitely optimal solutions for the Lagrange problem of optimal control defined on [0, ∞) under weaker convexity and seminormality hypotheses than those of previous authors. The notion of finite optimality has been introduced into the literature as the weakest of a hierarchy of types of optimality that have been defined to permit the study of Lagrange problems, arising in mathematical economics, whose cost functions either diverge or are not bounded below. Our method of proof requires us to analyze the continuous dependence of finite-interval Lagrange problems with respect to a prescribed terminal condition. Once this is done, we show that a finitely optimal solution can be obtained as the limit of a sequence of solutions to a sequence of corresponding finite-horizon optimal control problems. Our results utilize the convexity and seminormality hypotheses which are now classical in the existence theory of optimal control.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00938602
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  • 5
    Electronic Resource
    Electronic Resource
    On the existence of sporadically catching-up optimal solutions for infinite-horizon optimal control problems (1987)
    Springer
    Journal of optimization theory and applications 53 (1987), S. 219-235 
    Details
    ISSN: 1573-2878
    Keywords: Optimal control ; existence theory ; sporadically catching-up optimality ; infinite-horizon optimal control problems
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Abstract In this paper, we extend the existence theory of Brock and Haurie concerning the existence of sporadically catching-up optimal solutions for autonomous, infinite-horizon optimal control problems. This notion of optimality is one of a hierarchy of types of optimality that have appeared in the literature to deal with optimal control problems whose cost functionals, described by an improper integral, either diverge or are unbounded below. Our results rely on the now classical convexity and seminormality hypotheses due to Cesari and are weaker than those assumed in the work of Brock and Haurie. An example is presented where our results are applicable, but those of the above-mentioned authors do not.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00939215
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    Paper (German National Licenses)
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