A non-stochastic portfolio model for optimizing the transformation of an even-aged forest stand to continuous cover forestry when information about return fluctuation is incomplete

Key message

Non-stochastic portfolio optimization of forest stands provides a good alternative to stochastic mean-variance optimization when available statistical data is incomplete. The suggested approach has a theoretical background in the areas of robust optimization, continuous multicriteria decision-making, and fuzzy theory. Resulting robust portfolios only show slight economic losses compared to the efficient frontier of a stochastic optimization.

Context

Economic optimization addressing diversification in mixed uneven-aged forest stands is a useful tool for forest planners.

Aims

The study aims to compare two approaches for optimizing rotation age cohort portfolios under risk. Rotation age cohorts emerge from age-based regeneration-harvesting operations simulated for two tree species: Picea abies and Fagus sylvatica.

Methods

The first optimization approach is a stochastic mean-variance approach. The second is a non-stochastic optimization approach, which has rarely been applied to optimize tree species composition and the distribution of harvested timber over many periods. It aims at relatively good solutions, even if the deviation from the initially assumed return is very high. The objective function for both approaches is sensitive to the selection of various harvesting periods for different parts of the stand. For the stochastic approach, the objective function maximizes the annuitized net present value (economic return) for specific levels of risk by allocating area proportions to harvesting periods and tree species. In the non-stochastic approach, the allocation of area proportions instead minimizes the maximum deviation from the greatest possible economic return among many uncertainty scenarios (non-stochastic approach).

Results

Portfolios from both approaches were diverse in rotation age cohorts. The non-stochastic portfolios were more diverse when compared with portfolios from the efficient frontier, which showed the same standard deviation. However, P. abies clearly dominated the non-stochastic portfolios, while stochastic portfolios also integrated beech to a greater extent, but only in very low risk portfolios. The economic losses of the non-stochastic portfolios compared to the efficient frontier of the mean-variance approach lay between 1 and 3% only for different levels of accepted risk.

Conclusion

The non-stochastic portfolio optimization over a large uncertainty space is so far uncommon in forest science, yet provides a viable alternative to stochastic optimization, particularly when available data is scarce. However, further research should consider ecological effects, such as increased resistance against hazards of conifers in mixed stands.

     

Long-Term Effect of Nitrogen and Tillage Management on Soil Carbon Pools in the Semiarid Northern Great Plains

No-tillage and manure application effect on soil organic carbon (SOC) and total nitrogen (N) concentrations were studied under a 27-year-old 4-year rotation consisting corn (Zea mays L.)-soybean (Glycine max L.)-wheat (Triticum aestivum L.)-field pea (Pisum sativum L.). Under each crop, four applied N treatments were control, annual urea-N applications at the rate of 45 and 89 kg N ha^?1, and composted beef cattle feedlot manure-N at the rate 179 kg N ha^?1 applied once every four year. For each fertilizer treatment, no-till (NT) and conventional till (CT) were compared for basic soil properties, SOC, and total N within 0–15 cm soil. Manure application significantly reduced soil bulk density and increased SOC and total N over urea-N. Particulate organic matter, mineralizable N, and permanganate-oxidizable C fractions significantly related with SOC. Long-term manure additions and no-tillage had potential to improve soil compaction and maintain SOC over chemical fertilizer N and CT.     

Variations in the immune response to natural Schistosoma mattheei infections in calves born to infected mothers

During previous work Schistosoma antibodies and circulating antigens were detected at birth in the serum from some calves born to Schistosoma mattheei infected mothers. The objectives of the present survey were: (1) to investigate the proportion of calves, born to cows infected with S. mattheei, which have specific antibodies and circulating schistosome antigens present in their serum at birth and (2) to investigate whether the presence or absence of these specific antibodies and/or circulating antigens at birth may affect the pattern of a natural S. mattheei infection in calves from 4 to 5 months of age, when the colostral antibodies are thought to be of negligible importance. A total of 28 calves born to infected mothers were randomly selected. Faeces, serum and colostrum samples were collected from the cows at calving, serum samples were collected from the calves at birth (day 0), after intake of colostrum (day 1) and monthly thereafter up to the age of 10 months. Both serum and colostrum samples were analysed for IgG(H+L) against SWAP mattheei and schistosome circulating anodic antigen (CAA) levels. The calves were exposed to a natural challenge from the age of 4-5 months. Faecal samples were collected from the calves monthly, starting at an age of 5 months up to 10 months, and were examined for faecal egg counts. Nine (group 1) out of the 28 calves were found to have specific antibodies in their serum at birth, in 5 of them CAA levels were also detected. In the other 19 calves (group 2) no IgG(H+L) or CAA were detected. At the end of the study faecal egg counts and CAA levels were significantly lower in calves from group 1 compared to group 2. Results confirm earlier work that specific antibodies and circulating antigens may be present in serum from calves at birth, and show that these calves have lower faecal egg counts and CAA levels after exposure to a natural challenge.