تجزیه و تحلیل اقتصادی بهره برداری و بازسازی در طرح هایی با بهره وری وب سایت مشکل ساز

Although intensive managed plantations clearly increase the growth and yield of forests several papers refer to declining forest productivity. Therefore in this paper we study the impact of declining forest productivity on the land expectation value and the optimal rotation length. We start from the research by Lu and Chang (1996) and try to fill the gap between the stable site productivity (“best”) and the site mining (“worst”) cases. For that we extend the classical Faustmann model by availability of different recovering technologies. In general the model allows the analysis of the two plantation groups: “mining the site by high productive plantation followed by management of degraded areas” and “high productive plantation and regeneration cycling” with the same comparative static. The model, analysis and comparison with the two extreme cases in Lu and Chang (1996) leads to a detailed understanding of land use management when site productivity decline is possible. Particularly the relation between declining periods with intensive land use and land use alternatives after declining periods with regeneration can be well understood. Findings are: Not ever declining process asks for regeneration. Many declining processes can be stopped at early times by high cash flows after mining periods. Shortenings of the regeneration time can boost site mining intensities.

In 2005 the total amount of forest plantation area worldwide was 187.5 million hectares. While in most developed countries in the non-tropical zones investments in industrial forest plantations are reduced, the total tropical forest plantation areas more than doubled in the period 1995–2005 (ITTO, 2009). Although intensive managed plantations clearly increase the growth and yield of forests several papers refer to declining forest productivity (DFP): Fox (2000) explains the link between different factors affecting the productivity of plantation forests and shows how different management practices can decrease or increase the site productivity. Smith (1994) focuses on the effect on plantation management to soil fertility. He mainly deals with tree removals and harvest machinery effects in relation to different soil types. Corbeels et al. (2005) examine long-term changes in productivity of eucalyptus plantations under different harvest residues and nitrogen management practices with help of a modelling analysis. They show that the productivity in such short-rotation plantations over multiple rotations can be problematic. Theirs simulations suggest that retention of harvest residues is helpful for maintaining forest productivity, but that applications of nitrogen fertiliser will be necessary to maintain current levels of productivity in the long run. Nevertheless DFP may also play an important role in boreal forests (e.g. MacLellan and Carleton, 2003) and in temperate zone forests (Fiedler, 1990). Moreover, a similar declining productivity is observed in agriculture plantations with perennials such as sugarcane (Keertipala and Dharmawardene, 2000). Fortunately in the last two decades extensive empirical research on site management led to detailed and better understanding of sustained productivity in tropical and subtropical plantation forests (e.g. Nambiar, 2008 and Nambiar et al., 2004). Nambiar and Kallio (2008) pointed out that no major risks to soils were identified which cannot be managed by scientifically based practices. Commonly used technologies of forest plantation management to reduce or to prevent DFP are retention of tree residues (Corbeels et al., 2005, Vitousek and Matson, 1985, Tiarks et al., 2004 and Yamada et al., 2004), site preparations (Gresham, 2002, Vitousek and Matson, 1985 and Shaohui et al., 2000), fertilization (Corbeels et al., 2005, Yamada et al., 2004 and Fox, 2000) and irrigation (Stape et al., 2010). Many of the described technologies for preventing DFP reduce the land expectation value (LEV) owing to the raise of cost or lower revenues. Therefore different researchers and scientists assume that management practices with DFP are rational actions of forest owners in respect to the level of interest rates (e.g. MacLellan and Carleton, 2003) according to the numerical example of the farmer, miner and forester in the famous Interest Theory by Irving Fisher (1930, p. 133 and sqq.). For this reason MacLellan and Carleton (2003) plot out so called “productivity investment frontiers” to show under which discount rate the forest owner moves from a constant site productivity concept to a concept including DFP. However between constant and declining site management practices a lot of intermediate concepts are worth considering to reduce or to neutralize DFP. One example is to start with declining forest management in a high productivity class and change in a more extensive land management after some declining (e.g. Makeschin et al., 2008). Another land use similar to shifting cultivation and improved fallows as in agroforestry (Nair, 1993) is conceivable. Also “crop rotation” as a change of two forest types A and B, in which A represents a high productivity but also a high DFP rate and B stands for a low productive forest type however with a soil regeneration potential is worthy of mentioning. All these intermediate concepts are not very common in forest plantation management however they are well known in agriculture since a long time. By the way agriculture traditionally has long experiences with “short-rotation” over multiple rotations. Therefore it is useful at this point to recall that forest short-rotation plantations move closer to agriculture then to the traditional long-term forestry. In intensive managed plantations rotation ages between 5 years (eucalyptus) (Diaz-Balteiro and Rodriguez, 2006) and 25 years (pine) are common (ITTO, 2009). Tiarks et al. (2004) refer rotation ages between 6 (Eucalyptus urophylla, Guangdong, China; Acacia mangium, Riau, Indonesia) and 30 years (Pinus elliottii × P. caribaea, Queensland, Austalia). Sedjo (1999, p. 19) reckons that future rotations in US fiber farms will be shorter than 5 years. Not surprisingly, managers and researchers dealing with forest short-rotation plantations publish “agricultural” practices for forest plantations. Liu and Li (2010) study ecological problems of eucalyptus plantations in Maoming Xiaoling (China). They find crop rotation (tree–tree, tree–crop) and interplanting of eucalyptus plantations and crops as DFP countermeasures. Lukaszewicz and Olszowska (2003) study crop rotation of six forest tree species in forest nurseries and find positive effects on the soil enzymatic activity. Even Atkinson et al. (1979) refer that crop rotation of Douglas-fir and red alder shows considerable promise to profitability. In this paper we focus on the analysis of the intermediate concepts in forest short-rotation management to reduce or to neutralize DFP by filling the broad gap between the constant and the declining concepts as the two extreme points in a continuum. Fig. 1 shows the intermediate concept embedded into the two extremes.The constant net revenues conceptual type assumes that forest managers have found a concept to stabilize the site productivity by retention of tree residues, fertilization and similar technologies. This is the classical Faustmann concept under consideration of site stabilization technologies. Another conceptual type is to do nothing against DFP. This concept we call the site mining type, because forest plantation would manage as long as site productivity leads to satisfactory results. In the third conceptual type a highly profitable but site quality consuming production period and a less profitable but site quality improving regeneration period alternate. We call this type site recovering type. One should be mentioned that the down and up of the site recovering type in Fig. 1 is an example for only one possible structure. Other kinds of down and up are feasible too. The aim of this paper is to analyse the site recovering conceptual type of site productivity management and to compare the results with the results of both, the classical Faustmann model and the site mining model. Previous papers studied the impact of DFP on the land expectation value (LEV) (Faustmann, 1849): Routledge (1987) examined the effect of destructive logging technologies with the help of a modified Faustmann model. Lu and Chang (1996) worked with a “best” and a “worst” case scenario. Also, they studied the lengthening of the rotation age and land fertilization of land as two common approaches for reducing DFP. In this paper we follow the vein of the research by Lu and Chang (1996) where the “best” case is modelled by LEV=[V(t)−Pert](ert−1)−1LEV=[V(t)−Pert](ert−1)−1 with V ′(t ) = rV (t ) + rLEV and the “worst” case is: LEV=[V(t)−Pert](ert)−1LEV=[V(t)−Pert](ert)−1 with V′(t) = rV(t). The LEV represents the land expectation value, V is the forest stand value, t is the rotation age, P represents the regeneration cost, r is the interest rate. It is easy to see, that the “best” case model works with full and constant site productivity. In our language above the first model represents the constant site type, the second model represents the site mining type. In the following we extend the Lu-Chang-approach to the third concept, the site recovering type. As helpful basic examples, we used models for coppice forestry (Medema and Lyon, 1985 and Tait, 1986) as models with a mathematical treatment of production declining. Also helpful was the material of improvements in biotechnology (e.g. Johansson and Löfgren, 1985, p. 102 and sqq.; Löfgren, 1985). A second related approach is the model family which studies the optimal forest rotation period with evolving prices (e.g. Newman et al., 1985). This supports our structuring because between the mathematical analyses of price changes over time and the mathematical analyses of stock changes over time exist close connections (compare also Johansson and Löfgren, 1985, p. 27 and sqq.). However, the ability to our aim is limited because this model family analyses evolutions in only one direction. Also we cannot work with rotations alone but with production or regeneration periods, which means a single period can be composed of more than one rotation. Lastly, site productivity will decline depending on the intensity and the length of production as an internal result of plantation management whereas the price process is entirely external. A third helpful approach is the determination of the optimal cutting cycle for uneven-aged forest stands (e.g. Chang, 1981) because this kind of analysis considers downs and ups in the stock. The limitation here is that we cannot model the inner structure of the cycle. In summary we would like to analyse the site recovering type by focusing on the cycling between intensive production with declining site productivity and site regeneration phase however with less intensive production.

The analysis in this paper is only of interest in cases where DFP appears. In many other situations worldwide DFP is unimportant and the classical Faustmann analysis is correct and sufficient. Moreover in many parts of the world forest plantations have been established on degraded agricultural or pasture land. The productivity of several of these sites is degraded so much that they could no longer be used for the production of crops and livestock. Under these circumstances intensive forest plantations can even improve site quality and increase the site productivity (Fox, 2000). The economic study of such situations can be done with the analysis style of improvements in biotechnology (e.g. Johansson and Löfgren, 1985, p. 102; Löfgren, 1985). Also the analysis and the results of the optimal forest rotation period with evolving prices (e.g. Newman et al., 1985) are applicable with some carefulness. DFP is particularly problematic if it appears but is not anticipated. In such situations plantation management according to the Faustmann classic fails. LEVs are too high and determined rotation ages are too short. The smaller the interest rate the worse this error becomes. Although this problem can be of great interest and a qualified monitoring of site productivity is important it is beyond the scope of this paper. Instead we would like to address to the experts of soil science and site ecology and focus on the field where DFP is anticipated. The analysis of this paper should open the eyes to the broad spectrum of recovering technologies between the constant site productivity type and the site mining type. These concepts are less common in plantation forestry however widely-used in agriculture for a long time. Plantation forestry is more closely related to agriculture then to the traditional long-term forestry. Therefore we would like to indicate the importance of such recovering concepts to expand the frontier between constant site management and site mining of forest plantation management as we analysed above. Moreover the “critical” interest rate, where plantation management drops into site mining can be affected by the choice of the regeneration technology (α), the level of the initial establishment costs for regeneration (C) and the cash flow during the regeneration period (b). In search of practicable and profitable recovering concepts we found some relations which maybe helpful for appropriate developments and studies in plantation management: