Nursery management implies quality, productivity and economy of stock production. Seedlings quality is the first and most important parameter and other two should be subdued to the quality. As we are talking about the "optimum" seedling it should not be some abstract category. Optimum means the best possible result or highest degree which can be obtained in given conditions. In that light if we want to establish "optimum" seedling for use in reforestation we should start from conditions for reforestation on the given site. The critical environmental factors that limit survival and growth on specific outplanting site must be defined , and then tests that will determine how seedlings will respond to those factors must be applied. It also understands the definition of critical thresholds for optimal performance under specific site conditions. Long time ago, seedling quality has been defined as a "fitness for purpose". Regardless of how we define quality, or what criteria we use, high-quality seedlings are those that meet defined levels of survival and growth on a specific planting site. To establish seedlings standards on morphological features, height and RCD, hides a lot of risks. The very nature of problem is not how seedlings look but how they perform after planting. The explanation is very simple. Seedling's physiological conditions could be utterly altered from the moment of lifting to the moment of planting, due to stresses that occur. Seedling height might be manipulated through mineral nutrition and "minimum" seedling standards can easily be exceeded. Those seedlings suffer from lack of frost resistance and reduced drought resistance. Seedling standards for plantable seedlings should not be something embossed in a stone, but dynamically and interactive category as seedling quality lies between material attributes (water relations, mineral nutrition, carbohydrate status, bud dormancy, status of growth regulators, morphology) and performance attributes (survival and growth, fulfill of our goals ). Defining seedling standards demands determination of our goals which in turn depend of site conditions. Site conditions set the limits to our goals and the goals and site conditions together determine seedling standards necessary for achievement of our goals. Best regards to everybody David South wrote: > SThis posting is for those interested in discussing silviculture. > > Question: How does one go about determining the "optimum" seedling > for use in reforestation? > > Background: There are many seedling grade studies that have determined > the "minimum" seedling standards for a plantable seedling. Once these > "minimums" are established, nurseries tend to produce seedlings that > are just above the minimum. These seedlings are then (gradually) > accepted as the norm or "ideal." Any seedlings that are larger than > the norm would be "too hard to plant" (read too hard to plant quickly > by hand). Therefore, there is a tendency to reduce cost of seedling > production by producing seedlings near the minimum standards. > > I believe silvicultural research aimed at identifying the "optimum" > seedling for reforestation is lacking. For example, I just read a > paper that used seedlings grown in small containers (313 or 3 cm > diameter with a depth of 13 cm). Much detail was provided in the > paper (except the initial size of the seedlings). After one year in > the field, the diameter growth of the seedlings was less than 1 mm! > IMHO, I doubt these very small seedlings are "optimum" for > regeneration on these sites. Such small seedlings may need a lot of > help in the form of intensive weed control and mechanical site > preparation) in order to get them to grow. > > Of course there are two "optimum" stock types. One is the > biologically "optimum" (performs better than other ideotypes). The > other is the economically "optimum" (produces a higher NPV than other > ideotypes). I expect the "biologically" optimum seedling to have a > larger root mass than the "economically" optimum since the costs > associated with producing, shipping and planting enter into the > equation when determining the "economically" optimum seedling. > > Defining the biologically "optimum" seedling is relatively easy. > Seedlings of various sizes (and conditions) can be produced and > outplanted to determine the best field performance (say at a 2 meter > average height in the field). If the stock with the biggest roots > performs best (no point of diminishing returns identified), the study > is repeated using even larger "balanced" stock (until a plateau or > node is identified). > > A problem with identifying the "economic" optimum planting stock is > taking early growth results and predicting volume (or value) at > harvest. A big stumbling block is a lack of growth models that have > been developed for the establishment phase. One way to get around > this problem is to estimate the "years gained" from establishment. > This simply estimates the time gain from planting larger stock (see > for example: Blake, J.I., L.D. Teeter, and D.B. South. 1989. Analysis > of the economic benefits from increasing uniformity in Douglas-fir > nursery stock. Forestry Supplement 62:251-261). The estimation of > "years gained" is not a precise estimate (may vary with individual) but it seems > to be an accepted method (until adequate regeneration models are developed). > > Costs of site preparation will affect the "biologically" optimum seedling. If > costly methods of site preparation are used, then savings might result by > lowering the intensity of mechanical preparation while increasing the root mass > (and RCD) of the planting stock. For example, planting 12.5 mm stock with a > single bed and no herbicides sometimes does better than planting a 2.5 mm stock > on double beds plus herbicide. (see > www.forestry.auburn.edu/coops/sfnmc/data/ipm.html). > > Conclusion: If studies to determine the "economically" optimum planting > stock have been established, then we may have some confidence that we are not > wasting establishment money on helping small seedlings get established. If we > have not determined the "economically" optimum planting stock, then there is a > good chance we have accepted sub-optimum stock as the norm. > > ============== > > Looking forward to a good internet discussion. > > David South > School of Forestry > Auburn University > > A member of the Forester's Chapter for ZPG > > www.forestry.auburn.edu/people/faculty/biology/south/zpg/forester.html > > As always, views expressed here are my own > (and I am not speaking on the behalf of others). > > I use only 100% post-consumer paper in my home printer. (discarded used office > paper printed on one side) > > ====================================================================== The world > population is expected to double by the year 2100. > Therefore the annual demand for wood for energy (etc.) > will increase and might double (to more than 7 billion m3/yr). To provide > plantation wood for people in the future, > support the planting of trees on pastureland. > Set a goal of converting 8 million ha of pastureland/yr for the next 55 years. > This would increase tree plantations to about 5% of the world's landbase. > ====================================================================== > > Support Zero Population Growth for the United States > > http://www.igc.apc.org/zpg/index.html
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