What problems still exist in using natural regeneration?

Natural regeneration of forests and woodlands is the process by which new trees grow from seeds that have fallen and germinate where they have fallen.  The biggest problem with natural regeneration is that is unpredictable.  As a result, it cannot be used for commercial farming. For most of the last two or three hundred years, forests and woodlands have restocked by using transplants grown in nurseries. The young trees are planted in equidistant rows. This allows each tree the best possible change of optimal growth. 

When a virus infects a host cell, it uses the cell's machinery to make copies of its own genetic material in a process called replication. finally, during the process of self-assembly, that protein shell and the copies of the virus's genetic material are assembled into new viruses.