Hello! This sentence is a little difficult to give you a definitive definition of what you are asking. It is very context specific. If you had asked what this meant without the context of the sentence I would have assumed "return drafts" related to returning a draft of some sort or something like that. This is something you cannot understand simply by the definition of the individual words, and putting the two words together, yet separated from the rest of the sentence, would not work as well. The sentence allows some context to the definition of the phrase, though more context may help more. This sentence talks about energy expenditure and the environment. The phrase "return drafts" relates to how energy expended can be replenished. Therefore, first we must understand what the "expenditure of energy" actually means. Energy expenditure is the amount of energy needed to carry out a specific "thing." In this case, that "thing" might relate to the energy expended in relation to the environment. Therefore, "energy expended can be replenished only as the activities performed succeed in making 'return drafts' upon the environment" relates to the fact that in order to replenish these expenditures, one must return what was expended. These "return drafts" may relate to the idea of planting a tree for each tree that is cut down. Or it may relate to recycling or reusing plastic after use. The phrase "the only source of restoration" also aids in understanding the phrase. These "return drafts" are needed for restoration, and from this author's viewpoint, this is the only source of restoration. Therefore, restoration cannot possibly be obtained in any other way, pointing to the fact that it is an opinion. Hopefully this helps. It is a little difficult to deconstruct the meaning without more, but this summarizes what I understand from the sentence.

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