The word "nature" can mean different things, and any of those meanings can affect or impinge upon music. Discussions here tend to revolve around the nature of knowledge & experience, the nature of assessment, or human nature. In each case, some fundamental quality is indicated, whether inalterable or merely basic. Questions also revolve around whether certain things "naturally" occur, i.e. whether they occur without our intervention. More introspectively, one asks whether ideas & actions occur to us without any self-conscious forcing. We naturally eat, and all indications are that we naturally make music. To combine the two statements, it is of our nature to make music, but we do not necessarily make music naturally. Such a juxtaposition goes to the heart of the perceived separation between man & nature, in this case "nature" meaning the physical world of the universe. Music is connected to the physical world of nature in multifaceted ways, as is any complex human activity, a fact underscored by the use of "nature" to mean a fundamental or basic quality.
The medieval designation of music as a science of the quadrivium makes the connection between nature & music explicit, and such a scientific underpinning is maintained today, in various guises. While Boethius' notion of a hierarchy of musical activity proceeding from the "music of the spheres" has little currency, the mathematical description of symmetries & cycles certainly does. Music as vibration is totally amenable to such a description, and indeed the proportions inherent to musical intervals — as well as what we might call the grammar of music — continue to be discussed actively in this manner. In a world of tremendous traditional variety, the physics & physiology of sound are increasingly discussed in this manner, lending themselves to almost desperate attempts to unify differing cultural theories of musical value. Beyond the mathematical-physiological analysis of sound as an artefact, we can begin to grasp at questions such as: What is the structure and scope of music which humans "naturally" create? In this case, as in similarly motivated studies, the field of inquiry is restricted to "musically naïve" individuals, as the essence of music as art would mean immediate conflation of any boundaries. Moreover, any such study will eventually undo itself, as people learn & ponder its results.
We consider it possible to act unnaturally, and consider study & analysis unnatural. So be it. Retreating from the arena of humanity, let us consider "musical sounds" in nature per se. Birdsong has been a direct inspiration, as has whale song more recently, as well as sounds from other natural phenomena which we might not so readily identify as "musical." A clap of thunder can serve as punctuation, at least. Indeed, the sounds which we "naturally" hear are connected — quite evidently & directly — to the sounds which we are able to hear and understand. They frame our experience. And with the advance of industrial noise, together with the corresponding retreat of silence, our sonic frame of reference shifts. Contemporary style has reflected that shift, sometimes in provocative ways. Again, however, such a reflection is considered to be beyond the scope of "nature." We want nature to be something we observe, perhaps inspiring us. We want it to be a refuge from the industrial world, ironically from the same technology which was designed to protect us from the ravages of nature.
What then of natural inspiration and natural beauty in general? The idea that a scene might inspire an explicit sonic representation is far from new, expressed most clearly in the ancient Chinese qin repertory, but also in Western tone poems & other fashionable exhibitions of naturalism. (Indeed, the genesis of French impressionism is often linked to contact with oriental culture.) Nature might inspire us less directly too. The very idea of "inspiration" suggests a reference to nature, as it indicates a spark from outside of non-nature, the latter being the frame of our intellectual self-consciousness. Nature is always seen as a way around self-consciousness, if not as an outright escape from modern life & analysis. Nature can reintroduce us to human frailty, and still awe us with its power. It can demand our full attention in order to survive, quickly dispersing any vanities. It can provide perhaps the clearest glimpse of rite as omnipresent. Moreover, it can lend a sense of perspective, and a sense of perspective — a perspective — is precisely what we need in order to construct a scheme for aesthetic evaluation. We have a keen sense of what makes a landscape beautiful, even if it cannot be articulated, and such appreciation of nature is necessarily reflected in our assessment of musical quality. For instance, we might use terms such as grand, balanced, vibrant, flowing, or subtle in either case. And to which is the reference more immediate?
If musical assessment arises partly out of some underlying sense of natural beauty, what then of differing assessments — whether cultural or individual? One simplistic answer is that different cultures are often immersed in different natural landscapes. Flora, fauna, seasons, terrain... all can be different. What seems beautiful to one might seem mundane or frightening to another. This notion is probably something of a stretch, but when it comes to individual preferences, the different ways in which people relate to the natural world can perhaps be telling. The preference, for instance, that music be an escape from daily life could be compared to one's views on nature in relation to the industrial world. The position of "nature" in the world, whether as something to be feared or revered, is increasingly one of conflict. That conflict is more than merely an argument over resource usage, but goes to the heart of our nature with respect to nature. While the wild can be frightening, there is an animal magnetism to it as well. It is difficult to fear musical beauty in this way. Indeed, it is difficult for music to present itself as all-encompassing — it functions more as a gateway to other ideas or realities. Of course, it is possible for music to fill all of the senses, but not by merely listening. One must make music for oneself. That sort of "full sensuality" can be related to the transcendence of recognition, in which the rest of the world simply melts away. At that point, there is no nature, but at more mundane times, music is less immediate. It is more likely to reflect nature than to subsume it.
Between whistling a tune & postmodern analysis, music neatly reflects both the natural & "unnatural" aspects of human activity, leaving plenty of doubt regarding that boundary. As the modern world increasingly views nature as something apart from itself, there is a tendency to view music as something apart from us too.