Wiktionary
natural reserve
n. An area of land managed to conserve wildlife or plant habitat or other natural features.
Usage examples of "natural reserve".
It came with all the ardour which was the accumulation of long years behind a natural reserve.
If he hadn't been so callous as to ignore what he'd thought was a natural reserve rather than sexual fear.
Abdul was still slender, and though he had of necessity overcome his shyness, he had a natural reserve that kept him distant from his customers.
His natural reserve of spirit had returned in recent weeks and had deepened greatly, so that he seemed now not merely aloof and private, but bleak and lost in some terrible realm of his soul.
But a natural reserve, and the fact that every man present was known to be an expert with a gun, deterred them.