All wood flooring reacts to the presence of moisture by changing size and shape. This occurs because the timber is a natural product and cannot be expected to behave in the same way a manufactured product would.
During winter, rooms are often very dry because of constant use of heating systems and this can make wooden floorboards contract slightly which leads to small gaps appearing between boards.
In the summer humidity levels will rise and cause the opposite effect, and as the planks expand the gaps will disappear. If the moisture levels get too high, however, the floor will start to buckle.
This is why it is important to install the floor correctly using a recommended installation method. You should also be sure to follow advice on moisture testing, subfloor preparation and acclimatizing your floor, which can all be found in the solid wood flooring advice centre.
The majority of problems encountered with solid wood flooring involve inadequate subfloor preparation or improper installation so it is extremely important that these are not issues for your floor.