A tensioner for a fencing wire reel, which includes a tensioning member, and a housing for the tensioning member, characterised in that the housing and the tensioning member are configured such that when fencing wire passes through the housing in one direction, the tensioning member applies a first biasing force against the wire, and when fencing wire passes through the housing in the opposite direction, the tensioning member applies a second biasing force against the wire, the second biasing force being less than the first biasing force. A portable fence system for constructing a fence, which includes at least one fencing wire reel, and a reel housing for the at least one fencing wire reel, and includes the tensioner as described is also claimed.
