Profile Diagrams

Profile diagrams are not an essential part of permanent transect recording but can be useful particularly where structural changes are expected. In forest the centre-line tape of the transect can be used as a baseline for drawing a profile diagram of the plants as accurately as possible, either estimating heights by eye or using an abney‘ level or 4 m pole to measure heights. Alternatively, in forest where the density of plants does not allow a clear cross-section to be drawn, a profile diagram can be based on a tape stretched from tree to tree in a zig-zag manner. In this case only the tall trees touching the tape are drawn and then these should be indicated by showing the baseline of the profile diagram on the transect chart. With either alternative, the drawing of understorey plants is restricted to those greater than 0.3 m ht and growing within a metre-wide transect centred on the baseline. Only a segment of the crown of each of the taller trees is drawn but what is shown must be sufficient to convey a realistic picture of the vegetation structure. In comparing two forest profile diagrams of the same transect made at different times, it should be remembered that reliability will be greater at the lower levels.