Estimating aerial biomass in semi-natural vegetation from spectral reflectance measurements. 1. Preliminary experiences

A technique of calculating aerial green biomass from spectral measurements in the red and near infrared bands is increasingly being applied in vegetation studies. It is fast, non-destructive and can be directly applied from aircraft or satellite mounted sensors to large areas. Literature data illustrating the potential of the approach refer sofar generally to rather ideal situations in low, open, herbaceous vegetation. Before general application can be recommended a body of reference including various situations should be available. The present contribution indicates some disturbing factors such as the presence of flowers or shade and evaluates the applicability of the technique for a number of vegetation types. Results of tests in 11 semi-natural vegetation types are presented, ranging in height from 30-150 cm and in cover from 20-1 00%. Measurements were made with – as later appeared – non-optimal equipment and no correction could be made for variation in incoming radiation. Multiple sampling at three to five dates between April and July resulted in correlation coefficient values of 0.96, 0.95, 0.92. 0.91, 0.91, 0,88, 0.85. 0.82, 0.67, and -0.06 (in the last case Holcus lanatus dominant) for aerial biomass dry and the ratio. These relatively high values are critically examined. The data provide evidence for a rather general applicability of the technique, but also for a cautios approach and a mandatory calibration per (floristically and/or physiognomically) different vegetation type.