Biology session

The vegetation indices are suitable to estimate above-ground phytomass (plant mass), and to assess the state of health of the vegetation. The indices are created based on the electro wavelengths (400-1100nm) reflected by the plants and detected by the sensors. The usage of indices ranges from measuring the primary production, conservational grassland management to the research on the response of flora on climate change.

Hower, in high or dense vegetation the precision of the phytomass estimation based on indices decreases, because the overlapping leaves are out of the field of vision of the sensors, thus they underestimate the potential phytomass.

Therefore the purpose of the present research is to investigate the relationship between phytomass and vegetation indices in diverse grassland with high phytomass to increase the effectiveness of phytomass estimation based on indices.

Besides direct phytomass measurement (by cutting) we used different sensors (ceptometer, common and modified digital cameras, Tetracam) to estimate phytomass and compared the two results of the methods .

Unlike the generally known saturation curve (between the phytomass and the indices), the vegetation indices estimated correctly the phytomass up to a certain value, but above this, the relationship ceased. For example, a new index calculated by a modified Canon camera, showed a close linear relationship with the phytomass within a range (117 g m-2 - 462 g m-2; r2= 0.5, p<0.05, n=37), but above this - max. phytomass = 1398.5 g m-2- there was no correlation (r2< 0.01; n=53). We found out that the vegetation indices give a more reliable estimation of the fresh weight than the dried weight of vegetation.

Additionally, for vegetations at various heights and moisture contents certain indices are more efficient than others.

In our further research we wish to test the possibilities of remote sensing based on phytomass estimation, applying some corrections by using species-specific aridification and blooming indices.