<p>The interaction between radio waves and vegetation has been extensively studied for efficient wireless network planning. Both empirical and analytical models have been developed for this purpose. However, radio transmission within a wireless sensor network could be used for sensing the medium in the signal path in addition to data transmission within the network. Prior work suggested that radio waves interact strongly with water contained in vegetation. The dependence of radio waves on water is through its dielectric constant. In this thesis, the relationship between RF loss and water content in vegetation in the path of a radio communications link was modelled to study the feasibility of monitoring plant health using wireless communication networks.</p> <p>A model to calculate the RF loss through packed vegetation with different moisture content was developed. This model only considers the dielectric constant of the vegetation and does not include the air component of the tree canopy. The model was further extended to calculate RF loss through tree canopies. Both the models were verified against experimental measurements acquired using Eucalyptus leaves and trees. The results show that there is a positive non-linear relationship between RF loss in dB and water content expressed as effective water path (EWP) in mm. Vegetation thickness is also a factor in RF loss, however the contribution was minor compared to water content of vegetation. This work has quantified the relationship between RF loss and water within vegetation. It may lead to wireless sensor networks being repurposed to monitor, over periods of many years, changes in plant water status.</p>