A design-unbiased small estimator was tested in this study. This estimator combines terrestrial data from the Swiss National Forest Inventory (LFI) with ancillary data from stereo aerial images and airborne laser scanner (ALS) data. The estimator was tested for the two target variables: the percentage of forest and the timber volume. The efficiency of the estimator depends on the model precision of the target variable obtained with remote sensing data and other ancillary spatial data, which can potentially explain the spatial variation of the target variable. Canopy heights derived from stereo aerial images (ADS40) and ALS data were used as ancillary data. Regression models for the timber volume and the forest/non-forest decision of the LFI samples were calibrated within the cantons Appenzell Inner Rhodes and Appenzell Outer Rhodes and provided a coefficient of determination of roughly 60%. Adding the forest/non-forest decision from the aerial photo interpretation of the LFI as an explanatory variable slightly improved the models and allowed to gain a coefficient of determination of 65% for the timber volume and 85% for the forest/non-forest decision. Within the forest area, the canopy height models explained nearly 40% (ALS data) and 20% (ADS40 data) of the observed timber volume variability. This case study shows that using remote sensing data can increase the precision (in terms of the standard error) of the timber volume estimation in canton Appenzell Inner Rhodes by roughly 30%. The same is valid for the estimation of the percentage of forest. A reduction in the standard error of about 10% for the latter estimation was obtained by using the aerial images and nearly 25% using the ALS data.