EDIT

        //classification and term

        classificationBox = new ComboBox("Classification");

        classificationBox.setImmediate(true);

        classificationBox.setWidth("100%");

        //distribution area box

        //no classification selected label

        labelNoClassification = new Label(" - Please select a classification - ");

        leftContainer.addComponent(distAreaBox);

        leftContainer.setExpandRatio(distAreaBox, 0.1f);

        leftContainer.addComponent(namedAreaList);

        leftContainer.setSizeFull();

        rightContainer.addComponent(taxonTree);

        rightContainer.setExpandRatio(taxonTree, 1);

        rightContainer.addComponent(labelNoClassification);