Yes, Christmas trees can be toxic to cats if they chew on or ingest parts of the tree. The tree needles, sap, and other parts of the tree can cause gastrointestinal upset, including vomiting, diarrhea, and anorexia. In severe cases, cats may experience cardiac arrhythmias, respiratory difficulties, or even death. It is important to keep Christmas trees out of reach of pets and to monitor them closely if they are around a tree.