Complex sentence: Tantalum capacitors are less prone to "drying out", causing a decrease in capacitance as is often seen with aluminium electrolytic capacitors, particularly in hot environments thus they maintain their designed capacitance over long periods of time, (decades).
Split into simpler sentences: Tantalum capacitors are less prone to "drying out", causing a decrease in capacitance as is often the case with aluminium electrolytic capacitors particularly when used in hot environments. They maintain their designed capacitance under such conditions over long periods of time, (decades).