Dehydration temperatures for long-term preservation
The temperature varies not by how long you want to keep the item, but by what you are dehydrating. Consider a carrot. A raw carrot will keep for literally months. A cooked one at room temperature will not even keep for days. So, when you're dehydrating carrots (for example to reduce the weight of the food you take camping) you want to be sure not to cook them in the process. Now, consider raw meat such as jerky. This has a LOT of water in it. If you dry it at too low a temperature, it will spoil before you have reduced the water content enough. Same for a fruit puree. But herbs, if you have it too hot you will draw out the flavours and just keep dehydrated dust.

My dehydrator came with a book telling me what temperatures to use for what products. There are also words on the temperature dial. This is a cropped shot of my model on the manufacturer's website:



While you can't read the words, they say "fruit", "vegetables" etc. The coolest temps are for herbs, then it goes raising bread, making yogurt, then dehydrating veg, then fruit, and finally jerky. 

And just as you can't choose one temperature to use for dehydrating any and all food, nor can you assume one keeping time for any and all food. My book also tells me which things keep for months, and which for years. I don't think there's anything that will let your dried meat keep for years, but you should do ok with legumes and some vegetables.