We are all different. Some of us get cold easily and others tend to overheat, so deciding on what base layer you will wear on your trip will depend entirely on you. But, here are a few tips.
On a 1 day hike, if it’s warm you can wear a short sleeve top. Some people prefer to wear a long sleeve top to protect their arms from the sun. If that’s what you prefer, it’s good to wear a short sleeve base layer with a lightweight long sleeve button up shirt over the top.
Short sleeve base layer is also suitable on cool days with your mid layer on top.
If it’s cold, long sleeve top will be the most suitable.
One 2 to 3 day hikes, I recommend to bring one short sleeve and one long sleeve top.
On 4 to 5 day hikes, in warm weather, I recommend 2 short sleeve tops and 1 long sleeve top and in colder conditions, I recommend 1 short sleeve top and 2 long sleeve tops.
Remember that when you are wearing a short sleeve top, you need to apply sunscreen to your arms.