Waihao Spring is another heavily forested, pine-needly trail, though significantly easier than the Makawao loop. One trip around is a flat and steady 2.8 miles, without much uphill gain. There are some roots across the trail, so pay attention to your stride, but this is a nice easy trail run as far as trail runs in Hawaii go. It’s also a good shade option for those hot Maui days.
For a longer run, you can try some of the pleasantly shaded roads in the area, but they are narrow and have no shoulder.