Sorry about the Copy&Paste... Conifer trees
http://www.gardeningknowhow.com/composting/ingredients/composting-pine-needles.htm
Many people avoid using pine needles in compost because they think it will make the compost more acidic. Even though pine needles have a
pH between 3.2 and 3.8 when they fall from the tree, they have a nearly neutral pH after composting. You can safely add pine needles to compost without fear that the finished product will harm your plants or
acidify the soil. Working pine needles into the soil without composting them first may temporarily lower the pH.
Another reason why gardeners avoid pine needles in compost is that they break down very slowly. Pine needles have a waxy coating that makes it difficult for the bacteria and fungi to break it down. The low pH of pine needles inhibits the
microorganisms in compost and slows down the process even more.