A lot of the acids and solvents (terpenoids) leached from the pine straw and onto your roof. It's is typical asphalt shingles then those solvents and acids will accelerate the decomposition of your roof. Oaks are bad for that, too (tannic acid).

After the volatiles leach then decomposition of the needles accelerate and you get production of very long chain, acidic hydrocarbons called humic acids. These acids do not much affect pH but act as a great buffering material and also increase water-holding capacity of the soil. Also, The buffering will help make ions available to plants over a longer period of time rather than a big jolt and depletion. If you till organic matter into the soil the soil fungi and bacteria will begin breaking it down. This immediately depletes nitrogen and phosphorus, so you will initially see plant leaves become chlorotic (yellow). So you spray on a liquid foliar fertilizer and get the plants back to normal. Or you mix in fertilizer with the organic matter when you prepare your bed for planting. In either case you will increase the capacity of the soil to exchange ions (cation exchange capacity). Usually a good thing.