What are the three types of natural barrens that occur in Pennsylvania?

• A. Serpentine, shale, and sandstone
• B. Serpentine, limestone, and shale
• C. Limestone, granite, and serpentine
• D. Shale, sandstone, and limestone

Answer: (B)

Natural barren communities in Pennsylvania are defined by the geology of the site, with specific soils creating harsh growing conditions that select for tough plants. In Pennsylvania, the three recognized barren types occur on serpentine, limestone, and shale bedrock. Serpentine barrens form on serpentine rock, which yields soils that are low in calcium and rich in heavy metals, making them nutrient-poor and drought-prone—conditions that support a distinct, hardy plant community. Limestone barrens develop on calcareous limestone outcrops, where alkaline soils and shallow depths create stress for many plants, favoring drought-tolerant and calciphile species. Shale barrens occur on shallow, well-drained soils derived from shale, producing another set of harsh conditions that support specialized flora adapted to limited nutrients and moisture extremes. The other options mix rock types not typically recognized as barren types in Pennsylvania, so serpentine, limestone, and shale barrens best capture the common barren types found there.