Unknown. (2023). Pennsylvania department of forestry. Forest Research Institute.
शिकागो शैली (17वां संस्करण) प्रशस्ति पत्रUnknown. Pennsylvania Department of Forestry. Forest Research Institute, 2023.
एमएलए (9वां संस्करण) प्रशस्ति पत्रUnknown. Pennsylvania Department of Forestry. Forest Research Institute, 2023.
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