Question: What civilization's writing system did Ernst Wilhelm Förstemann contribute to the decipherment and understanding?

Context paragraphs:
Oral tradition: Oral tradition, or oral lore, is a form of human communication where in knowledge, art, ideas and cultural material is received, preserved and transmitted orally from one generation to another.  The transmission is through speech or song and may include folktales, ballads, chants, prose or verses.  In this way, it is possible for a society to transmit oral history, oral literature, oral law and other knowledge across generations without a writing system, or in parallel to a writing system.  Indian religions such as Buddhism, Hinduism and Jainism, for example, have used an oral tradition, in parallel to a writing system, to transmit their canonical scriptures, secular knowledge such as Sushruta Samhita, hymns and mythologies from one generation to the next.

Tenevil: Tenevil (Russian: Теневиль ) (ca. 1890–1943?)  was a Chukchi reindeer herder, living in the tundra near the settlement of Ust-Belaya in Russian province of Chukotka.  Around 1927 or 1928 he independently invented a writing system for the Chukchi language.  It has never been established with certainty whether the symbols in this writing system were ideograms/pictograms or whether the system was logogram-based.  Researchers have noted the abstract character of the symbols, which may be an indirect evidence that this writing system is entirely Tenevil's invention.

Galina Yershova: Galina Gavrilovna Yershova, or Ershova (Russian: Гали́на Гаври́ловна Ершо́ва ; born 17 March 1955) is a prominent Russian academic historian, linguist, and epigrapher, who specialises in the study of the ancient civilisations, cultures, and languages of the New World.  As an Americanist scholar, her area of expertise is in the field of Mesoamerican studies, and in particular that of the pre-Columbian Maya civilisation, its historical literature, and its writing system.  Yershova is a former student and protégé of the famed Russian linguist and epigrapher Yuri Knorozov, renowned for his central contributions towards the decipherment of the Maya script.

Cascajal Block: The Cascajal Block is a tablet-sized writing slab in Mexico, made of serpentinite, which has been dated to the early first millennium BCE, incised with hitherto unknown characters that may represent the earliest writing system in the New World.  Archaeologist Stephen D. Houston of Brown University said that this discovery helps to "link the Olmec civilization to literacy, document an unsuspected writing system, and reveal a new complexity to [the Olmec] civilization."

David H. Kelley: David Humiston Kelley (April 1, 1924 in Albany, New York – May 19, 2011) was a Canadian American archaeologist and epigrapher, most noted for his work on the phonetic analysis and major contributions toward the decipherment of the writing system used by the Maya civilization of pre-Columbian Mesoamerica, the Maya script.

Hyangchal: Hyangchal (literally "vernacular letters", "local letters" or "corresponded sound") is an archaic writing system of Korea and was used to transcribe the Korean language in hanja.  Under the "hyangchal" system, Chinese characters were given a Korean reading based on the syllable associated with the character.  The "hyangchal" writing system is often classified as a subgroup of Idu.  The first mention of "hyangchal" is the monk Kyun Ye's biography during the Goryeo period.  "Hyangchal" is best known as the method Koreans used to write Hyangga, vernacular poetry.  Today, twenty-five such poems still exist and shows that vernacular poetry used native Korean words, Korean word order, and each syllable was "transcribed with a single graph".  The writing system covered nouns, verbs, adjectives, adverbs, particles, suffixes, and auxiliary verbs.  The practice of "hyangchal" continued during the Goryeo Dynasty where it was used to record native poetry as well.

Yuri Knorozov: Yuriy Valentinovich Knorozov (alternatively Knorosov; Russian: Ю́рий Валенти́нович Кноро́зов ; November 19, 1922 – March 31, 1999) was a Soviet linguist epigrapher and ethnographer, who is particularly renowned for the pivotal role his research played in the decipherment of the Maya script, the writing system used by the pre-Columbian Maya civilization of Mesoamerica.

Maya script: Mayan script, also known as Mayan glyphs or Mayan hieroglyphs, was the writing system of the Maya civilization of Mesoamerica and is the only Mesoamerican writing system that has been substantially deciphered.  The earliest inscriptions found which are identifiably Maya date to the 3rd century BCE in San Bartolo, Guatemala.  Maya writing was in continuous use throughout Mesoamerica until the Spanish conquest of the Maya in the 16th and 17th centuries.

Ernst Förstemann: Ernst Wilhelm Förstemann (Danzig, September 18, 1822 – Charlottenburg, November 4, 1906) was a German historian, mathematician, doctor of linguistics and librarian, director of the Saxon State Library (German: "Sächsische Landesbibliothek" ) in Dresden.  He is known as a founder of onomastics and folk etymology studies in Germany, and also for his seminal contributions made in the early years of Mayanist research, towards the decipherment and understanding of calendrical elements in the pre-Columbian Maya script.

Decipherment: In philology, decipherment is the discovery of the meaning of texts written in ancient or obscure languages or scripts.  Decipherment in cryptography refers to decryption.  The term is used sardonically in everyday language to describe attempts to read poor handwriting.  In genetics, decipherment is the successful attempt to understand DNA, which is viewed metaphorically as a text containing word-like units.  Throughout science the term decipherment is synonymous with the understanding of biological and chemical phenomena.

Supporting paragraphs: Ernst Förstemann Maya script
Answer: Maya civilization