Silvanus was the Roman god of the woodland and agriculture. Originally Silvanus' duties were confined to the woods and forests. Later, Silvanus began to have extra attributes and became the god of farming and pasture, and probably of flocks and herds. Silvanus was seen as the patron god of shepherds.

Silvanus was the Roman counterpart of Silenus, the satyr-like, woodland spirit. Silvanus would later inherit some of Silenus' attributes, such as goat's horns and legs.

From: here
The Roman god of forests, groves and wild fields. As fertility god he is the protector of herds and cattle and is associated with Faunus. He shows many similarities with the Greek Pan (Silvanus also liked to scare lonely travelers). The first fruits of the fields were offered to him, as well as meat and wine--a ritual women were not allowed to witness. His attributes are a pruning knife and a bough from a pine tree.

From: here
Silvanus (Latin: "of the woods") was a Roman tutelary deity of woods and fields. As protector of forests (sylvestris deus), he especially presided over plantations and delighted in trees growing wild.[1][2][3][4] He is also described as a god watching over the fields and husbandmen, protecting in particular the boundaries of fields.[5] The similarly named Etruscan deity Selvans may be a borrowing of Silvanus,[6] or not even related in origin.[7]

Silvanus is described as the divinity protecting the flocks of cattle, warding off wolves, and promoting their fertility.[1][8][9][10] Hyginus states that Silvanus was the first to set up stones to mark the limits of fields, and that every estate had three Silvani:[11]

a Silvanus domesticus (in inscriptions called Silvanus Larum and Silvanus sanctus sacer Larum)
a Silvanus agrestis (also called salutaris), who was worshipped by shepherds, and
a Silvanus orientalis, that is, the god presiding over the point at which an estate begins.

Hence Silvani were often referred to in the plural.

Like other gods of woods and flocks, Silvanus is described as fond of music; the syrinx was sacred to him,[1] and he is mentioned along with the Pans and Nymphs.[2][12] Later speculators even identified Silvanus with Pan, Faunus, Inuus and Aegipan.[13] He must have been associated with the Italian Mars, for Cato refers to him as Mars Silvanus.[9]

Worship

The sacrifices offered to Silvanus consisted of grapes, ears of grain, milk, meat, wine and pigs.[1][5][15][16][17] In Cato's De Agricultura an offering to Mars Silvanus is described, to ensure the health of cattle; it is stated there that his connection with agriculture referred only to the labour performed by men, and that females were excluded from his worship.[9][16] (Compare Bona Dea for a Roman deity from whose worship men were excluded.) Virgil relates that in the very earliest times the Tyrrhenian Pelasgians had dedicated a grove and a festival to Silvanus.[8]

From: Wiki

Also see:
Cato's 'De Agricultura': Offering to Mars Silvanus
GoogleBook's -- Preview : The cult of Silvanus: a study in Roman folk religion