Which one of the following is not used for ex situ plant conservation?

Shifting cultivation leads to deforestation which, in turn, causes loss of biodiversity.

In ex situ conservation, threatened animals and plants are taken out from their natural habitat and placed in special setting where they can be protected and given special care. Zoological parks, botanical gardens, wildlife safari parks, seed banks, field gene banks, etc., serve this purpose. Shifting cultivation results into deforestation. Botanical gardens have a collection of living plants for reference. Seed banks store seeds as a source of germplasm. Field gene banks are a type of biorepository which preserves the genetic material. Shifting cultivation does not fall in this category. 

Shifting cultivation is an agricultural system in which a person uses a piece of land, only to abandon or alter the initial use a short time later. This system often involves clearing of a piece of land followed by several years of wood harvesting or farming until the soil loses fertility.