Forests to discover: Thorny forest, Madagascar



by LORENZO CIOTTI

Forests to discover: Thorny forest, Madagascar

The thorny forest in Madagascar extends along the coastal strip between the Mangoky River to the north-west and the Anosyennes mountain range to the south-east. It is a truly magical, suggestive and intriguing region, due to its particularity, its trees and its colors.

It is the driest region of Madagascar, characterized by a long dry season and very little rainfall, in some areas below 350 mm per year, and is inhabited by the Mikea, a hunter-gatherer population of about 900 people. The thorny forest is characterized by the presence of plant species that present particular mechanisms of xerophilic adaptation.

The animals that populate it are mammals, birds and reptiles. The forest is famous for didiereaceae, which represent 95% of the species found in this particular ecosystem. Among them the species of Didiereaceae occupy a prominent place.

It is a family of plants that have developed, by evolutionary convergence, adaptation mechanisms similar to the New World Cactaceae, such as the presence of small and leathery leaves and spinescence. These are mostly shrubby species but in some cases they can emerge in the form of trees over 10 m high, as for Alluaudia ascendens and Alluaudia procera.

The plants are spiny succulent shrubs and trees from 2–20 m tall, with thick water-storing stems and leaves that are deciduous in the long dry season. All of the species except Alluaudiopsis have a distinct youth form.

They start as small procumbent shrubs but eventually a dominant stem is produced that becomes a trunk. The forest is endangered due to deforestation resulting from the manufacture of charcoal and wood for construction.

The forest is characterized by the Didiereaceae

They appear as shrubs or real trees, varying in height from 2 to 20 meters.

They have characters of xerophilic adaptation similar to those of the Cactaceae, with which they are closely related. They have thorny stems capable of storing water and carrying out chlorophyll photosynthesis using the CAM metabolism, small and leathery deciduous leaves, produced in correspondence with the areola.

Most of the species are endemic to the thorny forest of southwestern Madagascar. Some species assigned to this family by the APG classification are widespread in eastern and southern Africa. They populate semi-desert environments with a low annual rate of rainfall.