Isalo National Park is located in the Ihorombe Region of Madagascar, in the southwestern part of the Fianarantsoa Province. The nearest town is Ranohira, and the closest cities are Toliara and Ihosy. The park’s landscape is made of sandstone that has been carved by wind and water erosion into rocky hills, flat plateaus, large open areas, and canyons as deep as 200 meters (660 feet). The area has rivers and streams that flow year-round, as well as many waterways that only flow during certain times of the year. The elevation ranges from 510 to 1,268 meters (1,673 to 4,160 feet).

History and significance

Isalo National Park was established in 1962 and has been managed by the Madagascar National Parks authority since 1997. The Bara people, a nomadic group who raise cattle (zebu), have lived in this area for many years. The park contains burial sites of the Bara people and older burial sites of the Sakalava people.

Isalo is mainly located in the dry deciduous forests ecoregion, where natural plants have decreased to about 60% of what they were originally. It also includes areas of the subhumid forests ecoregion, which is home to many species found only in Madagascar. This ecoregion is in serious danger because most of its native habitat has been lost or broken into small, separate areas. The woodlands in Isalo are dominated by the tapia tree (Uapaca bojeri), a tree found only in Madagascar's central highlands. Some of the largest remaining tapia woodlands are in Isalo.

The park has many plant species found only in very small areas. Thirteen plant species are found only in Isalo, and another 35 are rare, growing in 2 to 5 locations. The Sarcolaenaceae plant family, which exists only in Madagascar, includes two species (Sarcolaena isaloensis and S. chizolaena isaloensis) that are found only in Isalo National Park. The park also has unique lichens, including Isalonactis madagascariensis, which is only known to grow in Isalo.

Climate

Isalo National Park is located in the dry western part of Madagascar, within the western dry deciduous forest climate region. The area has a hot, dry climate with two seasons: a cooler and drier time of year, and a warmer and wetter time of year. Each season lasts about 5 to 7 months. Temperatures range from 15 to 32 degrees Celsius, with an average annual temperature of about 21.8 degrees Celsius. The average yearly rainfall is 791 millimeters (31.1 inches) at Ranohira. The least rain falls in June, averaging 2 millimeters (0.079 inches). December through February are typically the wettest months. Rainfall in January averages 199 millimeters (7.8 inches), but during the 2018/2019 wet season, heavy rain fell, with 526 millimeters (20.7 inches) recorded in January alone.

Geology

The Isalo Group, a sedimentary geological formation, is located in the southern part of the Morondava Basin and forms the Isalo Massif within the park. This group is up to 6,000 meters thick and dates back to the Triassic to early Jurassic periods. It consists of coarse-grained sandstone deposited by braided streams. Over time, wind and water erosion have shaped the Isalo Massif, creating deep canyons, sandstone domes, flat-topped mountains, and "runiform" mountains—steep-sided rock formations with unusual, carved shapes. The term "runiforme" comes from the French word for "carved." A 2024 archaeological study of man-made rock-cut niches at the Teniky site found them to date from the 10th to 12th centuries CE and may be linked to Zoroastrian origins.

Tourism

A local guide is needed for visitors entering the park, and guides and porters can be hired in Ranohira. Treks in the park can take several hours to a week or more. The park has several natural swimming pools that are popular with tourists and are good places to spot the Benson's Rock Thrush. The main threat to the park is illegal wildfires started in the park. These wildfires reduce the size of the forest and increase the area of grasslands used for cattle grazing.

Fauna

Fourteen mammal species live in Isalo National Park, including several types of lemurs. Over 100 bird species have been found here, including Benson's rock thrush (Monticola sharpei bensoni), the knob-billed duck (Sarkidiornis melanotos), and the Madagascar ibis (Lophotibis cristata). Twenty-four amphibians and 47 reptiles have been recorded in Isalo National Park, including several new "candidate" species. Species found only in the Isalo area include four amphibians (Gephyromantis azzurrae, Mantella expectata, Mantidactylus noralottae, and the Malagasy rainbow frog (Scaphiophryne gottlebei)) and one reptile species (Trachylepis nancycoutuae). Notable examples include the Madagascar ground boa (Acrantophis madagascariensis), Dumeril's boa (Acrantophis dumerili), and the white-lipped bright-eyed frog (Boophis albilabris).

Flora

A plant survey of the Isalo region started in 1910 with collections by Perrier de la Bâthie. Out of more than 400 recorded species in Isalo, only 10 are not native to the area. Most species (over 70%) are vascular plants that are found only in Madagascar. Thirteen species are found only in Isalo, and 35 are rare species found in only 2 to 5 locations. The table below lists species known only from Isalo National Park.

Some plant families are found only in Madagascar. Three of these families, Asteropeiaceae, Sarcolaenaceae, and Sphaerosepalaceae, can be found in Isalo. Within the Sarcolaenaceae family, two species—Sarcolaena isaloensis and S. chizolaena isaloensis—are found only in Isalo National Park.

Lichens

The lichens of Madagascar are not well studied, but more than 500 species have been recorded. Approximately 20 species live in the dry regions of the country. Some of these species have been found in the Isalo area, including the only known location for the species Isalonactis madagascariensis, which is found only in that specific region.

Vegetation

Isalo is mainly located in the dry deciduous forests ecoregion, an area where natural vegetation has decreased by nearly 40% of its original size. It also includes separate forest areas that are part of the subhumid forests ecoregion, a region that is home to many species found nowhere else in the world. This ecoregion is considered Critical/Endangered because only small areas of native habitat remain, and most of these areas are broken into small, disconnected parts. Six main habitats have been identified in Isalo National Park.

The sclerophyllous (hard-leaved, drought-resistant) woodlands in Isalo are mostly made up of the endemic tree tapia (Uapaca bojeri). This type of woodland is found only in Madagascar's central highlands. Some of the largest remaining areas of tapia woodlands are in Isalo. These woodlands have adapted to regular fires and are characterized by an open canopy mostly covered by tapia, though other trees may include species from the Euphorbiaceae family or the endemic Sarcolaenaceae family. The shrub layer includes plants from the Asteraceae, Rubiaceae, and Leguminosae families, while herbs and grasses form the main layer under the trees. Endemic Kalanchoe and Aloe species grow in this habitat.

These forests are found in moist areas, such as near streams or in deep ravines. Native forests in deep canyons include palm species (Ravenea and Dypsis), Breonadia salicina, Pterophylla sp., Voacanga sp., and Dracaena sp. However, some of these moist areas are now dominated by non-native species like Melia azedarach, Mangifera indica, or Eugenia sp.

Pandanus thickets, mainly made up of Pandanus pulcher, are found in shallower valleys or near small streams where the forest has been damaged and frequently burned.

This habitat is found in dry, rocky areas, including steep slopes and ridges. Although plant life is limited, several endemic species live here, including Xerophyta sp., elephant's foot (Pachypodium rosulatum var. gracilius), and the rare Aloe isaloensis.

Secondary shrub communities are found where the slopes of the Isalo Massif meet fields or pastures. Common species in these areas include Mimosa latispinosa, Vangueria madagascariensis, Maesa lanceolata, Aphloia theaeformis, Crotalaria sp., and Tamarindus indica.

Native grasslands, which were likely once limited to small areas, have grown larger due to frequent burning, mainly to support cattle grazing. Grasslands (also called pseudo-steppes) are now widespread in Isalo, dominated by Aristida similis, Aristida rufescens, Trachypogon sp., or Heteropogon sp. Regular burning keeps the grasslands intact and stops trees from growing back.

Gallery

• Sign indicating Isalo National Park
• Verreaux's sifaka at Isalo National Park
• Red-fronted brown lemur at Isalo National Park
• Red-fronted brown lemur displaying its teeth
• Red-fronted brown lemur
• Lemur catta
• Pachypodium rosulatum gracilius
• Elephants foot plant at Isalo National Park
• Elephants foot flower at Isalo National Park
• Waterfall and Piscine Naturelle
• Canyon des Makis
• Lush and dry landscape
• Eroded rock formations at Isalo National Park
• Standing stones at Isalo National Park
• Lichens growing on the rocks at Isalo
• Lichens growing on the rocks at Isalo National Park, Madagascar including Dermatiscum thunbergii