The Madagascar Spiny Forest at Los Angeles County Arboretum

By: James Henrich

James E Henrich is curator of living collections at Los Angeles County Arboretum & Botanic Garden, having previously worked at…

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Yellow flowers of Uncarina grandidieri frame a view of the Madagascar Spiny Forest. Photographs by Frank McDonough, except as noted

The Madagascar Spiny Forest at Los Angeles County Arboretum & Botanic Garden was the brainchild of Superintendent Timothy Phillips. Fascinated with unusual plants since childhood, it is no wonder that Tim developed an interest in Madagascan plants later in life. This new garden nicely complements nearby collections (South Africa, Australia, New World succulents, cacti), the Water Conservation Garden, and other gardens featuring plants from the mediterranean climate regions of the world. Though it had challenges, the Spiny Forest definitely meets the landscape requirements for a collection that tolerates and, in fact, thrives with low water consumption.

Tim’s passion for this project and the resulting garden experience is actually understated in his comments:

The Madagascar collection was and is an experiment of sorts, one that pushes the horticultural limits. It’s an adventure of the spiniest kind, and I have the pin-cushion memories to prove it! I wanted to create an immersion experience, one that would take our guests to an alien land—one that arouses curiosity, intrigue, and amazement. It is supposed to be a fun, interactive, botanical, and horticultural experience, with a subtle conservation education message.

View into the Madagascar Spiny Forest at The Los Angeles County Arboretum & Botanic Garden. Photograph by RGT

Climatic differences between Madagascar and the Los Angeles area are striking. Although the annual rainfall amounts in the Los Angeles area are similar to those of Madagascar’s spiny forest ecoregion, the rainy seasons are reversed: the Madagascan wet season coincides with the long warm days of summer, whereas California’s rains fall primarily in the cooler winter months. Seldom is there a total drought lasting for years in Los Angeles, unlike what has been observed in the spiny forests. Cultivated collections, such as this one, have the advantage of receiving supplemental irrigation during the heat of summer. To mitigate the challenge of wet winter conditions combined with near freezing temperatures, the Arboretum’s Spiny Forest garden consists of mounded beds of well-drained planting medium on a site with good southern exposure.

Pachypodium and other plants wrapped in fiberglass blankets, awaiting planting in the Madagascar Spiny Forest. Photograph by Timothy Phillips

Envisioning a Garden

To be clear, this garden was created with a mental vision and a wish list of plants, but no landscape plan. Arboretum crews and independent contractors implemented the entire vision for the garden through on-site decisions establishing the layout of boundaries and pathways and the placement of boulders and  plants.  Prior  to  breaking  ground  in  October 2006, the site held a waning collection of Crinum and other South African bulbs.

Regarding the paths, Tim recalls, “The pathways were designed to be aesthetically pleasing, yet accessible and durable. This was my first attempt at integrating multiple colors in pavement.” He had in mind an image of an eroded footpath in a denuded area of the spiny forest. Although it turned out perfectly, the contractors were dubious at first.

The pathway installation was carefully orchestrated. The outline of the pathways was first painted on the ground. Bender boards were staked along the outline. A standard sidewalk concrete mix was poured into place and leveled. The illusion of soil texture was achieved by tamping a single latex mold along the pathway.  Leaves and various arthropod shapes were also stamped into the moist concrete. The crowning touch was broadcasting various dyes over the surface of the still-moist concrete to simulate colors seen in the soils of the spiny forest. This was no simple concrete installation: because of the speed with which concrete sets, the many elaborations had to occur in rapid succession.

Next, a minimal irrigation system was installed that consists of quick couplers for easy hose access. Early in the planning process, Tim decided automatic irrigation would not be incorporated in the design because of the minimal need for water by the plants in the collection. Irrigation is applied by hand or with impact sprinklers.

Prior to groundbreaking, Tim worked with a contractor to create a custom planting mix that would be prepared off site. Although the natural soils of the spiny forest contain minimal organic matter, it was decided that some organic matter should be included in the custom mix to help retain moisture during summer,  which  is hotter in Los Angeles than in Madagascar. Several samples were evaluated, resulting in a blend consisting of equal portions of loam, coarse sand, and pumice, with about fifteen percent organic matter added. The pumice had an auspicious beginning as recycled waste from a local stone-washed denim processing plant. A bucket loader placed the soil mix into continuous two-to three-foot-deep mounds, which enhance both the aesthetics and the drainage of the garden. Under the watchful artistic eyes of several staff, a crane strategically placed Arizona pink boulders throughout the garden.

Familiar garden plants native to Madagascar’s spiny forest: crown-of-thorns (Euphorbia milii) and Madagascar periwinkle (Catharanthus roseus). Photograph by RGT

Plants, of Course

Tim Phillips and Jim Bauml, curator of living collections at the time, began searching for and procuring plants long before the garden was installed, and continued the process during and after completion of the hardscape. They individually selected the plant specimens, most of which were obtained, bare-root, from commercial nurseries in the San Diego area. Many plants remained bare root for days to weeks prior to planting—a testament to their resiliency. Others arrived in containers, especially the smaller species. The extendable-boom crane was again employed to position the largest plants on the mounds.

Spiny trunks were wrapped in several layers of fiberglass insulation to reduce damage from the lifting straps. Despite these protective wraps, installers sustained numerous puncture wounds and close encounters of the fiberglass kind. Critical to the survival of the field-dug specimens was maintaining the solar orientation of the plants: the north sides of field-grown plants would sustain sunscald on their trunks if planted with a southerly orientation. The smaller plants were placed after the large specimens had been set. When all plants were in the ground, the soil was covered with crushed Arizona pink stone, again to mimic colors seen in the Madagascan landscape. Red sandstone slabs were installed at the two entrances of the garden upon its completion in May of 2007; each slab provides an interpretive message about the garden.

Spiny is the keyword in the Madagascar Spiny Forest: Alluaudia humbertii (left) and A. procera (right)

Successes in Spite of Challenges

Despite the climatic differences between Madagascar and the Los Angeles area, the Arboretum’s Spiny Forest has seen some remarkable successes. The garden reaches its peak of beauty during the heat of summer. Most of the species in the collection have flowered, and viable seeds have been produced by Aloe suzannae, A. vaombe, rose periwinkle (Catharanthus roseus), Pachypodium lamerei, and mouse trap tree (Uncarina  decaryi). Seedlings of A. vaombe and rose periwinkle have begun to appear spontaneously in the garden.

Aloe vaombe

Those climatic differences do provide some challenges. Periodic applications of water are required to ensure the optimal performance of the plants from June through September. Wet winter conditions have created problems with root deterioration. Occasionally, severe winds have toppled some of the taller plants, but we simply stand them up, cover the roots with soil, and stake them for support; they readily re-root. Wind-storms have broken branches from a few of the larger specimens of Pachypodium and Moringa.

Pachypodium geayi. Photograph by RGT

The greatest challenge has been the frost; temperatures in the Arboretum have been recorded down to at least to the mid-20s F. The garden is on a slight south-facing slope, and colder air drains through the plantings at night, dropping from the heights of the nearby San Gabriel Mountains; it’s common to see frost on adjacent patches of turf in the early morning. During the winter of 2010-2011, there were three severe frost events. By the time the last frost was predicted, we decided to take the precaution of draping the larger plants with a lightweight fabric used to protect row crops against frost. With plants draped in white fabric, the garden suggested another landscape installation by the artist Christo; the only thing missing was his characteristic touch of vibrant color.

A Christo-esque scene with frost blankets covering sensitive plants


Frost has reduced the collection of one crown-of-thorns cultivar (Euphorbia milii ‘Jerry’s Choice’) by more than half, and virtually eliminated two others. Most of the aloes have survived the severe frost events, so far. Specimens of Moringa, Uncarina, other Euphorbia species, and Kalanchoe beharensis have sustained branch tip damage, but all have recovered completely once  growth  resumed in  spring. The Alluaudia and Alluaudiopsis species have been unaffected by frost. The Pachypodium species sometimes sustain damage, from leaf tip to complete defoliation; as long as the crown is not damaged, they flourish when spring temperatures rise. Pachypodium geayi appears to tolerate lower temperatures than P. lamerei. Plants of Operculicarya will often defoliate without any permanent damage. Neither Aloe suzannae nor A. vaombe have sustained any damage from cold temperatures.

Tiny leaves and sharp spines create a distinct pattern on stems of Alluaudia procera. Photograph by RGT

The fascination with plants native to the spiny forest is widespread, especially in Southern California. Here one can easily find species of Adenium, Aloe, Catharanthus, Dypsis, Kalanchoe, Moringa, Operculicarya, Pachypodium, Uncarina, and others. Most are available from specialty nurseries, bonsai clubs, cactus and succulent societies, and botanical garden plant sales.

Pachypodium lamerei

The public garden community is doing its part to display, preserve, and educate the public about the perils faced by plants in Madagas-car’s spiny forest. In addition to this outdoor garden at the Arboretum (the only one on the West Coast), other collections of Madagascar’s unique plants that can be seen in the United States include: the Lin Lougheed Spiny Forest of Madagascar at Fairchild Tropical Botanic Garden, Coral Gables, Florida; a collection of spiny forest plants in Koko Crater Botanical Garden, a satellite site of the Honolulu Botanical Gardens, Oahu, Hawaii; an indoor collection at Atlanta Botanical Gardens, Atlanta, Georgia; and the indoor Spiny Desert of Madagascar at Cleveland Botanical Garden, Cleveland, Ohio.

The success of the Arboretum’s Spiny Forest, along with these other public collections, will, we hope, encourage more plant enthusiasts to experiment with some of these plants in their own gardens and will inspire plant lovers every-where to help the flora of Madagascar survive the onslaught of forces that are currently devastating the vegetation of that island nation.

Mouse trap tree (Uncarina grandidieri)

The Island of Madagascar

Located in the Indian Ocean, off the east coast of Africa’s Mozambique at approximately 12o  to 25.5o S latitude, Madagascar covers 226,658 square miles, which is about forty-four percent larger than California. The estimated population of Madagascar was 21.9 million in 2011. Los Angeles, by comparison, is located further from the equator at about 34o N latitude, and its metropolitan population approaches two-thirds that of the entire nation of Madagascar.

The biota of Madagascar comprises seven ecoregions: two moist tropical broadleaf forests; lowland forests; sub-humid forests; ericoid thickets; dry deciduous forests; and spiny forests. The eastern seaboard is the wettest region, followed by the Ankaratra Mountains immediately to the west. The northernmost tip of the island and western and southern coastal regions are much drier. The island is noteworthy for having an inordinate abundance of endemic plants: ninety-five percent of its plant species and forty-eight percent  of  its  genera  are  endemic  to  the  spiny forest ecoregion alone.

Spiny forest, spiny thicket, and spiny desert are interchangeable names for the spiny forest ecoregion, which covers about 17,100 square miles, or the approximate area covered by Massachusetts and Vermont combined. This ecoregion is found in southern and southwestern Madagascar along the west coast, bounded on the north by the Mangoky River and  on  the  southeast by the western slopes of the Anosyennes Mountain chain. The mountain ranges to the east block the prevailing rains, creating a rain shadow where annual precipitation may range from 350 to 500 mm (14 to 20 inches). Years-long droughts have been known to occur, but the typical dry season lasts nine to eleven months.

The climate has distinct wet and dry seasons, with rain generally falling in spring and summer, from October to April (corresponding to March to September in Southern California). Soils are extremely  porous  and  contain  little  organic matter, which reduces water retention and makes it challenging for plants to absorb moisture. High temperatures typically peak at 30-33oC (86-91.4oF); low temperatures drop to 15-21oC (59-69.8oF) in the winter. The spiny forest ecoregion is relatively flat, with the elevation ranging from 55 to 200 meters (170 to 620 feet) as it rises from the coast to the mountains. The adverse environmental conditions of the spiny forest have caused its inhabitants to evolve numerous morphological adaptations for survival. Foremost among them is the predominance of spines that protect stems from sunburn and against grazing by herbivores, as many of the species have relatively nutritious photo- synthetic bark. Small leaves that are waxy and seasonally deciduous are common. Extensive root systems aid in absorbing water from the soil, and some species develop massive tubers for water storage. Enlarged succulent branches and trunks, some with expanded bases (caudexes) further aid in water retention. With xeric adaptations similar to those of the New World cactus family (Cactaceae), such as small leaves and spines, the didierea family (Didiereaceae) is endemic to and dominates the spiny thickets, but all members of the family are woody rather than succulent. The Vizcaino region of Mexico, where agaves and spiny- stemmed boojums (Fouquieria columnaris) predominate, may be the New World area most similar to the spiny forest of Madagascar.

Unfortunately, little of the spiny forest eco-region is formally protected. Of additional concern is that many of the plants and animals and their interrelationships are poorly understood. Time is running out for these forests; they are quickly disappearing and dissolving into fragmented islands, the result of deforestation for charcoal production, expanding agriculture (primarily corn), and wildfires intentionally set to prepare the land for cattle-grazing pastures.

Kalanchoe beharensis ‘Fang’

Plants of the Spiny Forest Garden

Plant families and genera that are thriving in this garden include:
Anacardiaceae (sumac and cashew family)
Operculicarya decaryi

Apocynaceae (dogbane family)
Catharanthus roseus
Cynanchum pachycladon
Pachypodium geayi
P. lamerei (
Madagascar palm)
P. lamerei
var. ramosum
Arecaceae (palm family)
Bismarckia nobilis
Dypsis decaryi
Hyphaene coriacea
Ravenea glauca
R. xerophila

Asteraceae (daisy family)
Senecio descoingsii

Crassulaceae (stonecrop family)
Bryophyllum
‘Pink Sparkler’
(B. diagremontiana x B. delagoense)
Kalanchoe beharensis
K. beharensis
‘Nudum’ and ‘Fang’
K. bracteata
‘Silver Mint’
K. fedtschenkoi
(lavender scallops)
K. pumila (dwarf purple kalanchoe)
K. tetraphylla,
K. tomentosa (panda plant)
Cucurbitaceae (cucumber family)
Seyrigia humbertii
Xerosicyos danguy
i (silver dollar plant)
Didiereaceae (didiera family)
Alluaudia ascendens
A. comosa
A. dumosa
A. humbertii
A. procera
(arbre pieuvre)
Alluaudiopsis fiherensis
Didierea madagascariensis

Euphorbiaceae (spurge family)
Euphorbia horombensis
E. kamponii
E. leucodendron
E. milii
var. tuilerena
E. umbraculiformis
Fabaceae (legume family)
Delonix decaryi
D. pumila

Malvaceae (mallow family)
Adansonia digitata
(in pots seasonally)
A. grandidieri
(in pots seasonally)
A. rubrostipa

Moringaceae (horseradish tree family)
Moringa drouhardii (maroserano)
M. hildebrandtii
Pedaliaceae (sesame family)
Uncarina decaryi
U. grandidieri

Plumbaginaceae (plumbago family)
Plumbago aphylla

Xanthorrhoeaceae (grass tree family)
Aloe acutissima var. antanimorensis
A. bulbilifera
var. paulianae
A. deltoideodonta
A. fragilis
A. ibityensis
A. millotii
A. suzannae
A. vaombe
Lomatophyllum occidentale