Desert ironwood primer – executive summary



Desert ironwood, or palo fierro in Spanish, provides many wildlife

and plants with habitat and sources important to their survival. While

scientists don’t consider ironwood endangered or threatened like a species,

its populations are dwindling quickly and recover very gradually after

exploitation. Its environmental importance comes largely with the roles

it plays for more than 500 other types of plants and creatures within the Sonoran

Desert. This report confirms ironwood’s critical role like a keystone

species and nurse plant to maintain desert bio-diversity

and makes strategies for its future protection.

Initiated with funding in the U . s . States Department of Interior

Border XXI project, our binational team launched this region-wide assessment

to assist guide land use decisions impacting ironwood habitat on sides

from the border. The research compiles almost all formerly printed literature

on ironwood ecosystem and analyzes data from 148 new study plots. The report

includes a double edged sword: first, an introduction to the environmental and historic

background of desert ironwood a discussion from the first comprehensive

binational study perennial plant diversity of ironwood habitats in

the Sonoran Desert, performed by our research team with this report.

Ironwood ecosystem

A sturdy legume tree, ironwood’s range carefully matches the limitations

from the Sonoran Desert, the only real world where it happens. The

only species within the genus Olneya, ironwood is notable because of its slow

growth rates and very dense wood. Its wood even sinks in water. While

scientists consider ironwood is the "old growth" tree from the desert,

standard tree-ring dating of their wood is tough. The Ironwood Alliance

is presently going after various ways up to now ironwoods. Estimates

show some trees to become 800 years of age, which is likely they live even

longer. Though lengthy-resided, ironwoods face many threats, both as seedlings

so that as mature trees, from habitat fragmentation, grazing, woodcutting,

and competition from exotic species.

Ironwoods blossom a lot early in the year as well as their blossoms lend a crimson

hue towards the landscape. The pea-type pods mature at any given time of the year when

very little else is producing fruit within the Arizona Uplands, resulting in a higher

dependence of wildlife on its seeds. Unlike other desert trees, ironwood

rarely sheds its leaves, to ensure that its canopy provides shade and protection

from frost and cause problems all year round.

Ironwood like a Keystone Species and Nurse Plant

Ironwood functions like a habitat modifying keystone species, that

is, a species that exhibits strong influences around the distribution and

abundance of connected species. Ironwood generates a series of influences

on connected understory plants, affecting their dispersal, germination,

establishment, and rates of growth in addition to reproduction. Scientists

call these environmental dynamics "nurse plant ecosystem". Mesquites and palo

verde also play this role, however, each tree suits slightly different

teams of plants in the "nursery". Ironwood may be the dominant nurse plant

in certain subregions from the Sonoran Desert.

As nurse plants, ironwoods provide safe sites for seed dispersal, seedling

defense against extreme cold and freezes, and sapling defense against

cause problems and damaging radiation. Additionally they work as prey refugia,

supplying herbs and cacti defense against herbivores preying on vulnerable

plant seedlings. Finally, like other legumes, they modify the soil composition

beneath their canopies, enriching the soil with nutrients for example nitrogen.

Ironwood, frequently the tallest tree in the habitat, attracts wild birds and

other seed dispersers who roost in the branches and produce a literal

"rain" of seeds and whole fruit. The mere existence of ironwood along with other

legume trees can increase the amount of bird species in desertscrub habitat

by 63%. Germination minute rates are greater and seedling survival rates better

because of the improved soil conditions. Plant health, survival and growth

will also be improved through the shade and defense against frost that ironwood’s

canopy offers. Thorny, low-sweeping branches repel herbivores, promoting

plant growth further. Consequently, the higher diversity of plants growing

in ironwood nurseries attracts a larger diversity of wild birds, both breeding

and migratory.

The connection between succulent cacti and ironwoods is particularly

extensively recorded. Recent reports reveal that with no cover

of desert legumes, the distributional ranges of saguaro, organ pipe, and

senita cactus would retreat many miles, to more southern, frost-free areas.

On freezing nights, the canopies of ironwood, below that the temperature

might be 4 C warmer compared to adjacent open areas, result in the critical difference

for vulnerable seedlings.

Ironwood plays an identical role in sheltering seedlings and saplings sensitive

to cause problems and radiation. Its canopy minimizes heat, damaging radiation,

and water stress among plants established in the shade. When stripped

of ironwood’s cover above them, some cacti really suffer

sunburn and die.

Additionally to becoming a buffer from such abiotic stresses as soil

and moisture conditions, ironwood buffers nursery plants from some biotic

stresses, especially those of herbivores. Thorny nurse plants can dramatically

reduce the quantity of predation on seedlings by small and big herbivores

for example cows, rabbits, and rodents. Occasionally, our prime quantity of

creatures that nest, burrow or seek refuge under ironwoods reduces this


Ironwood like a Cultural Resource

The numerous indigenous and ethnic cultures from the Sonoran Desert have lengthy

valued ironwood because of its cultural, in addition to environmental, sources. Traditional

products and purposes of ironwood include food, medicines, farming and

household implements, and ceremonial and ritual uses. Since most of

these uses utilized either renewable sources (pods, seeds, flowers)

or salvaged wood from already dead trees, their effect on ancient ironwood

forests was minimal.

The renowned contemporary cultural utilization of ironwood is as simple as the Seri

and Mexican carvers of seaside Sonora. The Seri started to carve elegant,

abstract renderings of native creatures within the 1960’s. They always employ dried,

already dead ironwood. Nearby Mexican communities rapidly copied the effective

types of the Seri carvings. However, their utilization of machines enables them

to create carvings for a price that is depleting the neighborhood way to obtain ironwood.

Tries to safeguard the ironwood forests in this region have to date been


The dense wood of ironwood burns very hot, which makes it the most well-liked

fuelwood in communities within the northern Mexico, where any kind of fuelwood

is scarce. Mesquite charcoal production for export towards the U.S. consumes

much more ironwood. Ironwood grows in mixed stands with mesquite and it is

cut lower being an illegal "by-catch" in exactly the same tuna nets kill

dolphins along with other species, though its harvest is generally intentional

instead of accidental. The Mexican charcoal industry boomed within the 1980’s

following the U.S. ecological laws and regulations banned highly polluting earthen pits,

a grossly inefficient method where 60% from the energy sheds. Through

the demands from the Seri yet others, the Mexican government now requires

permits for ironwood cutting, with no permits receive to chop ironwood

for charcoal production. Nevertheless the laws and regulations take time and effort to enforce, and

the motivation to chop dense, heavy ironwood is high among poor woodcutters

compensated through the weight of wood collected each day.

Threats to Ironwood

In Mexico, woodcutting alone causes a typical 17% decrease in ironwood’s

dominance within the plant life from the areas studied. The interest in wood

even transmits Mexicans within the U.S. border to chop ironwood from Organ Pipe

Cactus National Monument along with other protected areas. Other impacts threaten

ironwood habitat on sides from the border, especially habitat fragmentation

because of the rapid development of metropolitan areas for example Tucson, Yuma, Phoenix, Hermosillo

and Mexicali, and also the conversion of ironwood habitat to farming lands.

Grazing and competition by exotic species for example buffelgrass pose additional

serious threats to ironwood. Buffelgrass, a well known forage grass for cattle,

is extremely invasive. Research has shown it decreases plant species richness and

diversity in native plant communities and boosts the frequency of fires.

Fueled by buffelgrass, these hot burning wildfires destroy ironwood and

other trees and cactus. Among other threats, the populace explosion

within the Sonoran Desert has brought to growing recreational impacts in ironwood


Ironwood Diversity Study

After creating the different potential benefits mature ironwood trees

could provide to native plants and creatures within their habitats, we surveyed

16 sites scattered over the Sonoran Desert to find out whether ironwood’s

presence influenced bio-diversity very much the same whatsoever sites. Sampling

the perennial plant life in 148 new plots in 3 states, we determined ironwood’s

presence to become equally full of environmental importance in each and every subregion

from the Sonoran Desert where we measured it.

Quite simply, losing ironwood from habitats in almost any Sonoran Desert

subregion would diminish the general lushness of vegetative cover, especially

of vines. Nevertheless, the existence of ironwood in every subregion influenced

the variety of connected plants diversely, with great dissimilarities

in the kinds of understory plants found below ironwoods within the Arizona

Uplands and also the Central Gulf Coast of Sonora. In a nutshell, protecting ironwood

habitat in Pima County, Arizona, may benefit another mixture of native

species than could be conserved in ironwood habitats presently being protected

around the islands or coasts from the Gulf of California. Although ironwoods

and mesquites based in the same habitats share the majority of the same understory

species, ironwood favors some vines and shrubs greater than others, while

mesquite favors a rather different mix.

The abundance and canopy of understory plants found beneath ironwoods

varies based on their whereabouts, in the banks of dry washes in valleys

to individuals growing along small drainages on rocky slopes. Additionally, all

sizes of ironwoods don’t always function just as nurse plants

for other species. Youthful trees provide almost no protective microenvironment

whatsoever, as the large, dense canopies of ancient trees may become too

shady to permit much plant growth beneath them, as well as their greater branches

allow cows to forage under them in grazed areas.


Using a number of different measures of species diversity, richness, and

environmental importance, we’ve selected several sites as priorities for

new protection as well as for strengthened conservation management. Within the U.S.

condition of Arizona, the websites are: Ragged Top around the boundary of Pinal and

Pima Counties and also the Cocoraque Rock and Ironwood Picnic Areas on either

side of Brawley Wash in Avra Valley, Pima County. In Sonora, Mexico, the

sites are: Punta Santa Rosa north of Kino Bay, and Tecomate on Tiburn

Island, both on Seri Indian lands the southern reaches from the Sierra

El Pinacate north of Puerto Peasco (Rocky Point) and Rancho El Carrizo,

a personal ranch and masked bobwhite quail refuge near Carbo, Sonora. Although

other locations unquestionably deserve further study and protection, these websites,

using the already protected sites in Saguaro Park, Cabeza National

Wildlife Refuge, and Organ Pipe Cactus National Monument, could provide

the cornerstones for any regional reserve network to safeguard the bio-diversity

connected with ironwood habitats within the Sonoran Desert.


Desert Ironwood