Tesota Research Articles

Desert Fires Fueled by Native Annual Forbs: Effects of Fire on Communities of Plants and Birds in the Lower Sonoran Desert of Arizona

In 2005, fire ignited by humans swept from Yuma Proving Grounds into Kofa National Wildlife Refuge, Arizona, burning ca. 9,255 ha of Wilderness Area. Fuels were predominantly the native forb Plantago ovata. Large fires at low elevations were rare in the 19th and 20th centuries, and fires fueled by native vegetation are undocumented in the southwestern deserts. We estimated the area damaged by fire using Moderate Resolution Imaging Spectroradiometer and Normalized Difference Vegetation Index, which are more accurate and reduce subjectivity of aerial surveys of perimeters of fires. Assemblages of upland and xeroriparian plants lost 91 and 81% of live cover, respectively, in fires. The trees Olneya tesota and Cercidium had high amounts of top-kill. King Valley was an important xeroriparian corridor for birds. Species richness of birds decreased significantly following the fire. Numbers of breeding birds were lower in burned areas of King Valley 3 years post-fire, compared to numbers in nearby but unburned Alamo Wash. Although birds function within a large geographic scale, the extent of this burn still influenced the relative abundance of local species of breeding birds. This suggests that breeding birds respond to conditions of localized burns and slow recovery of vegetation contributes to continued lower numbers of birds in the burned sites in King Valley.

Vegetation, climate, and soil relationships across the Sonoran Desert

The distribution and abundance of dominant species and their relationships with soil and climate were investigated using a variety of multivariate statistics across 30 plots that spanned 50 000 km2 of the Sonoran Desert. Relationships between the distribution of Carnegiea gigantea and several of its nurse plant species (Ambrosia deltoidea, Ambrosia dumosa, Cercidium microphyllum, Larrea tridentata, Prosopis spp., Olneya tesota) were documented. A general east—west gradient was observed where temperature increases and precipitation decreases westwards and calcium levels, total organic carbon, particle size, and soil pH increase westwards. Western areas with high temperatures and low precipitation may have elevated levels of calcite and thus a high pH; the low rainfall limits calcium dilution within the soil. The gradient in soil pH likely governs the range of several species (e.g., Ambrosia deltoidea, A. dumosa, and Larrea tridentata) that were delineated by calcic soils in western areas from eastern regions with lower soil pH and higher precipitation. Thus, the distribution of the dominant species reflects a temperature—precipitation—calcium—pH gradient. We found that the pH gradient follows the precipitation gradient as much as the dominant species follow the pH or rainfall gradients. Although climate is thought to dominate the distributions of these species, we found that soil pH and texture are intimately intertwined and that their removal from analyses resulted in poorer explanatory power of species distributions.

Binding of PF2 Lectin from Olneya tesota to Gut Proteins of Zabrotes subfasciatus Larvae Associated with the Insecticidal Mechanism

Zabrotes subfasciatus (Boheman) is the main pest of common beans ( Phaselous vulgaris ). Wild legume seeds from Olneya tesota contain a lectin, PF2, that shows insecticidal activities against this insect. The binding of PF2 to midgut glycoproteins of 20-day-old larvae was evaluated using PF2 affinity chromatography. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) analysis of the proteins retained on the gel revealed several putative glycoproteins, ranging in mass from 17 to 97 kDa. Subsequent protein digestion and analysis by liquid chromatography-tandem mass spectrometry (LC-MS/MS) provided amino acid fragments that identified an α-tubulin, cytochrome c oxidase subunit I, an odorant receptor, and a lysozyme from available insect sequence databases. The potential of these proteins to serve as part of the mechanisms involved in the insecticidal activity of PF2 to Z. subfasciatus is discussed.

Comparative population analysis of desert ironwood ( Olneya tesota) in the Sonoran Desert

Olneya tesota (ironwood) is a keystone tree species that modifies the structure and function of Sonoran desert ecosystems. Presently, extraction of trees and branches in the region constitutes a severe risk for ironwood populations. We analyzed the size structure, two damage indicators (damaged basal area or “DBA” and percents of damaged individuals or “PDI”) for eleven ironwood populations in Sonora and Baja California, México. In four populations, we compared damage indicators obtained in 1992 and 2004. We found that in unexploited populations, small size categories (<500 cm 2 in basal area) and juveniles were better represented. In contrast in exploited populations large size individuals were severely damaged and lacked recruitment. Populations on the coast of Sonora have greater damage (up to 50% of the individuals), while those in the Baja California Peninsula exhibited less damage (smaller than 20%), with high juvenile recruitment (up to 40%). Historical comparisons of DBA and PDI exhibited non significant differences between 1992 and 2004 for three populations, and only in Bahia Kino population (Sonora) did the PDI decreased significantly. One population surveyed in 1992 (Sonoyta) was completely removed. Even that the damage seems to be constant, the damage indicators remain high, affecting the ecosystems dynamics.

Insecticidal Action of PF2 Lectin from Olneya tesota (Palo Fierro) against Zabrotes subfasciatus Larvae and Midgut Glycoconjugate Binding

Zabrotes subfasciatus (Boheman) is the main pest of common beans (Phaselous vulgaris). Some wild legume seeds may contain lectins with insecticidal activities against this insect. The larval developments of Z. subfasciatus on seeds of Olneya tesota (a desert wild legume) and on artificial seeds containing purified PF2 lectin were evaluated. PF2 susceptibility to proteolysis was assessed by incubation with midgut extract at different times. PF2 binding to midgut glycoconjugates was assessed by histochemistry. A reduced level of oviposition and a lack of emergence of adult beetles were observed in O. tesota seeds (compared to common beans), and in artificial seeds containing PF2 at 0.5 and 1%. PF2 was resistant to larval midgut proteolysis for 24 h, while PHA-E (lectin control) was fully digested after 4 h. Histochemistry analysis of midguts incubated with PF2 showed recognition for microvillae and possibly with peritrophic gel. On the other hand, PHA-E exhibited no interaction with larval midgut glycoproteins. Proteolysis resistance and glycan recognition could in part explain why PF2 is toxic to Z. subfasciatus while PHA is not.

Comparative performance of the giant cardon cactus ( Pachycereus pringlei) seedlings under two leguminous nurse plant species

Recruitment and survival of cacti in North American deserts are facilitated under the canopy of nurse plants. In the Sonoran desert, the giant cardon cactus ( Pachycereus pringlei) is associated with ironwood ( Olneya tesota) and mesquite ( Prosopis glandulosa) trees. We hypothesized that P. pringlei seedlings would perform better under ironwood than mesquite, on the basis of the mature individuals patterns of association. In Bahia Kino, Sonora, we conducted a field experiment from 1992 to 2000 comparing the performance of P. pringlei seedlings under randomly selected O. tesota, and P. glandulosa trees. Results indicated that P. pringlei seedlings under P. glandulosa had significantly higher survival and were significantly taller than those under O. tesota after 8 years. Micro-environment and soil properties beneath both trees did not differed significantly, while tree physiognomies differed only in height at the base of the canopy and basal area. As a deciduous tree, P. glandulosa provided more litter to the ground than O. tesota. These results therefore did not support our initial hypothesis. We discuss how other biotic factors such as differential seed dispersal might explain why P. pringlei establishment is more strongly spatially associated with O. tesota.

Multivariate characterization of Sonoran Desert vegetation in southwest Arizona using US Army field data

This paper describes the classification and ordination of Sonoran Desert vegetation using systematically collected data from the US Army Yuma Proving Ground (USYPG). Two classifications were created, one based upon relative plant cover derived from 100 m line transect data and one based upon relative plant density derived from 6 m . × 100 m belt transect data, with the belt transect being a lateral extension of the line transect. Both cluster analysis using Ward’s Method and TWINSPAN were used for classifying the data while Principal Component Analysis, Correspondence Analysis, Detrended Correspondence Analysis, and Non-Metric Multidimensional Scaling were used as ordination methods. Cluster analysis was superior to TWINSPAN in creating logical classifications comparable to published descriptions of vegetation communities found in the Lower Colorado Subdivision of the Sonoran Desert. Together, the ordination methods served to accentuate different aspects of the data including main gradients of species composition, in particular a gradient separating plots with riparian-af-finities from the main data set, a Larrea tridentata-Ambrosia dumosa gradient, and a gradient separating Encelia farinosa from the main data set. The main difference between the relative cover and relative density classifications was that the former under-represented cacti such as Opuntia bigelovii and the latter under-represented such as Parkinsonia microphylla and Olneya tesota. The classification methodology used in this study is useful for evaluating resource sampling strategies on U.S. Army bases in sparsely vegetated areas and the classifications could be used as a baseline for monitoring changes in vegetation communities.

Resource Use and Nesting Behavior of Megachile prosopidis and M. chilopsidis with Notes on M. discorhina (Hymenoptera: Megachilidae)

The nesting behavior of Megachile prosopidis Cockerell, Megachile chilopsidis Cockerell, and Megachile discorhina Cockerell was studied in trap nests placed near Tucson, Arizona. Quantitative differences among the five distinct nest plugs made by M. prosopidis are described. The nest plugs fall into three structural types. The first layer of capping material deposited in the first structural type is sand and an unidentified oral secretion mixed to form a hard layer. In the second structural type, the first layer is made of soft resin mixed with sand or organic matter. A third, less common, structural type includes those nests capped with pure resin. The dominant pollen host plant species was identified as Cercidium microphyllum (Torr.) Rose and Johnston (Fabaceae). Two other legumes, Prosopis velutina Wooton and Olneya tesota A. Gray, became important pollen sources late in the nesting season. Resin samples taken from the nest caps were indistinguishable, by gas chromatography, from resin of Encelia farinosa A. Gray (Asteraceae). The following parasites and predators were reared from the nests: Tricrania stansburyi Haldeman (Coleoptera: Meloidae), Lecontella gnara Wolcott (Coleoptera: Cleridae), Anthrax cintalpa Cole (Diptera: Bombyliidae), Stelis (Dolichostelis) perpulchra Crawford (Hymenoptera: Megachilidae), and Sapyga sp. Latreille (Hymenoptera: Sapygidae). New host records are reported for T. stansburyi, L. gnara, and A. cintalpa.

Purification and characterization of complex carbohydrate specific isolectins from wild legume seeds: Acacia constricta is (vinorama) highly homologous to Phaseolus vulgaris lectins

Vinorama isolectins (VL2–VL4) were purified from seeds of Acacia constricta (vinorama) using affinity chromatography on a fetuin-fractogel column followed by cationic-exchange chromatography. Each isolectin fraction presented a characteristic isoelectric point range from 5.5 to 8.4. Under native conditions, VL containing fractions migrated as tetramers of 133 kDa, while in SDS-PAGE, in presence of 2-mercaptoethanol, a single subunit band with M r of 34 kDa was observed. VL was found to be a glycoprotein with a 7.5% neutral sugar content. Antibodies to Phaseolus vulgaris lectins PHA and other wild legume lectins as Olneya tesota (palo fierro) PF2 and PF3, and Parkinsonia aculeate (palo verde) PV reacted with VL, but not with anti Glycine max agglutinin SBA or anti Lotus tetragonolobus agglutinin LTA. Furthermore, direct analysis of VL peptides showed sequences homologous to those reported in different lectins of the Phaseolus genus. VL2–VL4 did not have ABO serological or simple sugar specificity, but were inhibited by complex carbohydrates from fetuin and thyroglobulin. Asialofetuin carbohydrates strongly interacted with VL4 and VL3. Vinorama isolectins could be classified as “complex lectins”.

Habitat use by desert bighorn sheep in sonora, México

The use of habitat components by desert bighorn sheep ( Ovis canadensis ) was examined to explain sexual segregation of sheep in Sierra el Viejo, Sonora, Mexico. We evaluated 265 plots used by bighorns and 278 random plots from April 1997 to December 1998. Groups of segregated males and females preferred the elephant tree ( Bursera microphylla )-salvia ( Salvia mellifera )-limber bush ( Jatropha cuneata ) association (ESL) and avoided the foothill palo verde ( Cercidium microphyllum )-desert ironwood ( Olneya tesota ) association (FDD. Segregated females selected the ocotillo ( Fouquieria splendens )-desert agave (Agave spp.yhop bush ( Dodonoea viscosa ) (OAH) vegetation association, formed larger groups, were closer to escape terrain, and occupied more rugged areas during autumn and spring than males. Segregated females selected areas that provided more opportunities to evade predation than did males.

Research Observation: Desert Bighorn Sheep Diets in Northwestern Sonora, Mexico

We used microhistological analyses of fresh fecal pellets to determine seasonal diets of desert bighorn sheep (Ovis canadensis mexicana Merriam 1901) in northwestern Sonora, Mexico from April 1997 to December 1998. We identified 41 plant species (22 browse, 10 forbs, 5 grasses, and 4 succulents) in diets of bighorn sheep. We found no differences between diets of males and females, and diet diversity between sexes was similar (P > 0.05). Diet included: browse (45.7%), forbs (32.0%), succulents (17.8%), and grasses (4.5%). The consumption of succulents was higher during spring, decreased during summer, increased in autumn, and decreased in winter. Consumption of forbs was higher during winter and summer. Globemallow (Sphaeralceae spp.), desert agaves (Agave spp.), range ratany (Krameria parvifolia Benth.), buck-wheatbrush (Eriogonum spp.), foothill palo verde (Cercidium microphyllum [Torrey] Rose &Johnst.), Engelmann prickly pear (Opuntia engelmanii Salm-Dyck), desert ironwood (Olneya tesota A. Gray), and elephant tree (Bursera microphylla A. Gray) were consumed throughout the study. As biologists identify potential release sites for restoration of bighorn sheep in Mexico, studies of diet composition will provide managers with information for successful translocations. DOI:10.2458/azu_jrm_v55i6_tarango

Variation in mistletoe seed deposition: effects of intra‐ and interspecific host characteristics

We investigated differences in host infection by a desert mistletoe, Phoradendron californicum, and examined one of the processes that contributes to these differences: variation in seed deposition among host individuals and species. In the Sonoran Desert, P. californicum parasitizes the sympatric leguminous trees Olneya tesota, Cercidium microphyllum, Prosopis velutina, Acacia constricta, and Acacia greggii. We hypothesized that seed deposition depends on host height and crown architecture. At a site in Arizona, frequency of infection did not reflect host relative abundance. Olneya tesota was parasitized at a higher frequency than expected from its abundance and maintained the highest mistletoe loads per individual host. In contrast, P. velutina was infected less frequently than expected. Infection frequency increased with host tree height for all hosts. Mistletoe seed deposition by avian dispersers differed among host species and was disproportionately high in O. tesota and P. velutina. Seed deposition was higher in infected than in non‐infected host trees, and increased with tree height in O. tesota but not in C. microphyllum. We suspect that increased seed deposition with height in O. tesota may be due to the preference of seed‐dispersing birds for higher perches. Some host tree species, such as C. microphyllum and A. constricta, probably received fewer mistletoe seeds because birds avoid hosts with dense and spiny crowns. Mistletoe populations are plant metapopulations in which host trees are patches and the frequency of infection in each host species/patch type is the result of interspecific differences in the balance between mistletoe colonization and extinction. From this perspective, our study of host use and seed dispersal is a metapopulation study of patch occupancy and propagule distribution among available patch types. Our seed‐dispersal study demonstrates that the mechanisms that create pattern in patchy plant populations can be investigated in mistletoe systems.

Research observation: Desert bighorn sheep diets in northwestern Sonora, Mexico

We used microhistological analyses of fresh fecal pellets to determine seasonal diets of desert bighorn sheep (Ovis canadensis mexicana Merriam 1901) in northwestern Sonora, Mexico from April 1997 to December 1998. We identified 41 plant species (22 browse, 10 forbs, 5 grasses, and 4 succulents) in diets of bighorn sheep. We found no differences between diets of males and females, and diet diversity between sexes was similar (P 0.05). Diet included: browse (45.7%), forbs (32.0%), succulents (17.8%), and grasses (4.5%). The consumption of succulents was higher during spring, decreased during summer, increased in autumn, and decreased in winter. Consumption of forbs was higher during winter and summer. Globemallow (Sphaeralceae spp.), desert agaves (Agave spp.), range ratany (Krameria parvifolia Benth.), buck-wheatbrush (Eriogonum spp.), foothill palo verde (Cercidium microphyllum [Torrey] Rose Johnst.), Engelmann prickly pear (Opuntia engelmanii Salm-Dyck), desert ironwood (Olneya tesota A. Gray), and elephant tree (Bursera microphylla A. Gray) were consumed throughout the study. As biologists identify potential release sites for restoration of bighorn sheep in Mexico, studies of diet composition will provide managers with information for successful translocations.

Evaluación oxidativa de las mezclas de aceites de leguminosas del Desierto de Sonora con aceites de maíz y soja durante su almacenamiento

During storage, oils from seeds of wild legumes of the Sonoran Desert have shown greater stability than oils derived from conventional sources. In this work, oxidation process was evaluated during the storage (122 day) of mixtures of oils: Mezquite Prosopis juliflora, Gatuna Mimosa grahamii, Palo fierro Olneya tesota, Vino rama Acacia constricta, Palo de brea Cercidium praecox and Palo verde Parkinsonia aculeata with oils from soy and maize. Ratios were 1:1, 2:1 and 3:1. Evaluated parameters included: Peroxides (P.V.), Iodine (I.V.), Acid (A.V.), p-Anisidine (p-A) values. Results showed that mixtures containing wild and maize oil showed 2-4 meq/Kg as initial values of iodine, while after 122 days of storage the value was 4-7 meq/Kg. Mixtures containing soy oil presented 3-6 meq-Kg initially, and 8-15 meq-Kg were detected at the end experiment. No differences were observed in I.V. and A.V. values in maize mixtures. On the contrary, mixtures containing soy oil presented increments in I.V. Also, A.V. presented a slight increment in 1:1 mixtures. p-Anisidine values presented and small increment in maize mixtures (3:1 ratio) while this increment was larger in mixtures containing soy oils and Gatuna or Palo fierro oil. These latter oils when were mixed with maize oils presented the lowest increments in all evaluated indexes. The oils of palo fierro and blended gatuna with oil of corn didn’t present changes in their concentration in the palmitic and araquidic acid during the storage. The concentration of the oleic acid in the mezquite oils (3:1), gatuna (1:1, 2:1 and 3:1), vinorama (3:1), as well as the linoleic and erucic acids in gatuna in their three mixtures didn’t present changes neither alteration during the storage, for what you are considered the oils of palo fierro, gatuna and vinorama the most stable in the present study.

Aspergillus flavus and Aflatoxin Contamination of Leguminous Trees of the Sonoran Desert in Arizona

ABSTRACT Aspergillus spp. in section Flavi were frequently associated with desert tree legumes in uncultivated areas of the Sonoran Desert. Of 270 samples of debris and fruits of mesquite (Prosopis spp.), ironwood (Olneya tesota), acacia (Acacia spp.), and palo verde (Cercidium and Parkinsonia spp.), 87% were positive for A. flavus (S and L strains) and A. tamarii. A. flavus was the most common species (87%) among the 3,763 isolates examined. Mesquite pods were both the substrate from which A. flavus was recovered most frequently and the substrate from native habitats with the greatest aflatoxin content. In vitro, most desert legumes supported significant growth, reproduction, and aflatoxin production by A. flavus, with mesquite pods yielding 1 x 10(10) propagules/g and 5,000 mug/kg of aflatoxin B(1). Twenty percent of legume pods collected in the desert contained measurable quantities of aflatoxin, ranging from 1 to >2,500 mug/kg. Insect-damaged mesquite pods had significantly higher aflatoxin than intact pods. Legumes are apparently important reservoirs of aflatoxin-producing fungi and significant sources of aflatoxin contamination in the native Sonoran Desert habitats of Arizona.

Positive interactions under nurse-plants: spatial scale, stress gradients and benefactor size.

Positive interactions often play an important role in structuring plant communities and increasing biological diversity. Using three scales of resolution, we examine the importance of a long-lived desert tree, ironwood (Olneya tesota), in structuring plant communities and promoting biological diversity in the Sonoran Desert. We examined the positive effects of Olneya canopies of different sizes on plant communities in mesic and xeric habitats throughout the central Gulf Coast subregion of Sonora, Mexico. In xeric sites, Olneya canopies had strong positive effects on plant richness and abundance, and small positive effects on the size of plants, underscoring the role of facilitation in extreme environments. In mesic sites, Olneya canopies had very little effect on perennials and a negative effect on ephemeral richness, suggesting predominantly competitive effects in this less stressful environment. Overall, Olneya canopies increased biological diversity where abiotic stress was high, but did not increase diversity in more mesic areas. Thus Olneya canopies caused consistent shifts in plant-community structure among xeric and mesic sites, but not when these landscapes were combined. Benefactor size also mediated positive interactions, with larger Olneya canopies supporting larger perennials in both xeric and mesic sites. Thus stress gradients and benefactor size both influenced the balance of facilitative and competitive effects under nurse-plant canopies, and the spatial scale at which facilitative effects shape community structure.

Índices de oxidación en aceites de algunas leguminosas del desierto sonorense

The oxidation process of crude and refined oils from wild leguminous seeds: Prosopis juliflora (mezquite), Mimosa grahamii (gatuna), Acacia constricta , (vinorama) Olneya tesota , (palo fierro) Cercidium praecox (palo de brea) and Parkinsonia aculeata (palo verde) were evaluated during storage for 122 days, using corn and soybean oils as controls. Peroxide, Iodine, Acid and p-Anisidine values were determinated during 122 days of storage at room temperature. The wild leguminous raw oils showed results similar to those for the corn raw oil and lower than those of soybean raw oil. This behavior was similar for refinated oils. The rancid odor was detected after 5 days of storage in soybean oil and 40 days in vinorama oil, on the contrary, mezquite, palo verde and palo of brea oils presented this odor after 62 days, and for gatuna’s oil needed 135 days. Our results indicate that legume seed of Sonoran Desert could be a good alternative as source of oil.

Nurse Plants, Mycorrhizae, and Plant Establishment in a Disturbed Area of the Sonoran Desert

AbstractArbuscular‐mycorrhizal (AM) fungi stabilize the soil and enhance plant growth by alleviating nutrient and drought stress. Their contributions to agriculture are well known, but their role in desert ecosystems has received less attention. The AM status of perennial plants in disturbed and undisturbed plots were investigated in the Sonoran Desert near La Paz, Baja California Sur, Mexico to determine if AM fungi contribute to resource‐island stability and plant establishment. All perennial plants (46 species) in the study plots were AM, but root colonization varied widely (&lt;10 to&gt; 70%). Roots of plants that established in greatest numbers in plant‐free zones (colonizers) of disturbed areas were highly AM. Plants with trace (&lt;10%) root colonization (cacti of the tribe Pachycereae: Pachycereus pringlei, Machaerocereus gummosus, and Lemaireocereus thurberi; and Agave datilyo) established preferentially in association with nurse trees. The pachycereid cacti grew under Prosopis articulata and A. datilyo under Olneya tesota canopies. Of the nine species of trees and arborescent shrubs in the area, the mature (&gt;20 yr) nurse‐legumes P. articulata and O. tesota supported the largest number of under‐story plants. Younger plants had only occasional associates. AM propagule densities in plant‐free areas were lower than under plant canopies (40 vs. 280 propagules/kg soil). Occurrence of soil mounds (islands) under plants owing to soil deposition was related to the nature of the canopies and to the AM status of the roots. Island soils were enmeshed with AM‐fungal hyphae, especially in the upper layer (approximately 10 cm). Seedlings of P. pringlei, growing in a screenhouse for six months in soil collected under P. articulata, had a biomass ten times greater than plants growing in bare‐area soil. The results are consistent with the proposition that AM fungi contributed to the plant‐soil system of our study area by: (1) helping to stabilize windborne soil that settles under dense plant canopies; (2) enhancing the establishment of colonizer plants in bare soils of disturbed areas; and (3) influencing plant associations through differences in the mycotrophic status of the associates.

336 Seasonal Effects on Growth of Olneya tesota following Root Pruning

Seedlings of Olneya tesota A. Gray (desert ironwood) were grown in 12-L containers filled with a peatmoss and pumice substrate (1:1 v/v) for 3 months under simulated summer or winter Sonoran Desert conditions in a walk-in growth chamber. Growth room irradiance (550 mmol•m-2•s-1) was provided with an even mixture of mercury vapor and high-pressure sodium high-intensity discharge lamps. Growth room air temperature and relative humidity were ramped hourly to approximate typical summer or winter weather conditions based on mean seasonal climatological data for Phoenix, Ariz. For simulated summer conditions, maximum/minimum air temperature range was 40/28 °C and maximum/minimum relative humidity range was 25%/12%. Photoperiod was 16 h. For simulated winter conditions, maximum/minimum air temperature and relative humidity were 20/5 °C and 80%/35%, respectively. Photoperiod was 10 h. After 2 months, desert ironwood root systems were cleaned of substrate by floatation in a water bath, pruned to a length of 15 cm, repotted, and then grown for an additional month under the same conditions. Only 41% of desert ironwood survived root pruning under summer conditions compared with a 100% survival rate under winter conditions. For surviving desert ironwood, shoot and root extension growth was significantly greater under summer conditions.

EXPLOITATION AND CONSERVATION OF IRONWOOD (OLNEYA TESOTA) IN THE SONORAN DESERT

An increasing trend in desert ironwood (Olneya tesota) exploitation in Sonora has affected the population structure, growth, and recruitment of this species near the Gulf of California in the Sonoran desert. In a survey of protected and unprotected sites in Mexico and the United States, we determined that the damage has resulted in a significant reduction in the amount of shaded area for the plant communities. Exploitation is highest in the Mexican stands near the international border, but high basal area percentages of damaged trees were detected in protected areas in both the United States and Mexico. One area of particular interest is the administrative boundary of the Organ Pipe Cactus National Monument (ORPI) with Mexico, where harvesting of ironwood in the border creates a boundary effect with the ironwood populations that inhabit both sides of the ORPI border. Harvesting of ironwood is for firewood, charcoal, and wood carving.