Saguaro (Carnegiea gigantea) and organ pipe (Stenocereus thurberi) run up and down the southern face of Mesa Masiaca, Sonora.
I can now say that I have traveled to all four ends of saguaro country. I actually live near both the north end (about 10 to 15 miles south of Kingman AZ) and west end (the Whipple Mountains on the California side of the Colorado River opposite Lake Havasu City) and have obviously photographed and hiked extensively in those places. I’ve also passed through the east end of saguaro range (near Safford AZ) in years past and gone pretty far south in Sonora, Mexico. But I have never before this past weekend actually seen the southernmost population of wild saguaros, which occurs on the slopes of Mesa Masiaca, located about 25 miles southeast of the southern Sonoran town of Navojoa. This post shows photos of some of those saguaros.
Mesa Masiaca rises a couple hundred feet above the flat coastal plains of southern Sonora. A sizable microwave tower installation occupies a ridge atop the mesa.
At this southerly latitude, saguaros have trouble surviving in the increasingly thick tropical dry forest that dominates the landscape. The vegetation shifts out of Sonoran Desert and moves towards a wetter and more tropical climate dominated by numerous thorny small trees and large shrubs. The rainfall patterns and hot humidity combined with dense, competitive vegetation means that generally saguaro seedlings are unable to survive to reproductive maturity, and the plants are confined to the most open, driest, and rockiest slopes. At this particular outpost, conditions are still correct enough to enable saguaros to live amidst the dark basalt rocks of the mesa. They are absent from the flatter areas, and are no longer known to be found south of here. There are numerous other cactus species that take over the ecological niche fulfilled by saguaros, all the way down into Argentina, but saguaros come to an end here near Masiaca, Sonora.
Organ pipe cacti (foreground) are the most abundant columnar cactus of southern Sonora, occurring in extensive stands on some parts of the flats – at least the portions that have not been cleared for large scale agribusiness – and are common in lower densities on various hillsides.
Interestingly, I drove the entire north to south distribution of saguaros in only two days. I suspect that saguaros that originate near me in Yucca, Arizona at the north end of saguaro country would not necessarily enjoy the heat and humidity present near Masiaca in the south. I also strongly suspect that saguaros started from seed on plants growing near Masiaca would not tolerate the hard freezes of 15 to 20 F (-6 to -9 C) that happen here in winter annually, since the climate this far south is essentially frost-free. If I had to estimate which one would do better, it would be that the northern saguaros will adapt better to tropical Masiaca than the opposite situation.
Another tropical columnar cactus that appears in southern Sonora is the etcho, Pachycereus pecten-aboriginum. They look superficially a lot like organ pipes do, but they have a distinct woody trunk of about 2 meters high, darker green stems with a different rib count, and the golden-spined bristly fruits are completely different, among other anatomical and floral differences. One such fruit can be seen on one of the taller stems towards the left of the plant.
Obviously there is no way of fully knowing whether these hypotheses are accurate or not without actually testing it out. One would have to use seeds from both places and geographically switch their positions, and spend years, even decades, growing them into sizable plants and comparing notes as to performance. You would need a large enough sample size (probably hundreds of plants) and track them accurately in both locations over the course of decades in order to get a statistically valid analysis of growth rates, survival, and reproductive success. I don’t see this happening, but it’s still interesting to ruminate on.
The numerous mountain ranges of southern Sonora are beautiful and rugged, showing clear affinity to the so-called Sky Island mountain ranges of southern Arizona. Here, another stand of saguaros not too far north of Navojoa show that they are most prevalent upon well-drained and more open hillsides, as opposed to in the thicker thornscrub vegetation of the flatter areas. The date palm tree to the right probably demarcates the location of a small house belonging to a rural farmer or rancher.
After some discussion via Facebook comments, it was established that an easier way to determine genetic divergence in saguaros across various populations growing across the species sprawling natural range would be to do a specific type of DNA analysis. By sampling about 30 or so plants in each of at least five different geographical locales scattered widely across their range, and then running comparative DNA sequencing to determine how different those populations are on a genetic level, one can get a good sense of how heterogeneous the general saguaro population is.
If there is significant divergence between the genetics of a northern stand of saguaros near me in Yucca AZ and the Mesa Masiaca stand in the south, and a gradation of variance for groves in between, then it can be inferred that cold hardiness might potentially be a trait that was selected for by evolution in the north. Of course just because there might be some notable genetic differences doesn’t automatically mean that it is cold hardiness in particular that is being reflected; but it does indicate that there has been enough time elapsed to allow for those divergences to surface, and cold tolerance might be one such trait that was selected for. However if the saguaro DNA shows only minimal divergence and high similarity regardless of geographical origin, then it would be fairly safe to say that they are all likely to be roughly the same hardiness since there has been little genetic drift in whatever time they’ve been separated by those 800+ miles between north and south.
In the end, however, the question of cold tolerance variations is unlikely to be answered anytime soon. The question is primarily of interest to cactus enthusiasts and those who enjoy scientific inquiry in the ecological realm, but there is otherwise little demand for an answer to it. It has no major commercial applications and may not have much bearing upon future conservation one way or the other, and as such I’d expect that the question will remain in the formally unanswered category. After all, if one wants saguaros with extra cold tolerance for some reason, the most sensible option is simply to go to Yucca AZ and get seeds off of plants there, rather than heading much farther south for seeds.
Even if cold hardiness is similar across the entire range of saguaro country, without direct field-testing requiring decades and full-scale analysis of the results, it’s simply just easier to go directly to the north and get seeds from there. If there is a significant difference, then nature will probably have rooted out the answers long ago and made the plants on and near D:F Ranch hardier to withstand the rare, but deadly, sub-Arctic winter blasts that can and do occur here, where I live.
Regardless, it was great to finally get to see the southernmost wild saguaros on earth. By going that far away from my normal daily routine, I was able to experience a combination of both familiar and exotic landscapes spanning two neighboring nations. It was a pleasure to finally reach the fourth cardinal direction of saguaro country, at age 51 years old. 🌵💥💦❄️🇺🇸🇲🇽🌵
Some years ago I had some emails with Park Nobel, Environmental physiologist of cacti, now retired and aged 80. He told me he conducted experiments of saguaro cold hardiness in controlled environment, presumably with juvenile plants. He concluded hat saguaro, when properly acclimated, can withstand minimum temperature of -9 °C for few hours, at the condition that temperature raise up to 0 ° C within 24 hours. Indeed, in several book of ecology is reported that the demarcation line of saguaro distribution in the North correspond to the line of where occasionally fails to thaw. So this is probably the physiological limit of the species.
That does seem to be a fairly valid parameter of their distribution and limitation of cold tolerance. I have experienced temperatures as low as 12 F (-11 C) here and 18 F (-7 C) is not infrequent, happening once every 3 to 4 years it appears. Adult plants on southern slopes amidst large rocks probably do not see quite that low, perhaps a couple of degrees warmer. But it is important that daytime temps do rise above freezing. If that does not happen, it is damaging to adults and deadly to youngsters. Temps of only -1 to -2 C (just below freezing) that last for several days because of a fog layer will probably be worse for saguaros than a brief, colder drop that rises above freezing in the daytime. These sorts of steady below freezing temps really don’t occur in the Sonoran Desert, but they can happen in parts of central California, Texas, and elsewhere that saguaros don’t grow. It is pretty important that they get above freezing in the daytime, that much is clear.
In the Southernmost area of distribution freezing never occurs. I suspect that there saguaro are limited by occurrence of clay soils. They live well in the rocky slopes because the soil is well drained, while in flat areas higher clay content is likely to occur, and this easily lead to root rot, as I experienced myself several times.
Coming back to the Northernmost population it would be interesting to ascertain whether the acclimation is more pronounced in terms of minimum temperature, or rather in terms length of period below 0 °C.
Saguaros don’t thrive in finer texture silt and clay soils but will definitely live upon them if the climate and rainfall are suitable. But such soils in wetter climates will tend to support many legume trees and shrubs (and other plant families too, of course) that compete strongly with the seedlings. While seedlings require some shade and assistance to get started in deserts, if the competition and shading are too strict, then they may not survive, especially in denser soils and if those soils stay wet for more extended times. I think it is a combination of factors, not just soil.
Also rot isn’t the only things about dense soil that inhibits growth of cacti. It is the reluctance of small-particle soils to get adequately moist in low rainfall places. It takes proportionally more rain to make clay soil damp than coarser soils with a higher proportion of sand or rocks mixed in. In a low rainfall climate where saguaros survive on rocky hills and gravelly alluvial slopes, but not on finer silty or clay soils on the valley flats, it is soil dryness that stops seedlings from establishing and surviving. Rot isn’t really the issue, but drought. The exact same rainfall only a few hundred yards away on a rocky fan or slope can yield numerous saguaros. Vegetation is not dense on valley floors in the more arid deserts, so competition and shading isn’t an issue, but hot sun is. Most saguaros in the drier parts of their range don’t like clay soils because it doesn’t offer enough water or shade, and rotting isn’t the problem. But in southern Sonora it might be when combined with shade and dense plant coverage/competition.
There are places where there is a proper balance however, and there are finer soils on flat lands, with enough rainfall, and enough plant cover to provide nurse tree shade but not outcompete seedlings. These places are covered with many saguaros of different ages. You can see places that fit this description in south-central Arizona, southwestern Arizona, and central and northwestern Sonora. Of course the saguaros are even more common on hillsides in rocky soils, but the flats have numerous plants too. The texture is fine silt and clay even, but it is neither too dry nor too wet, and in those places saguaros will grow just fine when compared to the extremes of their range.
Climate change may alter the rainfall enough in the future that this will no longer be the case of course, but clay soils are not a total deal breaker for saguaro growth either. Again, I think it is a combination of factors that can vary from valley to valley.
Jan, I enjoyed this latest post very much since I love saguaros but doubt if I would explore their Southern most terminus. Interesting discussion as to whether hardiness of Northern versus Southern varieties are more sustainable. It makes me wonder whether climate changing trends may favor the Northern species since temps may increase over time, but moisture may not? Thanks for the enjoyable read. Jack
I address this point to some extent in replies to Enrico Ceotto and his comments, discussing the interplay between soil, rainfall, and associated plants. Climate change is a wild card and it is hard to predict how saguaros might respond in every given location. Overall, however, a reduction in rainfall reliability and increases in variability (greater floods, swinging back and forth between longer droughts and more severe heat waves) is likely to make seedling saguaro survival more tenuous. And obviously a reduction in rainfall amounts, not just their timing and spacing, will likely have a harmful effect upon saguaros and most other plants. Stability of temps and moisture availability is an asset to seedling survival, and not just for saguaros, but also to desert trees and shrubs that are just as important to the larger ecosystem.
Thanks for your feedback and glad you enjoyed the post. 🙂
Jan, I had direct evidence that both saguaro seedlings and juveniles plants can hardly survive on clay soils. The problem with clay soils is that they are rich in micropores (where water is stored against gravity) and very poor in macropores (where water flow away and therefore air and so oxygen remain). Many plants suffer the lack of oxygen that are determined in clay soil in case of heavy precipitation (tobacco is a good example). The explanation of drought on clay soils is not convincing, because more pronounced drought conditions are present for sure on rocky slopes where most of the rainfall water flow away, and only a little portion can be stored by the coarse soil. But the advantage in this case it that the abundant macroporosity allows the root to take advantage of the necessary presence of air and oxygen. Roots need oxygen for respiration.
We are talking past each-other on this point to some extent. I am not claiming that saguaros thrive on clay soils, because they do not. But clay soils are also much rarer in the desert than you appear to assume – the majority of soils in valleys in saguaro range are on the sandy side, grading down to fairly fine silt, but not as far as clay. So in a sense the point hardly matters because true clay soils are quite uncommon in saguaro country, and where they do exist, there are almost no saguaros upon them anyway.
Going on to the silt soil question, which is somewhat larger particle sizes, maybe almost being fine sand but not what we might normally call “sandy”, saguaros also do not favor those as much as they might sandier flats. Truly silty soils (again, not clay) are found mostly in the middle of the valleys at the lowest elevations the farthest distance away from the mountains which produce the largest particle sizes that are the hardest to carry in water flow. Saguaros are not prevalent in such soils, but occasionally they do exist.
Sandy desert soils in valleys are by far the most common types. They range from coarse sand mixed with gravel to fairly fine sand, but still recognizably sandy. Here is where rainfall starts to play a large role in whether saguaros can survive upon them. In places receiving about 200 MM of rain a year (8 inches) that are also fairly frost-free, these sandier flats are capable of supporting substantial vegetation communities with good diversity and that includes saguaros. This is indeed shown in the photo you emailed me of the flats west of Sonoyta, Sonora, Mexico, which is a place I visited and photographed in a blog post on the border wall that you can also find on this blog’s home page. But if you go farther west and northwest into Arizona, the valley saguaros nearly disappear because the rainfall quickly drops to only about 100 mm (4 inches) per year. The soil doesn’t change a great amount from the prevalent sand, but the rainfall does. There are also fewer other plant species and those that exist are more widely spaced. Water is the limiting factor. Meanwhile, saguaros continue to be present on the hillsides and rocky slopes in these drier areas. They are not as abundant as farther east, but they are present in moderate numbers, and absent from the valley soils, sandy or otherwise.
Here, near me at the northern end of saguaro range in Yucca AZ, the soils are uniformly sandy both below the mountains and also fairly far off into the centers of the local valleys. Most of the soils in this northwesternmost region of the Sonoran Desert are coarse sand mixed with small rocks, and rainfall averages between 150-225 mm a year (6 to 9 inches) depending upon distance from the mountains. The soils and rainfall profiles are not at all dissimilar to that of the Sonoyta region and Organ Pipe Cactus National Monument, AZ which lies directly across the border. Both are dominated by granitic mountain ranges, with some volcanic ranges, and saguaros love both types of substrate. Rainfall is similar. Yet I see a near total lack of saguaros on the flats near me. I know of a handful of widely spaced exceptions, located far apart and living isolated from the nearest saguaro colonies on mountains miles away; but aside from these loners on the flats near Yucca, they basically live only on the hillsides, generally those facing south, east, and west.
Why is this? Temperatures in winter. The Sonoyta region experiences very few frosts, sits at a lower elevation of about 150-200 meters (500-800 feet), is farther south, and whenever it does freeze the temps are usually only 1-2 C below freezing and only for a few hours. Meanwhile Yucca experiences significant frosts multiple nights per year, sometimes -5 to -7 C for up to 12 or 14 hours at a time, is farther north by several hundred KM, and sits at 600 to 1100 meters (1800 to 3500 feet). Cold air drains away from slopes on winter nights since it is denser, and the valleys might ironically be 2 to 5 C colder than nearby south facing rocky slopes. That is the difference: Cold winter air, not rain and not rotting. If my valley where Yucca is located were in central Sonora, Mexico but otherwise identical, there would no doubt be numerous saguaros on the valley floor and probably other more southerly cactus species joining them.
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You are overstating the case that it is rot that is responsible for the failure of saguaro seedlings to establish themselves in habitat on various soils, especially clay ones. I don’t dispute your direct experience that in Italy planting your saguaros in poorly drained clay soils would result in rotting. That would happen to me too in Arizona were I to use clay soil and water regularly, but it’s not indicative of field conditions in the wild. I would never recommend planting in clay soils in a climate receiving over 200 mm rain a year and even in places receiving less than that I still would not recommend planting in clay if it can be avoided. Which in the US deserts, it almost always can be avoided.
But onward to rot in habitat: At least 50% of saguaro country in Arizona and Sonora receives a maximum of 200 mm rainfall a year, and I suspect that it is probably more. Some regions of Sonoran Desert in the wetter eastern and southeastern locales in both MX and AZ might receive as much as 16 inches (400 mm) of rain per year. David Yetman and Alberto Burquez who guided the trip to this part of Sonora said that this southernmost region of Mesa Masiaca only receives an average of about 200 mm a year, despite the denser growth of vegetation and leguminous trees that occurs farther north with similar rainfall. This is probably because of the proximity of the reserve less than ~20 km (13 miles) from the ocean (Gulf of California) and the nearly tropical, frost free climate which enables much higher humidity for more months of the year than is found over most of the interior Sonoran Desert. More humidity plus frost free = higher plant diversity and density, and less water loss than in drier conditions, so what rain does fall lasts longer before evaporating.
The soil at Coteco Pitayal Reserve is quite dense, bordering between fine silt and clay, and it is quite flat so drainage is poor. David Yetman wrote in an article about the reserve that during rains, standing water that lasts for hours or even a day or two is not uncommon and that the roads become nearby impassable due to sticky clay gumming up the wheels and making everything slippery. Saguaros clearly do not like this soil and they are not found on the flats in or near the reserve. But I did observe several planted saguaros in homesteads, farms, and as landscaping in towns nearby and they appeared normal and healthy despite the dense soil, that must presumably be pretty similar to that at the reserve since they were close by. I didn’t take photos because I didn’t see it as that unusual or important, but saguaros are growing in these heavy soils, although they were planted there.
Also, is is important to note that the organ pipe cactus (Stenocereus thurberi), and several other species of cactus including Stenocereus alamosensis, Lophocereus schottii, Pachycereus pecten-aboriginum, Ferocactus herrerae, Mammillarias of two species (one is M. bocensis, the other I don’t know yet), and several Opuntia species all thrive in this sticky and occasionally waterlogged soil. Not to mention other succulents and caudiciform plants of several different families. Rot is clearly not a major issue for any of them. Maybe saguaros are the sole exception and are unusually rot prone, but given the abundance of other succulents and the presence of saguaros on rocks nearby, elevated just above the flats, where I assume pathogen spores are also capable of migrating to, I don’t believe that rot is the primary cause of saguaro absence on those soils. Especially since again I saw landscaped specimens in those same soils. It seems more likely that intense competition from other plants is a bigger factor, although without doing a study on decay, bacterial, and fungal pathogens I cannot rule out that they don’t play more of a role.
Rainfall plays a role in pathogenic matters too as you know. In the north of saguaro country, winter rain and occasionally snow is the norm. Wet, cold soils are a well-known cause of cactus mortality in gardens in cold winter climates, especially in springtime after a long stressful season below freezing for many weeks or even months. Summer heat and humidity can also cause rotting in cacti, again when also combined with cold winters that creates double-stress levels. In places where cacti are not native but are planted outdoors, rotting becomes a very significant issue. But in the Sonoran Desert, rotting does not play nearly as large of an issue as you seem to think it does. I am not saying it doesn’t happen (again, my blog addresses how to diagnose and treat bacterial necrosis, Erwinia cacticida, on the home page) but it’s not the defining reason for why saguaros live or don’t live on certain soils. Saguaros are clearly able to survive wet, cold soil during a typical winter, hard freezes, and several cm of snow once every 1-2 years; and they are also able to take months of sweltering humidity and mostly summer rainfall (with winter drought) in the south. I just don’t think seedling death is mostly due to rotting in most of saguaro habitat. It does play a role, but there are many more factors at work that are more prominent in my estimation.
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Lastly, the capacity of different soils to both absorb and give up water matters a lot to saguaro distribution. I admit that I am not a soil scientist myself, and I may have some details slightly wrong, so forgive me if I do. But I will say that a given volume of rain has different impacts upon different soils. Let’s say that a modest rain falls across a hypothetical stretch of desert encompassing the two main different soil types we’ve been discussing (sand and clay, with silt being considered intermediate but not specifically discussed.) Let’s say that it is one half inch, or 12.5 mm. This is neither a particularly large rain, nor is is too small to help water desert plants and benefit the ecology. I don’t want to make excessive extreme assumptions so that is why I choose a reasonable middle figure. Let’s also assume it is a gentle rain with no runoff, not a flash flood that falls so quickly that half of it flows away. In other words, it is a half inch of rain that fully penetrates the soil without flooding away.
A half inch of rain on dry and sandy soil with large pore spaces will penetrate at least 7 to 8 inches down (17.5 to 20 cm). In dense clay soil, that same rain might only dampen the dry soil only about 4 inches down (10 cm). Not only does that half inch of rain not reach as many roots on saguaros or other plants, but it is also retained closer to the surface, where the dry air and desert sun can more quickly evaporate the rain in less time. Meanwhile, despite the larger pore spaces of sandy soils that enable greater aeration, the fact that the soil is moist deeper down means slower water loss from surface evaporation. The plant roots have more time to respond to that rain, and there are more roots that the rain reached to begin with. So a half inch of rain on sandy soil is more effective to water desert plants than it is on clay soil. Plants can use it better and it lasts longer. This is a large reason for why desert plant communities are more diverse and abundant on sandy valley soils than they are on dense clay valley soils. Extending this over to saguaros, those also survive better on slopes with more rock and coarser soils in dry regions than on finer silt and clay soils nearby that got the same amount of rain.
On rocky slopes, yes, drainage is high, but there are also benefits to the plants living there as opposed to on flatter zones. For one, if a saguaro is growing amidst large rocks, those rocks shed most of their rainfall and direct it into soil pockets where the roots of the cacti are. Deep cracks and fissures between rocks allow rain to penetrate deeper than you might think, and where there is soil, saguaro roots will follow. If water reaches several feet deep into soil pockets between rocks in various clefts and cracks, then evaporation out of those deep clefts is comparatively slow. It is far slower than the mere 4 inches of dampening on clay soil on a valley flat. A saguaro cactus simply has much more opportunity to utilize the water that percolated into deep cracks between rocks and even into average sandy/gravelly soil than it does in clay.
Put another way, clay soils are drier given the same unit of rainfall due to lack of initial penetration, and faster evaporation rates since moisture is retained far closer to the soil surface. This dynamic alone explains why bajada slopes and rocky hills have far more diverse vegetation in a low-rainfall region than the valleys nearby that receive the same low rainfall do. And in places where sandy soils combine with adequate rainfall and minimal freezing, saguaros do quite well even if it is flat. Rotting isn’t a primary issue in the matter. It is much more about rainfall and temperatures and their effects upon different soil types across most of the saguaro’s natural range.
One more thing about saguaros growing on very rocky, well drained hillsides: The fact that rocks shed water off of their faces and to the side, into the cracks and soil pockets where saguaro seedlings can take root and send their root systems has a multiplying effect upon whatever sparse natural rainfall might occur. Effective precipitation amounts might be two to three times what actually falls from the sky since rocks are impermeable to water. This concentration effect is especially important when rainfall is low, since it can convert a barely-noticeable 6 mm of rain (a quarter inch) into a more usable 12.5 mm (a half inch) or even more in rocky soils, simply by directing the low rainfall into the places where plant roots can use it the best.
Think of it this way: When you place a plant right by the gutter downspout that drains water from your roof, every time it rains even a small amount, all of the water from the entire roof surface area flows to that same place. Perhaps only a few mm of rainfall fell, and it was spread across the roof, but since it was collected in the gutter and then directed to the plant growing at the downspout, it means far more water for that plant than actually fell from the clouds. Rocks, and especially large sloping rock faces, can double, triple, or quadruple the effective amount of water provided to a given saguaro cactus, not to mention also the other plants of the desert community. In some areas this can effectively turn only 150 mm of rainfall a year into something closer to 250 or 300 mm of rain. This is why saguaros do so much better on rocky slopes than on flats in more arid areas. It has nearly nothing to do with rotting during the rare and light rains that fall most of the time.
Seedling saguaros benefit directly from this multiplier effect of rocks doubling the effects of low rainfall. Seedlings are very vulnerable to drought while still young, and since they grow so slowly in the wild, they spend years being very small. Every single thing that helps them survive droughts helps them. Being located on a warm slope in winter; being protected by other larger plants that help provide shade and cover against summer heat, cold, and discovery by hungry animals; and being near water-shedding rocks are all factors that greatly increase the odds of a seedling surviving to maturity. Seeds that germinate on a dry, hot flat expanse of sand, with few protective plants, and especially upon denser silt or clay, stand next to zero chance of surviving. And it is because heat and drought and sun and cold and exposure to hungry rodents that this is the case. By comparison, rotting from pathogens is minimal, simply because most never survive past a few weeks in difficult soils and great exposure to risk.
I know this is a very, very long comment. I might actually turn it into a blog post someday and use some of the various photos I have to illustrate my points visually. Thanks for reading Enrico!
Thank you very much indeed. You gave me a great gift.
Thanks for this very interesting post, as I’m often trying to find the range limits of different species.
On iNaturalist I’ve read there are some saguaros near the New Mexico border, plus a few records about 15 miles northwest of Safford / under 10 miles north of Pima. There are many visible on Google satellite there (Markham Creek), but it looks to require high-clearance 4WD to access.
Are those the saguaros you’re referring to near Safford, or are there others?
I have not actually been to visit the easternmost wild and native saguaro populations near Safford and in the San Pedro River Valley/Gila River watershed region in person. My information is derived from a combination of discussions over the years with knowledgeable people, having read articles published in a couple of journals (like the Cactus and Succulent Journal of the CSSA) that discuss natural distribution of the saguaro species, and online sources that seem credible.
Additionally, I’ve not actually visited the iNaturalist site for saguaros, but I would be a bit skeptical of saguaro reports from too close to the New Mexico border since reports can vary in quality and provenance. Some iNaturalist reports are geographically misplaced, sometimes by many miles, while others are misidentified, and others may be of captive plants observed in landscapes or other human-associated spaces as opposed to being genuinely wild distribution. This is not to suggest that iNaturalist cannot provide valuable data, because it can; it’s simply to say that the info there may need to be tempered with analysis since individually mistaken anecdotal reports can skew the picture, even if it’s not intentional.
To my knowledge wild saguaros do not come much more than 60 to 80 miles from the NM state line, at the absolute closest. Any report of them being less than 50 to 60 miles is almost surely inaccurate, and I think that it’s honestly more likely to be closer to 100 miles. A few landscape saguaros have been planted in far southern NM (Las Cruces), as well as El Paso. These should not be counted as natural or wild any more than a saguaro planted in a southern European garden should. I do think that there is value in knowing the horticultural distribution of various plants for those purposes, even though my opinion is that they should be treated as separate (if related) spheres.
In any case I don’t know the precise location of the easternmost saguaros (presumably near Safford AZ) via direct personal experience. There’s also some question about whether a single, isolated plant separated by many miles from the next nearest “colony” of them should be considered part of the “range” in that regard, since extremely lonely outliers are functionally isolated in an ecological sense and will not likely ever reproduce on their own. |
This applies most accurately to the westernmost saguaros along the Colorado River in California. There is an actual viable, reproducing population of several hundred plants in the Whipple Mountains flanking the river near Parker Dam/Lake Havasu, and those can legitimately be considered a sustaining wild population center at the extreme western edge of their native range. There are one or two reported plants (likely wild, but singles, highly isolated) from Imperial and Riverside Counties in SE California that are farther west than the Whipple Mountains stands; but they exist in complete isolation from the next nearest saguaro(s) by 20 to 30 miles or more, and could therefore be ruled out as being part of the ecologically functional greater saguaro population. They might be of interest as a technical anomaly but aren’t really fully part of the native range in a more meaningful sense.
This dynamic applies to all saguaros and other organisms as well. The northernmost wild saguaros occur not far from me in NW Arizona, but there are enough of them to comprise a viable wild population with reproductive capacity. The same goes with the southernmost ones on Mesa Masiaca, which are also numerous enough to be considered ecologically operational. Anyway I hope this clarifies a bit, even though it wasn’t 100% your original question either. 😉
Thanks for your insights. I know what you say on mis-locations or mis-IDs on iNaturalist, or how others consider planted saguaros or escaped palo verdes, etc. as wild or native. A few reporters seem to be slow or hesitant to reveal locations they mention. But that’s more the exception than rule on most plant records I’ve seen. Plus, I’ve submitted a few hundred records of other plants on iNat.
Saguaros NW of Safford – both stands are sizeable in extent and quantity, so should be functional, reproducing populations as you state. iNat has only a small percentage of records of all that can be seen on Google Satellite, but that’s remote country. About 50 miles of saguaros can be seen on hillsides N of the Gila River valley starting west of Safford, or 7 miles N of Bryce along rugged terrain along Markham Wash. Another area is 2 miles N of Ft Thomas.
Whipple Mountains saguaros – that’s great you know of a stand of several hundred nearby. A few online articles including from California public TV imply how saguaros weren’t located on a trip there, probably to protect locations one can find on Calflora or iNat. Elsewhere online, more than one photo can be verified of saguaros in the Whipple Mountains, including via Google Street view from Parker Dam Road. Or as a boater there replied matter of fact to a Facebook question, “you can see a few (saguaros) right above “Cable Car Day Use Area”.
San Pedro River valley saguaros – N of Benson saguaros start as individuals or small groups of spears from recent reproduction, but they increase near Cascabel, some with arms and past winter damage evident. I drove several miles on dirt roads on both sides of that area in my Toyota Corolla, after suspecting it as saguaro territory based on climatology, and then spotting some armed saguaro shadows via Google Sat. On my blog, I posted some saguaros I spotted from both sides of that valley, with other posts to come. This June a few flowered…those on the west side of the valley with arms extend further south and closer to Benson, but still 12 miles NNW. By Redington saguaros with arms are numerous on hills, growing with Parkinsonia microphylla and P. florida. Worth a drive.
Someday I hope to see the saguaros documented in the NW Hualapai Mountains closer to you.