Population Dynamics of the Palm,
Washingtonia filifera, and Global Warming-a rebuttal
by Spenceri W -©1995-2011
(This article is a specific rebuttal to one of the same title by J. W. Cornett as published in the
San Bernardino county Museum Association Quarterly Volume 38 Number 2, summer 1991.)
This article was written because it appeared that statements which had been made by the rebutted article were indirectly or partially responsible for the imminent demise of certain native groves of Washingtonia filifera in Nevada.
In the aforementioned article, information is presented regarding population dynamics of the Palm: Washingtonia filifera, which is intended to make it evident that a perceivable increase over time in the numbers of Palms is due to a regional warming trend.
In the course of the article several apparent contradictions arise while certain observable factors
which could be valid appear to have been overlooked or understated. In this rebuttal these
contradictions as well as some of those overlooked factors will be discussed.
Body of Rebuttal:
First of all it is stated that "the available evidence indicates that the (the Desert Fan Palm) has never been more abundant or widespread than it is today, and that three lines of evidence will be presented which suggest that both the (current) expansion in range and the increase in the numbers of this species is a result of a regional (or global) warming trend." [sic] (words in parentheses mine.)
(Please note that this article specifically concerns itself with historical increases in the palm
which of course is assumed would need to correspond to historical increases in temperature.)
The first assertion is that "only the Desert Fan Palm and a few other family members have
entered temperate latitudes."
First of all I should like to point out that the worlds temperate areas or 'latitudes' have changed
dramatically many times over the millions of years this palm would likely have needed to
evolve. (Note: Argument appears restricted to 'general latitudes rather than 'regions with
common factors. Using strictly latitude may be misleading in this author's observation, since
temperate areas do not necessarily strictly follow latitudes and climates change dramatically for
instance as one moves longitudinally inland from warmer coastal air, or again as one changes
other environmental factors such as elevation.)
The most recent 'change' has indeed been a warming trend as far as this Palm is concerned and it
occurred about 18,000 or so years ago as the last of the great glacial ice masses were receding.
However, during the last 18,000 years no significant change has occurred in winter lows
in the Mojave (1) which would be significant enough to affect this plant as has been
suggested by Cornett.
Apparently the great ice sheets never reached the areas which now comprise the historical habitat of this Palm, but the "cool moisture laden winds from the receding glaciers blew southward into the area and what is now a desert was once covered with profuse vegetation." (2)
However since then, the entire Southwestern United states has apparently been a desert for about the last 15,000 years with little variation in climate. It is likely that whatever W. filifera persisted to present day was restricted to sources of moisture which have remained fairly constant
over that time until now. Those pockets of water are most likely entirely responsible for the surviving isolated groves of this plant where it persists to this day and the lack of that water is likely entirely responsible for the absence of the same plant in adjacent areas of the desert. No other factors seem to be more important than this. Other factors however may affect the increase or decrease of Palms within those isolated pockets and I will go over some of the more obvious factors which Cornett appears to have missed.
It should be noted that W. filifera possesses remarkably efficient reproduction capabilities - annually bearing literally hundreds of thousands of potentially viable 'rodent and animal-proof' seeds. It would appear short-sighted to imply that this plant remained "restricted" to a few streams and springs in protected arroyos due to some reproductive inability while certainly over that same time span long periods of abundant water and hospitable environmental factors prevailed in those same areas which now comprise massive areas adjacent to the Palm's now restricted recognized habitat.
To be specific when speaking about something so broad as Global warming trends however, please bear in mind that Cornett's contentions concerns themselves with a perceived increase in Palm numbers over the last century or even five decades, NOT millenia! In this amount of time little at all has changed in the way of record winter low temperature increases on a local level in the Mojave desert where he claims the spread is due to a much more subtle Global Warming trend. No recorded rise in specific local winter lows has occurred in the Mojave in the last 100 years which would be of any sufficient consequence to the spread of this already very cold hardy species. Global warming may indeed be occurring and in fact, I believe it is and it is an alarming phenomena. However, I am only concerned with Cornett's contention that somehow the local record winter lows of the Mojave desert has varied in any way in areas where he "claims" this palm has spread over the last 100 years. Specifically that any of those variations could be interpreted as significant to this Palm.
If a regional warming of winter lows is to account for the increase in palms. Then how is it that this same palm has not been increasing in numbers in still Warmer winter areas of the world? Tropical climates appear to have no bearing on the reproductive capacity of this subtropical plant. In fact, there is simply no data to prove that increased warmth affects this palms reproductive viability in any way. Avid Palm collectors on the world wide web have actually reported that they have trouble growing W. filifera in more tropical environments where record winter lows are already as much as 15 to 20f degrees higher than they are in the Mojave. Furthermore, if this Palm tends to "spread" where the winters lows are warmer, then why hasn't it spread long before now toward the south and toward Central America? Apparently it never has, and it apparently never did even when the climate we are told was much more moist and warm many thousands of years ago. Fossils far north of W. filifera habitat suggest that in fact this palm has retreated from the north to it's present day locations if anything.
Here again we must be reminded however that Cornett apparently is only concerned with historical increases in Palms to the north of Palm Springs over the last one hundred years. If the observer would simply understand that any major shift in population dynamics for any
species can probably be traced to major changes in that species environment, one has only to
ask: "What has really changed environmentally in the last 100 years that might affect this plant's
population ?" Also one needs to ask: "Which populations of this plant are we going to count in
our population dynamics figures?" (This point will become more relevant later.)
These questions point us to the following possibilities which should be examined: Those really
pressing environmental factors which have truly changed in the last one-hundred years would
more likely seem to include the following five factors:
The complete demise of Native American Palm seed harvesters which has undeniably
resulted in each Oasis accumulating literally hundreds of millions of viable seeds on their moist
soils thereby availing fairly unrestrained germination over the last 50 to 100 years.
Previously the Americans ate and collected the seeds and were almost certainly doing so for as
long as humans realized the food existed. This of course was very likely hundreds or thousands
of years ago. Or soon after man's first contact with the plant which would probably have been
around that time at the latest. It is highly doubtful given this Palm's typically riparian habit ...
and given the common scarcity of desert food to begin with, that this important food could have
somehow escaped the attention of the seed collecting aboriginal peoples of 10,000 years ago for
very long. (3) (The Palms riparian habit means the aborigines would have had clear and
abundant lifesaving circumstances assisting their early on discovery of this food.)
Remember some of the oldest seed harvester human artifacts in the United States are from the
Southwestern Deserts.(4) Desert food often scarce in supply probably meant that these aboriginal
harvesters likely wasted little. This food stores extremely well, is impervious to mice and
rodents and would most definitely have been put aside especially in years of bumper crops.)
Although conjecture, this factor could conceivably have played a major role in restricting and
reducing numbers of palm specimens in all oases for the many centuries since man first arrived.
In other aboriginal cultures which use palms it seems the reduction and even extinction of
numbers in the wild has always been a problem. Note the Jubaea Chilensis in Chile for wine.
The Ceroxylon palms of Columbia for wax, the Nannorrhops of Pakistan for baskets and the
Wounaan Indians of Central America.
These people weave baskets similar in many respects to the fine baskets of the Paiute and the
Cahuilla. Using the terminal buds of Astrocaryum standleyanum palms they coil this over the
core of Carludovica Palmata Palms. It should not be necessary to point out that the
Astrocaryum loses it's terminal bud as well as it's life in this process.
-2) The advent of wells and irrigation throughout the neighboring deserts of the palms habitat.
(Not just a little irrigation but massive amounts of water ...enough to turn the entire desert floor
green.) Water of course is one thing which has restricted this palm's spread into adjacent desert
areas up until now. This restriction has now been largely removed in huge areas.
-3) A massive influx in new plants by White settlers in both agricultural, home and wild
landscapes and their accompanying abundant flowers (not the least of which is the Tamarix
species) afforded Carpenter bees, (known to destroy large numbers of Palm inflorescence in
search of pollen) with masses of new flowers to forage. These bees could now afford to leave
the Palms less attractive and less abundant pollen alone. This could very conceivably account
for an large increase in Palm seed production over the last 100 years.
-4) Along with the above considerations, the increase in generalized Human populations, (in
neighboring communities which were once barren desert,) also created a more hospitable
environment for coyotes and birds all of which are known and recognized for spreading seeds of
-5) One more consideration, which isn't important in wild palm oases, but could affect local wild populations indirectly through adventive plantings is the use of Petroleum based nitrogen fertilizers. Clear results in increased seed production has been observed in heavily fertilized Palm plantings. The resultant abundant crops could perceivably affect locally wild or naturalized stands. This practice has only come into being over the last 100 years, and correlates perfectly with the time span for which Cornett's contentions are concerned.
This statement may be misleading. First of all the so called northern latitudes which are
apparently associated with "temperate" zones have clearly not been so throughout the evolution
of this or any other palm. Not only have temperate "latitudes" clearly changed drastically over
the course of this palm's evolution, but they have done so drastically and quickly many times.
What is temperate "latitudinally" today was not so in earlier times and vice versa. In fact, on
page 55 of Genera Palmarum ( Uhl & Dransfield 1987 ) -one will see that an abundance of
fossil palm leaves have been found in Colorado, Oregon Wyoming and British Columbia. (5) The
same article mentions locations in Greenland and Alaska as well.(6) Interestingly, the more
northerly the latitude, the greater the occurrence of fossil fan palms. Whereas in the southern
latitudes in what we would today consider the tropics there are few if any fossils of these palms
suggesting either that at one time these areas may have not been climatically suitable for this
type of vegetation or that palms are a more recent species there than in northern latitudes. If
anything can be derived from this it is that palms have drifted southward and not northward. In
any event, the greatest preponderance of Palm fossils in general appears to be in the northern
latitudes as far as the western Hemisphere is concerned.
Fossil evidence would appear to imply that Washingtonia is descended from early fan Palms to
the North and if anything it's range has been restricted to increasingly southern latitudes over
time. This of course would indicate a move south, not north.
Genera Palmarum goes on the state that: "During the cooling in the Miocene and Pliocene
there was a gradual restriction of palms to their present locations into the tropical and
subtropical floras in the extreme southern United States and Mexico. ...In South America
(where many Palms today are found) there are fewer (fossil) records of leaves and fruits..." (7)
(Parentheses and italics mine.)
The above statement is in direct contradiction to the implication that palms were among those
plants which later drifted northward. For although it is believed that many plants have "drifted
northward" into present day Southwestern United states this does not appear to have been the
case with Palms.
Secondly, There seems to be a general inclination to presuppose that palms all have "tropical"
affinities. This is simply not true. An abundance of palms are not found in the tropics at all. It
should not be automatically assumed that they evolved from there. It is just as likely that many
palms evolved in subtropical conditions just as they are found today. As a matter of fact most
of the oldest palms which include most species with palmate induplicate leaf forms such as
Washingtonia, are among the most cold tolerant palms on earth. Many of these palms may
tolerate below 15 degrees Fahrenheit. There are even palms which may take below 0 degrees
Fahrenheit. This is clearly inconsistent with any notion that Palms are all necessarily associated
with the tropics or that tropical affinity is obligate to palms. The "subtropics" are, after all, a
valid climatic zone on this world.
There are, in fact no native W. Filifera groves or specimens which may be found below (or even
near) the tropic of Cancer. Even Cornett places the geographic 'center' of distribution several
hundred miles north of that latitude.
Furthermore there is very little in the way of climactical differences between the areas
purported to be the center of W. Filifera distribution and the areas it is claimed the plant has
"invaded". Ironically in fact, any slight temperature differences that might be documented in
any of these "invaded" locales would most certainly prove to be colder if anything ...not
warmer! This is a direct contradiction to the hypothesis as stated which has contended that the
reason for the Palm's alleged spread could be due to a 'warming' trend.
Still even if the local climate Cornett is concerned with was now warmer by a few degrees as far as record winter lows go, this would never explain why already ancient
and established groves would suddenly begin to grow in size. This is not to be explained by a
"warming" trend since apparently the perfect conditions already existed for all these oases in order for these trees to have thrived. This is corroborated by the fact that these same palms growing in true tropical conditions which are known to have warmer winter lows apparently do not enjoy an increase in seed production.
On the contrary, this author believes it may be shown that the trees are not now suddenly producing any more seeds than they ever have.
Cornett himself has observed that some of the healthiest Palms bearing the largest numbers of
fruits are the landscaped street plantings in Palm Springs. Ammonium nitrates is only one out of
many possible causes. Here it becomes increasingly clear that conditions other than global
warming are more than likely responsible for any possible increase in Palm seed production.
(2)- In the second Line of "evidence" it is stated : "New palm oases have arisen primarily to the
north of the historic range of the species...suggesting that either the climate has warmed
sufficiently to allow this species to invade the region or the palms have recently adapted to
First of all the oases cited are primarily those near Warm Springs Nevada and Grapevine
Springs in Death Valley. These are included to support the theory of increased naturalized
numbers of palms even though remarkably, in other articles (which Cornett himself published
years prior) these are said to be recent adventive plantings by humans.
The article being rebutted was written in 1991, a full five years after the same author had
published an article (in 1986) about the Palms in Warm Springs. In this article it is stated that
those same palms were planted by a Mendis Cooper in 1880. His conclusion was that those
palms were therefore recent human introductions within the last 100 years effectively
correlating them with the dates now given for the spread of "wild" palms he has attributed to
global warming in these very groves in 1991.
NOTE: Although I have now published research which shows That local family tradition to be
seriously flawed, for our purposes here, the important thing to understand is that Cornett
himself ascribed to the Cooper story and printed it as likely fact. (Although the dates and places
are misconstrued since Mendis Cooper is placed in Warm Springs instead of Overton and 1880
instead of the correct date of 1893.)
Is it appropriate to at once consider these plants adventive or deliberately planted by humans,
while simultaneously considering them to be the products of a natural evolutionary cycle such
as global warming?
This same idea surely applies to grapevine springs, another northern grove mentioned by the
Grapevine springs is the water source for an elaborate castle outside of the Death Valley. This
castle was built at a time when Palm Springs California was very quickly gaining recognition
as the western hemisphere's version of Mecca. It has been published that the palms there were
planted in the 1930's by a landscape architect. Photographic records appear to confirm this.
Cornett visited and wrote a book about the area. Why would these palms be considered the
result of Global warming while also being considered the products of human introduction?
Furthermore Washingtonia did not exist in Northern or Coastal California at the turn of the
century. It did not take long however, for enterprising landscapers to cover the entire state of
California (along with much of the rest of the world's subtropics ) Now of course,
Washingtonia filifera are everywhere they never used to be. (At least not since the Pliocene.)
Surely one could not also attribute these "increases" to Global warming.
I think that neither the climate has warmed sufficiently to allow this species to invade nor has
the plant adapted to colder weather. For one thing, the weather at several of the "new"
locations mentioned, could hardly be considered any colder than twenty-nine palms which is
home to an old oasis which is figured in an aboriginal legend, (and which gets some of the
colder weather of all the oases, I might add) It is highly doubtful this species has made a
sudden genetic shift in favor of frost. In other writings Cornett notes that genetic differences
are nil among "isolated groves" and uses this fact to substantiate a hypothesis regarding the
recent "evolution " of the genus. After over 140 years of worldwide plantings of this genus
however, there has yet to emerge a new variety. Furthermore no gardener has as yet stretched
the limits of this palm's cold tolerances past what it has been known to endure in hard frosts at
some of the known and prior-to-historic locations of this palm, suggesting anecdotally at least,
that genetically derived cold tolerances for this plant have remained relatively the same over
the last 100 years.
Contrary to the claim that the Mojave is too cold for the genus, I have not found a single
location in the entire Mojave desert which is unsuitable for the Washingtonia filifera. (Unless
you count high elevations. But then if one counts higher elevations that one must also count the
higher elevations less than a mile from the most ancient Palm Groves at Palm Springs.)
Furthermore, according to very reliable and exhaustive Paleoclimatic surveys, the region has
most likely never been unsuitable as far as "cold" is concerned. Whether the area has always
been hydrologically suitable, of course is a different matter entirely.
The ability to survive cold is most likely a very ancient trait in palms. A majority of those taxon
considered the oldest by Genera Palmarum (according to fossil records), even today exhibit
incredible tolerance to frost. This does not appear to be a new development but rather an
ancient genetical makeup which has allowed this large family to survive many aeons to
A partial list of these very anciently known and very cold tolerant palms follows: (from fossils
listed in Genera Palmarum as being among the oldest)
Sabal- (known to take 0 degrees F)
Serenoa-(known to take 10 degrees F)
Livistona-(known to take 5 degrees F)
Trachycarpus-(known to take 5 degrees F)
Washingtonia-(known to take 12 degrees F)
Phoenix-(known to take 4 degrees F)
Chamaerops-(known to take 5 degrees F)
Rapidophyllum-(known to take 3 degrees F)
Nannorrhops-(known to take minus 5 degrees F)
Please note that this entire list is made up of induplicate palmate or costapalmate fan palms
excepting Phoenix. It should be noted however that Phoenix has been found in Texas fossil beds
and that Phoenix is furthermore related to the Washingtonia as part of the subtribe of
Livistoninae. Since Phoenix is ancient even in the Middle east it's presence in Texas suggests
that the origins of the Livistoninae family (of which Washingtonia is a member) is not only
extremely ancient but furthermore would appear to offer it an additional northern and western
(3)- Lastly, it is pointed out that the increase in palm numbers has occurred over the whole of
its geographic range.
I have personal firsthand experience with varying counts even with my own best efforts. In
other articles I have shown instances of vast and unexplained differences in counts between
reputable and honest people. (8) But here, Global warming is given credence before miscounts
are acknowledged as even possible. Even as fallible and as difficult to substantiate as they may
be, not once are the counts themselves brought into question. In fact it would almost seem the
counts are taken to be somewhat infallible even though there is photographic evidence that
some counts in 1986 of certain Oases have been askew by as much as a factor of 400%! (See
Article entitled "The Desert Fan Palm, evidence supports Relict status" a rebuttal -by William
Henderson was probably as thorough as he could have possibly been but once again his counts
have no way of being substantiated except by his own record. I do not challenge their validity
or usefulness. I do however, challenge using them in the way in which they appear to have been
used or perhaps as anything other than anecdotal tools without another more perfect way of
substantiating numbers. Still more frustrating however, it is positively known that Henderson
never included counts of Castle Creek or Warm springs in Nevada in his counts of Oases.
Surely most are aware of this, yet I don't find that any attention is paid to this omission even
though these numbers are used in the article.
It appears to be implied that because Henderson (or anyone else) didn't count these palms,
that they are "new oases" even though in other earlier research papers it is shown that there is
ample knowledge of the fact that these palms were extant early on in the twentieth century when
those other counts were made.
1-Adventive plantings should not be counted.
2-Oases which had previous heavy Aboriginal interaction should not be counted. Or should be
3-Instances near such developments as irrigation and new plant populations should be ignored.
4-The areas should be strictly monitored for coyote and bird populations as well as destructive
pollen collecting insects.
5-And lastly, the temperatures should be strictly recorded and trees should be tagged
and numbered and fruit production viability and numbers should be monitored as well as any
possible correlation to annual temperature fluctuations or deviations from normal.
These suggestions are strictly my own opinions but then I believe I have shown there may be a
need for such measures if one wishes to remain objective and credible with respect to these
types of hypotheses. It would appear that all of the other Oases (excepting the KOFA oasis) or
areas adjacent to the oases as well as animal populations and human factors have simply
changed too much environmentally in the past 100 years as compared to conditions believed to
exist anciently to assign such intrinsic factors as Global warming to any apparent fluctuations
in population dynamics.
In conclusion there is simply and absolutely no evidence at all to suggest
that any populations of Washingtonia filifera have either increased or been affected by any
factors such as "global warming" as has been suggested in the hastily published and unfounded contentions of James Cornett. All the factors and contentions which
Cornett has raised have other far more likely explanations than that which he has suggested by his under-researched explanation
of "Global Warming".
2. 3. 4. 5. 6. 7. 8.
2.Nevada's Valley of Fire- KC pub. 1976- p.18. (back)
3.When I met my first palm in 1979 - I immediately sampled the honey covered seed. (Which was \is delicious!) I was simply curious. I knew nothing about Palms at the time and had no knowledge of it's food value or historic use by Native Americans. Nor was I even hungry! (back)
4.About 8500 years ago in Southern Nevada -Southwest Museum Papers -number eight, -Gypsum Cave NV. -p. 71-R. E. Harrington-Los Angeles- 1933-1963 (back)
5."...all localities where palm leaves occur, often in abundance." (back)
6.Cornett himself notes this in other articles. (back)
7.Genera Palmarum, -Uhl & Dransfield Allen press -1987 p.55 (back)
8.The Desert Fan Palm-evidence still supports Relict status. Spencer, Winton 1996 unpublished lay report. -p.1 (relict.htm) (back)
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