Giant cardon (Pachycereus pringlei) populate deserts and low hills and
mountains of all sizes throughout the Baja California Peninsula in Mexico,
and travelers along the peninsula are familiar with this cactus. However,
in some "infected areas" the cardon show various degrees of decay. By closely
studying over 1000 infected young and mature cardon, it was possible to
reconstruct a pattern of decay.
because this term describes the most common visible symptom. We add the
word syndrome because it is not yet known whether the different decaying
phenomena detected in this study are caused by a single or by several agents.
Heavy infection with flat-top decay could create a plant that looks as if all its
branches were chopped off.
Although flat-top decay is the more common phenomenon we detected,
another form of degeneration occurs near the Pacific coast of the peninsula,
about 5 km south of the fishing camp of El Conejo (Location on map). Here, the
entire mature population (which is generally green elsewhere) turns gray or
even white, and the epidermis cracks. Many of the plants in this area are dying
from this ailment. This pattern is restricted to
a 3-km2 area. Decaying sites
Field surveys located four large, highly infected areas and three smaller
areas. The four large areas are: the island Espiritu Santo-Partida
(off the north coast of the city of La Paz), Mesa Prieta, El Conejo area,
and south of Bah?a Concepc?on. The smaller decay areas are: near
Laguna Balandra, surrounding the Tres Virgenes volcanic area, and the
eastern slopes of the Sierra San Francisco (for location and points
of entry, see map). Level of decay
Not all cardon are evenly decayed. It seems that the affliction is localized in
small areas (Laguna Balandra, Tres Virgenes, and the eastern slopes of Sierra
San Francisco) or much larger zones (probably more than 100 km2 around El Conejo
and Mesa Prieta, for example), while completely absent from other zones.
Affected and unaffected zones can be close.
The density of decaying cardon varied from site to site, highest at El
Conejo and on the islands of Espiritu Santo and Partida, and lowest in an
unnamed arroyo north of Loreto and in the southern part of the peninsula in
the Sierra de la Laguna. In the latter two sites, no plants were
affected (Map). Why decay of the population happened?
Degeneration, decay, or destruction of mature plant populations, especially
ones that reproduce very slowly and can live hundred of years, is a clear indication
of some major change that the old plants could no longer tolerate. This is the case for
cardon, the largest plant on the Baja California Peninsula and one of the most
massive of all cacti.
Only mature plants (a few meters tall and approx. 50–100 years old) flower
and produce seeds. Establishment of seedlings is poor. For the cardon, a falling
branch cannot re-root as is common for some other cacti. This further emphasizes
the extreme importance of old-growth cardon in sustaining its population.
The reason(s) why the giant cacti are dying is unknown.
Possibilities:
Of the two large islands in the Gulf of California that were
surveyed, one (Isla Cerralvo) is virtually unaffected. The other island
(Isla Espiritu Santo-Partida), which lies just 30 km to the north, but only
5 km from the site at Laguna Balandra, is heavily degenerated with dead
and decaying plants. The location of the two islands and the prevailing wind
patterns point to a pathogenic organism(s). However, reports of cacti pests
and pathogens in nature are rare. Therefore, one has to assume that, in their
natural habitat, cacti have high tolerance to pathogenic agents.
However, since the cardon may live hundreds of healthy years without
any infection, this might be a new pathogen or a modified opportunistic
microorganism. The appearance of the affection in limited areas resembles
the spread of a pathogenic agent from a small center. This type of phenomenon
is well documented for many bacterial and fungal pathogens.
Wind as the agent of transmission cannot explain the two locations
of the most severe infections so far found in the wilderness, between La Paz
and Cuidad Constitucion in the southern part of the peninsula: Mesa Prieta and El
Conejo (map), where most of the cardon were infected, although the number of
dead cardon is small. Possible explanations for the “non-lethal” nature of the
phenomenon there are:
What happened to a similar columnar cactus in the Sonora Desert?
Degeneration of the cardon cactus is not an isolated case among columnar
cacti. Giant saguaro (Carnegiea gigantea) of the northern Sonoran Desert of
Arizona (the very same desert where cardons are growing in its southern part)
have almost disappeared in the last decades. Most plants that currently grow
in the Saguaro National Monument in Arizona are relatively young.
The explanations for this die-off phenomenon have varied between
a depletion of the ozone layer that subjects the plants to excessive exposure
to ultraviolet irradiation, copper-smelting pollution, car pollution, freezing
temperatures, bacterial necrosis, and long-term precipitation patterns.
There is insufficient scientific evidence for any of these hypotheses.
It seems that none of the above explanations apply to decay of cardon.
Infected populations were found in extremely remote, barely accessible areas,
far from human activity. In these habitats, there is no industry or intensive
modern agriculture for hundreds of kilometers around, ruling out man-made
pollution.
Gray decay of cardon
Wind and pathogenic agents
