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cactus,
naturalIntensive grazing can prevent recruitment of saguaro seedlings [
47].
Various areas in the Sonoran Desert have been protected from domestic
livestock grazing for 50 years or more. One early study showed that
there was no significant (p>0.05) difference between saguaro abundance
on protected and unprotected plots [
8]. More recent studies, however,
have shown that saguaro increased by 33 to 200 percent in protected
areas [
27,
77]. Saguaro seedlings may be impacted negatively when nurse
plants are browsed [
47].
Models to predict saguaro age from growth parameters (for example,
height-age equivalents) have been developed [
28,
69].
In transplant experiments, mortality was 100 percent for unshaded
saguaro seedlings compared to 65 percent for shaded seedlings [
22].
Saguaro are susceptible to few diseases [
10]. Healthy saguaro often
wall off larvae tunnels, woodpecker holes, or other wounds [
47]. Some
necroses may occur, however, after mechanical damage to saguaro from
breakage, frost, or lightning [
71]. Insects, saprophytic yeasts, molds,
and bacteria readily inhabit and breed in saguaro necroses [
24,
66,
72].
Temperatures below 23 degrees Fahrenheit (-5 deg C) will damage saguaro.
Death will occur after exposure to below freezing temperatures for 29 or
more consecutive hours [
85]. Fluctuations in saguaro numbers often are
due to recurring catastrophic freezes [
37,
46,
69].
Saguaro is protected under the Arizona Native Plant Law. Cactus
poaching is of concern around Saguaro National Park and urban
centers [
90]. Natural environmental extremes in temperature and
drought, however, are more of a threat to the survival of this species
[
37].