The 2020 census is already underway in Southern Arizona, but the response so far has been dismal. The participants just stand there with their arms out, refusing to answer even basic questions.
Luckily, this is a saguaro census, so everyone gets counted no matter what.
βWhile the country is counting its people, weβre counting our saguaros,β said Don Swann, a biologist at Saguaro National Park since 1993.
The once-a-decade tradition began in 1990. The latest census got underway in October and is expected to continue into April.
Saguaro National Park covers more than 140 square miles, so Swann and his fellow census takers canβt count every cactus. Instead, they estimate the total population based on how many individual saguaros they find in 45 scientific plots β 25 in the parkβs eastern district and 20 in the western district.
Each plot was selected at random 30 years ago and covers almost 10 acres.
The counting is done by a handful of park staff members and interns, with crucial help from an irregular army of volunteers.
βWeβre looking for every saguaroβ
On a recent Thursday, Swann and company were joined in the field by 19 snowbirds and RVers calling themselves the Desert Trails Hikers.
βItβs not so much an official group, just a bunch of friends,β said Judie Schumacher, a winter resident from Minnesota who organized the outing.
They met in the morning at the parkβs Red Hills Visitor Center, where Swann delivered a quick safety briefing and an overview of the census.
βWeβre looking for every saguaro,β he told them. βOnce we find one, we flag it and take measurements.β
βWe donβt have a citizenship question, do we?β joked volunteer Craig Fobes.
Swann asked the group to be especially watchful for any βbaby saguarosβ that might be hiding in the brush beneath the palo verdes and other nursery trees. A bumper crop of babies could signal the end of a desert drought cycle that dates to the Clinton administration.
βItβs been about 25 years since weβve had a really good crop of (new) saguaros,β he said.
Swannβs safety briefing boiled down to this: βBe safe, collect great data and have a good time,β he said. βWe want to make sure you all come back in one piece and with a minimal number of spines in you.β
Subjects range from tiny nubs to βancestral giantsβ
After the pep talk, the volunteers piled into vehicles and caravaned down dirt roads to plot number 30, a patch of desert thick with jumping cholla at the heart of the parkβs Tucson Mountain District.
There they counted and cataloged 234 saguaros over the course of several hours, using tape measures, clinometers and trigonometry to determine the height of each plant. They also logged the GPS coordinates, counted the number of arms and bird holes, and made note of any crests or other growth abnormalities.
The saguaros were temporarily marked with small, numbered flags to keep them from being counted twice.
Flag K33 went to the plotβs smallest cactus, a spiny nub 2.5 inches tall that probably sprouted more than a decade ago. Flag K18 went to the tallest saguaro of the day, a 41-footer with five arms and almost 200 years of history hanging from its ribs.
βWe really are out here with these ancestral giants,β said Alexis Cardenas, a park service intern taking part in his first census.
The Desert Trails Hikers worked their way through about half of plot number 30 before quitting for the day. Another volunteer group walked the rest of the plot the following day, resulting in a grand total of 486 saguaros, 12 more than the 2010 census.
Swann said theyβre seeing more decreases than increases in the plots theyβve counted so far this year, but itβs too early to say which way the overall population might be trending.
Census takers know theyβre probably missing some of the smallest specimens, but those saguaros should show up in future counts a decade or two from now, assuming they live that long.
The famously slow-growing plants have a low survival rate early in life, when they are less drought-resistant and more vulnerable to being crushed, knocked over or snacked on. βOnce theyβre big enough to store water, theyβre so resilient,β Swann said.
A long-term look at a long-lived plant
In 2010, the census team collected data on more than 20,000 individual cactuses, then used computer modeling to come up with a parkwide population of 1,896,030 saguaros. That was a 14% increase over the 2000 census, and a whopping 40% more than the 1990 total.
βSince the project started, weβve seen a huge increase in the total number of saguaros, which has been really encouraging,β Swann said.
More than 300 volunteers helped with the 2010 census, and Swann expects at least that many to take part this time around. His calendar for the coming months is already crowded with cactus counters from conservation groups, high school classes, hiking and climbing clubs and the occasional family. He isnβt actively looking for any additional help.
βWe donβt have a shortage of volunteers, which is great,β he said. βPeople want to come out and interact with saguaros one-on-one, and this is a way to do that with science.β
Swann said the data theyβve been collecting over the past three decades should still be useful 50 to 100 years from now, as future scientists continue to track the distribution, growth and adaptability of the Sonoran Desertβs iconic plant.
βSaguaros live longer than we do. In order to understand them you have to study them across generations,β he said.
So if you miss your chance to take part this time around, donβt be too disappointed. Swann expects many of the saguaros being counted now to still be standing there with their arms out when the census takers return in 2030.
