|Some of the Palo Verdes were blooming like this one.|
|Others had very few flowers or none at all like the one above.|
This is what I found. Palo Verdes associated with Saguaros (Saguaros had to be at least three meters high) averaged 30% flowering within their canopy. Palo Verdes not associated with Saguaros averaged 42% of their canopy flowering. For all us statistical nerds, yes this was statistically significant for one-tailed, two-tailed, and paired t-tests! So the test does support our hypothesis that Saguaros are our competing Palo Verdes for water. Thus Palo Verde flowering is reduced.
This is all quite odd considering the Palo Verde is a well know nurse plant for the Saguaro Cacti. A nurse plant aids the establishment and growth of another plant, "nursing" another plant to life. The shade, nutrients, reduced temperature, and greater moisture under a Palo Verde are well known to "nurse" the establishment of young Saguaros. But apparently the Saguaro "bites the had that feeds it" later in life, out competing the Palo Verde for water and eventually killing it (according to other researchers).