Question: In the paper recently there was an article about blooming palo verde trees, and a claim that the reason for the bountiful flowers this year was due to additional carbon dioxide in the atmosphere. This struck me a totally ludicrous. My take is timely winter rains are the cause of bountiful flowers on any plant any year, not additional carbon dioxide!
Answer: In many plants the primary factors affecting flowering are day length, light intensity, temperature, soil moisture, and plant nutrition. Carbon dioxide in the atmosphere plays a critical role in photosynthesis and plant growth. If levels are too low, plant growth shuts down. In response to concerns about elevated carbon dioxide levels in the future associated with climate change, studies have been done to determine how these elevated levels will affect plant growth in the future. Some of this research found that plants grown at elevated carbon dioxide levels show earlier and higher production of flowers, fruits, and seeds. Keep in mind these studies were done at artificially elevated carbon dioxide levelsΒ . In the article you mentioned the quote from a local doctor said βThe reason we see palo verdes become so lush is that there is more carbon dioxide in the atmosphere.βΒ
Although we are currently experiencing the highest levels in many years, it would be difficult to show we had more flowers this year than last year based on increased levels of carbon dioxide. The more likely explanation is a combination of timely winter rains, as you mentioned, and a warm spring.
Peter L. Warren is the Forest Health Program Coordinator for the Arizona Department of Forestry and Fire Management. Questions, photos and videos may be emailed toΒ tucsongardensage@gmail.com
