Trees near me are bursting into bloom on naked branches. Native (redbud, willow) and exotic (apple, almond, quince) flower buds open while their leaves remain tight in buds. Evergreen woody plants like ceanothus, viburnum, and camellia are blooming wildly yet no new spring leaves grow. This isn’t just a temperate zone phenomenon, in the tropics some trees drop leaves at the beginning of wet season and flower at the end of the rainy period before new leaves have expanded. These tree flowers remind us of winter’s end, but nature isn’t rewarding us for making it through another annual stint of cold short days. The trees just do it for themselves and our pleasure is a fringe benefit.
Trees have their reasons for flowering before leafing out. The botanical term for this type of flowering is hysteranthous. Hyster is from the same root Latin and Greek words that mean womb or ovary and result in the word hysteria. Anthos means having flowers and is from the Greek word antho meaning flower.
The benefit to trees is two-fold. Wind pollination is favored when flowers bloom before leaves expand. For others, large floral display are more attractive to pollinators.
The Daily Bucket is a nature refuge. We amicably discuss animals, weather, climate, soil,
plants, waters and note life’s patterns spinning around us.
We invite you to note what you are seeing around you in your own part of the world, and to share your observations in the comments below.
|
Flower and leaf buds sometimes require a specific amount (degree and duration) of cold temperature before bud dormancy is broken and the bud can open. This is called vernalization, from the Latin vernus meaning of the spring. But a bud that has been vernalized won’t open without experiencing warm enough temperatures for a period after the cold requirement has been met.
Flowering time is triggered by various environmental parameters such as temperature and daylength, but flowering itself is regulated by a single gene called Apetala1. If the gene is active, the plant flowers.
Apetala1 generates the proteins that in turn switch on more than 1,000 genes involved in the flowering process. . .
When the Apetala1 gene turns on, it first commands other genes to send a "stop" signal to the plant's meristems [in herbaceous plants], effectively halting leaf production. Located in the areas of a plant where growth takes place, meristems are then alerted to instead begin making flowers.
Why some plants are hysteranthous, though, wasn’t investigated until a few years ago. Flower buds have a lower heat requirement than leaf buds. Both have similar vernalization (cold) requirement so when days grow warmer, flower buds open first.
While many studies have estimated the chilling requirements of flower buds (because insufficient chilling can cause uneven and even failed bloom threatening the production of some horticultural crops), comparative studies on the chilling and heat requirements of leaf and flower buds are rare.
“The heat requirements of plants is equally important for initiating flowering, leaf unfolding, photosynthesis and vegetative growth,” outlines Eike Luedeling, Senior Decision Analyst with the World Agroforestry Centre, who is co-author of a study comparing the chilling and heat requirements of leaf and flower buds on the fruit trees in the Beijing Summer Palace which was published recently in the scientific journal, Plant Diversity and Resources….
“We found the reason for the sequence of flowering and leaf unfolding was a large difference in heat requirements between leaves and flower buds,” explains Luedeling. “Flowers had much lower heat requirements compared with leaf buds whereas the chilling requirements for leaves and flower buds were about the same.”
Climate change is altering seasonal weather. What’s a tree to do when a suitable cold period has broken bud dormancy and warm temperatures trigger flower buds to open but then winter slams back in and freezes the first growth? This isn’t a new situation but happens more often now. Many trees have secondary flower and leaf buds that didn’t open at first. If the first set is killed by a cold snap, the unopened buds often survive and will open when warmer temperatures return. The second bloom (or leafing out) might not be as prolific as the first, but some fruits will grow and enough leaves unfurl for photosynthesis during summer.
Many flowers, leaves, and young fruits will survive a short freeze. Survival partly depends on the stage of growth. Unopened buds are tolerant of cold, so are young fruits. Sometimes watering the soil deeply helps plants survive a brief cold spell. The soil holds more heat and releases it into the cold air and just a few degrees of warmer temperatures around the plant can be enough.
Orchardists sometimes mist trees because the frozen spray on the trees keeps the temperature at 32oF. and protects from lower temperature. A friend has a small lemon tree in a pot on her deck and she kept it alive and the fruit ripening earlier this winter by stringing Christmas tree lights through the branches.
This spring is a season of discovery for me in a new home with trees I’d not yet seen flower. All the flowering plants except the first photo (willow) are blooming in my yard right now. Three different colors of camellias (rose, deep red, white with red stripes), apple and California bay laurel (not shown because they didn’t want their photos taken), viburnum, quince, a non-fruiting Prunus, and The Mystery Maybe Laurel Maybe a Rosaceae someone. Anyone ready to name the Mystery Tree?
SPOTLIGHT ON GREEN NEWS & VIEWS POSTS EVERY SATURDAY AND WEDNESDAY AFTERNOONS (PACIFIC TIME) ON THE DAILY KOS FRONT PAGE. BE SURE TO LOOK FOR THE STORIES YOU MISSED. RECOMMEND AND COMMENT TO THANK METEOR BLADES FOR HIS DEDICATED CURATION.
|