April is one of the two busiest months of spring in the Willamette Valley. The native wildflowers are blooming in greater and greater profusion, the peak burst extending into May. With the abundance of flowers, butterflies and other pollinators become increasingly visible.
The bigleaf maple flower clusters will be shifting gears. The trees that began with male flowers in early March are ready to open up their female flowers. The matching mating type switches from female to male flowers. Cross pollination is as successful as the cottonwoods with separate male and female trees. But cottonwood strategy means only the female half of the population produces seeds while in bigleaf maple every tree produces abundant, vigorous seeds.
Leafing out is burgeoning, too, along with flowering. Cottonwood spreads out individual tree leafing longer than any tree in our area. At the beginning of April half of the cottonwoods are still bare while half are covered with leaves. Within three weeks all the cottonwoods have a full canopy of bright green, shiny leaves. Why do our local great blue herons nest in late leafing trees? They seem exposed to predation much longer than if they used early leafing trees.
The Oregon white oak (Garry oak outside of Oregon) is simply slow to leaf out, the last of the native trees to fill out its canopy. This late leafing means that the herbaceous flowering plants under the oaks have a chance to flourish with plenty of sunlight nearly to the end of April.