Sep 15

The Oaks that flowered and fruited

Oaks (Fagaceae) are one of the peculiar plant families that make it especially challenging to understand how and when they flower and fruit. Why? The fruits you see at any given period could either be from a flowering that occurred in the same year, the year before it, or two years ago. Tracing flowering and fruiting events (also known as phenology) of oak trees requires meticulous observations and markings. Why? We don’t really conclusively know the phenological patterns of native oaks in Taiwan, and this means we can’t predict what will happen to their growth and their influence on other animals they interact with. Even though we have close to 42 native oak species, most of our planted oaks are not reproductively mature. It doesn’t mean that our monitoring efforts are in vain, no. It means that, for the moment, we can more closely understand the early growth phases of an oak’s life, and we would be able to know when an oak species actually becomes mature. For the ones that have matured, we created a brief summary of our observations from June 2023 to August 2024. There were 27 species consisting of 108 individuals that flowered (Table 1) and 18 species consisting of 52 individuals that fruited in this time period (Table 2).

Let’s look at two species in blue in particular, because a larger sample number can give us more reliable information. Even though most are few in numbers, we have to work with what we currently have.

Lithocarpus konishii (Konishii Oak) - 小西氏石櫟

Native to a small island in Southern China and Taiwan, the Konishii Oak had intact fruiting bodies all year round, but ones that actually grew into fruits were only occurring between May to August. We observed them flowering between April to November, and from other sources of literature, fruits start to grow the following year after flowering.

Quercus aliena (Oriental White Oak) - 槲櫟

The Oriental White Oak is widely distributed in East Asia, from Japan and Korea all the way down to China and Taiwan. We observed them flowering between February and September and fruiting shortly after from May to October. This observation is consistent with other literature.

Flowering events combined with climate data help inform when conditions are suitable for flowering in addition to the relationships between trees and pollinators. From a purely observational (and not scientific) standpoint, these planted oaks invite an abundance of insects and arachnids in the area, especially during summer. Despite how little is known about oak fruits in Taiwan, fruits are an important food source for bears in the central mountain range (and not the coastal mountains) and there are few reports of macaques feeding on them too. However, it is likely that squirrels play a relatively more important role in dispersing oak fruits in the coastal mountains. We have remarkably noticed that most fruits do not ripen and quickly drop or disappear.

Monitoring trees takes time and consistency. In years time, our monitoring efforts could hopefully fill the gaps to meet restoration purposes and improve ecosystem function of the forests around us. For example, we could identify which species can fill ecological niches missing. We could also identify which species can be more resilient than other species in a warming climate. To give another example, some oaks have deeper roots than other native forest trees and can be especially useful to prevent soil erosion in steep areas. We hope that in a few years, we will be able to make sound decisions in regards to what oak species to prioritize so that we propagate more of them and signify their conservation needs.

Some images displayed below

Quercus pachyloma fruiting