Rhododendron Blossom in spring
山羊百科，林文智老師的植物、山岳、攝影紀錄
Rhododendron Blossom in spring
Yushan Rhododendron, Nanhu Rhododendron and Formosan Rhododendron are three common species of alpine vegetation on the island. Their flowers are similar and the buds blossom at the same period. When spring comes, the Rhoda flowers dot the entire mountain.
Yushan Rhododendron species grows on the highest altitude compared to other species of the Rhoda plants. It spreads widely on the slopes between 1,000 to 3,500 meters high. Either it be among the Broad-leaf woodland, coniferous woodland, Yushan Arrow Bamboo grassland, the Yushan Round Cypress Woodland or on steep mountain walls, the Yushan Rhododendron can be seen almost everywhere. Its flowers either stands alone or in cluster blanket the entire mountain slopes, rendering one of the most splendid sights on the mountain. As such, in spring, Yushan Rhododendron is regarded as the beauty queen of the highland.
Blossom in spring
Differentiating Yushan Rhododendron, Nanhu Rhododendron and Formosan Rhododendron from their leaves
It is often difficult to differentiate among Yushan Rhododendron, Nanhu Rhododendron and Formosan Rhododendron for most climbers, as there flowers look similar and they all blossom at the same time.
Yushan Rhododendron, Nanhu Rhododendron and Formosan Rhododendron's appearances are either as small trees or shrubs. The Yushan Rhododendron and Nanhu Rhododendron's stems and inflorescence areas are hairy. However, the Formosan Rhododendron has no such characteristic. Leaf is perhaps the easiest part to tell them apart. The back of the Formosan Rhododendron leaves is in slivery white color and hairy, whereas the Yushan Rhododendron's leaves have dark red spots and the Nanhu Rhododendron's leaves are covered with brown color fine hairs. However, it is impossible to tell the difference from their flowers or fruits. All three species' flowers grow on the tips of the branches. Each bud consists of 5 to 15 whites to light purple bell-shape flowers and they blossom into an umbrella shape. The fruits are like apple.
Formosan Rhododendron grows on slightly lower altitude than the rest. They are commonly found between 600 to 2,400 meters altitude, with the bulk at 1,000 to 1,500 meters height. Formosan Rhododendron mostly scatters among temperate cypress woodland, coniferous and tropical broad-leaf tree woodland especially at Central area around Alishan. They seldom appear in large number together. Yushan Rhododendron and Nanhu Rhododendron mostly scatter all over the island's highland. A small number of Yushan Rhododendrons can be found at lower altitude around northern region such as the Chatien Mountain, Jinkuoshih etc. The Nanhu Rhododendron mainly scatters around Nanhu Mountain area. Very few grow on high altitude. A smaller number grows at mid altitude sections such as of the Chinsui Mountain and Fungshan.
Nanhu Rhododendron grows densely among Yushan Round Cypress Woodland. Very seldom does it grow at cliff, slope or Yushan Arrow Bamboo grassland. However, the Yushan Rhododendron grows densely among Yushan Round Cypress Woodland or slopes. A small number grows on coniferous woodland, hanging cliff, Yushan Arrow Bamboo grassland slope or Broad-leaf tree woodland. As the Yushan Rhododendron and Nanhu Rhododendron share the same habitat, their distinction is only through the differing characteristics of their leaves.
Blossom in spring
Winter snow and spring rain facilitating the flower blossoms
Yushan Rhododendron, Nanhu Rhododendron and the Formosan Rhododendron's life cycles are the same as others of the Rhoda species. The flowers grow ahead of the leaves. They are only affected by the differing weather condition. The flowering season for the southern mountain region is earlier by one week. However, in other areas especially at the Nanhu and Shiashan mountain areas, if the low temperature persists for too long, the flowering season would be delayed. If the snow level is thin or the spring rain is little, the number of flowers would lessen also. For instance, in 1991 and 1993, the flowering season came much later and the flowers withered much faster.
As the Rhododendron's shoot starts to germinate around November, the hash winter condition actually stimulate its growth. In the following year, the buds would grow only with sufficient spring rain. Else, the buds would wither or would expand but the flowers within have already withered. This melancholic occurrence happens often to Yushan or Nanhu Rhododendron at high altitude areas with unstable weather condition.
Formosan Rhododendron's flowering season begins in mid March and lasted for about a month. Its young leave and fruits would grow after mid April and the fruits are ripe by mid October. As the Formosan Rhododendron scatters at mid altitude level, unstable weather condition or pests seldom affect its life cycle. Unless mankind sabotages its habitat, the Formosan Rhododendron's growth is considered stable.
Layers of scale protect Yushan Rhododendron and Nanhu Rhododendron's young shoots during the gestation period. They are seldom affected by the outside world. Unless they encounter higher temperature in winter resulting in lesser flowers, the rhododendron buds each carries at least seven flowers within. However, even if the winter has thick snowfall or prolonged snowy period, It does not guarantee that the flowering would be plentiful. The shoots still need plenty of spring rain to germinate properly. As every March and April are monsoon season, spring rain comes continuously into the mountain area, providing plenty of needed water for the rhododendrons. Generally, the rain needs to continue for more than 2 weeks or else the buds would expand and wither. When this happens, future germination would be affected as well. Even if there were no heavy rainfall in the mountain area, so long as the moisture content is rich, the buds would still launch its full blossom.
Blossom in spring
Yushan Rhododendron and Nanhu Rhododendron's sensitivity to changes in weather condition
Yushan Rhododendron and Nanhu Rhododendron start to blossom in mid May for about a month's time. The blossom time in the north is slightly later especially in Nanhu and Shiashan mountain areas, where the blossom time is often in late May. However, when the flowers are in full blossom in early summer, they are extremely sensitive to the drastic temperature fluctuation between day and night on fine days, or thundershowers mixed with hailstones in the afternoon. The fragile flowers often drop off, as they could not withstand these heavy onslaughts. At night when the temperature is low, water droplets would freeze on the petals. When the daytime temperature rises, the flowers would suffer from dehydration and wither. Sometimes even the flowers inside the bud can not escape such fate.
This kind of frostbite does not occur every year. The most serious occurrence was on 1993 at Nanhu Mountain area, where more than half of the rhododendron flowers withered due to frostbite.
The Yushan and Nanhu Rhododendron are very sensitive to changing weather. If the rainfall is low during March and April, the buds have no sufficient moisture to grow and would eventually wither. For instance, in 1991 and 1993, the rainfalls were very low from March to April. Coupled with thin snow level on the previous year, the number of flowers was less than half of the other years. During those two years, the overall changes in the climatic condition have resulted in poor blossom. At the same time, the leaf buds sprout sparingly and earlier than usual. Under normal condition, three leaf buds would grow on each branch. However, during these times, there were only one or none at all. These developments would also affect the flowering condition on the following year. This is because the Rhodora buds grow on the tip of the branch and the leaf buds grow right near the first leaf beneath the buds.
During mid summer when the humidity is high, especially after the passing of typhoons or torrential rain, the leaves of the Yushan and Nanhu Rhododendron are infected with unknown bacterial at the edge. White circular lumps appear. The lumps would gradually expand to as big as thumb-size and the color would turn pinkish. Under severe condition, all the leaves on the tree are infected. Notwithstanding this, the lumps are not harmful to the trees. Such occurrence has been recorded at the central mountain area, especially on the Yushan Rhododendron at the eastern slope of the Yushan Main Ridge.
Blossom in spring
Thickening of the leaves in preparation for severe winter while awaiting the coming of spring
In fall, the temperature varies drastically between day and night. To survive this hash condition, the leaves of the Yushan and Nanhu Rhododendron gradually thicken and shrank to one-third or half of their original sizes. At the same time, the leave surfaces are covered with levels of waxy substance. At dawn, the leaves are often covered with hoarfrost. If the day is misty, different shapes of rime are formed. Either it is frost or rime; this condition does not last very long. On the other hand, if this happens in early fall, the leaves would easily suffer from frostbite. When this happens, the dead cells would spread inward and the whole leave would eventually wither and drop-off. This has often happen to the more mature leaves on the lower section of the tree stem.
When it is snowing on highland, unless the snow level is higher than the trees, or else, even under severe cold, the snow would not totally cover the Yushan and Nanhu Rhododendron trees. As the tree has many extensive branches, the ice melts quickly as soon as the leaves are exposed to sunlight, thus preventing the forming of rime. In severe winter condition, the low temperature actually contributes to the healthy growth of the buds. At this time, large buds can be seen at the tips of every branch, waiting for spring to release its full blossom.
The four seasonally changes have great impact on the life cycle of the Yushan and Nanhu Rhododendrons. Observers have to closely monitor its development all year round in order to gain a more comprehensive understanding of the plant's life cycle and characteristics. Else, it would be difficult to pinpoint their exact blossom time.
