The rimu is one of the conifer trees of the Southern Hemisphere, the so-called podocarps. It is a very large evergreen tree that is native and endemic to the New Zealand forests. It was formerly known as the red pine but this name is rarely used today.
The tree is part of the Podocarpaceae family, or the southern conifers. Along with other species like the totara or the kahitatea, the rimu forms the podocarpus forests in New Zealand. The North Island of New Zealand no longer has many such forests. The number of trees have constantly decreased due to logging and other human activities, although the rimu is not threatened in any way.
The rimu usually has a height between 20 and 25 m. It can even reach 50 m high, which is remarkable for a tree with a very slow rate of growth. Because of its height, it normally raises above other trees in the temperate rainforests. Some forests consisting almost exclusively of rimu exist as well, in particular along the west shores of New Zealand's South Island. The old pristine forest located near the National Park doesn't exist anymore but record high rimu trees, with a height of over 60 m, were said to be located there. It has a very long life, of about 800 or 900 years in total.
Normal rimu trunks have a diameter of around 1.5 m but very old or large trees might have a greater one. It grows upright, with a straight trunk. Leaves are located in spirals and tend to be longer on younger plants (7 mm) than on mature ones (about 2-3 mm). It is a dioecious species, with male and female flowers and cones found on separate trees. The flowers have a very long maturing time, and need about one year and a half after pollination for the seeds to develop fully. Every ripe cone is covered in red scales and has one or two seeds inside, about 4 mm long.
The scale is fleshy and popular with birds, who disperse the seeds in their droppings. The cones seem to be very important in the diet of some New Zealand species. Some of them, like the kakapo, actually seem to adapt their nesting period with the rimu cone production time.
The kakapo is a unique type of parrot that is unable to fly and is only active at night. It is threatened with extinction and its mating cycle seems to be modeled with the cone production of the rimu, which usually happens every few years. Unless the rimu cones have a content of aphrodisiac compounds for the birds, scientists believe that the kakapo time their breeding cycle because the tree offers plenty of food for their chicks.
The Podocarp is a primitive and ancient family of trees that have inhabited New Zealand even since it was a part of Gondwana, the huge single continent on Earth.
The rimu competes with the Kauri for the distinction of New Zealand's best quality timber. Since the Kauri could not be found South of Waikato, European colonists in the area mainly used the rimu as construction timber. In time, the large rimu forests were depleted by logging and its range decreased. The local government has stepped in and today it is illegal to cut rimus in public forests. The wood has become rare and only parts from roots and old tree leftovers are now used in crafting.
In years with a large production of cones, they were used as food by the local Māori. However, harvesting them was both difficult and dangerous because they only grow at the end of branches. Injuries while gathering the cones were common among the natives. They were aware of the constipating effect of eating too many fruits and used a drink prepared from Tutu flowers as a counter.
When it was found in large numbers, the rimu was the most important type of construction timber of New Zealand, alongside matai, totara and kauri. Other species are used today, mainly Pinus radiate. The rimu is still prized for its wood. Stumps and roots of trees cut a long time ago provide a limited source of wood that is used to craft small objects such as bowls.
The tree has both medical and industrial uses. The inside parts of the bark can be applied on lesions like cuts and burns. The gum can stop bleeding from wounds but is also edible, despite the very bitter taste. The bark is also effective when applied on burns, as a decoction or a crushed pulp. It also serves as an ingredient in the production of dark color dyes. The local tribe Ngāpuhi used it as a component in the black paint for their canoes.
The European colonists were aware of the excellent qualities of the rimu wood and used it extensively in the construction of both furniture and houses. The Māori used the wood to craft a variety of tools: canoes, torches, spears and various other tools and objects.
An unusual usage for rimu was found by Captain Cook, in his second visit to New Zealand. He brewed a beer from the rimu cones and gave it to his crew as a morale boost and to prevent scurvy. It was so successful that the captain kept the recipe for many years and used it again in his next visit to the shores of New Zealand.
The rimu can be found all over New Zealand, including the North Island, South Island and also Rakiura (or the Stewart Island). The western shores of the South Island have the largest remaining forests. However, the biggest specimens grow in the Waihaha, Whirinaki and Pureora Forests near Taupo, where they can be found mixed with other podocarp species.
The tree enjoys light soils with good drainage in places out of the reach of strong cold winds. For best results, the rimu requires a large amount of rain and water. It can grow in the shade and can't actually grow in full sun in locations with low moisture. It grows very slowly regardless of the conditions but the fastest rate is in humid areas, with warm summers and moderate winters. When cultivated, it does well alongside other trees. Since it is a dioecious species, trees of both sexes are needed for the production of seeds. It can barely survive in the hottest areas of New Zealand, where it doesn't grow well.
Seeds are a viable way of propagation and must be planted in the spring in compost with free drainage. It takes a period of one to three months at 20 degrees C in order for the seed to germinate. However, some people advise sowing the seed as soon as it matures in a cold frame, to speed up the slow germination. The young plants should be immediately moved into pots and sheltered in a greenhouse in the initial winter. After the last period of frost, they can be relocated to their future locations. Cuttings are an alternative method of propagation and have to be planted in the autumn from leading shoots.