Scientific name: green banyan

Alias: Pinus ponderosa, Ficus macrophylla, Datura stramonium.

Huangjiaoshu

There are many yellow horn trees in Chongqing. No matter on sidewalks, residential courtyards, entertainment places and campuses, there are yellow-horned trees everywhere.

The thick trunk supports the green crown like handfuls of green umbrellas, which is beautiful. Especially on the roadside fortress, the gap in the mountain wall grows lush and very lush. These yellow horn trees aroused our great interest. We consulted teachers, visited Uncle Zhou and Uncle Zeng, who are engaged in landscape technology, and made a field investigation on the growth characteristics of the yellow horn tree.

First, the growth characteristics of the yellow-horned tree on the fort.

From Shangqing Temple to Children's Palace, we found 93 yellow-horned trees growing on the cracks in the rock castle. Most of them are clustered, but they are 20-40 years old. These 93 yellow-horned trees are all growing well. Because the roots of the yellow horn tree spread and interweave on the rock surface, there is no crack in any fortress. On the contrary, we found a ginkgo tree in eling park, which is 35 years old, DBH is 32 cm, height is 13 m, crown is 5 m, and it is 30 cm away from the bulwark, and the bulwark has a crack of 13 cm. According to local memories, the cracks appeared about 10 years ago. It is estimated that the fortress here is expanding cracks at the rate of 1 cm per year.

The mortar joint of the city fortress is only 1 cm wide, and the filler seeds of the mortar joint are composed of lime, cement and river sand, and there is no soil at all. Why can the yellow horn tree grow on the fortress? After repeated investigation and discussion, we think that the key is that the root system of the yellow horn tree is very developed. Its roots have three characteristics:

First, the yellow horn tree grows fast and has strong permeability. In our investigation, we found that the roots of many yellow-horned trees growing on rocks are 2-3 times more developed than the trunks. The trunk diameter of a yellow horn tree on the fort ridge opposite the Municipal Pediatric Hospital is 8 cm, but its root diameter is 134 cm. The tree is 3 meters high and the crown is 4 meters, but one of its lateral roots is 16.5 meters long along the ridge, which is more than four times that of the crown. In addition, we also found that the roots of the yellow horn extend into the deep cracks of caves and air-raid shelters, and many fibrous roots and branched roots grow, some of which are suspended in the air for 70 cm to absorb the moisture in the humid air.

Second, the root of yellow horn has very strong adsorption. Its roots can grow on the surface of the earth or thrive around other objects like vines.

Third, the root of the yellow horn is also variable. In order to adapt to the changes of natural environment, sometimes its roots will grow from round to flat. What shape the gap in the natural terrain is, it will change into what shape. In addition, when the roots of two yellow angle trees collide, they will grow into thicker roots. Countless roots connected together will grow into a "big trunk", giving people the illusion that it is a trunk.

Second, the different characteristics of the yellow horn tree growing on steep rocks, soil slopes and flat land.

In an interview, an old gardener told us: "Yellow-horned trees like rocks best, and trees growing on the edge of rocks grow faster than those growing in soil." Is that really the case? We investigated more than 100 trees growing in eling park, Futuguan and Beiquan Park. Most of the ancient yellow-horned trees really grow on the top of the rock and near the water, and most of them grow better than those growing in forest soil, and their roots are much more developed. Why is this? Is it the stone that determines its growth rate? After repeated observation, we found that the crown of the yellow horn tree always extends obliquely out of the hanging rock and into the lake. This shows that the yellow horn tree is trying its best to win the sunshine. Almost none of these trees have obvious trunks, but they are all clustered. Even if there is, the branch point is below 2 meters. Compared with the crown width, the height of the tree is mostly 1: 2. Yellow horn trees are mostly isolated trees on the edge of rocks, so that they can get enough light to meet their growth and development needs. Is it really slower for the yellow horn tree to grow in the soil than on the stone? According to records, the DBH of the wild yellow-horned tree growing on the rock edge is about 65438 0.2 meters, with an average of about 65438 0.2 cm per year. However, the isolated yellow-horned tree cultivated in the soil outside the eling park basin garden gets enough light and nutrients, and its growth period is about 28 years, and its DBH is more than 60 cm. Therefore, there are more yellow-horned trees growing alone in the soil than rocks.

However, if the yellow horn tree grows with many other trees and shrubs on slopes and flat land, its ability to grow tall will be poor. When we observe in natural and wild mixed forests and coniferous forests, we often can't even see the shadow of the yellow horn tree. This shows that the competitiveness of yellow horn tree is not strong. This tells us that when planting yellow horn trees, we should plant them in an open area with plenty of sunshine and water.

Third, the characteristics of the growth of the yellow horn tree at the water's edge.

Yellow horn trees not only like sunlight, but also need a lot of water. According to our measurement, the area of each leaf is about 20-60 square centimeters, which is 3-6 times that of Cinnamomum camphora and Osmanthus fragrans leaves. So yellow horned trees consume much more water than they do. Where there is water, where there is humid air, the yellow horn tree is always desperately rooted there, growing many fibrous roots and aerial roots to meet its own survival needs.

Can the yellow horn tree develop into an aquatic plant? We took this question to eling park and Ronghu Lake in Shaping Park for observation. There are 22 yellow horn trees growing here. Because of cleaning the bottom of the lake and releasing water, we clearly saw the whole picture of the growth of yellow horn roots in the water, which surprised us. It turns out that the root of the yellow horn can grow in the crack of hard rock, and once it reaches into the water, it will be "bitten off" by the water. We observed along the lake and found that there are many countless fibrous roots below the water level line of the lake, some of which are as long as 1.3 meters, and generally about 0.3 meters long. From this, it can be judged that although the yellow horn tree likes water very much, it can't survive in water because its roots are soft and easy to be corroded by water. Then, why can the yellow horn tree growing in the North Hot Spring Waterfall withstand the erosion of calcareous spring water at 25℃ for decades without dying? It turned out that there was a thick layer of moss in front of the main lateral root of the 6-meter rock, forming a thick curtain, which prevented the direct erosion of the root of the yellow horn by the spring water.

Fourth, strange parasitic phenomenon.

The roots of the yellow horn tree can adapt to many environments like vines, and it has the special ability to parasitize other trees and isolated rocks. There is an annual seedling parasitic on the trunk of a live camphor tree. The roots of seedlings extend into the cortex along the cracks in the trunk of Cinnamomum camphora to absorb water and nutrients. There is also a four-year-old yellow horn tree parasitic on a dead tree in eling park flower garden. Even three yellow-horned trees were parasitized on a 300-year-old (dead) Pistacia chinensis tree near Huayan Temple Lake for 40 years, which revived the dead trees. At a height of 6 meters, the roots of trees are connected around the trunk and fall to the ground, forming a fake trunk. Only by careful observation can people find that Pistacia chinensis is surrounded by the roots of yellow horns. A yellow-horned tree in eling park is parasitic on a boulder with a height of 4. 15m and a width of l m, and its root system closely surrounds the boulder, just like a trunk. The sign on the tree reads: "This tree is a huge stone tree left over from the original pear garden, with a stone body attached to it, which is magnificent. DBH1.75m, tree height16m, crown width18.4m, and tree age 150 years or more. It is one of the key protected ancient trees in Chongqing. " The result of our observation and measurement is that the true trunk of this bare tree should be more than 4. 15 meters, and the trunk diameter is only 55 cm. According to the diameter of the trunk, the age of this tree is about 60 years old. We also found that all the roots of the yellow horn have no ability to sprout new buds. Therefore, although the yellow horn tree has strong parasitic ability, it is impossible to reproduce its offspring with its roots.

Five, the role of yellow horn tree in mountain city greening

Because many advantages of the yellow horn tree adapt to the geographical characteristics of the mountain city, people in the mountain city call it the "city tree". A large number of yellow horn trees have been planted in industrial and mining areas, sidewalks, rock castles, entertainment places and courtyards. 1 12 planted yellow horn trees on the 24-meter-high bulwarks on both sides of the south bridge head of Jialing River (three bulwarks were built, each with a width of 1 m), which turned the stone wall into a green wall, not only greening the environment, but also strengthening and maintaining the bulwarks. On Beibei Street, we saw someone building a house under a yellow corner tree, which lowered the indoor temperature and played the role of air conditioning. In the park, people dig up the soil, improve the position of the roots and form isolated ornamental trees. According to the soft and easy-to-tie and easy-to-trim characteristics, people woven the yellow corner branches into screens and cultivated them into very unique and beautiful bonsai, which were exhibited at home and abroad and won the appreciation of many visitors.

There is still a lot of knowledge about yellow horn trees, and our investigation activities are still going on. According to its characteristics of strong adaptability, good shading and strong anti-pollution ability, the yellow horn tree will play a greater role in greening and beautifying the motherland.