The rapid urban development of Hong Kong in the past few decades has left little room for tree growth. Urban parks, which usually located at the centre of tall buildings and concrete roads, become the most suitable site to plant trees. Although trees could easily be found in Urban Park, however, the tightly packed city has created a lot of stresses on their growth. Due to this reason, trees in urban park tend to possess some common characteristics and problems. In order to get a more thorough understanding towards the relationship between environmental conditions and tree growth, a survey of 32 trees has been carried out in the Victoria Park.
Victoria Park has been chosen in this survey because there are high number and varieties of trees species, common tree problems could easily be found there. In addition, questions such as how tree growth in the human settlement could be studied. 32 trees with distinct problems were selected and information such as tree height, crown diameter, sites characteristic, arboricultural defects and disorder has been recorded. Each tree is being assessed closely.
Tree characteristics are resulted from the environment conditions of the urban areas such as poor soil quality and planting materials. After the site visit, we found that trees in Hong Kong Urban Park tend to exhibit some characteristics just like the dominance of exotic species and they usually possess some common tree problems. An individual tree that possesses several problems at once is not uncommon.
A) Dominance of Exotic Species
84.3% of the trees out of 32 are exotic species. Exotic species such as Acacia confusa, Aleurites moluccana and Casuarina equisetifolia could commonly be found in Victoria Park. The reason behind is exotic species can generally perform better in adapting to the surrounding environments. Urban areas such as Hong Kong always create harsh environmental conditions for tree growth. Only trees with high ability of environmental adaptation can survive. Casuarina equisetifolia is a good example to illustrate this point. It is an exotic species, which originated from Australia. They are usually located on the coastal area with sandy and rocky beaches. Casuarina equisetifolia have a strong ability to resist drought, wind and salt spray. As there are moisture deficiency on the sandy and rocky beaches, the leave of Casuarina equisetifolia are needle-shape, which can reduce water loss from transpiration effectively. In Hong Kong, water shortage is also a common phenomenon as rainfall mainly concentrated in summer. In addition with the heat island effect, Casuarina equisetifolia can still survive under harsh environment like Hong Kong. So it is widely planted in the past.
Apart form the ability to adapt to the surroundings; trees that can perform other functions would also be considered to plant in urban Hong Kong. In order to ameliorate on the harsh urban environment, trees that have a quick greening effect are widely plated such as Aleurites moluccana. Besides, Cassia surattensis, a fast growing flowering tree can perform the function of beautifies the urban area. This tree is said to have visual impacts on the nearby environment.
B) Tree problems
Trees in Hong Kong urban park tend to have various problems in response to the surrounding environmental conditions. During the visit, many tree problems could be found. Examples are multiple stems, unbalanced crown; many water sprouts, and all the tree problems found during survey have been summarized in Table 1. Frequency of the problems has also marked in the table. By obtaining such kind of information, we can identify what are the most serious problems and what are the possible causes of these common tree problems.