2007年3月27日 星期二

Tree Planting - 24/3/2007

Afforestation
1) Tree planting history in Hong kong
Period 1870s to 1940s - aims : Health and aesthetic reasons.
Period 1950s to 1980s - aims : Soil erosion control, Water supplies improvement,
Fire Prevention and suppression and landscaping.
1980s onward - aims : Ecological restoration
Tree planting shortens the process of regenerating forest by skipping the status of grassland and shrubland in forest succession but start-jumping at secondary forest status by planting tree seedlings.
A wide range of native and exotic species has been tried but less than a dozen have been extensively planted with a high degree of success.
2) Pros and cons of planting exotic and native trees
Exotic tree species
The exotic tree species used in Hong Kong are fast growing and survive on very degraded sites. Some species, such as Acacia confusa, are fire tolerant and can be used to form a fire-break.
Most of the exotic species are monocultures. In some cases, monocultures of exotic trees can even suppress natural understorey regeneration and are often more susceptible to pest attack.
The invasion of native woody species, especially in young plantations, is significantly impaired by management practices such as weeding.









The mist is not so heavy. I can only see things within 50 meters. I did not take so many photos as I had to help them to dig holes for palnting seedling.
There are twelve students and two teachers to plant 50 seedlings in 1 hour and thirty minutes.


















2007年3月26日 星期一

Tree Planting - 17/3/2007

Forest Succession
Succession ------------->
Disturbed - Land -----> Grassland -----> Shrubland -----> Broad-leaved secondary forest
Disturbance <-------------
Reforestation can occur naturally by ecological succession. Grasslands persist largely in areas that have been burned in the 5 - 10 years and graudually replaced by shrubland in the absence of fire.
However, hill fires retard the process of succession, thus the freguently burned areas are kept in the stage of grassland.
On favourable sites, native Machilus - dominated secondary forest, 10-15 m in height, can develop in 30-50 years after destruction, provided that there is no any other disturbance.
Forest succession is apparently much slower on sites, which are remote from treeseed sources or where the soil has been severely degraded.
The natural secondary forests in HOng Kong have developed since 1945.
There are some 400 native tree species in Hong Kong. The majority are confined to the upland remnant sites, which have not succeeded in invading secondary forests. Their seed dispersers have been wiped out in Hong Kong due to habitats destruction. Therefore, by planting native tree species that are not naturally well dispersed can enhance the diverity of our forests.
Above article is extracted from Kadoorie Farm and Botanic Garden printout.
Due to the heavy mist in the upper farm, The Tree Planting activity is changed into a Guided Tour in Lower farm.
Causes of Deforestation in Hong Kong : ????
Afforestation : coming soon