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LCQ7: Replacement of senescent Acacia confusa

Following is a question by the Hon Hui Chi-fung and a written reply by the Secretary for Development, Mr Michael Wong, in the Legislative Council today (January 17):
 
Question:
 
Since the seventies of the last century, the Government has planted Acacia confusa (Acacia) extensively in the countryside and the urban areas to prevent soil erosion, stabilise slopes and increase vegetation. Some tree experts have pointed out that as the average life span of Acacia is 50 to 60 years, those trees are in senescence, they will gradually wither with the risk of collapsing, posing safety hazards to members of the public. In this connection, will the Government inform this Council:
 
(1) of the number of Acacia on government lands that were removed by the authorities in the past five years, and their distribution;
 
(2) of the current number of Acacia on government lands and their distribution, and whether it has compiled statistics on the age of those trees and examined their health conditions; and
 
(3) whether it has formulated a plan to gradually remove senescent Acacia and replace them by planting trees of other species; if so, of the implementation timetable, the estimated expenditure and the number of Acacia involved, as well as the species of the new trees to be planted and their places of origin?

Reply:

President,

My reply to the three-part question raised by the Hon Hui Chi-fung is as follows:

(1) In the past five years from 2012-13 to 2016-17, during routine tree maintenance, the core tree management departments removed around 13 000 Acacia confusa (Acacia) beset with health or structural problems or severe damage caused by inclement weather, posing potential risk to the public. These Acacia were located mainly on roadside slopes, in public housing estates, parks, as well as recreational facilities and venues.  Their distribution is set out below:
 
Core tree management department Number of Acacia removed Total
2012-13 2013-14 2014-15 2015-16 2016-17
Agriculture, Fisheries and Conservation Department (AFCD) 116 155 172 127 247 817
Architectural Services Department (ArchSD) 869 840 606 1 059 1 305 4 679
Civil Engineering and Development Department (CEDD) 29 27 36 38 31 161
Drainage Services Department (DSD) 9 21 70 34 17 151
Highways Department (HyD) 732 809 735 806 953 4 035
Housing Department (HD) 218 420 289 424 325 1 676
Leisure and Cultural Services Department (LCSD) 185 247 265 305 202 1 204
Water Supplies Department (WSD) 191 86 2 56 99 434
 
(2) According to the Development Bureau's Tree Management Information System, as at December 31, 2017, the number and distribution of Acacia in areas of high pedestrian and vehicular flow are set out as follows:
 
Core tree management department Distribution of Acacia in
high pedestrian and vehicular flow areas
Total
Hong Kong Kowloon New Territories
AFCD 348 110 7 138 7 596
ArchSD 704 4 262 9 993 14 959
CEDD 1 4 1 578 1 583
DSD 17 29 718 764
HyD 3 529 4 138 16 054 23 721
HD 2 617 12 445 2 972 18 034
LCSD 11 758 4 039 10 811 26 608
WSD 45 1 893 706 2 644
 
In accordance with the "Guidelines for Tree Risk Assessment and Management Arrangement", every year before the onset of wet season, tree management departments are required to undertake tree risk assessments and implement timely mitigation measures (including removal of dead branches, tree pruning, pest and disease control, cabling, etc.) for trees (including Acacia) in areas of high pedestrian and vehicular flow to maintain tree health and stable structure so as to minimise tree failure. We do not have statistics on the age of individual Acacia.

(3) Generally speaking, during routine tree maintenance and tree risk assessments outlined above, tree management departments will remove Acacia that are in senescence, unstable structure, poor health conditions with potential risk of failure. Depending on actual site conditions, suitable native tree species, such as Liquidambar formosana, Machilus spp., Gordonia axillaris and Schima superba, etc., will be planted as replacement. Tree maintenance and planting are part of routine duties of tree management departments and no additional resources are involved.

Nevertheless, in view of the substantial number of Acacia on roadside slopes, in mid-2016, the HyD launched the "Enhancement of Vegetated Slopes Programme" to progressively replace the ageing Acacia. The HyD consulted all district councils on the programme in 2016. In the past two years, the HyD has launched 16 pilot schemes in which around 340 senescent Acacia with poor health and structural conditions were replaced, with an expenditure of approximately $5 million.  The distribution of Acacia removed in the 16 pilot schemes is as follows:
 
District Number of Acacia removed (Note)
Eastern 30
Southern 20
Wan Chai 10
Kowloon City 50
Sham Shui Po 40
Wong Tai Sin 20
Islands 30
Sai Kung 10
Sha Tin 40
Tai Po 50
Kwai Tsing 10
Tuen Mun 20
Yuen Long 10
Note: Figures rounded off to the nearest 10

After removing the Acacia, the HyD has planted around 340 trees and 100 000 shrubs and ground covers as replacement. These included native plants, such as Gordonia axillaris, Cinnamomum burmannii, Sterculia lanceolata, Pongamia pinnata, Liquidambar formosana, Rhododendron simsii, Rhaphiolepis indica, Ixora chinensis, etc., and naturalised plants, such as Rhododendron pulchrum, Gardenia jasminoides, Ligustrum sinense, etc. The tree stocks are mainly sourced from Southern China.

Currently, the HyD is conducting detailed tree surveys to ascertain the distribution, extent, tree health and site conditions, etc. of the Acacia plantation areas to work out the priorities of the replacement programme. For 2018-19, the HyD preliminarily plans to replace the senescent Acacia in 13 slopes with an expenditure of approximately $4 million. Upon the completion of the detailed tree surveys in other areas, the HyD will finalise the phased programme timeline and the expenditure required.

The programme to replace senescent Acacia mentioned above received the Silver Award under the "Landscape Management" category of the Hong Kong Institute of Landscape Architects Design Awards in 2016, and an Honourable Mention under the "Analysis and Master Planning" category of the International Federation of Landscape Architects Asia-Pacific Region Landscape Architecture Awards in 2017, showing that this programme is well recognised by the industry.

Ends/Wednesday, January 17, 2018
Issued at HKT 18:20
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