Hong Kong International Urban Forestry Conference 2020 Acacia Management and Beyond Kathy Ng Chief Landscape Architect MLA MSc FHKILA RLA ISA CA ISA TRAQ HKIUD BEAM Pro 17 January 2020 This is an abridged version of the original presentation. Approval from Highways Department (and the original source of photos) have to be obtained for any form of copying, reprinting and reproducing. Landscape Division1 Highways Department Government Trees - Urban Areas (exclude Country Parks)

around 1.7 million

Highways ArchSD, WSD, 0.60 M Department DSD, HD & (35%) Others (HyD)

LCSD

Stonewall

Trees Other departments HyD . Around 150 nos.

Note: 1. Data as at March 2019 2. Source : Controlling Officer’s reply examination of estimates of expenditure, 2018-19, for Special Finance Committee 2 Highways Department

over 10000

Expressways Slopes +

HyD SIMAR slopes

11 km² (total open space in HK - 25 km2)

3 Urban Forestry cultivation and management of trees … physiological, sociological and economic well-being of urban society… (Jorgensen, 1970)

…multi-managerial system… wildlife habitats, outdoor recreation opportunities, landscape design, recycling of municipal waste… (Society of American Foresters, 1974)

…longer-term policies and plans for urban tree resources, and is connected to different sectors…

…multidisciplinary …participatory (Konijnendijk et al, 2005)

4 Acacia Stonewall Trees

Aging trees under stress Eucalyptus Background – Acacia

6 Background - Life cycle of Acacia confusa (台灣相思)

1950s 2010s Near future

Acacia plantation scheme Senescent stage

• life expectancy is about 50 years • soil erosion control/ vegetation cover • Health or structural condition of Acacia decline • slope stabilization faster at sites with poorer growing condition with shorter life expectancy • improvement of the fertility of soil

The Ecology and Biodiversity of (Dudgeon, Corlett, 2004) 7 Senescent Acacia

May 2018

Declined structural stability

- heavy leaning and poor self-correction

- poor stem taper and high height-to-diameter ratios

- high susceptibility to wind thrown

June 2018 8 Senescent Acacia

Deteriorating health

- high susceptibility to drought, soil compaction and secondary pathogens when injury occurs

9 Senescent Acacia Low ecological value - exotic , not provide appropriate fruits for local wildlife

- hinder the natural propagation and growth of native plants - reduction of light, moisture, nutrients and space

- allelopathy

- decline in one-go

10 Background – Acacia 1400 HyD’s Maintenance Record on Acacia Removal Note* Seven typhoons were recorded in 2013 (when compared with four to five in other years) The heaviest annual rainfall record was recorded in 2013 (among 2010 – 2015). 1200

1000

800

1282 600

892 400 808 863 824 721

200 443 284 341

0 2010 2011 2012 2013 2014 2015 2016 2017 2018 (Source: HyD) Year No. of Acacia trees

35% of all reported tree failure cases - Acacia (Tree Management Office, November 2012)

11 Objectives

Public Safety Sustainability Biodiversity

12 Programme Workflow

13 1 Planning Ahead

• academia • overseas + local tree experts • Tree Management Office • District Council + public

14 2 Prioritization of Risk and Work

Apple Daily News

15 2 Prioritization of Risk and Work

Acacia tree group survey form Prioritization Total score 3.樹木大小 (Tree size) (Higher priority) (>75分) 4.場地狀況 1.目標評估 (Site conditions) (Target rating) (Moderate priority)

5.場地紀錄 (50-75分) (Site sensitivity) 2.倒塌風險 (Failure potential) (Lower priority) Total score 100 (<50分)

16 3 Implementation

GEO Technical Guidelines on Landscape Treatment for Slopes 17 3 Implementation

Native trees Tsing Nam Road, Tsing Yi

Mallotus paniculatus Sterculia lanceolata Litsea glutinosa Microcos nervosa (白楸) (假蘋婆) (潺槁樹) (布渣葉)

Native shrubs and ground covers

Psychotria asiatica Diospyros vaccinioides Psychotria serpens Litsea rotundifolia Ilex asprella (山大刀) (小果柿) (蔓九節 ) (豺皮樟) (梅葉冬青)

18 3 Implementation Biodiversity Enhancement Native Planting Schedule (Sample)

Spacing Chinese Name Botanical Name (mm) Trees 餘甘子 Phyllanthus emblica 5000 潤楠 Machilus spp. 5000 豆梨 Pyrus calleryana 5000 桑樹 Morus alba 5000 小果鐵冬青 Ilex rotunda var. microcarpa 5000 假蘋婆 Sterculia lanceolata 5000 大頭茶 Gordonia axillaris 3500 Shrubs 梅葉冬青 Ilex asprella 500 車輪梅 Rhaphiolepis indica 300 崗菍 Rhodomytus tomentosa 300 野牡丹 Melastoma malabathricum 300 九節 (山大刀) Psychotria asiatica 300 朱砂根 Ardisia crenata 300 梔子 (白蟾) Gardenia jasminoides 300 Ground cover 腎蕨 Nephrolepis auriculata 200 Climber 薜荔 Ficus pumila -

Note* Trees in small size (e.g. whips/ light standard trees) will be used to minimize the root pruning and cost for planting on site 19 3 Implementation – Pilot Scheme

Wong Tai Sin Pui Man Street

20 3 Implementation – Pilot Scheme

Shatin Yuen Chau Kok

21 4 Reuse • Upcycling

22 4 Reuse • Upcycling

23 5 Monitoring, Evaluation and Enhancement

24 5 Monitoring, Evaluation and Enhancement 中環蛺蝶 美鳳蝶 蛇目褐蜆蝶 報喜斑粉蝶 珍貴嫵灰蝶 古樓娜灰蝶 Neptis hylas Papilio memnon Abisara echerius Delias pasithoe Udara dilecta Nacaduba kurava .

斑鳳蝶幼蟲 白弄蝶 鈕灰蝶 銀線灰蝶 檀方粉蝶 黑邊裙弄蝶 Larva of Chilasa clytia Abraximorpha davidii Acytolepis puspa Spindasis lohita Dercas verhuelli menaka

戈芬氏鳳頭鸚鵡 白腰文鳥 珠頸斑鳩 紅耳鵯 Cacatua goffiniana Lonchura striata Spilopelia chinensis Pycnonotus jocosus

25 5 Monitoring, Evaluation and Enhancement

26 5 Research Environmental Performance Evaluation and Pathological Assessment of Acacia Slopes

Objectives

• management measures to reduce Acacia failure

• long-term maintenance plan

• strategic replacement planting design

• suitable replacement planting matrix for sustainable management

27 5 Research

Pathological Assessment • Develop sets of parameters for evaluating Acacia slopes → Determine the needs and priorities for removal of Acacia trees

Soil Properties Assessment • Collect soil samples → Analysis and compare data collected from pre-replacement period to post-replacement period

Bird, and spider Survey • Conduct surveys on species, biological community found on site → Determine the effects of replanting on biodiversity at study sites

Microclimate and air quality Assessment • Carbon uptake • Transpirative cooling • Air pollutant update • Air pollutant formation → Estimate air quality and climatic effects before and after replanting

28 6 Community Outreach

29 30 Community Bonding

31 Community Bonding

32 Community Bonding

Saw mill Wood dryer

Correctional Services Department Wood workshop

33 Community Bonding

34 Community Bonding

35 Ecological Corridor Enhancement

36 Slopes as the ecological corridor - re-connect community + habitats

Existing greenery

HyD Registered Slopes

Node of connection

Mapping of greenery area and HyD SIMAR slopes in Tseung Kwan O Seasonal distribution, size and type of fruits

Examples of bird species in Tseung Kwan O District

(Source: Hong Kong Wildtracks, HKBU library) Wildlife habitats + major flows of pedestrians and cyclists

Blow-up Scenario 1 - Tunnel junction

Blow-up Scenario 2 – Along cycling and pedestrian path Site photos of existing situation Managing large tree quantity + aging trees over 80% tree over 5m

Proactive Urban Forestry Management - new technology –satellite/aerial photos, VIS, MMS, UAV, LiDAR

• inspection • data collection • analysis • proactive measures • feedback + monitoring

UAV inspection of Eucalyptus Tuen Mun Road

41 Tree Tagging Service Tree Attribute Survey Tree Location Survey

Tree Database

42 43 Trial Application

January 2017

March 2018

Tree Health Tracking

44 Ultimate Goal

HYPERSPECTRAL SIGNATURE LiDAR MULTISPECTRAL IMAGES

HEALTH AI DETECTION EARLY WARNING SYSTEM

45 Vision

Thank you 46