Using Native Plant Species in Forest Restoration ... - Rainforestation

Using Native Plant Species in Forest Restoration and 

Slope Rehabilitation in Hong Kong, China 

Dr. Billy C.H. Hau 

School of Biological Sciences, HKU 

chhau@hku.hk 

MAINSTREAMING NATIVE SPECIES‐BASED FOREST RESTORATION 

University of the Philippines‐Diliman 

Quezon City, Philippines 

July 15–16, 2010

~ 7 million people in 1,100 km 2 but…

- Inhibit only 25 % of the land area 

- 75 % of the land is hilly 

- 40 % of the land is Country Park 

(all on government land)

Geography 

Tropic of Cancer 

Hong 

Kong

The Hong Kong Climate Diagram 

1961-1990 averages: 23 °C / 2,214.3 mm 

70 

140 

60 

120 300 

Temperature (degree C) 

50 

40 

30 

20 

100 

80 

60 

40 

Rainfall (mm) 

10 

20 

0 

1 2 3 4 5 6 7 8 9 10 11 12 

Month 

0 

Season: 

Dry 

Wet 

Dry

Past vegetation of Hong Kong 

Bischofia javanica

Deforestation in Hong Kong – completed 500-800 yrs ago! 

Wu Kau Tang 

Tai Mo Shan

The last major territory-wide deforestation in HK 

happened in the second World War 

Hong Kong 1946 – 1967 (Stoke, 2005)

Afforestation in Hong Kong - History 

Over 200 years of environmental forestry history 

- Soil erosion and hill fire control 

- Watershed forest for drinking water 

- Forestry is never important

Reforestation on road-side slopes in 

countryside areas 

Acacia 

confusa

Reforestation in Hong Kong 

– exotic species 

Lophostemon confertus 

Acacia confusa 

Melaleuca quinquenervia 

Eucalyptus sp.

Monoculture of Lophostemon confertus

Current natural vegetation of Hong Kong 

Degraded hillside 

grassland 

Shrubland 

Secondary forest 

Shrubland/forest transition

The vegetation cover of Hong Kong in the 90s 

Vegetation cover 

Area 

(km 2 ) 

Shrublands 396 37 

Grasslands 177 16.5 

Secondary forest 86 8 

Plantation 62 5.8 

(Dudgeon & Corlett 1994) 

% of the total land 

area 

Public demand on using native species for 

biodiversity conservation was on the rise!!!

Only a few native species were 

occasionally used by the 

government since after the 

Second World War 

Castanopsis fissa 

Liquidambar 

formosana 

Schima superba 

Machilus breviflora

Government’s excuses then: 

• Native tree species often failed to establish on 

exposed sites; 

• Even if they survived, they grew slowly; 

• Lack of seedling supply of native trees; 

• Even if seedlings are available, they are 

expensive. 

‣ Many EIA planting projects in the 90s specified 

the use of native species but had to revert back 

to exotic species because of the lack of 

commercial supply of native tree seedlings

Yet, Hong Kong is rich in tree species 

390 native species in 67 families and 192 

genera (Fagaceae, Lauraceae) 

Up to the 1990s… 

Little is known about the 390 native tree 

species in HK: 

• Flowering and fruiting phenology 

• Silvicultural information 

• Seedling growth conditions in nursery 

and in the wild

Since the mid-1990s… 

Using native tree species for forest restoration in HK 

Government 

Academics 

Environmental 

NGOs 

Slow or reluctant 

to act 

• Field surveys 

• Field experiments 

• Public campaign 

• Set up a native tree 

nursery 

Continue to use 

exotic tree species 

in reforestation 

• Natural succession 

• Forest restoration 

barriers 

• Restoration methods 

• Promote native 

species 

• Native species 

silviculture

Research 

Natural forest succession in 

Hong Kong 

Grassland 

10 yrs 

Shrubland 

30-40 yrs 

Secondary 

forest 

(Chau 1994; Zhuang & Corlett, 1997)

Source: Yip, 2002 

Research: Natural barriers to forest regeneration in HK 

Tai Mo Shan (957 m)

Tai Mo Shan

Natural 

barriers to 

forest 

regeneration 

in HK 

Modified from 

Nepstad et al. 1990 

Degraded 

hillside 

Nutrient 

Drought 

_ 

Fores 

t 

Dispersal 

+ _ 

Mature 

Germination 

Trees 

_ 

Sprouting 

Grazers 

_ Non-trophic animal 

Growth 

damage 

_ _ 

Attractants? 

Seed Pool Relict seeds 

Fruiting 

_ Predators 

Shade 

Seedling 

Pool 

Relict roots

Natural barriers – seed dispersal 

Au, Corlett & Hau 2006 

• Compared seed 

dispersed into 

grassland, shrubland 

and forest of Tai Mo 

Shan for 2 years 

• Results: seed input 

into grassland was 

surprisingly high 

• Qualitative difference 

between habitats


Au, Corlett & Hau 2006 

• Birds especially bulbuls are the major seed dispersers 

• 85% of the taxa and >99% of the seeds trapped 

• Estimated displacement is > 1 km in dry season (Weir & 

Corlett 2006) 

Red-whiskered Bulbul 

Pycnonotus jocosus 

Light-vented Bulbul 

Pycnonotus sinensis


Summary: 

1.Only a sub-set of the local tree flora is 

dispersed naturally on the degraded 

hillside 

2.The seed rain is adequate for the 

development of woody vegetation cover 

3.Birds especially the bulbuls are the major 

seed dispersers

Natural barriers – seed predation 

Hau, 1997; Chung 2006 

• Compared both grassland & shrubland sites 

• Rodents are the major seed predators (Niviventer 

fulvescens; Rattus sikkimensis) 

• High temporal and spatial variations 

• Predation rate could reach 100% in 2 weeks 

• Predation rate in grassland is much lower than 

that in shrubland 

Seed predation is patchy in space & time. It is also a 

selective barrier on forest regeneration but will not 

significantly reduce the availability of woody seeds 

for forest succession.

Natural barriers – seed germination 

Chick, 2005 

• Tested the germination of 23 common native 

tree species on Tai Mo Shan grassland 

• Most species can germinate 

• At least 6 species have germination rates 

higher than 60% and larger than 50% of the 

germinated seedlings survived after a year. 

Adverse conditions in the field for germination such 

as drought; lack of shade again act as selective 

barriers only.

Natural barriers – seedling growth & 

survival 

Hau & Corlett 2003 

Tested using 4 native tree species: 

‣ below ground competition with grasses 

‣ seasonal drought 

‣ low soil fertility 45 degrees 

All 3 factors can 

significantly impair 

seedling growth but that 

their relative importance 

differs among species.

Natural barriers - Seedling growth & 

survival 

Hau & S0 2003 

• Reported another 8 native species planted on a 

grassland at Tai Mo Shan 

• Survival (2 year) between ~50 – 97% for all 

except one species. 

• Reached 2 m in two 

years for most of 

the species

Natural 

barriers 

All natural 

barriers tested 

appears to be 

selective 

barriers only! 

Modified from 

Nepstad et al. 1990 

Degraded 

hillside 

Mortality 

Drought 

_ 

Fores 

t 

Dispersal 

+ _ 

Mature 


Trees 

_ 

Sprouting 

Grazers 

_ Non-trophic animal 

Growth 

damage ? 

_ _ 

Attractants? 

Seed Pool Relict seeds 

Fruiting 

_ Predators 

Shade 

Seedling 

Pool 

Relict roots

1997 

Up to 50,000 

seedlings/ year 

Local seeds 

Field planting trials

Since 1997… 

• 200 native tree and some shrub species 

of over 200,000 seedlings produced. 

• For use in voluntary, commercial and 

government reforestation projects 

• Public education programmes 

• Also used in supporting research works 

of local universities (8 MPhil projects 

and numerous undergraduate projects) 

• And some basic research works


tests 

Cell tray-75 compartments 

- > 121 species tested 

- 75 species > 50 % germination rate 

- plus 30 other species known to germinate 

well from past experiences

Nursery growth rate tests 

- Around 90% of the species grown in the nursery could rich 

the transplanting size of 30-50 cm in 18 months.

Other research work in the 

nursery 

Quality 

stock 

Mycorrhizas 

Nitrogenfixing 

native 

tree species 

Genetic 

diversity

Other research work in the nursery 

• Mycorrhizas 

• Genetic diversity 

• Nitrogen-fixing native tree species 

- Examined the N-fixing ability 

of native legume species 

- Attempted artificial 

inoculation in seedling 

production 

- Ng and Hau 2009

Other field planting trials in different restoration sites 

3 years 3 years 

5 years 5 years

Research works in exotic plantations 

Lee, Hau & Corlett 2005; 2008 

‣Natural regeneration in exotic tree plantations 

Lee 2004; Yu 2007 

‣ Enrichment planting/direct seeding of native 

species in exotic plantations 

Hung 2010 

‣ Thinning plus enrichment planting/direct 

seeding of native species in exotic plantations

From 57 native species in 8 planting trials: 

Framework species criteria 

Toughness 

Attractiveness to wildlife/ Early 

production of wildlife resources 

Regenerative ability 

Keystone species 

Architecture 

Vigour 

Species with limited dispersal 

mechanism 

Species (13 species) 

Gordonia axillaris; Schefflera heptaphylla; 

Mallotus paniculatus 

Schefflera heptaphylla; Mallotus paniculatus; 

Microcos paniculata; Ardisia crenata; 

Melicope pteleifolia; Aporosa dioica 

Schefflera heptaphylla; Mallotus paniculatus; 

Microcos paniculata; Choerospondias axillaris; 

Machilus breviflora 

Aporosa dioica; Litsea glutinosa, Ilex rotunda, 

Schefflera heptaphylla 

Mallotus paniculatus; Choerospondias axillaris 

Schefflera heptaphylla; Machilus breviflora; 

Gordonia axillaris; Cyclobalanopsis championii 

Cyclobalanopsis championii; C. neglecta; C. 

edithiae; Lithocarpus harlandii

Propagating the framework tree species 

Species 

Family 

Easy to 

propagate 

Notes 

Ardisia crenata Myrsinaceae No Low growth rate 

Choerospondias axillaris Anacardiaceae Yes 

Cyclobalanopsis championii Fagaceae Yes Forming Ectomycorrhizas 

Cyclobalanopsis neglecta Fagaceae Yes Forming Ectomycorrhizas 

Gordonia axillaris Theaceae No Low germination & growth rates 

Ilex rotunda Aquifoliaceae No Low germination rate 

Machilus breviflora Lauraceae Yes 

Mallotus paniculatus Euphorbiaceae Yes 

Melicope pteleifolia Rutaceae No Low germination rate 

Microcos paniculata Tiliaceae Yes Medium germination rate 

Schefflera heptaphylla Araliaceae Yes 

Schima superba Theaceae No Low germination rate 

Zanthoxylum avicennae Rutaceae Yes Medium germination rate

No. of trees planted in Hong Kong 

Year 

1999/00 1.5 

2000/01 1.6 

2001/02 1.8 

2002/03 2.5 

2003/04 3.2 

2004/05 1.8 

2005/06 2.3 

2006/07 2.0 

2007/08 1.6 

2008/09 1.3 

Total 19.6 

No. of trees planted in HK (million) 

On average, 90% were 

planted in hillside reforestation 

Source: Development Bureau Greening Website 

http://www.devb-wb.gov.hk/greening/en/index.htm

The vegetation cover of Hong Kong 

Dudgeon & Corlett 1994 ERM 2002 

Vegetation cover Area (km 2 ) % of the total 

land area 

Area (km 2 ) 

% of the total 

land area 

Shrublands 396 37 224.5 20.1 

Grasslands 177 16.5 347.8 31.1 

Secondary forest 86 8 184.0 16.5 

Plantation 62 5.8 1.8 0.16 

Despite forest succession and active 

reforestation, the forest cover in Hong Kong 

is not increasing significantly in the last two 

decades.

North Lantau 

Tai Mo Shan 

Robin’s Nest (Hung Fa Leng) 

Shek O

The impact of hill fire

The impact of hill fire 

Hill fires in Hong Kong 

• 1159 fires from 1993-2004 in Country Parks (on 

average 105 fires/yr) 

• Most frequently burnt are grassland and 

shrubland 

• Closed canopy forests do not burn 

• There is no natural hill fire in HK 

Anthropogenic hill fires 

‣ Festival fires (Apr., Oct.) 

‣ Accidental fires (careless visitors) 

‣ Arson

Ecological reforestation - The landscape 

approach 

• The current afforestation approach on site by 

site basis in Hong Kong does not work! 

• Many young planting sites have 

been destroyed by hill fires in 

the last decade costing millions 

of dollars 

• A new reforestation approach 

on landscape level integrating 

fire prevention is needed

Forest reforestation - The landscape approach 

A Feasibility Study of Hill Fire Management on Tai 

Mo Shan using GIS Analysis (Chan 2005) 

1 km strip from 

the boundaries 

of the 3 

Country Parks


a. Historical fire data (1993-2004) - from the government 

Fire Control Centre 

b. Vegetation map - from ERM Hong Kong Ltd. 

c. Geographical data - from Lands Department 

d. Registered grave sites - from Lands Department 

• Historical fires 

‣ Fire frequency 

‣ Fire size 

• Vegetation (fuel) 

‣ Close canopy forests 

‣ Shrubland 

‣ Grassland 

• Topology 

‣ Slope 

‣ Aspect 

‣ Elevation 

• Man-made structures 

‣ Grave sites 

‣ Roads & paths 

‣ Build-up areas 

‣ Villages 

• Weather data 

‣ Wind


RESULTS 

Festival fires: Fire sources and fire prone areas


RESULT Non-festival Fires: Fire sources and fire prone areas


RESULT: Fire break design


Conclusion for Tai Mo Shan 

- First 10 years or so should focus on firebreak 

construction to isolate fire sources;


Conclusion for Tai Mo Shan 

- After the firebreaks become effective, allow 

natural succession to restore native biomass; 

- Assist succession by adding plant diversity; 

- Use cheaper methods such as direct seeding; 

planting island patches or corridors linking 

established forest patches to speed up 

succession. 

This scheme could be applied to other parts of HK

From the late 90s to now… 

• The government has included more native species 

in its restoration project (normally not more than 

50%); 

• The government is conducting large scale thinning 

and enrichment planting in exotic plantations; 

• Commercial nurseries have steady supply of a 

limited number of native tree and shrub species (c. 

20 species) 

• The government is also planting more native tree 

and shrub species on roadside slopes 

• The landscape level restoration approach is yet to 

be adopted by the government.

Experiences from Hong Kong 

‣ Landscape level approach is needed for large 

scale reforestation 

‣ Identify the real barriers (natural and artificial) to 

forest regeneration 

‣ Reset priorities. In our case, fire prevention 

obviously has much higher priority. 

‣ Natural succession alone can only restore native 

biomass, human intervention is needed to restore 

diversity. 

‣ Lobbying the Government is important

References 

Au, A.Y.Y., Corlett, R.T. & Hau, B.C.H. 2006. Seed rain into upland plant communities 

in Hong Kong, China. Plant Ecology, in press. 

Chan, W.H. 2005. A Feasibility Study of Hill Fire Management in Hong Kong Country 

Parks using GIS Analysis. MSc Dissertation, The University of Hong Kong. 

Chau, K.C. 1994. The Ecology of Fire in Hong Kong. PhD Thesis, The University of 

Hong Kong, Hong Kong. 

Chick, H.L. 2005. Direct seeding of native species for reforestation on degraded 

hillsides in Hong Kong, China. MPhil thesis, The University of Hong Kong. 

Chung, K.P.S. (in press). The role of seed predation on natural forest regeneration in 

Hong Kong, China. PhD. thesis, The University of Hong Kong. 

Dudgeon, D. and Corlett, R.T. 1994. Hills and Streams: An Ecology of Hong Kong. 

Hong Kong University Press, Hong Kong, 234 pp. 

ERM (Environmental Resources Management Hong Kong Ltd.). 2002. Environmental 

Baseline Survey Report: Terrestrial Habitat Mapping and Ranking Based on 

Conservation Value. Environmental Protection Department, the Government of 

the Hong Kong SAR, Hong Kong. 80pp.

Hau, C.H. 1997. Tree seed predation on degraded hillsides in Hong Kong. Forest 

Ecology & Management, 99:215-221. 

Hau, B.C.H. & Corlett, R.T. 2003. Factors affecting the early survival and growth of 

native tree seedlings planted on a degraded hillside grassland in Hong Kong, 

China. Restoration Ecology, 11(4):483-488. 

Hau, B.C.H. and So, K.K.Y. 2003. Using native tree species to restore degraded 

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Using Native Plant Species in Forest Restoration ... - Rainforestation

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