Propagating framework tree species to restore seasonally dry tropical forest: Implications of seasonal seed dispersal and dormancy

Abstract

One effective approach to forest restoration in degraded tropical forestland is the so-called ‘framework species method’ which involves planting 20–30 indigenous forest tree species to re-establish a basic forest structure that catalyses the recovery of biodiversity. For the seasonally dry tropical forests of Doi Suthep-Pui National Park in northern Thailand, a provisional list of 36 potential framework species was compiled, from 19 different families representing a broad spectrum of the tree flora. This paper examines the seed germination characteristics of these species when grown as a nursery ‘crop’ for planting to restore degraded sites, focussing on germination phenology and dormancy. It considers how such characteristics affect the first stage of nursery production from seed collection to pricking out seedlings in the nursery. Twenty-nine species had a germination percentage of 60% or greater, which is acceptable for nursery production. The median length of dormancy (MLD) ranged from 7 days in the case of Erythrina subumbrans to 219 days for Lithocarpus garrettianus. Germination was defined as rapid if the MLD occurred within 3 weeks, and slow if occurring after 12 weeks. Twelve species germinated rapidly and eight germinated slowly, the remainder being intermediate. Seedling emergence ranged over a period of 7 days in the case of Erythrina stricta and E. subumbrans to 322 days in the case of L. garrettianus.

Full text

Propagating framework tree species to restore seasonally
dry tropical forest: implications of seasonal seed
dispersal and dormancy
David Blakesley
a,*
, Stephen Elliott
b
, Cherdsak Kuarak
b
, Puttipong Navakitbumrung
b
,
Sudarat Zangkum
b
, Vilaiwan Anusarnsunthorn
b
a
Horticulture Research International, East Malling, West Malling, Kent ME19 6BJ, UK
b
Science Faculty, Biology Department, Forest Restoration Research Unit, Chiang Mai University, Chiang Mai 50200, Thailand
Received 4 December 2000; received in revised form 10 April 2001; accepted 10 April 2001
Abstract
One effective approach to forest restoration in degraded tropical forestland is the so-called ‘framework species method’
which involves planting 20–30 indigenous forest tree species to re-establish a basic forest structure that catalyses the recovery
of biodiversity. For the seasonally dry tropical forests of Doi Suthep-Pui National Park in northern Thailand, a provisional list
of 36 potential framework species was compiled, from 19 different families representing a broad spectrum of the tree flora.
This paper examines the seed germination characteristics of these species when grown as a nursery ‘crop’ for planting to
restore degraded sites, focussing on germination phenology and dormancy. It considers how such characteristics affect the
first stage of nursery production from seed collection to pricking out seedlings in the nursery. Twenty-nine species had a
germination percentage of 60% or greater, which is acceptable for nursery production. The median length of dormancy (MLD)
ranged from 7 days in the case of Erythrina subumbrans to 219 days for Lithocarpus garrettianus. Germination was defined
as rapid if the MLD occurred within 3 weeks, and slow if occurring after 12 weeks. Twelve species germinated rapidly
and eight germinated slowly, the remainder being intermediate. Seedling emergence ranged over a period of 7 days in
the case of Erythrina stricta and E. subumbrans to 322 days in the case of L. garrettianus.#2002 Elsevier Science B.V. All
rights reserved.
Keywords: Tropical forest restoration; Seed dormancy; Germination; Seedling development; Framework tree species
1. Introduction
Deforestation is a serious environmental problem
throughout the tropics causing rural poverty, water-
shed degradation and loss of biodiversity. Efforts to
restore forests are increasing, but such efforts are
often limited due to lack of knowledge about how to
propagate the majority of indigenous tree species. One
effective approach to forest restoration is the ‘frame-
work species method’ (Goosem and Tucker, 1995;
Lamb et al., 1997; Tucker and Murphy, 1997) first
developed to restore forest in degraded areas of
Queensland’s Wet Tropics World Heritage Site in
Australia. The method depends on tree planting to
restore basic forest structure which then encourages
Forest Ecology and Management 164 (2002) 31–38
*
Corresponding author. Tel.: þ44-1732-84-3833;
fax: þ44-1732-84-9067.
E-mail address: david.blakesley@hri.ac.uk (D. Blakesley).
0378-1127/02/$ – see front matter #2002 Elsevier Science B.V. All rights reserved.
PII: S 0378-1127(01)00609-0

the recovery of biodiversity. Seven years after planting
20–30 framework tree species in degraded grassland
sites in Queensland, the regenerating forests devel-
oped closed canopies up to 8.7 m tall and was
naturally colonised by up to 49 additional tree species
(Tucker and Murphy, 1997). Framework tree species
are fast growing with dense spreading canopies which
rapidly shade out weeds. They also provide resources
for wildlife (such as fruit, nectar or perching sites) at
an early age. Animals (especially birds and bats)
attracted by such resources, disperse the seeds of
additional non-planted tree species into the planted
sites, thus accelerating the return of biodiversity. Seed
of framework species should be easy to collect and
germinate in nurseries. A reasonable growth rate is
also required in the nursery to ensure efficient use of
nursery space and facilities.
Although detailed information exists on the propa-
gation of commercially valuable tree species, very
little is known about potential framework tree species,
which tend to be non-commercial, indigenous forest
tree species with high ecological value but low or
unexplored economic value. For the vast majority of
the huge diversity of forest tree species in Southeast
Asia flowering, fruiting and germination phenology
are not known and propagation techniques have not
yet been developed. Of the 36 potential framework
species reported here, only Bishofia javanica,Dua-
banga grandiflora,Hovenia dulcis and Prunus
cerasoides have been studied previously (Datta and
Sharma, 1989; Frett, 1989; Kamaluddin and Grace,
1993; Kopachon et al., 1996; Hardwick et al., 1997)
and none within the context of producing a ‘crop’of
framework species.
Producing a wide range of framework tree species is
far more complex than mass propagation of a small
number of commercial plantation species. Indigenous
tree species in Thailand produce seeds at different
times throughout the year. However, seeds of tree
species in seasonally dry tropical forests in the neo-
tropics tend to germinate at the beginning of the rainy
season (Garwood, 1983), providing seedlings with
sufficient time to establish a good root system before
onset of drought conditions during the following dry
season. However, it is not clear how germination
phenology and year-round seed dispersal affect the
nursery operation. What may be the optimum strategy
to enable trees to establish themselves naturally may
work against the needs of small-scale tree nursery
managers.
A list of 36 potential framework species from 19
different families was drawn up, based on pilot studies
in the nursery, preliminary field trials over 3 years and
fruiting characteristics. This included pioneers such as
Melia toosendan and climax species such as H. dulcis.
Key families include the Moraceae (four species),
Meliaceae (two species), Leguminosae (two species)
and Fagaceae (six species) (Table 1). The list is
necessarily provisional because long-term field trials
are needed to determine the age at which the listed tree
species first produce wildlife resources and the degree
to which they enhance biodiversity recovery. The
present paper examines seed germination character-
istics of potential framework species when grown as a
crop, focussing on dispersal, germination phenology
and dormancy. It considers how such characteristics
affect the first stage of nursery production, from seed
collection to pricking out seedlings in the nursery. It
also reviews the suitability of the species as frame-
work species based on the essential criterion of seed
germination.
2. Materials and methods
2.1. Study site
Trees were propagated in a nursery at 1000 m
elevation near the headquarters of Doi Suthep-Pui
National Park, north-west of Chiang Mai, northern
Thailand (l88510N latitude and 988540E longitude).
The area experiences a monsoonal climate with
pronounced dry and wet seasons. Average annual
precipitation recorded at nearby weather stations at
similar elevations ranges from 1670 to 2094 mm. The
wet season lasts from May to October and the dry
season from November to April.
All the seed was collected in natural or slightly
disturbed forest ecosystems close to the nursery
between elevations of 700–1600 m. This elevation
range covers all the major forest types in the park,
including the deciduous forest associations of the
lowlands (deciduous dipterocarp oak, bamboo decid-
uous forest and mixed evergreen deciduous forest) and
the evergreen forest of the uplands (Maxwell and
Elliott, in press).
32 D. Blakesley et al. / Forest Ecology and Management 164 (2002) 31–38

2.2. Seed germination
Seeds of the 36 potential framework species were
collected from single parent trees of each species
when fruits were mature and ripe. Fruits were cut from
branches or collected from the ground only if they
were ‘fresh’and undecayed. Following the removal of
the fruit pericarp, seeds were sown within 2–3 days
of collection into modular plastic trays, on to the
surface of a medium of two parts forest soil to one
part coconut husk. For each species, 72 seeds were
divided into three replicate batches of 24 which were
Table 1
Forest types, altitudinal ranges (northern Thailand) and fruit types of potential framework species
Species Family Forest type
a
Altitude range (m) Fruit type
Balakata baccata (Roxb.) Ess. Euphorbiaceae MED/E 400–500 Drupe
Bischofia javanica Bl. Euphorbiaceae BD/MED/E 525–1250 Drupe
Callicarpa arborea Roxb. var. arborea Verbenaceae DDO/BD/MED 375–1250 Berry
Castanopsis calathiformis (Skan) Rehd. and Wils. Fagaceae EP 1050–1500 Nut
Castanopsis tribuloides (Sm.) A. DC. Fagaceae MED/E/EP 900–1685 Nut
Cinnamomum iners Reinw. ex Bl. Lauraceae MED/E 700–1425 Berry
Debregeasia longifolia (Burm. f.) Wedd. Urticaceae MED/EP 525–1685 Achene
Duabanga grandiflora (Roxb. ex DC.) Walp. Sonneratiaceae MED/E 650–1450 Capsule
Eriobotrya bengalensis (Roxb.) Hk. f. forma
multinervata Vidal
Rosaceae E 1000–1650 Drupe
Erythrina stricta Roxb. Leguminosae BD/E/EP 400–1680 Pod
Erythrina subumbrans (Hassk.) Merr. Leguminosae MED/E 500–1680 Pod
Eugenia albiflora Duth. ex Kurz Myrtaceae MED/E/EP 800–1525 Berry
Eurya acuminata DC. var. wallichiana Dyer Theaceae E 1000–1500 Berry
Ficus altissima Bl. Moraceae BD/MED 350–1050 Fig
Ficus racemosa var. racemosa Moraceae MED 350–500 Fig
Ficus semicordata B.-H. ex J.E. Sm. Var. semicordata Moraceae BD/E/EP 350–1550 Fig
Ficus subulata Bl. var. subulata Moraceae MED/E 825–1400 Fig
Gmelina arborea Roxb. Verbenaceae BD/MED/E/EP 350–1475 Drupe
Heynea trijuga Roxb. ex Sims Meliaceae BD/MED/E/EP 550–1680 Capsule
Hovenia dulcis Thunb. Rhamnaceae E 1025–1300 Capsule
Lithocarpus elegans (Bl.) Hatus. ex Soep. Fagaceae B/MED/EP 450–1450 Nut
Lithocarpus garrettianus (Craib) A. Camus Fagaceae B/MED/E 550–1100 Nut
Manglietia garrettii Craib Magnoliaceae E 1050–1600 Aggregate
follicle
Markhamia stipulata (Wall.)
Seem. ex K. Sch. var. kerrii Sprague
Bignoniaceae BD/MED/E/EP 950–1500 Capsule
Melia toosendan Sieb. and Zucc. Meliaceae MED/E 700–1450 Drupe
Michelia baillonii Pierre Magnoliaceae MED/E 650–1100 Aggregate
follicle
Nyssa javanica Polygalaceae MED/E 550–1400 Drupe
Ostodes paniculata Bl. Euphorbiaceae E 1000–1350 Capsule
Phoebe lanceolata (Nees) Nees Lauraceae MED/E/EP 550–1550 Drupe
Planchonell punctata Flet. Sapotaceae DDO/BD/MED/E/EP 350–1525 Berry
Prunus cerasoides D.Don Rosaceae MED/E/EP 1050–1685 Drupe
Quercus semiserrata Roxb. Fagaceae MED/E/EP 800–1675 Nut
Quercus vestita Rehd. and Wils. Fagaceae E/EP 1200–1600 Nut
Rhus rhetsoides Craib Anacardiaceae MED/E/EP 650–1550 Drupe
Sapindus rarak DC. Sapindaceae MED/E 625–1620 Drupe
Spondias axillaris Roxb. Anacardiaceae MED/E/EP 700–1600 Drupe
a
BD: bamboo and deciduous; DDO: deciduous dipterocarp oak; MED: mixed evergreen and deciduous; E: evergreen; EP: evergreen and
pine (sensu Maxwell and Elliott, in press).
D. Blakesley et al. / Forest Ecology and Management 164 (2002) 31–38 33

randomly assigned to different benches and watered
daily. Each replicate consisted of 24 adjacent compar-
tments ð3:5cm3:0cm7:0cmÞin one-seed tray.
Seed trays were placed on the top of concrete benches,
partially shaded under a transparent plastic roof
(approximately 40% full sunlight, similar to the light
intensity in partially regenerating gaps). Once the first
pair of leaves had fully expanded, seedlings were
Table 2
Seed germination data of potential framework tree species, suitable for forest restoration plantings in northern Thailand
Species Seed collection
month
Mean germination
percentage
a
(S.D.)
MLD (days)
b
Time over which
seeds germinated
(days)
b
Germination and
synchrony
categories
c
Balakata baccata (Roxb.) Ess. December 25 (6.3) 67 112 IG/AS
Bischofia javanica Bl. November 43 (14.6) 85 154 SG/AS
Callicarpa arborea Roxb. var. arborea August 67 (21.7) 86 63 SG/IS
Castanopsis calathiformis (Skan)
Rehd. and Wils.
June 61 (19.2) 16 42 RG/IS
Castanopsis tribuloides (Sm.) A. DC. September 83 (8.3) 31 42 IG/IS
Cinnamomum iners Reinw. ex Bl. April 75 (8.3) 17 63 RG/IS
Debregeasia longifolia (Burm. f.) Wedd. March 100 (0) 15 14 RG/S
Duabanga grandiflora (Roxb. ex DC.) Walp. April 86 (2.9) 31 42 IG/IS
Eriobotrya bengalensis (Roxb.)
Hk. f. forma multinervata Vidal
September 79 (3.6) 16 203 RG/AS
Erythrina stricta Roxb. May 67 (33.3) 10 7 RG/S
Erythrina subumbrans (Hassk.) Merr. April 39 (2.4) 7 7 RG/S
Eugenia albiflora Duth. ex Kurz May 71 (12.5) 24 147 IG/AS
Eurya acuminata DC. var. wallichiana Dyer March 69 (6.4) 60 126 IG/AS
Ficus altissima Bl. March 97 (2.4) 34 105 IG/AS
Ficus racemosa var. racemosa February 92 (4.2) 27 70 IG/IS
Ficus semicordata B.-H. ex J.E.
Sm. var. semicordata
March 92 (5.0) 52 41 IG/IS
Ficus subulata Bl. var. subulata January 71 (8.3) 60 175 IG/AS
Gmelina arborea Roxb. March 83 (18.2) 25 14 IG/S
Heynea trijuga Roxb. ex Sims November 83 (14.4) 96 203 SG/AS
Hovenia dulcis Thunb. August 71 (15.0) 97 154 SG/AS
Lithocarpus elegans (Bl.) Hatus. ex Soep. September 69 (9.6) 143 231 SG/AS
Lithocarpus garrettianus (Craib) A. Camus September 56 (37.3) 219 322 SG/AS
Manglietia garrettii Craib October 74 (4.8) 81 140 IG/AS
Markhamia stipulata (Wall.) Seem. ex K.
Sch. var. kerrii Sprague
March 56 (2.1) 13 15 RG/.S
Melia toosendan Sieb. and Zucc. April 67 (15.0) 15 70 RG/IS
Michelia baillonii Pierre June 31 (6.9) 101 63 SG/IS
Nyssa javanica July 67 (19.1) 39 70 IG/IS
Ostodes paniculata Bl. November 53 (16.8) 124 203 SG/AS
Phoebe lanceolata (Nees) Nees April 79 (4.2) 44 56 IG/IS
Planchonella punctata Flet. June 89 (1.7) 17 35 RG/IS
Prunus cerasoides D.Don March 74 (4.8) 52 63 IG/IS
Quercus semiserrata Roxb. June 92 (7.2) 18 35 RG/IS
Quercus vestita Rehd. and Wils. September 74 (13.4) 14 21 RG/S
Rhus rhetsoides Craib December 50 (50.0) 24 28 IG/IS
Sapindus rarak DC. January 83 (8.3) 45 98 IG/AS
Spondias axillaris Roxb. March 43 (4.8) 11 21 RG/S
a
Three replicates.
b
Pooled replicates.
c
RG: rapid germination; IG: intermediate germination; SG: slow germination; S: synchronous; IS: intermediate synchrony; AS:
asynchronous.
34 D. Blakesley et al. / Forest Ecology and Management 164 (2002) 31–38

pricked out and transplanted into individual contain-
ers. Germination was monitored throughout the ger-
mination period and was defined as emergence of
any part of the shoot. The dates of the first and last
seeds to germinate were recorded, and the median
length of dormancy (MLD) calculated (pooling
individuals of each species from the three replicate
batches) from the germination times of all seeds which
germinated.
3. Results
Germination percentage, one of the key selection
criteria for framework species, ranged from 25 to
100% (Table 2). However, 80% of species had a
germination percentage of 60% or greater, which is
more acceptable for this type of nursery operation.
Only three species had low germination percentages:
Balakata baccata (25%); Michelia baillonii (31%);
Erythrina subumbrans (39%). However, these species
still qualify as potential framework species due to
other attributes, such as high growth rate in containers
or good field performance (unpublished data).
The MLD ranged from 7 to 219 days. For the
purposes of nursery production, germination was
defined as rapid if the MLD was 21 days or less,
and slow if the MLD was 84 days or more. Twelve
species could be classified as having rapid germina-
tion: Castanopsis calathiformis;Cinnamomum iners;
Debregeasia longifolia;Eriobotrya bengalensis;Ery-
thrina stricta;Erythrina subumbrans;Markhamia
stipulata;Melia toosendan;Planchonella punctata;
Quercus semiserrata;Quercus vestita;Spondias
axillaris. In contrast, Bischofia javanica,Callicarpa
arborea,Heynea trijuga,Hovenia dulcis,Lithocarpus
elegans,Lithocarpus garrettianus,Michelia baillonii
and Ostodes paniculata were categorised as having
slow germination. The remaining 16 species had
MLD’s of between 3 and 12 weeks and could be
regarded as having intermediate germination rates.
Considering the framework species as a whole,
most species (28 or 78%) fell into the categories of
rapid or intermediate germination. Of the 21 species
collected in the late dry and early wet season, only one
species, Michelia baillonii germinated slowly (Fig. 1).
In contrast, of the 15 species collected in the late wet
and early dry season, seven species germinated slowly
(19% of the total); the remaining eight were inter-
mediate or rapid. This seasonal variation resulted in a
peak in nursery germination in the first-half of the year,
when the median seeds of 72% of species germinated
(Fig. 2). This coincided with the end of the latter part of
the dry season and the early part of the wet season.
Fig. 1. The relationship between the MLD and the month of seed collection of species collected in Doi Suthep-Pui National Park (700–
1600 m asl). Each point represents an individual species.
D. Blakesley et al. / Forest Ecology and Management 164 (2002) 31–38 35

Seedling emergence ranged over 7 days for both
Erythrina spp. to 322 days for L. garrettianus. For tree
production in the nursery, germination was defined as
synchronous if all seedlings of a given species
emerged within 21 days, and highly asynchronous if
this occurred over a period of more than 84 days.
Seven species germinated synchronously, six of which
also had an MLD of less than 21 days (Table 2):
Debregeasia longifolia;Erythrina stricta;Erythrina
subumbrans;Markhamia stipulata;Quercus vestita;
Spondius axillaris. The other species which germi-
nated synchronously, Gmelina arborea, also germi-
nated relatively rapidly, with an MLD of 25 days.
Species exhibiting highly asynchronous germination
were distributed across intermediate- and slow-
germinating species. Of the latter group of species,
none germinated synchronously; 63 days was the
shortest time of seedling emergence, and the mean
emergence time for the eight species was 164 days.
4. Discussion
Few phenological studies have been reported with
the framework species described in this paper. The most
studied has been Hovenia dulcis, with several reports on
seed germination (Frett, 1988, 1989; Kopachon et al.,
1996) and the successful micropropagation of axillary
buds from mature trees (Echeverrigaray et al., 1998).
Hardwick et al. (1997) studied germination and
emergence of Prunus cerasoides collected on Doi
Suthep, and also found that it fruited late in the dry
season with a high germination percentage. Bischofia
javanica has previously been propagated from seed,
and grown in controlled environments to stimulate
different forest canopies (Kamaluddin and Grace,
1993). This study showed that B. javanica has a wide
acclimation potential to the changing light levels, which
may occur in gaps. There is a report of soft rot on
seedlings of Duabanga grandiflora (Datta and Sharma,
1989). Although there are a number of other publi-
cations relating to related taxa within the families
reported here, particularly in America and the neo-
tropics, no other relevant work has been published
on the potential framework species described in this
paper.
Because of the rainfall patterns in a seasonally dry
tropical forest, the ideal time to plant out container-
grown tree seedlings is at the start of the wet season. It
is a considerable challenge to produce a crop of
seedlings, of a plantable size, of 36 framework tree
species, all to be dispatched at the same time of year
when seeds are available at different months through-
out the year and they exhibit widely different rates of
germination and growth in the nursery. The present
study has shown that nursery production of such a
‘collection’of native species, about which very little is
known, presents considerable logistical problems for
Fig. 2. Number of species located in Doi Suthep-Pui National Park (700–1600 m asl), whose median seed emergence falls in each month.
36 D. Blakesley et al. / Forest Ecology and Management 164 (2002) 31–38

the nursery manager, even to get the seedlings to the
point of pricking out into containers. The first of these
is that to propagate 36 framework species, at least one
collection trip would be required in every month of the
year and probably more in March, April and
September when 18 species (50% of the framework
species) are available for collection. Furthermore,
these species exhibit considerable variation in dor-
mancy and germination synchrony. It can be clearly
seen from the scatter plot of MLD (Fig. 1) that species
with seeds dispersed in the late dry/early wet season
tend to germinate quickly in the nursery, whereas
those with species dispersed towards the end of the wet
season and into the dry season, are likely to have a
much longer dormancy period. Seven of the frame-
work species appear to be ideal for nursery production,
because they are collected at one time of the year in the
late dry/early wet season (with the exception of
Quercus vesita) and germinate rapidly and synchro-
nously. These species, therefore, require minimum
time in the germination facility where they are
particularly susceptible to pests and diseases. The
other species collected at this time (with the exception
of Michelia baillonii) have intermediate germination,
and vary in the synchronicity of germination, and
include species such as Eurya acuminata and Ficus
subulata which are highly asynchronous. Another
predictable group of species, in terms of nursery
planning, are those dispersed in the late wet/early dry
season which germinate slowly and also asynchro-
nously.
Whilst it is beyond the scope of this paper to
consider the manipulation of growth and development
of framework species in containers, it is clear from the
above discussion that seedlings will be ready for
pricking out throughout the year. Further work is now
underway to assess the second stage of nursery
production of these species, from pricking out through
to weaning and dispatch.
Acknowledgements
FORRU was funded with financial support from
Riche Monde (Bangkok) Ltd. and United Distillers
PLC. Shell Forestry Limited, the Biodiversity
Research and Training Programme and the Science
Faculty of Chiang Mai University sponsored the
research described in this paper. Other donors have
included The Fagus Anstruther Memorial Trust, The
Peter Nathan Trust, The Robert Kiln Charitable Trust,
The Barbara Everard Trust for Orchid Conservation,
Mr. Alan and Mrs. Thelma Kindred, Mr. Nostha
Chartikavanij, Mr. R. Butterworth and Mr. James C.
Boudreau. The authors thank J.F. Maxwell for iden-
tifying the tree species named in this paper. Voucher
specimens are stored at the Chiang Mai University
Herbarium, Biology Department. The authors are
grateful to all research assistants and volunteers who
assisted with data collection and processing and care
of the plants in the nursery including: Jumpee
Bunyadit, Thonglaw Seethong, Tim Rayden, Kevin
Woods, Rungtiwa Bunyayod and Janice Kerby. The
Head and staff of Doi Suthep-Pui National Park
Headquarters provide essential collaboration for
FORRU’s research. We are especially grateful to
the Head of the National Park, Mr. Paiboon Sawet-
melanon, Mr. Amporn Panmongkol (Deputy Head)
and Mr. Prasert Saentaam.
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