S HO R T CO MM UN IC AT IO N
Forest regeneration under Tectona grandis
and Terminalia amazonia plantation stands managed
for biodiversity conservation in western Panama
Brett T. Wolfe • Daisy H. Dent • Jose´ Deago • Mark H. Wishnie
Received: 24 October 2013 / Accepted: 7 August 2014 / Published online: 20 August 2014
 Springer Science+Business Media Dordrecht 2014
Abstract Plantations of Tectona grandis in Central America are widely perceived to
suppress forest regeneration in their understories, yet few studies have tested this
assumption. We surveyed the understory woody vegetation growing in 7-year-old stands of
T. grandis and the native tree species Terminalia amazonia in a plantation in western
Panama that was managed with both commercial timber and biodiversity conservation
objectives. We predicted that if T. grandis suppressed forest regeneration then the un-
derstories of T. grandis stands would have a lower density of woody stems, smaller stems,
and fewer species than stands of T. amazonia. None of our predictions were supported.
Densities of woody stems were 0.56 ± 0.21 m-2 (mean ± SE) and 0.64 ± 0.10 m-2 in T.
grandis and T. amazonia understories, respectively. Stem height structure was similar
under both species, where stems\1 m height dominated. Understory species richness did
not differ between the two species; in total, 27 and 30 woody species were sampled in T.
grandis and T. amazonia stands, respectively. However, understory species composition
differed between the two crop species. Overall, our results are inconsistent with the idea
that T. grandis plantations suppress forest regeneration and suggest that the lack of woody
vegetation in other T. grandis plantation understories may be attributable to management
actions, such as understory thinning, rather than species effects of T. grandis. Further
B. T. Wolfe (&)  D. H. Dent  J. Deago  M. H. Wishnie
Native Species Reforestation Project (PRORENA), Center for Tropical Forest Science, Smithsonian
Tropical Research Institute, 401 Roosevelt Ave, Balboa, Ancon, Panama, Republic of Panama
e-mail: btwolfe@gmail.com
Present Address:
B. T. Wolfe
Department of Biology, University of Utah, Salt Lake City, UT 84112, USA
D. H. Dent
Biological and Environmental Sciences, University of Stirling, Stirling FK9 4LA, UK
M. H. Wishnie
Seaview Natural Resource Consulting, LLC, Seattle, WA 98107, USA
123
New Forests (2015) 46:157–165
DOI 10.1007/s11056-014-9448-2
research is needed to compare T. grandis and native species for their effects on forest
regeneration.
Keywords Diversity  Native species  Reforestation  Restoration
Introduction
Reforesting degraded lands in the tropics, such as abandoned cattle pastures, has the
potential to restore ecosystem services and biodiversity (Martinez-Garza and Howe 2003;
Ciccarese et al. 2012). Tree plantations are often promoted as a means of encouraging
forest regeneration on degraded lands because they stabilize soils and accelerate the
development of diverse communities, including plants, birds, and insects (Lugo 1992;
Yirdaw 2001; Hartley 2002). Tree plantations tie economic incentives to ecological
rehabilitation, providing a practical option for large-scale reforestation in developing
countries that occupy most tropical areas (Lamb 1998). When ecological rehabilitation
goals are incorporated into tree plantations, it is important to understand how decisions
such as species selection affect forest regeneration in plantation understories.
On highly degraded lands, barriers to recolonization by native forest species, such as a
lack of seed arrival, grass invasion, and topsoil loss, inhibit secondary forest regeneration
(Lamb et al. 2005). Studies throughout the tropics have found that tree plantations can
serve as ‘catalysts’ for secondary regeneration in these areas, whereby they increase the
stem density and species richness of understory plant communities compared to areas
without planted trees (Parrotta et al. 1997; Lamb et al. 2005). The mechanisms responsible
for these increases are thought to be trees’ ability to attract seed-dispersers (Wunderle
1997), suppress grasses through shading (Kuusipalo et al. 1995; Jones et al. 2004), and
improve soil conditions through litter inputs (Parrotta 1992). However, tree species vary
greatly in their effects on understory regeneration (Powers et al. 1997; Slocum and Horvitz
2000). For example, among four crop tree species in experimental trials in Costa Rica, the
density and species richness of understory woody stems ranged 0.15–0.79 stems m-2 and
0.10–0.26 species m-2, respectively, 6 years after plantation establishment (Carnevale and
Montagnini 2002).
Throughout Central America, Tectona grandis L.f. (teak)—a species native to Southeast
Asia—is commonly used in commercial plantations. For example, in 2008 it accounted for
63.7 % of the plantation area in Panama (ANAM 2009). T. grandis is widely perceived to
inhibit understory forest regeneration and cause soil erosion, yet there is remarkably little
evidence that its effects are different from those of native species (Pandey and Brown
2000; Healey and Gara 2003; Evans and Turnbull 2004; Leopold and Salazar 2008). We
used a timber plantation in western Panama that was planted in a mosaic of monocultures
of various tree species to compare the understory vegetation in stands of T. grandis and the
native species Terminalia amazonia (J.F. Gmel.) Exell. (Hereafter, the two focal crop
species are referred to by genus name.) Experimental and commercial plantations of
Terminalia have been shown to encourage recruitment of seedlings in the understory
compared to unplanted areas (Cusack and Montagnini 2004; Butler et al. 2008). We
predicted that if Tectona inhibits understory regeneration, then the understory in stands of
Tectona would have lower density of woody stems, stems with smaller stature, and lower
species richness compared to stands of Terminalia.
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Methods
Study site
This study was conducted in Las Lajas, Panama (81530W, 8150N), located within the wet
tropical zone, with mean annual rainfall of 4,600 mm and a three-month dry season
between January and April (van Breugel et al. 2011). The study site is 50 m above sea level
and 8 km from the Pacific coast. Underlying soils are loamy clay and cattle pasture is the
dominant land-use in the region. Data were collected on the Los Rios plantation owned by
Futuro Forestal SA. Native forest was cleared in the 1920s for use as cattle pasture, which
was abandoned in the 1990s and left fallow and relatively undisturbed until 1998–1999
when the naturally regenerating vegetation (except large trees of select species) was
cleared by hand and tractor and the plantation was established.
The plantation was composed of 7-year-old monocultures of Tectona, Terminalia, and
four other native tree species interspersed in a 68.9 ha area (Fig. 1). Plantation manage-
ment embraced many of the biodiversity-enhancing actions proposed by Lamb (1998), e.g.
wide bands near an intersecting river were left uncleared and unplanted to allow natural
forest regeneration. Within the monoculture plantation stands, Tectona was planted at
3 m 9 3 m spacing while Terminalia was planted at 5 m 9 5 m spacing. Understory
vegetation was cut with machetes for 2 years following planting. In the Tectona stands,
vegetation was subsequently uncut except for vines that wrapped around crop trees. In the
Terminalia stands, rows ca. 2.5 m wide were regularly cut with machetes in the vegetation
around crop trees. Spaces between rows were left uncut except for branches that entered
cut rows. The most recent of these cuts was made 6 weeks prior to sampling. Organic
‘‘bokatchi’’ fertilizer (a mix of fermented chicken manure, calcium, rice pellets, sawdust,
ashes, and other ingredients) was applied to a\1 m diameter circle around each crop tree
twice annually for three to 4 years following planting. Crop trees of both species were
thinned one to 3 months prior to sampling.
Sampling design and analysis
In stands of each of the focal crop species, understory vegetation was sampled within eight
randomly located 10 m 9 10 m plots (Fig. 1). In October–November 2005, all free-
standing woody plants with height[15 cm were measured for height and identified in the
field or collected for later identification at the herbarium of the Smithsonian Tropical
Research Institute, Panama City, Panama. Diameter at breast height (DBH, 130 cm height)
was measured for individuals with DBH [ 1 cm. For analyses of understory vegetation we
excluded stems [ 10 cm DBH, which were likely present when the plantations were
established and therefore not subject to the influence of crop species during recruitment.
Previous studies have effectively detected differences in understory plant communities
among crop tree species with similar or smaller sapling areas (e.g. Powers et al. 1997;
Carnevale and Montagnini 2002; Jones et al. 2004). A 20 m 9 20 m plot was centered on
each understory-sampling plot in which crop trees were measured for DBH with a diameter
tape and height with a clinometer. These data were then used to calculate the crop-tree
stem density, basal area, mean height, and mean DBH in each stand.
To test whether stem density of understory plants varied between stands of Tectona and
Terminalia, we used Student’s t test with Welch’s correction for unequal variance. We
tested whether understory stem height structure varied between stands of the two crop
species by grouping stems into height classes (15–99, 100–200, [200 cm) and assessing
New Forests (2015) 46:157–165 159
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the density of stems of each height class within each plot. ANOVA was used to test for
differences in stem density among plots with crop species, height class within plot, and
their interaction as fixed effects. For this analysis, stem density was log transformed to
obtain homoscedasticity.
To examine the effect of crop species on understory species richness we constructed
species-accumulation curves using individual-based rarefaction in EstimateS version 9
(Colwell 2013). We used the criteria of overlapping 95 % confidence intervals to deter-
mine whether the accumulation curves differed between crop species. To assess whether
understory plant communities differed between crop species, we used non-metric multi-
dimensional scaling (NMDS) to graphically represent variation in species composition
among plots. For this analysis we used the metaMDS function in the R package vegan
(Oksanen et al. 2013), which calculated the Bray-Curtis distance between each pairwise
plot combination using a Wisconsin transformation of the square root of species abun-
dances. To test whether the understory communities differed between crop species, we
used a permutational multivariate analysis of variance (PERMANOVA) with the adonis
function in vegan (Oksanen et al. 2013). For this analysis, the Bray-Curtis distance
between plots was used as the response variable.
Results
A total of 950 woody plants of 39 species and 24 families were sampled in the plantation
understory (woody plants\10 cm DBH; Table 1). Woody plant density was similar in the
understories of Tectona and Terminalia stands; 0.56 ± 0.21 m-2 (mean ± SE) and
0.64 ± 0.10 m-2, respectively (t = 0.46, df = 9.95, P = 0.66). The height structure of
understory vegetation was also similar between the crop species (Fig. 2). Stems\100 cm
tall were dominant under both crop species (F = 51.7; df = 2, 28; P \ 0.001) while stem
Fig. 1 Map of the study area with inset showing the location of the study site, Las Lajas, Panama. Stars
indicate the locations of sample plots in stands of Tectona and Terminalia
160 New Forests (2015) 46:157–165
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Table 1 Number of plants of each species sampled in stands of Tectona grandis and Terminalia amazonia
Family Species Crop species
Tectona Terminalia
Melastomataceae Melastomataceae sp5 185 35
Annonaceae Xylopia frutescens Aubl. 73 9
Melastomataceae Miconia argentea (Sw.) DC. 56 51
Flacourtiaceae Casearia arguta Kunth 28 83
Rubiaceae Genipa americana L. 24 6
Dilliniaceae Curatella americana L. 8 6
Tiliaceae Tiliaceae sp1 8 4
Flacourtiaceae Casearia commersoniana Cambess. 6 4
Anacardiaceae Mangifera indica L. * 6 0
Piperaceae Piper hirtellipetiolum C. DC. 6 67
Siparunaceae Siparuna guianensis Aubl. 6 17
Malpighiaceae Byrsonima crassifolia (L.) Kunth 5 8
Rutaceae Zanthoxylum setulosum P. Wilson 5 12
Sterculiaceae Guazuma ulmifolia Lam. 3 1
Cecropiaceae Cecropia peltata L. 2 4
Melastomataceae Melastomataceae sp1 2 1
Annonaceae Xylopia aromatica (Lam.) Mart. 2 106
Fabaceace Pseudosamanea guachapele (Kunth) Harms 1 0
Boraginaceae Cordia alliodora (Ruiz & Pav.) Oken 1 33
Fabaceae Diphysa americana (Mill.) M. Sousa 1 2
Myrtaceae Eugenia sp1 1 0
Fabaceace Fabaceae sp1 1 0
Rubiaceae Psychrotria sp1 1 0
Araliaceae Schefflera morototoni (Aubl.) Maguire, Stey. & Frod. 1 1
Simaruaceae Simaba cedron Planch. 1 0
Anacardiaceae Spondias mombin L. 1 0
Lamiaceae Tectona grandis L.f. * 1 0
Clusiaceae Vismia baccifera (L.) Tr. & Pl. 1 21
Anacardiaceae Anacardium excelsum (Bert. & Balb. ex Kunth) Skeels 0 5
Meliaceae Cedrela odorata L. 0 1
Coccolospermaceae Cochlospermum vitifolium (Willd.) Spr. 0 4
Tiliaceae Luehea seemannii Triana & Planch. 0 9
Melastomataceae Melastomataceae sp2 0 11
Melastomataceae Melastomataceae sp3 0 1
Melastomataceae Melastomataceae sp4 0 2
Lauraceae Nectandra sp1 0 1
Annonaceae Oxandra sp1 0 1
Apocynaceae Stemmadenia sp1 0 2
Combretaceae Terminalia amazonia (J.F. Gmel.) Exell 0 6
Species that were identified only to the level of family or genus are listed with codes consisting of the family
name or genus name, respectively, followed by a morphospecies number. Asterisks indicate species that are
not native to Panama
New Forests (2015) 46:157–165 161
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density did not vary between crop species in any height class (P [ 0.42). However, the
structure of crop trees did vary between the two species; Tectona trees were larger and
more closely spaced than Terminalia trees (Table 2).
The total number of species sampled was similar in the Tectona and Terminalia stands,
27 and 30 species, respectively. Species accumulation curves indicated no significant
difference between the two crop species in their understory species richness, the 95 %
confidence intervals overlapped throughout the curves (Fig. 3).
The composition of the understory plant communities varied between the two crop
species. NMDS showed a trend for clustering within crop species, especially along axis 2
(Fig. 4). PERMANOVA analysis confirmed this visual trend; there was a significant effect
of crop species on understory species composition (F = 2.06; df = 1, 15; P = 0.023).
Twenty species were shared between stands of the two crop species, while eight species
were restricted to Tectona stands and 11 were restricted to Terminalia stands. The most
abundant species sampled in the Tectona and Terminalia stands were Mestomataceae sp5
(42 % of sampled plants) and Xylopia frutescens (22 % of sampled plants), respectively
(Table 1). All species sampled in the Terminalia stands were native to Panama while two
species in the Tectona stands were not native to Panama: one Tectona seedling and six
Mangifera indica (mango) seedlings (Table 1).
Discussion
In a timber plantation managed with biodiversity conservation objectives, the understories
of Tectona and Terminalia stands developed similar woody stem density, height structure,
and species richness (Figs. 2 and 3). Since Terminalia has been shown to foster forest
regeneration compared to unplanted abandoned pastureland (Cusack and Montagnini 2004;
Butler et al. 2008), our results are inconsistent with the common assumption that Tectona
suppresses forest regeneration in its understory. Both crop species developed stem densities
Terminalia Tectona Terminalia Tectona Terminalia Tectona
< 100 cm 100−200 cm > 200 cm
Stem height class
0.0
0.2
0.4
0.6
0.8
1.0
1.2
St
em
 d
en
sit
y 
(st
em
s 
m
−
2 )
Fig. 2 Stem density of woody understory vegetation, stratified by size class, in stands of Terminalia and
Tectona. Each circle represents one plot. Boxes enclose the 25th and 75th quartiles and are bisected by the
medians. Bars extend to the 5th and 95th quartiles
162 New Forests (2015) 46:157–165
123
within the range of similarly aged (7 years-old) experimental plantations of native tree
species in Costa Rica (0.01–25.86 m-2; Powers et al. 1997).
The species composition of understory woody stems differed between Tectona and
Terminalia stands (Fig. 4), which is a common result among experimental trials that have
measured understory plant communities below various crop tree species (Montagnini
2011). At the time of sampling (7 years after plantation establishment) Tectona crop trees
were larger and more closely spaced than Terminalia trees (Table 2). Such features of
overstory structure have been shown to influence patterns of understory regeneration
(Jones et al. 2004), yet we are unable to distinguish what factors led to the divergence in
understory composition between our crop species. Moreover, on a nearby plantation,
Terminalia stands obtained higher basal area than Tectona stands after 20 years (Griess
and Knoke 2011). Therefore, if overstory structure did affect the plant communities that we
measured, then differences between Terminalia and Tectona stands are likely to change as
the stands mature.
Healey and Gara (2003) found that a 10-year-old Tectona plantation in Costa Rica had
lower densities of woody stems and species than a nearby 12-year-old abandoned pasture.
The authors concluded that Tectona suppressed forest regeneration. However, it is likely
that the manual thinning of recruits under Tectona, rather than Tectona per se, suppressed
regeneration. The plantation studied by Healey and Gara (2003) cleared recruiting
understory vegetation for the first 5 years of plantation establishment, creating a seven-
year head start for recruitment in the abandoned pasture, which likely contributed to the
higher stem density there. Similarly, Leopold and Salazar (2008) found that understory
stem density and species richness were lower on a commercial Tectona plantation than on
nearby seven-to-eight-year-old mixed-species restoration plantation sites in Costa Rica; yet
they did not report management practices for the plantations, which likely differed greatly
considering the divergent goals of commercial and restoration plantations. We know of no
other studies that have quantified understory recruitment on Tectona plantations in the
Neotropics.
Understory thinning is a common practice in Tectona plantations (Pandey and Brown
2000) and has been implicated as causing high erosion rates (Bell 1973), leading to the
perception that Tectona suppresses understory recruitment. In our study, management
actions differed slightly between the Tectona and Terminalia stands, consistent with the
particular silvicultural recommendations for the crop species. Tectona was planted at closer
spacing than Terminalia and its understory was not cut after the initial 2 years while rows
were regularly cut in the understory of Terminalia. Since shading grass-dominated areas
increases the rates of germination, survival, and growth of tree seedlings (Hooper et al.
2002), the management actions in Tectona stands likely favored forest regeneration more
than the management actions in Terminalia stands, as they would reduce the time to
canopy closure and increase the uncut area available for plants to grow[15 cm height. We
Table 2 Crop tree characteristics
Crop
species
Stem density (ha-1) DBH (cm) Tree height (m) Basal area (m2 ha-1)
Tectona 600 ± 35 15.4 ± 0.6 15.8 ± 0.8 11.2 ± 0.9
Terminalia 409 ± 31 13.2 ± 0.6 13.9 ± 0.4 5.9 ± 0.5
T test
results
t = 4.1, df = 13.9,
P = 0.001
t = -2.4, df = 14,
P = 0.03
t = -2.2, df = 11.2,
P = 0.05
t = 5.2, df = 11.6,
P = 0.0002
Values are stand-level mean ± SE
New Forests (2015) 46:157–165 163
123
conclude that understory recruitment was similar under Tectona and Terminalia stands
within a plantation that was managed for both biodiversity conservation and timber pro-
duction, when subjected to the species’ particular silvicultural practices. However, in order
to better understand how Tectona and native tree species affect understory vegetation more
rigorous experiments are needed.
Acknowledgments We thank Iliana Armie´n and Andreas Eke for facilitating research at the Futuro
Forestal plantations, Emilio Mariscal for training, Carolina Sarmiento for help in making Fig. 1, and two
anonymous reviewers for helpful comments on the manuscript. This research was undertaken as part of
PRORENA, a collaborative native species reforestation research project between the School of Forestry and
Environmental Studies of Yale University and the Center for Tropical Forest Science at the Smithsonian
Tropical Research Institute. Financial support for PRORENA has been provided by the Frank Levinson
Donor-Advised Fund at the Peninsula Community Foundation, the Levinson Family Foundation, and the
Grantham Family Foundation.
0 100 200 300 400 500
0
10
20
30
Number of individuals
N
um
be
r o
f s
pe
cie
s
Fig. 3 Rarefaction-based species accumulation curves for woody understory vegetation in stands of
Terminalia (filled circles) and Tectona (open circles). Bars represent the 95 % confidence intervals
−0.8 −0.4 0 0.4 0.8
−0.8
−0.4
0
0.4
0.8
NMDS Axis 1
N
M
D
S 
Ax
is 
2
Fig. 4 Non-metric
multidimensional scaling
(NMDS) plot of understory
woody vegetation in stands of
Terminalia (filled circles) and
Tectona (open circles)
164 New Forests (2015) 46:157–165
123
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