117
Pollen limitation failing reproductive 
success in selected animal pollinated 
trees of tropical moist deciduous forest 
of north-eastern hill region, India
Abstract
The aim of this study was to estimate reproductive effort and success in tropical 
trees and to examine the effect of pollen limitation on reproductive success. Pollen 
limitation was assessed through pollen supplementation experiment to contrast the 
open pollination treatment. The taxa selected were Bombax ceiba, Erythrina stricta 
(ornithophilous trees), Lagerstroemia speciosa, Mesua ferrea and Schima wallichii 
(entomophilous trees). Index of pollen limitation was highest in Bombax ceiba 
and Erythrina stricta (both self-incompatible species). The remaining three species 
were partially self-incompatible with favouring selfing in Lagerstroemia speciosa 
and Mesua ferrea and supporting outcrossing in Schima wallichii. Therefore, the 
high index of pollen limitation in Bombax ceiba and Erythrina stricta might be due 
to the effect of either lacking quality pollen or lacking bird pollinators. All five 
species produce a large amount of pollen at individual tree level in the order of 
108 (Erythrina stricta) to 1010 (Mesua ferrea). Fruit and seed set following pollen 
supplementation were higher than the open pollination (as control) in all studied 
species. Pollen limitation in this study is likely associated with the effectiveness 
of pollinator and their frequency, as all the studied species had produced ample 
pollen at tree crown level which ultimately leads to pollinator resource limitation 
in tropical trees.
Izvleček
V raziskavi smo ocenili razmnoževalni napor (proizvodnja peloda) in uspeh trop-
skih dreves in preučili vpliv omejitve peloda na razmnoževalni uspeh. Omejitev 
peloda smo ugotavljali z odprto oprašitvijo, ki smo jo primerjali s poskusom doda-
tnega opraševanja. Izbrali smo vrste Bombax ceiba, Erythrina stricta (ornitofilna dre-
vesa), Lagerstroemia speciosa, Mesua ferrea in Schima wallichii (entomofilna drevesa). 
Indeks omejitve peloda je bil najvišji pri vrstah Bombax ceiba in Erythrina stricta 
(obe vrsti sta samoneoplodni). Preostale tri vrste so bile delno samoneoplodne; 
večjo naklonjenost samooploditvi imata vrsti Lagerstroemia speciosa in Mesua ferrea, 
medtem ko je pri vrsti Schima wallichii spodbujana navzkrižna oploditev. Do vi-
sokega indeksa pelodne omejitve pri vrstah Bombax ceiba in Erythrina stricta lahko 
pride zaradi pomanjkanja kvalitetnega peloda ali odsotnosti opraševalcev. Vseh pet 
vrst proizvaja velike količine peloda na posameznem drevesu, od 108 (Erythrina 
stricta) do 1010 (Mesua ferrea). Količina plodov in semen, ki so posledica dodatne-
ga peloda, je bila večja kot pri odprti oprašitvi (kontroli) pri vseh vrstah. Pelodna 
omejitev je bila rezultat omejene količine in kvalitete peloda. Ker so vse preučevane 
vrste proizvedle dovolj peloda v krošnjah, je verjetno razlog za pelodno omejitev pri 
tropskih drevesih povezana z uspešnostjo opraševalcev in njihovo pogostostjo.
Key words: pollination, pollen 
limitation, pollen quantity, bird 
pollination, pollination success.
Ključne besede: opraševanje, 
pelodna omejitev, količina peloda, 
opraševanje s ptiči, uspeh oprašitve.
Corresponding author:
Vinod Prasad Khanduri
E-mails: khandurivp@yahoo.com
Received: 10. 10. 2020
Accepted: 23. 9. 2022
1 Department of Forestry, College of Forestry, VCSG Uttarakhand University of Horticulture and Forestry, Ranichauri, Tehri Garhwal, Uttarakhand, India
Vinod Prasad Khanduri1 
DOI: 10.2478/hacq-2022-0014 22/1 
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Introduction
Tropical plants have remarkably varied sexual systems, 
breeding systems, flower morphology, and phenology 
(Bawa, 1990). Plant reproductive system forms ecosys -
tem vitality through regeneration, speciation and ecolo-
gy of organisms (Ollerton et al., 2011; Lever et al., 2014). 
Mating system (selfed, mixed and outcrossed) has been 
recognized as a best tool to decipher genetic diversity 
or population genomics of plants (Glemin et al., 2006; 
Wright et al., 2008; Jadwiszczak, 2017). The population 
genetic structure of a species is influenced by self-com-
patibility, self-incompatibility and inbreeding depression 
(Charlesworth & Charlesworth, 1987; Holsinger, 2000; 
Duminil et al., 2007; Portillo Lemus et al., 2022). How -
ever, inbreeding depression is the key factor that control 
evolution of plant breeding system (Hufford & Hamrick 
2003; Devaux et al., 2019). Such studies on long lived 
tree species are lacking (Ferriol et al., 2011; Rodger & 
Johnson, 2013, Cristóbal-Pérez, 2020; Ahlinder et al., 
2021; Khanduri et al., 2022). Tree flowering, pollination 
and reproductive systems have been recognized as im-
portant parts of tree improvement, breeding and man-
agement of silvicultural practices (Nikanishi et al., 2015; 
Khanduri & Sukumaran, 2019). 
The complete development of floral characters along 
with the rate of pollen production in tree species is help-
ful in understanding the detailed pollination mecha-
nism and barriers in pollination biology (Etcheverry 
et al., 2008; Khanduri et al., 2019). Furthermore, the 
quantity of pollen production is important to (i) deter-
mine the amount of genes a population can spread (Liu 
et al., 2015), (ii) establish an airborne pollen forecasting 
(Voukantsis et al., 2010; Csépe, 2020), (iii) assess the 
relative density of atmospheric pollen grains of every 
species in a forest ecosystem (Charalampopoulos et al., 
2013), (iv) predict production of seeds in a reproductive 
season (Allison, 1991), (v) determine the availability of 
pollen for pollinators to achieve pollination success (Mu 
et al., 2017; Khanduri et al., 2015; Sukumaran et al., 
2020), and (vi) assess genetic homogeneity of a popula -
tion through ample pollen exchange among individuals 
(Dufaÿ et al., 2008; Ramos et al., 2016).
The pollination mechanism in tree species is highly 
significant for biological studies in ecology, co-evolution, 
variation and speciation, classical and applied genetics 
and plant breeding (Van der Niet et al., 2014). The suc -
cess and failure of pollination is a prerequisite in plant 
breeding and for obtaining better crop yields (Wilcock 
& Neiland, 2002). Variability in forest tree crops is 
controlled by the breeding system, of which pollination 
mechanism forms an integral component (Hilje et al., 
2015). Knowledge of the breeding system is also im -
portant for managing breeding populations and for de-
signing efficient genetic conservation strategies (Rao & 
Hodgkin, 2002). 
Ecologically, plant – animal interactions is the most 
important phenomena without which reproductive 
success and reproduction cannot be achieved. Similarly 
without plants, the animals that dependent on flower 
resources, viz. pollen, nectar and other rewards, may 
lose their population (Kearns et al., 1998). Therefore, the 
plant – animal interactions are considered as the most 
significant classes of ecological interactions (Ollerton, 
2017). Animal pollination has been reported to increase 
fruit and seed set for about 75% of the world’s leading 
food crops (Klein et al., 2007). Majority of animals 
have the potential to be successful pollinators when 
they visit the flowers. However, the effectiveness of 
pollinators depends on the abundance of animal in a 
community; the predilection for that animal to contact 
anthers, bear pollen, and touch stigmas; and whether or 
not the animal travels to visit other flower of the same 
species (Rodriguez-Rodriguez et al., 2013). About 94% 
of tropical plants relay on animal pollination (Ollerton 
et al., 2011). Tropical forest ecosystem has high species 
richness which implies that the animal pollinators may 
be specific for interactions with other taxa resulting to 
species evolution (Pauw & Stanway, 2015; Moles & 
Ollerton, 2016). A high number of tropical trees are 
animal pollinated and majority of them are of insect 
pollinated particularly bees pollinated (Bawa, 1990). 
Comparatively a small number of plants are pollinated 
by birds or mammals (Devy & Davidar, 2003, Fleming 
& Muchhala, 2008). 
The shortfall in seed production that plants experience 
due to inadequate pollen receipt (where pollen is either of 
inadequate quantity or quality) compared to a situation 
where ideal pollination has been represented by pollen 
limitation (reproductive success limited by pollen). Pollen 
limitation arises if there are not enough visitors, or if there 
is not sufficient production of pollen, or if there is a lack 
of conspecifics to mate with. Study of pollen limitation 
is important to see (i) if there is potential to improve 
seed production, and (ii) if abundance of pollinators 
may be low and plant reproduction in the wild may be 
threatened. Pollen limitation has been examined from 
various perspectives viz. (i) pollen limitation of female 
reproduction (Bierzychudek, 1981; Burd, 1994); (ii) 
‘pollination crisis’ (Kearns et al., 1998); (iii) the role of 
pollen limitation in plant populations (Ashman et al., 
2004; Knight et al., 2005; 2006); (iv) methodology 
for pollen limitation (Wesselingh, 2007); (v) pollinator 

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dependence and self-incompatiblity on pollen limitation 
(Rodger & Ellis, 2016); and (vi) insufficient delivery 
of outcross pollen and self-incompatiblity on pollen 
limitation (Khanduri et al., 2019). Pollen limitation is 
best assessed by pollen supplemental hand pollination 
experiments in which fruit and seed set using hand 
pollination is compared with that of naturally pollinated 
flowers (Burd, 1994). When reproductive success 
is significantly high in supplemental pollination as 
compared to that of open pollination, pollen limitation is 
confirmed (Chen & Zuo, 2018; Khanduri et al., 2019). 
Most of the pollen limitation studies are restricted to the 
herb and shrub species (Ashman et al., 2004; Cosacov 
et al., 2008; Wolowski et al., 2013; Chen & Zhao, 2017). 
However, pollen limitation experimentally in tree species 
is sparse (González-Varo et al., 2009; Van Etten et al., 
2015; Khanduri et al., 2019) because the crown height 
in trees is difficult to approach for conducting the hand 
pollination experiments.
This study aims to 1) estimate the reproductive effort 
and success of five tropical tree species, 2) examine 
whether the reproductive success is influenced by pollen 
limitation, and 3) assess inbreeding depression for each 
analysed species for which the data was used on the basis 
of experimental work done by the author (Khanduri, 
2016), and the average value calculated for fruit set, seed-
set and seed germination was taken. The study species 
were (i) Bombax ceiba (an economically important 
on account of the presence of floss surrounding the 
seeds, which is used for making pillows, cushions, 
etc.; (Khanduri & Kumar, 2017a), (ii) Erythrina stricta 
(medicinally useful; Kirthikar & Basu, 1987; Khanduri 
et al., 2021), (iii) Lagerstroemia speciosa (medicinally 
important; Khanduri, 2014), (iv) Mesua ferrea (high 
medicinal potential; Khanduri & Kumar, 2017b) and (v) 
Schima wallichii (commercial timber tree; Khanduri et 
al., 2013). The results of the study will be of immense 
value for understanding the behaviour of pollen grains in 
nature and, subsequently for various tree improvement 
and breeding programmes to forest geneticists, 
silviculturists and evolutionary biologists because of 
their adaptive and practical significance. The extent of 
variation in reproductive success on all the analyzed five 
tropical tree species within individual stand is highly 
valuable for tree improvement programme and has 
also the potential to conserve the genetic composition 
of a species. The results of the study would further be 
utilized for provenance research and development of seed 
orchards, seed production areas and genetic testing of 
the selected species.
Materials and methods
Study site
The study was conducted during the flowering season in 
the years 2010 and 2011 in a tropical moist deciduous 
forest of Bethlehem Vengthlang, situated in the district 
Aizawl of Mizoram State in the north-eastern hill region 
(NEH) of India. The study area was located at 23º 43’ 
47.5” N Latitude and 92º 43’ 53.5” E Longitude at an 
elevation of 900 m above sea level (asl). Average rainfall 
in the study area was 1900– 2100 mm and mean an-
nual temperature was 19.0º C. There is a dry season of 
six months, from October to March. The studied tropical 
forest was mature, mixed, uneven-aged/irregular with the 
associations of 18 tree species.
Species description
Five flowering tree species were selected for study, rep-
resenting a variety of floral characters, pollination syn-
dromes and breeding systems. These included the Bombax 
ceiba (large-sized flowers, self-incompatible and com-
monly accepted as bird pollinated, Khanduri & Kumar 
2017a), Erythrina stricta (cross pollinated and character-
istically ornithophilous flowers, Etcheverry & Alemán 
2005; Khanduri et al., 2021), Lagerstroemia speciosa (rela-
tively large-sized flowers and entomophilous tree), Mesua 
ferrea (medium sized flower and entomophilous tree) and 
Schima wallichii (relatively smaller size flowers and ento-
mophilous tree).
Flower, pollen and seed production
Flower and pollen production along with ovule number 
per flower was assessed by choosing ten trees each of five 
investigated tree species as per the method of Khanduri et 
al. (2015). The ovule number per tree for each analysed 
species was calculated by multiplying the ovule number 
per flower with number of flowers per tree. The num-
ber of seeds per fruit was estimated at the time of fruit 
maturity of each analysed species. The time of fruit ma-
turity was different for different species, i.e. 1.5 months 
for B. ceiba and E. stricta, 6 months for M. ferrea and 
9 months for L. speciosa and S. wallichii. Fruit develop-
ment was monitored in 15 days interval for B. ceiba and 
E. stricta and after every one month intervals for remain-
ing three species. 50 mature fruits of each species which 
have been matured through open pollination were har-
vested to estimate number of seeds produced per fruit/
pod. Number of seeds per fruit and subsequently for 50 
fruits was counted manually and an average value (seeds 

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per fruit) for each species was calculated. The number of 
fruits/pods per tree was calculated by multiplying num-
ber of fruits per sub-branch (in case of B. ceiba, M. fer-
rea and S. wallichii) and per inflorescence (for E. stricta 
and L. speciosa) by the number of sub-branches /inflores-
cences per branch, which was multiplied by the number 
of fruit bearing branches per tree. Number of seeds per 
tree was calculated by multiplying the average number 
of seeds produced per fruit by the number of fruits pro-
duced per tree following open pollination.
Flower visitation
Flowers visitors were recognized by observing 10 individu-
als of each of the five tree species, for two-hour periods, 
at peak stages of flowering. Bird visitors to flowers were 
identified using 8×40 binoculars at a distance of 8 to 10 
meter to avoid disturbance to the visitors, and the number 
of visits by each species was recorded. Visitation frequency 
was recorded as visit per small branch for B. ceiba and visit 
per inflorescence for E. stricta. Photographs of the birds 
foraging nectar from the flower was also taken. The stand-
ard method used by Dawson & Bull (1975) was followed 
to measure the relative abundance of bird species. 
The insect visitors to flowers were identified by taking a 
sample of several inflorescences enveloped in a pillowcase 
and tapping the branch to dislodge insects. The insects 
were captured in a collecting jar (Oldroyd, 1958), and 
killed by inserting cottonwool soaked in ethyl acetate. 
Later, the specimens were examined and identified upto 
genus and species level. Sampling was replicated on ten 
randomly selected individuals of all insect-visited tree 
species. 
Pollen supplementation experiment 
and pollen limitation
Pollen supplementation experiment was performed to 
assess pollen limitation. The selected ten trees of each 
analysed species were used to carry out the experiment. 
Pollen from each study species was collected from the 
neighbouring trees growing at a distance of 50 to 80 m 
from the experimental trees. Collected pollen grains from 
different trees of each species were mixed and kept in 
air-tight vials and stored at 4
 o
C in the refrigerator prior 
to use. Flowers of each tree species was emasculated be-
fore anthesis and isolated with fine net. Collected pol-
len grains were applied to the stigmas of isolated flowers 
during peak receptivity using brush and isolated again till 
the completion of flowering in the population. Aceto-
carmine test (Zheljazkov et al., 2021) was done to check 
the viability of pollen grains before application. For open 
pollination, flowers in different inflorescences and sub-
branches were tagged and left to natural pollination by 
insects and birds. Each pollination treatment (pollen sup-
plementation and open pollination) was applied on 20 
flowers per individual tree distributed on 4–5 branches in 
case of B. ceiba, M. ferrea and S. wallichii because of the 
solitary flowers on the branches. While 10 inflorescences 
distributed on 5 branches per individual tree for E. stricta 
and L. speciosa were selected for pollination treatment. 
A total of 1200 flowers were marked and monitored for 
fruit set and brood size, 600 and 600 as open pollination 
and supplemental pollination, respectively for B. ceiba, 
M. ferrea and S. wallichii. Whereas a total of 400 inflo-
rescences, 200 for supplemental pollination and 200 for 
open pollination for E. stricta and L. speciosa, were se-
lected for fruit set. Branches within a tree were pooled 
for each treatment for data analyses. Percent conversion 
of flowers to fruits was calculated by dividing the aver-
age number of converted fruits produced following open 
pollination and supplemental pollination by the number 
of flowers selected/manipulated at the time of pollination 
per tree for each species. A comparison of fruit set fol-
lowing open pollination and supplemented pollination 
was made and presented in a bar diagram to differentiate 
between two treatments.
The values obtained for fruit set following open polli-
nation and supplemented pollination in each species was 
averaged. First the fruit set was obtained for each indi-
vidual tree and then averaged across trees for each species. 
A factorial analysis of variance was done to test the effects 
of species, tree individuals, pollen level and interaction 
of trees and pollen level on fruit set using JMP statistical 
software pro 14. 
For each analyzed tree species, fruit set obtained for 
both treatments were used to calculate a pollen limitation 
index expressed as: PL = 1 – OP/SP, where OP repre-
sents fruit set of open pollination and SP represents the 
fruit set of supplemental pollination treatments following 
Larson & Barrett (2000). Fruit set percentage was used 
to estimate the pollen limitation index which is a widely 
used measure of fertility for pollen limitation (Larson & 
Barrett, 2000). Index of pollen limitation varies from zero 
to one, with zero indicating no pollen limitation and one 
showing full pollen limitation (e.g., Larson & Barrett, 
2000; Tamura & Kudo, 2000; Lázaro & T raveset, 2006). 
Seed germination
Seed germination test of each studied species was done 
under laboratory conditions. Mature seeds of each species 
were taken and placed in the Petri-dishes with Whatman 
blotting paper. Thirty seeds with three replications in the 

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Petri-dishes were used in each species. The germination 
tests were conducted under room temperature and the 
Whatman blotting paper was used as a germination me-
dia, which was moistened with the running tap water so 
that the result of seed germination would be similar to 
that of the natural conditions.
Inbreeding depression
The inbreeding depression was calculated by using the 
formula; δ = 1 – Ws/Wo; Where δ = inbreeding depres-
sion, Ws = the result of progeny from self-pollination 
and Wo = the outcome of progeny from cross-pollination 
(Lande & Schemske, 1985). A delineation inbreeding 
depression value of δ = 0.5, signified that the selfing is 
preferred below the value and beyond which outcrossing 
is favoured (Lande & Schemske, 1985). 
Results
Flower, pollen and ovule production
Among the 5 study species, 3 are deciduous and 2 are 
evergreen in nature. The deciduous species, viz.  Bombax 
ceiba, and Erythrina stricta  blooms when they are devoid 
of foliage. The flowers of analysed species are large in size, 
showy with a striking colour, full of nectar (Bombax ceiba, 
Erythrina stricta), and abundant pollen that can be visible 
from a long distance to attracts the pollinators, both birds 
and insects. The flower phenology, morphology, time of 
the day when anthesis starts, number of anthers and their 
arrangements in the flower, and secretion of nectar from 
nectaries is presented in Table 1. There was variation in 
the amount of pollen production per anther in different 
species. The maximum number of pollen grains per an-
ther was recorded in B. ceiba, followed by M. ferrea and 
Table 1: Flowering traits of five selected tropical trees.
Tabela 1: Značilnosti cvetov petih izbranih tropskih dreves.
Study species Flower phenology Flower morphology Number of anthers  
and their arrangements 
in the flower
Secretion of 
nectar from 
nectaries
Bombax ceiba Flowering: second week of 
January to first week of March; 
Anthesis: 05:00 to 11:00 hr 
of the day
Anther dehiscence:  
half an hour after anthesis 
Bisexual, large cup shape flower red to 
orange colour. Calyx green and leathery, 
corolla consists of five petals, tubular at 
the base 
Infinite; Occurs in five 
bundles
Nectar 
production 
starts at 
anthesis in 
the morning 
Erythrina stricta Flowering: second week  
of February to third week  
of March.
Anthesis: 06:00 to 11:00 hr 
of the day
Anther dehiscence:  
half an hour after anthesis
Bisexual, one well-developed bright 
red standard petal, two greenish-red 
keel petals, two poorly developed very 
light-red wing petals. Keel petals form 
a carinal-like structure that holds nectar 
inside.
10; Monadelphous, 
usually bend up wards 
facing the standard  
petal
Nectar 
secretion 
starts from 
anthesis on-
wards.
Lagerstroemia 
speciosa
Flowering: Mid April to  
mid July
Anthesis: 06:00 to 10:00 hr 
of the day
Anther dehiscence: half
an hour after anthesis
12–15mm long calyx, funnel- or bell 
shaped, six-lobed, fleshy, brownish in 
colour;
petals often six, inserted near the mouth 
of the calyx tube, pink to pinkish white 
or mauve-purple, clawed, wrinkled.
Infinite; arranged in 
several rows
Flowers do 
not produce 
nectar.
Mesua ferrea Flowering: mid March to  
first week of May
Anthesis: 05:00 to 10:00 hr 
of the day.
Anther dehiscence:  
one hour after anthesis.
White flowers with four large corolla 
free, fleshy, retuse, and spreading; calyx 
four green.
Infinite; free and  
connate at the base.
Nectar 
secreted in 
traces at the 
beginning of 
anthesis.
Schima wallichii Flowering: Third week of 
March to first week of May.
Anthesis: 06:00 to 10:00 hr 
of the day
Anther dehiscence:  
one hour after anthesis.
Flowers are conspicuous, with five 
connate white, dialypetalous and 
actinomorphic corolla 
Infinite; inserted  
around the style head
Nectar 
secretion 
starts at the 
beginning of 
anthesis

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Table 2: Reproductive effort, pollen limitation and fecundity in five tropical tree species (± SE).
Tabela 2: Razmnoževalni napor, pelodna omejitev in plodnost pri petih vrstah tropskih dreves (± SE).
Studied variables Bombax ceiba 
(2011)
Erythrina stricta
 (2011)
Lagerstroemia speciosa 
(2010)
Mesua ferrea 
(2010)
Schima wallichii 
(2011)
Pollen grains/ anther 14160±1005 1022±78.64 956±60.62 3564±202.4 1932±110.42
Pollen grains per T ree 1.20±0.11×109 1.26±0.32×108 9.19±1.14×108 6.12±0.20×1010 1.60±0.40×109
Flowers per T ree 1232±132 13426±3416 4542±254 14986±1235 6274±1306
Fruit set (%) open pollination 50.18±5.42 35.46±3.16 74.2±2.64 60.20±2.74 68.84±3.24
Ovule numbers per flower 372±20.60
307.3
08±0.76
5.65
154±10.86
133
1–4 22±1.84
15.4
Ovule numbers per tree 446204±2850 108562 ±1986 698894 ±5786 30250 ±1042 141254 ±2190
Seed numbers per tree (open pollination) 168845±1680 31378± 876 389018 ± 3986 24200 ± 986 55197 ± 1288
Pollen limitation index (fruit set) 0.3088 0.3233 0.0413 0.2850 0.1152
Pollen limitation index (seed set) 0.3833 0.0334 0.1368 0.1342 0.2522
Seed Germination (%) 63±2.46 87±4.56 53±2.56 60±2.16 67±4.42
Inbreeding depression (δ) 1.0 0.82 0.39 0.37 0.52
S. wallichii. The least was estimated in L. speciosa. An an-
ther of B. ceiba produces 4 times more pollen than the 
anther of M. ferrea. The production of pollen grains per 
tree was maximum for M. ferrea (6.12 ± 0.20 × 10
10
), 
followed by S. wallichii (1.60 ± 0.40 × 10
9
) and B. ceiba 
(1.20 ± 1.1× 10
9
). This pattern of variation in different 
species is due to variation in the production of anthers 
per flower and flowers per tree. The production of ovule 
numbers per tree was estimated maximum for L. speciosa, 
which was 1.5, 5.0, 6.4 and 23.0 times more than the 
ovule number per tree for B. ceiba, S. wallichii, E. stricta 
and M. ferrea, respectively (Table 2). Seed germination 
was recorded between 53 and 87% in the study species. 
The maximum was recorded for E. stricta and minimum 
for L. speciosa. The results of inbreeding depression sug-
gests that B. ceiba, and E. stricta are outcrossed species 
whereas L. speciosa and M. ferrea inclining towards selfing. 
S. wallichii is persuading towards outcrossing (Table 2). 
Pollen limitation 
All the studied species have shown that maximum re-
productive success is not achievable due to pollen limita-
tion. Pollen limitation index was weaker for L. speciosa 
and S. wallichii (Table 2). The lowest pollen limitation 
index was recorded for L. speciosa (0.0413). The supple-
mentation of pollen grains had significantly augmented 
the fruit set in all the five tropical tree species (Figure 1). 
There was a significant effect of pollen addition on fruit 
set in respect of different studied species (p<0.0054) and 
among individuals of a species (p<0.0026). The pollina-
tion treatments (pollen level) and the interaction of trees 
and pollination treatments had also shown a significant 
(p< 0.0001) effect to fruit set (Table 3).
Figure 1: The mean fruit set of five tropical tree species under pollen 
limitation treatments, i.e. open pollination vs supplemental pollina-
tion. Vertical bars represent standard error. 
Slika 1: Povprečna količina plodov za pet dreves tropskega gozda v 
različnih obravnavah pelodne omejitve, t.j. odprta oprašitev v prim-
erjavi z dodatno oprašitvijo. Navpične črte predstavljajo standardno 
napako.
Table 3: ANOVA statistics for the effects of species, trees and 
pollination treatments on fruit set.
Tabela 3: Analiza ANOVA vpliva vrst, dreves in opraševalcev 
na količino plodov.
Response variable Df F P
Species 4 24.34 0.0054
T rees 9 18.64 0.0026
Pollen level (Pollination treatments) 1 30.38 0.0001
T rees × Pollen level 9 26.82 0.0001
Df = degrees of freedom, F = F-ratio, p = probability

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Flower pollinators
Varieties of birds were recorded visiting flowers of B. ceiba 
and E. stricta (T able 4 and Figure 2). The highest frequen-
cy of bird visitation was recorded in the morning hours 
to both species. Pycnonotus cafer was recorded visiting the 
flowers of B. ceiba and E. stricta throughout the day ex-
cept between 12:00 to 15:00 h. Bimodal pattern of visita-
tion to the flowers of B. ceiba was recorded for Dicrurus 
adsimilis ailbiritus and Turdoides caudata. Similar pattern 
to the flowers of E. stricta was observed for D. leucophaeus 
and Zosterops palpebrosus. Fourteen species of birds were 
observed visiting to the flowers of both tree species. Nine 
species were common to both Bombax and Erythrina spe-
cies. P . cafer and D. macrocercus was the most prevalent 
flower visiting bird species for B. ceiba (T able 3), which in 
case of E. stricta was P . cafer and D. leucophaeus ( T able 4). 
A strong correlation between the visitation rate and abun-
dance of each bird species was observed for both tree spe-
cies (spearman’s test for correlation: B. ceiba: rs = 0.9; 
E. stricta: rs = 1.0). D. a. ailbiritus and P . cafer were ob-
served showing close contact with the stamen and pistil of 
the B. ceiba flower while foraging the nectar that has been 
shown in Figure 2B and 2A, respectively. Similarly, the 
bird species i.e. P. cafer (Figures 2E), Chloropsis aurifrons 
(Figures 2G. i) and D. eucophaeus (Figures 2H. ii) were 
recorded as effective bird pollinators for E. stricta, as all 
are indicating close contact to the reproductive parts of 
the flowers of Erythrina while foraging the nectar.
Visitation of insects was recorded in all the five studied 
tree species (Table 4). Hymenoptera, Lepidoptera, Dip-
tera and Coleoptera were the recorded flower-visiting in-
sect orders. Highest diversity of insects was observed for 
S. wallichii, followed by L. speciosa and M. ferrea  ( T able 5). Table 4: Bird visitors/pollinators abundance in Bombax ceiba and Erythrina stricta.
Tabela 4: Abundanca ptic obiskovalk/opraševalk na vrstah Bombax ceiba in Erythrina stricta.
Scientific Name of Bird Bird Visit per branch at different hour  
Bombax ceiba
Bird Visit per branch at different hour  
Erythrina stricta
Hours 06:00–08:00 0800–1000 1000–1200 1500–1700 0600–0800 0800–1000 1000–1200 1500–1700
Pycnonotus cafer 8 12 4 8 6 10 04 5
Pycnonotus melanicterus flaviventris - - 4 2 - 6 7 3
Pycnonotus jocosus - 8 7 5 - - - -
Dicrurus adsimilis ailbiritus 18 - - 8 - - - -
Dicrurus hottentottus 6 6 - - - - - -
Dicrurus macrocercus 9 7 - - - - - -
Dicrurus leucophaeus - - - - 8 10 - 8
Dicrurus paradiseus - 12 - - - 8 - -
Macronous gularis - 14 - - - 12 - -
Stachyridopsis ruficeps 14 - - - - 8 - -
Heterophasia gracilis - 6 - - - 4 - -
Turdoides caudata 4 - - 3 - - - -
Zosterops palpebrosus - - - - 6 - - 4
Falco severus 2 - - - 2 - - -
Cuculus micropterus 6 - - - 4 - - -
Chloropsis aurifrons - - - - - 4 - -
Table 5: Insects visiting the flowers of analyzed tropical forest trees.
Tabela 5: Vrste žuželk, ki so obiskovale cvetove preučevanih dreves tropskega gozda. 
Order Family Scientific Name Visited tree species
Hymenoptera Apidae
Apis cerena Erythrina stricta, Mesua ferrea Lagerstroemia speciosa, Schima wallichii 
Apis florea Mesua ferrea, Lagerstroemia speciosa
Xylocopa spp Bombax ceiba, Erythrina stricta, Mesua ferrea Lagerstroemia speciosa, Schima wallichii
Diptera Calliphoridae Chrysomya megacephala Lagerstroemia speciosa
Lepidoptera Lycaenidae Arhopala eumolphus Mesua ferrea, Schima wallichii
Lepidoptera Hesperiidae Matapa aria Schima wallichii
Lepidoptera Geometridae Cabera pusaria Schima wallichii
Lepidoptera Geometridae Dysphania militaris Schima wallichii
Lepidoptera Zygaenidae Callamesia midama Schima wallichii
Lepidoptera Zygaenidae Eterusia aedea Schima wallichii
Lepidoptera Noctuidae Alypia spp Schima wallichii
Coleoptera Scarbaeidae Maladera castanea Schima wallichii

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Figure 2: A. Redvented Bulbul (Pycnonotus cafer) making contact with the stigma of the Bombax flower during nectar foraging, B. Dicrurus 
adsimilis albiriltus touching reproductive parts of Bombax flower effectively while taking nectar, C. Black-crested Bulbul (Pycnonotus melanicterus 
flaviventris) sitting to the Erythrina flower to probe the nectar, D. Ashy Drongo (Dicrurus leucophaeus) resting in the Erythrina flower bough; 
E. Red-vented Bulbul (Pycnonotus cafer) showing full contact with the floral reproductive parts of Erythrina; F . Indian white-eye (Zosterops 
palpebrosa) ready to go to another flower of Erythrina after taking nectar from the sitting flower; G(i). Golden-fronted Leafbird (Chloropsis 
aurifrons) showing valuable contact with essential reproductive parts of the Erythrina flower at the time of foraging nectar; H. (i) Golden-fronted 
Leafbird taking rest just after probing the nectar and (ii) Ashy Drongo (Dicrurus leucophaeus) during foraging of the Erythrina flower.
Slika 2: A. Pycnonotus cafer v stiku z brazdo cveta vrste Bombax med hranjenjem z medičino, B. Dicrurus adsimilis albiriltus se dotika 
reproduktivnih delov cveta vrste Bombax med odvzemom medičine, C. Pycnonotus melanicterus flaviventris sedi na cvetu vrste Erythrina in išče 
medičino, D. Dicrurus leucophaeus počiva na veji s cvetom vrste Erythrina; E. Pycnonotus cafer v polnem stiku z razmnoževalnimi deli vrste 
Erythrina; F . Zosterops palpebrosa se pripravlja na let na drug cvet vrste Erythrina po tem, ko je popil medičino; G(i). Chloropsis aurifrons v stiku z 
razmnoževalnimi deli cveta vrste Erythrina v času pitja medičine; H. (i) Chloropsis aurifrons počiva po pitju medičine in (ii) Dicrurus leucophaeus) 
med prehranjevanjem na cvetu vrste Erythrina.
i
i
ii

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Discussion
The amount of pollen produced by a tree is to recompense 
for low pollination efficiency and warrant fertilisation. Pol-
len quantity and quality provide in measuring and forecast-
ing several factors, e.g. crop yield in trees (Allison, 1990; 
Hirayama et al., 2005; Iwaizumi & Takahashi, 2012) and 
yield in agriculture crops (Westgate et al., 2003), fruit size 
and production of seeds (Faegri & Iversen, 1989; McK-
one, 1990; Baskin & Baskin, 2018), ancient and current 
vegetation (Moore et al., 1991; Rogers, 1993; Obigba, 
2021) and respiratory allergy symptoms from specific taxa 
to human beings (Filon et al., 2000; Gioulekas et al., 2004; 
Damialis et al., 2011; Sousa-Silva et al., 2021). In the pre-
sent study the amount of pollen produced by individuals 
of selected five species was considered as pollen quantity 
which can be consumed by the animals and can be lost to 
the environment (through abiotic factors). However, while 
taking the pollen and nectar, the animals carry dislodged 
pollen on their body to the receptive part of pistil of the 
other flowers that achieves pollination.
Among the five studied tropical tree species, two tree 
species, viz. B. ceiba and E. stricta, are bird pollinated 
(Khanduri, 2016). Despite a high production of pollen 
grains at tree crown level in the order of 10
9 
in case of B. 
ceiba and 10
8
 for E. stricta, the index of pollen limitation 
in both species is highest as compared to other studied 
three species. This clearly is indicating that the pollination 
failure in both species is due to unavailability of quality 
pollen from neighbouring trees in the absence of sufficient 
pollinator resources (i.e. bird). However, presence of high 
number of bird pollinators in both tree species indicating 
that the pollinator resources are sufficient. Nevertheless, 
the birds were observed foraging several flowers simul-
taneously within a tree during their visit which leads to 
geitonogamy (inter-flower selfing) pollination and both 
tree species are self-incompatible indicating pollination 
failure due to pollen quality. The other three species, i.e. 
S. wallichii, L. speciosa and M. ferrea are insect pollina-
tor dependent and partially self-incompatible, which have 
shown lower pollen limitation. Xylocopa bee was the key 
pollinator for L. speciosa and M. ferrea due to proper physi-
cal fitness of Xylocopa bee to the flowers of both species 
(Khanduri, 2014; Khanduri & Kumar, 2017b). Xylocopa 
bee makes frequent visit to the several flowers within a 
crown of a tree and other trees in a population with a very 
high foraging speed (Khanduri, 2014; Khanduri & Ku-
mar, 2017b), indicating ample pollination success to both 
tree species ultimately leading to weaker pollen limitation. 
In Schima wallichii, the important pollinators were Apis 
cerena, Dysphania militaris and Xylocopa spp. Apis cerena 
that stay in the single flower for about 3 minutes and 
feed on pollen grains leading to self-pollination. Honey 
bees are considered to be the best and efficient pollinators 
among insects. They have the quality which is commonly 
known as floral fidelity in which bees visits the flowers 
of the same crop repeatedly either for pollen or nectar 
or both till the end of the bloom. In this way, chances 
of pollination are highly secured. Dysphania militaris and 
Xylocopa spp make frequent interflower movement within 
a tree and between trees in a population leading to geito-
nogamy and xenogamy pollination in S. wallichii. Pollen 
limitation using fruit set and seed set in S. wallichii was 
moderate among the five studied tropical tree species and 
the mating system of S. wallichii is partially self-incom-
patible supporting outcrossing (Khanduri, 2016), indi-
cating that the pollination failure is due to quality pollen 
limitation and limitation of pollinator resources. 
Pollen limitation has been reported greater for self-
incompatible than self-compatible species (Knight et al., 
2005; Larson & Barrett, 2000). Self-incompatible species 
depend on the pollen from neighbouring trees and rely on 
pollinators visit frequency to effect pollen transfer for pol-
lination success whereas, self-compatible or partially self-
incompatible species might be capable to produce seeds 
by receiving mixed pollen loads of self- and cross-pollen 
(Schoen & Lloyd, 1992). Self-pollen is prohibited from 
fertilizing ovules in self-incompatible species while self-
compatible species may form seeds from self-fertilized 
ovules, but with lower germination success due to in-
breeding depression. Therefore, pollen limitation would 
be minimal for self fertile species, which however, leads to 
low pollen-quality limitation and reduced inbreeding de-
pression (Duminil et al., 2009). Partially self-incompati-
ble species with mixed pollen loads seems to have higher 
pollen limitation than self compatible species, but lower 
than the self-incompatible species. The estimated pollen 
limitation in the present study was found at par to that of 
the other studies of insect/bird pollinated species. For ex-
ample, a study consisting of 21 shrub and herb species of 
tropical communities at Itatiaia National Park, southeast-
ern Brazil revealed pollen limitation in 11 species with the 
overall pollen limitation index value was 0.39 (Wolowski 
et al., 2013). The pollen limitation index of 0.335 was 
reported in Zygophyllum xanthoxylum, a self-compatible 
species from the Gansu Province of Chiana (Chen & 
Zhao, 2017). The reported value is slightly higher than 
the value observed for partially self-incompatible species 
in the present study. Nevertheless, a high pollen limita-
tion index of 0.478 on fruit set basis and 0.575 for seed 
set data basis was recorded in self pollinated tree species 
i.e. Sophora microphylla from New Zealand (Van Etten et 
al., 2015). The index of pollen limitation for seed set is 
lower than the fruit set for Erythrina stricta, Lagerstroemia 

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Pollen limitation in tropical trees
speciosa and Mesua ferrea whereas the value was higher in 
case of Bombax ceiba and Schima wallichii. 
The supplementation of pollen was found to be increas-
ing the fruit and seed set significantly in all five studied 
species. Confirmation from earlier studies implies that 
supplementation of pollen enhances the fruit/seed set, 
size and weight of a seed in a flower (Campbell, 1993; 
Yang et al., 2005; Gómez et al., 2010; Bartoš et al., 2020). 
Pollen limitation was the resultant of both limited pollen 
quantity and quality (Colling et al., 2004). The pollen 
quantity limitation in this study is related with the ef-
fectiveness of pollinators and their frequency (Ashman et 
al., 2004; Chen & Zuo, 2019), as all the studied species 
had produced ample pollen in order of 10
8
 to 10
10
 at tree 
crown level ultimately leading to pollinators limit fecun-
dity in tropical trees. However, pollen limitation here 
may be a matter of quality rather than quantity (Aizen & 
Harder, 2007; Bona et al., 2022), on the basis that visita-
tion rates appear to be high but there is a high proportion 
of movements between flowers on the same tree, poten-
tially leading to geitonogamy.
Conclusions
Pollen limitation is influenced by pollen quantity and 
quality, leading to pollinators limit fecundity in selected 
tropical trees. The self-incompatible species of Bombax 
ceiba and Erythrina stricta (both bird pollinated) produce 
low fruit and seed set in open pollination condition there-
by proclaimed greater pollen limitation as compared to 
that of other three species, i.e. S. wallichii, L. speciosa and 
M. ferrea, which are partially self-incompatible and insect 
pollinated and have revealed lower pollen limitation. In 
out-crossed/self-incompatible species pollination success 
is achieved only when the flowers with receptive stigmas 
receive pollen from neighbouring trees in the population 
and is also dependent on visit frequency of pollinators for 
effective pollen transfer whereas, partially self-incompat-
ible or self-compatible species have the chances of secure 
pollination by accepting mixed pollen (self- and cross-
pollen) leading to produce more seeds. 
Acknowledgements
This work was supported by the Council of Scientific and 
Industrial Research (CSIR), Government of India, New 
Delhi, vide its project no. 38(1186)/08/EMR-II.
Conflict of interest
The authors declare that they have no conflict of interest.
Vinod Prasad Khanduri  https://orcid.org/0000-0002-
3858-7121
References
Ahlinder, J., Giles, B. E., & García-Gil, M. R. (2021). Life stage-
specific inbreeding depression in long-lived Pinaceae species depends 
on population connectivity. Scientific Reports, 11(1), 1–15. 
Aizen, M. A., & Harder, L. D. (2007). Expanding the limits of the 
pollen‐limitation concept: effects of pollen quantity and quality. 
Ecology, 88(2), 271–281.
Allison, T. D. (1990). Pollen production and plant density affect 
pollination and seed production in Taxus canadensis. Ecology, 71(2), 
516–522.
Ashman, T. L., Knight, T. M., Steets, J. A., Amarasekare, P ., Burd, 
M., Campbell, D. R., Dudash, M.R., Johnston, M.O., Mazer, S.J., 
Mitchell, R. J., Morgan, M. T., & Wilson, W. G. (2004). Pollen 
limitation of plant reproduction: ecological and evolutionary causes 
and consequences. Ecology, 85(9), 2408–2421.
Bartoš, M., Janeček, Š., Janečková, P ., Chmelová, E., T ropek, 
R., Götzenberger, L., Klomberg, Y., & Jersáková, J. (2020). Are 
reproductive traits related to pollen limitation in plants? A case study 
from a central European meadow. Plants, 9(5), 640.
Baskin, J. M., & Baskin, C. C. (2018). Pollen limitation and its effect 
on seed germination. Seed Science Research, 28(4), 253–260.
Bawa, K. S. (1990). Plant-pollinator interactions in tropical rain 
forests. Annual Review of Ecology and Systematics, 21, 399–422.
Bierzychudek, P . (1981). Pollinator limitation of plant reproductive 
effort. The American Naturalist, 117(5), 838–840.
Bona, A., Kłosowski, S., Jadwiszczak, K. A., & Petrova, G. (2022). 
Flowering and quality of seeds and pollen in endangered populations 
of Betula humilis. Trees, 36(1), 313–324.
Burd, M. (1994). Bateman’s principle and plant reproduction: the role 
of pollen limitation in fruit and seed set. The Botanical Review, 60(1), 
83–139.
Campbell, D. R., & Halama, K. J. (1993). Resource and pollen 
limitations to lifetime seed production in a natural plant population. 
Ecology, 74(4), 1043–1051.
Charalampopoulos, A., Damialis, A., Tsiripidis, I., Mavrommatis, T., 
Halley, J. M., & Vokou, D. (2013). Pollen production and circulation 
patterns along an elevation gradient in Mt Olympos (Greece) National 
Park. Aerobiologia, 29(4), 455–472.
Charlesworth, D., & Charlesworth, B. (1987). Inbreeding depression 
and its evolutionary consequences. Annual Review of Ecology, Evolution 
and Systematics, 18, 237–268.
Chen, M., & Zhao, X. Y. (2017). Effect of pollen and resource 
limitation on reproduction of Zygophyllum xanthoxylum in fragmented 
habitats. Ecology and Evolution, 7(21), 9076–9084.
Chen, M., & Zuo, X. A. (2018). Pollen limitation and resource 
limitation affect the reproductive success of Medicago sativa L. BMC 
Ecology, 18(1), 1–10.
Chen, M., & Zuo, X. A. (2019). Effect of pollen limitation 
and pollinator visitation on pollination success of Haloxylon 
ammodendron (CA Mey.) bunge in fragmented habitats. Frontiers in 
Plant Science, 10, 327.

22/1 
• 2023, 117–129
127
Khanduri
Pollen limitation in tropical trees
Colling, G., Reckinger, C., & Matthies, D. (2004). Effects of pollen 
quantity and quality on reproduction and offspring vigor in the rare 
plant Scorzonera humilis (Asteraceae). American Journal of Botany, 
91(11), 1774–1782.
Cosacov, A., Nattero, J., & Cocucci, A. A. (2008). Variation of 
pollinator assemblages and pollen limitation in a locally specialized 
system: the oil-producing Nierembergia linariifolia (Solanaceae). 
Annals of Botany, 102(5), 723–734.
Cristóbal-Pérez, E. J., Fuchs, E. J., Olivares-Pinto, U., & Quesada, M. 
(2020). Janzen-Connell effects shape gene flow patterns and realized 
fitness in the tropical dioecious tree Spondias purpurea (Anacardiaceae). 
Scientific Reports, 10(1), 1–12.
Csépe, Z., Leelőssy, Á., Mányoki, G.,  Kajtor-Apatini, D., Udvardy, 
O., Péter, B., Páldy, A., Gelybó, G., Szigeti, T., Pándics, T., Kofol-
Seliger, A., Simčič, A., Leru, P .M., Eftimie, A.M., Šikoparija, B., 
Radišić, P ., Stjepanović, B., Hrga, I., Večenaj, A., Vucić, A., Peroš-
Pucar, D., Škorić, T., Ščevková, J., Bastl, M., Berger, U., & Magyar, 
D. 2020: The application of a neural network-based ragweed pollen 
forecast by the Ragweed Pollen Alarm System in the Pannonian 
biogeographical region. Aerobiologia, 36(2), 131–140. 
Damialis, A., Fotiou, C., Halley, J. M., & Vokou, D. (2011). Effects of 
environmental factors on pollen production in anemophilous woody 
species. Trees, 25(2), 253–264.
Dawson, D. G., & Bull, P .C. (1975). Counting birds in New Zealand 
forests. Notornis, 22(2), 101–109.
Devaux, C., Porcher, E., & Lande, R. (2019). Mating systems and 
avoidance of inbreeding depression as evolutionary drivers of pollen 
limitation in animal-pollinated self-compatible plants. Annals of 
Botany, 123(2), 327–336.
Devy, M. S., & Davidar, P . (2003). Pollination systems of trees in 
Kakachi, a mid‐elevation wet evergreen forest in Western Ghats, India. 
American Journal of Botany, 90(4), 650–657.
Dufaÿ, M., Vaudey, V., De Cauwer, I., Touzet, P ., Cuguen, J., & 
Arnaud, J. F . (2008). Variation in pollen production and pollen 
viability in natural populations of gynodioecious Beta vulgaris ssp. 
maritima: evidence for a cost of restoration of male function?. Journal 
of Evolutionary Biology, 21(1), 202–212.
Duminil, J., Fineschi, S., Hampe, A., Jordano, P ., Salvini, D., 
Vendramin, G. G., & Petit, R. J. (2007). Can population genetic 
structure be predicted from life-history traits?. The American Naturalist, 
169(5), 662–672.
Duminil, J., Hardy, O. J., & Petit, R. J. (2009). Plant traits correlated 
with generation time directly affect inbreeding depression and mating 
system and indirectly genetic structure. BMC Evolutionary Biology, 
9(1), 1–14.
Etcheverry, A. V., & Alemán, C. E. T. (2005). Reproductive Biology 
of Erythrina falcata (Fabaceae: Papilionoideae) 1. Biotropica, 37(1), 
54–63.
Etcheverry, A. V., Alemán, M. M., & Fleming, T. F . (2008). Flower 
morphology, pollination biology and mating system of the complex 
flower of Vigna caracalla (Fabaceae: Papilionoideae). Annals of Botany, 
102(3), 305–316.
Faegri, K., Kaland, P . E., & Krzywinski, K. (1989). T extbook of pollen 
analysis (No. Ed. 4). John Wiley & Sons Ltd..
Ferriol, M., Pichot, C., & Lefèvre, F . (2011). Variation of selfing rate 
and inbreeding depression among individuals and across generations 
within an admixed Cedrus population. Heredity, 106(1), 146–157.
Filon, F . L., Bosco, A., Barbina, P ., Sauli, M. L., & Longo, L. R. 
(2000). Betulaceae and Corylaceae in T rieste (NE-Italy): Aerobiological 
and clinical data. Aerobiologia, 16(1), 87–91.
Fleming, T. H., & Muchhala, N. (2008). Nectar‐feeding bird and bat 
niches in two worlds: pantropical comparisons of vertebrate pollination 
systems. Journal of Biogeography, 35(5), 764–780.
Gioulekas, D., Papakosta, D., Damialis, A., Spieksma, F ., Giouleka, 
P ., & Patakas, D. (2004). Allergenic pollen records (15 years) and 
sensitization in patients with respiratory allergy in Thessaloniki, 
Greece. Allergy, 59(2), 174–184.
Glémin, S., Bazin, E., & Charlesworth, D. (2006). Impact of mating 
systems on patterns of sequence polymorphism in flowering plants. 
Proceedings of the Royal Society B: Biological Sciences, 273(1604), 
3011–3019.
Gómez, J. M., Abdelaziz, M., Lorite, J., Jesús Muñoz‐Pajares, A., & 
Perfectti, F . (2010). Changes in pollinator fauna cause spatial variation 
in pollen limitation. Journal of Ecology, 98(5), 1243–1252.
González-Varo, J. P ., Arroyo, J., & Aparicio, A. (2009). Effects of 
fragmentation on pollinator assemblage, pollen limitation and seed 
production of Mediterranean myrtle (Myrtus communis). Biological 
Conservation, 142(5), 1058–1065.
Hilje, B., Calvo-Alvarado, J., Jiménez-Rodríguez, C., & Sánchez-
Azofeifa, A. (2015). T ree species composition, breeding systems, and 
pollination and dispersal syndromes in three forest successional stages 
in a tropical dry forest in Mesoamerica. Tropical Conservation Science, 
8(1), 76–94.
Hirayama, K., Ishida, K., Tomaru, N. (2005). Effects of pollen 
shortage and self-pollination on seed production of an endangered 
tree, Magnolia stellata. Annals of Botany, 95, 1009–1015.
Holsinger, K. E. (2000). Reproductive systems and evolution in 
vascular plants. Proceedings of the National Academy of Sciences, 97(13), 
7037–7042.
Hufford, K. M., & Hamrick, J. L. (2003). Viability selection at three 
early life stages of the tropical tree, Platypodium elegans (Fabaceae, 
Papilionoideae). Evolution, 57(3), 518–526.
Iwaizumi, M. G., & Takahashi, M. (2012). Effects of pollen supply 
and quality on seed formation and maturation in Pinus densiflora. 
Journal of Plant Research, 125(4), 517–525. 
Jadwiszczak, K. A., Kłosowski, S., Zalewska, I., Banaszek, A., & 
Chrzanowska, A. (2017). Genetic diversity and sexual reproduction in 
relict populations of Betula nana. Silva Fennica, 51(2), 5643.
Kearns, C. A., Inouye, D.W., & Waser, N.M. (1998). Endangered 
mutualisms: the conservation of plant–pollinator interactions. Annual 
Review of Ecology, Evolution and Systematics, 29, 83–112.
Khanduri, V. P ., Sharma, C. M., Kumar, K. S., & Ghildiyal, S. K. 
(2013). Annual variation in flowering phenology, pollination, mating 
system, and pollen yield in two natural populations of Schima wallichii 
(DC.) Korth. The Scientific World Journal, 2013, 350157.
Khanduri, V. P . (2014). Annual variation in floral phenology and 
pollen production in Lagerstroemia speciosa: an entomophilous tropical 
tree. Songlanakarin Journal of Science and T echnology, 36(4), 389–396.

22/1 
• 2023, 117–129
128
Khanduri
Pollen limitation in tropical trees
Khanduri, V. P ., Kumar, K.S., & Sharma, C.M. (2015). Role of pollen 
production in mating success in some tropical tree species. Brazilian 
Journal of Botany, 38(1), 107–112.
Khanduri, V. P . (2016). Mating system and seedling growth of five 
tropical tree species. Scientia Forestalis, 44(110), 509–517.
Khanduri, V. P ., & Kumar, K.S. (2017a). Reproductive effort and 
success in Bombax ceiba L. in a tropical forest of Mizoram, Indo-
Burma region of North-East India. Brazilian Journal of Botany, 40(1), 
157–166.
Khanduri, V. P ., & Kumar, K. S. (2017b). Pollen production and 
release in Mesua ferrea Linn.(Guttiferae): a spatio-temporal pattern. 
Aerobiologia, 33(1), 13–21.
Khanduri, V. P ., & Sukumaran, A. (2019). Pollen dispersion in Myrica 
esculenta (Myricaceae): a dioecious anemophilous tree species of 
Himalaya. Aerobiologia, 35(4), 583–591.
Khanduri, V. P ., Kumar, K. S., Sharma, C. M., Riyal, M. K., & Kar, 
K. (2019). Pollen limitation and seed set associated with year-to-year 
variation in flowering of Gmelina arborea in a natural tropical forest. 
Grana, 58(2), 133–143.
Khanduri, V. P ., Kumar, K. S., Sharma, C. M., Riyal, M. K., Kar, K., 
Singh, B., & Sukumaran, A. (2021). Passerine birds supporting cross 
pollination in Erythrina stricta Roxb. Dendrobiology, 85, 117–126.
Khanduri, V. P ., Sharma C. M., Riyal, M. K., & Sukumaran, A. 
(2022). Racial hybridization and inbreeding depression in Cedrus 
deodara (Roxb.) G. Don. Kastamonu University Journal of Forestry 
Faculty, 22(1), 47–55.
Klein, A. M., Vaissière, B. E., Cane, J. H., Steffan-Dewenter, I., 
Cunningham, S. A., Kremen, C., & Tscharntke, T. (2007). Importance 
of pollinators in changing landscapes for world crops. Proceedings of the 
Royal Society B: Biological Sciences, 274(1608), 303–313.
Knight, T. M., Steets, J. A., & Ashman, T. L. (2006). A quantitative 
synthesis of pollen supplementation experiments highlights the 
contribution of resource reallocation to estimates of pollen limitation. 
American Journal of Botany, 93(2), 271–277.
Knight, T. M., Steets, J.A., Vamosi, J. C., Mazer, S. J., Burd, M., 
Campbell, D.R., Dudash, M.R., Johnston, M.O., Mitchell, R.J., & 
Ashman, T. L. (2005). Pollen limitation of plant reproduction: pattern 
and process. Annual Review of Ecology, Evolution and Systematics, 36, 
467–497.
Lande, R., & Schemske, D. W. (1985). The evolution of self-
fertilization and inbreeding depression in plants. I. Genetic models. 
Evolution, 39(1), 24–40.
Larson, B. M., & Barrett, S. C. (2000). A comparative analysis of 
pollen limitation in flowering plants. Biological Journal of the Linnean 
Society, 69(4), 503–520.
Lázaro, A., & T raveset, A. (2006). Reproductive success of the 
endangered shrub Buxus balearica Lam. (Buxaceae): pollen limitation, 
and inbreeding and outbreeding depression. Plant Systematics and 
Evolution, 261(1), 117–128.
Lever, J. J., van Nes, E. H., Scheffer, M., & Bascompte, J. (2014). 
The sudden collapse of pollinator communities. Ecology letters, 17(3), 
350–359.
Liu, M., Compton, S. G., Peng, F . E., Zhang, J., & Chen, X. Y. 
(2015). Movements of genes between populations: are pollinators more 
effective at transferring their own or plant genetic markers?. Proceedings 
of the Royal Society B: Biological Sciences, 282(1808), 20150290.
McKone, M. J. (1990). Characteristics of pollen production in a 
population of New Zealand snow‐tussock grass (Chionochloa pallens 
Zotov). New Phytologist, 116(3), 555–562.
Moles, A. T., & Ollerton, J. (2016). Is the notion that species 
interactions are stronger and more specialized in the tropics a zombie 
idea?. Biotropica, 48(2), 141–145.
Moore, P . D., Webb, J. A., & Collinson, M. E. (1991). Pollen Analysis, 
2nd edn Blackwell.
Mu, J., Yang, Y., Luo, Y., Su, R., & Niklas, K. J. (2017). Pollinator 
preference and pollen viability mediated by flower color synergistically 
determine seed set in an Alpine annual herb. Ecology and Evolution, 
7(9), 2947–2955.
Nakanishi, A., Yoshimaru, H., Tomaru, N., Miura, M., Manabe, T., & 
Yamamoto, S. I. (2015). Inbreeding depression at the sapling stage and 
its genetic consequences in a population of the outcrossing dominant 
tree species, Castanopsis sieboldii. Tree Genetics & Genomes, 11(3), 1–10.
Obigba, S. O. (2021). Understanding Past and Present Vegetation 
Dynamics using the Palynological Approach: An Introductory 
Discourse. In Vegetation Index and Dynamics. Eds. Carmina, E. C., 
Ortiz, A. C. Canas, R. Q. & Musarella, C. M., PP 1-21, IntechOpen.
Oldroyd, H. (1958). Collecting, Preserving and Studying Insects. 
Hutchinson & Co. Publishers Ltd.
Ollerton, J. (2017). Pollinator diversity: distribution, ecological 
function, and conservation. Annual Review of Ecology, Evolution and 
Systematics, 48, 353–76.
Ollerton, J., Winfree, R., & Tarrant, S. (2011). How many flowering 
plants are pollinated by animals?. Oikos, 120(3), 321–326.
Pauw, A., & Stanway, R. (2015). Unrivalled specialization in a 
pollination network from South Africa reveals that specialization 
increases with latitude only in the Southern Hemisphere. Journal of 
Biogeography, 42(4), 652–661.
Portillo Lemus, L. O., Harang, M., Bozec, M., Haury, J., Stoeckel, 
S., & Barloy, D. (2022). Late-acting self-incompatible system, 
preferential allogamy and delayed selfing in the heteromorphic invasive 
populations of Ludwigia grandiflora subsp. hexapetala. Peer Community 
Journal, 2.
Ramos, S. L. F ., Dequigiovanni, G., Sebbenn, A. M., Lopes, M. T. 
G., Kageyama, P . Y., de Macêdo, J. L. V., Matias, K., & Veasey, E. A. 
(2016). Spatial genetic structure, genetic diversity and pollen dispersal 
in a harvested population of Astrocaryum aculeatum in the Brazilian 
Amazon. BMC Genetics, 17(1), 1–10.
Rao, V. R., & Hodgkin, T. (2002). Genetic diversity and conservation 
and utilization of plant genetic resources. Plant Cell, Tissue and Organ 
Culture, 68(1), 1–19.
Rodger, J. G., & Ellis, A. G. (2016). Distinct effects of pollinator 
dependence and self-incompatibility on pollen limitation in South 
African biodiversity hotspots. Biology Letters, 12(6), 20160253.
Rodger, J. G., & Johnson, S. D. (2013). Self-pollination and 
inbreeding depression in Acacia dealbata: Can selfing promote invasion 
in trees?. South African Journal of Botany, 88, 252–259.
Rodríguez-Rodríguez, M. C., Jordano, P ., & Valido, A. (2013). 

22/1 
• 2023, 117–129
129
Khanduri
Pollen limitation in tropical trees
Quantity and quality components of effectiveness in insular pollinator 
assemblages. Oecologia, 173(1), 179–190.
Rogers, C. A. (1993). Application of aeropalynological principles 
in palaeoecology. Review of Palaeobotany and Palynology, 79(1–2), 
133–140.
Schoen, D. J., & Lloyd, D. G. (1992). Self-and cross-fertilization in 
plants. III. Methods for studying modes and functional aspects of 
self-fertilization. International Journal of Plant Sciences, 153(3, Part 1), 
381–393.
Sousa-Silva, R., Smargiassi, A., Kneeshaw, D., Dupras, J., Zinszer, 
K., & Paquette, A. (2021). Strong variations in urban allergenicity 
riskscapes due to poor knowledge of tree pollen allergenic potential. 
Scientific Reports, 11(1), 1–13.
Sukumaran, A., Khanduri, V. P ., & Sharma, C. M. (2020). Pollinator-
mediated self-pollination and reproductive assurance in an isolated tree 
of Magnolia grandiflora L. Ecological Processes, 9(1), 1–9.
Tamura, S., & Kudo, G. (2000). Wind pollination and insect 
pollination of two temperate willow species, Salix miyabeana and Salix 
sachalinensis. Plant Ecology, 147(2), 185–192.
Van der Niet, T., Peakall, R., & Johnson, S. D. (2014). Pollinator-
driven ecological speciation in plants: new evidence and future 
perspectives. Annals of Botany, 113(2), 199–212.
Van Etten, M. L., Tate, J. A., Anderson, S. H., Kelly, D., Ladley, J. 
J., Merrett, M. F ., Peterson, P .G., & Robertson, A. W. (2015). The 
compounding effects of high pollen limitation, selfing rates and 
inbreeding depression leave a New Zealand tree with few viable 
offspring. Annals of Botany, 116(5), 833–843.
Voukantsis, D., Niska, H., Karatzas, K., Riga, M., Damialis, A., & 
Vokou, D. (2010). Forecasting daily pollen concentrations using 
data-driven modeling methods in Thessaloniki, Greece. Atmospheric 
Environment, 44(39), 5101–5111.
Wesselingh, R. A. (2007). Pollen limitation meets resource allocation: 
towards a comprehensive methodology. New Phytologist, 174(1), 26–37.
Westgate, M. E., Lizaso, J., & Batchelor, W. (2003). Quantitative 
relationships between pollen shed density and grain yield in maize. 
Crop Science, 43(3), 934–942.
Wilcock, C., & Neiland, R. (2002). Pollination failure in plants: why 
it happens and when it matters. Trends in Plant Science, 7(6), 270–277.
Wolowski, M., Ashman, T. L., & Freitas, L. (2013). Community-wide 
assessment of pollen limitation in hummingbird-pollinated plants of a 
tropical montane rain forest. Annals of Botany, 112(5), 903–910.
Wright, S. I., Ness, R. W., Foxe, J. P ., & Barrett, S. C. (2008). 
Genomic consequences of outcrossing and selfing in plants. 
International Journal of Plant Sciences, 169(1), 105–118.
Yang, C. F ., Sun, S. G., & Guo, Y. H. (2005). Resource limitation 
and pollen source (self and outcross) affecting seed production in two 
louseworts, Pedicularis siphonantha and P . longiflora (Orobanchaceae). 
Botanical Journal of the Linnean Society, 147(1), 83–89.
Zheljazkov, V. D., Semerdjieva, I. B., Stevens, J. F., Wu, W., 
Cantrell, C. L., Yankova-Tsvetkova, E., & Astatkie, T. (2021). 
Phytochemical investigation and reproductive capacity of the 
bulgarian endemic plant ppecies Marrubium friwaldskyanum Boiss. 
(Lamiaceae). Plants, 11(1), 114.