H.S.Suresh?R.Sukumar

Introduction

Community-wide phenology of dry forests is well-documented in several locations across the Indian sub-continent and elsewhere in the tropics(Prasad and Hegde 1986;Bhat 1992;Singh and Singh 1992;Murali and Sukumar 1993,1994;Kushwaha and Singh 2005;Singh and Kushwaha 2006;Nanda et al.2010;Suresh and Sukumar 2009;Opler et al.1976;Borchert 1994;Borchert et al.2002;Rathkey and Lacey 1985).There are also species-specific studies on phenology(Alder and Kielpinski 2006;Sloan et al.2007;Thakur et al.2008;Bajpai et al.2012).The phenology of the genus Ficus(Family Moraceae)is remarkable as fig phenology is associated with the sex of the individual tree and a species-specific pollinator wasp(Patel 1996;Harrison et al.2000;Yu et al.2006).There are species-specific studies of Ficus species to help understand the differences with other species in the dry forest community(Corlett 1984,1987;Patel 1997)and the reproductive phenology among epiphytic and non-epiphytic figs(Corlett 1984;Putz et al.1995;Yu et al.2006).Many Ficus species have asynchronous phenology amongst individuals within a species and across species(Corlett 1984;Patel 1996;Harrison et al.2000;Yu et al.2006)and therefore present interesting systems for research.The asynchrony among figs has resulted in supplies of resources during lean seasons,and figs also produce fruit year-round that are resources for frugivores in tropical forests and thus may be called a keystone species(Kannan and James 1999;Ragussa-Netto 2002;Pereira et al.2007).Environmental factors have a significant influence on the phenology of dry forest tree species(Murali and Sukumar 1993,1994;Borchert et al.2002;Suresh and Sukumar 2009).However,data on the influence of climate on fig phenology and the seasonality of various phenophases are either lacking or scarce.We ask the following questions:(1)Do the different phenophases of figs synchronize with other species?(2)Do the same set of environmental factors influence different phenophases of figs?(3)Do figs have strong seasonality with different phenophases?

Figs in the dry forests of Mudumalai are not common but the genus is the most speciose in the 50 ha forest dynamics plot but their density over a hectare is low(Sukumar et al.1992).Common figs in Mudumalai are Ficus benghalensis L.,Ficus drupacea Thunberg.,Ficus tsjckela Roxb,Ficus virens Aiton,Ficus hispida L.f.,Ficus religiosa L.(Suresh et al.1996).Among these species,F.tsjahela is one of the most abundant figs found in Mudumalai forests.Most fig species start as epiphytes and grow into large strangling plants.Figs produce a fleshy inflorescence which is pollinated by species-specific wasps generally referred to as ‘fig wasps’and produce a fleshy fruit‘syconia’on terminal branches.For a detailed review on figs and its association with wasps see Frank(1989).Ficus leaves are exploited as fodder for captive elephants and its impact on survival of figs is still unknown.

Materials and methods

Study area

The research was conducted in dry forests of Mudumalai which is situated in the foot hills of the Nilgiri hills in Nilgiri district,Tamilnadu.Mudumalai is one of the elephant reserves in the country and also a tiger reserve,and is surrounded by large tracts of dry forests;north is Bandipur National Park,west lies the Wyanaad Wildlife Sanctuary,south is the Gudalur forest division and east is the Sigur Reserve.There is a distinct rainfall gradient along west(wet)to east(dry).And accordingly vegetation ranges from moist deciduous forests in the west to dry thorn forest in the extreme east.Dry deciduous forests are in the centre.[The moist deciduous forest is characterized by the association of ‘Tectona-Lagerstoremia-Anogeissus-Dalbergia’]The dry deciduous forests are characterized by‘Anogeissus-Terminalia-Tectona’and ‘Anogeissus-Tetona’.Dry thorn forests ‘Acacia-Ziziphus’association(Champion and Seth 1968).Mudumalai has been the field research site for research on flora and fauna by the Center for Ecological Sciences(CES),Indian Institute of Science.CES is conducting long-term ecological research on forest dynamics(Sukumar et al.1992,2005;Suresh et al.2010).The flora is relatively well understood(Sharma et al.1977;Suresh et al.2006).

Methods

Eleven sexually mature individuals belonging to three different species of Ficus were monitored every month for different phenophases for 8 years(2000–2008)as a part of long-term phenological studies in dry forests.About 335 reproductively matured trees belonging to 55 species are being monitored as a part of long-term phenological studies in Mudumalai.Trees were marked with unique tag and care was taken to monitor the tree on the same day each month unless prevented by either elephants or rain.Vegetative phenology includes leaf initiation,expansion and senescence.Reproductive phenology includes the appearance of syconia(the fleshy fruit)and mature syconia.Each phenophase was qualitatively scored for the extent of time in the canopy.The sum of scores for all phenophases in vegetative and reproductive phenologies would be 100.Similar protocol was observed with other marked trees belonging to different species along the transect.

Data on climate was collected from the CES weather station at Kargudi(11°57′01′N Lat.and 76°64′61′E Long.).Rainfall is the total rainfall in a month in millimeters;the number of rainy is the total number in a month irrespective of the amount of rainfall.The maximum and minimum temperatures are the mean daily temperatures over 1 month period.Sunshine hours is hours of sunshine recorded every day and expressed as mean hours of sunshine of a day over a given month.Soil moisture is the mean weight difference between wet and dry soils from ten different locations along the transect expressed as a percent.Five hundred grams of soil were collected and weighed,and after air drying,weighed again to get the dry weight.The difference between fresh weight and dry weight is expressed as soil moisture(%).The average of the ten values was considered as the soil moisture of the month.

Analysis

The measurable unit is the intensity of a phenophase in a given month.We define ‘intensity’as the average extent of a phenophase in the canopy for all individuals weighted with the proportion of species participating in that given month.Phenophase intensity is a better unit of measurement as it accounts for both numbers of species as well as number of individuals of that species.

The intensity of a phenophase was compared with the phenophase intensity of other species and the variability over months and years was analyzed using ANOVA.Simple non-parametric correlations were performed at both corresponding and lag periods between phenophases and environmental factors.Multiple regressions were carried out to bring out the most influencing variable on a given phenophase.Circular statistical procedures were performed to understand the seasonality of a phenophase.Questions answered include:(1)Are different phenophases cyclic or random?(2)How strong is the seasonality?We converted the day of observation in a month to angles following Zar(2007)and used ‘STATISTIXL’(http://www.statistixl.com),a software excel spread sheet,to estimate different parameters of circular statistics.Rayleigh’s test of uniformity was performed to understand seasonality.The vector r measured the strength of the seasonality and has no units and ranges from 0(completely random)to 1(completely seasonal)(Morellato et al.2000).

Results

Intense leaf flush was seen in February–April(Fig.1)and leaf expansion in April–July.The maximum senescence of leaves was in December–February(Fig.1).The pattern of leaf initiation amongst the fig species was not significantly different from the rest of the community(KS test,NS)while leaf expansion(KS test,D=-0.257,p＜0.005)and senescence(KS test,D=-0.381,p＜0.001)were different(Fig.2).The variability of intensity of leaf flushing amongst figs was not significant(ANOVA,NS)but across months,it was significant(ANOVA,F=8.51,p＜0.00001).The inter-annual variation of leaf expansion was not significant(ANOVA,NS)but across months it was significant(ANOVA,F=12.40,p＜0.00001).A similar pattern was observed with leaf senescence across months(ANOVA,F=13.04,p＜0.00001).

Fig.1 Intensity of various phenophases of leafing among Ficus spp.of dry forests,Mudumalai

Flowering activity was in March–April(Fig.3).Low intensity flowering was in July,September and November.The variability in flowering intensity across years and months was not significant(ANOVA,NS).Syconia were initiated during January to May with a peak in July(Fig.4).Mature syconia were seen towards the end of the monsoon(Fig.4).The intensity of flowering(KS test,D=-0.773,p＜0.001),syconia initiation(fruit)(KS test,D=-0.453,p＜0.001)and the maturity of syconia(KS test,D=-0.628,p＜0.001)were significantly different across months between fig and non-fig species with very high variability in figs(Fig.5).Variability in intensity of initiation of syconia across years and months was not significant(ANOVA,NS)among fig species.The variability in intensity of mature syconia across years and months was not significant(ANOVA,NS)among the fig species.

Different phenophases of figs are influenced by environmental factors.Environmental variables such as rainfall,temperature and sunlight influence leaf initiation when correlated independently.Moisture-related variables such as rainfall,soil moisture and number of rainy days had negative influence on leaf initiation while maximum temperatures and sunshine were positive(Table 1).Minimum temperatures had negative influences with lag periods(Table 1).Multiple regression was significant with corresponding months (r=0.63, F (6, 90)=10.03,p＜0.0001)with maximum temperatures(+ve)as the significantly influencing factor.Maximum temperatures explained 91%of the total variation.Increases in temperatures with corresponding months enhanced leaf initiation.The number of hours of sunshine was the most influencing factor with 1 month lag period and the regression was significant(r=0.58,F(6,89)=7.65,p＜0.0001).In fact sunshine explained the variation completely.A 2-month lag period regression was significant(r=0.64,F(6,88)=10.27,p＜0.0001)with maximum temperatures negative and hours of sunshine having a positive influence.Sunshine explains more than 70%of the variation and together with the maximum temperatures explain about 93%of the variation.

Rainfall and the number of rainy days had a significant negative influence on the initiation of syconia with the corresponding months,while maximum temperatures and sunshine had a positive influence(Table 2).Moisture-related factors had a significant negative influence with lag periods(Table 2);sunshine had a positive influence with lag periods(Table 2).

Fig.2 Comparison of intensities of leafing phenophases among Ficus spp.and non-Ficus species in the dry forests.a Leaf expansion,b leaf senescence

Multiple regression with corresponding months was significant(r=0.36,F(6,90)=2.33,p＜0.03),though no single factor was significant.With the stepwise regression,maximum temperature and sunshine explained the initiation of syconia with the corresponding month.Maximum temperatures explained 90%of the total variation.A 1 month lag period regression was not significant.A 2-month lag period was significant(r=0.46,F(6,88)=4.10,p＜0.001)with maximum and minimum temperatures being influential factors.However,the variation was explained by a combination of soil moisture and the number of rainy days along with temperature.

Fig.3 Intensity of flowering among Ficus spp

Fig.4 Intensity of fruiting among Ficus spp

The maturity of syconia was influenced by maximum temperatures and sunshine with a 2-month lag period.Correlations with either corresponding months or a 1-month lag period were not significant(Table 3).Multiple regressions with both corresponding months and 1-month lag period were not significant.Though a 2-month lag regression was not significant,the forward stepwise regression was(r=0.31,F(2,92)=5.02,p＜0.008)with the number of rainy days having a positive influence.The number of rainy days explained over 75%of the total variation.

Vegetative phenophases of the figs are significantly seasonal(Table 4).Intense leaf initiation amongst figs was observed early March(dry season).Leaf expansion took place around mid-May(pre-monsoon)and by the end of September(end of the first rainy season),most figs had mature leaves.Leaf senescence occurred in early January.Leafing patterns correspond with the rest of the community.A value of the vector‘r’that measures the strength of the seasonality is high with vegetative phenophases(Table 4).Reproductive phenophases among figs were significantly seasonal(Table 4).Syconia(flowers)are initiated around late-February(mid dry season).Young syconia are initiated around mid-May(pre-monsoon)and mature fruits in late September and early October(end of the rainy season).The strength of seasonality with respect to fruiting phenophases is low,indicating that fruiting stages are more random in nature.Synchrony with the fig community was high,compared to the non-fig community(Table 5).Leafing phenophases had high synchrony compared to the synchrony of the syconia stage.However,there was high asynchrony among different phenophases of non-fig community(Table 5).

Discussion

Ficus in Mudumalai are the leaf-exchange type with no leafless period as seen in Panama(Windsor et al.1989).Though F.religiosa is deciduous,leaf flush is almost simultaneous with leaf senescence.Leaf flush in figs is in the dry season,which is in accordance with reports from other dry forests(Windsor et al.1989;Patel 1997;Harrison et al.2000;Singh and Singh 1992;Murali and Sukumar 1993;Yadav and Yadav 2008;Nanda et al.2010).Young leaves are seen in the wet season in an African aseasonal forest(Tweheyo and Lye 2003)and the pattern of leaf flush in fig and non-fig species is not different.Similar results were obtained at a dry forest site in peninsular India(Patel 1997),in Asia(Malaysia)(Harrison et al.2000)and in Africa(Zimbabwe)(Damstra et al.1996).Figs showed asynchrony amongst species and individuals in Panama(Windsor et al.1989).However there was synchrony in the dry forests of Mudumalai.However,the pattern of leaf expansion and senescence with fig and non-fig species was different with shifts in intensity across months.The lack of herbivory due to adaptations such as tomentose leaves,thick cuticles and milky latex of the fig leaves may shape the expansion time in figs that are temporally out of context with other species in the community.There was no interannual variation with any of the leaf phenological events,suggesting uniformity or cyclicity of leafing.However,there was significant difference across months,suggesting strong seasonality with leafing events.This may lead to greater synchrony among different leafing phenophases.Flowering,i.e.,initiation of syconia,happens around the same time as leaf flush in the dry season as observed in Uttar Pradesh(Bajpai et al.2012)and in Sarawak(Harrison et al.2000).But the correlation between the events is statistically not significant which contradicts the pattern observed by F.citrifolia in Brazil(Pereira et al.2007),although none of the fig species in Mudumalai are cauliflorous.But the results suggest that these two events occur simultaneously,supporting Janzen(1967);the similar pattern was observed among Ficus spp.in Brazil and Panama(Windsor et al.1989;Pereira et al.2007).The dry season leafing and flowering(syconia initiation)may be attributed to facilitation in the conversion of starch to sugars through increased temperature and sunshine(Borchert 1994).There was one peak in flowering observed in Mudumalai,contrasting with other dry sites of the peninsula(Patel 1997).The intensity of flowering among figs was different from other species in the community.

?Fig.5 Comparison of intensities of flowering and fruiting among Ficus spp.and non-Ficus species in the dry forests of Mudumalai.a Flower initiation,b fruit initiation,c fruit senescence

Table 1 Spearman’s correlations between environmental factors and leaf initiation(p values)

Table 2 Spearman’s correlations between environmental factors and flower initiation(p values)

Table 3 Spearman’s correlations between environmental factors and maturity of syconia(p values)

Table 4 Seasonality in different phenophases of vegetative and reproductive phenologies

Table 5 Synchrony observed in various phenophases of Ficus spp.and non-Ficus communities in a dry forest

Fruiting has been observed throughout the year in the neotropics(Milton et al.1982;Milton 1991;Ragussa-Netto 2002)and in the old world tropics(Corlett 1987;Borges 1993;Tweheyo and Lye 2003;Zhang et al.2006).Young fruits are seen throughout the year but mature syconia are concentrated in the post monsoon period in Mudumalai.The lack of variability across months suggests an absence of synchrony in maturity across trees,which is in contrast with intra-crown synchrony that facilitates bird dispersal(Lambart and Marshall 1991).This pattern has been observed in several studies and attributed to climate(Corlett 1987;Ragussa-Netto 2002;Tweheyo and Lye 2003).

Moisture-related factors had significant negative influence on leaf flush among figs,both with corresponding and lag months when assessed independently.This is consistent with the pattern observed in community-wide phenology of other dry forests(Singh and Singh 1992;Bhat 1992;Murali and Sukumar 1993;Yadav and Yadav 2008;Nanda et al.2010;Suresh and Sukumar 2009).But rainfall and associated ‘water storage’showed no significant influence on leaf flush in southern Brazil(Pereira et al.2007).Rainfall has a positive in fluence on leaf phenology by Australian figs(Spencer et al.1996).Maximum temperature and sunshine with corresponding and lag periods in fluenced leaf initiation when all factors were pooled.This pattern was observed also with non- figs(Suresh and Sukumar 2009).The in fluence of temperature on vegetative phenology was also observed with figs in southern Brazil(Pereira et al.2007).Vegetative phenology of figs in Mudumalai along with other species in the community seems to support the ‘insolation’hypothesis(van Schaik et al.1993).

Moisture-related factors had significant negative influence on the initiation of syconia,suggesting that dry conditions favor syconia development as observed in Brazil(Pereira et al.2007).Sunshine had a positive influence on the initiation of syconia throughout,suggesting that clear days favor their initiation.A similar set of environmental factors influenced the initiation of flowers in dry forests(Suresh and Sukumar 2009).Similar explanations may explain the dry season flowering among figs,and the initiation period also seems to coincide with wasp activity(Pereira et al.2007).The strong seasonality in rainfall and dispersal time of figs could be major factors in evolution of dry season flowering.Increase in temporal distribution of rainfall 2 months prior influences the maturity of syconia.None of the other environmental variables seem to have significant influence.However,among neo-tropical figs,temperature has a negative influence,suggesting that syconia mature in cool wet periods(Pereira et al.2007).The maturity of figs in Mudumalai was significantly influenced by temperature and sunshine with the lag periods.Both factors had negative influence when tested independently.However,among figs in the neotropics,temperature had no influence on the maturity of syconia(Pereira et al.2007).The most significant factor that influenced syconia maturity was temporal distribution of rainfall.Figs need temporally spread rainfall by 2 months lag to have their syconia mature.

The different phenophases of figs is distinctly seasonal.This is in agreement with community-wide phenology of Mudumalai(Suresh and Sukumar 2009).Distinct seasonality was also reported from other sites(Patel 1997).Community-wide phenophases show non-random patterns with different phenophases in most seasonal forests(Singh and Singh 1992;Morellato et al.2000).Vegetative phenophases in Mudumalai were more synchronized compared to reproductive phases.Similar patterns were observed in dry forests of Coorg(Patel 1997).But relatively high synchrony was reported with the reproductive phase in Sarawak(Harrison et al.2000).The randomness of reproductive phases has been reported in several studies across the globe(Windsor et al.1989)and is also attributed to the sex of the plant.Some individuals have shown seasonality in their reproductive phase at the community level.There was no seasonality among figs in Panama(Windsor et al.1989).The random nature of fruiting phenophases can be attributed to individual pollination success.However,figs in Mudumalai show significant seasonality but the strength of the seasonality is relatively low.Significant seasonality could have evolved in Mudumalai possibly due to low densities of figs.Strong seasonality in flowering among figs is presumed to have evolved around wasp activity,and with fruiting,around favorable conditions for seed germination.However,sex of individual trees is also a factor in evolution of seasonality(Patel 1997).The fig community is a conglomeration of several species with relatively high synchrony with several phenophases,while there was high asynchrony among the non-fig community.Though synchrony is a species-specific property,rigorous research is urgent to understand fig biology.

AcknowledgementsWe thank the Ministry of Environment and Forests,Government of India for funding CES.We thank Tamilnadu Forest department for permissions.We would like to express our gratitude to forest officials of Mudumalai reserve for their support and cooperation.We thank Mr.C.M.Bharanaiah for his cooperation during field observations.We thank Mr.Mani and Mr.Selva for their help during field work.We thank our field guides Mr.Bomman,Mr.Krishna,Mr.Siddan,Mr.Maran,Mr.Kunmari,Mr.Rajan,Mr.Aloo and Mr.Manban for their help during field observations.We would like to thank our colleagues at the CES field station for their encouragement and support.Finally we thank two referees for their comments on the manuscript.We also thank copy editor for the editorial inputs.

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