Detrimental effects of low atmospheric humidity and
forest fire on a community of western Himalayan butterflies
Peter Smetacek
The
Butterfly Research Centre, The Retreat, Jones Estate, Bhimtal, Nainital,
Uttarakhand 263136, India
Email:petersmetacek@rediffmail.com
Date
of publication (online): 26 April 2011
Date
of publication (print): 26 April 2011
ISSN
0974-7907 (online) | 0974-7893 (print)
Editor: George Mathew
Manuscript
details:
Ms # o2307
Received 07 September 2009
Final received 02 January 2011
Finally accepted 10 March 2011
Citation: Smetacek, P.
(2011). Detrimental effects of low atmospheric humidity and forest fire on a
community of western Himalayan butterflies. Journal of
Threatened Taxa 3(4): 1694–1701.
Copyright: © Peter
Smetacek 2011. Creative Commons Attribution 3.0 Unported License. JoTT allows
unrestricted use of this article in any medium for non-profit purposes,
reproduction and distribution by providing adequate credit to the authors and
the source of publication.
Author Details: Peter Smetacek runs the Butterfly
Research Centre in Bhimtal, Uttarakhand. He has worked on Lepidoptera for more
than 30 years and has published 50 scientific papers. He is the first Indian to
discover and describe a butterfly taxon, Neptis miah varshneyi. He has described a dozen moths
and butterflies new to science.
Acknowledgements: I am grateful
to the Rufford Small Grant Foundation, U.K. for funding this work; to Ashok K.
Nayak of the Directorate of Coldwater Fisheries Research, Bhimtal for rainfall
data and to the anonymous referees whose comments considerably improved this
paper.
Abstract:Compared to previous years, the period from October 2008 to
March 2009 showed marked reductions in species number and population size in
the butterfly community of the Maheshkhan Reserve Forest, Nainital District,
Uttarakhand. Desiccation of pupae
due to abnormally low atmospheric humidity after the failure of seasonal rains
appears to have been a major cause of this reduction. The drop in humidity also appears to be linked to the
unusual spread of fires affecting broadleaf forests, one of which in May 2009
wiped out the remaining Maheshkhan butterfly community.
Keywords:Climate change, forest fire, Himalaya, Kumaon, Lepidoptera,
pupal desiccation.
For images, tables -- click here
Introduction
The
Kumaon Himalaya adjoin the western border of Nepal, and along with the Garhwal
Himalaya further west comprise the Indian state of Uttarakhand. In Nainital District of the Kumaon
Himalaya the Gagar range is southernmost, rising from the Gangetic plain at
roughly 400m elevation to Naini Peak near the town of Nainital at an elevation
of 2600m. Rainfall is heavy,
between 2029mm and 3048mm (80 to 120 inches) annually (Osmaston 1927) with 80%
of the precipitation received during the south west monsoon between June and
September, while 20% arrives during the remainder of the year, mostly during a
fortnight of winter rains in January or February.
Maheshkhan
Reserve Forest (roughly at 29026’7”N & 79035’40”E)
lies west of the town of Bhowali, extending from the crest of the Gagar range
and Gagar Peak (2400m) to the village of Shyamkhet (roughly 1800m). The forest comprises of a mix of Chir
Pine (Pinus
roxburghii) and dense subtropical evergreen
forests of Himalayan oaks (Quercus
floribunda, Q. leucotrichophoraand Q.
glauca) and other species (Alnus nepalensis, Rhododendron arboreum, Pieris ovalifolia,
etc.). This forest is the
headwaters of the Khalsa River, which is a perennial rain-fed tributary of the
Gola River.
Besides
many butterfly species, the forest is home to mammals such as Sambar and
muntjacs, leopards, common langurs, yellow-throated martens, with occasional
reports of Himalayan Black Bear.
The
Maheshkhan forest has been visited sporadically during the spring and summer
months since 1986. During the 24
years, the forest was visited more than 100 times during the summer months from
March to June. During the summer
months, there are often swarms of butterflies in the ravines and along streams
of this forest. As soon as the
south west monsoon reaches and the rainy season begins in June, the butterflies
stop congregating at water. Evidence from my breeding experiments indicates that there are broods of
most species during the rainy season, but not as numerous as the spring and
summer broods. The individuals
comprising these broods do not congregate at water and are not as frequently
seen as the dry season spring and summer broods.
Weather
parameters, particularly atmospheric humidity, are known to have a decisive
effect on biodiversity. This is
usually amply illustrated with the textbook comparison of faunal diversity of
hot deserts on one hand, with tropical rainforest communities on the other. Butterflies, too, occur in greater
variety and profusion in areas of heavy rainfall as compared with low rainfall
areas. For example within India
the northeastern states are home to over a thousand species of butterflies,
compared to the plains of Uttar Pradesh with less than a hundred, or the Thar
Desert with less than 50 species (Peile 1937). While the effect of humidity on such extensive landscapes is
well known, relatively little is known about factors that limit the abundance
and distribution of butterfly species within smaller landscapes, such as
hillsides or forests. In this
study, an attempt is made to evaluate the effect of reduced atmospheric
humidity on butterfly populations in the Maheshkhan Reserve Forest in the
Kumaon Himalaya.
Materials
and Methods
Data
pertaining to butterfly population trends in this forest area has been
generated through observations made during past visits since 1986. During 2009, a rigorous survey was made
for 65 days during March to May. The forest was surveyed from 1000 to 1400 hr, after which butterfly
activity is greatly reduced. Since dawn and dusk is the period of activity for
most Grypocera (Hesperiidae), these are not included in this paper, although a
few species were observed during the daytime.
Observations
The
observations were mainly made during the summer months from April to June when
butterflies congregate in the ravines and along streams of this forest and are
consequently easily observed. Certain species like Lasiommata
schakra (Kollar) do not visit water, but these
butterflies were encountered along paths and elsewhere in the forest. Also, not much attention was paid to
groups such as YphthimaHübner; MycalesisHübner; EuremaHübner, etc. A single specimen of
the recently described taxon Ypthima
kedarnathensis Singh was recorded in Maheshkhan
(Smetacek 2010). A list of
butterfly species observed in Maheshkhan Reserve Forest since 1989 is given in
Table 1. However, Y. kedarnathensishas not been included in Table 1 pending confirmation of its taxonomic status.
In
2009, the winter rains failed (Table 2), with practically no precipitation
between the end of September 2008 and April 2009, resulting in a rather dry
spring and summer 2009. Although
there were very meager rains during the winter of 1998–1999, due to which
some annuals did not germinate the following spring causing a drop in numbers
of a butterfly species dependent on them (Smetacek 2002), the effects on
butterfly populations then were by no means so widespread or as severe as
experienced during spring and summer 2009 due, evidently, to the failed winter
rains. The State Government
officially declared the district to be affected by drought in 2009.
I
had the good fortune to visit the forest rather frequently in spring and summer
2009, due to which it was possible to track the presence or absence of the
butterfly species that make up the community there. As the season progressed, it became evident that the reduced
number of species and butterflies was not solely a matter of delayed emergence
caused by the lack of sufficient atmospheric humidity, but a matter of
desiccated pupae resulting in the death of butterflies before they could
emerge. This became evident when
all the overwintering pupae I had bred the previous autumn dried out and died
by April 2009. Even pupae formed by larvae in April 2009, which should have
emerged the following month, dried out and died. Upon opening the pupae, I found fully developed but
desiccated moths that had not managed to emerge (Unfortunately, it was not
possible to identify them since the wings had not expanded). Only a single overwintering Hyles nicaea lathyrus(Walker) (Lepidoptera: Sphingidae) pupa from the cold desert of Ladakh survived
to emerge on 19 May. No doubt,
being a xerophytic species, it found nothing unusual in the dryness of spring
and summer.
The
Chir Pine forest patches in the Reserve Forest burnt twice in 2009: once in
April, when the humus of the previous year burnt and again a fortnight later in
May, when the trees shed their resinous needles. In one major fire in May, even
the broadleaf forest burnt over most of the area, after which butterfly
populations dropped almost to zero and I discontinued observations. The fact that forest fires in broadleaf
forests resulted in an almost total decimation of the butterfly population,
while regular annual fires in Chir Pine forests in the adjoining areas do not
greatly affect butterfly populations, strongly suggests that the butterfly
populations concerned do not depend on Chir Pine forest for survival. Once broadleaf forests begin to burn,
the effect on insect biodiversity is devastating.
Discussion
The
Maheshkhan Reserve Forest has changed little during the more than two decades
it has been studied. Cattle, which
were frequently met during the 1990s, are now absent but local women lopping
broadleaf trees for cattle fodder are met more frequently than 20 years
ago. On the whole it is a well
preserved forest, and with perennial streams rising in some of the ravines
presents a most interesting case study for what a forest should be like in
order to regulate the water regime of perennial rain fed springs and streams in
this area. Over the years a total
of 95 butterfly species have been identified with certainty from this forest.
Many are common and some which are reportedly rare or even very rare in other
parts of their range, such as Neptis
narayana and Euaspa ziha(Evans 1932) are common.
The
only thing that changed in 2009 compared with earlier years was that the winter
rains failed, although Maheshkhan got a sprinkling of snow on 12 February 2009
(Image 1). This was evidently not
enough to offset the dryness experienced during March to May, which caused the
State Government to declare a state of drought in the district in May. On the basis of the fact that all the
pupae from different areas in Nainital district that I had overwintering
indoors dried out in Bhimtal, roughly 20km away, it is reasonable to assign a
similar reason to the failure of the spring and summer broods of 50 species
comprising 52.6% of the total species recorded from this forest.
The
most conspicuous absence was of Delias sanaca,
which is extremely common every summer. To give an idea of the numbers
involved, I discovered many dead butterflies in a small stream in the forest on
04 June 1998, presumably poisoned by pesticides infiltrating into the water
from apple orchards on the other side of the hill. The figures of dead individuals from my notes are: Delias sanaca200+; Aporia
agathon 200+. There were still many more individuals of both species
flying about on that and subsequent days. While D. sanacapresumably feeds on members of the parasitic Loranthaceae in the larval stage, A. agathonhas been recorded on Berberis
chitra in the area. In the summer of 2009, there were some A. agathonabout, but very many fewer individuals than was usually the case. Both these species appear to be
univoltine in the area. The eggs
of A.
agathon are laid in batches of up to a
hundred. Two batches of these eggs
located on leaves of Berberis
chitra in May 2009 and left in situfailed to hatch out, presumably due to desiccation. One could therefore predict that there would be a reduced
number of A.
agathon about in the spring and summer of
2010.
The
Neptini were another interesting discovery. For more than 20 years, I have observed the following
species regularly in the forest. N. narayanais usually common, as common as N. sankara. N. anantausually is about in fewer numbers. To give an idea of numbers, one might see
around 20 N.
narayana every day for a few weeks in May and
June; roughly the same number of N. sankaraand perhaps three to four individuals of N. ananta a
day during the same period. While the larval host plants of N. narayana, N. sankara, N. anantaand N.
mahindra in the area are unknown, N. somafeeds on Celtis
australis (Wynter-Blyth 1957 as N. yerburyi). Normally this group is found in hilly
regions with moderate to heavy rainfall, attaining their greatest diversity in
the wetter part of North Eastern India and Indo-China. Their nearly complete absence during
2009 strongly suggests that their overwintering stages are susceptible to
desiccation, which is probably a major factor restricting their range to wetter
regions.
Of
the butterflies that managed to maintain their population levels in 2009, Dodona dipoeaand D. eugenesare noteworthy, since their allies, D. durgaand D.
ouida seem to have suffered. The former two,
although bred on bamboo in the Mussoorie area in Garhwal (Mackinnon & de
Nicéville 1897–1898), have only been bred on the plant Myrsine semiserratain this area (mihi). This plant grows in damp, shady
ravines, where the larvae were apparently not only preserved from desiccation
but also from forest fires.
The
Troidini are of interest, since 2009 marked the re-appearance in Maheshkhan of Byasa polyeuctesafter a gap of nearly 20 years. Byasa dasaradaand Atrophaneura aidoneuswere about in the usual numbers. The absence of Troides
aeacus from Maheshkhan Reserve Forest is
noteworthy, since it feeds on the same species of Aristolochiaas the other Troidini mentioned above (mihi). It was seen on the northern face of the
range during the 1970s and is common in pockets in other parts of the Gagar
range.
The
Lycaenidae as a whole appear to have suffered greatly. The Hairstreaks, comprising ChrysozephyrusShirozu & Yamamoto and EuaspaMoore in this area, were almost wiped out, as were PratapaMoore and TajuriaMoore. Horaga onyx,
which feeds on Coriaria
nepanensis, a common plant in the area, was
about, for I saw and photographed one of them and there were doubtless others
of this elusive species about.
Panchala ganesaswarms by the hundred in ravines during May and June. It was about in greatly reduced numbers in 2009. Arhopala dodoneaand A.
rama, which are on the wing throughout the
year lower down at 1500m elevation, were about in their usual numbers. All these three species have been bred
on Oak Quercus
leucotrichophora in neighbouring Garhwal (Wynter-Blyth
1957) and this is presumably their hostplant in the area. Since A. dodoneaand A. ramaappear to have a brood during the winter months at 1500m elevation, it is
likely that they have a brood later than P. ganesain Maheshkhan, too, although one would not expect them to have a winter brood
in Maheshkhan considering that it snows there every year in winter.
The
other butterflies that feed on Quercus leucotrichophorain the larval stage, Dophla patalaand Sephisa
dichroa, failed to appear in 2009. Since the trees were healthy and only
deviated from normal in shedding their leaves in May, which is a month later
than usual, it is assumed that the pupae of both these Nymphalids suffered due
to desiccation.
For
the remaining species, not enough is known about their early stages to
understand their presence or absence during the summer of 2009. It is apparent, though, that sustained
low atmospheric humidity levels are capable of drastically altering the
composition of a butterfly community in high humidity areas.
The
observations noted above strongly suggest that butterflies such as the Neptini,
some DeliasHübner and AporiaHübner species, etc, require a certain minimum level of atmospheric humidity to
survive. If this falls below a
certain level for a sufficient length of time, as during the winter of
2008-2009 (Table 2), the species can be exterminated from an area, despite the
continued presence of their larval host plants.
The
observations noted above draw attention to the importance of humidity levels
for butterfly communities. As with
the example of a chain, which is as strong as its weakest link, many butterfly
species appear to require a certain minimum amount of atmospheric humidity
throughout the year in order to survive in an area. A dry spell of even a few months can wipe out populations in
an area, even if the dry spell falls during a period when most butterflies are
in their pupae, which is usually considered the stage least susceptible to
desiccation.
Even
more drastic than low atmospheric humidity levels is the effect of forest fires
in Himalayan broadleaf forests. Chir pine patches and forests in the area burn almost every year without
any major effect on the butterfly community. In 2009, for the first time, I saw broadleaf forest in the
area burn: the effect was immediate and drastic, for the butterfly population
was practically wiped out within the week.
Conclusion
Desiccation
during the early stages is evidently one of the major factors preventing many
butterfly species from colonising what would otherwise appear to be suitable
habitat. Such species evidently
require a minimum amount of atmospheric humidity throughout the year. If this requirement is not met, entire
broods fail to emerge and a population can be wiped out. Atmospheric humidity
levels are probably a major factor responsible for the restricted distribution of
some butterflies that feed on widespread plants during the larval stage. Forest fires in Himalayan broadleaf
forests are extremely destructive to butterfly communities in the area and are
probably the most potent threat to butterfly communities in the short
term. In the long term, habitat
destruction is probably the most serious threat, since this results in the
extinction of butterfly communities from an area.
References
Anonymous (2010). Hydromet
Division.India Metereological Department. http://www.imd.gov.in/section/hydro/distrainfall/webrain/uttarakhand/nainital.txt.
Accessed on 30 October 2010.
Evans, W.H. (1932). The Identification of Indian
Butterflies. 2nd Edition. Bombay
Natural History Society, Bombay, 454pp+ 32pl.
Mackinnon P.W. & L. de
Nicéville (1897-1898). Butterflies from Mussoorie and the Dun
Valley. Journal
of the Bombay Natural History Society11: 205–221; 368–389; 585–623.
Osmaston, A.E. (1927). A
Forest Flora for Kumaon. Government Press, Allahabad, 34+605pp.
Peile, H.D. (1937). A
guide to collecting butterflies of India. Staples, London, 14+312pp+25pls.
Smetacek, P. (2002).The genus PontiaFab. (Lep.: Pier.) in the Kumaon Himalaya. Journal of the Bombay Natural History Society 99
: 224–231.
Smetacek, P. (2010). Ypthima kedarnathensisA.P. Singh (Lepidoptera: Nymphalidae: Satyrinae) from the Kumaon Himalaya. Journal of Threatened Taxa2(13): 1390–1391.
Wynter-Blyth, M.A. (1957). Butterflies of the Indian Region. Bombay
Natural History Society, Bombay, xx +523+72pls.