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Linking Climate Change and Tree Productivity
in Ranomafana National Park, Madagascar
by
Patricia C. Wright, Benjamin Greene. Jessica Scirbona, Paul Rakotonirina, Armand
Razafitsiafajato, Jean de dieu Ramarolahy, and Paul Rasabo, Stony Brook University,
Stony Brook, New York, USA and Centre ValBio, Ranomafana, Madagascar
DRAFT without FIGURES OR TABLES
This paper is prepared for the Conservation International Workshop “Climate Change in
Madagascar-January 28-31, 2008
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SUMMARY
Madagascar has the highest levels of endemism and endangerment for more species than
any other country in the world (Myers et al., 2000, Mittermeier et al., 2006). In Madagascar there
is evidence that even low-level disturbance can have a large impact on forest dynamics and
wildlife populations (Dehgan, 2003, King et al., 2005, Wright, 2006, Irwin, 2006, Arrigo-Nelson,
2006). Madagascar wildlife is closely aligned with natural systems exemplified by a 6 month
hibernation by small mammals and amphibians, and strict seasonal breeding in lemurs and most
wildlife (Wright, 1999, Wright et al., 2005). Many lemur species are on the brink of extinction
(Mittermeier et al., 2006) and these species will be further challenged by changes in climate
(Dunham et al., 2008). In order to better understand the impact of climate on the fauna and flora
of the eastern rainforests of Madagascar, our research team at Ranomafana National Park has
been monitoring daily temperature, daily rainfall, and monthly phenology and fruit production of
over 200 individual trees, as well as lemur demography and feeding behavior. Although our data
shows that mean annual rainfall totals are not changing, our data do suggest an increase in
number of dry season months. In response to these subtle climatic differences are changes in
fruiting patterns in some species of trees. The impact of major worldwide weather phenomena
such as El Nino on fruit productivity has been noted in the Americas and Borneo (Foster, 1982,
Wright et al., 1999. Harrison, et al., 2000, Hughes et al., 2000). As reported in the tree
monitoring study presented here, El Nino and drought years also effects tree productivity in
Madagascar. It has been documented that El Nino events have been increasing in their frequency
in the past decade (Federov and Philander, 2000, Timmermann et al., 1999) . We have
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preliminary data that suggest a decrease in successful reproduction in lemurs during years with
extended dry seasons (King et al., 2005, Wright et al., 2008). We have found that lemur survival
decreases by 65% during El Nino years and our mathematical modeling of lemur populationa
suggest a serious endangerment problem may be just ahead, even within protected areas
(Dunham et al., 2008). The analysis of the daily temperature data over a 20 year period did not
show high temperatures rising or annual temperatures increasing in the rainforest. However
minimum temperatures during the cold season were higher during the past ten years, compared
to the previous decade. Future analysis will establish if this higher minimum temperature has an
effect on tree reproduction. Our long term research points out the importance of monitoring a
wide range of ecosystem changes in conjunction with monitoring rainfall and temperature trends
through time to understand the far-reaching consequences to biodiversity.
INTRODUCTION
Madagascar is home to more endemic families and genera than any other conservation
'hotspot' in the world, and high rates of habitat loss and other anthropogenic disturbances
severely threaten native species (Myers et al., 2000). Over 80% of the forest cover has already
been lost and the populations of many remaining species are small and fragmented (Whitmore,
2000). The government of Madagascar has recently committed to increasing its protected areas
from 1.7 million hectares to 6 million hectares (Goodman & Benstead, 2005).
While there have been much research discussing the effects of habitat loss and hunting
pressures on the viability of wildlife populations (Irwin et al., 2005, Lehman, 2002, Lehman et
al., 2005, Mittermeier et al., 2006), the confounding effects of recent climate change and global
climate cycles such as El Niño Southern Oscillations (ENSO) have rarely been broached
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(Dunham et al., 2008). Given the potential role of human-induced climate change in altering the
frequency of ENSO events (Fedorov & Philander, 2000; Timmermann et al., 1999), there is a
critical need to assess the impact of climate changes on fruiting patterns of the forest trees which
in turn effect the viability of wildlife populations.
The high frequency of ENSO in the last few decades has raised questions about how
human-induced climate change is affecting or will affect the frequency of ENSO (Fedorov &
Philander, 2000; Timmermann et al., 1999). In Madagascar and southern Africa, ENSO events
have been documented to cause drought (Thomson et al., 2003) and vegetation changes (Ingram
& Dawson, 2005) which may negatively affect wildlife (Gould et al., 1999; Wright, 1999). The
prospect of increased ENSO events in Madagascar is daunting given the severity of other
anthropogenic threats to its biodiversity. A recent study showed that the immediate effects of an
ENSO year can decrease lemur populations by 65% (Dunham et al., 2008).
A further indication that climate change is affecting wildlife is shown in two studies of
lemur demography. A demographic study of the Milne Edward’s sifaka (Propithecus edwardsi
Mayor et al., 2004) showed that group sizes are variable, but overall populations may be
diminishing (Pochron and Wright, 2003, Pochron et al., 2004). When the effect of rainfall on
infant survival was examined (King et al., 2005), it was found that climate may have a serious
impact. The results of comparing years with more dry season months to those years with more
equal rainfall showed that infant survival was negatively impacted by the increase in dry months
(Wright, 2006; Wright et al., 2008). This same trend was found in a long term study of
demographics of Eulemur fulvus rufus at Ranoamafana National Park (Overdorff et al., 2008).
In order to isolate the impact of many possible variables that may be affecting these
wildlife populations, such as historic selective logging, predation events or stochastic
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demographic changes (Pochron and Wright, 2003, Karpanty and Wright, 2006, Arrigo-Nelson,
2006), we have examined the effect of daily temperature, monthly rainfall and ENSO years on
the food of the wildlife. By monitoring fruit production of rainforest trees at Ranomafana over
the past 20 years, we can target the impact that weather and climate has on fruiting production
and patterning.
METHODS
At Ranomafana National Park, located at (21 degrees, 16’ 38’’ South, 47 degrees 23’ 50’’
East) we have monitored individual mature trees over a 20 year period. Reproductive status and
new leaf flush have been evaluated monthly for 25 canopy and mid-storey tree species between
1987 and 2007. This first set of 25 species include 15 genera and 17 families. Four examples of
each species were originally chosen in 1987 for a total of 100 trees. In 1997 four individuals
from an additional 25 species were added to the phenology. This increases the monthly
monitored sample to 50 species (200 trees) from more than 26 genera and 19 families. The
families represented by three or more species include Clusiaceae, Myrtaceae, Moraceae,
Sapindaceae, Lauraceae, and Anacardiaceae. Dead trees are replaced with new individuals from
the same species. Originally all trees had a dbh larger than 10cm and mature individuals were
chosen. For the first ten years growth measurements by dbh occurred every five years. For the
past ten years dbh has been measured annually. Tree crowns have been evaluated from the
ground using binoculars by local botanists trained by Missouri Botanical Garden. Reproductive
status was scored on a five-point scale. Sterile trees were scored zero. Trees with from one
reproductive structure to 25% of the crown bearing reproductive structures were scored one.
Trees with 26–50%, 51–75% and 76–100% of the crown bearing reproductive structures were
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scored two, three and four, respectively. These data are useful for comparing fruiting and
flowering patterns to rainfall and temperature changes over this time period. These data have
recently been entered into an excel spreadsheet for analysis.
During the first sixteen years of this study (1987-2003), daily rainfall amounts were
measured using a standard rainfall cylinder in metric units, placed in an open area near the
research cabin inside the park. In 2003 a rainfall cylinder was placed in an open area next to the
Centre ValBio, about a kilometer northeast of the original research cabin. A maximum-minimum
thermometer with temperature measured in Centigrade units was placed under the canopy inside
the forest near the research cabin from 1987-2003. One individual is responsible for collecting
the rainfall and temperature data at 6am each morning. These data are entered into the computer
each week.
RESULTS
Annual rainfall amounts over the twenty year period varied from a low of 1,794mm in
1997 to over 4000mm in 1996. On average 3,000mm of rain a year fell at Ranomafana National
Park from 1987-2007, This rainfall mean is comparable to the national weather station mean of
Ranomena and Ranomafanana rainfall from 1960-1980. However, there is a difference in
pattern, when the variability of the rainfall each month is examined. Compared to the previous
decades, the years 1987-2007 had more rain in the rainy season and more months that contained
less than 100mm rain. Between 1960 and 1985 90% of the years had 11 or 12 “wet” months of
more than 100mm of rain, while from 1986-2007 60% of the years had months with more than
100mm of rain.
The monitoring of the fruit production of the trees showed that individual fruiting of trees
was highly variable with less than a quarter of the trees monitored producing fruit each year.
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Comparing the decade 1987-1996 to the decade 1997-2007 the fruit productivity drops from a
mean of 25% to a mean of 9% of the trees giving fruit. Although fruits are available all year, the
months from April to August show little fruiting and are limited to two or three fruiting species
each month during this period. Some trees do not fruit the year after ENSO years,. These
preliminary results show a huge decrease in fruit production over the past decade at Ranomafana
and this decrease in food availability could result in a negative impact on wildlife populations.
DISCUSSION
Conservation of the wildlife of Madagascar has been a target of the government of
Madagascar and conservationists for the past fifteen years (Myers et al., 1987, Myers et al.,
2000, Mittermeier et al., 2005). The rampant deforestation of from 1.7-4.7% of the remaining
forests of Madagascar, as well as hunting for food by humans, have been major factors
threatening biodiversity (Irwin et al., 2000, 2005, Lehman, 2002, Achard, 2002). Although
reports on the negative affects of drought on lemur populations in the dry south of Madagascar
have been published (Jolly et al., 2002, Gould, 1999), there have been no countrywide
examination of whether and how climate change is affecting the biodiversity. By examining
twenty consecutive years of records of populations of lemurs, tropical trees, rainfall and
temperatures at one site (Ranomafana National Park), we begin an attempt to understand the
dynamics between climate change and biodiversity in the eastern rainforests of Madagascar.
Although there are shorter (2-6 year) databases collecting flowering and fruiting activity
on Malagasy trees from the western dry forests of Kirindy Forest (near Morandava) and Beza
Mahafaly (south of Tulear), the Ranomafana Tree Phenology project is the only database that has
monitored individual trees over a twenty year period in Madagascar. Simultaneously we have
collected daily rainfall and maximum-minimum temperatures for this same twenty year period.
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Our preliminary analyses of these long term databases from Ranomafana National Park show
that climate and adult forest tree productivity may be closely linked.
The accumulated data from Ranomafana suggests that changing global weather cycles
may compound with deforestation and hunting to speed the threat to wildlife populations. We
now know that the average fecundity of lemurs is over 65% lower during El Niño years
(Dunham et al., 2008). In addition there is more lemur infant mortality during years with an
extended dry season (King et al., 2005, Wright, 2006, Wright et al., 2008). The analysis
presented in this paper shows that fruit productivity in this forest has diminished by half in the
last decade. The fact that this lower fruit crop can be linked with years with more dry season
months, may indicate that climate change is a partial cause for this decrease.
In addition, temperature increases may also have a negative effect on fruit productivity
and cryptic forest dynamics that may impact negatively on wildlife survival. Recent evidence
from Costa Rica suggests that in years with higher minimum temperatures, increases in
circumference of rainforest trees stops (Clark and Clark, in press). If an increase in minimum
temperatures also arrests tree growth in Madagascar rainforest and this is coupled with lack of
reproductive activity in these forest trees, this trend could have a major impact in the long term
fitness of the endangered species that rely on these trees for food.
Phenological databases of the span and completeness of this Ranomafana dataset are rare
in the tropics. Joseph Wright on Barro Colorado Island, David and Deborah Clark in Costa Rica,
Tim O’Brien in Indonesia and Colin Chapman in Kibale Forest in Uganda have comparable
datasets over this time period (see Chapman et al., 2005a, b; Clark, 2007; Wright et al. 1999). It
is important to take a comparative approach to understanding the effects of climate on tropical
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trees worldwide. We then need to look at the impact on endangered populations of wildlife and
develop effective management strategies.
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ACKNOWLEDGEMENTS
In Madagascar we would like to thank the National Association for the
Management of Protected Areas (ANGAP), Department of Water and Forests, and
the Ministry of the Environment, Water and Forests and the CAFF/CORE
committee for authorization to do this research. Many thanks to B. Andriamihaja
and A. Feistner and staffs of MICET, Centre ValBio, and ICTE for logistical help.
Funding for the long-term monitoring was provided from the David and Lucile
Packard Foundation, Douroucouli Foundation, the Wenner-Gren Foundation, the
John D. and Catherine T. MacArthur Foundation, National Geographic Society,
National Science Foundation, Earthwatch Institute, and Stony Brook University.
The late Georges Rakotonirina and Michael Todd are acknowledged for setting up
the phenology tree system in 1987. Both G. Rakotonirina and William
Rakotonirina took data for the first decade. Tiana Razafindratsita and Aimee are
gratefully acknowled for collecting much of the first ten years of climate data.
Jukka Jernvall graciously assisted with data analysis. Our appreciation to Lee
Hannah from Conservation International for inviting us to share our data for the
Climate Change Workshop held in Madagascar January 28-31.
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