12

The Himalayas are one of the largest 
mountain ranges in the word having 
distinctive landscapes, ecosystems, 

climatic variation, and geological features (Olson 
and Dinerstein, 2002). These mountains are one 
of the most sensitive and fragile ecosystems to 
climate change impacts (Shrestha et al., 2012). 
The regional climate of this mountain range is 
dominated by the Indian summer monsoon that 
extends from June to September and the western 
disturbance from December to March (Cannon 
et al., 2015). The eastern part of the region is 
mainly affected by the summer monsoon which 
arrives from the Bay of Bengal. The intensity of 
the summer monsoon decreases from the east 
to the west (Lang and Barros, 2004). On the 
other hand, the western part receives most of the 

rainfall in the winter because of the westerlies, 
which brings moisture from the Arabian, 
Mediterranean, and Caspian Seas (Ahmed et 
al., 2011). The availability of moisture greatly 
decreases from the east to the west because of this 
atmospheric circulation. These climatic patterns 
and availability of moisture affect the growth and 
distribution of the plant species in the region of 
the Himalayas (Sharma and Gupta, 1997). 

We can use dendrochronological tools to 
understand the most limiting climatic factor for 
the growth of the species (Speer, 2010). Several 
studies have been done in the Himalayas to 
relate the growth of plants and climate (Dawadi 
et al., 2013; Aryal et al. 2018; Khan et al., 
2018; Shah et al., 2018; Bhandari et al., 2019). 

Growth-climate relationship of Pinus wallichiana 
in three different parts of the Himalayas

S. Bhandari1* and J. H. Speer1

1. Department of Earth and Environmental System, Indiana State University, Terre Haute, Indiana, United States of America.
* E-mail: Sbhandari2@sycamores.indstate.edu

We have used six tree-ring width chronologies of Pinus wallichiana from the Himalayan 
region, which are available in the International Tree-Ring Data Bank (ITRDB), to 
determine their growth trends through time and the growth-climate relationship. 
Each of the chronologies downloaded from the ITRDB was detrended using an 
Age-dependent Cubic Smoothing Spline with a 20-year starting spline stiffness in 
the RCSigfree Software Program. We broke the six chronologies into three regions 
based on natural breaks between the sample sites. Altogether, three composite 
chronologies were made, one each from Bhutan, Nepal, and Pakistan. The average 
value for common periods was taken from each of those two chronologies to make a 
composite chronology. Across the three regions, the growth was lowest in the 1810s 
and has increased since 1980s. The growth showed a significant positive response 
to the winter temperature (November-February) in the eastern Himalayas in Bhutan. 
The chronology from Nepal showed that the growth of this species had a significant 
positive response to the self-calibrated Palmer Drought Severity Index of the previous 
year’s December and the current year’s January and March. In the western Himalayas 
of Pakistan, the growth of the same species is positively correlated to the annual self-
calibrated Palmer Drought Severity Index. Winter temperature limits the growth of this 
species in the eastern Himalayas where there is enough moisture whereas the growth 
of this species is primarily limited by moisture in the western Himalayas. 

Keywords: Drought, Moisture, Pinus wallichiana, Temperature, Tree-ring

Banko Janakari, Vol 30 No. 1, 2020 Pp 12‒20 https://doi.org/10.3126/banko.v30i1.29177 



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Pinus wallichiana, one of the native plant 
species to the Himalayas, has been frequently 
used in dendroclimatic studies (Yadav and 
Bhattacharyya, 1997; Cook et al., 2003; Cook et 
al., 2010; Asad et al., 2017; Gaire et al., 2019). 
This species, commonly known as Blue pine, is 
a large evergreen conifer distributed across the 
Himalayas, spanning from northeast Pakistan 
to Yunnan in southwest China (Devkota, 2013). 
This species usually prefers to grow on deep 
moist soils, in pure as well as mixed stands with 
Cedrus deodara, Picea smithiana, Abies pindrow 
and Quercus sps. At the higher altitude above 
3,000 m, it is associated with birch and juniper 
(Yadav and Bhattacharyya, 1997). Generally, 
pine trees are sensitive to moisture, and have 
strong common signals compared to other species 
(Thapa et al., 2017). In this research, we have 
used six tree-ring chronologies of P. walllichiana 
from the Himalayas region, which are available in 
the International Tree-Ring Data Bank (ITRDB) 
to understand its growth trends and its climate 
response across the Himalayas.

Materials and methods 
Chronology development

The International Tree-Ring Data Bank holds 
six chronologies of P. wallichiana with two 
from Bhutan, two from Nepal, and two from 
Pakistan (Table 1). Each of these chronologies 
were downloaded from the International Tree-

Ring Data Bank and detrended using an Age-
dependent Cubic Smoothing Spline with a 20-
year starting spline stiffness followed by signal 
free standardization in the RC Sigfree Software 
Program (Melvin and Briffa, 2008). This 
detrending method retains the most low-frequency 
variability in the chronology while reducing 
the effects from juvenile growth (Melvin et al., 
2007). The average value for common periods 
was taken from each of those two chronologies 
in each region to make a composite chronology. 
Altogether, three composite chronologies were 
made, one each from Bhutan, Nepal and Pakistan. 

Growth-climate relationship

Temperature (1901−2017, CRU TS 4.02), 
precipitation (1901−2017, CRU TS 4.02), and 
the self-calibrating Palmer Drought Severity 
Index, scPDSI (1901−2016) Global 3.25 (Van 
Der Schrier et al., 2013) were taken from KNMI 
Climate Explorer (Trouet and Oldenborgh, 
2013). These climatic parameters were correlated 
with each of the chronologies in the TREECLIM 
package in R (Zang and Biondi, 2015) to find 
the growth-climate relationship. The growth-
climate relationship identifies the most limiting 
factor for the growth of the trees. Spatial 
correlation was carried out between each of the 
tree-ring chronologies and climate parameters 
in the KNMI Climate Explorer (Trouet and 
Oldenborgh, 2013). 

Table 1: Brief description of Pinus wallichiana's chronologies in ITRDB

Sample location Principal Investigators Sample 
duration Latitude Longitude

Nangay, Bhutan Edward Cook, Paul J Krusic and Dorji 
Dukpa (Cook et al., 2010) 1625−2003 AD 27.4 90.7

Pembu, Bhutan Edward Cook, Paul J Krusic and Dorji 
Dukpa (Cook et al., 2010) 1741−2005 AD 27.2 89.3

Bhratang, Nepal Edward Cook, Paul J Krusic, and 
Philip D. Jones (Cook et al., 2003) 1796−1994 AD 28.4 84.1

Alubari, Nepal Edward Cook and Paul J Krusic, and 
Philip D. Jones (Cook et al., 2003) 1803−1993 AD 28.4 83.4

Astore-Rama, 
Pakistan

Edward Cook, Jonathan Palmer 
and Moinnudin Ahmed (PAGES 2k 
Consortium, 2013)

1317−2005 AD 35.3 74.8

Mushkin, 
Pakistan

Edward Cook, Jonathan Palmer 
and Moinnudin Ahmed (PAGES 2k 
Consortium, 2013)

1730−2007 AD 35.5 74.7



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Results and discussion

We have constructed three composite chronologies 
one each from Bhutan, Nepal and Pakistan. 
Our composite P. wallichiana chronology from 
Bhutan in the eastern Himalayas spans over 
263 years- from 1741 to 2003 AD based on the 
common period between the chronologies (Figure 
1a). This chronology showed a sharp decline in 
the growth of this species in the early 1800s while 
the growth was higher during 1750−1800 AD, 
1930−1960 AD and 1975−2003 AD. The growth 
of this species in Bhutan showed a significant 
positive correlation with winter temperature 
(Figure 2). The spatial correlation between the 
ring-width and CRU temperature also indicates a 
strong correlation with winter temperature in the 
eastern Himalayas (Figure 3).

Figure 1: (a) A 263-year (1741−2003) long 
chronology of P. wallichiana from Bhutan

Figure 1: (b) A 191-year (1803−1993) long 
chronology of P. wallichiana from Nepal, and 
(c) A 276-year (1730−2005) long chronology of 
P. wallichiana from Pakistan

Figure 2: Correlation between the tree-ring width of P. wallichiana from Bhutan and CRU 
temperature



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Bhandari & Speer

Figure 3: Spatial correlation between the tree-ring width of P. wallichiana from Bhutan and 
November-February average CRU TS4.02 temperatures during 1902−2003 (p<0.1%)

Similarly, a 191-year (1803−1993) long 
chronology of P. walllichiana was made from 
Nepal in the central Himalayas (Figure 1b ). 
This chronology showed that the growth of this 
species was suppressed in the early 19th century 
and the growth has increased since the 1980s. 
The tree-ring chronology of P. wallichiana from 
the central Nepal Himalayas showed a positive 

correlation with the scPDSI of December of 
the previous year and January and March of 
the current year (Figure 4). This indicates that 
winter moisture limits the growth of this species 
in the central Himalayas of Nepal. Interestingly, 
the chronology of this species showed low 
spatial correlation with the scPDSI in the central 
Himalayas of Nepal (Figure 5). 

Figure 4: Correlation between the ring-width chronology of P. wallichiana from Nepal and CRU 
scPDSI



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Figure 5: Spatial correlation between tree-ring width of P. wallichiana from Nepal and December−
January average CRU scPDSI 3.26e during 1901−1993 (p<0.1%)

We also developed a 276-year long chronology 
of P. wallichiana from Pakistan (Figure 1c). The 
growth was suppressed in the 19th century while 
it was above average in the 20th century. This 
chronology was found to positively correlated 
with annual scPDSI (Figure 6) indicating that 

moisture availability affects the growth in western 
Himalayas of Pakistan. The spatial correlation 
between ring-width of the same species from 
Pakistan and January−June average CRU scPDSI 
showed a strong drought signal in the western 
Himalayas (Figure 7). 

Figure 6: Correlation between a tree-ring width chronology of P. wallichiana from Pakistan and 
CRU scPDSI



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Figure 7: Spatial correlation between tree-ring width of P. wallichiana from Pakistan and January−
June average CRU scPDSI 3.26e during 1901−2005 (p<0.1%)

All three chronologies of P. wallichiana from 
three different parts of the Himalayas showed 
a sharp decline in growth in the 1810s. This 
coincides with the eruption of an unidentified 
volcano in 1809 (Cole-Dai et al., 1997) and 
that of Mt. Tombara (Indonesia) in 1815. The 
decline in growth in this period might be because 
of extreme climate triggered by the explosion 
of these volcanoes. These eruptions may have 
caused the Asian monsoon failure for a few years 
after the events (Anchukaitis et al., 2010) and may 
have reduced moisture availability. The growth 
of conifer and Himalayan birch from the central 
Himalayas, Nepal (Thapa et al., 2017; Gaire et 
al., 2019; Liang et al., 2019), Tsuga dumosa from 
eastern Himalayas (Borgaonkar et al., 2018) and 
junipers from western central Asia (Esper et al., 
2002) were also suppressed in the 1810s. The 
growth of this species is above average in the 
last decades of the 20th century. Several studies 
(Esper et al., 2002; Asad et al., 2017; Bhandari et 
al., 2019; Gaire et al., 2019) from the Himalayan 
region have also shown increased growth of 
different conifer species in the last decade of 20th 
century. The growth-climate relationship showed 
that winter temperature limits the growth of this 

species in the eastern Himalayas of Bhutan. The 
positive relation between tree-rings and winter 
temperatures may indicate that in the good 
winter months this species might experience 
photosynthesis and store carbohydrates for the 
subsequent growing season. The P. wallichiana 
trees of the central Himalayas in Nepal showed 
a positive correlation with winter moisture. In 
the winter season, the amount of rainfall is low 
in the region, which finally could not provide 
enough moisture for the growth of trees. Recently 
published articles (Sigdel et al., 2018a; Thapa 
and St. George, 2019) also indicated that the 
growth of pine in Nepal is limited by winter 
moisture. Precipitation in the form of snow or 
rainfall during the winter is an important source 
of moisture for plants during the following season 
(Borgaonkar et al., 2018). The ring-width of this 
species showed a strong positive correlation with 
the annual scPDSI in the western Himalayas of 
Pakistan. The total annual rainfall decreases 
from eastern to western Himalayas, causing the 
western part to have a moisture deficit (Cannon et 
al., 2015) which limits the growth of the species 
(Sharma and Gupta, 1997). In the dry and semi 
dry areas of the Himalayas, high moisture and 



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cool temperature could be helpful for the growth 
of this species (Treydte et al., 2006; Sigdel et al., 
2018b; Gaire et al., 2019).

Conclusion

The growth of P. wallichiana was sharply 
suppressed in the 1810s, and was increased in 
the late 20th century in the three different regions 
of the Himalayas. The sharp suppression of 
growth in the 1810s coincided with two volcanic 
eruptions. The growth of this species showed a 
winter temperature signal in the moist region of 
the eastern Himalayas in Bhutan and a drought 
signal in the dry to semi dry region of the western 
Himalayas. This species has a great potential 
for the study of both temperature and drought in 
the Himalayas. We will be able to have a better 
understanding of the growth-climate relations of 
this species in the Himalayan region if we can 
gather more chronologies from this species and 
collect the remnants from this species to extend 
its chronologies further back in time.

Acknowledgements

The first author is grateful to the Department of 
Earth and Environmental System, Indiana State 
University for providing a graduate teaching 
assistantship. We are thankful to Dr. Edward 
Cook, PAGES 2k Consortium, and their entire 
team for sharing their P. wallichiana chronologies 
to the International Tree-Ring Data Bank.

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