Species Distribution and Ecological Niche Modelling of Alnus Species in Nepal
Date
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
Department of Botany
Abstract
lnus (Alder) is important taxa in agroforestry system because of its ability to fix
atmospheric nitrogen. Himalayan alder species such as A. nepalensis and A. nitida are proven
to be very useful in traditional as well as contemporary agroforestry practice. This implies to
the importance of studying biogeographical distribution of these species to identify the
climatical suitable zone. The climatic suitable zone of two species of genus Alnus were
modelled using a subset of least correlated bioclimatic variables for current condition (19502000),
topographic
variables
(DEM
derived)
and
Landuse
Landcover
(LULC)
data.
MaxEnt method was used to predict the suitability of Alnus species based on 79 randomly
distributed points (67 of A. nepalensis and 12 of A. nitida). Four models were produced for
each species in a stepwise combination of variables. The best model was choosen against
random model based on AUC value of Maxent using ANOVA and t-test. The model selected
for further analysis comprises mean AUC value of 0.889 for A. nepalensis and 0.946 for A.
nitida. The environmental variables that best explained the current distribution of the species
were identified and used to project the climatically suitable niche into the future, and identify
the suitable areas for mixed agroforestry. The most favourable conditions for A. nepalensis
were located in Central Nepal in the moist North-West facing slope and degraded hilly region
above Siwalik range from East to West; whereas, that of A. nitida was located in drier SouthEast
facing Western Himalaya along river valley of Nepal. The model reveled that the
Dhaulagiri Range and Annapurna range separates habitat of two Alnus species in Nepal. The
rising mountain slopes in the northern region even acts as barriers for A. nepalensis
distribution. Presence of rough terrain of high Himalaya fragmented the habitat of A. nitida.
The major contribution factor for distribution in Nepal was found to be precipitation of
warmest quarter and precipitation of drier quarter for A. nepalensis and A. nitida respectively.
The model revealed that climatically suitable area occupied for A. nepalensis is ca. 47610
km
2
and A. nitida ca. 14690 km
2
in current scenario. While in the future projection of SRESA1B
scenario
for
2050,
A.
nepalensis
was
found
to
decrease
its
suitability
area
by
ca.
16720
km
2
whereas that of A. nitida decreases by ca. 3405 km
2
. Prediction for SRES-A1B scenario
2050 shows significant loss in area of Alnus species (15.74% for A. nepalensis and 5.38% for
A. nitida) as compared to the suitable area gained ( 7.32% for A. nepalensis and 0.67% for A.
nitida). The unchanged stable areas in Hilly region are probable sites for the introducing
these species in the agroforestry system.