Impacts of Climate Change on Abies spectabilis : an approach integrating a Species Distribution Model (MaxEnt) and a Dynamic Vegetation Model (LPJ-GUESS)

Abstract: Recent global warming trends, particularly in the arctic regions and Himalayas are modifying forest structure and function, notably biogeographical changes in tree species distribution together with alteration in Net Primary Production (NPP), Leaf Area Index (LAI) and Carbon biomass. These alterations are most pronounced in mountain environments, carrying significant impacts on woody species which are more sensitive to temperature changes. This study was done to elucidate the changes in the suitable habitat area, elevation shift, relative coverage, net primary production and carbon biomass for Abies spectabilis in Manaslu conservation area, Nepal. Being a dominant ecotone species in the Nepal Himalayas, Abies spectabilis is likely to bear the significant climate change impact. This study used future climate scenario output from the CCSM4 climate model (RCP 2.6) in two vegetation modeling approaches - the empirical MaxEnt (Maximum entropy) and process-based LPJ-GUESS (Lund-Postdam-Jena General Ecosystem Simulator). Plant occurrence data were collected through published literatures, online source and from the Herbarium records. Environmental driving data were obtained from the Worldclim- Global Climate Data and from the Royal Netherlands Meteorological Institute (KNMI). The findings show that both the models are in excellent agreement with the current distribution of [i]Abies spectabilis[/i], verified by error rate and Cohen's Kappa. The rate of species movement is predicted to be 14 meters per decade (MaxEnt) and 30 meters of altitude per decade (LPJ-GUESS). in terms of suitable habitat area, MaxEnt predicts reduction of 3 % of the suitable area by the year 2050 while LPJ-GUESS predicts the area to be reduced by 20.5 %. In addition, LPJ-GUESS predicts reducing coverage of [i]Abies spectabilis[/i] from the lower-temperate climatic zone (2000-2500 masl) and increasing coverage in lower-alpine climatic zone (4000-4500 masl) in the coming future. The species will respond to climate warming by increasing its Leaf Area Index, Net Primary Production and Carbon biomass. LPJ-GUESS predicts an increase of 64 (gC m-2 yr-1) mean net primary production by the 2050 scenario (corresponding to a 30.18 % increase relative to modelled current NPP values). Carbon biomass will increase by the mean value of 0.33 (KgCm-2) (corresponding to a 19.87 % increase relative to modelled current cmass values). It is found that annual temperature range and precipitation seasonality (MaxEnt) influence the current distribution while in the future, mean temperature of the coldest quarter will shape the geographical distribution of [i]Abies spectabilis[/i].