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Vol. 23 No. 4 - October 2017

Shift in plant species distribution and regeneration potential

due to global warming and climate change in Himalayan region

 By:Ashish Kr. Mishra and Rana Pratap Singh*

The geographic ranges of most plant and animal species are limited by climatic factors, including temperature, precipitation, soil moisture, humidity, and wind. Any shift in the magnitude or variability of these factors in a given location will impact the organisms living there. Species sensitive to temperature may respond to a warmer climate by moving to cooler locations at higher latitudes or elevations. Himalayan forests having unique climatic conditions support unique vegetation types. The plants are strongly adapted to the narrow range of altitude for the specific habitats as a marginal shift in altitude may change the climatic condition significantly. Himalaya generates different conditions, to support unique and isolated ecosystems along the altitudinal rise. The Himalayan forests are considered as a biodiversity hub which provides an excellent opportunity to investigate the climatic effects on plant distribution. Though the response of global warming has been widely studied on the Himalayan vegetation shift, it is difficult to predict how concurrent changes in climatic factors affect the species distribution. Despite the uncertainties, ecological models predict that the distribution of world biomes will shift as a result of the climate changes associated with increased greenhouse gases in multiple ways. The distribution and size of the populations of plants and animals within those biomes will also change, with potential consequences for the functioning of ecosystems and for humans who are dependent on many ecosystem goods and services.

Shift in plant species distribution in relation to global warming

A change in the agro-climatic conditions of an area can affect the population dynamics of plants, animals and microbes which are living there and as a consequence,.the structure and function of the entire ecosystem can also get modified. It is evident that the high altitudinal vegetation is directly influenced by global warming; these habitats are considered very sensitive and vulnerable to the climatic change phenomena emerging as a key factor to regulate the future ecological relations in the different ecosystems and biomes. The climate-induced species range shifts have been reported along altitudinal and latitudinal gradients. The spread of tree species involves several factors, including dispersal, regeneration on a suitable site, maturation, and seed production. If climate changes faster than trees can disperse to new and more suitable areas, the composition of the forest may change and the survival of some species could be at risk. Global-scale models are also inadequate to evaluate the indirect effects of climate, such as disturbances from pests, disease, fire, flooding, and wind damage. It is expected that changing climate may shift the vegetation towards the upside or lower elevation, which may change the composition of the forests in near future.

Species capability to shift along the altitudinal range depends on species tolerance efficiency of warming effects, their seed dispersal capability and their competitive ability. Only the species which have ability to compete effectively with species occurring at higher altitudes would be able to shift upward. There are three types of upward shifting that occurs in Himalayan ranges: (1) upward shift in entire altitudinal range with little or no change in range width, (2) upward altitudinal shift on higher side of the range but no change on the lower side of the range and, (3) altitudinal range squeezed at lower ends but no upward shift (Figure 1) (Singh & Singh, 2013). In general, altitudinal range in several species is squeezed because they are intolerant to warmer temperatures, and are unable to expand their range towards the upper side.

The recent climate change is mainly comprehended as a result of modification of natural climatic conditions and the chief factors which favour it are natural as well as anthropogenic. For meeting the ever increasing energy demands, human activities such as burning of fossil fuels and deforestation have resulted in the increased concentration of green house gases in the natural environment. Among the various green house gases, carbon dioxide is considered as the most important and its level has increased from 270 parts per million (ppm) prior to industrialization to the value of 410 ppm in year 2017 (Kahn 2017). The impacts of climate change are seen to be more pronounced in the sensitive high altitude regions especially in the mountainous environments.

The retreat of Himalayan glaciers during the last two decades and the formation of several glacial lakes evidenced the role of global warming. During the past century, the average global air temperature near the earth’s surface has been estimated to increase at the rate of 0.74 ± 0.18ºC (1.33 ±0.32ºf). The global mean land surface has warmed by 0.27º C per decade since 1979 (Guisan et al. 2005). The last decade of the 20th Century and the beginning of the 21st have been the warmest periods in the entire global instrumental temperature records. Certain naturally occurring gases, such as carbon dioxide (CO2) and water vapour (H2O), trap heat in the atmosphere causing a greenhouse effect. Burning of fossil fuels, like oil, coal, and natural gas is adding CO2 to the atmosphere. The current level did not reach this level during the past few million years.

Although plants have moved across the landscape in response to changing climate for millennia, projections of contemporary climate change suggest that forest tree species and their populations will need to migrate faster than their natural ability in search of more suitable environment. Therefore, climate change and adaptation strategies, such as assisted migration, have gained attention since 20th Century (Williams, 2013). During the past 30 years, a few climate changes and adaptation strategies have been proposed. One strategy is assisted migration (Peters and Darling 1985), defined as the movement of species and populations to facilitate natural range expansion in direct management response to climate change. Climate has played a major role in shaping vegetative growth, composition, and genetic variation across the landscapes. Long-lived species, such as trees, will lag behind short-lived species in their ability to adapt and track suitable climatic conditions. It may take several generations (centuries to millennia) for a tree population to become adapted through evolution to a new climate. Evidence from the fossil record and from recently observed trends proved that changing climate has a profound influence on species range expansion both upward and downward. Ecological ‘fingerprints’ of climate change appear across a wide range of taxonomic groups and geographic regions and are being identified with increasing frequency.

Chen et al. (2011) have reported that terrestrial organisms are currently shifting their distribution range along the latitude or elevation in response to changing climate. Using a meta-analysis, they estimated that the distribution of species has recently shifted to higher elevations at a median rate of 11.0 meters per decade, and to higher latitudes at a median rate of 16.9 kilometers per decade. These rates are approximately two and three times faster than previously reported migration rates. Parmesan and Yohe (2003) compiled studies on many species including alpine herbs, birds, and butterflies, and found an average poleward shift of 6.1 km per decade. The timber lines in European mountains have been recorded to have moved upward by nearly 200 m since the early twentieth century (Grabherr, 2010). Furthermore, because initiation and cessation of growth are influenced by temperature, precipitation and light, the forest ecosystems are likely to experience phenological imbalances with longer growing seasons such as the bud break may occur earlier in the spring, making those individual trees susceptible to weather events (e.g., freezing temperatures and snowfall). In the assisted migration of plants, forest tree species are highlighted most often because of their economic value and focus on climate change research; however, assisted migration conducted for economic rather than conservation reasons is also cited as a major barrier to implementation.

Shift in plant species distribution in Indian Himalaya

In different district of central Indian Himalayas, Panigrahy et al. (2010) reported upward shifting of alpine tree line and reported 360-430 m upward shift in Uttarkashi (360 m), Tehri Garhwal (400 m), Rudraprayag(390 m), Bageshwar (430 m), Chamoli (360 m) and Pithoragarh (390 m). A study conducted by Telwala, (2011), in the north-east India (Sikkim Himalaya) suggests that many of the 124 endemic plant species investigated, demonstrated a prolonged upward shift over the past 150 years (from 1850 - 2010) with a mean species shift in altitudinal range of 237.9±219.8 masl. The upward shift in species’ range was between 100m to 400m in 70% of the species but, in extreme cases, the range shift was 600-800m. About half of the endemic species, showed an upward shift on upper side of their range, leading to an altitudinal expansion on the range. In Kashmir Himalaya the rate of upward shifting of the regional plants depends upon the extent of changes in the local climatic conditions and by other factors including anthropogenic pressures that operate differently in each mountain systems of the world (Agnihotri et al., 2017). As per Kumar et al., 2010, flowering in Rhododendron arboretum, and its other associate like banj oak has shifted by 25 to 30 days whereas time of leafing by around 2 weeks. Himalayan blue pines (Pinus wallichiana), Bhojpatra (Betula utelis) and Abies spp. are on the move too in western Himalaya. From past few decades, nuisance weed Parthenium hysterophorus and the water fern Azolla cristata have shifted in the formerly temperate climate of the Kashmir Himalayas. Historical range shift of plant species like Rhodiola bupleuroide, Rheum nobileSaussurea stella , Saussurea uniflora and Ponerorchis chusua has been recorded in Northeast Himalaya (Telwala et al. 2013). Migration of tropical species, including some pines (e.g. Pinus merkusii), from lowland areas of South Asia to the Himalaya is indicated to have occurred in the geological past during warmer climate phase whereas Bombax ceiba, and Butea frondosa have penetrated into the Himalayan ranges through migration along rivers that have cut deeply into mountains.

Changes in regeneration behaviour of plants in Indian Himalayas

It is important to understand how evolution and ecological potential of different life forms helps them to adapt climate change (Woodward and Kelly 2008), because Himalayan forests are greatly affected by climate change, water availability and temperature. The regeneration potential of any forest directly depends on biotic and abiotic characteristics and its geographic distribution (Gairola et al. 2012). Regeneration patterns of species population can address climate change by adaptive evolution or by migrating association to survive in their favourable climate. Forest ecosystems depend on adequate regeneration potential of tree species to be healthy and sustainable. Himalayan forest composition and ecosystem services depend on forest structure and regeneration potential which are considered to be changing in the alignment of tree population over time. Economically important plant species have repeatedly been reduced from Himalayan forests due to climate change, species shift and other natural or anthropogenic disturbances. These phenomena have ultimately affected forest regeneration (Sharma 2016). Emergence and establishment of seedlings in the oak dominated forests under their natural habitat conditions in Garhwal Himalaya is reported to be unsatisfactory (Bisht & Kuniyal 2013). In Indian lower Himalayan parts, the regeneration in Sal (Shorea. robusta) is known to be a problem, because its seeds are ready to germinate by mid-June when the commencement of monsoon is uncertain. Availability of seeds, which are often limited for Himalayan temperate species and competition among species for space, light and water, may be the reasons for non-regeneration of certain tree species.

 

*School of Environmental Science, Babasaheb Bhimrao Ambedkar University, Lucknow. E-mail: cceseditor@gmail.com


This article has been reproduced from the archives of EnviroNews - Newsletter of ISEB India.


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