Indian cardamom-coffee hot spots are one of the two unique and important tropical mountain ecosystems globally for a growing variety of crops, e.g., spices, fruits and vegetables. The other is located in Guatemala, where maize and tapioca are also cultivated along with cardamom and coffee. Generally, farmers' livelihoods in tropical mountain agriculture in southern India depend largely on growing high-value spice crops and seasonal vegetables and fruit crops. These hot spots in India have peculiar environments mainly due to altitudinal variations and specific geographical locations concerning the Indian monsoon and its seasonal winds. Agroecosystems in tropical mountains are highly sensitive and vulnerable to climatic change, thereby reduction in crop yields. Agriculture across the world is under stress leading to diminishing returns and productivity. The relative rates of yield increase for all of the major cereal crops as well as plantation crops are already declining (Ainsworth and Ort, 2010; Murugan et al. 2012).
The world's coffee-cardamom sector provides employment and livelihood for over 60 million people in the tropics. It is considered the second largest employment sector in the world after the oil industry. Correspondingly, India is the sixth and second-largest coffee and cardamom producing country globally, accounting for over 4 and 40% of the world's production, respectively. More than 92% of the Indian coffee and the entire cardamom production come from Karnataka, Kerala and Tamil Nadu. Area, production and productivity of coffee are maximum for Karnataka, followed by Kerala and Tamil Nadu. Kerala is the leading producer of small cardamom in the country, chased by Karnataka and Tamil Nadu. The major share of coffee and cardamom production in India originates from small to medium farms, which are more vulnerable to climatic change and variability. Both cardamom and coffee prefer elevation induced natural forest ecosystem for sustainable production. Cardamom being more closely related to rain forest environment the sufficient surface soil moisture is indispensable. Coffee, which requires cooler subtropical climatic conditions, is relatively less sensitive to drought under optimum natural forest shade. Hence, these crops are predominantly cultivated both in the high ranges and the high uplands of the Western Ghats (WG) in southern India. Except the Upper Pulney hills (UPH), where many temperate fruits and vegetable crops are also mainly farmed, the other hot spots are cultivated with only high-value spices and plantation crops. Most coffee farms in these states are concentrated in the WG high uplands. The rich history of coffee cultivation in Pulney hills is very old, whereas it is relatively new and peculiar to Cardamom hills (CH). Both Arabica and Robusta spoils approximately 50% share in acreage.
Upper Pulney hills (UPH) are the largest highland massif in southern India (Raith et al. 1997). Geographically, the unique Pulney hills form a part of the widest portion in the entire WG, which are considered one of the Global Biodiversity hot spots. Fyson et al. (1915) first published authentic and science-based information about the biotic richness flowering plants of the temperate Kodaikanal hills. One of the Global Atmospheric Watch (GAW) stations was positioned in Kodaikanal hills considering the geographical superiority over other hills in India5. South of the Himalayas, the longest high-plateau (7700 feet msl) is supposed to have more diversified agricultural/sylvicultural/sylvipastoral and socio-economic significance and activities than the other hot-spots.
According to (Smith, 1895), the overall climate of the UPH used to be a splendid one, combining many of the advantages of tropical and temperate regions; for instance, the mean relative humidity varied from 47% in March to 83% in August and the mean for the year being 72%. The actual annual total rainfall around 1895 was 47.5 inches at the observatory site. Still, slightly increased rainfall (20% more) was reported for a station little away from the observatory at higher elevation cliffs (61 inches). The rainfall was spread over all months, being highest for August (21 days) and lowest for March (3 days). There were 2065 hours of sunshine annually. The impact of orography characterizes the rainfall pattern over these high ridges and valleys. Hence the rainfall activity spread across all the seasons rather than a single season. The western high ridge plateau of the hills experiences a temperate environment. At the same time, the lesser elevated eastern (1000–2000 msl) slopes enjoy the tropical and subtropical climate, which mostly comes under Lower Pulney hills (LPH). Overall, the average annual total rainfall, 41%, 35%, and 24%, correspondingly contributed by northeast and southwest monsoon and summer months. Thus, the entire region has a magnificent climate with many advantages of tropical and temperate regions. That is why a variety of crops ranging from temperate fruits (Pear and Plum) to vegetables (Cole crops, Beans) further to tubers (Potato and Carrot) and plantation crops (coffee and pepper) are successfully cultivated in these hills throughout the year. And, as such, any change taking place in the patterns of climate parameters, for instance, temperature and rainfall, attracts value amongst researchers and agriculturalists concerned.
The main factors that control the growth and development of diseases in plants are temperature and precipitation (water) by affecting factors such as the plant pathogen's survival, vigor, rate of multiplication, sporulation, direction, distance of dispersal of inoculums, and rate of spore germination and penetration (Yáñez-López et al. 2014). Hence, studies assessing the impact of climate change in agriculture have mainly focused on the effects of temperatures and precipitation while considering agricultural production and the impact of insects, pests and diseases. Increases in the growing season change the evapotranspiration and have implications on the water demand in managed ecosystems (Anandhi et al. 2013a & 2013b). Specific stages of growth (e.g., flowering, pollination and grain filling) are susceptible to weather conditions and critical for final yield (Lavalle et al. 2009). As global temperature rises, crops will increasingly begin to experience failure in traditional production regions, especially if climate variability increases and precipitation lessens or becomes more variable. Atmospheric temperature and rainfall variability play a significant role in crop growth and yield.
Climate change in managed ecosystems is likely to alter the availability and distribution of freshwater (e.g., floods, droughts) while simultaneously increasing the demand for water from rivers and impacting groundwater availability (Allan et al., 2013). In addition, rising temperatures have shown to impact the phenology of plants and insect (Anandhi et al., 2016) [shifts in the timing of plant and insect activity]. Plant response to climate change is realized through a complex set of interactions among CO2 concentration, temperature, solar radiation, and precipitation. Temperature, precipitation, sunlight, and air humidity are also primary climate factors that control the growth and development of insects, pests, and diseases in crops (Esbjerg and Sigsgaard, 2014). However, observed data on climate variables such as solar radiation and humidity for these hot spots are sparse compared with rainfall and temperature (Anandhi et al. 2012 & 2016).
The production physiology of coffee is unique among crops. The crop prefers a sub-tropical (cool dry) condition for growth with optimum temperature being18-26˚C. However, it requires another particular condition of inductive stress followed by a medium to heavy rainfall that triggers the entire flowering process. The tricky physiology coffee of flowering has been probed, and on which convincing results are available. The term blossom showers give a meaningful representation of how much summer showers means to productivity in coffee. This could also be why nature has placed the original habitat of coffee in an area with tropical showers blend with cool winters.
The flowering aspects of coffee have been extensively studied and documented (Huxley, 1970; Browning, 1975) and extensively reviewed by Cannell (1985). This is points to the summer stress and summer showers as pre determinants of flowering requirement. The crux of these works revolves around the production of hydrolytic enzymes brought about by a favorable balance of hormones, namely GA/Auxins that initiates flowering. There is also compelling evidence to suggest a reduction in abscisic acid levels, which releases the dormancy of flower buds with the receipt of the first rains (Barros et al., 1978; Rena et al., 1994). Thus, the three critical requirements of inductive stress, the blossom showers and backing rains, are the most critical aspects that govern flowering and productivity in coffee. The timely receipt of showers and the intensity to break down the dormancy of flower buds are the points of immediate concern in the WG. Limited water availability can cause an increase in crop failure (defined as the complete loss of crops on a farm)7. The LPH where coffee is grown is now seen to have a prolonged drought situation in summer, posing a challenge to the very existence of the crop there. The case in CH is that the summer shower has become erratic and subjected to cause increased stress often. Wynad district in Kerala, where coffee is mainly grown as a sole crop, climate change has been felt, and coffee production and productivity have been rendered vulnerable. This has led to an agrarian crisis, with farmers resorting to suicide as it is the mainstay of livelihood. The neighboring Coorg district in Karnataka has not yet frequently witnessed climate change compared to Kerala and Tamil Nadu, mostly because large-scale deforestation is yet to occur.
The cardamom sector is much more organized with very high inputs, but this Zingiberaceous crop is very sensitive to climatic vagaries. This is also another crop that requires little stress during early February and with the onset of monsoon profusely tillers under rainfed condition. It is from the base of such healthy tillers or stout tillers that the panicle arises. Longer wet spells drive the production of panicles from the previous season tillers. Another important aspect is that the lengthening of the panicles bearing the flowers and the consequent fruit set is again dependent on the length of wet spells or otherwise has to be managed or supplemented by irrigation.
Thus, we have two typical clear cut crop stages with distinct requirements that is dependent on environmental conditions
Inductive summer stress followed by summer showers for floral induction of coffee followed by backing rains for berry set and development and
Stress followed by rains for tillering (emergence of new shoots) and panicle initiation from the base of stout tillers and panicle growth and flowering and fruit set with persistent rains in cardamom.
Any limitation to this sequence or change in the intensity and calendar of events like prolonged or frequent drought, non-receipt of timely rainfall and delayed and non-optimal receipt of continued rainfall could offset the entire production cycle, leading to reduced crop yields. Thus, the critical environmental conditions have paved the way for different phenophasic development in both crops.
Relative rates of yield increase for all of the major cereal crops are already declining1. The assumptions such as yield improvements from the latter half of the 20th century will continue may not be sound because they are based on historical temperature-crop yield relationships, potential ceilings to crop yields, and limitations to expansion of agricultural lands1. Under conditions of climate change and increased human activity, the stresses and vulnerabilities associated with a water supply and water demand will increase significantly across the world (Allan et al. 2003).
Agriculture is vulnerable to climate change and variability through direct (i.e., abiotic) effects on crop development and yield (e.g., changes in temperature or precipitation) as well as through indirect effects arising from changes in the severity of pest, insect, and disease pressures; availability of pollination services; and performance of other ecosystem services that affect agricultural productivity (Walthall, 2012; Anandhi and Blocksome, 2017). However, continuous long-term data on climate variables such as solar radiation and humidity are sparse compared with rainfall and temperature (Anandhi et al. 2012 and 2016). Present and future climatic change may present unprecedented challenges to coffee-cardamom cultivations by influencing crop distribution and production and increasing the economic and environmental risks associated with the production systems. Therefore, critical analysis and insights into the observed climatic variability and yield of crops could be useful for scientific and farming communities to better manage the delicate Indian cardamom- coffee hot spots.