**Abstract**

Tropical and subtropical forests have diverse ecological functions but are most disturbed due to climatic changes. Peer-reviewed articles, books and reports were searched and downloaded to analyze the effect of climatic changes on tropical and subtropical forests and highlight the need for conservation efforts to ensure sustainable supply of ecosystem services. These forests store largest share (55%) of global terrestrial carbon pool. But the projected rise in temperature (4o C), CO2 levels (495 ppm) and changes in precipitation regime by 2100 are expected to cause significant changes in ecosystem productivity and nutrient turnover rate making forests more vulnerable to climate change. High temperature with low rainfall reduces tree growth, increases soil carbon fluxes by accelerating rate of nutrient cycling, restricts the range of pollinators and increases pest infestation (*Phytophthora cinnamomi*) affecting ecosystem health and future food security. Increase in heat waves increase the incidence of wild fires and degrade ecosystem quality. Climate change also reduces the scenic beauty, ecotourism and associated economic and mental health benefits. Proactive measures must be taken to mitigate the likely causes of climate change and efforts should be taken to conserve the existing forest reserves to ensure sustainable supply of the ecosystem services.

**Keywords:** climate change, tropical forest, subtropical forest, ecosystem services, nutrient turnover, carbon stock

### **1. Introduction**

Forests globally cover 4.06 billion hectares (31%) of land area and provide diverse ecosystem services mainly categorized as regulatory, provisioning, supporting and cultural services [1, 2]. These services have use (tangible) and non-use (in-tangible) values. The use values encompass a diverse array of benefits to the humankind in term of provision of food, timber, shelter and fuel-wood. The non-use benefits include

climate regulation, nutrient cycling, flood protection, oxygen production, and prevention of soil erosion, recreation, scenic beauty and spiritual services [3, 4]. All of these services are vital for the mankind and ecological communities to sustain on this planet but are under constant threat from changing climate [5].

The uncontrolled anthropogenic activities related to urban and industrial expansions, fossil fuel burning, deforestation, and land use land cover (LULC) changes have caused rise in atmospheric CO2 levels. Since the pre-industrial times (back in year 1800), 50% increase (280–412 ppm) in the CO2 concentration has been observed causing 0.85°C rise in global temperature [6, 7]. The CO2 concentration has risen with a growth rate of 5.1 GtC/yr during 2011–2020 [7]. The emissions are expected to reach the dangerous level of 495 ppm by the year 2100 and are projected to raise global temperature by 4°C [8–10]. This warming trend has already affected forest ecosystems globally and can further reduce the supply of ecosystem services [11, 12].

Geographically, tropical and subtropical forests are located at 23.5o N and 23.5o S latitude in the regions delimited by 18°C to –3°C isotherms according to the Koeppen Geiger climate classification. These forests are characterized by little variation in overall temperature and comparatively high rainfall. These forests cover parts of Asia, Africa, South America and Australia having distinguished features such as seasonal leaf fall, physiographic position, leaf size and canopy structure [13].

Among all the other forest types, the tropical and subtropical forests host most diverse array of tree species and also contribute significantly in carbon sequestration [14]. Out of 2.4 GtC/yr stored annually by global forests, about 55% of this is stored in tropical and subtropical forests while boreal and temperate forests store only 32% and 14% of it respectively [15]. Along with climate regulation, these ecosystems are also a source of livelihood for the local communities, provide food security and maintain ecological health. Yet these tropical and subtropical forests are at the forefront of changing climate due to their geographical location. The climate change impacts on the ecosystem services of the tropical and subtropical forests are considered a major threat in current century. The projected increase in temperature up to 4°C can cause significant changes and alternations in the ecosystem structure and the functions [8]. The different effects of climate change like increase in temperature, CO2 concentration and changes in rate of precipitation cause many negative impacts on the ecosystem services of the tropical and subtropical forests [16]. These climatic changes might cause tree species to shift their range towards poles and also affect rates of nutrient turnover [17, 18]. Therefore, there is a dire need to prioritize conservation and restoration efforts to protect the ecological functions of these ecosystems.
