Tropical Ecology 59(3): 417–430, 2018 ISSN 0564-3295 © International Society for Tropical Ecology www.tropecol.com Understanding the role of slope aspect in shaping the vegetation attributes and soil properties in Montane ecosystems SHIPRA SINGH School of Environmental Sciences, Jawaharlal Nehru University, New Delhi-110067, India Abstract: Montane ecosystems are a remarkably diverse ecosystem, mainly characterised by hillslope asymmetry, i.e., hillslope variation as a function of slope angle and slope aspect. Slope angle, aspect, and elevation are considered as the primary factors creating spatial variation, causing differences in vegetation growth and distribution, ecosystem functioning, and processes. Differences in slope aspect cause differences in air and soil temperature, moisture content, evaporation, which creates microclimatic zonation, and that these differences are closely associated with alterations in vegetation structure and composition. North-facing shady slopes are supported with thick and dense vegetation with nutrient-rich soil, whereas, thin and scattered vegetation along with weaker soil development with higher erosion rates in south- facing sunny slope. However, the information related to the effect of the slope aspect in different latitudinal areas is still unclear. In this review, an effort has been made to collate the studies dealing with different facets of the slope and aspect in varied latitudinal regions and how it influences ecosystem processes and soil properties in the montane ecosystem. The present literature survey shows that the slope aspect has its maximum effect in the mid-latitudinal region. In the low-latitudinal region, the slope aspect shows no consistent differences between the opposite aspects. The effect could be seen in its lowest limit in the higher-latitudinal region. The slope aspect is a crucial parameter in montane forest ecosystems and for sustainable forest management measures, which cannot be neglected for studying topography related vegetation dynamics. Moreover, water and soil conservation measures should be applied precisely on drier and warmer aspects. Key words: Biodiversity, elevation, insolation, slope angle, slope aspect. Introduction is the most important one among the three (Busing 2005), and these three factors together determine There has been a keen interest among plant the microclimate and spatial distribution patterns ecologists to ponder slope aspect related issues in of vegetation. Within one elevation, slope aspect, vegetation communities since the 1850s region slope angle, and soil type are responsible for forest (Gilliam et al. 2014). The effects are more dynamics (Shank & Noorie 1950). Alexander von pronounced in mountainous regions, which are set Humboldt was the principal individual to portray apart by steeper slopes (Pepin et al. 2015). The the latitudinal as well as a corresponding three main topographic features, which rule over elevational gradient to be majorly responsible for the patterns and trends of vegetation in the fundamental understanding of species mountainous regions are elevation, slope aspect, composition and diversity along an altitudinal and slope angle (Titshall et al. 2000). The elevation gradient (Fischer et al. 2011). Changes in *Corresponding Author; e-mail: [email protected] 418 SLOPE ASPECT SHAPES VEGETATION ATTRIBUTES IN MONTANE ECOSYSTEMS vegetation pattern as well as soil properties are the lower latitudinal area remains unclear very pronounced along the elevation gradient (Méndez‐Toribio et al. 2016). because of the increased climatic variation over Beaty & Taylor (2001) and Sternberg & relatively lesser distances (Dahlgren et al. 1997; Shoshany (2001) have made observations that the Lomolino 2001). Increased vegetation cover can northern slope with dry regions have improved lead to improved slope soil shear strength, soil vegetation in the northern hemisphere. This may quality, reduction in soil erosion (Chau & Chu perhaps not be valid for regions that do not 2017; Liu et al. 2014; Yuan et al. 2016) thus experience water limitations in the northern facilitating ecosystem restoration. Differences in hemisphere. Dearborn & Danby (2017) in his study microclimatic conditions also create a difference in in Kluane Region, southwest Yukon, Canada soil types influencing its development and (60.7°N) suggested that vegetation attributes processing (Egli et al. 2006) as well as affect the varied more as a function of slope angle and slope soil stability (Schoorl et al. 2004). Additionally, it aspect rather than elevation. South-facing slopes also affects the soil temperature, air temperature showed increased soil temperatures and deeper and moisture content (Bennie et al. 2006; Sidari et active layers in comparison to north-facing slopes, al. 2008). The effect of topographical positions while differences related to slope angle occurred (slope aspect and slope angle) on vegetation only on north‐facing slopes. While few studies composition and structure has been extensively suggest the effect of elevation to be more studied in temperate forests (Sharma et al. 2010a, pronounced as compared to the slope aspect in b, c), temperate grasslands (Gong et al. 2008), such regions (Zhang et al. 2013). This review Mediterranean or tropical humid communities builds on to enhance the comprehension of the (Gilliam et al. 2014), tundra ecosystem (Dearborn diverse impact of slope aspect on vegetation and & Danby 2017) and boreal forest ecosystems soil properties in different latitudinal regions; and (Astrom et al. 2007). However, the relationship extract information in regards to the plantation between vegetation structure and composition as and other practices for the local communities that well as soil properties in the Montane ecosystem are reliant directly or indirectly on it. Thus, an as a result of the effect of slope angle, aspect and attempt has been made to increase awareness elevation is still a matter of debate. There is a among policy-makers and conservators, which will complex relation between vegetation communities, be directly helpful in an effective overall sustai- soil properties and slope aspect in the Montane nable forest management. region, which requires local specific study to fully understand the relation between them. Effect of slope aspect on vegetation attributes There is still a lack of knowledge and in the montane ecosystem understanding of how the slope aspect causes changes in forest properties and how this effect Vegetation, defined as an array of plant varies along latitudinal degrees in both the species and the dominant life forms, include trees, hemisphere. It remains unclear what is the most shrubs, grasses, and forbs (Burrows 1990). Forest critical factor that is maximally affected by is a unit of vegetation having physiognomic and changes in the slope aspect (Warren 2010). For structural features so articulated that it appears example in the low-latitudinal area, Maass et al. distinct from other units (Champion & Seth 1968). (2005) found no significant difference in the tree Each forest group is related to an aspect, usually height between northern and southern slopes in having a southern and a northern counterpart, the seasonally dry forest of Chamela in West which differs in species composition (Singh & Mexico (19.5°N). Also, tree density was found to be Chaturvedi 2017). The two different aspects form a significantly higher in the southern slopes change in patterns and trends of structure and whereas, Gallardo-Cruz et al. (2009) in his study composition of the vegetation (Chmura 2008). The on the seasonally dry tropical landscape (Mount maximum effect of topography (slope angle, aspect, Cerro Verde, Oaxaca (17°N) suggested that and elevation) tends to occur in montane forest vegetation structure did not show significant ecosystems characterised by stratification with changes linked to the topographical positions, respect to elevation. In low latitudinal regions, although a perceptible floristic composition vegetation cover shows specifically no consistent difference was noticed along with the topographic differences between the northern and southern inclination. Therefore, the effect of topography in aspects. In mid-latitudinal regions, the northern SHIPRA SINGH 419 aspect shows increased vegetation density in such as livestock grazing, extraction of firewood, comparison to the southern aspect. The effect is are supposed to be higher on the lower reaches of much pronounced in such regions. hill slopes, particularly those with moderate Ohsawa et al. (1985) in his study on Mount steepness (<7%) in Brazilian Savanna Steppe Kerinci, Sumatra (1.6°N) suggested that the (14°S) (da Silva et al. 2014). There is a decrease in latitude is the primary factor causing altitudinal forage availability with increasing slope angle, and zonation patterns, creating the most complex also, lower availability of vegetation suggests vegetation pattern on subtropical mountains lower foraging (Sigua & Coleman 2010). The slope where the two floristic realms, the Boreal and aspect may lead to successional changes after Palaeotropical, meet. The role of slope aspect in disturbances, such as clear-cutting and felling Mt. Kilimanjaro (3°S) was found to be less humid (Astrom et al. 2005; Okland et al. 2003). Such and warmer on the north-east slopes than south vegetation contrasts provide habitat edges that slopes (Pepin et al. 2017). Vegetation zonation in also influence wildlife. Studies conducted on montane forests of Mt. Meru