Rubin, Sagar and M, Soubadra Devy (2022) The Impact of Anthropogenic Disturbance to the Canopy Microclimate of Tropical Forests in the Southern Western Ghats, India. ORIGINAL RESEARCH, 5: 734448.
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Abstract
Microclimates affect species assemblages and functions of tropical forest ecosystems (Chen et al.,1999) and microclimatic conditions experienced by several organisms may be quite different from the macroclimatic conditions (De Frenne et al., 2013; von Arx et al., 2013). With global warming predicted to exceed 1.5C and 2C in the 21st century (IPCC, 2021), non-climatic anthropogenic pressures, that is, activities directly resulting in adverse impacts on natural ecosystems, especially forest degradation and fragmentation may worsen microclimatic conditions by reducing the buffering effect (Ewers and Banks-Leite, 2013). Forest degradation has shown to increase the severity of understory microclimatic conditions (Blonder et al., 2018; Jucker et al., 2018). For instance, local air temperatures have been found to be as much as 13.6C greater in logged forests as compared to primary forests (Senior et al., 2017). Further, the role of intact canopy cover, a feature of old-growth forests (primary forests, henceforth) has a buffering effect on the understory microclimate, offsetting and reducing the severity of macroclimatic variations (De Frenne et al., 2019; Zellweger et al., 2019). Such effects in the canopy microclimate are not as well explored. Canopies host a high diversity of arthropods (Erwin, 1982; Basset et al., 2008, 2012), particularly beetles (Stork and Grimbacher, 2006). Species unique to the canopy have been observed in the range of 20–30% (Stork and Grimbacher, 2006; Ulyshen and Hanula, 2007; Schroeder et al., 2009) and display very high microhabitat specialization (Wardhaugh et al., 2013). A characteristic feature of tropical rainforests is the presence of vascular epiphytes, which represent approximately 9% of the extant vascular plant diversity (Zotz, 2013). Larger trees, an indicator of older trees, support complex epiphytic communities (Woods et al., 2015; Woods, 2017). Hence, epiphyte communities in old-growth forests are often more diverse than disturbed and secondary forests (Barthlott et al., 2001; Woods and DeWalt, 2013). Consequently, it is no surprise that the presence of
epiphytes positively contributes to arthropod diversity in tropical forests (Cruz-Angón et al., 2009; Díaz et al., 2012). The reasoning for the positive association between epiphytes and arthropod abundance and diversity may lie in the fact that epiphytes may offer refuge and resources to arthropods (Nadkarni, 1994). Thus, old-growth trees with greater diversity, abundance, and even size (biomass) of epiphytes may attract a greater abundance and diversity of arthropods. Stuntz et al. (2002a) report substrates with cooler temperatures in the proximity of certain epiphyte species as compared to exposed branch surfaces of host trees, and indicate that this factor, along with the size (biomass) of canopy epiphytes could contribute to the positive association of epiphytes and arthropods (Stuntz et al., 2002b).Increased forest degradation and fragmentation are wellknown to adversely impacted insect communities (Klein, 1989;Feer and Hingrat, 2005; Nichols et al., 2007) through direct exposure to higher ambient temperatures (Piyaphongkul et al.,2012; Woods, 2013; Zhang et al., 2014) and indirectly, such as through changes in host plant qualities. For instance, the leaf surface temperature increases the body temperature of small arthropods on the leaf (Caillon et al., 2014), and higher temperatures can affect several adult phenotypic aspects both within generations and even between generations (Crill et al.,
1996). Further, the light intensity has been found to potentially impact the vertical distribution of insects in forests. For instance, Grossner (2009) found light intensity as one of the potential factors affecting the diversity of Heteroptera across vertical strata in beech and oak dominated forests. The understanding of impacts of forest degradation on beetles remains mixed, as some have highlighted the negative effects of fragmentation on beetle
species richness and community composition (Feer and Hingrat, 2005; Jung et al., 2018; Salomão et al., 2019), however, some do not demonstrate a clear direction of the impact of fragmentation (Davies and Margules, 1998). In tropical forests, secondary stands support fewer epiphytes as compared to primary stands (Barthlott et al., 2001; Nadkarni et al., 2004; Padmawathe et al., 2004; Woods and DeWalt, 2013). Forest clearances also adversely affect vascular epiphytes through changes in the microclimate (Zotz and Bader, 2009), such as drier microclimates in secondary forest (Gradstein et al., 2008) or loss of shade-adapted species (Benítez et al., 2012). For instance, Psygmorchis pusilla Dodson and Dressler (Orchidaceae) showed reduced biomass and floral spikes at just 3C above its optimum
temperature (Vaz et al., 2004). Increases in light intensity have shown to reduce relative growth rates of a vascular epiphyte (Laube and Zotz, 2003) as well as photoinhibition (Stancato et al., 2002) which could eventually lead to dieback and reduced numbers in environments with higher light intensity. The need for prioritizing research on microclimate and its impact on forest biodiversity has been indicated (De Frenne et al., 2021). The importance of the microclimate has been recognized for decades, but our understanding of biotic responses to microclimates in the context of human land-use change is still in its infancy (Santos and Benítez-Malvido, 2012; De Frenne et al.,
2021). Further, such work is lacking in Indian rainforests in spite of the existence of two biodiversity hotspots (Myers et al., 2000)— the Western Ghats and the Indo-Burma region. Epiphytes form an important part of the rainforest canopy in the southern Western Ghats including several endemics (Parthasarathy, 1988; Ganesan and Livingstone, 2001). Similarly, beetles also form a major component of the insect taxa (Devy and Davidar, 2003; Mohanraj et al., 2014). The responses of these taxa to environmental change have been little quantified. To provide further insights into the impacts of disturbance on microclimatic variables, beetle and epiphyte communities, we focused on the following two questions: 1) Does the canopy microclimate (temperature and light intensity) differ between primary and secondary forest
stands? 2) Do beetles and canopy vascular epiphytes differ between primary and secondary forest stands? Throughout this paper, we use the word “canopy” or “forest canopy” referring to the overstorey defined as the “stratum of trees that have outgrown the other vegetation in a forest to have their uppermost crown foliage largely of fully in direct sunlight, usually as a relatively continuous layer (excluding gaps)”
(Moffett, 2006). We use the word “crown” or “crown-tree” when referring to the top limbs and leaves of individual trees (from the lowermost limb, excluding the trunk). We chose an evergreen wet tropical forest site, with a known history of varying gradients of logging. Hence, there exist intact, old-growth stands, in close proximity to logged stands. The sites were chosen with the expectation of markedly distinct light and temperature levels in the primary and secondary forests, while the elevation and climatic conditions experienced were the largely very similar. To the best of our knowledge, this is the first study in Indian tropical moist forests to study beetle and vascular epiphyte community responses to microclimatic differences in primary and secondary forest canopies.
Item Type: | Article |
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Additional Information: | Copyright of this article belongs to authors |
Uncontrolled Keywords: | canopy, beetles, vascular epiphyte, microclimate, tropical wet forest |
Subjects: | A ATREE Publications > G Journal Papers |
Divisions: | SM Sehgal Foundation Centre for Biodiversity and Conservation |
Depositing User: | Ms Suchithra R |
Date Deposited: | 13 Oct 2025 06:36 |
Last Modified: | 13 Oct 2025 06:36 |
URI: | http://archives.atree.org/id/eprint/627 |