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Diversity and Distribution of Herbaceous Plants Along a Tropical Rainfall Gradient in Western Ghats, India.

紀錄類型:	書目-電子資源 : Monograph/item
正題名/作者:	Diversity and Distribution of Herbaceous Plants Along a Tropical Rainfall Gradient in Western Ghats, India./
作者:	Venugopalan Nair Radhamoni, Harikrishnan.
面頁冊數:	1 online resource (162 pages)
附註:	Source: Dissertations Abstracts International, Volume: 85-01, Section: B.
Contained By:	Dissertations Abstracts International85-01B.
標題:	Ecology. -
電子資源:	http://pqdd.sinica.edu.tw/twdaoapp/servlet/advanced?query=30249667click for full text (PQDT)
ISBN:	9798379779139

Diversity and Distribution of Herbaceous Plants Along a Tropical Rainfall Gradient in Western Ghats, India.
Venugopalan Nair Radhamoni, Harikrishnan.

Diversity and Distribution of Herbaceous Plants Along a Tropical Rainfall Gradient in Western Ghats, India. - 1 online resource (162 pages)

Source: Dissertations Abstracts International, Volume: 85-01, Section: B.

Thesis (Ph.D.)--Yale University, 2023.

Includes bibliographical references

Tropical forests hold most of the vascular plant life on earth. Much of our understanding on the diversity patterns and drivers of plants in tropical forests is based on studies on trees, which form only a quarter of the plant diversity in these forests. Over 40% of plant diversity in some tropical forests is comprised of understory herbaceous angiosperms (herbs). Despite such high species richness, and their critical role in the functioning of forest ecosystems, our knowledge on the diversity patterns and drivers of herbs is poor, compared to trees. This knowledge gap not only precludes any claim on a comprehensive understanding of tropical forest ecosystems, but also hinders our ability to predict changes to plant communities and forest ecosystems as a whole. With ongoing changes to climate and increasing human pressure threatening to drastically change tropical forest ecosystems, it is critical to understand the patterns and drivers of herb community diversity and composition, and include them in conservation and restoration strategies. In my dissertation, I investigated the spatial and temporal patterns and drivers of herb communities in 13 one-ha plots across a rainfall gradient in a seasonally dry tropical forest landscape in the Western Ghats, a global Biodiversity Hotspot, in southern India.In the first chapter, I examined the drivers of herb diversity (α-diversity) at the landscape (across 1-ha plots) and at local scales (among 1x1m subplots). At the landscape scale, herb diversity was strongly and negatively correlated with rainfall and soil moisture, contrasting with previous studies on tropical forest trees, including in the same forest plots. As water was not limiting, it appears that understory light, which was negatively correlated with rainfall, was driving this diversity pattern along the gradient. The seasonal impact of water limitation on herbs became evident during the dry season, when diversity was uniformly low throughout the gradient. Once water limitation was lifted during the rainy season, herbs in more open (drier) plots took advantage of higher light availability, increasing the diversity. Herb diversity in subplots also increased with light availability, and its effect was stronger at wetter (more closed-canopy) plots. Herb diversity showed a negative relationship with increasing subplot soil moisture in all sites and seasons, which suggested that high moisture is negatively affecting herb diversity, due to water-logging or via other factors related to moisture (e.g., pathogens). In short, my results showed that while understory light limited herb diversity at both local and landscape scales, both lack of water during the dry season and the excess of water also were found to limit diversity.In the second chapter, I compared the spatial patterns and drivers of compositional variation (β-diversity) of herbaceous versus tree communities along the gradient. Given that herbs have seemingly lower dispersal abilities, higher evolution rates, lower drought tolerance, etc., compared to trees, I expected among-plot compositional variation of herbs to differ from that of trees. I estimated the taxonomic and phylogenetic β-diversity of both plant groups and partitioned the relative influences of spatial and environmental predictors (rainfall, temperature, soil and fire) on the β-diversity values. Against my expectations, both taxonomic and phylogenetic β-diversity patterns for herbs and trees along the gradient were remarkably similar. Both plant groups also showed high species and phylogenetic turnover among communities. Also, against expectations, spatial predictors explained taxonomic compositional variation of herbs and trees similarly, and more deep phylogenetic compositional variation in trees than in herbs. Most of the compositional variation of both herbs and trees were explained by rainfall and temperature, while the influence of fire and soils were low and varied among groups and metrics used. The results suggest a strong impact of environmental filtering, and that both plant groups have spatially unique compositions along the gradient. This, and the specific influence of rainfall and temperature found are relevant for conservation and management strategies of these plant communities, particularly considering the ongoing global changes.In the third chapter, I examined the temporal (seasonal) variation of herb community composition (β-diversity) in the 1-ha plots along the rainfall gradient. I calculated the temporal β-diversity of each plot and examined how it varied along the gradient. Specifically, I tested whether temporal β-diversity was related to seasonal variation in four abiotic factors: soil moisture, soil temperature, land surface temperature, and understory light. I also classified herb species into three groups based on their ecological strategies with respect to dry-season drought (escapers, evaders, and endurers) and regressed the community-level proportion of dry-season strategies of herbs against temporal β-diversity and seasonal variation in abiotic factors. As expected, I found low-rainfall plots showing higher temporal β-diversity. I found that temporal β-diversity increased with an increase in the proportion of annual plants (escapers) in the community, decreased with an increase in the proportion of plants whose above-ground parts live through the dry season (endurers), and showed no relationship with that of plants that survive the dry season by shedding above-ground parts (evaders). Land surface temperature emerged as an important factor, correlating with temporal β-diversity and all dry-season strategies. Soil moisture was correlated with temporal β-diversity and two of the strategies. The results suggest that herbs adopt dry-season strategies more as a response to heat stress than to water deficit, and that air temperature, not root-zone temperature, is critical in shaping herb diversity and composition. Given that ongoing climatic changes are thought to alter seasonal variations of precipitation and temperature, these results are relevant from a conservation perspective.To summarize, in this dissertation, I present multiple facets of diversity variation of herbaceous communities along a strong resource gradient in one of the most threatened tropical ecosystems. Both herbaceous plants and SDTFs are among the least studied plant groups and forest types, respectively, in tropical regions, and my work reveals fresh and valuable insights into both. Specifically, I showed that while patterns of one aspect of herb diversity (α-diversity) can differ from that of tree communities in a forest landscape, the patterns of another aspect of diversity (β) of both groups could be remarkably similar to each other. I also showed how seasonal variation in critical abiotic factors influences herbaceous communities, and how plant adaptations to those factors play a crucial role in sustaining diversity and shaping community composition. The results provide support for the critical role of environmental filtering in shaping patterns of both diversity and composition of plant communities in tropical forests. The findings add considerably to the current understanding of tropical plant ecology and offer insights to guide biodiversity conservation and restoration decision-making.

Electronic reproduction.
Ann Arbor, Mich. :
ProQuest,
2023

Mode of access: World Wide Web

ISBN: 9798379779139Subjects--Topical Terms:

516476
Ecology.
Subjects--Index Terms:

BiodiversityIndex Terms--Genre/Form:

542853
Electronic books.

Diversity and Distribution of Herbaceous Plants Along a Tropical Rainfall Gradient in Western Ghats, India.
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504 $a Includes bibliographical references
520 $a Tropical forests hold most of the vascular plant life on earth. Much of our understanding on the diversity patterns and drivers of plants in tropical forests is based on studies on trees, which form only a quarter of the plant diversity in these forests. Over 40% of plant diversity in some tropical forests is comprised of understory herbaceous angiosperms (herbs). Despite such high species richness, and their critical role in the functioning of forest ecosystems, our knowledge on the diversity patterns and drivers of herbs is poor, compared to trees. This knowledge gap not only precludes any claim on a comprehensive understanding of tropical forest ecosystems, but also hinders our ability to predict changes to plant communities and forest ecosystems as a whole. With ongoing changes to climate and increasing human pressure threatening to drastically change tropical forest ecosystems, it is critical to understand the patterns and drivers of herb community diversity and composition, and include them in conservation and restoration strategies. In my dissertation, I investigated the spatial and temporal patterns and drivers of herb communities in 13 one-ha plots across a rainfall gradient in a seasonally dry tropical forest landscape in the Western Ghats, a global Biodiversity Hotspot, in southern India.In the first chapter, I examined the drivers of herb diversity (α-diversity) at the landscape (across 1-ha plots) and at local scales (among 1x1m subplots). At the landscape scale, herb diversity was strongly and negatively correlated with rainfall and soil moisture, contrasting with previous studies on tropical forest trees, including in the same forest plots. As water was not limiting, it appears that understory light, which was negatively correlated with rainfall, was driving this diversity pattern along the gradient. The seasonal impact of water limitation on herbs became evident during the dry season, when diversity was uniformly low throughout the gradient. Once water limitation was lifted during the rainy season, herbs in more open (drier) plots took advantage of higher light availability, increasing the diversity. Herb diversity in subplots also increased with light availability, and its effect was stronger at wetter (more closed-canopy) plots. Herb diversity showed a negative relationship with increasing subplot soil moisture in all sites and seasons, which suggested that high moisture is negatively affecting herb diversity, due to water-logging or via other factors related to moisture (e.g., pathogens). In short, my results showed that while understory light limited herb diversity at both local and landscape scales, both lack of water during the dry season and the excess of water also were found to limit diversity.In the second chapter, I compared the spatial patterns and drivers of compositional variation (β-diversity) of herbaceous versus tree communities along the gradient. Given that herbs have seemingly lower dispersal abilities, higher evolution rates, lower drought tolerance, etc., compared to trees, I expected among-plot compositional variation of herbs to differ from that of trees. I estimated the taxonomic and phylogenetic β-diversity of both plant groups and partitioned the relative influences of spatial and environmental predictors (rainfall, temperature, soil and fire) on the β-diversity values. Against my expectations, both taxonomic and phylogenetic β-diversity patterns for herbs and trees along the gradient were remarkably similar. Both plant groups also showed high species and phylogenetic turnover among communities. Also, against expectations, spatial predictors explained taxonomic compositional variation of herbs and trees similarly, and more deep phylogenetic compositional variation in trees than in herbs. Most of the compositional variation of both herbs and trees were explained by rainfall and temperature, while the influence of fire and soils were low and varied among groups and metrics used. The results suggest a strong impact of environmental filtering, and that both plant groups have spatially unique compositions along the gradient. This, and the specific influence of rainfall and temperature found are relevant for conservation and management strategies of these plant communities, particularly considering the ongoing global changes.In the third chapter, I examined the temporal (seasonal) variation of herb community composition (β-diversity) in the 1-ha plots along the rainfall gradient. I calculated the temporal β-diversity of each plot and examined how it varied along the gradient. Specifically, I tested whether temporal β-diversity was related to seasonal variation in four abiotic factors: soil moisture, soil temperature, land surface temperature, and understory light. I also classified herb species into three groups based on their ecological strategies with respect to dry-season drought (escapers, evaders, and endurers) and regressed the community-level proportion of dry-season strategies of herbs against temporal β-diversity and seasonal variation in abiotic factors. As expected, I found low-rainfall plots showing higher temporal β-diversity. I found that temporal β-diversity increased with an increase in the proportion of annual plants (escapers) in the community, decreased with an increase in the proportion of plants whose above-ground parts live through the dry season (endurers), and showed no relationship with that of plants that survive the dry season by shedding above-ground parts (evaders). Land surface temperature emerged as an important factor, correlating with temporal β-diversity and all dry-season strategies. Soil moisture was correlated with temporal β-diversity and two of the strategies. The results suggest that herbs adopt dry-season strategies more as a response to heat stress than to water deficit, and that air temperature, not root-zone temperature, is critical in shaping herb diversity and composition. Given that ongoing climatic changes are thought to alter seasonal variations of precipitation and temperature, these results are relevant from a conservation perspective.To summarize, in this dissertation, I present multiple facets of diversity variation of herbaceous communities along a strong resource gradient in one of the most threatened tropical ecosystems. Both herbaceous plants and SDTFs are among the least studied plant groups and forest types, respectively, in tropical regions, and my work reveals fresh and valuable insights into both. Specifically, I showed that while patterns of one aspect of herb diversity (α-diversity) can differ from that of tree communities in a forest landscape, the patterns of another aspect of diversity (β) of both groups could be remarkably similar to each other. I also showed how seasonal variation in critical abiotic factors influences herbaceous communities, and how plant adaptations to those factors play a crucial role in sustaining diversity and shaping community composition. The results provide support for the critical role of environmental filtering in shaping patterns of both diversity and composition of plant communities in tropical forests. The findings add considerably to the current understanding of tropical plant ecology and offer insights to guide biodiversity conservation and restoration decision-making.
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