東華大學圖書館 |

The Role of Tree Traits During Transitions from Savanna to Forest.

紀錄類型:	書目-電子資源 : Monograph/item
正題名/作者:	The Role of Tree Traits During Transitions from Savanna to Forest./
作者:	Flake, Samuel Walker.
出版者:	Ann Arbor : ProQuest Dissertations & Theses, : 2021,
面頁冊數:	181 p.
附註:	Source: Dissertations Abstracts International, Volume: 83-05, Section: B.
Contained By:	Dissertations Abstracts International83-05B.
標題:	Vegetation. -
電子資源:	http://pqdd.sinica.edu.tw/twdaoapp/servlet/advanced?query=28747833
ISBN:	9798494443489

The Role of Tree Traits During Transitions from Savanna to Forest.
Flake, Samuel Walker.

The Role of Tree Traits During Transitions from Savanna to Forest. - Ann Arbor : ProQuest Dissertations & Theses, 2021 - 181 p.

Source: Dissertations Abstracts International, Volume: 83-05, Section: B.

Thesis (Ph.D.)--North Carolina State University, 2021.

This item must not be sold to any third party vendors.

Throughout much of the tropics, savannas (ecosystems with an open tree canopy and an understory of C4 grasses) are maintained by fire. In the absence of fire, forests may expand into former savannas, disrupting ecosystem functioning and outcompeting the unique, diverse savanna flora. In this dissertation, I address several knowledge gaps in the forest expansion process: what sorts of species are driving forest expansion? Do these types of species have differences in growth rates or mortality rates that might explain the rates of expansion? How do differences in allometries among species contribute to the rate of canopy closure?As forests expand into savannas, the species composition shifts. I measured several functional traits of three groups of trees and shrubs: savanna specialist trees (which often persist even with frequent fires), forest specialist trees (which are often excluded by fire, but are shade tolerant and form tall canopies), and generalists (which can persist in both environments). Generalist species are the primary contributor to forest expansion, with forest specialist species colonizing later. Generalists and forest species have similar trait distributions, but savanna species have a distinct strategy that favors defense against fire and high insolation. As forests expand in savannas, the average values of traits shift from a conservative strategy to an acquisitive strategy, reflecting changes to the environment that occur with canopy closure.I used a ten-year record of permanent tree plots to quantify how growth rates and mortality rates differ between savanna specialists and generalist species. Generalists grow much faster than savanna species in the open, contributing to their ability to rapidly expand into savannas. Savanna species and generalist species grow at similar rates when growing under dense canopies, but savanna species die at a much faster rate in the shade. This phenomenon helps explain the patterns of species replacement that occur with forest development, as fastgrowing generalists come to dominate the canopy and savanna species are suppressed in the shade. Their sensitivity to competition makes it unlikely that savanna species could support a closed canopy stand on their own.Leaf area is an important trait that influences both growth rates and the rate of canopy closure. The scaling between leaf area and stem size is fundamental to both tree physiology and stand dynamics. I measured the leaf area of savanna species, generalists, and forest species both in the open and in the shade in order to compare leaf area allometry and the plasticity of leaf area. Generalist and forest species both supported more leaf area than savanna species, principally because they have larger canopies rather than denser canopies. This difference might explain why these types of species grow faster than savannas species. The leaf area of generalists and forest species was not sensitive to shading, larger savanna species supported much less leaf area when grown in the shade, which may predispose them to higher mortality rates. These results provide a potential mechanism for the differences in growth and mortality among functional types. The lower leaf area of savanna species provides another reason that they cannot form a closed-canopy forest.

ISBN: 9798494443489Subjects--Topical Terms:

3560047
Vegetation.

The Role of Tree Traits During Transitions from Savanna to Forest.
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520 $a Throughout much of the tropics, savannas (ecosystems with an open tree canopy and an understory of C4 grasses) are maintained by fire. In the absence of fire, forests may expand into former savannas, disrupting ecosystem functioning and outcompeting the unique, diverse savanna flora. In this dissertation, I address several knowledge gaps in the forest expansion process: what sorts of species are driving forest expansion? Do these types of species have differences in growth rates or mortality rates that might explain the rates of expansion? How do differences in allometries among species contribute to the rate of canopy closure?As forests expand into savannas, the species composition shifts. I measured several functional traits of three groups of trees and shrubs: savanna specialist trees (which often persist even with frequent fires), forest specialist trees (which are often excluded by fire, but are shade tolerant and form tall canopies), and generalists (which can persist in both environments). Generalist species are the primary contributor to forest expansion, with forest specialist species colonizing later. Generalists and forest species have similar trait distributions, but savanna species have a distinct strategy that favors defense against fire and high insolation. As forests expand in savannas, the average values of traits shift from a conservative strategy to an acquisitive strategy, reflecting changes to the environment that occur with canopy closure.I used a ten-year record of permanent tree plots to quantify how growth rates and mortality rates differ between savanna specialists and generalist species. Generalists grow much faster than savanna species in the open, contributing to their ability to rapidly expand into savannas. Savanna species and generalist species grow at similar rates when growing under dense canopies, but savanna species die at a much faster rate in the shade. This phenomenon helps explain the patterns of species replacement that occur with forest development, as fastgrowing generalists come to dominate the canopy and savanna species are suppressed in the shade. Their sensitivity to competition makes it unlikely that savanna species could support a closed canopy stand on their own.Leaf area is an important trait that influences both growth rates and the rate of canopy closure. The scaling between leaf area and stem size is fundamental to both tree physiology and stand dynamics. I measured the leaf area of savanna species, generalists, and forest species both in the open and in the shade in order to compare leaf area allometry and the plasticity of leaf area. Generalist and forest species both supported more leaf area than savanna species, principally because they have larger canopies rather than denser canopies. This difference might explain why these types of species grow faster than savannas species. The leaf area of generalists and forest species was not sensitive to shading, larger savanna species supported much less leaf area when grown in the shade, which may predispose them to higher mortality rates. These results provide a potential mechanism for the differences in growth and mortality among functional types. The lower leaf area of savanna species provides another reason that they cannot form a closed-canopy forest.
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