Thesis (Ph. D.)--University of Missouri-Columbia, 2001. / Typescript. Vita. Includes bibliographical references (leaves 287-292). Also available on the Internet.

Thesis (doctoral)--Swedish University of Agricultural Sciences, 2001. / Appendix reprints five papers and manuscripts, four co-authored with others. Includes bibliographical references. Also partially issued electronically via World Wide Web in PDF format; online version lacks appendix.

Thesis (Ph. D.)--University of Missouri-Columbia, 2001. / Typescript. Vita. Includes bibliographical references (leaves 287-292). Also available on the Internet.

Light availability in forest understories is a well recognized constraint on sapling growth, but limitations in soil nitrogen (N) availability, and the link to foliar photosynthetic capacity, typically receive less consideration in describing stand dynamics. My primary hypothesis is that light and soil N availability have species-specific effects on photosynthetic activity and growth, and that together these resources will better define understory development in complex forests. To test these relationships, I examined 1) soil N indices and the tradeoffs between soil fertility and light attenuation in old-growth forest understories; 2) the effects of light and N constraints on understory sapling foliar N concentration (N%), N per unit area (Na), and natural abundance of ¹³C; 3) the effects of light and soil N supply on species growth and photosynthetic activity in a factorial field experiment; and 4) the mechanisms responsible for the stagnation of understory saplings. Soil N indices incorporating dissolved inorganic N and organic N were useful in characterizing differences in N supply among contrasting sites. Understory light availability declined with increasing soil N supply, while understory Abies lasiocarpa had strong correlations between foliar N% and soil N availability, despite shading effects. In partial-cut forests, understory Tsuga heterophylla and Picea glauca x sitchensis had consistent foliar N% across gradients of light availability; in contrast, foliar N% of Betula papyrifera and Thuja plicata declined with increasing shade, which would distort assessments of soil fertility and perhaps contribute to increased mortality of these species in deep shade. Strong correlations between foliar Na and ¹³C or growth increment suggest foliar N per unit area is the simplest integration of light availability and N nutrition on leaf photosynthetic activity. Ontogenic interactions that occur among foliar attributes and tree size in forest understories, especially for saplings < 1 m in height, contribute to time effects on growth patterns and emphasize the need for long-term studies of species autecology and stand dynamics. My experimental manipulation of light and N supply on saplings was ineffective, and future research using natural gradients in site productivity may be more fruitful in defining species response to light and N interactions.

Our objective was to identify the major barriers to natural regeneration of tree species in abandoned Panamanian pastures as a first step in formulating management strategies to facilitate forest recovery. We tested whether fire, seed dispersal, and the presence of an introduced grass, Saccharum spontaneum L., were barriers to forest regeneration. We examined growth, survival, and density of both experimentally-introduced and naturally-regenerating tree seedlings using a series of multifactorial experiments. / We found that seed dispersal limits forest regeneration. Large-seeded species have the highest performance in the Saccharum spontaneum, but were found in the lowest abundance in natural conditions. Small-seeded species were most frequently observed, but they have the lowest survival. We conclude that dispersal limitations preclude entry of the larger-seeded species. Distance from the forest limits dispersal of many small-seeded species. Fire is a major barrier to natural regeneration because it lowers species diversity.

A major environmental concern throughout the tropics is deforestation. While many forests are in a state of crisis, such an encompassing narrative can obscure significant instances where forest-cover expands. This research investigates the geography of forest regeneration in rural Costa Rica from a social and institutional perspective. Attracted to the Pacific coast, foreigners purchase farms, change the patterns of land ownership, and extensively promote secondary forest growth. Environmental change and a declining agriculture sector have forced peasants to sell or abandon land and diversify their livelihoods. Two conservation NGOs collaborate at an institutional level to promote reforestation and consolidate protected properties into the Mesoamerican Biological Corridor. Drawing on foreign funding, they serve as an avenue through which external visions of land management become reproduced locally. This case illustrates how the values and management decisions of a constellation of actors synergistically interlink to influence local land-use and ultimately join to expand forest-cover.

Light availability in forest understories is a well recognized constraint on sapling growth, but limitations in soil nitrogen (N) availability, and the link to foliar photosynthetic capacity, typically receive less consideration in describing stand dynamics. My primary hypothesis is that light and soil N availability have species-specific effects on photosynthetic activity and growth, and that together these resources will better define understory development in complex forests. To test these relationships, I examined 1) soil N indices and the tradeoffs between soil fertility and light attenuation in old-growth forest understories; 2) the effects of light and N constraints on understory sapling foliar N concentration (N%), N per unit area (Na), and natural abundance of ¹³C; 3) the effects of light and soil N supply on species growth and photosynthetic activity in a factorial field experiment; and 4) the mechanisms responsible for the stagnation of understory saplings. Soil N indices incorporating dissolved inorganic N and organic N were useful in characterizing differences in N supply among contrasting sites. Understory light availability declined with increasing soil N supply, while understory Abies lasiocarpa had strong correlations between foliar N% and soil N availability, despite shading effects. In partial-cut forests, understory Tsuga heterophylla and Picea glauca x sitchensis had consistent foliar N% across gradients of light availability; in contrast, foliar N% of Betula papyrifera and Thuja plicata declined with increasing shade, which would distort assessments of soil fertility and perhaps contribute to increased mortality of these species in deep shade. Strong correlations between foliar Na and ¹³C or growth increment suggest foliar N per unit area is the simplest integration of light availability and N nutrition on leaf photosynthetic activity. Ontogenic interactions that occur among foliar attributes and tree size in forest understories, especially for saplings < 1 m in height, contribute to time effects on growth patterns and emphasize the need for long-term studies of species autecology and stand dynamics. My experimental manipulation of light and N supply on saplings was ineffective, and future research using natural gradients in site productivity may be more fruitful in defining species response to light and N interactions.

Thesis (M.E.S.)--Baylor University, 2007. / Includes bibliographical references (p. 147-153).

Thesis (Ph.D.)--University of Western Australia, 2007.

Thesis (M.S.)--Oregon State University, 1998. / Typescript (photocopy). Includes bibliographical references (leaves 53-56). Also available via the World Wide Web.