Terrestrial ecosystem dynamics across Quaternary glacial terminations: Paleoecological insights from California and Malesia
Restricted (Penn State Only)
- Author:
- Benfield, Adam
- Graduate Program:
- Geosciences
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- May 03, 2024
- Committee Members:
- Donald Fisher, Program Head/Chair
Erica Smithwick, Outside Unit Member
Sarah Ivory, Special Member
Peter Wilf, Major Field Member
Sarah Ivory, Chair & Dissertation Advisor
Roman DiBiase, Outside Field Member - Keywords:
- Palynology
Ecology
Indonesia
Tropics
Mono Lake
Pollen
Pleistocene - Abstract:
- Earth’s hotspots of terrestrial biodiversity assembled into their modern state via a dynamic history of geologic, ecological, and climatic change. Yet today, most ecosystems have been heavily degraded by anthropogenic disturbances and are under severe pressure as climate changes over the 21st century and beyond. In order to conserve these ecosystems, it is essential to understand how ecosystems work, how and when they assembled into their present state, and how they have functioned in the past. The severe anthropogenic degradation, coupled with limited windows of direct observations, make it difficult to characterize how ecosystems fundamentally operate and respond across centuries and millennia of climate and environmental changes. Terrestrial ecosystems have been extremely dynamic over the last million years, reorganizing on regular cycles of global glaciation and deglaciation. These glacial-interglacial cycles are convenient natural experiments, allowing paleoecologists to explore repeated ecological responses to climate and environmental changes as Earth’s terrestrial ecosystems organized into their modern state over the Quaternary period. This dissertation examines the role that cycles of Quaternary glacial-interglacial environmental change have had in shaping the modern ecology and biogeography of two biomes: the semi-arid steppe of the Great Basin, USA and the tropical rainforests of the Malay Archipelago. These environments serve as two end members along environmental and ecological gradients of precipitation, tree cover, canopy stratification, and fire regimes. At Mono Lake, California, I used fossil palynomorph analysis, coupled with microcharcoal counts, to document changing vegetation composition, megafauna activity, and fire regimes from 16 – 9 ka, the last deglaciation. At Lake Towuti, Indonesia, I used fossil palynomorph analysis, coupled with microcharcoal counts and organic biomarker indicators of paleoclimate to understand how climate drove the assembly of interglacial rainforests on Sulawesi during the last two glacial-interglacial terminations (24 – 9 ka and 155 – 125 ka). Both ecosystems exhibited substantial responses to the extreme climate change events of deglaciation, indicating that these ecosystems are sensitive to climate changes locally and by global climate changes driven by abrupt processes at high northern latitudes. Around Mono Lake, fire regimes played an important role in forcing canopy changes during abrupt climate changes such as the Younger Dryas and Bølling–Allerød during the last deglaciation. During the Pleistocene, woodlands responded to these climate change events by rapidly changing their structure, in-filling or opening within ~100-200 years. These rapid changes appeared to have put significant pressure on megafauna in the basin, as the abundance of the coprophilous fungal spore Sporormiella declined in a step-wise fashion at each major abrupt climate change period. The modern steppe ecosystem rapidly developed at the Pleistocene-Holocene boundary, potentially playing a role in the final extirpation of megafauna. On Sulawesi, the modern rainforest ecosystems developed more gradually over ~7,000 years following the Last Glacial Maximum (~22 ka), as heavily disturbed, and fire-prone dry tropical forests of the late Pleistocene were replaced by modern rainforest communities into the early Holocene. During the penultimate glaciation (~130 ka), rainforests around Towuti were dominated by different and substantially more diverse vegetation communities than those seen during the last glacial transition. The ecological transitions which occurred during the last two glacial-interglacial transitions imply that climate conditions during glacial terminations have a strong impact on the subsequent, interglacial rainforest communities. In particular, the data from Lake Towuti show a positive relationship between palynological richness and temperature, implying that floristic diversity on Sulawesi becomes restricted during glacial periods. Together, the pollen results from both regions show contrasting responses in vegetation composition and ecological structure of terrestrial ecosystems in eastern California (rapid) and Indonesia (gradual).