Paleobotanical records provide opportunity to deepen an understanding of plant community ecology
by reconstructing the outcome of large-scale ecological ‘experiments’ in Earth’s past. However,
limited ability to describe ancient communities via plant functional traits and ecological strategies,
rather than (para)taxonomic composition, can hinder the relevance of constructed datasets. Many
functional traits are not measurable on fossil leaves and the link between leaf morphology and
ecological strategy are currently unresolved. To help fill this gap, we analyze leaf traits applicable to
fossil leaves (i.e., morphology, vein density, leaf mass per area) sampled at the community-scale
from modern plots spanning successional gradients, where plant function and ecological strategies
are expected to vary, in three different forest types: temperate deciduous forest (North Carolina,
USA), tropical rainforest (Malaysian Borneo), and a tropical dry forest (Minas Gerais, Brazil).
Preliminary results will be presented to draw empirical links between morphological leaf traits and
ecological strategy.
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Ecological Strategy of Pacific Northwest Forests During the Miocene Climatic Optimum
The U.S. Pacific Northwest (PNW) hosts an extensive suite of Miocene-aged fossil plants sites, with
the potential to document changes in plant community ecology in response to regional climatic
change during the Miocene Climatic Optimum (MCO; 17-14 Ma) and the ensuing Middle Miocene
Climatic Transition (MMCT; ~14 Ma). The MCO was the most recent period of sustained global
warming and thus provides some analogy to anthropogenic climate change. An important
component of characterizing plant community ecology is the diversity and prevalence of ecological
strategies present within a community. Many previous paleoecology studies rely on a nearest living
relative approach to infer components of ecological strategy (e.g., plant functional types) from fossil
plant assemblages. In contrast, much work in neo-ecology stresses the importance of functional traits
in elucidating prevalent ecological strategies and functional diversity within plant communities.
Here we take advantage of exquisitely preserved leaf compression fossils from Clarkia, northern
Idaho (~16.9 Ma), representing the height of the MCO, to measure leaf functional traits and
elucidate ecological strategies of dominant species in this ancient temperate mixed
conifer-deciduous-evergreen forest. We focus on 13 species, representing the most abundant
angiosperm taxa in the assemblage, including Betula, Castanea, and Quercus. We reconstruct
assimilation rates using gas exchange modeling, address leaf hydraulic efficiency by measuring leaf
vein density, and reconstruct water use efficiency by accounting for the ratio of carbon assimilation
to transpirational water loss. As these species are prevalent in many other Miocene floras of the
PNW, this study provides a benchmark by which to interpret changes in the dominance or presence
of these species through time and, by inference, how Miocene climatic changes impact the
functional composition and diversity of this forest type. We are also providing an example of how
present-day mixed deciduous forests may respond to current anthropogenic changes in CO 2.
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- Award ID(s):
- 1924390
- PAR ID:
- 10463442
- Date Published:
- Journal Name:
- Botany
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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The US Pacific Northwest (PNW), including Washington, Oregon, and Idaho, hosts an extensive suite of Oligocene–Miocene fossil plant sites that have the potential to showcase terrestrial vegetation and climate response to several pronounced environmental perturbations. These include the Mid-Miocene Climatic Optimum (MMCO; ca. 17-14 Ma), the Middle Miocene Climatic Transition (MMCT; ca. 14-13 Ma), and the eruption of the Columbia River Basalts (~95% of its volume 16.7 to 15.9 Ma). This collaborative study focuses on 18 PNW fossil plant sites spanning ca. 32 to 10 Ma, many of which have extensive pre-existing macrofossil collections. First, we radiometrically date interbedded tuffs at these sites to establish a high-resolution temporal framework, using U-Pb/CA-ID-TIMS. We present new dates for the Clarkia/Emerald Creek, Alvord Creek, Juliaetta, Pickett Creek, Whitebird, and Trout Creek fossil sites. Within this temporal framework, we are: 1) documenting regional climate change in the PNW during the MMCO and MMCT using paleobotany-based paleoclimate proxies, and 2) providing an integrated perspective on the response of plant communities to these mid-Miocene environmental changes by combining macrofossil, palynomorph, and phytolith evidence. Taken together, these data will provide a regionally-comprehensive perspective on the sensitivity of terrestrial vegetation and climate to global climatic events known more extensively from marine records.more » « less
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