Paleoecology Lecture Notes Fall 2024 PDF

Ecology is the study of the relationships between living things and their environment. Paleoecology = ecology of the past What was the ecology of the New York City area like 12,000 years ago? Was it warmer or colder? Were the plants and animals the same? Why would we want to know this? Knowledge f...

Ecology is the study of the relationships between living things and their environment. Paleoecology = ecology of the past What was the ecology of the New York City area like 12,000 years ago? Was it warmer or colder? Were the plants and animals the same? Why would we want to know this? Knowledge from the past may help us understand what we see today. Maybe we can use this information to predict or prepare for the future. An example of famous paleoecology science paper that showed us what happened in the past so we can understand patterns of glaciation and know what to expect in the future is by Hays, Imbrie and Shackleton. They used ocean cores, forams*, oxygen isotopes and found evidence supporting: ice ages occur and last for about 100,000 years and that they are separated by warm phases that last about 10,000-20,000 years. We are in a warm phase now. *Foraminifera: simple, aquatic, amoeboid protozoans (mostly marine); indicators of salinity, temperature, oxygen ratios During an ice age: Ice sheets grow larger Sea levels get lower Plants and animals redistribute themselves. Ice conditions today: Ice conditions 18,000 years ago: How does a glacier grow? More snow falls than that which melts in the summer; it accumulates. This is how much of the US was covered with ice during the Last Glacial Maximum, 18,000 years ago. Vegetation distribution today………………………………………………..………and at the Last Glacial Maximum: Did NYC look something like this 12,000 years ago? ice , mastodons, sabertooth cats, tundra vegetation……. How can we find out? To trace the ecology of the past you need evidence: -Fossils of microscopic size (microfossils) are everywhere and abundant. -Microfossils are biological indicators of past environments. -If you know the ecological requirements of the various fossil species and their current geographic distributions, you can infer the environmental conditions of where you found them. An example of microfossils: Pollen grains: microscopic structures that carry male genetic material from one plant to the next; indicators of vegetation. Here are some pictures of pine pollen, hickory pollen and basswood pollen: Palynology: the study of pollen and spores The reconstruction of a vegetation history is largely dependent on fossil pollen. Pollen and spores have a highly resistant outer layer that facilitates excellent preservation. Principles of pollen analysis Plants produce enormous amounts of pollen pollen grains have distinctive surface sculpture which permits identification of the plant species or family that produced the pollen each spring/summer, the pollen released into the atmosphere eventually returns to the earth’s surface = pollen rain Pollen rain that falls on lakes/ponds/bogs gets preserved in the bottom sediments. Each year a layer of pollen is deposited, leaving a signature of the vegetation that produced it. If a palynologist locates a lake or bog that has not been disturbed, they have found a potential record of vegetation. The pollen analysis includes identification of no less than 300 grains per layer and the tallying of each type. For example 80 oak pollen grains, 20 hemlock grains, etc. How do you get the pollen out of the lake? Find the deepest part of the lake, it will typically have the thickest sediments. Core the sediments with a hand driven piston-corer. Wrap and label each core segment and bring to the lab. How do you isolate the pollen from the lake mud? Take 1cc sediment samples from the core at close intervals. Process using sieves and various chemicals to remove unwanted components from the sediment. Mount the resulting pure pollen suspension on a slide and begin microscopic analysis. Plant macrofossils: are fossil seeds, needles, buds, twigs, etc. can often be identified to the species level can confirm local presence of a taxon at the study site can provide valuable material for radiocarbon dating. can be isolated from pollen-bearing sediments by sieving and identified using a dissection microscope, reference material and pictorial keys paper birch seeds Forest, climate, and fire history of the Hudson Highlands, southeastern New York during the last >12,500 years (TMG): The Late-glacial (>12,500 years ago (BP)): dominated by herbaceous and shrub types: with some trees, Pine (Pinus) and Spruce (Picea) possibly represents a tundra-like environment with scattered trees. More Late-glacial (12,500-11,000 BP): onset of organic deposition into each pond and the first occurrence of seeds and other plant macrofossils and large increases in pollen influx to the ponds indicates development of a mixed boreal coniferous - temperate deciduous woodland (Spruce, Fir, Paper Birch,Oak, Ostrya/Carpinus, and Ash. = dramatic environmental change (climatic warming) began at 12,500 years ago. Younger Dryas (11,000-10,000 BP) : An abrupt climatic flip back to cold conditions occurred at approximately 11,000 years ago and lasted for roughly 1000 years. This happened because the Gulf Stream ocean current was shut off for 1000 years due to glacial melt water reducing the salinity of the current. This cool climatic episode is inferred from the dominance of Spruce, Fir, and Alder with a reduction of Oak, Ash, and Ostrya/Carpinus. Holocene: Warm conditions, similar to the present, were established by 10,175 years ago. This is inferred from expanding Oak-dominated forests and invasion by White Pine, followed by Eastern Hemlock at 9645 years ago and replacement of Paper Birch (cold tree) by Gray Birch (warm tree) at approximately 9575 years ago. The early and middle Holocene (10,000 - 2000 BP) : Featured immigration of other tree taxa: American Beech (Fagus grandifolia) at 8100 BP Hickory (Carya) at 6200 BP American Chestnut (Castanea dentata) at 3600 BP Native American influence on vegetation: sources: archaeological, paleoecological, dendrochronological, and ethnobotanical research, as well as traditional ecological knowledge Native Americans actively managed the landscape through activities such as burning and cultivation to increase the mast yields of their favorite native plants notable favorites: hickory, oak, chestnut, walnut: important sources of fat and carbohydrates began as early as the Middle Archaic Period (approximately 8,000 to 5,000 years ago) refs in Fern, Rachel R., et al. "Native American landscape modification in pre-settlement south-west Georgia." Landscape History 41.1 (2020): 57-68. Arrival of Euroamericans (about 1700 AD): Euroamerican settlement of the Hudson Highlands is well-documented in the pollen record: rises in Ragweed, Grass, and Composites signal land clearance and decreased percentages of Oak, Pine, and Eastern Hemlock reflect the harvest of each taxon. Increased charcoal signals use of fire in connection with land-clearance, wood-related industries (charcoal, iron, and brick manufacturing), and operation of railroads (track fires)). Decline of American chestnut (Castanea dentata) due to a fungal pathogen is introduced at New York City in 1904. In 1909, only 1 to 2% of Castanea in the Hudson Highlands was affected by the pathogen; by 1915, most Castanea were killed. Prior to the blight, Castanea represented 35% of the trees in the forest with as much as 70% on mid-elevation slopes. This sequence is evident in the pollen record. What about fire throughout this history? Fossil charcoal was more abundant during the last 10,000 years than between 12,500 and 10,000 years ago. High values of Oak pollen in association with continuous charcoal influx for some 9000 years suggest that fire played an important role in the development and maintenance of Oak forest. How do you know the ages of these vegetation events? Radiocarbon dating (AMS method) Match ages of historical events with corresponding signals in the fossil record (for example the Ragweed Rise). Pollen diagram showing vegetation history for the last ten thousand years at Black Rock Forest. Data from Sutherland Pond (Maenza-Gmelch, 1997): What is the cause of the observed pattern of glaciations? The most widely accepted theory is the Milankovitch Theory of Orbital Forcing: Milankovitch proposed that cyclical changes in the relative positions in the earth and the sun (orbital geometry) influence the amount of solar radiation received on earth. These variations in solar radiation affect the contrast between summer and winter temperatures. If summers are not warm enough to melt the previous year’s snow then ice sheets grow.  ~100,000 year cycle 41,000 year cycle 21,000 year cycle Dendroclimatology (Dendrochronology) is the science of determining past climates from tree rings. Tree rings are wider when conditions favor growth, narrower when times are difficult. Evergreen trees at the edge of Alaska’s tundra are growing faster, suggesting that at least some forests may be adapting to a rapidly warming climate. How did we find this out? Tree ring samples show that both tree-ring width and density shot up starting a hundred years ago, and rose even more after 1950. (Trees are thought to absorb a third of all industrial carbon emissions, transferring carbon dioxide into soil and wood. Far northern ecosystems may play a future role in the balance of planet-warming carbon dioxide that remains in the air.) Ref: LDEO Tree Ring Lab watch: https://www.youtube.com/watch?v=xmZO7aRgcW4 up to 1 minute 12 seconds Cross section of the trunk of a red oak tree In an annual ring one can distinguish the early wood (light band) with large, thin walled cells and the late wood (dark band) with small, thick walled cells. The early wood, formed in the spring, has an important role in the transportation of liquids in upward direction. The function of the late wood, on the other hand, is providing stiffness to the trunk. cross section of tree trunk tree core Ice cores: Trapped air bubbles form an archive of past atmosphere and temperature. An 800,000 year record comes from Dome C in Antarctica. If you have time you might enjoy watching "Chasing Ice" on Netflix.