Plan for upcoming posts, concerning last few topics of megafaunal effects - shows papers analysed and considered for elucidation in last posts (not formally written up due to time constraints).
Biogeochemistry
Megafauna
play a crucial role in unlocking nutrients that would otherwise be locked in
woody biomass for decades – a feature that is particularly salient in low-productivity
/ nutrient-poor regions. Hobbs
NT (1996) Modification of ecosystems by ungulates. McNaughton SJ, Banyikwa FF,
McNaughton MM (1997) Promotion of the cycling of diet-enhancing nutrients by
african grazers
Lateral
movement of nutrients Doughty CE,
Wolf A, Malhi Y (2013) The legacy of the Pleistocene megafauna extinctions on
nutrient availability in Amazonia. Wolf A, Doughty CE, Malhi Y (2013) Lateral diffusion of
nutrients by mammalian herbivores in terrestrial ecosystems
Oceans,
whales etc transfer from deep ocean to surface Doughty CE, et al. (2016) Global nutrient transport in a world of giants
Connectivity
between continental and ocean nutrient pumps may have joined together into a
global nutrient pump working in the opposite direction to abiotic nutrient
flows of weathering to ocean sediments (as outlined above) - magnitudes very high!
Megafaunal effect on Climate Change
Having
already looked at the likely effect that climate change can have on megafauna,
an interesting consideration is the effect megafauna can have on climate
change.
Brault MO, Mysak LA, Matthews HD, Simmons CT (2013)
Assessing the impact of late Pleistocene megafaunal extinctions on global
vegetation and climate
Release of
greenhouse gases via biogeochemical cycling, eg cattle, also wild animals Smith FA, Elliott SM, Lyons SK (2010) Methane emissions
from extinct megafauna. Smith
FA, et al. (2016) Exploring the influence of ancient and historic megaherbivore
extirpations on the global methane budget. Zimov S, Zimov N (2014)
Role of megafauna and frozen soil in the atmospheric CH4 dynamics.
0.08 – 0.2 Celsius global cooling from Pleistocene
megafaunal extinction – potentially contributed to Younger Dryas cold episode. Shift to
increased woody vegetation post megafauna (as covered earlier in ecosystem physical structure) could
also contribute to cooling, acting as a sink for CO2 – however, counteracted by
potential decreases in albedo caused by said tree cover Bonan GB (2008) Forests and climate change: Forcings,
feedbacks, and the climate benefits of forests.
Potentially to the order of 0.2 C post
extinction, thus counteracting greenhouse effect at global scale.
Trampling /
grazing also capable of altering albedo in the absence of tree cover -
Eg snow trampling in winter can
reduce soil temperatures by 15-20 C. Grazing removes removes dark brush,
exposing bright snow, increasing albedo, cooling surface.
Full
accounting of megafaunal effects on climate, including methane
emissions, soil greenhouse gas emissions, changes in surface albedo and
evaporation still to be done – thus far not known with any certainty what the full contribution of
megafauna is.
