Humans, Climate, and Pine Forests

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The pines are abundant, and widespread. Does that mean they’re doin’ just fine?

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“A crucial implication of these patterns is that broad geographic
ranges and high abundances provide no guarantee of stability in range
or abundance under altered climate regimes of the future.”

“Å  the unprecedented rates of climate change predicted in many future
scenarios may outstrip the natural capacity of pines to disperse into
newly suitable territory.”
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Human Impacts in Pine Forests: Past, Present, and Future*

David M. Richardson, Philip W. Rundel, Stephen T. Jackson, Robert O.
Teskey, James Aronson, Andrzej Bytnerowicz,
Michael J. Wingfield, and Serban Proches

The Annual Review of Ecology, Evolution, and Systematics
December 2007
Annu. Rev. Ecol. Evol. Syst. 2007. 38: pages 275-97

First published online as a Review in Advance on September 5, 2007

Key Words
air pollution, biological invasions, conservation, fire, land use

Abstract
Pines (genus Pinus) form the dominant tree cover over large parts of
the Northern Hemisphere. Human activities have affected the
distribution, composition, and structure of pine forests for
millennia. Different human-mediated factors have affected different
pine species in different ways in different regions. The most
important factors affecting pine forests are altered fire regimes,
altered grazing/ browsing regimes, various harvesting/construction
activities, land clearance and abandonment, purposeful planting and
other manipulations of natural ecosystems, alteration of biotas
through species reshuffling, and pollution. These changes are
occurring against a backdrop of natural and anthropogenically driven
climate change. We review past and current influence of humans in pine
forests, seeking broad generalizations. These insights are combined
with perspectives from paleoecology to suggest probable trajectories
in the face of escalating human pressure. The immense scale of impacts
and the complex synergies between agents of change calls for urgent
and multifaceted action.

EFFECTS OF CLIMATE CHANGE ON PINE FORESTS
Pines have been subjected to climatic changes throughout their
evolutionary history. The well-documented history of the past 20,000
years, spanning the last glacial-interglacial transition, is
especially relevant for understanding the future of pines in the
context of ongoing and future global climate change. Å . A crucial
implication of these patterns is that broad geographic ranges and high
abundances provide no guarantee of stability in range or abundance
under altered climate regimes of the future. Seed dispersal was not a
major limiting factor to postglacial pine migration; both
wind-dispersed (e.g., P. banksiana, P. ponderosa) and bird-dispersed
species (P. edulis) expanded their ranges northward rapidly. However,
the unprecedented rates of climate change predicted in many future
scenarios may outstrip the natural capacity of pines to disperse into
newly suitable territory.

Within already established ranges, pine forests have undergone
progressive changes in composition and disturbance regime as climate
changed. Fire regimes in montane and boreal pine forests have varied
dramatically in the past 10,000 years as temperature and moisture
regimes changed (Brunelle et al. 2005, Carcaillet et al. 2001).
Climate-driven expansions and contractions of pines at upper and lower
treeline and at parkland/forest boundaries are well documented (e.g.,
Lloyd & Graumlich 1997, Lyford et al. 2003, Lynch 1998). Pine
populations in forests have increased and decreased in the past few
thousand years in response to climate change (Booth & Jackson 2003,
Schauffler & Jacobson 2002). Dendroecological studies indicate
demographic and fire-regime responses to climate changes over the past
few centuries in boreal and montane pine forests and semiarid pine
woodlands of North America (Bergeron et al. 2004, Gray et al. 2006,
Swetnam et al. 1999).

“Ongoing and future climate changes will affect pine-dominated
ecosystems in complex ways. Climatic changes will change disturbance
regimes, demographic structure, growth rates, and stand composition.”
“Models of realized distributions of pines species to climate-change
scenarios indicate that the ranges of many pine species will be
displaced, often dramatically, in a greenhouse world (Figure 3).
Although these scenarios are probably poorly suited for predicting the
future distributions of pines and other species, they provide good
indications of the magnitude of biogeographic change that we should
expect.”
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