Don't miss the section a the
bottom on Research Opportunities for Students
on my projects!!!
Barton, A.M.,
T.W. Swetnam, and C.H. Baisan. 2001 Arizona pine (Pinus arizonica) stand dynamics:
local and regional factors in a fire-prone madrean gallery forest of
Southeast Arizona, USA. Landscape
Ecology 16: 351-369
In southwestern North America, large-scale climate patterns appear to
exert control on moisture availability, fire occurrence, and tree
demography, raising the compelling possibility of regional
synchronization of forest dynamics. Such regional signals may be
obscured, however, by local, site-specific factors, such as disturbance
history and land use. Contiguous sites with similar physical
environments, lower and middle Rhyolite Canyon, Arizona, shared nearly
the same fire history from 1660-1801, but then diverged. We
related stand dynamics of Arizona pine (Pinus arizonica) to fire
history and drought severity and compared the dynamics in the two sites
before and after the divergence in fire frequency. Fires occurred
during unusually dry years, and possibly following unusually moist
years. Arizona pine exhibited three age structure peaks: two (1810-1830
and 1870-1900) shared by the two sites and one (1610-1640) only in
middle Rhyolite. The latter two peaks occurred during periods of
unusually low fire frequency, suggesting that fire-induced mortality
shapes age structure. Evidence was mixed for the role of
favorable moisture availability in age structure. As expected,
moisture availability had a prominent positive effect on radial growth,
but the effect of fire was largely neutral. The two sites differed only
moderately in stand dynamics during the period of divergence,
exhibiting subtle age structure contrasts and, in middle Rhyolite only,
reduced growth during a 49-year fire hiatus followed by fire-induced
release. These results suggest that, despite local differences in
disturbance history, forest responses to regional fire and climate
processes can persist.
Jack pine on Great Wass Island:
The research project on the
ecology of jack pine woodlands on Great Wass Island as a collaboration with students. Jack pine is a
northern species that reaches the southeastern limit of its
distribution in the Downeast area of Maine. Great Wass Island has one
of the largest populations of jack pine in Maine, as well as many rare
plants and ecosystems. Jack pine is typically a fire-dependent
species that is replaced by more shade tolerant species (e.g., spruce)
in the absence of fire. It also is typically a species of dry
sandy soils or outcrops. Surprisingly, there's very little
evidence of fire on Great Wass Island over the past century. Also
puzzling is that large stands of jack pine occur in wet peat
bogs. We are using a combination of tree-ring analysis and aerial
photographic analysis to address several questions: (1) how has jack
pine persisted on the island without fire, (2) has jack pine invaded
bogs only in the past century, and (3) what drives the waves of
regeneration (short periods over the last century during which this
species has established many new individuals) apparent in our data on
jack pine ages. I've provided two abstracts from recent presentations by
students on this work. Dan Grenier and I are (as of spring 2004) completing
the cross dating of cores for this project.
Recently, I submitted a grant proposal (with Julia
Daly of UMF and Ann Dieffenbacher-Krall and George Jacobson of UM
Orono) to the National Geographic Society to extend work to the
paleoecology of the bogs. An abstract from that proposal is
provided below.
Ten students have worked with
me on the project so far, and it has been a great success and lots of
fun. The abstracts below, from the Spring 2000 UMF symposium,
should provide an ideas of the range of projects we're
pursuing. See
below for student research opportunities on this project.
Dan Grenier. Jack
pine in the absence of fire on Great Wass Island, ME: bog and outcrop
populations
We investigated the population
dynamics of jack pine on rock outcrops and in bogs at the southeastern
margin of its distribution, in mid-coast Maine. Jack pine is
typically a fire-dependent species, which is replaced by more
shade-tolerant species, such as spruce, in the absence of fire.
Using analyses of age structure and seedling establishment, we assessed
whether jack pine is self-perpetuating on Great Wass Island, where
there is little evidence of past fire. The stands generally
exhibit patterns indicating self-perpetuating populations, although
clear pulses of recruitment synchronized among sites are also apparent,
especially in outcrop stands. Factors other than fire, such as
climatic fluctuations, are most likely to account for these
pulses. Compared to outcrops, bogs tend to have relatively young
populations with vigorous trees and many seedlings. These results
suggest recent invasion of bogs by jack pine, perhaps as a result of
bog succession or climate fluctuations. This is the first
documentation of bog populations of this species, although this has
been found for similar fire-associated, stress-tolerant pines.
Max Postvanderburg and
Stasia Savasuk. Invasion of bogs on Great Wass Island by Jack
Pine: an aerial photographic analysis
The Great Wass Island Project,
led by Dr. Andrew Barton, has documented, for the first time, the
occurrence of jack pine in bogs. This is unusual given that jack
pine typically grows on dry soils subject to frequent fire, both of
which are not characteristic of Great Wass Island. Results from age
structure analyses suggest that jack pine invaded these bogs in the
20th century, whereas those portions of the population occurring on
outcrop sites appear to be much older. We are attempting to test
this hypothesis by using aerial photographs, which exist for much of
the US from before 1950 to the present. After intensive searching, we
found and obtained aerial photographs for three dates: 1996, 1975, and
1940. Using three bog sites for which age structure data now exist, we
will be comparing the three photos to examine the extent of invasion of
jack pine and other tree species over a 56-year period (1940 to 1996).
We will describe our analytical methods, preliminary results, and future
projects that may aid in understanding jack pine population patterns on
Great Wass Island.
Andrew M. Barton, Julia F.
Daley, Ann C. Dieffenbacher-Krall, and George L. Jacobson.
Paleohistory of Disjunct Plants and Fire in Coastal Plateau Bogs on
Great Wass Island, Maine. Summary of Grant Proposal Submitted in
2004.
The eastern coast of Maine is botanically distinct from the rest
of the state. The cool, maritime climate harbors a unique
assemblage of rare and disjunct northern flora, especially in coastal
plateau bogs, a peatland-type confined to a short stretch of the far
eastern coast. Great Wass Island supports the largest area of
these bogs as well as an extensive disjunct stand of Pinus banksiana at
its southeastern geographic limit. Recent work has revealed that
P. banksiana, a species usually confined to xeric sites, began invading
coastal plateau bogs on the island in the early 20th century. We
propose to address two sets of issues using analyses of fossil pollen,
macrofossils, and charcoal in peat cores: (1) the colonization and
subsequent dynamics of this unique northern plant assemblage in
response to climate since glacial retreat (~13,000 years before
present) and (2) the more recent dynamics of P. banksiana in these
bogs, in particular whether the recent invasion is part of a
fire-driven cycle or a response to recent environmental change.
We will analyze peat cores employing standard techniques, including
radiocarbon dating, examination of contiguous 2- to 5-cm intervals,
identification of periods of fire activity, pollen recognition at 100-
to 200-year resolution, and the use of an extensive reference
collection for identification of pollen and macrofossils. This
project would illuminate some fundamental biogeographic and
conservation issues regarding the responses of the unique flora of
coastal plateau bogs to past climates and fire as well as to ongoing
climate alterations.
This project is a
collaboration among Nancy Prentiss (instructor in Natural Sciences, two
students (Lauri Brewster and Annie Cox), and myself. The goal of
Phase I of the research, which has now been completed, was to document
which non-native woody invasive plants occurred in the Farmington
area and to examine their origin and habitat relationships. In
addition to presentations at UMF by Lauri and Annie, I gave a talk on
the work at the fall 2003 New England Invasives Summit in Framingham,
MA. We have an article on the research in press in Biological Invasions (see Recent Publications), and I published
a magazine article in Natural New
England in winter 2004. I'm now thinking about the next
step in this project. Below is the Abstract from our in press
paper.
Barton,
A.M., L. Brewster, A. Cox, and N. Prentiss. In press.
Nonindigenous invasive woody plants in a rural New England town. Biological Invasions
We examined the distribution and abundance of non-indigenous
woody invasive plants in Farmington, Maine, a rural New England town in
a forested landscape. We found 12 invasive species and more than
7 patches per km from surveys on 33 transects (54.3 km) along field
edges, abandoned railroad-right-of-ways, riparian zones, and
roadsides. Invasive abundance was greater than for undeveloped
roadsides in a forested landscape in Upstate New York, but apparently
lower than for more developed areas of the northeastern U.S., where, in
contrast to western Maine, invasives have extensively penetrated forest
interiors. Invasive abundance increased with amount of lawn and
proximity to town, suggesting a close association between local
horticulture and the spread of woody invasives. Invasive
abundance and diversity were highest in riparian areas, probably due to
relatively high levels of propagule pressure. Species differed in
the extent of invasiveness, ranging from those still dependent on
planted parent trees to fully invasive populations that had spread well
beyond their planted origins. The invasive species recorded in
this study have caused ecological and economic damage elsewhere.
The lower levels of invasiveness in Farmington are likely a result of
the isolation, small human population, and forested landscape rather
than low levels of invasibility. This suggests the potential for
future risks, and the importance of intervention while populations can
still be eradicated or controlled.
The "Work Initiative" program at UMF has greatly enhanced research opportunities and atmosphere. Here's how it works. Professors decide on appropriate faculty-student collaborations for the summer or during the school years, and the university pays students to work on the project (up to $1000 per semester and $2000 during the summer).
I've had about 15 students work with me over the
last six years. Some, usually younger students, have acted as
assistants to older students and to me. As students gain more
experience, they take on more responsibility and independence.
Students have given talks at national scientific meetings and
co-authored a paper with me published in a peer-reviewed scientific
journal. I've also had students work with me on "green campus"
projects, such as the successful effort to design the new UMF Education
Building as a green, environmentally sensitive building.
Projects that students could work on in 2004-2005
are the following:
(1) Invasives plants in the Farmington area,
(2) Peat coring and pollen analysis on Great Wass Island (if we get
funding), and
(3) Green campus projects, especially focusing on carbon dioxide
emissions and energy conservation.
Come by, call, or email me to talk about
opportunities for you.