The
four papers below draw on large populations of trees in urban areas in order to
model or characterize growth and survival given the biological, social, and
environmental factors at play. The months and years following planting are a
tenuous period in a tree’s life. The first two papers model replanting success
in dramatically different environments (ranging from Sub-tropical to Temperate
North America) from both biological and sociological perspectives. Most
long-lived urban tree species that survive planting and become established in
the landscape will experience some level of human-induced (i.e., construction)
or environmental disturbance during their lifetime. The latter two papers
identify conditions that contribute to mature tree mortality and/or failure.
Factors
Influencing Urban Tree Planting Program Growth and Survival in Florida, United
States
Andrew
K. Koeser (Presenter),
Edward F. Gilman, Maria Paz, and Chris Harchick
Planting projects with
high mortality represent both an economic loss and ecological disservice once
one accounts for the input and materials associated with tree production and
installation. With many urban tree planting initiatives underway (including
several higher profile million-tree endeavors), continual assessment is needed
to gauge overall program success. Past planting projects funded by the Florida
Forest Service (FFS) were revisited 2 to 5 years after installation to document
tree survival. Additionally, various site (e.g., soil compaction, installed
irrigation) and tree-related (e.g., species, nursery production method, initial
size at planting) factors were noted to assess their impact on tree growth.
Results, show that the overall survival percentage for the 26 sites (over 2350
trees) was high, with 93.6% of trees alive at the time of inspection. On-site
irrigation played a significant role in tree survival and growth, especially
for Magnolia grandiflora (97.7% survival on irrigated sites; 73.8%
survival on non-irrigated sites). Findings from this work validate the effectiveness
of current FFS program policies, which include required maintenance of tree
quality (e.g., no die-back) within the first year after planting, and offer
further insights regarding the impacts of season of planting and initial size
of nursery stock on plant growth and development.
Explaining planted-tree survival and
growth in urban neighborhoods using a social-ecological systems perspective: A
study of recently-planted trees in Indianapolis (United States)
Jessica
M. Vogt
(Presenter),Shannon Lea Watkins, Sarah K. Mincey, Matthew S. Patterson, and
Burnell C. Fischer
Tree-planting success in urban environments is not
well understood. This presentation uses a data set of over 1300 trees planted
in Indianapolis, Indiana (United States) to answer the question: What characteristics of trees, the
biophysical environment, the community, and institutions predict survival and
growth of trees in neighborhood tree-planting projects? We combine Ostrom’s
social-ecological systems framework and the Clark et al. model of urban forest
sustainability to inform the selection of variables that may influence tree
outcomes. We use a probit model to predict tree survival, and multiple linear
regression to predict tree growth rate, both with random effects at the neighborhood
level. We find that tree characteristics more strongly influence tree growth
than survival, and that characteristics of the biophysical environment,
community, and institutions influence both survival and growth. Future research
should continue to examine tree survival and growth in the context of the urban
forest as a social-ecological system.
Urban Tree Longevity and Construction:
Following a Milwaukee, WI, USA Street Tree Population
Richard J. Hauer
(Presenter), Andrew K. Koeser, Kelly Norris, and Randy Krouse
Urban trees face many stress
factors linked to adverse site conditions, environmental extremes, and physical
disturbances. These factors affect tree survival in urban areas. This
presentation shows the impacts of construction on street tree longevity,
growth, and condition. A street tree population in the city of Milwaukee,
Wisconsin (United States) was followed for over 25 years with three assessments
conducted in 1979, 1989, and 2005. In 1979, prior to street construction,
baseline measurements of tree condition, tree size, tree species, and site
attributes were made. These factors were measured again in 1989 and 2005 and
comparisons were drawn between trees affected or spared by nearby construction
activity. The effects of construction and other factors on tree longevity were
determined with multivariate logistic regression. Cross validation showed our
model was able to successfully predicted survival nearly 85% of the time. We
found that: 1.) tree survival varied by species; 2.) trees were more likely to
die as trunk diameter increased; 3.) as planting space width decreased in the
tree lawn tree longevity decreased; and 4.) tree longevity decreased as tree
condition decreased. Trees were twice as likely to die when exposed to redevelopment
activities. Finally, results show a tree preservation program developed by
Milwaukee in the mid 1980’s has led to less tree mortality and a lower
reduction in tree condition when trees are subjected to construction compared
to results before the tree preservation program.
Failure of Boulevard Trees During Wind-Loading Events
Gary Johnson
Boulevard
tree failures (i.e., full or partial windthrow failures at or below ground
line) range from catastrophic and widespread losses to seemingly random and unpredictable
events depending on the wind loading event. Wind loading events in the Mi range
in velocity from 30 miles/hour (48 Km/hour) gusts or sustained winds to EF-5
tornadoes of greater than 190 miles/hour (305 Km/hour). The greater the wind
velocity, the more likely are catastrophic tree losses, especially in root
plate compromised landscapes such as boulevards (the planting area between
public sidewalks and street curbs). However, when boulevard tree failures
greatly exceed other landscape tree losses in the same area, predictable
architectural, site, or compromised stability situations become suspect –
especially from the perspective that they may be preventable to some degree.
A
straight-line windstorm struck portions of the Minneapolis/Saint Paul
metropolitan area of Minnesota (United States) on June 21, 2013, resulting in
significant tree failures. A rapid assessment by the Department of Forest
Resources, University of Minnesota suggested that the majority of the tree
failures were in boulevards compared to parks and residential landscapes. From
August through December, a detailed analysis of the fallen trees was conducted.
Variables documented included: species, size, boulevard width, soil texture,
soil compaction, recent (within five years) adjacent construction activities,
and type of or construction work completed (e.g., sidewalk replacement, curb
replacement, complete street and sidewalk infrastructure renewal). Results from
this study offer two pragmatic perspectives: 1.) a protocol for collecting
storm damage data pertinent to sustainable boulevard tree populations and 2.) a
better tree selection and placement process for street tree designs for
communities in regions prone to wind-loading events.