Reference Conditions and Ecological Restoration:

A Southwest Ponderosa Pine Perspective
 Ecological Restoration:
 “the process of reestablishing to the
extent possible the structure,
function, and integrity of indigenous
Used in this research to:
1. develop a deeper understanding of ecosystem structure
and function
2. bring about conditions as close as possible to reference
condition so that natural processes can continue
3. communicate with land managers and the public about
ecosystem change and factors to be considered in setting
management objectives
Ecological restoration is not a fixed
set of procedures
 However, a consistent set of questions and concerns are
 1. what constitutes natural state and processes for these
 2. What was the role of humans before and after
 3. What are appropriate reference conditions and variables
to measure?
 4. What is ecological
 5. What treatments are best
for restoration?
 Evolutionary Environment:
 The
environment in
which a species
or group of
species evolved
 The
environment of
Evolutionary environment for
ponderosa pine (pinus ponderosa)
 Most widespread member of
subsection Ponderosae
 First appears in fossil record in
Miocene in Western Nevada
 Mobile in evolutionary time
 Environment includes many
short term disturbances
Native American Role
 Inhabited ponderosa
pine habitat for
millennia prior to the
late 1800s
 Influenced habitat
through cultural,
hunting, agriculture, and
burning practices
 Natural frequency of
fires gave human caused
ignitions to have a
relatively minor impact
Anglo-American and Hispanic
 Hispanic settlement began in
16th century, however, impact
was localized
 Anglo-American settlement of
Northern Arizona began in the
 Around the 1870’s industrial
scale resource exploitation,
domestic livestock grazing, fire
 Introduced species, disruption of
natural processes, and land use
practices changed evolutionary
 Reference Conditions:
 1. A spectrum and
variability of natural
conditions in ecosystem
composition, structure,
and function
 2. a point of reference against which to evaluate
changes in ecosystems
 3. A criterion for measuring the success of
ecological restoration treatments and ecosystems
management experiments
Reference Conditions
 In theory reference
conditions should take
into account all
ecosystem components:
Biogeochemical cycles
Disturbance processes
Abiotic factors
 Is it possible to put this
theory into action? Why
or why not?
Reference Conditions
 Some suggest working
with only a small set of
keystone species or
highly interactive
 Is this methodology
better or worse in terms
on restoring the
Establishing Reference Conditions
Baseline/Reference Conditions
 1) Determine key variables
 2) Quantify key disturbance
 3) Use dendroecological
 4) Use other lines of
 5) Determine current and
historical understory
herbaceous and shrub
Select Key Variables
 Small
 Evolutionary environment of ponderosa pine
 Practical to quantify
Key Disturbance Regimes
 High frequency, low intensity
 Low frequency, High intensity
 Fire frequency flucuated
 Cessation of frequent fire after settlement
Quantify Forest Structure/ Pattern
• Before and after Anglo-American settlement
• Current structure provides past vegetative structure
• 1-4 trees per hectare before
• Hundreds to thousands of trees per hectare after
Structure/Pattern cont.
 Density and pattern varies from place to place
 Picking particular date is important for site restoration
Multiple Line of Evidence
 Historical
 Early Historical
 Results from other
 Early Forest or Land
Understory Herbaceous and Shrub
 Rapid nutrient turnover
 Provide fuel
 Plant biodiversity
Understory cont.
 Dendroecological reconstruction techniques are
 Use separate study sites
Based on Reference Conditions
 Develop an ecological restoration plan tailored to
specific ecological & management concerns at each
project site.
• Specific Example:
– Gus Pearson Natural
Area (GPNA)
• General Framework
Restoration Treatment 1
Leave All Pre-settlement Trees
 Trees predate the fire regime disruption date (~1870-1880).
 Argument against:
 some pre-settlement trees (>120yrs) would have been thinned
by surface fires.
 Basal area (and density) of pre-settlement trees today may be
on the high end of the pre-1870 reference conditions
 Counter Argument:
 Logging has removed most of the pre-settlement trees
 Unharvested areas, low natural mortality rates that existed
prior to fire regime disruption, have increased under the
competitive stress of dense post-settlement forests.
Restoration Treatment 2
2. Retain post-settlement trees to replace dead presettlement trees; while restoring the species
composition, density, age, biomass distribution and
tree pattern present around the time of fire regime
 Other post-settlement trees are thinned and removed
off site or burned in place
 Buffer of 150%-300% of the pre-settlement tree density
to compensate for post-treatment mortality.
Restoration Treatment 3
3. Protect the pre-settlement and large post-settlement
trees from cambial girdling and root mortality by
raking forest floor fuels from tree base.
 In many cases more than 100yrs of accumulated fuels
Restoration Treatment 4
4. Burn under prescription
with repeated surface fires
to approximate the
natural fire cycle.
 Fire prescriptions are
designed to consume
thinning residues and
forest floor fuels with
minimal impact on
retained trees.
Restoration Treatment 5
5. If natural
regeneration of the
herbaceous and
shrub communities
is inadequate, then
the treated area with
a native species mix
as needed.
Restoration Treatment 6 & 7
6. Control exotic plant species.
7. Regulate grazing of
ungulates so that the
treated area can
recover and so
herbaceous fuels will
be adequate for
repeated burning at
natural intervals.
In General
 Two pronged rationale behind these ecological
restoration treatments
 1. Facilitating partial recovery of ecosystem structure
and function can lead to reestablishment of natural selfregulatory processes. Eventually leading to restoration
of at least part of the original ecosystem dynamics.
 2. Both restoration of ecosystem structure and
reintroduction of fire are necessary for restoring rates of
decomposition, nutrient cycling, and net primary
production to more natural, pre-disruptive dates.
Structure and Function
 Debate whether restoration of frequent-fire
ecosystems must include “intentional structural
restoration” (thinning) or if fire alone could do the job.
 Depends upon:
Specific species compositions
Fire Alone
 Accomplished with low-intensity surface fires every 2-
10yrs on large area with no structural manipulation.
 BUT: Southwestern Ponderosa Pine and lower
elevation mixed conifer forests have had an increase in
tree densities and fuel accumulations over past century
 now fire would burn canopy
 fire no longer functions as it did pre-settlement forests
Early Experiments:
Simple fire reintroduction often had detrimental effects
from a restoration perspective.
 In 1976: Post-burn,
 Old-growth pine trees were killed by cambial girdling
and root mortality.
 Post-settlement poles and saplings were not adequately
thinned by fire.
 GPNA: Post-settlement trees were removed and litter
raked prior to burning.
 Restored area had signs of higher microbial activity and
positive responses from old growth trees.
Limitations of our ecological
restoration approach
 -Limitations associated with almost any land management
activity, especially involving tree thinning and prescribed
Common Problem
 Project implementation is often derailed by disagreements
over treatment details and by insufficient funding.
 Even when groups appear to advocate identical tree
thinning and prescribed burning treatments, arguments
over tree diameter limits, single vs. multiple entries, and
residual forest density have slowed progress.
Other Pitfalls
 History between agencies or people involved could
inhibit restoration plan.
 Low value of small-diameter trees from thinning
contribute to low funds.
 Many times no funds available for land management
agencies and fall short of adaptive management ideals.
Even when things look good…
 -Once projects are operationally implemented, limitations
still arise from concerns over
 smoke from fires
 slash disposal
 short-term aesthetic degradation
from thinning and prescribed fires
National Parks and Designated
Wilderness Areas
Land is mandated to be managed in its natural condition.
 Arguments arise because of the initial damage done from
thinning can be seen as incompatible with park regulations.
 Grand Canyon National Park
 Developing small-scale tests of thinning treatments in areas
where fire-only no longer works from too much fuel.
 Wilderness-sensitive restoration work may rely heavily on
humans and animal-powered operations, trading higher costs
for decreased mechanical impacts.
 Goal is not to create a copy of pre-settlement forest,
 Forest is reasonably close match to the pre-settlement forest,
conserving the structure and pattern of the slowest developing
organismic variables (old trees) and providing resources for
native herbaceous plants and shrubs to return their natural,
more productive state.
 Strict Restoration
 Broadly consistent with management goals for parks,
wilderness, and natural areas
 Restoration practices may not be easily implemented
 Liberal Restoration
 approach is central for ecosystem management approaches on
public lands
 Neither pre-settlement ecosystem nor any other ecosystem
is ideal for providing habitats for each species or for all the
commodity and amenity needs of humans; nor is a relatively
open forest best to maximize wood production, or provide
dense cover for animals.
 Real ecosystems cannot simultaneously meet all of these
objectives either.
Hope of restored ecosystems is to reduce and perhaps
reverse human-caused degradation, conserve the most
fragile links of natural systems and reduce the
potential for catastrophic ecosystem change.

similar documents