Long-term environmental effects of conifer removal to achieve Aspen release in near stream areas within the Northern Sierras : progress report, May 2003 through May 2007

2007·2.4 MB·English

by  Tate, Kenneth W

Historic, archived document

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scientific knowledge, policies, or practices.

PROGRESS REPORT
May 2003 through May 2007

For the project

LONG-TERM ENVIRONMENTAL EFFECTS OF CONIFER REMOVAL TO
ACHIEVE ASPEN RELEASE IN NEAR-STREAM AREAS WITHIN THE
NORTHERN SIERRAS

Submitted to

Lassen National Forest

Submitted by

Principal Investigator
Kenneth W. Tate, Ph.D.
Rangeland Watershed Specialist
One Shields Ave
Mail Stop One
Department of Plant Sciences
University of California
Davis, CA 95616-8780
Voice: 530-754-8988
Fax: [phone]
Email: [email protected]

Project Team
Bobette Jones, Melanie McFarland, Tom Rickman, Al Vasquez: USFS LNF
David Burton: Aspen Delineation Program
Shannon Cler: UC Davis
David Lile: UCCE Lassen County
Tate, Progress Report 2007 1
1. EXECUTIVE SUMMARY
Following the adaptive management framework, several USFS Districts and Forests in California have begun to
implement prescriptive conifer removal in conifer encroached aspen stands to conserve the stands, stimulate aspen
regeneration, and recruit future cohorts of aspen to achieve full stand restoration. The purpose of the project
detailed in this progress report is to provide the monitoring framework to assess the impacts of conifer removal
from encroached riparian aspen stands on aspen recruitment, stream water quality, streamflow, stream canopy,
stream temperature, aquatic macroinvertebrate community and aquatic habitat, and riparian soil quality. This
project is a collaborative effort between USFS, UC Davis, and the interagency Aspen Delineation Program. Support
has been provided as funding and in kind contributions from the USFS Region 5 Fish Habitat Relationships
Program, the Lassen National Forest, and the Department of Plant Sciences at UC Davis. Over the past 5 years this
collaborative venture has fostered the development of several complementary projects, greatly expanding the
current scope of applied research focused on aspen conservation, restoration and management in the region.

Specific to the Lassen National Forest, three conifer removal projects have occurred during this project: 1) January
2004 Bogard Units project on 2 stands at Pine and Bogard Creeks; 2) August 2005 summer phase of the McKenzie
project at Pine and Bogard Creeks; 3) September 2006 Brokeoff project at Bailey Creek. The purpose of the
adaptive management study detailed in this report is to collect and report data to evaluate a suite of possible in-
stream and near-stream impacts resulting from these projects. In this progress report we provide specific
information about each of the projects, the monitoring design and analysis strategy, monitoring accomplished to
date, as well as results available to date (May 2007). This report amends and updates all previous progress reports
for this project, incorporating subsequent years of data collection.

Given the availability of both pre and post treatment data, we have focused the results section of this progress
report on the evaluation of impacts of the January 2004 (Bogard Units project) and August 2005 (McKenzie
project) on in-stream and soil parameters. We were able to find no consistent water related impacts from either
project (i.e., water quality, water temperature, or macroinvertebrates). The January 2004 Bogard Units project did
significantly reduce stream canopy cover and increase solar input to treatment reaches. There was no change in
stream canopy of solar input associated with the August McKenzie project. There was a statistically significant
increase in soil bulk density associated with the 0 to 3 inch soil depth following the January 2004 Bogard Units
project, but we suspect this was an artifact of our sample design and inherent spatial variation in forest soil
properties. There was no change in bulk density associated with the August 2005 McKenzie project based upon a
cluster monitoring strategy designed to control for the impacts of spatial variation on repeatability of sample
collection. Overall, results suggest that conifer removal projects implemented and monitored to date have had no
negative impacts on stream habitat quality, stream hydrologic function, or water quality. Impacts on soil bulk
density are minimal to non-existent. Data and analysis results supporting these conclusions are reported in Section 6
of this progress report.

2. BACKGROUND
Trembling aspen (Populus tremuloides michx.) occurs in the montane zone of California’s Sierra
Nevada/Cascade range. In the West, aspen is considered a keystone species providing critical habitat to
support plant and animal biodiversity in the region. Declines in the health and distribution of aspen stands
across the region have been observed over the past century. That decline continues today. Much of this
decline is attributable to conifer encroachment stimulated by the absence of natural fire regimes, as well
as historic and current heavy browsing by domestic and native herbivores. The results of an aspen
inventory conducted from 2000-2005 to assess the current status and risk of loss of 681 aspen stands
(~95% of known stands) totaling 3,654 acres on the Eagle Lake Ranger District, Lassen National Forest
documented that 77% of stands were at high risk of being lost. At least 37 known stands have expired
with no living aspen present and no means of recruitment. If broad scale conservation and restoration
action is not implemented immediately, a large majority of stands on that district may be lost. Conifer
encroachment is the major risk factor associated with 96% of inventoried stands. These data reflect the
condition of most aspen stands in the region, and provide a credible argument for the immediate release of
Tate, Progress Report 2007 2
conifer encroached aspen stands followed by subsequent restoration actions such as controlling excessive
grazing.

The advanced state and landscape scale of conifer encroachment induced aspen decline in the northern
Sierra Nevada and southern Cascade indicates that: 1) restoration actions must occur sooner rather than
later if the ecological services of aspen are to be preserved in the region (Jones et. al 2005); and 2)
significant planning and implementation costs will be associated with restoration of degraded aspen
stands. Logically and practically, prescriptive conifer removal has the potential to conserve a large
number of conifer encroached aspen stands in the region which would otherwise transition to coniferous
forest. Prescriptive conifer removal also has the potential to generate revenue to defray costs and fund
additional restoration efforts such as protection from grazing. Jones at al. (2005) used prescriptive conifer
removal in four extremely degraded aspen stands, releasing the stands to actively recruit and establish
several new cohorts of aspen, thus conserving the stands. Additional research is required to quantify
ecological service potentials (e.g., herbaceous plant diversity, avian habitat structural complexity) and
determining site constraints (e.g., precipitation, elevation) so that achievable restoration targets can be set.

Broad scale implementation of prescriptive conifer removal in the region is an issue because a significant
number of degraded stands are associated with riparian areas such as streams (Photos 1 and 2). Protection
of riparian areas from silvicultural activities has justifiably strong legal and social support. However,
conifer encroached riparian aspen stands that are not released will expire and overall riparian and
landscape habitat complexity and biodiversity will continue to decline. Two causes as worthy as the
protection of riparian areas and the conservation of aspen are surely not mutually exclusive, rather one
could reasonably hypothesize that the restoration of riparian aspen stands would actually enhance overall
riparian health. So, what are the negative impacts to riparian resources associated with aspen restoration
initiated by prescriptive conifer removal? Which components of riparian resources are susceptible to
negative impact: soils, water quality, aquatic habitat? If there are negative impacts, are they short or long-
term? Will the ecological services that a restored aspen stand provides to the riparian area and the
landscape out-weigh short or even long-term negative impacts to riparian resources? Answering these
core questions is crucial to initiating an informed, broad-scale conservation and restoration of riparian
effort for aspen stands in the region.

Adaptive management is an iterative process to identify and refine management to achieve defined natural
resources objectives. It is founded upon active, not passive management. Conservation and restoration of
aspen stands will require active, adaptive management. Adaptive management provides the manager, as
well as other stakeholders, with the quantitative evidence that either: 1) progress is being made towards
natural resources objectives and appropriate management practices are in place; or 2) progress towards
natural resource objectives is not being made and management needs to be adapted. Central to this
process is establishment of clear and measurable objectives, flexibility in management paradigms and
implementation, and a data-based monitoring and evaluation framework to inform management of
progress towards objectives. The management challenge we are facing is to design and implement
prescriptive conifer removal strategies sufficient for conservation and restoration of encroached riparian
aspen stands with minimal short-term and no long-term negative impacts on riparian resources. The
overall goal of this project is to provide the monitoring and evaluation framework to assess impacts on
riparian resources and progress towards aspen stand conservation and restoration.

Our specific monitoring objectives are to:

1) Evaluate the effectiveness of conifer removal as a means of successful aspen recruitment and stand
establishment. Completed (cid:57)
Tate, Progress Report 2007 3
2) Conduct pre- and post- conifer removal monitoring of key stream attributes to evaluate effects on
water resources. January 2004 Bogard project Completed (cid:57) August 2005 McKenzie Project and
September 2006 Brokeoff Project On-Going
3) Conduct pre- and post- conifer removal monitoring of soil attributes to evaluate effects on soil
quality in riparian areas. January 2004 Bogard project Completed (cid:57) August 2005 McKenzie
Project and September 2006 Brokeoff Project On-Going
4) Extend and report the findings of this project to improve our ability to achieve Riparian
Conservation Objectives as part of the Aquatic Management Strategy. On-Going for all Projects

Photo 1 and 2. Unhealthy Pine Creek riparian aspen stands encroached by conifers and without recruitment.

3. Treatment and Study Unit Definitions
A few definitions are provided here for clarity and consistency. The treatment is the removal of conifers
from within degraded aspen stands located within stream riparian areas. The conifer removal strategy is
designed to fully release aspen from conifer dominance, and may include a combination of commercial
harvest, service contract and hand-thinning (Photo 3). The method and season in which conifers are
removed will vary because each stand has different opportunities and constraints. Recent experience on
the Lassen National Forest (LNF) indicates that the treatment should emphasize whole tree removal of
conifers, of both pre-commercial and commercial size. Typically, all conifers less than 30” will be
removed, except for conifers directly contributing to streambank stability or other site-specific benefits.
Hand-felling of small diameter conifers may occur post-harvest. As a control, allowing evaluation of the
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impacts of treatment, we selected degraded riparian aspen communities in the vicinity of each aspen stand
scheduled for treatment implementation (e.g., Photo 1).

There are two study units in this project, as illustrated in Figure 1. For the purposes of examining aspen
recruitment and soil quality parameters (Objective 1 and 3), the study unit is the area within each
degraded aspen stand (treatment and control study stand). For the purposes of examining stream
parameters (Objective 2), the study units are stream reaches (treatment and control study reach) adjacent
to treatment and control aspen stands as defined by stream monitoring stations located above and below
adjacent study stands. Discrete sampling stations, plots, and transects (experimental units) have been
established within aspen stand and above and below stream reach study units to allow collection of
appropriate pre- and post treatment data to achieve the project objectives. For instance, stream monitoring
stations are situated to monitor changes in stream flow and water quality through study reaches. Soil
sampling stations are situated to provide a representative sample of the whole study stand.

Photo 3. Encroached aspen stand liberated from conifer encroachment by an over-snow winter conifer removal project
(Jan 2004) on Pine Creek, Eagle Lake National Forest. Photo taken May 2005.

4. Monitoring Design and Analysis Overview
The study design is based upon consistent, simultaneous monitoring before and after treatment application
of treated and control study stands and adjacent stream study reaches (Figure 1). Statistical analysis is
applied to this data to determine the magnitude and significance (statistical, not ecological) of response(s)
of treated stands/reaches relative to control stands/reaches before v. after treatment implementation. For
instance, stream temperature is collected above and below both control and treatment reaches both before
and after conifer removal from the adjacent treatment stand. With this data set we can statistically test if
say the treatment resulted in increased stream temperature gain through the treatment reach following
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treatment. The pretreatment data from the control and treatment reaches serves as a benchmark,
quantifying the increase in temperature through the treatment reach relative to the control reach prior to
our treatment application. To determine if there is an increase in stream temperature through the treatment
reach following treatment, we analyze all the data (before and after, above and below) to determine if
there is a significant interaction between the factors location (above v. below conifer removal study site)
and time (before v. after treatment). We are employing a linear mixed effects analysis to conduct this
analysis to account for repeated measures introduced in the data set due to repeated sampling of the
sample stations. A detailed, basic explanation of this analysis approach applied as a case study to stream
temperature can be found at the following website, (Tate et al., 2005
http://californiaagriculture.ucop.edu/0503JAS/toc.html).

The basic form of this linear model is:

y = b + b *(time) + b *(location) + b *(time X location)
0 1 2 3
y = water temperature, soil organic matter level, etc.
time = before or after treatment
location = treatment or control, above or below

The terms b , b , b , and b are coefficients estimated by a commercial statistical package (S-Plus 6.0)
0 1 2 3
using a best fit approach known as restricted maximum likelihood. The significance of each coefficient (b
≠ 0) is determined via a conditional t-test. For our purposes of determining treatment effect, we are
mainly interested to determine if b is significant. We use this model to test the hypothesis that the relative
3
difference in y between treatment and control, or above and below, changed from before to after treatment
by testing the significance of b (b = 0, b ≠ 0). If b is significant (b ≠ 0), then the change in stream
3 3 3 3 3
temperature above v. below the treatment stand changed significantly from before to after treatment
implementation.

This approach does not assume above and below, or treatment and control, are originally identical (i.e.,
replicates), but it does assume that the only major change during study period was in the treatment unit
(conifer removal) and that the control was in a stable state throughout the time of comparison (before and
after treatment). The same fundamental design and analysis approach described above for stream
temperature is being applied for all variables of interest (e.g., stream canopy, water quality, soil bulk
density).

5. Study Sites
At the outset of this project in early 2003, aspen stands and associated stream reaches selected for
inclusion into the project: 1) were either scheduled or expected to be scheduled for implementation of a
conifer removal treatment in the next 1 to 3 years; 2) had sufficiently similar stands and stream reaches in
the vicinity to serve as controls; and 3) represented the range of precipitation regime found on LNF. Study
stands and stream reaches at locations on Pine-Bogard Creeks, Butte Creek, and Brokeoff Meadow
(Bailey Creek) were enrolled in the study (Figures 2a&b, 3, and 4). We selected sites near the confluence
of Pine and Bogard Creeks on the Eagle Lake Ranger District due to treatment application scheduled for
the January 2004 (Figure 2b “Bogard Units”) and August 2005 and January 2006 (Figure 2b
“Aspen_Enhance_Summer” and “Aspen_Enhance_Winter”). We selected stands and stream reaches on
Butte Creek (at the boundary of ELRD and the Hat Creek Ranger District) and Brokeoff Meadow
(HCRD) because both timber sales are expected to be scheduled for implementation in the within next
few years. Butte Creek is a dry site, Pine-Bogard Creeks represents wet eastside conditions, and Brokeoff
Meadow is located on the west-slope representing the highest precipitation regimes of LNF. To date (May
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2007) the January 2004 Bogard Unit, the August 2005 McKenzie, and September 2006 Brokeoff projects
have been implemented. The January 2006 McKenzie project has not been conducted on Butte Creek.

Figure 1. Illustration of study layout for a paired control and treatment aspen stand and associate stream study reach.
Control
Reach
Treatment
Control
Stand
Stand
Tr
e
at
m
e
Stream monitoring stations nt
R
e
Aspen monitoring transects a
c
h
Soil moisture monitoring stations
Soil quality monitoring stations

Figure 2a. Pine and Bogard Creek stream sampling locations and names.
Tate, Progress Report 2007 7
Figure 2b. Pine-Bogard Creek study location with monitoring stations and treatment areas marked.

Tate, Progress Report 2007 8