Black Ash Decline in Northern Minnesota:
Preliminary Results
Center for
Research on
Ecosystem
Change
Brian Palik1, Mike Ostry1, Rob Venette1, Ebrahim Abdella2,
1 USDA Forest Service, Northern Research Station
2Department of Forest Resources, University of Minnesota
Black ash (Fraxinus nigra) decline has been
noted with increasing frequency in northern
Minnesota over the last decade. For
instance, over 27,000 acres were affected in
Minnesota in 2004.
Methods:
Result 2:
● 21 stands sampled in 2006 in Carlton, Itasca, St. Louis
Counties
● Mean age of healthy overstory trees in declining
stands was significant lower than mean age of
declining trees in the same stands and all trees in
healthy stands (Figure 2).
● All black ash trees on 3-5 plots per stand measured for
health status, age and size
● Plots and sites characterized for wetness status, depth
to mineral soil, and insect and disease symptoms
● Individual tree ages were unrelated to health status
(data not shown).
Mean Tree Age (yrs)
● Most (but not all) declining stands were located in the
eastern part of the study area, while most healthy
stands were located in the western part of the study
area.
Concerns:
Region-wide decline of black ash has ecologic,
cultural, and economic consequences related
to:
● Timber use for paneling & veneer
● Native American use for basket making
● Importance in systems that have already
lost American elm
80
60
200
0
Fig. 5. Densities of black ash seedlings and saplings by stand group.
Values are means +/- standard errors.
S tan d G ro u p
● Declining stands had significantly greater depth to a
mineral layer (thicker organic layer) than healthy
stands (Figure 4).
20
Declining
Healthy
Stand Group
Figure 1. Distribution of tree condition by stand group (healthy vs. declining).
Values are means +/- standard errors.
Figure 3. Mean wetness
index by stand group
(declining vs. healthy).
0=dry, 3=very wet.
Values are means +/standard errors.
2.5
2.0
1.5
1.0
0.0
Declining
1. Quantify black ash decline and mortality in
stands across northeastern Minnesota.
● Decline of overstory trees in susceptible stands may be
related to tree age, since healthy trees in these stands
averaged 20 years younger than declining trees in the
same stands.
● Both declining and healthy stands contained seemingly
healthy regeneration cohorts, but densities were higher
in healthy stands.
● We observed no obvious causal insect or disease
organisms on declining trees.
Healthy
Stand Group
Ongoing Work
1.6
2. Relate decline and mortality to stand-scale
factors including:
Figure 4. Mean depth to
a mineral layer by stand
group (declining vs.
healthy). Values are
means +/- standards
errors.
1.4
Depth (m)
1.2
1.0
0.8
0.6
In 2007, we sampled an additional 31 stands in Lake, St.
Louis, Carlton, Aitkin, and Itasca Counties. Analysis is
ongoing to determine if the preliminary findings reported
here are consistent. Additionally, we are examining
suscessional trends in declining stands.
0.4
Acknowledgements
0.2
3. Quantify black ash regeneration patterns in
declining and healthy stands.
● Regionally, black ash stands show marked differences
in frequency of declining trees.
● Decline is associated with wetter conditions and deeper
depth to a mineral layer (site more prone to anoxic,
saturated conditions).
0.5
● Tree and stand age
Summary Points:
● Tree age was unrelated to decline in healthy stands.
3.0
0
Objectives:
● Insects and diseases
● Site hydrology
Healthy
Stand Group
H ealth y
● Declining stands were significantly wetter than healthy
stands, at the time of sampling (Figure 3).
40
400
20
Result 3:
60
600
40
Figure 2. Mean overstory (>4 in) tree ages by stand group. Values are
means +/- standard errors.
Healthy Trees
Declining Trees
Dead Trees
800
Declining
Wetness Index
● Insects or disease
80
100
D eclin in g
100
Percent of Trees
● Altered site hydrology
1000
H ealth y T rees
D eclin in g Tre es
0
● There were no obvious causal insects or diseases
associated with declining stands.
● Cohort senescence
● There was little indication of decline symptoms in the
regeneration cohort.
1200
● The 21 stands differentiated into two groups: one with
substantial decline (Declining) and one with minimal
decline (Healthy) (Figure 1).
Black ash decline in other regions has been
related to spring drought. Other potential
causes include:
● Black ash regeneration density was higher, although
highly variable, in healthy stands (Figure 5).
120
Result 1:
Causes:
Result 4:
Stems per Acre
The Problem:
0.0
Declining
Healthy
Stand Group
Thanks to Manfred Mielke and the Forest Service Forest
Health Monitoring program for support of this work.