The potential for uneven-aged silviculture in restoration ...Hara.pdf · The potential for...
Transcript of The potential for uneven-aged silviculture in restoration ...Hara.pdf · The potential for...
The potential for uneven-aged silviculture in restoration and management of old forests
Kevin L. O’HaraUniversity of California - Berkeley
• Uneven-aged – 3 or more age classes• Multiaged – 2 or more age classes• Selection systems – uneven-aged silvicultural
systems• Stocking control – the process of controlling the
amount and distribution of growing stock• Cutting cycles – intervals between harvest entries
in multiaged stands
Uneven-aged – a.k.a.
• Continuous cover forestry• Near-natural• Close-to-nature• Nature-based• Back-to-nature
Common North American stocking control procedure
0
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Diameter Classes
Num
ber o
f tre
es
• Q-factor = quotient of number of trees in a diameter class to the number in the next larger diameter class. For a q-factor of 1.5, 100 trees in one diameter class requires 67 in the next larger class.
• Meyer suggested “virgin” stands were “balanced” because he observed their diameter distributions were straight lines on semi-logarithmic scales.
• The “balanced” stands were capable of yielding a constant volume while maintaining the structure.
• Meyer considered virgin stands to be balanced “because they have been maintained for long periods of time by natural processes of growth and mortality.”
• He promoted using the forests of an entire county or state to determine the appropriate balanced diameter distribution.
Meyer also developed this
diagram to represent the balance between
size classes in uneven-aged stands. The Swiss stand was
seen as more balanced because of
its position in the middle of the
diagram.Meyer 1952. Journal of Forestry
Swiss stand
US stand
From Smith et al. 1997
Another definition of the balanced uneven-aged stand is based on age/size classes occupying equal amounts of growing space.
• This form of “balance” is analogous to area control forest regulation at the stand level. Each age class occupies equal amounts of growing space and many more small than large trees are required for full site occupancy.
• The miniature even-aged forest model allowed for estimation of growth and stocking relationships using even-aged yield tables.
Summary: the “balanced” stand
• Straight line on semi-log scale• Found in “virgin forests”• Harvest = growth• Similar amounts of volume in each size class• Each age/size class occupies equal area
Cutting Cycles
• Balanced stand concept implied that any stand with a different structure was out of balance.
• Cutting cycles were therefore short to maintain the balanced structure
Tree Diameter Classes
Num
ber o
f Tre
es
Mortality overestimatedDensities too highRotated sigmoid distribution may be more common
Alternative diameter distributions
4 (youngest) 3 2 1 (oldest)
Age classes
Num
ber
of tr
ees
infreq firefreq firevar. reten.
Regeneration events in complex stands are the result of combinations of appropriate conditions for germination and early tree growth, and presence of seed sources. Disturbances play a major role.
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tree diameter (in)
num
ber o
f tre
es
ponderosa pine with 4 cohorts
Regeneration events in complex stands are the result of combinations of appropriate conditions for germination and early tree growth, and presence of seed sources. Disturbances play a major role.
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1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30
tree diameter (in)
num
ber o
f tre
es
ponderosa pine with 4 cohorts
Basal area – Multiaged stands
Year
1900 1920 1940 1960 1980 2000
Bas
al A
rea
(m2 /h
a)
0
10
20
30
40
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70
(O’Hara et al. 2007)
Shannon H (size diversity) – Multiaged stands
Year
1900 1920 1940 1960 1980 2000
Sha
nnon
Siz
e D
iver
sity
0.4
0.6
0.8
1.0
1.2
1.4
1.6
(O’Hara et al. 2007)
Shannon H diversity – even-aged
Year
1900 1920 1940 1960 1980 2000
Sha
nnon
Siz
e D
iver
sity
0.4
0.6
0.8
1.0
1.2
1.4
1.6
(O’Hara et al. 2007)
Shannon species diversity (H) for basal area –Multiaged stands
Year
1900 1920 1940 1960 1980 2000
Sha
nnon
Div
ersi
ty -
Basa
l Are
a
0.0
0.2
0.4
0.6
0.8
1.0
1.2
(O’Hara et al. 2007)
European model
• Increasing stocking• Expanding diameter range• Increasing species diversity• For these very old, long-term research plots,
Plenter system is still evolving.
Increment with Constant LAI
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Stocking Scenarios
Volu
me
Inc
(m3/
ha/y
r)Gross Increment
Recoverable Increment
(O’Hara 1996)
TOTAL Leaf Area Index (LAI) 6Cohort 1 Cohort 2 Cohort 3 Cohort 4 TOTAL
Number of Trees/Cohort/Hectare 50 12 25 40 127Percent of LAI/Cohort 90 7 2 1 100
Cohort 1 Cohort 2 Cohort 3 Cohort 4 TOTALLeaf Area Index/Cohort ECC 5.4 0.4 0.1 0.1 6.0Leaf Area Index/Cohort BCC 1.8 0.1 0.0 1.8Leaf Area/Tree (m̂ 2) ECC 1000.0 350.0 48.0 15.0BA/Cohort (m̂ 2/ha) ECC 26.9 2.1 0.4 0.1 29.5BA/Cohort (m̂ 2/ac) BCC 8.6 0.2 0.1 8.9Avg. Vol. Increment/Tree (m̂ 3/yr) ECC 0.13 0.02 0.00 0.00Avg. Vol. Increment/CC (m̂ 3/ha/yr) 3.9 0.2 0.1 0.0 4.2Quadratic Mean DBH/Cohort (cm) ECC 73.4 41.5 12.7 5.7Tree Vigor (cm̂ 3/m̂ 2/yr) 99.410 76.925 68.914 48.700Stand Density Index ECC 280.0 27.0 8.4 3.8 319.3Stand Density Index BCC 112.5 4.0 2.4 118.9
Ponderosa pine MASAM - MONTANAUSER-SPECIFIED VARIABLES
DIAGNOSTIC INFORMATION
(O’Hara et al. 2003)
Uneven-aged – What’s wrong
• Obsession with maintaining precise diameter distributions
• Not “natural” as practiced• Notion of the “balanced stand” is arbitrary• “Baggage” of uneven-aged• Traditional means of managing uneven-aged
stands are therefore not appropriate for old forests
Multiaged – What’s Right• Many sustainable options: single-tree,
variable retention, groups• Sustainable old forest structures can take
many forms.• This is a tremendous advantage because it
provides flexibility for land managers.• Complexity in stand structure with treatments
that are not all the same and may be simpler to design and implement
• Multiaged stands have lots to offer: continuous cover, carbon storage, more natural for some situations