COST EFFECTIVENESS OF
NATURAL REGENERATION FOR SUSTAINING PRODUCTION CONTINUITY IN COMMERCIAL PINE
PLANTATIONS
T. R.
CLASON
Professor, Louisiana State
University Agricultural Center, Hill Farm Research Station, Homer, LA
71040
Abstract--Reforestation is a
key to production continuity in commercial pine plantations. Although natural and artificial
regeneration methods have been used successfully for pine seedling
establishment, it is seedling growth during early stage of plantation
development that affects the financial potential of a pine plantation. A study was initiated to determine the
effect of regeneration method on seedling growth and development. A seed tree regeneration harvest was
compared with a clear cut and plant regeneration harvest. The growth of the natural stand was
compared with planted plantations with initial stocking densities of 1,200 and
680 seedlings per acre. In
addition, the impact of mechanical and chemical site preparation and herbaceous
weed suppression was evaluated.
Merchantable volume at age 15 varied between reforestation methods,
seedling stocking densities and vegetation management practices being 540,
1,715, 2,730 and 3,440 feet3 per acre for natural plantation and
three planted plantations, respectively.
Age 15 land expectation values for the respective reforestation methods
were 135, 170, 785 and 1,053 dollars per acre.
INTRODUCTION
On cut over timber land,
productivity of commercial loblolly pine (Pinus taeda L.) plantations
depends on seedlings competing successfully for finite levels of soil resources.
Reforestation phase of plantation development includes site preparation,
regeneration (seedling establishment) and post-establishment weed
suppression. Although competitive
pressure exerted by an existing plant community hampers early seedling growth,
seedling establishment plays a pivotal role in the reforestation process. Regenerated stands should be adequately
stocked with well distributed seedlings to optimize soil exploitative potential
during the first growing season.
During the first growing
season, competition from hardwood brush and herbaceous weeds reduces seedling
survival and decreases early diameter and height growth. Thorough site preparation suppresses
this initial interference, but as the growing season progresses, encroaching
vines, resurgent hardwood brush and unwanted pine seedlings begin to compete
vigorously for growing space.
Regeneration method, natural or artificial, can have a significant impact
on mitigating competitive interference during the seedling stage of plantation
development.
Natural regeneration methods
have been used successfully to establish seedlings on cut over pine plantations
but seedling density is usually excessive.
Since pine diameter growth loss has been detected in both dominant and
intermediate crown classes of 3-year-old plantations at seedling densities that
exceed 500 trees per acre (TPA) (Sprinz and others 1979), natural regeneration
may not be a cost effective seedling establishment method for commercial pine
plantations. A study was initiated
to determine the cost effectiveness of reforestation methods on growth and
development of commercial pine plantations. Growth of a seed tree regenerated
plantation will be compared with clear cut and plant regenerated plantations
with seedling planting densities of 1,200 and 680 seedlings per
acre.
METHODS
Data from two studies were
used to compare natural and artificial regenerated pine plantation development
and growth. The studies were established at the Hill Farm Research Station on
the same site but in different years, 1955 and 1984. Predominant soil types are Mahan fine
sandy loam (clayey, kaolinitic, thermic Typic Halpludults) and Wolfpen loamy
sand (loamy, siliceous, thermic Arenic Paleudalfs) with a 25-year site index for
loblolly pine of 70 feet.
1955
Study
The study was initiated
during 1955 in a 25-year-old understock stand of old field loblolly and
shortleaf pine (Pinus enchinata Mill) that had a stocking density of 167
TPA and mean DBH of 7.7 inches.
The stand was sub-divided into 16 0.5 acre plots. Twelve plots were
randomly selected for a seed-tree regeneration harvest that left a residual
stand of approximately seven loblolly pines per plot. The four remaining plots were clear cut
and prepared to plant pine seedlings.
The study treatments were as follows: 1) Seed Tree Harvest and seedbed
preparation by disking (STD); 2) Seed Tree Harvest and seedbed preparation by
burning (STB); Seed Tree Harvest and no seedbed preparation (STCK); and Clearcut
Harvest, mechanical site preparation and plant at 1,200 TPA, 6 ft x 6 ft
spacing, (PMS). All logging slash
was piled and burned in August 1955 followed by seedbed and mechanical site
preparation treatments. The STD treatment was broadcast disked to a depth of 4
inches with a standard lift-type tandem disk harrow, the STB treatment was
burned in September, and the PMS treatment was burned and then disked.
Treatments were replicated four times and randomly assigned to the designated
harvest plots. After 5 years, all
seed trees were removed.
1984
Study
This study was initiated
following a clear cut harvest of the 1955 study. The study area was chemically site
prepared with glyphosate applied at 4 lbs. a.i./acre, and loblolly pine
seedlings were planted at a 8 ft x 8 ft spacing (680 TPA). Three levels of herbaceous weed and two
levels of woody brush suppression were combined in a factorial manner to
establish six vegetation management regimes of varying intensity. Vegetation
management regimes, in descending order of intensity, were: VMR 1) post-planting
herbaceous weed suppression for 2 years and woody brush (hardwood and pine)
suppression; VMR 2) post-planting herbaceous weed suppression for 1 year and
woody brush suppression; VMR 3) no herbaceous weed suppression and woody brush
suppression; VMR 4) post-planting herbaceous weed suppression for 2 years and no
woody brush suppression; VMR 5) post-planting herbaceous weed suppression for 1
year and no woody brush suppression; and VMR 6) no herbaceous weed suppression
and no woody brush suppression.
Regimes were replicated six times and assigned in completely random
manner to 36 0.3 acre plots.
Herbaceous weed suppression treatment was applied with a backpack sprayer
using sulfometuron methyl at 1.5 oz. a.i./acre in early spring of the first and
second growing seasons. Woody brush
suppression treatment was a backpack application of triclopyr amine at 2 lbs.
ae/acre in the spring of the fourth growing season to suppress hardwood brush
and woody vines and to eliminate every third row of pine seedlings. Pine stocking density in the woody-brush
suppression treatment plots was reduced to approximately 350 TPA. Growth data from the VMR 5 (PCSHWS) and
VMR 6 (PCS) plots were used for the natural and artificial regeneration
comparisons.
Growth data for both studies
were collected periodically through
age 15. Age 15 DBH and
height were used to compute age 15 individual pine merchantable volume at a
3-inch inside bark diameter (Van Duesen and others 1981). Actual and published cost and revenue
values were used to compute treatment net present value (NPV) and land
expectation value (LEV). Growth
data within studies were analyzed using SAS general linear model analysis of
variance procedures at a 0.05 level of probability. NPV and LEV were used to compare
treatment cost effectiveness among studies.
RESULTS
1955 Study
Growth
Stand growth differences
were detected among reforestation treatments. Although seed tree seedbed preparation
did not affect stand productivity, mean seed tree treatment and the PMS
treatment growth attributes were significantly different (Table 1) . Mean seed tree treatment merchantable
tree density exceeded the PMS treatment density by 800 TPA (Table 1). However, seed tree basal area and
merchantable volume were 47percent and 60 percent less than the PMS treatment
(Tables 1 and 2). Pulpwood and
chip-n-saw volume differed between seed tree and PMS treatments with seed tree
respective volumes being 465 and 710 feet3 per acre less than the PMS
treatment (Table 2). Tree diameter
distribution varied between seed tree and PMS treatments. Fifty-two percent of the seed tree
merchantable stems fell within the 2- to 4-inch DBH class, while 91 percent of
the PMS stems were greater than 4 inches (Table 3).
1984 Study
Growth
Mean tree DBH and height and
stand basal area and merchantable volume differed significantly between
treatments (Tables 1 and 2). No
stand density differences were detected at age 15, but tree survival rates
averaged 78 percent and 85 percent for the PCS and PCSHWS treatments. Although the PCS treatment had 47 fewer
trees, mean tree DBH and height were 0.4 inches and 2 feet less than the PCSHWS
treatment. Basal area and
merchantable volume treatment differences
were 33 feet2 per acre and 710 feet3 per acre. Treatment volume differential was
reflected in product volume distribution, PCSHWS chip-n-saw and sawtimber
volumes exceeded the PCS volumes by 690 feet3 per acre (Table
2). Tree DBH distribution varied
between treatments with PCSHWS treatment having 95 more trees in the 8-inch and
larger DBH class, and 66 percent were 10 inches or larger (Table 3).
Table 1--Age 15 stand growth
attributes by reforestation treatmenta
|
Reforestation
Treatment |
Stand Density |
DBH |
Height |
Basal Area |
|
|
Trees/Acre |
Inches |
Feet |
Feet2/Acre |
|
Seed Tree
(Disked) |
1,400 |
3.5 |
33 |
94 |
|
Seed Tree
(Burned) |
1,421 |
3.5 |
32 |
95 |
|
Seed Tree
(Untreated) |
1,407 |
3.5 |
33 |
94 |
|
Planted MS(1200
TPA) |
618 |
6.4 |
42 |
138 |
|
Planted CS(680
TPA) |
534 |
7.0 |
45 |
142 |
|
Planted CS(680 TPA
HWS) |
581 |
7.4 |
47 |
175 |
aAll trees greater than 1.0 inch
dbh
Table 2--Age 15 product volume
distribution by reforestation treatment
|
|
-----------------------Product
Volume----------------------- | ||||
|
Reforestation
Treatment |
Total |
Pulpwood |
Chip-N-Saw |
Sawtimber | |
|
|
--------------------------Feet3/Acre----------------------- | ||||
|
Seed Tree
(Disked) |
540 |
540 |
----- |
----- | |
|
Seed Tree
(Burned) |
545 |
545 |
----- |
----- | |
|
Seed Tree
(Untreated) |
540 |
540 |
----- |
----- | |
|
Planted MS(1200
TPA) |
1,715 |
1,005 |
710 |
----- | |
|
Planted CS(680
TPA) |
2,730 |
670 |
2,030 |
40 | |
Table3--DBH size class distribution
by reforestation treatment
|
|
---------------------------------------Reforestation
Treatment----------------------------------- | ||||||
|
DBH Class |
Seed Tree
Disked |
Seed Tree
Burned |
Seed Tree
Untreated |
Planted
MS-1200 |
Planted
CS-680 |
Planted
CS-680-HWS | |
|
Inches |
-----------------------------------------------Trees/Acre--------------------------------------------- | ||||||
|
<1.5 |
1,147 |
1,614 |
653 |
61 |
----- |
----- | |
|
1.6-3.5 |
731 |
743 |
734 |
1 |
----- |
----- | |
|
3.6-5.5 |
667 |
666 |
660 |
127 |
----- |
----- | |
|
5.6-7.5 |
2 |
2 |
2 |
418 |
138 |
90 | |
|
7.6-9.5 |
----- |
----- |
----- |
71 |
382 |
430 | |
|
>9.6 |
----- |
----- |
----- |
----- |
14 |
61 | |
|
Total |
2,547 |
3,025 |
2,049 |
678 |
534 |
581 | |
Financial
Comparisons
Since seed tree treatment
growth was similar for all seedbed preparation treatments, two seed-tree options
were compared by pooling growth data, assuming no seedbed preparation cost and
leaving or removing seed-tree stand for the 15 year comparison period. Therefore, financial comparisons
treatments were seed tree with no seed tree removal, seed tree with seed tree
removal at age 5, PMS, PCS and PCSHWS.
Cost values were determined by actual and published costs (Dubois and
others 1999). Revenue values were
based on the mean 10-year Louisiana stumpage prices for pulpwood, chip-n-saw and
sawtimber between 1991 and 2000.
Seed tree treatment costs included the value of the residual seed trees,
while planted treatment costs included site preparation, seedling purchase and
planting, and herbaceous weed suppression for the PCSHWS treatment. All costs and revenues were
discounted at a 8 percent interest rate.
Regeneration method did
influence the financial potential of commercial pine plantations. At an
8 percent discount
rate, failure to capture seed-tree
value resulted in a negative NPV and LEV at age 15 (Table 4). Although seed-tree removal at age 5
produced positive NPV and LEV values, these values were less than any of the
planted treatments. Initial
planting density and site preparation method impacted the financial potential of
the planted treatments, PMS treatment NPV and LEV were $422 and $ 615 per acre
less than PCS treatment (Table 4).
Although there was no cost differential between mechanical and chemical
site preparation, chemical site preparation provided better vegetation
suppression during early seedling growth and development. First year herbaceous weed suppression
(PCSHWS) improved the financial potential of chemically site prepared planted
plantations, increasing NPV and LEV by $187 and $188 per
acre.
Table 4--Age 15 financial comparisons
by reforestation treatment
|
Reforestation
Treatment |
Costs |
Revenues |
NPV |
LEV |
|
|
-----------------------Dollars/Acre------------------------ | |||
|
Seed Tree (No
Harvest) |
440 |
48 |
(-392) |
(-244) |
|
Seed Tree
(Harvest) |
440 |
532 |
92 |
135 |
|
Planted MS(1200
TPA) |
194 |
311 |
117 |
170 |
|
Planted CS(680
TPA) |
164 |
702 |
538 |
785 |
|
Planted CS(680 TPA
HWS) |
200 |
921 |
721 |
1,053 |
CONCLUSIONS
Reforestation practices had
a significant impact on the financial potential of commercial pine
plantations. 1. Seed tree regeneration method was the
least cost effective reforestation method.
Excessively stocked plantations were susceptible to intraspecific
competition which reduced growth productivity.
2. In planted plantations, chemical site
preparation was more cost-effective than a low intensity mechanical
treatment.
3. Wider spaced planting density and first
year weed suppression improved reforestation cost effectiveness on the planted
plantations
LITERATURE
CITED
Dubois, M. R., K. McNabb,
and T. J. Straka. 1999. Costs and trends for forestry. Forest Landowmer 58(2):
3-8.
Sprinz, P., T. Clason, and
D. Bower. 1979. Spacing and thinning effects on the
growth and development of a loblolly pine plantation, pp. 1-42 In T.
Clason (Ed.) For. Res. Rep., North Louisiana Hill Farm Exp. Stn., Louisiana
Agric. Exp Stn., Homer, LA.
Van Duesen, P. C., A. D.
Sullivan, and T. C. Matney.
1981. A prediction system
for cubic foot volume of loblolly pine applicable through much of its
range. South. J. Appl. For. 5 (4):
186-189.