ArticlePDF Available

Robust models for smallholder forests

Authors:
Jerome K Vanclay at Southern Cross University
Jerome K Vanclay
Download full-text PDF
Read full-text
Download citation

Abstract

Forest management faces a contradiction: superb decision support systems are available, but only for few forests because the necessary requisites (data, computers, advisors) often remain elusive. Thus many forests and managers are hampered by a lack of information to guide management, and this handicap falls particularly heavily on community and smallholder forests. Whilst the best decision support requires detailed and reliable data, useful advice can nonetheless be provided with simple models that are easily calibrated and have been shown to be robust in diverse situations. This paper presents the underlying framework for a set of simple models that are easily calibrated and reliable under plantation scenarios. It illustrates the calibration and use of these models for several tropical plantation species, demonstrates the implications that can be inferred, and discusses the data required to calibrate these models for new situations. This paper presents the underlying framework for a set of simple models that are easily calibrated and reliable under plantation scenarios.
Content uploaded by Jerome K Vanclay
Author content
All content in this area was uploaded by Jerome K Vanclay on Apr 16, 2019
Content may be subject to copyright.
Indian Forester, 143 (9) : 852-855, 2017
http://www.indianforester.co.in ISSN No. 0019-4816 (Print)
ISSN No. 2321-094X (Online)
ABSTRACT
Forest management faces a contradiction: superb decision support systems are available, but only for few forests because
the necessary requisites (data, computers, advisors) often remain elusive. Thus many forests and managers are hampered
by a lack of information to guide management, and this handicap falls particularly heavily on community and smallholder
forests. Whilst the best decision support requires detailed and reliable data, useful advice can nonetheless be provided
with simple models that are easily calibrated and have been shown to be robust in diverse situations. This paper presents
the underlying framework for a set of simple models that are easily calibrated and reliable under plantation scenarios. It
illustrates the calibration and use of these models for several tropical plantation species, demonstrates the implications
that can be inferred, and discusses the data required to calibrate these models for new situations.
Key words: Robust models, Data, Framework, Smallholder forest, Plantation scenarios.
This paper presents the underlying framework for a set of simple models that are easily calibrated and
reliable under plantation scenarios.
Introduction
Many forest owners need better information and
advice about their management options, especially for
small private forests where private research is impractical.
Experienced silviculturalists can often formulate good
advice by subjectively appraising the size and variation of
trees within a stand, but many small holders and their
advisors lack that experience, and may be reluctant to thin
trees to waste without compelling evidence.
One problem is that these smallholders and their
advisors don't have access to good models to assist them
to explore options. Worldwide, the availability of
plantation growth models is unequal – there are
thousands of models for a few select species (such as
Pinusradiata), but thousands of species for which there
are no models. This lack of advice is particularly severe for
smallholder forests and for plantings of native species.
A few models (such as 3PG, Sands, 2001, 2010) can
be adjusted for any species in any location – but this is not
simple, requires an experienced specialist, and in the case
of 3PG involves estimating some 50 parameters. That's too
complicated for most smallholders and their advisors, who
need something easier and more efficient.
Growth models do not need to be so complicated.
The bare essentials involve just three trends…
1. The underlying rate at which trees grow – the height
growth pattern with age is a long-established reliable
measure.
2. The effect of competition – one useful measure is the
response of tree diameter to crowding, and
3. An indication of self-thinning, or the death rate due to
crowding.
If a model can estimate of these three trends, it's
well on the way towards useful growth estimates.
Robust Growth Patterns
Several packages are available to facilitate curve-
fitting, and some of these constrain curves to biologically-
relevant patterns (Hyams, 2005), but often require
substantial amounts of data and rarely ensure a reliable fit
when data are scarce. However, Vanclay (2010) has
demonstrated a series of relationships, applicable to the
three trends mentioned above, that remain reliable even
when data are scarce.
The height-age curve is a well-established basis for
estimating site index, and there are many equations
available to describe these curves – but most are too
complicated for practical use when data are scarce.
However, the relationship between height and the square
root of age is quite close to a straight line, and gives a
consistent, if approximate, fit for a wide range of species
and sites over long periods (Vanclay, 2010). Transforming
plantation age to the square root of (age-0.5) often results
in a straight line through the origin that can be
characterized with a single parameter, and can thus be
estimated with few data. Fig. 1 illustrates the 50-year trend
of this relationship calibrated using age 5 data from a
national database of eucalypt growth data (West and
Mattay, 1993; Mattay and West, 1994). Whilst this
relationship (the dashed line in Fig. 1) is not exact, it does
provide a good approximation over long periods.
ROBUST MODELS FOR SMALLHOLDER FORESTS
JEROME K. VANCLAY
Southern Cross University, Lismore NSW 2480, Australia
Another simple relationship quantifies the relationship
between diameter, height and stocking. The graph of
Diameter against (Height-1.3)/Log (Stocking) tends to
result in a straight line through the origin, and can describe
the pattern of stand development for decades (Vanclay,
2009). Thinning operations can cause a temporary
perturbation to this relationship, but it quickly reverts to
the long-term trend. Figure 2 shows the pattern of mean
diameter in 97 plots of Eucalyptus pilularis, all measured
more than 8 times, and illustrates that this pattern remains
close to a straight line for long periods of time.
It is a little more difficult to estimate mortality, but if
the limiting stand basal area can be identified, then the
self-thinning pattern can be modelled. If independent
estimates of the limiting basal area are unavailable, then it
can be estimated from just three items – the initial
stocking (N ), the current stocking (N ), and the current
0 t
basal area (G). These three data enable the limiting basal
t3 -1/3
area Gmax, to be estimated as G[1-(N /N ) ] which in
t 0
turn, can describe the whole-of-life pattern of self
thinning. This has been tested empirically and applies to
many species in many locations (Vanclay and Sands, 2009).
It seems audacious to predict long-term stand
growth from just 3 parameters, namely the height-age
gradient, the diameter-height gradient, and the maximum
basal area, but it has been shown empirically that these
parameters can provide consistent approximations of tree
growth over decades. Vanclay (2010) has shown that these
parameters may provide 80-year predictions with a bias of
only about 5%. This may not be sufficient precision to
manage a multi-million dollar industrial plantation
program, but it is sufficient to provide a useful tool for
smallholders, for whom this simplicity and ease of use may
be very helpful.These three key parameters can be
inserted into a freely-available spreadsheet (cheekily
called 1PG, available from the author), to enable useful
projections that encourage thoughtful evaluation of
management options (Grant et al., 2012).
Testing the model
So how well does it work in practice? The current
version of 1PG was trialed first in small plantation of
whitewood (Endospermum medullosum) in Vanuatu
established as part of a development assistance project.
The planting included a sufficient range of age, stocking,
and tree sizes, that we could be confident of the results
(Grant et al., 2012). The model offered some unexpected
insights – for instance, many project staff favoured wide
spacings, but financial analyses using the 1PG model
suggested that a stocking of 600/ha would be a good
compromise (Grant et al., 2012).
Word of the Vanuatu study soon spread, and there
was a request to try the approach with African mahogany
(Khaya sensgalensis) plantations in northern Australia.
Although the database was restricted to 37 plots all aged
less than 12 years, the approach provided useful estimate
well received by the grower.
This success with modest databases begged the
question: what is the smallest amount of data that will
nonetheless provide an adequate model for plantation
management decisions? An innovative spacing (Vanclay,
2006) in the Philippines provided an opportunity to test
the model with the indigenous species known as Mayapis
(Shorea palosapis, Gregorio et al., 2012). These
experimental data indicated a good estimate of the size-
density trend, but estimation of the height-age pattern
0.5
Fig. 1: Long-term trend in height versus (Age-0.5)
Fig. 2: Long-term trend of the relationship between Diameter and
(H-1.3)/Ln(N).
2017] 853
Robust models for smallholder forests
Indian Forester, 143 (9) : 852-855, 2017
http://www.indianforester.co.in ISSN No. 0019-4816 (Print)
ISSN No. 2321-094X (Online)
ABSTRACT
Forest management faces a contradiction: superb decision support systems are available, but only for few forests because
the necessary requisites (data, computers, advisors) often remain elusive. Thus many forests and managers are hampered
by a lack of information to guide management, and this handicap falls particularly heavily on community and smallholder
forests. Whilst the best decision support requires detailed and reliable data, useful advice can nonetheless be provided
with simple models that are easily calibrated and have been shown to be robust in diverse situations. This paper presents
the underlying framework for a set of simple models that are easily calibrated and reliable under plantation scenarios. It
illustrates the calibration and use of these models for several tropical plantation species, demonstrates the implications
that can be inferred, and discusses the data required to calibrate these models for new situations.
Key words: Robust models, Data, Framework, Smallholder forest, Plantation scenarios.
This paper presents the underlying framework for a set of simple models that are easily calibrated and
reliable under plantation scenarios.
Introduction
Many forest owners need better information and
advice about their management options, especially for
small private forests where private research is impractical.
Experienced silviculturalists can often formulate good
advice by subjectively appraising the size and variation of
trees within a stand, but many small holders and their
advisors lack that experience, and may be reluctant to thin
trees to waste without compelling evidence.
One problem is that these smallholders and their
advisors don't have access to good models to assist them
to explore options. Worldwide, the availability of
plantation growth models is unequal – there are
thousands of models for a few select species (such as
Pinusradiata), but thousands of species for which there
are no models. This lack of advice is particularly severe for
smallholder forests and for plantings of native species.
A few models (such as 3PG, Sands, 2001, 2010) can
be adjusted for any species in any location – but this is not
simple, requires an experienced specialist, and in the case
of 3PG involves estimating some 50 parameters. That's too
complicated for most smallholders and their advisors, who
need something easier and more efficient.
Growth models do not need to be so complicated.
The bare essentials involve just three trends…
1. The underlying rate at which trees grow – the height
growth pattern with age is a long-established reliable
measure.
2. The effect of competition – one useful measure is the
response of tree diameter to crowding, and
3. An indication of self-thinning, or the death rate due to
crowding.
If a model can estimate of these three trends, it's
well on the way towards useful growth estimates.
Robust Growth Patterns
Several packages are available to facilitate curve-
fitting, and some of these constrain curves to biologically-
relevant patterns (Hyams, 2005), but often require
substantial amounts of data and rarely ensure a reliable fit
when data are scarce. However, Vanclay (2010) has
demonstrated a series of relationships, applicable to the
three trends mentioned above, that remain reliable even
when data are scarce.
The height-age curve is a well-established basis for
estimating site index, and there are many equations
available to describe these curves – but most are too
complicated for practical use when data are scarce.
However, the relationship between height and the square
root of age is quite close to a straight line, and gives a
consistent, if approximate, fit for a wide range of species
and sites over long periods (Vanclay, 2010). Transforming
plantation age to the square root of (age-0.5) often results
in a straight line through the origin that can be
characterized with a single parameter, and can thus be
estimated with few data. Fig. 1 illustrates the 50-year trend
of this relationship calibrated using age 5 data from a
national database of eucalypt growth data (West and
Mattay, 1993; Mattay and West, 1994). Whilst this
relationship (the dashed line in Fig. 1) is not exact, it does
provide a good approximation over long periods.
ROBUST MODELS FOR SMALLHOLDER FORESTS
JEROME K. VANCLAY
Southern Cross University, Lismore NSW 2480, Australia
Another simple relationship quantifies the relationship
between diameter, height and stocking. The graph of
Diameter against (Height-1.3)/Log (Stocking) tends to
result in a straight line through the origin, and can describe
the pattern of stand development for decades (Vanclay,
2009). Thinning operations can cause a temporary
perturbation to this relationship, but it quickly reverts to
the long-term trend. Figure 2 shows the pattern of mean
diameter in 97 plots of Eucalyptus pilularis, all measured
more than 8 times, and illustrates that this pattern remains
close to a straight line for long periods of time.
It is a little more difficult to estimate mortality, but if
the limiting stand basal area can be identified, then the
self-thinning pattern can be modelled. If independent
estimates of the limiting basal area are unavailable, then it
can be estimated from just three items – the initial
stocking (N ), the current stocking (N ), and the current
0 t
basal area (G). These three data enable the limiting basal
t3 -1/3
area Gmax, to be estimated as G[1-(N /N ) ] which in
t 0
turn, can describe the whole-of-life pattern of self
thinning. This has been tested empirically and applies to
many species in many locations (Vanclay and Sands, 2009).
It seems audacious to predict long-term stand
growth from just 3 parameters, namely the height-age
gradient, the diameter-height gradient, and the maximum
basal area, but it has been shown empirically that these
parameters can provide consistent approximations of tree
growth over decades. Vanclay (2010) has shown that these
parameters may provide 80-year predictions with a bias of
only about 5%. This may not be sufficient precision to
manage a multi-million dollar industrial plantation
program, but it is sufficient to provide a useful tool for
smallholders, for whom this simplicity and ease of use may
be very helpful.These three key parameters can be
inserted into a freely-available spreadsheet (cheekily
called 1PG, available from the author), to enable useful
projections that encourage thoughtful evaluation of
management options (Grant et al., 2012).
Testing the model
So how well does it work in practice? The current
version of 1PG was trialed first in small plantation of
whitewood (Endospermum medullosum) in Vanuatu
established as part of a development assistance project.
The planting included a sufficient range of age, stocking,
and tree sizes, that we could be confident of the results
(Grant et al., 2012). The model offered some unexpected
insights – for instance, many project staff favoured wide
spacings, but financial analyses using the 1PG model
suggested that a stocking of 600/ha would be a good
compromise (Grant et al., 2012).
Word of the Vanuatu study soon spread, and there
was a request to try the approach with African mahogany
(Khaya sensgalensis) plantations in northern Australia.
Although the database was restricted to 37 plots all aged
less than 12 years, the approach provided useful estimate
well received by the grower.
This success with modest databases begged the
question: what is the smallest amount of data that will
nonetheless provide an adequate model for plantation
management decisions? An innovative spacing (Vanclay,
2006) in the Philippines provided an opportunity to test
the model with the indigenous species known as Mayapis
(Shorea palosapis, Gregorio et al., 2012). These
experimental data indicated a good estimate of the size-
density trend, but estimation of the height-age pattern
0.5
Fig. 1: Long-term trend in height versus (Age-0.5)
Fig. 2: Long-term trend of the relationship between Diameter and
(H-1.3)/Ln(N).
2017] 853
Robust models for smallholder forests
was hampered by poor early growth of the plantings.
Nonetheless, height measures at ages 3.9, 4.5 and 5.5
years gave parameters consistent with other estimates.
Thus it appears that the model can be calibrated
sufficiently with scant data, although it appears desirable
to have data from stands older than 4 years.
A final challenge came when the Philippine NGO
Genesyssought assistance with biomass forecasts from
bioenergy trials. Their data were drawn from small plots,
planted at 1x1m and measured bimonthly for only 22
months, and they sought guidance about future growth
rates and effective management regimes. Despite these
modest data, estimates obtained in this way were
consistent, if slightly higher, than comparable estimates
from larger, longer-term smallholder plantings.
Smallholders tend to plant this species on poor sites with
minimal management, so it is not surprising that the well-
tended Genesys trial exhibited higher growth, especially
for the height-age pattern – and it was reassuring to see
the close correspondence between these estimates.
Clearly, these are not strong empirical tests, but
such testing has been examined elsewhere (Vanclay, 2010)
and the paragraphs above report user acceptance of the
approach. Evidently this method can be applied to a wide
range of situations, even with minimal data. More
sophisticated models retain an important role in research
and industrial management, but simple approaches such
as the one illustrated here can make a useful contribution
in situations where data are scarce, funds are limited,
modelling skills are elementary, or plantings involve small
areas or lesser-known species.
Conclusion
This series of studies with the 1PG model leads to
several conclusions. Firstly, a strength of this approach is
that it is objective - it does not depend on an advisor 'liking'
a species (or not); rather, it offers a way to make an
impartial assessment of a species performance and its
potential.
Predictions can be tested easily, by comparing with
other data, or by gathering data from the same plot at a
later occasion – and it is easy to adjust the model on
receipt of updated estimates. It is parsimonious and
requires just three trends, with one parameter for each
trend.The estimates can be made, and the model run, with
few data and modest computing resources – any
spreadsheet software will suffice, and only beginner skills
in spreadsheet use are needed.The approach supports
adaptive forest management (Sayer et al., 1997) – if a
manager has just one plot that is a little older than the bulk
of the plantings, then the model and that “head-start” plot
can be used to investigate options and fine-tune the
management of the main estate.
Acknowledgements
This work has drawn inspiration from, and relied on contributions from many colleagues involved in several
projects. Important contributions were made by colleagues at Southern Cross University (Doland Nichols and others),
University of the Sunshine Coast (John Herbohn and others), and Visayas State University (Nestor Gregorio and others).
The work was funded in part by ACIAR projects ASEM/2010/050, ASEM/2006/091, ASEM/2003/052, and FST/2005/089
y?kq/kjd ouksa ds fy, lUrqfyr ekWMy
thjkse ds- okuDys
lkjka'k
ou izca/u ,d fojks/kHkkl dk lkeuk djrs gS% mRd`"V fu.kZ; lgk;rk iz.kkfy;ka miyC/ gSa] fdUrq dqN ouksa ds fy, D;ksafd vko';d
lkefxz;ka (vk¡dM+k] dEI;wVlZ] lykgdkj) izk;% nqxzkZg; jgrh gSaA bl izdkj izca/u esa ekxZn'kZu gsrq lwpuk ds vHkko dh otg ls vusdksa ouksa ,oa
izca/dksa dks ck/k igqaprh gS vkSj ;g vM+pu fo'ks"kdj leqnk; vkSj y?kq/kjd ouksa ij Hkkjh iM+rh gSA tcfd loksZÙke fu.kZ; lgk;rk dks fo'oLr ,oa
fo'olhu; vk¡dM+ksa dh vko';drk gksrh gS] fiQj Hkh mu lk/kj.k ekWMyksa ds lkFk mi;ksxh lykg miyC/ djkbZ tk ldrh gS ftUgsa vklkuh ls
va'k'kksf/r djrs gSa vkSj fofo/ fLFkfr;ksa esa lUrqfyr n'kkZ;k x;k gSA bl 'kks/i=k esa mu lk/kj.k ekWMyksa ds ,d lSV ds fy, :ijs[kk izLrqr dh xbZ gS]
ftUgsa vklkuh ls va'k'kksf/r dj ldrs gSa vkSj jksi.k ifjn`';ksa ds rgr fo'oluh; gSaA ;g vusdksa m".kdfVca/h; jksi.k iztkfr;ksa ds fy, bu ekWMyksa
ds va'k'kks/u ,oa mi;ksx ij izdk'k Mkyrk gS] mu tfVyrkvksa dk izn'kZu djrk gS ftUgsa vuqekfur dj ldrs gSa] vkSj u;h fLFkfr;ksa ds fy, bu
ekWMyksa ds va'k'kks/u gsrq okafNr vk¡dM+ksa ij fopkj&foe'kZ djrk gSA
References
Grant J., Glencross K., Nichols D., Palmer G., Sethy M. and Vanclay J. (2012). Silvicultural implications arising from a simple simulation model for
Endospermummedullosum in Vanuatu. International Forestry Review, 14(4): 452-462.
Gregorio N.O., Herbohn J.L. and Vanclay J.K. (2012). Developing establishment guidelines for Shoreapalosapis in smallholder plantings in the
Philippines. International Forestry Review, 14(4): 492-501 https://www.curveexpert.net/
Mattay J.P. and West P.W. (1994). A collection of growth and yield data from eight eucalypt species growing in even-aged, monoculture forest.
CSIRO Forestry and Forest Products, User Series 18.
Sands P.J. (2001). 3PGPJS—a user-friendly interface to 3-PG, the Landsberg and Waring model of forest productivity. Cooperative Research
Centre for Sustainable Production Forestry and CSIRO Forestry and Forest Products Technical Report, (29).
Sands P.G. (2010). 3PG PJS user manual.
st
Sayer J.A., Vanclay J.K. and Byron N. (1997). Technologies for sustainable forest management: Challenges for the 21 century. Commonwealth
Forestry Review, 76:162-170.
Vanclay J.K. (2006). Experiment designs to evaluate inter- and intra-specific interactions in mixed plantings of forest trees. Forest Ecology and
Management, 233:366-374.
Vanclay J.K. (2009). Tree diameter, height and stocking in even-aged forests. Annals of Forest Science, 66:702.
Vanclay J.K. (2010). Robust relationships for simple plantation growth models based on sparse data. Forest Ecology and Management,
259:1050–1054.
Vanclay J.K. and Sands P.J. (2009). Calibrating the self-thinning frontier. Forest Ecology and Management, 259:81-85.
West P.W. and Mattay J.P. (1993). Yield prediction models and comparative growth rates for six eucalypt species. Australian Forestry, 56: 211-
225.
Hyams D. (2005). Curve Expert Version 1.37. A comprehensive curve fitting package for Windows.
854 The Indian Forester [September 2017] 855
Robust models for smallholder forests
was hampered by poor early growth of the plantings.
Nonetheless, height measures at ages 3.9, 4.5 and 5.5
years gave parameters consistent with other estimates.
Thus it appears that the model can be calibrated
sufficiently with scant data, although it appears desirable
to have data from stands older than 4 years.
A final challenge came when the Philippine NGO
Genesyssought assistance with biomass forecasts from
bioenergy trials. Their data were drawn from small plots,
planted at 1x1m and measured bimonthly for only 22
months, and they sought guidance about future growth
rates and effective management regimes. Despite these
modest data, estimates obtained in this way were
consistent, if slightly higher, than comparable estimates
from larger, longer-term smallholder plantings.
Smallholders tend to plant this species on poor sites with
minimal management, so it is not surprising that the well-
tended Genesys trial exhibited higher growth, especially
for the height-age pattern – and it was reassuring to see
the close correspondence between these estimates.
Clearly, these are not strong empirical tests, but
such testing has been examined elsewhere (Vanclay, 2010)
and the paragraphs above report user acceptance of the
approach. Evidently this method can be applied to a wide
range of situations, even with minimal data. More
sophisticated models retain an important role in research
and industrial management, but simple approaches such
as the one illustrated here can make a useful contribution
in situations where data are scarce, funds are limited,
modelling skills are elementary, or plantings involve small
areas or lesser-known species.
Conclusion
This series of studies with the 1PG model leads to
several conclusions. Firstly, a strength of this approach is
that it is objective - it does not depend on an advisor 'liking'
a species (or not); rather, it offers a way to make an
impartial assessment of a species performance and its
potential.
Predictions can be tested easily, by comparing with
other data, or by gathering data from the same plot at a
later occasion – and it is easy to adjust the model on
receipt of updated estimates. It is parsimonious and
requires just three trends, with one parameter for each
trend.The estimates can be made, and the model run, with
few data and modest computing resources – any
spreadsheet software will suffice, and only beginner skills
in spreadsheet use are needed.The approach supports
adaptive forest management (Sayer et al., 1997) – if a
manager has just one plot that is a little older than the bulk
of the plantings, then the model and that “head-start” plot
can be used to investigate options and fine-tune the
management of the main estate.
Acknowledgements
This work has drawn inspiration from, and relied on contributions from many colleagues involved in several
projects. Important contributions were made by colleagues at Southern Cross University (Doland Nichols and others),
University of the Sunshine Coast (John Herbohn and others), and Visayas State University (Nestor Gregorio and others).
The work was funded in part by ACIAR projects ASEM/2010/050, ASEM/2006/091, ASEM/2003/052, and FST/2005/089
y?kq/kjd ouksa ds fy, lUrqfyr ekWMy
thjkse ds- okuDys
lkjka'k
ou izca/u ,d fojks/kHkkl dk lkeuk djrs gS% mRd`"V fu.kZ; lgk;rk iz.kkfy;ka miyC/ gSa] fdUrq dqN ouksa ds fy, D;ksafd vko';d
lkefxz;ka (vk¡dM+k] dEI;wVlZ] lykgdkj) izk;% nqxzkZg; jgrh gSaA bl izdkj izca/u esa ekxZn'kZu gsrq lwpuk ds vHkko dh otg ls vusdksa ouksa ,oa
izca/dksa dks ck/k igqaprh gS vkSj ;g vM+pu fo'ks"kdj leqnk; vkSj y?kq/kjd ouksa ij Hkkjh iM+rh gSA tcfd loksZÙke fu.kZ; lgk;rk dks fo'oLr ,oa
fo'olhu; vk¡dM+ksa dh vko';drk gksrh gS] fiQj Hkh mu lk/kj.k ekWMyksa ds lkFk mi;ksxh lykg miyC/ djkbZ tk ldrh gS ftUgsa vklkuh ls
va'k'kksf/r djrs gSa vkSj fofo/ fLFkfr;ksa esa lUrqfyr n'kkZ;k x;k gSA bl 'kks/i=k esa mu lk/kj.k ekWMyksa ds ,d lSV ds fy, :ijs[kk izLrqr dh xbZ gS]
ftUgsa vklkuh ls va'k'kksf/r dj ldrs gSa vkSj jksi.k ifjn`';ksa ds rgr fo'oluh; gSaA ;g vusdksa m".kdfVca/h; jksi.k iztkfr;ksa ds fy, bu ekWMyksa
ds va'k'kks/u ,oa mi;ksx ij izdk'k Mkyrk gS] mu tfVyrkvksa dk izn'kZu djrk gS ftUgsa vuqekfur dj ldrs gSa] vkSj u;h fLFkfr;ksa ds fy, bu
ekWMyksa ds va'k'kks/u gsrq okafNr vk¡dM+ksa ij fopkj&foe'kZ djrk gSA
References
Grant J., Glencross K., Nichols D., Palmer G., Sethy M. and Vanclay J. (2012). Silvicultural implications arising from a simple simulation model for
Endospermummedullosum in Vanuatu. International Forestry Review, 14(4): 452-462.
Gregorio N.O., Herbohn J.L. and Vanclay J.K. (2012). Developing establishment guidelines for Shoreapalosapis in smallholder plantings in the
Philippines. International Forestry Review, 14(4): 492-501 https://www.curveexpert.net/
Mattay J.P. and West P.W. (1994). A collection of growth and yield data from eight eucalypt species growing in even-aged, monoculture forest.
CSIRO Forestry and Forest Products, User Series 18.
Sands P.J. (2001). 3PGPJS—a user-friendly interface to 3-PG, the Landsberg and Waring model of forest productivity. Cooperative Research
Centre for Sustainable Production Forestry and CSIRO Forestry and Forest Products Technical Report, (29).
Sands P.G. (2010). 3PG PJS user manual.
st
Sayer J.A., Vanclay J.K. and Byron N. (1997). Technologies for sustainable forest management: Challenges for the 21 century. Commonwealth
Forestry Review, 76:162-170.
Vanclay J.K. (2006). Experiment designs to evaluate inter- and intra-specific interactions in mixed plantings of forest trees. Forest Ecology and
Management, 233:366-374.
Vanclay J.K. (2009). Tree diameter, height and stocking in even-aged forests. Annals of Forest Science, 66:702.
Vanclay J.K. (2010). Robust relationships for simple plantation growth models based on sparse data. Forest Ecology and Management,
259:1050–1054.
Vanclay J.K. and Sands P.J. (2009). Calibrating the self-thinning frontier. Forest Ecology and Management, 259:81-85.
West P.W. and Mattay J.P. (1993). Yield prediction models and comparative growth rates for six eucalypt species. Australian Forestry, 56: 211-
225.
Hyams D. (2005). Curve Expert Version 1.37. A comprehensive curve fitting package for Windows.
854 The Indian Forester [September 2017] 855
Robust models for smallholder forests
... Although there has been progress in developing models for commercial plantation forests, less attention has been given to smallholder and community forests (Tiryana et al. 2021), partly due to data limitations (Vanclay et al. 1995); nevertheless, recent efforts have been made to develop robust models to address data limitations in such forests (Vanclay 2017). In Indonesia, most available allometric volume models are for tree species like jabon (Anthocephalus cadamba (Roxb.) ...
View
... Provision of suitable data (Vanclay 1991;Vanclay et al. 1995) remains an obstacle to the development of models to support forest landscape restoration, although robust models for data-poor situations are emerging (Vanclay 2010(Vanclay , 2017. This study draws on earlier work to evaluate competition in four species that are potential candidates for both smallholder plantations and forest landscape restoration. ...
Competition in a Mixed-Species Planting with Four Contrasting Tree Species
Article
Full-text available
  • Oct 2022
Mixed-species systems are well-suited to smallholder and community forestry, but reliable evidence regarding and procedures to assess species performance in such systems is scarce. This field trial uses a pair of clinal plots with varying spacing and species composition to gain insights into competition between four species proposed for landscape rehabilitation in the Philippines. We examine the efficiency of this compact clinal trial in revealing growth traits of four species (Paraserianthes falcataria, Pterocarpus indicus, Shorea palosapis, Swietenia macrophylla) in mixed plantings. The use of a size-distance competition index allowed an assessment of the competitive and collaborative influences between four tree species. Within the expected general trend for diameter increment to decline with increasing competition, there were indications that Shorea palosapis is a benign competitor that may stimulate the growth of neighbouring individuals. Paraserianthes falcataria is a strong competitor that is also strongly impacted by competition, especially through antagonistic intraspecific competition. Paraserianthes falcataria appears well suited as a solitary tree in a field or village, whereas Shorea palosapis seems ideal for plantations, in both monoculture and mixed plantings. The clinal spacing and mixture trial, when examined using a size-distance competition index based on diameter increment, revealed useful insights into species performance. Pterocarpus indicus exhibits strong intraspecific, but low inter-specific competition, so appears well-suited for polyculture plantings. Of the four species trialled, Swietenia macrophylla appears to be best-suited as a monoculture species as it exhibits the lowest intraspecific competition.
View
... A growth model can be considered as an abstraction of reality, by which the key relationships of a selected biological mechanism are being conceptualised (Vanclay, 2017). Forest growth models therefore, provide platforms for forest managers to predict the growth, even without years of experience (Vanclay, 1994, Chaudhuri et al., 1995. ...
Prediction of the Early Growth of Plantation Grown G. walla
Article
Full-text available
  • Nov 2021
Certain tree species of Thymalaeaceae family produce highly fragrant, valuable resin called agarwood inside the stems, branches and roots due to a defence mechanism to protect internal tissue damage from invading microorganisms. Gyrinops walla is the only native tree species bearing the agarwood resin production ability which is growing in the low and mid elevations of wet climates of Sri Lanka. After some years of discovering the ability to produce agarwood resins in of G. walla, private sector investors planned to establish small and medium scale plantations using this species. However, information on G. walla growth rates under plantations conditions were not available, which are essential for the effective management. Therefore the present study aimed at constructing height and diameter prediction models for the early stages of G. walla plantations. For this purse, monthly measured height and diameter data of 40 plants of an even-aged G. walla plantation were used. Several non-linear and 2nd and 3rd order polynomial models were initially tested, keeping age as the single explanatory variable. Among them, the best performances were given by the 2nd order polynomial models for both height and diameter variables. Both models had R2 over 99.0 and root mean square error and mean absolute difference less than 0.10, proving high accuracy. Fitted line plots also did not indicate deviations of the residuals. Though the models built in this study are recommended for predicting the early plantation growth of G. walla, future research should be conducted to validate them till the maturity of the trees. Keywords: G. walla, polynomial regression, growth modelling, plantation, height, diameter
View
... Provision of suitable data (Vanclay 1991, Vanclay et al 1995 remains an obstacle to the development of models to support forest landscape restoration, although robust models for datapoor situations are emerging (Vanclay 2010(Vanclay , 2017. This study draws on earlier work to evaluate competition in four species that are potential candidates for both smallholder plantations and forest landscape restoration. ...
Competition in a Mixed-Species Planting With Four Contrasting Species
Preprint
Full-text available
  • Jul 2021
Background: Mixed-species systems are well-suited to smallholder and community forestry, but reliable evidence regarding and procedures to assess species performance in such systems is scarce. This study concern a field trial with a pair of clinal plots varying spacing and species composition that offered insights into competition between four species proposed for mixed-species plantings by smallholders for landscape rehabilitation in the Philippines. Results: Use of a size-distance competition index allowed an assessment of the competitive and collaborative influences between four tree species. Within the expected general trend for growth to decline with increasing competition, there were indications that Shorea palosapis is a benign competitor that may stimulate the growth of neighbouring individuals. Paraserianthes falcataria is a strong competitor that is also strongly impacted by competition, especially through antagonistic intraspecific competition. Paraserianthes falcataria appears well suited as a solitary tree in a field or village, whereas Shorea palosapis seems ideal for plantations, in both monoculture and mixed plantings. Conclusion: Pterocarpus indicus exbibits strong intraspecific, but low inter-specific competition, so appears well-suited for polyculture plantings. Of the four species, Swietenia macrophylla appears to be best-suited as a monoculture species as it exhibits the lowest intraspecific competition.
View
Field trials to develop Improved Silviculture in Forest Restoration
Presentation
Full-text available
  • Sep 2023
Discusses trials and analyses to support forest landscape restoration
View
Yield prediction models and comparative growth rates for six eucalypt species
Article
Full-text available
  • Jan 1993
Stand stem volume yield prediction models are presented for six eucalypt species Eucalyptus regnans F. Muell., E. obliqua L'Her., E. delegatensis R. Baker. E. pilularis Smith, E. grandis Hill ex Maiden and E. diversicolor F. Muell. The data set used was collected over many years by eight of the major forestry agencies of Australia. It included data only from fully stocked, monospecific stands which had received no major natural or unnatural disturbance throughout their life-times. The bulk of the data was collected from regrowth forest, but some data from plantation forest were also included. The data did not sample formally or fully the entire area of natural occurrence of the six species. These data limitations must be borne in mind when applying the models. A site-index equation is developed for each species and these are then used in developing the stand stem volume yield prediction models which were based on the commonly used Schumacher model. The models are then used to compare growth rates of these species. It is shown that E. diversicolor has the most rapid early growth rate in stem volume and E. pilularis has the slowest. The other species are intermediate in growth rate between these two and do not differ greatly between each other.
View
Developing Establishment Guidelines for Shorea palosapis in Smallholder Plantings in the Philippines
Article
Full-text available
  • Dec 2012
A series of trials examining fertilizer-shading interactions on the island of Leyte (Philippines, 11°N) revealed that the endemic dipterocarp mayapis () benefits from shade trees, either directly above or to the east, during the early stages of plantation establishment. Although it can attain 2 cm/year diameter increment in plantations, mayapis exhibits poor growth and survival under wide spacing, when waterlogged and in exposed bare soil. Indications that early growth can be hampered by high soil temperatures warrant further research and development of practical planting techniques for smallholders. Spanish Una serie de ensayos que examinaron las interacciones entre sombreado y fertilizante en la isla de Leyte (Filipinas, 11°N), revelaron que durante las etapas iniciales del establecimiento de la plantación, la dipterocarpácea endémica mayapis (Shorea palosapis) se beneficia de la presencia de árboles de sombra, ya sea directamente por encima o bien localizada al este. Aunque incremento diamétrico en plantaciones puede alcanzar los 2 cm/año, mayapis muestra un crecimiento y una supervivencia pobres bajo espaciamientos amplios, así como en los suelos anegados o los desnudos y expuestos. Ciertos indicios de que el crecimiento inicial puede verse obstaculizado por altas temperaturas del suelo merecen investigación adicional y el desarrollo de técnicas de plantación prácticas para pequeños propietarios. French Une série d'essais examinant les interactions engrais/ombre sur l'île de Leyte (Philippines, 11 degrés N) a révélé que le dipterocarp mayapis (Shorea palosapis) endémique profite des arbres offrant un ombrage, directement au dessus ou vers l'est, pendant les premiers stades de son établissement en plantation. Bien qu'il puisse atteindre des croissances de diamètre de 2 cm/an dans les plantations, le mayapis connait maigre croissance et survie quant il est trop espacé, noyé ou exposé sur la terre nue. Des indications que la croissance initiale peut être empêchée par des fortes températures du sol encouragent une recherche plus poussée et un développement de techniques pratiques de plantation pour les petits exploitants.
View
Silvicultural Implications Arising from a Simple Simulation Model for Endospermum medullosum in Vanuatu
Article
Full-text available
  • Dec 2012
Whitewood () is a tree species that shows promise for plantation timber production in Vanuatu, but few growth data are available to inform yield forecasts. Three simple relationships summarizing stand dynamics, namely height-age, diameter-height-stocking, and mortality-basal area relationships, were calibrated with data from 15 plots to form the basis of a model for silvicultural and management decisions. Despite the simplicity of the model, it offers predictions consistent with independent data. The model suggests that the optimal silviculture involves planting 635 stems/ha, thinning at 20 and 26 years, and clearfelling at age 36 when trees have a diameter of 55 cm dbh. However, many options offer a net present value within 5% of this nominal optimum. The flexibility to vary the timing and intensity of harvests over a wide range while maintaining good financial returns, coupled with good growth and timber properties, suggests that whitewood warrants further domestication and promotion in Vanuatu. Spanish Madera blanca (Endospermum medullosum) es una especie arbórea prometedora en Vanuatu para la producción de madera en plantaciones, pero hasta la fecha son pocos los datos de crecimiento disponibles como para poder hacer pronósticos sobre el rendimiento. Se calibraron tres relaciones simples que resumen la dinámica de un rodal, como son las relaciones entre altura-edad, diámetro-altura-existencias, y mortalidad-área basal, por medio de datos de 15 parcelas, los cuales constituirían la base de un modelo de decisiones silviculturales y de gestión. A pesar de su simplicidad, el modelo ofrece predicciones compatibles con datos independientes. El modelo sugiere que la silvicultura óptima consiste en la plantación de 635 árboles/ha, la realización de raleos a los 20 y 26 años, y una tala rasa a los 36 años, cuando los árboles han alcanzado un DAP de 55 cm. Sin embargo, son muchas las opciones que ofrecen un valor actual neto dentro del 5% de este óptimo nominal. Esta flexibilidad de poder variar el turno y la intensidad de las talas dentro de un amplio intervalo, manteniendo a la vez un excelente rendimiento financieros, junto con un aceptable crecimiento y unas buenas propiedades de la madera, sugiere que madera blanca merece ser domesticada y fomentada en Vanuatu. French Le bois blanc (Endospermum medullosum) est une essence d'arbre prometteuse pour la production de bois de coupe en plantations à Vanuatu, mais peu de données de croissance sont disponibles pour informer les prédictions de production. Trois relations simples, synthétisant la dynamique des plants: âge et hauteur, la relation diamètre/hauteur, et les relations entre la mortalité et la base, ont été calibrées avec des données provenant de 15 plants, pour former la base d'un modèle destiné à informer les décisions de sylviculture et de gestion. Malgré la simplicité du modèle, ce dernier offre des prédictions confirmées par des données indépendantes. Le modèle suggère qu'une sylviculture optimale comprendrait la plantation de 635 individus par ha, un élagage à 20 et 26 ans, et une coupe à 36 ans, quand les arbres auraient atteint un diamètre de 55 cm dbh. Toutefois, plusieurs options présentent une valeur actuelle nette dans une marge à 5% de cet optimum nominal. La flexibilité de varier le moment et l'intensité des récoltes sur une grande surface, tout en préservant des bénéfices financiers appréciables, ainsi qu'une croissance solide et des propriétés du bois maintenues, suggèrent que le bois blanc mérite une domestication et une promotion plus poussées à Vanuatu.
View
Experiment designs to evaluate inter- and intra-specific interactions in mixed plantings of forest trees
Article
Full-text available
  • Sep 2006
  • FOREST ECOL MANAG
A review of three mixed-species trials reveals the utility of competition indices for evaluating inter- and intra-specific interactions between trees, the desirability of experiments that span a range of tree spacing and composition to inform calibration of these competition indices, the need for extremes of species composition and stand density to calibrate response surfaces, and the far-reaching impact of edge-effects. Experiment layouts commonly used for mixed-species trials in forestry (such as replacement series) rarely provide a strong basis to calibrate competition indices and response surfaces. Alternative designs involving systematic changes in species composition may offer a better basis for calibrating response surfaces, especially when used in conjunction with designs that vary tree spacing systematically. Systematic spacing designs (such as Pudden clinal plots, Marynen plaids and Nelder fans) are well established, but designs that vary composition systematically are less common. The Goelz triangle and an alternative are contrasted to illustrate how both may offer inspiration when designing trials for mixed-species research in forestry.
View
Calibrating the self-thinning frontier
Article
Full-text available
  • Dec 2009
  • FOREST ECOL MANAG
Calibration of the self-thinning frontier in even-aged monocultures is hampered by scarce data and by subjective decisions about the proximity of data to the frontier. We present a simple model that applies to observations of the full trajectory of stand mean diameter across a range of densities not close to the frontier. Development of the model is based on a consideration of the slope s=ln(Nt/Nt 1)/ln(Dt/Dt 1) of a log-transformed plot of stocking Nt and mean stem diameter Dt at time t. This avoids the need for subjective decisions about limiting density and allows the use of abundant data further from the self-thinning frontier. The model can be solved analytically and yields equations for the stocking and the stand basal area as an explicit function of stem diameter. It predicts that self-thinning may be regulated by the maximum basal area with a slope of -2. The significance of other predictor variables offers an effective test of competing self-thinning theories such Yoda's -3/2 power rule and Reineke's stand density index. Comment: Typos corrected, missing reference added
View
Technologies for Sustainable Forest Management: Challenges for the 21st Century
Article
Full-text available
  • Jan 1997
Technology will help to address the challenges for sustainable forestry in the 21st century. Some of the challenges will include the shift of production from native forest to plantations in areas of comparative advantage, more efficient processing delinking end-use products from raw wood characteristics, increased demand, better information technologies to support decision makers, and more options for conserving biodiversity. Definitions of sustainability will vary in time and space as society’s expectations and aspirations change, so there can be no 'silver bullet' to ensure sustainability. However, progress may be facilitated with a systematic approach to forest management embracing the usual planning cycle: formulation of objectives, preparation of a strategy, planning, implementing, monitoring, and reappraisal. This requires a good understanding of each particular situation. Managers need good resource assessment and decision support systems; they must foster stakeholder participation in decisions, costs and benefits; and ensure effective procedures to resolve conflicts. Within an appropriate system, technical advances such as better machines and new implements may help to make a difference, but will not in themselves ensure sustainability. The important technologies for sustainable forestry are those that foster better communication between stakeholders and allow informed decisions spanning scales from the gene to the ecosystem. This remains an important challenge for forest managers in their search for sustainability.
View
Robust relationships for simple plantation growth models based on sparse data
Article
Full-text available
  • Feb 2010
  • FOREST ECOL MANAG
Three equations predicting height H = β1(t − 0.5)0.5, diameter D = β2(H − 1.3)/ln N, and mortality dN/N = −2(G/Gmax)3dD/D from plantation age (t), stocking (N) and basal area (G) can be calibrated with few data (even a single observation) for plantations in which re-measured data and growth models are unavailable. Despite having only three parameters to be estimated, these equations extrapolate reliably and allow objective forecasts of future plantation growth performance that may serve as useful first approximations until more precise growth models can be developed.
View
Tree diameter, height and stocking in even-aged forests
Article
Full-text available
  • Apr 2009
  • ANN FOR SCI
• Empirical observations suggest that in pure even-aged forests, the mean diameter of forest trees (D, diameter at breast height, 1.3 m above ground) tends to remain a constant proportion of stand height (H, average height of the largest trees in a stand) divided by the logarithm of stand density (N, number of trees per hectare): D = β(H − 1.3)/ ln(N). • Thinning causes a relatively small and temporary change in the slope β, the magnitude and duration of which depends on the nature of the thinning. • This relationship may provide a robust predictor of growth in situations where scarce data and resources preclude more sophisticated modelling approaches.
View
A collection of growth and yield data from eight eucalypt species growing in even-aged, monoculture forest. CSIRO Forestry and Forest Products
  • Jan 1994
  • J P Mattay
  • P W West
Mattay J.P. and West P.W. (1994). A collection of growth and yield data from eight eucalypt species growing in even-aged, monoculture forest. CSIRO Forestry and Forest Products, User Series 18.
3PGPJS-a user-friendly interface to 3-PG, the Landsberg and Waring model of forest productivity. Cooperative Research Centre for Sustainable Production Forestry and CSIRO Forestry and Forest Products Technical Report
  • Jan 2001
  • P J Sands
Sands P.J. (2001). 3PGPJS-a user-friendly interface to 3-PG, the Landsberg and Waring model of forest productivity. Cooperative Research Centre for Sustainable Production Forestry and CSIRO Forestry and Forest Products Technical Report, (29).