Taking stock. An annotated bibliography of logging damage and recovery in tropical forests and the results of new research in Ghana
Item
Title
Taking stock. An annotated bibliography of logging damage and recovery in tropical forests and the results of new research in Ghana
Date
1999
Language
English
Abstract
This paper summarises the results of a DFID/FRP project (R6716
-
Impact of harvesting on forest mortality and regeneration in the high forest zones of Ghana. The aim of this project was to improve our knowledge of the negative impacts of logging tropical rain forests, and to recommend improvements to the logging system, with particular yet not exclusive reference to Ghana. There are two components to this: a bibliography and the description of field research conducted under the project. An annotated bibliography covers literature on: logging damage and recovery; forest regeneration and theallometry, growth, reproduction and death of trees related to logging disturbance. The bibliography covers tropical forests in general. A separate bibliography on impacts of logging on biodiversity as a whole, particularly covering zoological aspects, was prepared separately by A. Grieser-Johns as an early output of R6716 and is appended. The rest of the paper describes five topics addressed to various degrees by fieldwork under the FRP project. In each section, a brief overview is provided of the literature relevant to that topic. The introductory
Section 2
describes the context of logging in Ghana, and explains some of the general background to the report. We emphasise that the main tool for controlling the impact of logging in Ghana is the process of yield allocation and stock map production. In
Section 3
we summarise previous and new research on
extraction damage
, concluding with theobservation that reduction of damage should be a main criterion for efficient stock maps. Some species cause moredamage than others when trees of a particular size are felled, so we emphasise that there is scope for optimisation ofstock map production through a cost/benefit type analysis based on this, particularly as most logging damage isassociated with felling gaps, with another significant component due to their extraction. Unfortunately, the data onfelled trees is limited to the few species that happened to have been felled within the scope of our study.In
Section 4,
tree allometry
,
we seek to refine models relating to extraction damage, by study of therelationships between crown size and tree bole diameter. Trees are categorised according to maximum sizes attainedand variation of their crown widths in relation to bole diameter. There is a trend for large-crowned trees to be thespecies associated with greater felling damage, so it is possible to extend tentatively the conclusions from Section 3to a greater range of species. Allometric data was incidentally compiled on a wide range of species as we believe itwill be useful for more sophisticated approaches to stand modelling and PSP analysis.Trees are retained in logged forest for a number of reasons including their role as seed trees, supposedly topromote regeneration of logged forest. As part of an appraisal of this aspect of the stock map, studies were made on
tree maturity
(
Section 5)
and on
patterns of established regeneration
related to potential seed tree (
Section 7)
.In
Section 6
, we discuss in depth
the regeneration of logged forest in PSPs,
describing
12 out of Ghana’s600 Permanent Sample Plots established about 10 years ago, which happen to have been logged at various times upto more than 30 years ago. In all these plots, it is possible to see scars due to skidding and felling of trees, andpatterns associated with the recovery of vegetation in these scars are described from various points of view. In eachcase about half of the hectare plot, referred to as the ‘Apparent Extraction Network’ (AEN), has tree regeneration thatis severely reduced relative to general trends in Ghana, and more specifically relative to the less damaged otherhalves of the plots. Mortality associated with logging has returned to normal levels after about 30 years, but the AENforest is generally lower in basal area and timber regeneration. We suggest that damage, probably compaction to thesoil by logging machinery may be responsible for a medium or long term reduction in the site productivity.The
implications and recommendations
of these studies for the Ghana Forest Service are mentioned at theends of each section, and are summarised in
Section 8
. One of the main problems with existing practice, apart fromthe poor recovery from damage - probably due to soil damage by extraction machinery- has been the increasinglycomplicated, and variously fuzzy and incompletely justified guidelines, contributing to poor implementation, even ofessential and well-founded procedures.
Any attempt to improve the system by refining rules and regulationsmust at the same time make it easier to implement, monitor and successively improve them
.Briefly, we propose that stock maps be produced on computers. The current Interim Yield formulae should bereplaced by more species-specific ones, but these components of a more general yield algorithm should be seenmore as a safety net than a primary directive of yield allocation. Such ‘maximum yield’ equations should include moreelements linked to the specific compartment details, for instance by increasing mortality parameters where moreindividuals are to be allocated in the same area. The current notion that a compartment has a simply-determined absolute yield would evolve into a process that maximises the proposed yield by manipulating the proposed patternof exploitation. An ongoing trial should be established, involving actual logging activities, but in a system where therules of stock map production are tinkered with- modified slightly and gradually – and successively refined based onfeedback from monitoring. This will amount to setting up a system whereby stock map production is allowed to evolvethrough trial and selection of the best variants. Many of the existing rules, particularly the less well-founded ones,would have to be tightened up to encode them on the computer, a fact which in itself will be beneficial. We makevarious recommendations for candidate rules for early modification.The efficiency of the process could be monitored and successively optimised in terms of economic and relatedecological considerations, or indicator indices, with results returned from the monitoring process. An earlyrequirement would be to define these, but we make suggestions. Optimisation would seek to adjust the spacingpattern, species and sizes of retained and exploited trees to manipulate the pattern of extraction damage andoptimise regeneration from seed trees, and the measured condition of the forest as a whole. Concurrent trials areneeded to address improvement of skid trail recovery, either by altering machinery used, or by directly manipulatingthe soil of abandoned skid trails. More work is needed to refine girth limits, which should be retained as an additionalsafety net, but probably modified to a girth window with a reduced lower limit for some species, but with upper limitsas well, to avoid logging trees that are likely to be hollow and yet still fully capable of seed production.
-
Impact of harvesting on forest mortality and regeneration in the high forest zones of Ghana. The aim of this project was to improve our knowledge of the negative impacts of logging tropical rain forests, and to recommend improvements to the logging system, with particular yet not exclusive reference to Ghana. There are two components to this: a bibliography and the description of field research conducted under the project. An annotated bibliography covers literature on: logging damage and recovery; forest regeneration and theallometry, growth, reproduction and death of trees related to logging disturbance. The bibliography covers tropical forests in general. A separate bibliography on impacts of logging on biodiversity as a whole, particularly covering zoological aspects, was prepared separately by A. Grieser-Johns as an early output of R6716 and is appended. The rest of the paper describes five topics addressed to various degrees by fieldwork under the FRP project. In each section, a brief overview is provided of the literature relevant to that topic. The introductory
Section 2
describes the context of logging in Ghana, and explains some of the general background to the report. We emphasise that the main tool for controlling the impact of logging in Ghana is the process of yield allocation and stock map production. In
Section 3
we summarise previous and new research on
extraction damage
, concluding with theobservation that reduction of damage should be a main criterion for efficient stock maps. Some species cause moredamage than others when trees of a particular size are felled, so we emphasise that there is scope for optimisation ofstock map production through a cost/benefit type analysis based on this, particularly as most logging damage isassociated with felling gaps, with another significant component due to their extraction. Unfortunately, the data onfelled trees is limited to the few species that happened to have been felled within the scope of our study.In
Section 4,
tree allometry
,
we seek to refine models relating to extraction damage, by study of therelationships between crown size and tree bole diameter. Trees are categorised according to maximum sizes attainedand variation of their crown widths in relation to bole diameter. There is a trend for large-crowned trees to be thespecies associated with greater felling damage, so it is possible to extend tentatively the conclusions from Section 3to a greater range of species. Allometric data was incidentally compiled on a wide range of species as we believe itwill be useful for more sophisticated approaches to stand modelling and PSP analysis.Trees are retained in logged forest for a number of reasons including their role as seed trees, supposedly topromote regeneration of logged forest. As part of an appraisal of this aspect of the stock map, studies were made on
tree maturity
(
Section 5)
and on
patterns of established regeneration
related to potential seed tree (
Section 7)
.In
Section 6
, we discuss in depth
the regeneration of logged forest in PSPs,
describing
12 out of Ghana’s600 Permanent Sample Plots established about 10 years ago, which happen to have been logged at various times upto more than 30 years ago. In all these plots, it is possible to see scars due to skidding and felling of trees, andpatterns associated with the recovery of vegetation in these scars are described from various points of view. In eachcase about half of the hectare plot, referred to as the ‘Apparent Extraction Network’ (AEN), has tree regeneration thatis severely reduced relative to general trends in Ghana, and more specifically relative to the less damaged otherhalves of the plots. Mortality associated with logging has returned to normal levels after about 30 years, but the AENforest is generally lower in basal area and timber regeneration. We suggest that damage, probably compaction to thesoil by logging machinery may be responsible for a medium or long term reduction in the site productivity.The
implications and recommendations
of these studies for the Ghana Forest Service are mentioned at theends of each section, and are summarised in
Section 8
. One of the main problems with existing practice, apart fromthe poor recovery from damage - probably due to soil damage by extraction machinery- has been the increasinglycomplicated, and variously fuzzy and incompletely justified guidelines, contributing to poor implementation, even ofessential and well-founded procedures.
Any attempt to improve the system by refining rules and regulationsmust at the same time make it easier to implement, monitor and successively improve them
.Briefly, we propose that stock maps be produced on computers. The current Interim Yield formulae should bereplaced by more species-specific ones, but these components of a more general yield algorithm should be seenmore as a safety net than a primary directive of yield allocation. Such ‘maximum yield’ equations should include moreelements linked to the specific compartment details, for instance by increasing mortality parameters where moreindividuals are to be allocated in the same area. The current notion that a compartment has a simply-determined absolute yield would evolve into a process that maximises the proposed yield by manipulating the proposed patternof exploitation. An ongoing trial should be established, involving actual logging activities, but in a system where therules of stock map production are tinkered with- modified slightly and gradually – and successively refined based onfeedback from monitoring. This will amount to setting up a system whereby stock map production is allowed to evolvethrough trial and selection of the best variants. Many of the existing rules, particularly the less well-founded ones,would have to be tightened up to encode them on the computer, a fact which in itself will be beneficial. We makevarious recommendations for candidate rules for early modification.The efficiency of the process could be monitored and successively optimised in terms of economic and relatedecological considerations, or indicator indices, with results returned from the monitoring process. An earlyrequirement would be to define these, but we make suggestions. Optimisation would seek to adjust the spacingpattern, species and sizes of retained and exploited trees to manipulate the pattern of extraction damage andoptimise regeneration from seed trees, and the measured condition of the forest as a whole. Concurrent trials areneeded to address improvement of skid trail recovery, either by altering machinery used, or by directly manipulatingthe soil of abandoned skid trails. More work is needed to refine girth limits, which should be retained as an additionalsafety net, but probably modified to a girth window with a reduced lower limit for some species, but with upper limitsas well, to avoid logging trees that are likely to be hollow and yet still fully capable of seed production.
Collection
Citation
“Taking stock. An annotated bibliography of logging damage and recovery in tropical forests and the results of new research in Ghana,” CSIRSpace, accessed September 8, 2024, http://cspace.csirgh.com/items/show/174.