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СообщениеДобавлено: 30 мар 2016, 16:37 
Татьяна Хакимулина, сотрудник Гринпис

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Greenpeace Russia has produced a map of stand replacement return intervals in the world’s northern forests (north of 40 º northern latitude), which helps to evaluate whether recent forest management (at the scale of one hundred thousand ha*) may lead to forest depletion, also taking into account actual forest losses due to natural or semi-natural stand-replacement events.

The map was first released in Russian on Jan. 14, 2016.

The high-resolution map in PDF format: T. Khakimulina, A. Yaroshenko. Stand Replacement Return Intervals in the Northern Forests in 2000-2013. Greenpeace Russia, 2016


The periodic replacement of old forest stands by young ones is characteristic to the majority of forests in northern countries. This replacement may happen as the result of spontaneous disturbances (such as fires, windthrows, insect outbreaks and forest diseases) as well as the result of forest management (particularly clearcuts). In these cases natural and semi-natural disturbances and forest industry compete for the same resource – productive forest stands. Even if logging alone does not exceed the annual allowable cut level and the scale of spontaneous stand replacement events does not exceed historical averages, the cumulative impact of all these factors may lead to quick depletion of forests.

Considering this when evaluating whether forest management may in fact lead to forest depletion, it is important to take into account the impact of both logging and actual forest loss due to various natural or semi-natural factors. Under a clearcut system to account for all these factors we suggest the uniform indicator, based on spatial forest characteristics – stand replacement return interval (SRRI). SRRI is an estimated (using the “moving window” method, see methodology) average period of time during which each particular site (within the area under consideration or “moving window”) would undergo a complete replacement of old forest stands by young ones, under the condition that the rate of tree cover change would be the same as recently: during the period of time with reliable and suitable data records available for calculation.

SRRI is an analogue of the rotation period average for all forests within a clearcut system, but it is calculated by taking into account clearcuts as well as other remotely detectable stand-replacing events.

Data source and methodology

The suggested SRRI map covers all areas north of the 40th degree, i.e. all worlds’ boreal (taiga) forests as well as a significant part of the forests in the temperate zone.

The stand replacement return interval (in years) was calculated based on spatial tree cover change data with a “moving window” method* using the following formula:

SRRI = T×(A/B), where
T — period of time under analysis, in years;
А — forest area within the moving window**, ha;
В — area within the moving window where the stand replacement took place during the time T, ha.

For the input we used the publicly available global dataset on tree cover change over 13-year period (from 2000 to 2013) by the University of Maryland – Global Forest Change (Hansen, Potapov, Moore, Hancher et al). These data are based on Landsat satellite imagery with a spatial resolution of 28.5 m.

The analyzed time period T was 13 years – due to the remote sensing data for both years 2000 and 2013 reflected area state not for the beginning and the end of these years, but approximately for the middle of each of these years.

The three main products from the mentioned dataset were used to calculate SRRI: two maps of tree cover as of the years 2000 and 2010, which also reflected forest canopy density and a map of tree cover loss over the 13-year period from 2000 to 2013. Prior to the analysis all maps were re-projected and the spatial resolution reduced to 30 meters per pixel.

Forests with canopy density less than 50% were excluded from all three datasets. The latest allowed excluding the large portion of low-productivity forests from the analysis. The 50% threshold is very close to the value that has shown best quantitative correspondence of the mentioned data on tree cover to the official forest statistics - 49% (P.V.Potapov, S.A. Turubanova, A.Tyukavina, A.M.Krylov, J.L.McCarty, V.C.Radeloff, M.C.Hansen. Eastern Europe's forest cover dynamics from 1985 to 2012 quantified from the full Landsat archive. Remote Sensing of Environment 159 (2015) 28-43).

To determine the forest area A, also taking into account forest gain during the considered period, we used the sum of the two resulted tree cover maps (as of 2000 and 2010) with 50% or higher canopy density. The differences in the original resolution of the two maps could possibly lead to a slight overestimation of such forests’ total area.

*The SRRI was calculated with “moving window” method. This method implies that statistics for each pixel of the map was calculated based on all data falling in to the boundaries of a circle (“window”) built around the pixel using a constant radius. **The radius was corresponding to the accepted size of the moving window of one hundred thousand ha – and equaled 17.84 km. The one hundred thousand ha window size was accepted since it is often referred to as the minimal size for the large-scale forestry operations in the boreal countries (e.g. by the FSC voluntary forest certification system).

Geographic coordinate system and projection applied for calculation:
Projection: Lambert_Azimuthal_Equal_Area (North_Pole)
False_Easting: 0,0
False_Northing: 0,0
Central_Meridian: 0,0
Latitude_Of_Origin: 90,0
Geographic Coordinate System: GCS_WGS_1984

Interpretation and implementation of the map

The stand replacement return interval map for the first time allows for systematic continental scale approach to detecting problematic areas where recent forest management may lead to significant sustainability problems, by also taking into account actual forest losses due to spontaneous stand-replacing events.

The smaller the SRRI – the more intensely the forest is logged and (or) the greater is the scale of tree cover loss. SRRI can be compared to a rotation period known to be appropriate for a particular area. If in some area the SRRI value is smaller than the rotation period most widely used in northern forests (80-120 years), it means that the rate of annually clearcut or otherwise replaced forest stands is greater than what would be acceptable in the most intensive sustainable forest use. Small SRRI values clearly indicate that within the examined area the use of forests is unsustainable.

The stand replacement return interval is based on spatial data only and does not account for species composition, productivity of forest stands and other parameters. Thereby it allows to only preliminarily estimate the scale of forest management failure by pointing to the areas, where recent overexploitation and (or) losses of forest stands lead to the degradation of the forest cover and depletion of forest resources. Even with medium and large SRRI values (80-160 years and longer) the use of economically valuable forests could in fact be unsustainable due to a shift in species composition, depletion of quality and productivity of forest stands as a result of high grade logging and other reasons. To correctly estimate whether forest management with such SRRI values does not cause the depletion of forests, it is necessary to provide an additional analysis separately for coniferous- and deciduous-dominated forest stands as well as for productive and unproductive forests. Such calculation is currently impossible to carry out at the country scale and especially at the scale of all the world's boreal forests due to lack of the appropriate uniform datasets.

The SRRI map can be useful for forest management strategic planning, while evaluating the possibility of new large forest development projects, and also for voluntary forest certification.

The map can be of great help for development of FSC voluntary forest certification system: it allows to preliminarily assess whether the criterion 5.2 (related to sustainability of forest use) and Principle 9 (on the protection of high conservation value forests) are fulfilled.

If the forest area under FSC evaluation, fully or partially overlaps with a zone of small stand replacement return intervals (smaller than cut ages for coniferous stands, dominated in taiga forests) – it means that with high probability the forests in this area are used too intensely, or loss of forest stands as a result of spontaneous stand replacement events is too great, and forest management in this area is unsustainable. This unsustainability perhaps can be temporary and compensated by an intensive forest management and reforestation - but this must be carefully checked in each particular case. In the regions with predominating extensive forest management model the low values of SRRI with a guarantee indicate that forest management is unsustainable.

If a forest tenure contents high conservation value forests, which require to be completely set aside from transportation development and forest management (e.g. intact forest landscapes, or planned protected areas with strict protection regime) and at the same time it overlaps with low SRRI values, it means that forest industry extracts maximum of what can be extracted from the particular forest area without lowering cut-rates with respect to forests, which should be set aside. This usually leads to a rapid depletion of forest resources outside the high conservation value forests, and becomes the main source of future threats to these forests. Thus, even if the high conservation value forests are excluded from logging at the particular time, the low values of SRRI in adjoining areas would indicate that the threat to these forests still exists, and setting these valuable forests aside is most likely only temporary.

The red and bright orange colors on the map (SRRI values less than 100 years) – represent areas where forest use and forest losses are happening at the greatest scale. Such SRRI values if in the areas with dominating extensive model of forest use (representing large portion of worlds’ boreal forests) clearly indicate unsustainable forest management and excessive forest loss. In theory such values can be sustainable in case of dominance of intensive forest management - however they indicate that forest increment is extracted nearly in full without possibly any reserves of forest stands for comprehensive conservation of wildlife.

The light orange and yellow colors (SRRI values 100-160 years) – represent areas with moderate intensity of forest use and (or) moderate forest loss. For areas with dominating intensive forestry such SRRI values may correspond to sustainable forest management, while also allowing to preserve part of the forest by setting it aside from logging. But in the areas with dominated extensive model of forest use (where intense extraction of forest resources is not compensated by an equally intense reforestation) these SRRI values also would guarantee prevalence of unsustainable use of forests.

The green colors (SRRI more than 160 years) - are areas with generally low recent intensity of forest use (with no separation of forests by species composition, productivity, accessibility, etc.), and with a relatively small forest loss. Preliminarily the forest use on these areas can be assessed as sustainable. However, the use of most economically valuable forest categories (as productive coniferous forest stands) may still be unsustainable and lead to depletion of such forests. Moreover in some cases such SRRI values can be predetermined by previous overexploitation or earlier (before 2000) catastrophic losses of forests.

Important notes (inaccuracies and limitations)

The stand replacement return interval map is based on the global remote sensing data, and may, of course, contain local inaccuracies, generally leading to an overestimation of SRRI (i.e. underestimation of sustainability problem): over an inaccurate assessment of the total forest area, underestimation of forest use and losses.

SRRI map does not take into account the distribution of forests by species composition and stand quality and therefore may not display or may underestimate the areas where forest use or loss are particularly high in some particular categories of forests (e.g. in productive coniferous forests, well-drained forests, etc.).

SRRI map is based on satellite data with 30-meter spatial resolution and therefore does not consider changes in tree cover, associated with selection logging and very small-scale clearcuts, as well as small-scale natural disturbances. In some cases, this may also lead to an underestimation of forest use unsustainability (especially in areas where major share of logging is represented by high grading and other similar selective logging).

Authors of the map would be grateful for any feedback.
E-mails: tatiana.khakimulina@greenpeace.org (Tatiana Khakimulina), alexey.yaroshenko@greenpeace.org (Alexey Yaroshenko)

Authors thank their colleagues from the University of Maryland for data assistance and the Greenpeace colleagues who provided valuable comments and helped at the various stages of this work.

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