Felling Cycle Research Articles

Estimating the stock recovery rate using matrix models

The stock recovery rate, that is the ratio of the exploitable wood stock at the end of a felling cycle over the exploitable wood stock at the beginning of this cycle, is a key parameter used in the management plans of the natural forests in central Africa. Estimating this rate requires a model of forest dynamics. Forest managers usually use a formula that is based on a simple model that assumes constant vital rates. A generalization of this formula is based on matrix models of population dynamics. The stock recovery rate at the end of the k th felling cycle can be simply computed using matrix models. The asymptotic stock recovery rate (that is the limit as k tends to infinity) is the asymptotic growth rate (that is the dominant eigenvalue) of a transition matrix that includes harvest. The estimate of the stock recovery rate can be completed by its confidence interval using bootstrap methods. When applied to sapelli ( Entandrophragma cylindricum, Meliaceae), a major timber species in central Africa, it turns out that a few thousands observations are required to estimate the stock recovery rate with an accuracy of at least 10%. The number of observations available on an experimental site in the Central African Republic does not permit to do better than an accuracy of about 45% at level 95%. This does not permit to conclude whether the asymptotic stock recovery rate is greater or less than one. As a conclusion, in management plans in central Africa, stock recovery rates should be given together with an indication of the variability of their estimate (standard error or confidence limits).

Influence of estimators of the vital rates in the stock recovery rate when using matrix models for tropical rainforests

The stock recovery rate, the ratio of the wood stock at the end of a felling cycle over the wood stock just before logging, is a key parameter for the management of tropical rainforests. It is thus essential to predict it with a reliable precision. It can be predicted using the stock recovery formula or Usher matrix models, that are projection matrix models for size-structured populations. Both depend on estimates of vital rates, that are mortality rates, recruitment rates and upgrowth rates. The precision of estimation of the stock recovery rate is related to the amount of data available for the estimation of vital rates and to the type of estimator used. As data on tropical tree species are scarce, the choice of an appropriate estimator for vital rates is crucial. Classical estimators include the proportion estimator and estimators based on the conditional expectation of diameter increments. We show that the later are biased and define a correction that partially corrects this bias. In all, 14 estimators of the vital rates were compared in this study, to predict the stock recovery rate of Dicorynia guianensis, a major timber species in French Guiana. These estimators were compared on the basis of the prediction error, of the sensitivity of the stock recovery rate to diameter intervals, and of the bias and variance of the stock recovery rate estimator. The predicted stock recovery rate varied greatly depending on the estimator used for vital rates, with even contradictory conclusions as whether the stock depletes or increases. However some the estimators were strongly biased and gave unreliable estimates. Which estimator was the most statistically efficient depended on sample size. The proportion estimators had a small bias and a large variance and were efficient for large samples, whereas the estimators based on the conditional expectation of diameter increments had a large bias and a small variance and were efficient for small samples. The former were more sensitive to the diameter breakpoints than the latter.

BIOMASS AND BIOENERGY FROM BAMBUSA BAMBOS (L) VOSS, BESCH. PLANTATION OF BIHAR, INDIA

ABSTRACT Biomass accumulation and stored energy content of Bambusa bambos (L.) Voss were assessed for different age classes at Pusa on the northwest alluvial plain of Bihar. The energy fixed by bamboo was: • 3.28 TJ ha−1 in a 3-year-old plantation, • 3.97 TJ ha−1 in a 4-year-old plantation, and • 4.96 TJ ha−1 in a 5-year-old plantation. The energy capture efficiencies (photosynthetic radiation) for the above ground and culms for the same three age classes were: • 4.01% & 3.64%, • 3.61% & 3.31% • 3.23% & 3.30%. The contributions in the form of bioenergy for the same three age classes from:- • culms was 63.8%, 64.33% & 64.64%, • branches 21.9, 21.71 & 21.54, • foliage 4.8, 4.5 & 4.3, • rhizomes 8.6, 8.75 & 8.75 and • roots 0.67, 0.68 & 0.66. Using a 3 year felling cycle and culm selection silvicultural system, approximately 6,000 hectare would be required; or on a 4 year cycle 5,000 hectares, or on a 5 year cycle over 4,000 hectares to provide fuel to operate a 50 MW generating station. Gregarious clump flowering followed by the death of the clumps is to be expected after 40–45 years.

Protected reserves within tropical forests managed for timber production: recommendations using Bolivia as a case study

The Bolivian forestry law requires that 10 per cent of areas under forest management must be set aside as ‘ecological reserves’, serving as protected areas from resource extraction. These guidelines appear to be based largely on reserve design theory from the conservation biology literature including recommendations for large, contiguous blocks of reserves interconnected with other protected areas through corridor networks. Such recommendations, however, are largely applicable to protected areas that are embedded within fragmented landscapes or where there is signifi cant threat of deforestation. In contrast, protected areas within managed forests in Bolivia are surrounded by areas of largely intact forest subjected to low-intensity reduced impact logging and where logging occurs with a felling cycle not less than 20 years. Following an analysis of the current Bolivian law, conservation goals, and pertinent literature, we argue that issues of size and connectivity are perhaps less important within landscapes dominated by areas under forest management for timber production compared to protected areas imbedded within fragmented landscapes. It may, therefore, be more effective to disperse ecological reserves throughout management units to protect critical habitat and sites prone to damage from logging.

Sustainability of reduced-impact logging in the Eastern Amazon

Damage caused by reduced-impact logging (RIL) was assessed in 18 plots 1 ha each in a terra firme rain forest of Eastern Amazon (Brazil, Paragominas). Mean logging intensity was 6 trees ha −1 and the resulting commercial volume 21 m 3 ha −1. On average, logging damage affected 16% of the original stand while skidtrails occupied 7% (661 m 2 ha −1) of forest soil area. Canopy openness doubled to a mean of 11%. Of the variables studied, “number of trees harvested or felled per plot” gave the best correlation to “proportion of damaged or destroyed trees”. Damage to each diameter class was distributed in accordance with relative abundance of trees (dbh ≥ 20 cm) in the original population before logging, suggesting that all diameter classes were affected equally. The sustainability of timber management applying RIL was evaluated through the calculation of the recovery level of commercial trees in three different scenarios. In the most optimistic scenario (growth rate of 5 mm year −1 and 1% annual mortality), after 30 years, only 50% of the commercial stand would recover, provoking a drastic reduction of the harvesting intensity at the second felling cycle. Within a 30-year felling cycle (i.e. the legal felling cycle duration in the Brazilian Amazon) and even under RIL systems, the present logging intensity occurring in the study area (6 trees ha −1) is not compatible with sustainable yield production on a long-term basis. For the study area, only the implementation of silvicultural treatment ensuring that the remaining potential crop trees grow at 4–5 mm year −1 would guarantee a logging intensity of 3–4 trees ha −1 (10–14 m 3 ha −1) 40 years after the first harvest. This study showed that in the Amazon, RIL alone is clearly not sufficient to achieve sustainable forest management. More sophisticated silvicultural systems must be urgently elaborated and implemented to ensure that the forest will still be sustainably managed on a long-term basis. This issue is particularly important in the case of Brazil as a new law allowing the creation of 500,000 km 2 of forest concessions by 2010 has been recently approved by the congress.

Soil CO2 efflux in uneven-aged managed forests: temporal patterns following harvest and effects of edaphic heterogeneity

Forest management is expected to influence soil CO2 efflux (FCO2) as a result of changes in microclimatic conditions, soil proper- ties, and root dynamics. We measured FCO2 during the growing seasons of 2003 and 2004 in both gap and non-gap locations within stands ranging from 0 to 10 years after the most recent harvest in a selection-managed northern hard- wood forest in central Ontario, Canada. Soil temperature, moisture, pH, depth to bedrock, and organic matter content were also measured to examine relationships between FCO2 and soil properties. Timber harvesting resulted in large changes in FCO2 that varied with time since harvest. Immediately following harvest (year 0) FCO2 in gaps increased by ~55%, declined to 20- 40% below pre-harvest levels during years 1-3, and recovered to pre-harvest levels 5-6 years post-harvest. A similar temporal pattern, but with smaller changes, was found in non-gap locations within harvested stands. We suggest that the initial increase in FCO2 is due to a combination of root decay, soil disturbance, and increased soil temperature in gaps, while the subsequent decrease and recovery are caused by the gradual regrowth of active roots. We also found strong effects of soil temperature, depth to bedrock, and soil water content on FCO2; however, soil pH and soil organic matter concentration had no detect- able effects. Our results suggest that selection harvests mainly influence FCO2 through changes in tree root respiration, and that the net result is a decrease in FCO2 through the entire felling cycle.

The monoculture vs. rotation strategies in forestry: formalization and prediction by means of Markov-chain modelling

The monoculture strategy of forest management, where the same tree species (e.g., Picea abies) is cultivated in a number of successive planting–growing–felling cycles, is generally considered to be economically efficient, yet not sustainable as it reduces biodiversity in the forest. The sound alternative suggests a long-term strategy of forest management in which different forest types rotate either with planting after clear cutting, or by natural forest succession, yet the commercial output remains dubious. We suggest an approach to formalization and modelling forest dynamics in the long-term by means of Markov chains, the monoculture strategy resulting in an absorbing chain and the rotation one in a regular chain. The approach is illustrated with a case study of Russkii Les, a managed forest located in the Moscow Region, Russia, and the nearby forest reserve having been used as a data source for undisturbed forest dynamics. Starting with conceptual schemes of transitions among certain forest types (states of the chain) in the monoculture and rotation cases, we estimated the transition probabilities by an original method based on average duration of the corresponding states and on the likelihood of alternative transitions from a state into the next one. Formal analysis of the regular chain reveals an opportunity to achieve particular management objectives within the rotation strategy, in particular, to get the distribution of forest types in accordance with an adopted hierarchy of their commercial values, i.e. more valuable types have greater shares.

Using models to predict recovery and assess tree species vulnerability in logged tropical forests: A case study from French Guiana

A major challenge for forest managers is to define the optimal cutting cycle to ensure that the resource is sustained in the long term. Matrix models of forest dynamics allow time-projection of diameter-class distributions and thus assessment of the time needed, after logging, to recover a given part of the exploitable stock. They are easy to build and they only require, as input variables, the diameter structure of the population(s) under scope. However, such models are based on a coarse description of tree population dynamics and must be used with caution. In particular, as trees are only described from a diameter threshold (usually 10 cm dbh), recruitment of a new tree cannot be linked with the preceding generation since too much time elapsed between seed dispersal and the installation of a 10-cm recruit. This causes predictions of matrix models to be highly questionable in the long term when ingrowth to larger dbh classes greatly depends on the way recruitment has been modelled. We used a case study from French Guiana to test whether or not a simple matrix model is reliable enough to help forest managers choose between management alternatives. We focused on the major timber species Dicorynia guianensis Amshoff (Caesalpiniaceae) harvested under a selective cutting regime. We compared predictions of D. guianensis stock recovery in the short and long term provided by two models: StoMat, a non-regulated matrix model, and SELVA, a single-tree distance dependent model explicitly simulating the entire species life cycle. Both models were independently calibrated on data from Paracou permanent sample plots. We showed that: (i) the short-term recovery of the exploitable stock predicted by StoMat is reliable for a large range of disturbance conditions; (ii) recruitment implementation in StoMat does not influence projections until the third felling cycle; (iii) for shared initial stand conditions SELVA and StoMat give consistent mid- and long-term predictions: the simple recruitment model used into StoMat could efficiently summarise the regeneration processes of the species under low felling intensity. Our results indicate that the current felling regime used in French Guiana may not be sustainable on a long-term basis. In any case, no more than 60% of the initial stock would be recovered after logging. We conclude that simple models can provide as reliable predictions as more complicated ones. They may be sufficient to assess the recovery of a species’ exploitable stock even in the long term, or at least assess the (un)sustainability of particular harvesting regimes.

Management of bamboo (Dendrocalamus strictus) forests in Western Himalayas

The paper describes the management and yield regulation of Dendrocalamus strictus forests of Western Himalayas. The study covered an area of 284.12 ha. The forests were stock mapped and partial enumeration carried out. Growing stock and annual increments were assessed (average clumps 911.2/ha; average number of culms 37.794/clump and 34,438/ha; average number of manus 5,566/ha). Forests are to be managed under Selection System. The entire forests shall be worked together on a felling cycle of 4 years. The yield is to be regulated by number of bamboos recruited during the felling cycle. Provisions of cleaning for the removal of dead, dry, decay, and congested culms is made to improve and maintain the healthy clumps. Average yield of 12,000 bamboos (27 tonnes air dry) against gross increment of 20,000 bamboos per ha during the felling cycle is prescribed. For the entire forest the prescribed yield of bamboos will be 6,00,000 numbers with an approximate weight of 1,350 tonnes. With the scientific management of forests and strict compliance of felling rules, the forests will achieve normalcy in due course to provide sustained yield in perpetuity.

The use of diameter distributions in sustained-use management of remnant forests in Benin: case of Bassila forest reserve in North Benin

One of the fundamental basis in the development of sustained-use management systems is the determination of the minimal logging diameters (MLD) and the felling cycle compatible with sustainable logging operations. The method used in the present study to determine the MLD and felling cycle is based on the growth rate and the diameter class distributions of the most important merchantable species in Bassila forest reserve, North Benin. The calculations of the MLD and cutting cycle are done using both the class distribution of the stem diameter and basal area of nine valuable timber species selected within the most important commercial species of this forest reserve, in order to assess the difference between these two approaches. Values of MLD and cutting cycle duration obtained using the stem class distribution or the basal area class distribution are in general the same. The MLD calculated for nine timber species varies from 35 to 65 cm. The cutting cycle period obtained is 18 years for the bell-shaped type species and 24 years for the inverse J-shaped type species. For the bell-shaped type species, the mean percentage of recruitment obtained with 18 years felling cycle is about 60% considering the number of the loggable stems and 34% of the loggable basal area. As far as the inverse J-shaped type species are concerned, 24 years felling cycle will allow 55% of mean recruitment considering the number of the loggable stems and 19% of the loggable basal area. For the whole forest stand, 22 years cutting cycle is obtained allowing 57% recruitment of the loggable stems and 23% recruitment of the loggable basal area.

Helicopter-based natural forest management for New Zealand’s rimu ( Dacrydium cupressinum, Podocarpaceae) forests

The management of indigenous conifer forests in Westland, South Island, New Zealand has focussed largely on harvest of the Podocarpaceae tree rimu ( Dacrydium cupressinum). Today, key management objectives are to maintain the pre-harvested state of the forest in terms of biomass, tree size ranges (especially old trees), natural spatial patterns, relative proportions of the major tree species, and forest timber quality. This approach to natural forest management is based on utilizing heavy-lift helicopters, pre-empting mortality by harvest of a proportion of single unthrifty rimu trees, and an auditable GPS-based forest record system. A transition matrix model is used to determine the expected natural mortality rate and the sustainable harvest is based on pre-empting a proportion of the mortality over a 15-year felling cycle. Trees with significant wildlife features (e.g. cavities and large epiphyte loads) are not harvested. Even natural forest management can impact ecological processes through loss of senile trees, pre-empting forest tree windfall, altering spatial patterns of forest structure and facilitating pest and weed spread. However, because of the dynamic nature of these forest environments, the impact of forestry should be insignificant over major natural disturbance events. The best way to ensure that key management objectives are realized is to adopt an adaptive management approach that involves regularly monitoring of key forest attributes and frequent recalculation of the sustainable harvest model.

Stand Dynamics of Dipterocarp Trees in Cambodia's Evergreen Forest and Management Implications : A Case Study in Sandan District, Kampong Thom

The purpose of this study was to explore the stand dynamics of dipterocarp species in evergreen forest as a basis for devising suitable management systems for Cambodia's forests. The data for this study were obtained from a two-year UNDP-funded forest inventory project in Sandan district of Kampong Thom province. A sample of 18 clusters located in evergreen forest were analyzed. Based on the average stand volume per hectare, this evergreen forest was further divided into poor (less than 200m3), medium (200-300 m3) and rich (greater than 300 m3) forests. Dipterocarps contributed 50 m3 (36%), 109 m3 (43%) and 163 m3 (53%) in poor, medium and rich forests, respectively. The dominant dipterocarps species were CHBG (Dipterocarpus turbinatus), CRMS (Vatica astrotricha) and PHDK (Anisoptera glabra). To estimate the forest potential and allowable cut of dipterocarps stands, trees of DBH greater than 45cm were analyzed. Cambodia's silvicultural treatment prescribes that only 30% of stands are extracted on a selective felling cycle of 25-30 years. On the basis of this silvicultural treatment and management experience in Southeast Asia, the harvest potential of Cambodia's forest was estimated to vary from 20 m3/ha (6 trees) to 54 m3/ha (13 trees); approximately 65% of which was dipterocarps. These figures are more than double the current harvest rate of 10 m3/ha. However, applying such a new management system might cause forest degradation if there is no long-term political commitment to management and research from the government and parties involved. Permanent and regular research on stand dynamics and other influential factors are required to ensure the sustainability of forest resources. Forest management can no longer be concerned solely with timber production; thus, harvesting and research in non-timber forest products should also be included in the management plan. Keyword: Cambodia, dipterocarps, evergreen forest, forest management

Effect of silvicultural treatment on growth and mortality of rainforest in Surinam over long periods

Results of silvicultural experiments in Surinam, carried out since 1965, have shown that volume increment of marketable timber species can be effectively stimulated by treatments such as liberation and refinement. Such refinement might, for example, initially reduce the basal area of non-marketable species from ca. 20 to 6 m 2/ha and the total basal area to some 10 m 2/ha. The effects of these treatments, however, generally last for limited periods of <10 years. Even in a forest management set-up with relatively short felling cycles of 20–30 years, treatment has to be repeated to be fully effective. In three experiments, including a large-scale field trial, the treatment stimulated increment and recruitment but both slowed down markedly with time. Mortality is variable, but has a tendency to increase with stronger interferences. The large-scale field trial, which had received a single initial treatment, has grown enough volume for a second harvest of 20–30 m 3/ha after 20 years. Increment and final stand structure would have been much improved with three treatments during the cycle as originally planned.

Analysis of a model currently used for assessing sustainable yield in indigenous forests

Problems are identified in the use of a variant of the Usher matrix model to underpin the harvest of beech (Nothofagus spp.) and rimu (Dacrydium cupressinum) on the West Coast of the South Island. The model has been suggested as a means of determining the harvest that is sustainable in the sense of maintaining the present forest structure, and uses as inputs the size structure and estimates of size‐specific radial growth rate. The model contains a bias because the equations for transition coefficients in the projection matrix assume an inappropriate geometric model for stage duration. The effect is to overestimate population growth by about 22% over a 15 year felling cycle. Alternative formulae are given for a more realistic model of fixed stage duration. The mortality rates needed to maintain the initial size structure of the population may be inferred from recursive formulae that are derived here separately for the geometric and fixed models of stage duration. Using a model with fixed stage duration it is found that the method is unworkable, in the sense that no set of mortality rates can be found to keep observed stand structures constant. The estimate of sapling recruitment number used in the harvest calculations does not appear to be well‐founded. Even assuming that the forest is in a steady state and natural mortality is known, the assumption that harvest mortality substitutes for natural mortality rather than adding to it appears to be unwarranted. I suggest that matrix models cannot be used to determine ecologically sustainable forest management without additional information on natural forest dynamics and the response to harvesting.

Forest Management Problems in Cambodia : A Case Study of Forest Management of F Company

A fast growing population and the need for food and forest products coupled with the great demand for wood and rapid economic development in the developing world have brought sustainable forest management under continuous uncertainty. Deforestation in the developing world has been relatively high. But recently, it has been more widely recognized that over-exploitation of forest products and non-forest products is prejudicing the sustainability of the world's forests. Cambodia has been chosen as a case study to test this hypothesis regarding sustainable forest management. There are two main types of forests in Cambodia, namely dryland and edaphic forests, covering a total area of 10.59 million ha or 58% of the total land area. It had been reduced from 12.32 million ha in 1973 as a result of wars and political instability over the last 25 years. Against a background of government instability, great domestic and foreign demands for wood in recent years have resulted in Cambodia's forests being over-exploited. To prove this, a selective 25-year felling cycle system used by F Company was analyzed with the aid of various statistical tools. The analysis shows that although the growing stock of F's evergreen forest is as low as 82 m3/ha due to illegal logging, the company has exploited 7m3/ha or 9% of the total stock. This was 6 percentage points higher than the sustainable cutting rate of Cambodia's evergreen forest. This supports the hypothesis of over-exploitation. The result also shows that there is still a large number of residual trees with diameter less than 45 cm, which are available for extracting over the next 25 years if they are properly managed. Strong enforcement mechanisms for forest monitoring and control are needed to stop illegal logging, to prevent over-exploitation and to manage the residual trees for long-term availability of forest resources. Keyword: Cambodia, forest management, selective felling, tree classification

A Comparison of Skyline Harvesting Costs for Alternative Commercial Thinning Prescriptions

Abstract Harvesting production and costs were examined for three alternative silvicultural prescriptions at two sites in the Coast Range of Oregon. Thirty-three-year-old Douglas fir stands were commercially thinned to residual densities of 247, 148, and 74 trees per hectare (tph) [100, 60, and 30 trees per acre (tpa), respectively]. Detailed time studies were conducted on manual felling and uphill skyline yarding with small yarders. Separate regression equations were developed to predict delay-free felling cycle time and delay-free yarding cycle time. The 74 tph [30 tpa] treatment had the highest production rate and was the least costly to harvest. Total harvesting costs of the other two treatments averaged from 6.0% (148 tph [60 tpa]) to 12.3% (247 tph [100 tpa]) more than the 74 tph [30 tpa] treatment.

An unconventional approach to timber yield regulation for multi-aged, multispecies forests. II. Application to a South African forest

The development and implementation of the senility criteria yield regulation system to the multi-aged, multispecies forests of the southern Cape, South Africa, is described. The described yield regulation system aims to maximise the sustainable yield with minimised artificial impact on the ecology and minimised managerial input. The felling cycle is 10 years, which is still considered compatible with the prevailing natural disturbance regime. Harvestable trees are not defined by minimum harvestable diameters, but according to signs of senility or reduced remaining life expectancy (e.g. percentage crown dieback or base rot). These criteria are determined for canopy species in accordance with species-proportional turnover rates. The gross increment of the stand is thus realised as harvest through periodic mortality preemption by harvesting those trees which have reached a defined level of senility or reduced life expectancy. Advantageous characteristics of the senility criteria yield regulation system relate to guaranteed sustainability, compatibility with nature conservation aims, optimal productivity and managerial simplicity and flexibility. The potential of the system for wider application is discussed.

Experience with the tropical shelterwood system of regeneration in natural forest in Nigeria

The Nigerian tropical shelterwood system (T.S.S.) was a major management preoccupation of the Forestry Service in western and mid-western Nigeria during the 1950s, and altogether about 200 000 hectares of forest were treated under this system. The method was developed in response to what, at the time, was regarded as a need for an extensive system of regeneration which could keep up with, and be financed from, the earnings from forest exploitation. It was intended to obtain sustained or improved yields, particularly of the primary economic species, to supply mainly export markets. The system consisted of canopy opening, by poisoning unsaleable trees with sodium arsenite to promote survival and growth of seedlings of valuable species, and also climber cuttings and cleanings in order to control climbers and herbaceous weeds. The treatments were begun 5 years before exploitation. Originally the felling cycle was fixed at 100 years, and a final crop of 25 fully grown trees per hectare was regarded as acceptable, compared with actual removals at the time of about 5 trees per hectare on average. Satisfactory regeneration was regarded as a minimum of 100 well grown seedlings and saplings of listed economic species per hectare. The system was abandoned primarily because it did not make sufficiently intensive use of the land to compete with other forms of land use, such as cocoa, oil palm, or arable crops. Something more obvious than natural regeneration methods had to be done with the land if it was to remain in forestry use, and during the 1960s the emphasis changed to artificial regeneration, particularly by ‘taungya’. In the 1970s it has become apparent that, owing to Nigeria's limited area of high forest estate, intensive forestry would be required to meet future home requirements. It now seems that the system could not be economic because of the paucity of valuable regeneration and because of the relatively slow growth rates in natural forest. Silviculturally there was the difficulty of reconciling the need to open the canopy and yet at the same time to control growth of climbers and herbaceous weeds. Natural forest is not adapted to withstand heavy exploitation nor to maintain high increments. Though timber crops can produce high increments in the humid tropics, they may need to be established by planting and considerable capital investment may be required for the purpose.

A Long-Term Plan for Conversion to Monocyclic Working in the Central Forest Reserves of South Mengo District, Buganda Province, Uganda (O.D.C. 24)

SummaryFactors are discussed which have to be taken into account in converting to monocyclic working in South Mengo forests with a rotation of about 70 years. A plan is described in which this would be achieved over a 40-year conversion felling cycle. Suggestions are made for control of exploitation during the conversion cycle and an account is given of proposed silvicultural treatments for the same period.