An alternative Silvicultural approach in managing logged-over forests

Based on the reality of production forest management so far, logged-over forest improvement activities generally have received less attention, giving rise to the notion that the management of logged-over areas is not being taken seriously. In general, regeneration and maintenance of remaining stands as a component of the silvicultural system has not been carried out. Silviculturists must address these developments and respond to rapidly changing expectations and global paradigm shifts in how forests are viewed. Silviculturists are challenged to develop silvicultural practices, including silvicultural systems that support the function and dynamics of forest ecosystems, and maintain biodiversity and ecosystem resilience while providing needed wood and non-timber products. In the context of production forest management, the adaptation differences of commercially valuable species in terms of their position in the natural vegetation development stage can be used as a consideration in the development of silvicultural system determination. Thus, the choice of silvicultural system to be applied reflects the condition of the forest. Alternative silvicultural approaches are characterized by several aspects, including selective cutting, diversity, and combination of mixed species with natural regeneration, and avoidance of intensive site-preparation methods.


Introduction
The history of the use of natural production forests in Indonesia with the dynamics of changes in its silvicultural system has moved from exploitative forestry which is more oriented towards timber production.Management practices have typically led to mono-specific production.Such practices can include planting on both sides of the main road or areas of former timber stockpiling or natural regeneration, while timber stand improvement practices to control species composition, tree size, and quality have not been carried out, hereafter called "conventional" forest management.
The concept of the Indonesian Selective Cutting and Replanting System (TPTI) is an individual selective cutting system with a diameter limit in which to ensure the sustainability of the forest, the lowest stem diameter for commercial species is set, namely 40 cm for permanent production forest (HP), and 50 cm for forest limited production (HPT).This selective cutting system with a diameter limit will only be successful if the distribution of tree sizes and regeneration is large enough, and if logging is carried out under very strict supervision.When the natural forest is in good condition, which is still dominated by primary forest, then the application of a silvicultural system of selective cutting (TPTI) is a good choice because this system is considered to be able to maintain forest sustainability.The TPTI system incorporates silvicultural measures against potential trees to increase forest value both in quality and quantity for the next cycle.Other silvicultural measures include planting in open areas and enrichment planting in fewer regeneration blocks.The TPTI system is the utilization of un-even aged forest ecological processes starting from the level of seedlings, saplings, poles, and trees that occur in logged areas towards the formation of balanced stands.The acceleration of this growth succession lies in the composition of the remaining stand and its silvicultural practices.In the early 2000s, the era of Intensive Forestry began in the management of natural forests in Indonesia, which had begun to pay attention to habitat, carbon, water systems, and biodiversity.The Ministry of Forestry has begun encouraging natural forest managers to apply Intensive Silviculture (Silin) techniques.At that time the application of the TPTJ silvicultural system or selective cutting and line planting system was interpreted as intensive silviculture.Improvements to the Silin method have been carried out to obtain good results in the field, for example, spacing, plant species, areas for silin, and width of the planting line.Therefore, the understanding of intensification does not only apply to the land preparation of planting but also includes its maintenance.
Application of Silin requires a great deal of money as well as a dedicated and motivated staff.Planted seedlings are then tended annually for 3 years to keep them lianas-free and to reduce shade from encroaching plants.Silin guidelines call for a pre-commercial thinning of planted trees at 5-10 years but this treatment has not yet been implemented.The medium-term silvicultural results of Silin, as applied in PT.Sari Bumi Kusuma, are impressive, with seedling survival rates of about 70% and rates of stem diameter increments consistently averaging about 2 cm per annum, based on 10-14 years of post-planting data from permanent sample plots [1,2].At first glance, TPTJ seems easy to implement in the field and does not cause many problems.However, the problem actually, is that the growth of the line planted varied greatly because the conditions of canopy cover along the planting path varied greatly.There must be action or maintenance to widen the planting path gradually, and this requires a lot of money Taking into account these problems, since 2018 the gap technique was introduced as an alternative approach for enrichment planting in logged-over areas.The gap planting technique is easier to apply in the field, there is no need to make new or artificial gaps, the gaps formed as a result of logging, minimum site preparation for planting, and the natural regeneration in the gaps are maintained.Furthermore, the gap pattern approach in managing logged-over forests can be regarded as an alternative approach.This approach is not only limited to silvicultural techniques but includes the silvicultural system.

Development of Silvicultural System
There are 2 (two) silvicultural systems that are generally applied in managing the production of natural forests by Forest Utilization Business Permits (PBPH), namely TPTI (Indonesian Selective Logging and Replanting) and TPTJ (Selective Logging and Lane Planting).There is no silvicultural system that applies in general but must comply with the ecological characteristics and requirements for the application of the silvicultural system.In general, TPTI can be applied to permanent or limited production forests, both primary natural forests and logged-over forests, whether in dry or wetlands.The slope that is still permitted for the application of TPTI is a maximum of 40% with a cutting diameter limit of 40 cm for permanent production forests and 50 cm for limited production forests.TPTJ can only be applied to permanent production forests in the form of logged-over forests, both on dry and wet soils.The maximum allowable slope for TPTJ is 25% with a cut diameter limit of 40 cm [3].
The implementation of enrichment in the TPTI system is somewhat different from the TPTJ system.In the TPTI system, planting sporadically (irregularly distributed) with non-optimal growth space is one of the weaknesses of the TPTI system in terms of enrichment in logged-over areas.The growing space in the logged-over area is not designed in such a way that it is suitable for the species to be developed.On the other hand, in the TPTJ system, the enrichment areas are designed in the form of lanes with a width of between 3-5 meters.This is in accordance with the requirements for growing species from the Dipterocarp group which require shade for their initial growth.If we look at species enrichment, there are two important things, namely the suitability of the species for the site and increased productivity.
We cannot show the plants resulting from the enrichment of the TPTI system in the field.This is different from the TPTJ system, which makes it easy to find enrichment plants in the form of strip plants.In the TPTJ system, planting paths are made intensively, the paths must be really clean, so they are often referred to as clean paths.This is often a contradiction.In one hectare, openings for planting lines are 1500 square meters or 15%.Biodiversity in planting paths is in the spotlight.The positive thing about this system is that there are planting activities in lanes on logged-over areas.Since the implementation of the intensive silvicultural technique of gaps and lanes in 2018, the echo of TPTJ as a system has become less because managers of forest concession prefer to return to TPTI with their choice of silin techniques that can be gaps and or lanes.
In natural forests, the silvicultural system is related to the scale of disturbance and the strategy of target species that will be developed for regeneration and stand establishment.Therefore, the question is whether we can maintain forest complexity, namely species diversity and production in sustainable production forest management.Sustainable management of forest resources requires, among other things, that biodiversity (species composition and stand structure) and ecological processes be maintained [4,5,6].
To demonstrate whether the selected silvicultural system will achieve the forest management objectives set out in the planning document, including forest productivity, and biodiversity.The silvicultural system must be consistent with natural forest management objectives, in accordance with ecological conditions, and capable of implementing reasonable actions (silvicultural practices) to increase forest productivity and consider biodiversity aspects.
From a silvicultural perspective, natural forest management practices mean appropriately using the fundamental processes that regulate forest ecosystems for management purposes.In other words, as stated by Larsen [7], the development of natural forest silvicultural systems must consider the adaptability of species in the sense of maintaining species composition, increasing productivity, maintaining biodiversity, and protecting adjacent ecosystems.Thus, the silvicultural approach in forest management always places the ecosystem as the center of achieving productivity (ecosystem function) but also pays attention to habitat quality (ecosystem structure).
The research results of Pamoengkas et al. [8] show that the climax type group is more dominant than the pioneer type group in ex-logged production forest areas using a selective logging system in Central Kalimantan (Figure 1).The environmental conditions of the logged-over areas provide benefits for the climax species group starting from the seedling, sapling, pole, and tree level to grow.The completeness of the strata of a stand can be used as an assessment of the natural rejuvenation potential.Data shows that the proportion of climax species groups in all logged-over forest plots (LoA) and Germplasm Conservation Areas (KPPN) for seedling level ranges from 56-83%, while sapling level is slightly lower between 44-57%, pole level between 50 -73%, and tree level 55-84%.
In relation to ecologically sustainable natural forest management, the implementation of a silvicultural system of individual selective cutting produces small or medium-sized gaps that support the growth of climax tree species [9,10].
One of the first steps in developing a silvicultural system is to analyze the similarities between the composition of the species that make up the stand at the canopy level (pole or tree level) and the species at the seedling or sapling level of regeneration to gain an understanding of the recovery process resulting from a disturbance known as grain [11].The grain analysis approach describes the closeness between species composition at the tree level (_1) and regeneration (_2) as seen in Figure 2.This analysis is to determine whether the composition of regeneration in logged-over areas is the same (similar) or different from the composition of species that make up tree level.The figure shows the position of proximity between tree communities and regeneration in each of the plots studied.This research indicated that plot 6 (six) years after logging (TJ6) had relatively close tree level (TJ6_1) and regeneration (TJ6_2) species composition when compared with other plots [12].[12] The final step in determining the silvicultural system is to analyze the relationship pattern between tree density per hectare and tree diameter.Research by Pamoengkas and Andini [12] shows that the pattern of the relationship between the number of trees per ha and tree diameter in all logged-over forest plots and primary forests has the same trend, namely forming an inverted J curve or negative exponential curve (Figure 3).

Figure 3.
The pattern of the relationship between tree density and stem diameter [12] The choice of silvicultural system from the results of the analysis of the two components above, as a reflection of the condition of the forest area, is as follows: 1.The vegetation that makes up the canopy (tree) level is also found at the level of regeneration (seedlings/saplings) expressed by the shortest distance (TJ6) as shown in Figure 2, while the tree diameter distribution curve is inverse J-shaped (inverse J-shaped, negative exponential) as in Figure 3. Vegetation species at the seedling/sapling and tree level have the characteristics of being shade tolerant.This condition of vegetation resources indicates that the opening of the canopy/gap is small (small-scale disturbance regime), so to maintain the natural regeneration of the target species (Dipterocarp species) it works well by applying individual selective logging with a limited diameter (single-tree selection system).For this reason, the TPTI system is more appropriate to apply to this area.2. The vegetation found at the canopy level (trees) is different from the regeneration level (seedlings/saplings) which are depicted with long distances (TJ1, TJ2, TJ3, TJ4, TJ5, TJ7, and HP) as shown in Figure 2 with an inverted J-shaped diameter distribution curve (Figure 3).Vegetation at the regeneration level is intolerant, while types at the tree level are tolerant.Vegetation conditions like this indicate wide canopy openings (large-scale disturbance regime).Based on this, the appropriate silvicultural system is selective cutting in groups, either strips or overlaps.

Alternative Silviculture Approach
The alternative silviculture approach expresses a set of silvicultural principles, including avoidance of clearcutting, natural regeneration, structural diversity with a special emphasis on diversity of stand structures, mixed species-promotion of mixed-species stands, avoidance of intensive operationsminimization of intensive site preparation [13,14,15,16].An alternative silvicultural approach, in Europe is known as close-to-nature forestry and continuous cover forestry, then in Indonesia, it is known as intensive silviculture with gap or strip patterns.All of these approaches reflect on forest management.Silviculturists tend to see a greater role for silvicultural interventions, reflecting the longer history of managed forests.
In Indonesia, we are familiar with two Intensive Silviculture or silvicultural intensive (Silin) techniques, namely the gap and lane technique.The lane method, which was previously predicted to be a solution to improve the productivity of logged-over forests, in fact not easy in the field.One factor that becomes an obstacle, namely the growing conditions vary along the planting lane so that plant growth is very diverse.Combination of 2 or more species is recommended.In addition, the lane pattern causes land clearing to be too large, around 15% in one hectare, and the preparation of the planting area is carried out intensively.In the gap technique, land preparation is carried out minimally.The area is relatively open and minimizes damage to the stand.Land clearing techniques can be carried out by cutting down and clearing all vegetation at the planting point of gaps that have the potential to shade plants, except for protected, rare, and healthy economic/commercial value tree species at all stages of plant regeneration (seedlings, saplings, poles, and trees).The results of Aqmar's research (2018) showed that the growth response of 3-year-old Shorea leprosula had an average diameter and height of 7.81 cm and 5.92 m, respectively, or an average increment of diameter and height of 2.60 cm/year and 1.97 m/year.The choice of species according to field conditions.The Silin gap technique has good prospects in increasing the productivity of logged-over forests.

Conclusions
The alternative silvicultural approach that is presented here focuses more on ecological arguments which are very important both for a technical aspect and silvicultural system.The limitations in applying the gap pattern that is proposed as an alternative vary between forest areas, but it is easy to apply in the field, and very promising growth and intensification of land preparation can be avoided.The development of a silvicultural system should be based on the diversity of species adaptations.

4 Figure 1 .Figure 2 .
Figure 1.Stand structure of climax and pioneer group at Logged over Area and Germ Plasm Conservation Area