“Forever forest” is possible in both protection and production forest. Protection forest is mainly for watershed protection and biodiversity conservation, while production forest is mainly for lumber and wood production and other forest products extraction.
In production forest, there are two major approaches to achieve a “forever forest”. First is in the case of mono-crop culture (single-tree specie only) or few-crops which have same maturity period. You plant and harvest the trees in rotation, so that every year there is tree harvest and tree planting on the same block or area. This is done by sub-dividing the forest plantation area into blocks.
For instance, the chosen specie is eucalyptus; or if using two-crops culture, eucalyptus and gmelina. With good forestry and silvicultural practices (from seed selection to good seedling production to pruning and thinning), the trees are to be harvested after 12 years. So the whole area is to be subdivided into 12 blocks. On the first year of operation, only block 1 will be planted with eucalyptus (at the start of regular rainy season, June) while the other 11 blocks can be planted with vegetables, corn, bananas, or other short-duration crops; or grazing land for goats, cows, other farm animals. This is to make the land productive and earning. On the second year, block 2 will be planted with either eucalyptus or gmelina, leaving only 10 blocks for agricultural and animal husbandry activities, and so on.
On the 12th year, the whole area will be planted with eucalyptus (and gmelina if deciding on two-crops culture). On the 13th year, say January, block 1 will be harvested -- all trees, clear-cutting method. Just like one harvests all rice or all corn plantation. Fallow period (do nothing, just clear the area) for a few months. By June of same year, start planting again in the whole block. And the cycle is repeated forever.
One can decide to shift to other species, say longer-duration but better-price species like mahogany and narra. Just re-block the whole area piecemeal, or buy or lease the adjoining lands and expand the number of blocks from 12 to 25 or 30.
The second approach is selective cutting when having many species of varying maturities, various heights, on the same production forest area. For instance, you introduce a few short-duration trees like gmelina and eucalyptus in an area where the predominant forest vegetation are dipterocarp species like lauan, tanguile, yakal, narra, teak, kamagong, molave, and so on. Selective cutting or logging can result in “forever forest” since only mature, over-mature, and sick or defective trees will be removed, leaving the other trees nearby to grow taller and bigger.
In a multi-species, multi-layer forest, smaller and younger trees hardly have access to full sunlight, as well as have low access to minerals and nutrients in the soil, as the bigger and older trees tend to get all the space for sunlight and root extraction of soil nutrients. Once these mature and over-mature trees are removed, spaces for sunlight and soil nutrients extraction are freed for the shorter and younger trees to enjoy and expand. Sick and defective trees, even if they are not yet matured, have to be removed too, to prevent them from harboring the pests or diseases that affected them, from multiplying and expanding to other trees.
In this kind of forest ecosystem, vines and shrubs, especially thorny ones, abound. Unless they are known to have any medicinal or industrial uses, they should be removed from the trees as they tend to choke the trunks and climb up to the top, competing with the trees’ leaves for sunlight. The stronger and longer vines also cling from one tree to another, pulling the weaker and thinner trees towards bigger ones, depriving the former the opportunity to grow straight.
When a portion or the whole of the plantation area is properly terraced with rocks and big stones, dried leaves and branches, as well as fallen and dead smaller trees will decay and become rich topsoil someday, and average elevation of the land should be increasing by several centimeters every year. Such regular and cumulative increases in topsoil should make the entire plantation even more productive.
Agro-forestry in a multi-species, multi-layered forest environment can be practiced in a very limited way. For sure, only those plants and crops that thrive on poor and limited sunlight will flourish. Among such plants are orchids, wild mushrooms, ginger, and rattan. These plants can be cultured for commercial production, or at least for household consumption.
A production forest can also be used for forest park and eco-tourism resort. People, especially urbanites, love watching big trees. Instead of cutting those mature and over-mature trees for wood and lumber, they can be retained to grow older, and the forest developer can make money from the resort (entrance fee, rental of cottages, souvenir shops and restaurants, etc.). Of course some trees far from the main park can be cut for the wood and lumber needs of the resort’s cottages and furnitures.
“Forever forest” are better attained under private ownership of forest land. Competition among forest and mountain resort developers and owners will drive them to keep bigger and healthier trees, to introduce innovations like canopy walks (a walk atop of one tree to another via hanging and rope bridges), well-maintained creeks and waterfalls.