Teak Wood Harvest — How to Fell and Process Teak Wood from Java

Teak wood (Tectona grandis) belongs to the Lamiaceae family, originating from Southeast Asia. Teak wood can reach heights of 30-40 meters when mature. Its leaves are large (30-60 cm long), resembling tobacco leaves, and fall during the dry season (teak is a deciduous tree). The flowers are small and white, appearing during the rainy season. The bark is rough and ranges in color from gray to brown. Teak wood has two main layers: heartwood which is golden brown in color and sapwood which is lighter in color. The heartwood contains natural tectoquinone oil which makes the wood resistant to termites and water resistant.

Teak wood that is best for furniture must be 40-80 years old. At this age the heartwood has grown perfectly and the proportion of heartwood is greater than sapwood. Signs of trees that are ready to be felled: stem diameter at breast height (DBH, diameter at breast height) minimum 30-40 cm, tree bark is rough and cracked, and the tree is no longer growing tall (has reached maximum height). Perhutani uses a rotation cycle (rotation cycle) of 60-80 years. Younger trees can be felled for building timber, but the quality is not as good as old wood.

Girdling (ring-barking) yaiku motong kulit wit saubengine batang kanthi lebar 10-15 cm, ngilangi lapisan kambium. Proses iki ditindakake 1-2 taun sadurunge nebang. Tujuane supaya kayu alon-alon kelangan banyu lan getah, dadi luwih entheng lan luwih garing nalika ditebang. Kayu sing wis di-girdling luwih gampang digaringake lan luwih sithik pecah-pecah nalika proses pengeringan. Girdling ditindakake ing mangsa ketiga nalika aliran getah paling sithik. Motong kulit nganggo kapak utawa bendo kanthi ati-ati — aja nganti motong kayune, cukup ngilangi kulit lan kambiume.

Nebang kayu jati paling apik ditindakake ing mangsa ketiga (Juni-September ing Jawa) nalika kadar banyu ing kayu paling endhek. Mangsa ketiga wit jati wis nggugurake godhonge lan aliran getah mandheg. Kayu sing ditebang ing mangsa ketiga luwih cepet garing, luwih sithik pecah, lan luwih tahan rayap tinimbang kayu sing ditebang nalika mangsa udan. Aja nebang nalika udan deras utawa lemah teles — bahaya kepleset lan kayu gampang kotor.

Sadurunge nebang, nemtokake arah tumbruge wit (directional felling). Deleng arah angin, condong alami wit, lan papan kosong kanggo tumbrug. Gawe takikan arah (notch cut) ing sisih sing pengin dituju wit ambruk: takikan ngisor (undercut) sudut 45 derajat lan takikan ngisor horisontal, mbentuk takikan segitiga kira-kira sepertelu diameter batang. Banjur gawe potongan tumbrug (back cut) saka sisih kosok bali, luwih dhuwur sithik tinimbang dasar takikan arah. Sisane kayu antarane takikan arah lan potongan tumbrug dadi engsel (hinge) sing ngontrol arah tumbruge wit. Nganggo baji (wedge) kanggo mbantu ngarahake tumbrug. Kabeh wong kudu adoh saka zona bahaya sadurunge wit ambruk.

Sawise wit ambruk, motong batang dadi gelondhongan (log) kanthi ukuran sing dibutuhake. Panjang gelondhongan standar biasane 2-4 meter kanggo mebel, utawa luwih dawa kanggo kayu bangunan. Ukur lan tandhai nganggo kapur sadurunge motong. Motong ing titik-titik cabang gedhe lan ing papan sing ana cacat (simpul, bengkok). Pang-pang lan cabang cilik dipotong dadi kayu bakar utawa arang. Saben gelondhongan ditandhai nomer urut lan ukurane kanggo pencatatan.

Kulit wit diilangi saka gelondhongan kanggo nyepetake proses pengeringan lan nyegah serangga sing seneng manggon ing ngisor kulit. Nganggo bendo utawa drawknife kanggo ngilangi kulit. Kulit jati rada kandel (1-2 cm) dadi perlu tenaga ekstra. Ngilangi kulit nalika kayu isih anyar luwih gampang tinimbang nalika wis garing. Kulit wit jati bisa digunakake kanggo bahan atap tradisional utawa dijur dadi mulsa.

Ing potongan melintang (cross-section) gelondhongan, bisa dideleng rong lapisan sing beda werna. Kayu teras (heartwood) ana ing tengah, wernane coklat emas nganti coklat peteng, lan ngandhut lenga alami (tectoquinone) sing gawe tahan rayap lan banyu. Kayu gubal (sapwood) ana ing pinggir, wernane luwih padhang (kuning nganti coklat padhang), lan ora tahan rayap. Kanggo mebel kualitas dhuwur, mung kayu teras sing digunakake. Kayu gubal bisa digunakake kanggo bangunan sing ora kena udan utawa kanggo papan kering sing dilindungi. Proporsi kayu teras nambah saka umure wit — mulane wit tuwa luwih larang.

Pilih papan sing rata, garing, lan ana sirkulasi angin apik kanggo papan pengeringan. Lemah kudu dikeras utawa dikasih fondasi supaya ora lembab. Gawe fondasi saka balok utawa watu setinggi minimal 30-40 cm saka lemah supaya gelondhongan ora kena lembab saka ngisor. Papan pengeringan kudu ana atap utawa tutup kanggo nglindhungi saka udan langsung lan panas srengenge langsung — panas langsung gawe kayu pecah-pecah. Angin kudu bisa mili bebas liwat tumpukan kayu.

Logs or boards are arranged by inserting stickers (wooden separators) between each layer. Stickers are usually sized 2x2 cm or 3x3 cm, made from dry wood that has been treated with anti-fungal. The distance between stickers is approximately 60-90 cm. Stickers must be arranged straight vertically from bottom to top so that the weight is evenly distributed and does not bend. Natural drying (air drying) of teak wood requires 6-12 months depending on the thickness of the wood and weather conditions. The target moisture content is 12-15% for furniture. Each cubic meter of dry teak wood weighs approximately 640-720 kilograms.

Sajrone proses pengeringan, mriksa kayu kanthi rutin saben 2-4 minggu. Deleng tandha-tandha pecah ujung (end checking) — iki lumrah nanging yen pecah gedhe, lapisi ujung gelondhongan nganggo lilin utawa cat kanggo nyuda pecah. Deleng tandha jamur (biru utawa ijo ing permukaan) — yen ketemu, tambahi sirkulasi angin lan kurangi kelembaban. Ukur kadar banyu nganggo moisture meter — tancepake jarum ing kayu lan maca angka ing layar. Kayu siap digunakake yen kadar banyu wis tekan 12-15%.

Sawise garing, gelondhongan diklasifikasi miturut kualitase. Grade A (paling apik): kayu teras dominan, serat lurus, ora ana simpul utawa cacat, werna rata — kanggo mebel premium. Grade B: ana simpul cilik utawa serat rada bengkok, isih apik kanggo mebel umum. Grade C: akeh simpul, serat ora rata, utawa ana bagian gubal sing akeh — kanggo bangunan utawa konstruksi. Faktor-faktor sing mengaruhi grade: proporsi kayu teras vs gubal, jumlah lan ukuran simpul (knot), kelurusan serat (grain), werna, lan ukuran pecah. Kayu jati grade A regane bisa 2-3 kali lipat saka grade C.

Kayu jati sing wis garing disimpen ing gudang utawa papan sing tutup, garing, lan sirkulasi angin apik. Tetep nganggo sticker ing antarane lapisan supaya angin bisa mili. Kayu aja ditumpuk langsung ing lemah — nganggo palet utawa fondasi setinggi 20-30 cm. Jaga kelembaban udara ing gudang 50-60% lan suhu 15-25 derajat Celsius. Kayu jati wis ngandhut tectoquinone alami sing anti rayap, nanging tetep dijaga supaya ora kena banyu utawa kelembaban dhuwur sing bisa gawe jamur. Kayu jati sing disimpen kanthi bener bisa awet nganti pirang-pirang taun tanpa rusak.

Ing Jawa, kabeh alas jati negara dikelola dening Perhutani (Perum Perhutani) miturut Undang-Undang Kehutanan. Nebang jati tanpa ijin kalebu tindak pidana illegal logging. Kanggo nebang jati saka alas negara kudu nduweni SKSHH (Surat Keterangan Sahnya Hasil Hutan) utawa dokumen SVLK (Sistem Verifikasi Legalitas Kayu). Jati saka kebun rakyat (hutan rakyat) bisa ditebang kanthi ijin saka pemerintah desa. Sistem tebang pilih (selective logging) lan reboisasi (nandur maneh sawise nebang) penting kanggo njaga kelestarian alas jati. Saben wit sing ditebang kudu diganti kanthi nandur bibit anyar. Sertifikasi FSC (Forest Stewardship Council) utawa PEFC nambah nilai jual kayu ing pasar internasional.