tổng quan những nghiên cứu thảm thực vật rừng dễ cháy và dự báo cháy rừng một số thảm thực vật rừng quan trọng trên thế giới quản lý động thực vậtphân loại thảm thực vật rừng thảm thực vật rừngkhái niệm thảm thực vật rừng vai trò của thảm thực vật rừng thảm thực vật rừng nhiệt đớithảm thực vật rừng cúc phươngthảm thực vật rừng việt nam
Density management Manage density are silvicultural treatments used to adjust spatial structure (horizontal direction) of the forest stands The treatments are very important applied to enhance stand composition, structure, growth, health, quality, and the production of specific benefits desired Basically, the concept of density management activities is controlling competition between trees in the forest stands Ways to control competing species What is thinning? A cultural treatment made to reduce stand density of trees primarily to improve growth, enhance forest health or recover potential mortality (SAF 2008) What is thinning? Thinning is a silviculture treatment implemented between regeneration and final harvest, to increase the economic productivity of stands Normal thinning does not significantly alter the gross production of wood volume Thinning can be commercial or non-commercial, depending on landowner objectives and local markets for cut materials Regeneration is not an objective of thinning; over-story gaps are small and should close rapidly Reasons to thin Enhance the vigorous growth of selected trees through the removal of competitors Improve the diameter of target trees and reduce the length of cutting cycle Improve tree morphology to enhance valuable trees The importance of tending an even-aged stand is illustrated by comparing these two plots in the famous Star Lake thinning experiment started by Fred Wilson with red pine planted in 1913 (WFMG, 2011) Economic objectives of thinning Harvest most merchantable material produced by the stand during the rotation Increased value from rapidly growing larger diameter trees Increased value from improvements in product quality When thinning How and when thinning is applied depend on: Landowner objectives and wanted benefits Ecological considerations (e.g site quality, species composition, stand structure, and stand condition) Economic considerations (e.g costs and benefits, local markets) Social considerations (e.g regulations, aesthetics) Other past and planned management activities When thinning Selecting removed trees Negative selection: removal of suppressed and poorly formed trees (shown in grey) without considering the growth of remaining trees Selecting removed trees Positive selection: competing trees are removed (shown in grey) to maximize the growth of the ‘best’ trees (shown in yellow) 10 Negative selection vs Positive selection Negative selection Positive selection 11 Effect of Thinning on Stand Growth Production function for an evenaged stand thinned three times 12 Effect of Thinning on QSD Thinned Thinning increasing slope due to better radial growth of residual trees QSD (mean basal area) Thin Thin Unthinned Time 13 Spacing vs Diameter 14 Density vs Diameter 15 Stocking density vs crown development P Radiata @ age 20, Woollens et al (2002) 16 Timing of thinning effect diameter growth responses Early thinning can yield increased diameter growth when compared to later or no thinning 17 Forest Health 18 Fire Hazard 19 Methods of thinning Mechanical thinning Low thinning Crown thinning Free thinning Chemical thinning Monkey method Selection thinning 20 Mid- or late-rotation fertilization Short rotation plantation forestry Provide material for wood product processing Produce saw logs Economic trade-offs Large investment (intensive cultivation) Increased growth rate 21 Mid- or late-rotation fertilization Site specific Soil testing Crop requirements Growth response decreases as the percentage of sand or clay content in a soil increases 22 Mid- or late-rotation fertilization Usually applied when site is fully occupied and there is little competing vegetation Crown ratio >30% Combine with thinning if stands overstocked or small crown ratio 23 Thinning and Fertilization The growth response is additive, fertilization in conjunction with thinning, this is a beneficial midrotation practice To realize the full benefits of fertilization, not thin or harvest within six years of fertilizing Thin dense stands (those with a BA greater than 130) prior to or within two years of fertilization 24 Common fertilizers in southern pines Phosphorus (P) - triple superphosphate (TSP), and diammonium phosphate (DAP) Nitrogen (N) - ammonium nitrate and urea Potassium - Muriate of potash (MOP) NPK together can have 2-3X effect in loblolly, longleaf, and slash pine stands 25 ... trees QSD (mean basal area) Thin Thin Unthinned Time 13 Spacing vs Diameter 14 Density vs Diameter 15 Stocking density vs crown development P Radiata @ age 20, Woollens et al (2002) 16 Timing... plots in the famous Star Lake thinning experiment started by Fred Wilson with red pine planted in 191 3 (WFMG, 2011) Economic objectives of thinning Harvest most merchantable material produced by... benefits, local markets) Social considerations (e.g regulations, aesthetics) Other past and planned management activities When thinning Selecting removed trees Negative selection: removal of suppressed