Uneven aged system: a sequence of silvicultural treatments designed to maintain and regenerate a stand with three or more age classes Thinning, regeneration and harvesting usually occur simultaneously (time), but may vary across the stand (space). The harvested trees are essentially replaced by growth on the younger trees left in the stand.
Uneven-aged vs Even aged A stand with trees of three or more distinct age classes, either intimately mixed or in A forest stand or forest type in which relatively small (10-20 year) age differences exist between individual trees small groups Uneven-aged Silvicultural Systems •Uneven aged system: a sequence of silvicultural treatments designed to maintain and regenerate a stand with three or more age classes •Thinning, regeneration and harvesting usually occur simultaneously (time), but may vary across the stand (space) The harvested trees are essentially replaced by growth on the younger trees left in the stand Uneven-aged Silvicultural Systems • Normally used to harvest, regenerate and tend forest cover types that will regenerate and grow under partial shade • Regenerate under partial canopies following minor disturbances like felling trees as individuals, groups, and in small patches • Uneven-aged systems refer to the general category of selection silvicultural systems Balanced uneven-aged • • • • Balanced stands have equivalent amount of growing space occupied by each age class N/ha Reverse-J age or size class distribution Age classes are intermixed In theory, one could annually cut the current annual increment indefinitely without degrading forest - ax Y = ke D 1.3 Advantages • • • • • • Protection for regeneration Ongoing seed supply from mature trees High vertical complexity and continuous canopy cover Sustained regular yield from a single stand Stability of forest conditions/structure Full site utilization in long term Disadvantages • • Requires skilled labor • • Difficult to regenerate shade intolerant species Logging damage regeneration to residual trees and Need to protect regeneration throughout cutting cycle Selection systems Three basic characteristics, which largely determine the silvicultiral consequences of selection systems are: • Minimum diameter • Length of cutting cycle • The tree selection decision (to retain or cut) Minimum diameter Land owner Conflict (concessionaires) Forester (researchers) As smaller as posible As larger as posible (45-50 cm for sawnwood) (long term goals and sustainability) Experiense has shown that the system is more safely if the MD is not fixed at the lowest level Minimum diameter Havest volumne is decrease when DM is increase Harvestable volume in relation to minimum harvestable diameter (East Mindanao, Philippines) The tree selection decision With the uneven-aged silvicultural systems, the tree selection decision (to retain or cut) considers main factors: • • • Species desirability Tree quality Desired age and size class distribution 18 Selection cutting systems • • • Single-tree Selection Group Selection Patch Selection 19 Single-tree Selection The single tree selection system is defined as an uneven-aged silvicultural system in which new age classes are created by the removal of individual trees of all size classes, more or less uniformly throughout the stand 20 Single-tree Selection • • • Individual trees of various size and age classes are periodically removed to provide space for regeneration, and promote the growth of remaining trees To recruit and release regeneration, trees are removed singly and in small groups, creating canopy gaps less than 250 m2 in size The overstory provides a seed source, and modifies understory conditions to create a favorable environment for the reproduction, competition, and growth of certain species 21 Single-tree Selection • • • This system favors the regeneration and maintenance of shade tolerant species Trees are selected for removal from all size classes (to achieve desired residual density levels) The goal is to achieve an optimum distribution of size and age classes so each contains a sufficient number of quality trees to replace those harvested in the next larger size class 22 Single-tree Selection 23 Group Selection The group selection system is defined as a silvicultural system that removes trees in defined groups to create stand openings with a width less than two times the height of adjacent mature trees, and that manages the area as an uneven-aged stand 24 Group Selection • • • • Trees are periodically removed in groups to create conditions favorable for the regeneration and establishment of new age classes (cohorts) The largest canopy opening is approximately two-times tree height The overstory provides a seed source, and modifes understory conditions to create a favorable environment for the production, competition, and growth of certain species This system favors regeneration and maintenance of shade tolerant and mid-tolerant species; shading effects will vary across the canopy opening The distribution of regeneration openings may be regular, or irregular depending on variations in stand condition, such as the age, size, vigor, quality, composition, and health of groups of trees 25 Group Selection • This method of stand-level cut determination is termed area regulation The total area to be harvested from a stand determines basing on – – – The length of the cutting cycle, The planned rotation age of the groups The percentage of the unit available for long-term management • Example: in an even-aged stand that has a rotation age of 100 years, 92% of the stand is available for group selection management and the cutting cycle is 25 years • A rotation of 100 years with a cutting cycle of 25 years will support four age classes (25 years, 50 years, 75 years and 100 years old) • The percentage of the available area that can be harvested at each stand entry is 23% of the stand area per cutting cycle( 92% divided by 4) 26 Group Selection 27 Strip Selection • Strip selection, a modification of group selection, is a system to manage uneven-aged stands essentially composed of many small even-aged patches • Narrow strips, of a width less than two times the height of the adjacent mature trees, are progressively cut generally in linear strips distributed throughout the stand 28 Strip Selection • The basic principles influencing strip orientation include minimizing damaging effects on the residual stand (e.g., wind), and optimizing shading • In areas where drought and excessive daytime heat would likely affect regeneration adversely, strips could be oriented east-west to maximize shading of cut strips; in this case, northern strips would be cut first • Site preparation and follow-up release may be needed to establish desired regeneration 29 Patch Selection 30 Remember! Selective cutting is not the same as a selection system 31 Requirements for success • • • • Moderately to very shade tolerant species Long-lived species that grow well even at older ages and respond to thinning Regular (maybe periodic) seed crops Seed that germinates in undisturbed soil and shady environment 32 ... cycle, The planned rotation age of the groups The percentage of the unit available for long-term management • Example: in an even-aged stand that has a rotation age of 100 years, 92% of the... • Uneven- aged systems refer to the general category of selection silvicultural systems Balanced uneven- aged • • • • Balanced stands have equivalent amount of growing space occupied by each age. . .Uneven- aged Silvicultural Systems Uneven aged system: a sequence of silvicultural treatments designed to maintain and regenerate a stand with three or more age classes •Thinning,