Silviculture Systems Flashcards
(29 cards)
1
Q
what is a silviculture system
A
A defined program of silviculture treatments to achieve specific stand structure objectives during the whole life of the stand
Achieves regeneration and desired age structure
2
Q
Describe the process to select an silviculture system
A
- Establish stand mgmt objectives
- Relate objective(s) to stand structural goals
Target stand: species mix, layers, age class, size/scale, rotation length, site occupancy, spatial distance, special structural attributes - Assess the site/constraints:
biological/ecological; operational; administration/costs
going out and collecting data for SP - Choose th emost appropriate silviculture system and monitor its implementation
3
Q
What are the goals of a silviculture system
A
- meet landscape/stand level objectives
- meet the goals and obj’s of landowner
- provide availability of timber and non timber resources
- produce a planned harvest of forest products
- accommodate biological/ecological concerns to ensure sustainability
- provides for regeneration and seral stage development
- effectively use growing space
- consider and minimize risks from insects, disease, etc.
4
Q
what are stand structural objectives, and what needs to be defined to accomplish them?
A
stand structural objectives are designed to define the target stand, in order to achieve stand mgmt objectives
Accomplished by defining:
- species mix
- canopy layers
- age class
- scale(size of stand)
- rotation length
5
Q
describe a block clearcut
A
- often planted (interior of blocks are far from natural seed source)
- non-regen considerations dictate block size/shape
- used for major pest outbreak areas, wind damaged stands
6
Q
describe strip clearcut
A
- used to harvest a stand over a period of time (3-7 years) by removing strips
- takes advantage of natural regeneration(wind a concern)
TYPES:
- alternate(2 pass)
- progressive (3 or more passes)
- strip width defined by seed fall distance
want to use on difficult sites to plant or when you want to favour naturals
7
Q
describe patch clearcut
A
- <1ha and managed as a discrete even aged unit
- intent is to regenerate naturally from adjacent stand or surrounding timber
- >50% of cleared area is affected by the edge
- used for caribou habitat, visuals
8
Q
describe progressive clearcut
A
- old style
- progressively harvest a watershed extending clearcut boundaries over a short period of time(several years)
9
Q
Describe seed tree silviculture system
A
- environmentally similar to clearcut except harvesting excludes trees selcted for the purpose of providing seed for next crop
- select correct species, correct phenotypes
- some planting usually done to support naturals
- survey 2-3 years post harvest and fill plant accordingly
- seed trees may or may not be removed post harvest(removal cut)
10
Q
Describe the three types of seed tree silviculture systems
A
- uniform seed tree: seed trees left uniformly throughout block ; spacing depends on species, dispersal distance, 2 passes, other objectives; allows easier choice of desired species/phenotypes
- Group seed tree: groups of trees left in block uniformly ; allows for retention of dead wildlife trees during harvest; fits skidding pattern better; visual quality
- Combination: group and uniform seed tree. Typically non-timber values are involved
11
Q
General shelterwood info
A
- mature stand removed in a series of cuttings to promote the establishment of an even aged forest under the shelter of the old one
- natural and/or planting
- over wood provides shelter to the regen until the seedlings no longer require the shade. at this point overwood is removed over small portion of rotation)
- amount of initial removals determined by environment needed for regen (species) and site conditions (aspect, slope, etc)
12
Q
Describe uniform shelterwood
A
Leave trees left uniformly spaced providing shelter. involves 3 cutting steps:
- preparatory(trimming)cut: to ready stand for established cut by encouraging crown expansion, wind firmness(root growth) and cone production, prepare forest floor
- establishment cut:2-5(up to 10) yeras after prep cut or regen cut. Cut but leave trees needed to provide shelter(and seed). Correct species, distribution, and density required.
- Removal cut: 2-5 years(up to 10) years after established cut. Remove shelter trees post regen delay period-typically on snow pack to protect regen. May or may not be carried out-you have th eoption of turning shelter trees into reserves
13
Q
Describe Natural Shelterwood
A
- Often called an overstory removal (one entry:removal cut)
- regen already established
- requires a well-stocked, acceptable understorey
- need to have 2x the stocking to allow for damage during harvest
- must be economical to harvest understorey and save the regen
- may have to fill plant to meet TSS
- unmanaged, or old harvested selection block
14
Q
describe a group shelterwood system
A
- small group openings are created (1-2 tree lengths in diameter)
- adjacent trees provide shelter for naturals and/or planted trees in the gap
- once regenerated, cuts are expanded or new openings are created
- eventually entire stand (unless reserves) is harvested in 20-30 years
- BA REMOVAL:
1st, 2nd and 3rd pass all 20-40%
15
Q
describe a strip shelterwood system
A
harvesting is done in narrow strips that advance progressively through the block over the regen period
16
Q
describe irregular shelterwood system
A
- irregular refers to variation in tree heights in new stand
- versatile system-unifrom, strip or group(spatial variations)
- defined by timing of cuts
- regen period is extended so long removal cut is deferred for up to one rotation
- actual stand structure objective is between even aged and uneven aged
- favours shade tolerant species unless opening size is large enough to promote shade intolerant species
17
Q
describe nurse crop shelterwood system
A
- similar to natural shelterwood but overstory trees are a different species than those in understory
- establishment cut leaves overstory nurse trees, removal cut takes them away
- eg: stands that were established after large disturbances where two or more species establish at same time
18
Q
describe variable retention, what makes it different from other systems, and what are the challenges with using this system?
A
- Requires individual trees or groups of trees to be distributed over the entire area of the cutblock
- More than 1/2 the total area of the cutblock must be under the influence of standing trees
- different from other systems in that it leaves many trees on site to manage for biodiversity, visuals, water quality, and sustainability
- operationally variable retention is difficult and complicated which makes it expensive
19
Q
The number and distribution of leave trees in a seed tree or shelterwood system depends on:
A
- silvics
- operational constraints/site constraints
- resource objectives for the silvicultural system used
- stand constraints
20
Q
what is the difference between a seed tree and clearcut with reserves?
A
seed tree: excluded trees selected for the purpose of providing seed for the next crop- may or may not be removed post harvest
cc with reserves: trees are left for reasons other than silvicultural(regen) purposes
21
Q
uniform seedtree vs. grouped seed tree
A
- uniform allows easier choice of desired species/phenotypes
- groups allow for windthrow resilience(species variation and non timber operability)
- groups allow for: retention of dead wildlife trees during harvest; fits skidding pattern better; visual quality
22
Q
Criteria used to select leave trees for seed tree or shelterwood systems
A
- windfirm
- appropriate species
- genetically superior (robust)
- no health issues
- appropriate distribution
23
Q
describe group selection
A
- small groups averaging 1-2 hectares in size are periodically harvested from larger stand areas.
- used to progressively regenerate and manage stands with an uneven –aged class distribution or where encouraging an uneven distribution would best meet the management objectives.
- management area becomes a multi-aged mosaic of even-aged groups that eventually develops into an uneven-aged forest
- This system can be effective where moderate to low levels of competition are expected, but poses some risk where competition from unwanted vegetation is heavy.
24
Q
describe single tree selection
A
- Single tree selection removes individual trees of all size classes more or less uniformly throughout the stand to maintain an uneven-aged stand and achieve other stand structural objectives
- stands appear open, with many gaps
- used for most tolerant species in area
- Usually guidelines for residual stocking, maximumdiameter, diameter distribution (usually expressed by a “q-ratio”), and cutting cycle are used during each entry
25
how did variable retention start in BC?
* introduced in BC by Clayogquot scientific panel in 1995
26
describe the four key types of reserves
RIPARIAN:
* protection of habitat features (vegetation, snags, access to water sources, water resources, etc)
WILDLIFE TREE:
* acheive habitat required for wildlife
* cavity feeding, nesting and perching for birds
* stand level reserves
* must retain throughout rotation or replace if lost
* a % of WTP is determined for the timber forest land base within a BEC subzone
DISPERSED:
* individual trees for biodiversity and structure
AGGREGATE:
* groups of trees for biodiversity or structure.
* For variable retention, \>50% of unit has to be under influence of leave trees
27
describe the difference between even aged and uneven aged stands
EVEN AGED:
* Length of regen: less than or equal to 20% of standard managed rotation
* # of age classes: usually 1-2.
* Canopy characteristics: well developed canopy, uniform height, may be gaps from rock outcrops and disease centeres
* Most trees in average diameter class
* in nature, occurs after major disturbance
UNEVEN AGED:
* length of regen: in perpetuity
* # of age classes: 3+
* canopy characteristics: uneven, highly broken/irregular, many gaps
* shade tolerant species favored
* most species in smalles age/size class
* cuts made throughout rotation
28
explain BDq in terms of single tree selection
* b: residual growing stock (basal area)
* D: maximum diameter retained after cutting cycle (dbh)
* q: distribution of growing stock among various diameters
* These are the three parameters used to create an inverse-J diameter distribution using a single tree selection silviculture system.
29
what is meant by a cutting cycle, and how do you choose one?
* number of years between harvest entries
* Use periodic annual growth data and time the cutting cycle to coincide with the return of the stand to full stocking (a density at which mortality is about to set in)
* usually set in increments of 10 years for easier admin
