and Other Related Measurements Site and Stocking and Other Related Measurements

Height as a Measure of Site Quality Tree Height in relation to tree age has been found to be the most practical, consistent and useful indicator. What was discussed earlier as the limiting factor to fast growth?

Site Index The average total height and age of dominant and co-dominant trees in well-stocked, even-aged stands at a given age. Typically the base age for hardwoods is 50. Some softwoods use 25 years for the reference age. For example, if the SI50 for a tree is 75, we are saying that the average height of dominant trees at age 50 for this stand is 75 feet.

Crown Class Dominants - Crowns receive full light from above, and partly from the side. Trees extend above the general crown levels Co-dominants - Crowns form at the general level of the canopy. Crowns receive full light from above, but little from the sides. Intermediates - Crowns generally below the dominants and co-dominants, but extending up into the general canopy level. They receive little or no direct light from above, nor the sides. Overtopped or Suppressed - Crowns entirely below the general level of the canopy. They receive no direct light from above, nor the sides.

Crown Class

Crown Closure Measured by what?

Crown Closure Spherical Densiometer Hemispherical photography Aerial photography CLASSES Very Sparse 1-9% Sparse 10-29% Low 30-49% Medium 50-69% Dense 70-84% Very Dense 85-100%

Tree Age Even-aged - The range of tree ages generally does not exceed 20% of the rotation age assumed. Uneven-aged - Three or more distinct age classes, either intimately mixed, or in clumps.

Increment Borer

Site Index Total Heights and Ages of dominant and/or co-dominant trees are measured and curves are fitted. Varies by species and region.

Site Index Limitations Exact Stand age is often difficult to determine (diffuse porous wood, false rings and drought rings, skill with borer), and small errors can cause relatively large changes in the site-index estimate. Alternate methods of determining stand age can include counting branch whorls (if applicable species) or historical information

Site Index Limitations - continued Not well suited to uneven-aged stands, areas of mixed-species composition, or open lands. Stand volume variables (DBH, stem form) are not taken into account. Site-Index is not a constant, it changes periodically with climate and management. Varies by species within the same site. So if you plan to change the site to a new species, it is difficult to predict.

Factors that Influence SI

SI Alternatives Growth index Output from a mechanistic growth model Tree diameter Stand volume Output from a mechanistic growth model Indicator plants NPP, evapotranspiration Leaf area index Can be assessed remotely

Site Index real world use Growth Intercept Models: These species-specific models are designed explicitly for young stands (5-50 years breast height age). The growth intercept technique estimates site index from the average annual height growth of site trees, which is determined either from the distance between annual branch whorls or from the height and breast height age of the tree. Site Index-Biogeoclimatic Ecosystem Classification (SIBEC) Models: This comprehensive tool correlates site index with site series within biogeoclimatic ecosystem classification (BEC) units and site series. The BEC system is designed specifically for British Columbia’s ecosystems. This model is best used for very young stands, very old stands, and stands not suitable for other methods. 

Indicator Plant Approach Curves fitted to measured data relating the presence of certain plants to the site quality for trees on a given site.

Site Index from Soil

Soil Survey Forest lands Site Index -  Measurements of site index are usually extended to a number of like soils where data are unavailable. Erosion hazard Equipment limitations Seedling mortality Windthrow hazard Plant competition Trees to plant

Site Productivity Measures

Principles and their implications Tree Growth Principles and their implications

General Growth Curve

Change in Tree Weight

Mean Annual Increment Increase in cubic-foot volume per acre per year Curves fit to known data – usually takes the equation form below MAI = Constant X Site Index +/- Intercept Attempts to predict future Annual volume growth

Annual Growth Increment Generalized Chart for conifers

The concept of forest site productivity in terms of current annual volume increment vs age. The concept of forest site productivity in terms of current annual volume increment vs age. The full site potential for wood production (horizontal line) is only briefly realized by a given forest stand (bold line). Management practices may increase or decrease stand productivity (dashed lines) at any stage of stand development and these changes may be permanent or transient. For simplicity, the site potential is considered constant. Skovsgaard J P , and Vanclay J K Forestry 2007;81:13-31 © Institute of Chartered Foresters, 2007. All rights reserved. For Permissions, please email: journals.permissions@oxfordjournals.org

Stocking And Stand Density

Stand Density Quantitative measurement of the stand describing the degree of stem crowding within a stocked area. As in: 150 stems/acre Stocking refers to the adequacy of a given stand density to meet some management objective. Often expressed on a basal-area basis comparing current condition to ideal.

Growth vs. Growing stock

The thinning response hypothesis. The thinning response hypothesis. For many tree species, stand volume growth is thought to be independent of thinning practice for a range of thinning grades stretching from the unthinned stand, down to a residual basal area of ∼50 per cent of maximum basal area. The accumulation of maximum basal area occurs in unthinned stands only. Skovsgaard J P , and Vanclay J K Forestry 2007;81:13-31 © Institute of Chartered Foresters, 2007. All rights reserved. For Permissions, please email: journals.permissions@oxfordjournals.org

Assmanns theory of natural, optimal and critical basal area. Assmanns theory of natural, optimal and critical basal area. For given site conditions and a given spacing or initial stem number at stand establishment, the unthinned stand or control plot will support the highest possible basal area of live trees at any stage of stand development. This is referred to as the natural basal area (NBA). The basal area at which the largest stand volume growth is achieved during the period concerned is referred to as the optimum basal area (OBA). The basal area at which volume growth is 5 per cent less than at the optimum is referred to as the critical basal area (CBA). In this example, optimum basal area is located at 83 per cent of the natural basal area. Here, volume growth is at 102 per cent. A 5 per cent reduction in volume growth, compared with that at the optimum, appears at a basal area of 60 per cent. Here, volume growth is at 96.9 per cent, compared with the unthinned stand. Skovsgaard J P , and Vanclay J K Forestry 2007;81:13-31 © Institute of Chartered Foresters, 2007. All rights reserved. For Permissions, please email: journals.permissions@oxfordjournals.org

Stocking A description of the number of trees, basal area, or volume per acre in a forest stand compared with a desired level for a management objective Central Hardwood Stocking Chart 

Stocking Charts Vary by species Vary by site quality Compare current stand conditions to desired in order to make prescriptions