Transcript Site Index
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. 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 codominant trees are measured and curves are fitted. Varies by species and region. Site Index Limitations 1. 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 2 3 4 5 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 o Tree diameter o Stand volume • Output from a mechanistic growth model o Indicator plants o NPP, evapotranspiration • Leaf area index o Can be assessed remotely Site Index real world use • • Growth Intercept Models: These speciesspecific 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 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. Skovsgaard J P , and Vanclay J K Forestry 2007;81:13-31 © Institute of Chartered Foresters, 2007. All rights reserved. For Permissions, please email: [email protected] Stocking Stand Density Quantitative measurement of the stand describing the degree of stem crowding within a stocked area. Growth vs. Growing stock The thinning response hypothesis. Skovsgaard J P , and Vanclay J K Forestry 2007;81:13-31 © Institute of Chartered Foresters, 2007. All rights reserved. For Permissions, please email: [email protected] Assmanns theory of natural, optimal and critical basal area. Skovsgaard J P , and Vanclay J K Forestry 2007;81:13-31 © Institute of Chartered Foresters, 2007. All rights reserved. For Permissions, please email: [email protected] 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