Forest Investment Account (FIA) - Forest Science Program
FIA Project Y071158

    Structural Recruitment: factors affecting survival and growth of residual immature trees after clearcut overstory harvesting
Project lead: Lloyd, Ruth
Contributing Authors: Lloyd, Ruth A.; Todd, Melissa A.; Meggs, Jeffrey M.
Imprint: [BC] :, 2007
Subject: Forest Investment Account (FIA), Growth (Plants), British Columbia
Series: Forest Investment Account (FIA) - Forest Science Program
In recent years, there has been increased emphasis on retention of structural features such as coarse woody debris and immature understory trees during clearcut harvesting in the sub-boreal Interior. These features serve to 'lifeboat' species and processes during early seral stages and will enrich the developing stand with structural features that would otherwise be absent. Retention of immature understory trees may also contribute to future recruitment of large live and dead stems. To date, these trees have been retained primarily for biodiversity reasons rather than to augment conifer stocking. Stem densities are generally low, such that the resulting stand is considered an even-aged plantation, not an uneven-aged stand resulting from overstory removal. This project focuses on survival and growth of sapling and pole-sized immature trees that remain in the cutover area after clearcut harvesting defined as trees >1.5m in height and <17.5cm diameter at breast height (dbh) as these will be easily distinguishable from planted stock and, due to their larger size, have greater potential to contribute to diversity in the developing stand. The project does not include trees remaining within wildlife tree patches (WTPs), or residual mature trees >17.5cm dbh, which are generally not found on clearcuts. In the study area, residual immature trees are almost invariably subalpine fir. Considerable work has been done on developing and assessing management strategies that promote the retention of stand-level structures and attributes at the time of harvest (Lloyd 2003, 2005; Lloyd and Todd, 2003; Densmore et al 2004; Zielke et al, 2003) but it is not certain what becomes of them. Research currently underway in Prince George (C. Delong, pers. comm.; FIA project Y05 1073) to understand and predict snag and CWD dynamics in sub-boreal spruce and Engelmann spruce-subalpine fir forests includes immature trees remaining after clearcut harvest in the modeling process but uses data from the Aleza Lake shelterwood project to predict growth. Data from this research will be available for further parameterization of the immature trees model varial in that project. Several studies in Alberta have investigated understory retention of white spruce in boreal mixedwood forests (Lieffers and Grover, 2004; Greene et al., 2002; Navratil et al., 1994) but conditions differ in that harvesting was designed to protect understory trees, which are intended as future crop trees, and the density of retained stems is much higher than is usual in clearcuts in B.C. Herring (1977) investigated growth of residual immature and advance regeneration (<1.5m tall) subalpine fir 10-30 years after diameter-limit cuts in the Kamloops area, but did not investigate mortality, and several studies have investigated sapling growth and mortality in partial cuts in B.C. (e.g. Kobe and Coates, 1996; Wright et al., 1998; Wright et al., 2000). However, little research has been done on the persistence of residual immature trees and their contribution to structural diversity through the life of the regenerating stand in clearcuts, where mortality may be more related to windthrow and sunscald rather than competition and suppression. Retention of residual stems is a key component of the operational CWD retention practices (Lloyd and Todd, 2003; Lloyd 2005) developed for the Morice-Lakes IFPA as part of the larger dead wood management strategy developed for that initiative. However, the survival and growth of residual immature trees in clearcut areas in B.C. after harvest is poorly understood, even though considerable effort has been invested in maintaining them. Retention of residual immature live trees serves several purposes: they provide habitat in a clearcut area that is otherwise devoid of trees, potentially 'lifeboating' some species through the stand initiation phase they can continue to grow during stand development, providing trees that are significantly larger than planted stock they may reach 'large live tree' size by rotation age. To fulfil these functions effectively, residual immature live trees must not only be maintained during harvest but must also survive and grow in the drastically changed conditions that follow. We propose to investigate factors affecting the survival and development of residual immature subalpine fir trees in areas clearcut between 1995 and 2000 and to use the results to guide abundance and configuration of future residual immature tree retention in clearcut areas. We expect that tree morphology (height, diameter) and configuration of retention (patch vs single tree) will affect the survival and growth of immature residual trees retained after harvest. We expect to test this by collecting measures of growth and survival for residual immature trees of varying sizes and in various retention configurations,. We also describe the risk of windthrow as related to soil conditions, distance to timbered edge and tree crown characteristics.
Contact: Lloyd, Ruth, (250) 846-5763,


Executive Summary (20Kb)

To view PDF documents you need Adobe Acrobat Reader, available free from the Adobe Web Site.

Updated August 16, 2010 

Search for other  FIA reports or other Ministry of Forests and Range publications.

Please direct questions or comments regarding publications to