Competition thresholds for the survival and growth of ponderosa pine seedlings associated with woody and herbaceous vegetation

Abstract

Application . A quantitative understanding of the competitive influence of woody and herbaceous vegetation on young conifers is required to make appropriate vegetation management decisions in new plantations . Knowing the biological thresholds of competition for the survival and stem-volume growth of conifer seedlings, such as ponderosa pine, can provide a basis for evaluating the need and objectives for vegetation control treatments .Abstract . Patterns of survival and stem-volume growth for planted seedlings of ponderosa pine (Pinus ponderosa Doug] . ex Laws .) competing with various levels of woody and herbaceous vegetation were derived from three previous studies-one in Oregon and two in Montana. Negative hyperbolic curves of opposite concavity describe the relation between the abundance of woody or herbaceous vegetation and (1) the survival and (2) the stem volume of the pine seedlings . From these curves, two types of competition thresholds for managing forest vegetation are identified : (1) maximum-response threshold-a level of vegetation abundance where additional control measures will not yield an appreciable increase in tree performance ; and (2) minimum-response threshold-a level of vegetation abundance that must be reached before additional control measures will yield an appreciable increase in tree performance . The maximum-and minimum-response thresholds for pine stem volume occurred at lower levels of vegetation abundance than those for pine survival . Thus, forest managers may need to consider ponderosa pine survival and stemvolume growth as separate objectives when managing woody and herbaceous vegetation in young plantations . Knowledge of maximum-and minimum-response thresholds also can be used to improve herbicide prescriptions .

Competition and critical-period thresholds for vegetation management decisions in young conifer stands

“…ex Laws. ), however, indicate that tree survival and stem volume growth respond differently to the abundance of neighbouring plants (Wagner et al 1989). The curves have different shapes and, therefore, different competition thresholds (Fig.…”

“…The competition threshold has been defined as the "weed density at which yield loss begins to occur" (Cousens 1987). For forests, the competition threshold has been defined as the level of vegetation abundance where there is an abrupt increase or decrease in the rate-of-change in tree growth or survival (Wagner et al 1989).…”

Lodgepole pine and trembling aspen competition: Neighbourhood studies within 22 to 39 year-old pine plantations of northern British Columbia

“…1 model (Table 7) was used to explore a prediction of competition response thresholds using concepts published by Wagner et al (1989). The calculation of a minimum growth response competition level (such as 20% of maximum) was considered subjective (Wagner 2000) and found inconclusive, since model results suggested the maximum response threshold was effectively zero.…”

“…Clearly there is a need to revise the freegrowing standards to align with current research evidence and address concerns over the legal definition of a free-growing stand and possible impeded stand growth (BC MFLNRO 2015). Performance-based standards are needed to ensure tree level surveys are linked to long-term stand level performance (Wagner et al 1989). Silviculture prescriptions and treatments that fail to address aspen competitive strength will lead to varying levels of aspen dominance and therefore varying levels of pine growth reduction.…”

“…Most published studies have focused on early establishment performance prior to canopy closure based on measurements of aspen competition in young pine from small plots. Some studies are without an aspen-free treatment from which to quantify a zero competition environment, which may confound attempts to define growth threshold impacts (Wagner et al 1989). Many of the published aspen competition studies were established in response to the government's need for evidence to support regeneration standards and free-growing guidelines (Lieffers et al 2008, Dhar et al 2015.…”