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

Abstract

Thresholds define the time when management action is required to prevent a loss in yield, but have remained relatively elusive in forest vegetation management. Hundreds of studies quantifying the effects of competing vegetation in young forest stands, however, have produced reasonably consistent patterns and magnitudes of tree responses. These consistencies reveal a set of general guidelines that can be used to assist forest managers in deciding when vegetation management treatments are needed. Among the variety of vegetation management thresholds that have been defined, competition and critical-period thresholds can be interpreted from existing forest vegetation research. Competition thresholds define the vegetation density at which yield loss begins to occur and varies depending on whether the manager's objective is to maximize survival, height increment, basal area growth, or biomass. These interactions also appear to vary depending on whether woody or herbaceous plants are the principal competitors. The critical-period threshold defines the time period when vegetation control must occur to prevent yield loss. Results from one critical-period study indicate that capturing the potential for conifer growth requires control of vegetation for the first several years after planting.Key words: interspecific plant competition, forest vegetation management, intensive silviculture, stand dynamics Le seuil se dCfinit comme le moment oii une intervention de contr6le est requise pour prCvenir une perte de rendement, mais ce tenne est demeur6 relativement Cvasif en matikre de contr6le de la vCgCtation forestikre. Des centaines d'ktudes quantifiant les effets de la vCg6-tation concurrente sur de jeunes peuplements forestiers ont cependant produit des patrons relativement conformes ainsi que d h i t le spectre de la rCponse des arbres. Ces uniformitCs revklent un ensemble de lignes directrices gCnCrales qui peuvent 6tre utiliskes pour aider les arnCnagistes forestiers B prendre une decision lorsque des traitements de contr6le de la vCgCtation sont requis. Parmi la variCt6 de seuils de contr6le de la vCgCtation qui ont Ct C dCfinis, les seuils de compktition et de p6riode critique peuvent &tre interpdtts B partir de la recherche effectuCe sur la vCgCtation forestikre. Le seuil de compCtition dCfinit la densit6 de la vCgCtation selon laquelle une perte de rendement commence B se former et varie 5 . savoir si l'objectif de I'amCnagiste est de maximiser la survie, la croissance en hauteur, la croissance en surface terrikre ou la biomasse. Ces interactions semblent Cgalement varier B savoir si des plantes ligneuses ou herbacCes constituent les principaux concurrents. Le seuil de la pCriode critique dCfinit la pCriode de temps oii le contr6le de la vCgCtation doit 6tre effectuer pour prCvenir la perte de rendement. Les rCsultats tires d'une Ctude d'une pCriode critique indiquent que pour maximiser le potentiel de croissance des coniferes, il faut contr6ler la vegetation au cours des premikres annCes qui suivent la plantation. Mot...

Seedling size and woody competition most important predictors of growth following free-to-grow assessments in four boreal forest plantations

“…This result contradicts those of many vegetation management research trials that suggest herbaceous and woody competition negatively affect conifer growth (c.f. Wagner 2000, Balandier et al 2006. Wagner (2000) summarized results of experiments from across North America and concluded the consensus in the published literature was that during the initiation and the beginning of the stem-exclusion phases of plantation development 6 herbaceous competition is more important than woody competition.…”

“…Wagner (2000) summarized results of experiments from across North America and concluded the consensus in the published literature was that during the initiation and the beginning of the stem-exclusion phases of plantation development 6 herbaceous competition is more important than woody competition. Wagner (2000) noted that woody and herbaceous vegetation reduces the early volume growth potential of crop trees by about 20% to 30% and 70% to 80%, respectively, underscoring the significant effects of herbaceous species on early growth. For coastal Douglas-fir (Pseudotsuga menziesii [Mirb.]…”

“…This lack of documentation may be attributed to the lack of published longer-term results (cf. Wagner 2000). Balandier et al (2006) summarized a global set of literature that indicated different effects on conifer growth related to various life forms of competitive species at different phases of stand development.…”

“…Based on published information (e.g., Wagner 2000, Balandier et al 2006, the free-growing assessment rules used in Ontario that focus on the effects of small shrubs, large shrubs, and trees may require more consideration of the effects of herbaceous vegetation. While current standards may ensure that the planted seedlings occupy the site, they may not ensure those crop trees are free-to-grow if herbaceous competition significantly reduces growth.…”

“…The second alternate hypothesis is designed to identify the period during which the various classes of competitors significantly influence crop tree growth, as discussed in the summaries published by Wagner (2000) and Balandier et al (2006). In all three hypotheses, we assume that conifer growth is adjusted to account for initial differences in tree size.…”