Abstract
The 10th-growing season performance of planted eastern white pine (Pinus strobus L.) seedlings was evaluated in response to herbaceous and woody vegetation control treatments within a clearcut and two variants of the uniform shelterwood regeneration system (single vs. multiple future removal cuts). Herbaceous vegetation control involved the suppression of grasses, forbs, ferns and low shrubs for the first 2 or 4 growing seasons after planting. Deciduous woody vegetation control treatments, conducted in combination with the herbaceous treatments within a response-surface design, involved the permanent removal of all tall shrubs and deciduous trees at the time of planting, at the end of the 2nd or 5th growing seasons, or not at all. In general, the average size of planted pine was related positively to the duration of herbaceous vegetation control and negatively to delays in woody control. White pine weevil (Pissodes strobi Peck) altered these trends, reducing the height of pine on plots with little or no overtopping deciduous woody vegetation or mature tree cover. Where natural pine regeneration occurred on these plots, growth was similar but subordinate to the planted pine. Data from the three sites indicate that at least 60% of planted pine may be expected to reach an age-10 height target of 2.5 m when overtopping cover (residual overstory + regenerating deciduous) is managed at approximately 65% ± 10%, and total herbaceous cover is suppressed to levels not exceeding 50% in the first five years. On productive sites, this combination may be difficult to achieve in a clearcut, and requires fairly rigorous vegetation management in shelterwood regeneration systems. Currently, synthetic herbicides offer the only affordable and effective means of achieving such vegetation control.
Highlights
Eastern white pine (Pinus strobus L.) was important during the post-colonial development of northeastern North America, providing building materials and generating economic value that fueledForests 2016, 7, 175; doi:10.3390/f7080175 www.mdpi.com/journal/forestsForests 2016, 7, 175 development and infrastructure throughout the continent [1,2]
We studied planted pine performance as a response-surface defined by 3 levels of the duration of herbaceous vegetation control (H; 0, first 2 or first 4 years) and 4 levels of the timing of woody vegetation control (W; year 0, 2, 5 or none, where year refers to the number of growing seasons since planting) (Figure 1)
Above-average diameters were observed in all plots receiving early herbaceous and woody vegetation control and those plots receiving aggressive herbaceous control, coupled with late woody release
Summary
Forests 2016, 7, 175 development and infrastructure throughout the continent [1,2]. Today, this species continues to retain relatively consistent high lumber values, while garnering significant appreciation for its wildlife, recreational and spiritual values [3]. Difficulties plaguing the regeneration success of white pine have precipitated a significant decline in its abundance and dominance throughout its former range [4,5]. These losses can largely be attributed to damage caused by white pine blister rust (Cronartium ribicola J.C. Fisch.). The partially shaded understory environment of the shelterwood is deemed to reduce rust infection potential by lowering humidity levels during spore dispersal, and reduce weevil incidence by lowering ambient temperatures and terminal shoot diameters to levels that disfavor oviposition, larval development and survival [12,13]
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