Forest Investment Account (FIA) - Forest Science Program
FIA Project Y103103

    Regeneration, Growth and Potential Value of Bitter Cherry as a component of young complex stands on Southern Vancouver Island
Project lead: Brian Danjou (Ministry of Forests and Range)
Contributing Authors: Brown, Kevin R.; Douglas, Mary-Jane; Negrave, Roderick W.; Antos, Joseph A.
Subject: Forest Investment Account (FIA), British Columbia
Series: Forest Investment Account (FIA) - Forest Science Program
In low-elevation forests of south coastal BC, complex, mixed-species stands often develop when early successional deciduous hardwoods regenerate in plantations intended to contain one or two species of conifers. Silvicultural interventions to remove these naturally regenerating hardwoods are expensive and may reduce both the ecological and economic value of the stand. These early successional hardwood species are characterized by prolific reproduction and rapid juvenile growth1, which makes them formidable competitors. However, most of the hardwood species found in coastal BC also have substantial commercial value. Ecologically appropriate management of such species in conifer plantations requires knowing how their regeneration varies with site and stand management and if benefits of retaining the species offset costs of removal.

We propose to examine the natural regeneration and growth of bitter cherry, Prunus emarginata, a species that has received little study. Bitter cherry can aggressively colonize lowland forest sites of south coastal B.C. following disturbance: after harvest of coniferous stands, bitter cherry can regenerate at a high density (>20,000 stems ha-1). Similar densities of pin cherry in the northeastern U.S. at age 3 reduced heights of deciduous associates by 25% through 15 years2. Densities of bitter cherry associated with growth reductions of planted conifer seedlings are unknown. However, in order to meet stocking standards and achieve free growing status for planted conifers, licensees effectively must remove all cherry from the plantation, typically and at much expense.

Although bitter cherry is a concern for conifer regeneration, the species is also a valuable resource. The wood of larger trees is desirable for woodworking-related value-added products345; regional hardwood mills readily process cherry logs when available, but limited availability constrains utilization of the resource. Cherry is often milled as an alternative when log supplies of red alder are limiting. Fruits and seedlings are also a preferred food source for wildlife.

Maintaining appropriate densities of cherry in young plantations depends on understanding its regeneration ecology. Hence, this proposal is closely linked to priority topic 1.1c Complex stands-natural regeneration. Bitter cherry regeneration occurs mainly from a soil seed bank7; germination and emergence of bitter cherry seedlings are probably promoted by canopy removal and soil disturbance by logging, as occurs with pin cherry in eastern North America. The seedbank strategy is favored when disturbance intervals are shorter than the lifespan of seed in the soil. Thus, cherry regeneration may increase if conifer stands are harvested at younger ages. Regeneration of cherry may also vary with degree of soil disturbance and canopy retention at harvest. Therefore, cherry regeneration should be related to both how often and the way in which conifer stands are harvested. Hence, the proposal is also consistent with priority topics 2.1a, Complex stands - Relationships between residual stand structure and understory recruitment and development and 2.1b, Complex stands - Development and monitoring of the impact of various stand treatment regimes on regeneration.

We will examine bitter cherry reproduction and early growth as they relate to cherry abundance in the CWHxm BEC unit of southern Vancouver Island. This information is a key to ecologically-based management of cherry-conifer complexes. Bitter cherry ecology is poorly documented, so we also address other topics critical to its management. Understanding competitive effects of high densities of cherry on planted conifers provides context for the regeneration studies and guidance in how to manage cherry in conifer plantations. Also, since cherry is potentially valuable, it is useful to document its potential growth and perceived value. Our study will address the following questions: a) What is the competitive effect of bitter cherry on early conifer growth? b) How do stand age and site series affect cherry seed bank viability? c) Is cherry regeneration affected by partial cutting? d) How does soil disturbance influence cherry regeneration? e) What is the site series relationship to attainment of commercial size in cherry and f) How does the sawmilling community regard the commercial potential of cherry?

Competitive effects (part 1) of cherry will be assessed near Jordan River in TFL25 in an existing 4-year-old Douglas-fir and western red cedar plantation containing more than 20 000 stems ha-1 of cherry. The site is classified as CWHxm site series 05 and previously contained a mixed conifer stand. Portions of the site were manually brushed, with adjacent areas left intact. In 2007-8, we will examine multi-year effects of high densities of cherry on growth of planted conifer seedlings on the site beginning in 2007-08(part 1).
Seed bank populations will be examined (part 2) in stands of varied ages and site series near to the competition study. The lifespan of bitter cherry seed is unknown, although viable seeds were fewer in 100-year old than in younger stands. Shorter plantation rotations may increase the abundance of cherry if it regenerates following harvest, but is not brushed prior to producing seed. Longer rotations (e.g., > 100 years) may lead to decreased abundance if seed viability decreases over time. Hence, we will assess seed banks in stands representing: (a) recently harvested (competition study site) (b) ca. 40 years (accelerated harvest) (c) ca. 60 years (current harvest age) and (d) > 100 years (lengthened rotation). As a surrogate for assessing effects of partial cutting of conifer stands on cherry abundance, seedling emergence and early growth will be examined in relation to conifer canopy presence (part 3). Emergence and survival plots will be established along transects extending from under a mature conifer canopy to the open cutblock. To assess effects of soil disturbance on emergence and growth (part 4), we will relate cherry seedling establishment to substrate and past soil disturbance . Because abundance may vary with seed number, rather than substrate or soil disturbance, we will also study emergence and survival in small disturbance plots (part 4b). To better assess the product potential of cherry, we will initiate an exploratory study of tree size in relation to site class and age (part 5) and survey hardwood mill operators and wood users as to their perception of the species (part 6).

Please note that Kathryn Willis is not part of the project team in 2008-09, due to re-assignment to other duties within the MFR. Duties originally planned for this team member will be completed by other members in the team.

References: (1) Grime, 1979, Plant strategies and vegetation processes; (2) Ristau and Horsley 1999, Can J For Res 29:73; (3) S. Roscoe, Woodland Flooring, Comox, Oct. 2005; (4) S. Flynn, S.I. Woodlot Assn, Oct. 2005; (5) D. Middleton, Oregon Coast Myrtlewood, July 2006 (all pers. comm.); (6)Crouch, G. 1968. J. Wildl.Man. 32:542; (7) Oakley and Franklin 1998, Can J Bot 76:1725
Related projects:  FSP_Y081103FSP_Y092103


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Updated August 19, 2010 

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