Forest Investment Account (FIA) - Forest Science Program
FIA Project Y091053

    Stand dynamics over 15 years in old-growth forests in the Coast Forest Region
Project lead: Mackinnon, Andy (Ministry of Forests and Range)
Contributing Authors: West, Heather; Saunders, Sari; MacKinnon, J. Andrew; Davis, Todd
Subject: Forest Investment Account (FIA), British Columbia
Series: Forest Investment Account (FIA) - Forest Science Program
Coastal temperate rainforests span broad gradients in temperature, moisture and continentality. These systems extend from WA, southern OR to southeast AK, including coastal BC (e.g., Schoonmaker et al. 1997; see attachment for full citations). Foundational studies on old growth dynamics have been conducted in southeast AK (e.g., Alaback and Juday 1989), southern BC (e.g., Lertzman et al. 1996) and WA (e.g., Spies and Franklin 1991),.. However, there has been little coordination of data collection or analysis, and no formal assessment of old growth characteristics across the biome. Remeasurements of old growth stands in WA indicate that current definitions of old growth structure may not apply at environmental extremes (Acker et al. 2006). Standardized, comparative studies across this climatic and geographic gradient would contribute to comprehensive models of natural structure and function and to information about old growth characteristics for forest managers.

In addition to quantifying the structural complexity of old-growth coastal temperate rainforests, we also need to understand their temporal dynamics. The structure of our coastal old-growth forests changes over time as trees grow and die, become snags and are recruited to coarse woody debris, and as coarse woody debris decays and disappears. It is this life, death and decay that imparts a structural complexity to these forests that provides important habitat, nutrient cycling (e.g., carbon sequestration), and hydrological interception and storage, generally lacking in younger, less complex stands.

In 1992 and 1993 Project Partner Paul Alaback and BC collaborators (including Principal Investigator Andy MacKinnon) established a series of stand-level monitoring plots along BC's coast. This project will re-visit, re-locate and re-measure these plots in the Kitlope, Tahsish-Kwois and Tofino Creek watersheds, over two sampling seasons. The data from 1992/93, and the data from 2008/2009, will individually provide us with detailed spatial data on stand structure. A comparison of the 1992/93 structure and the 2008/09 structure will allow us an unprecedented opportunity to quantify changes in structure over time.

Structural complexity in vertical and horizontal space is a definitive feature of coastal temperate forest systems (e.g., Zenner 2000). This patterning within old growth forests of the biome (as per Franklin and Van Pelt 2004) develops through interactions of fine scale gap dynamics (e.g., Lertzman et al. 1996) and broader-scale dynamics imposed by exogenous disturbance (Larson and Franklin 2006); the resultant mosaic may be a unique, emergent property of the old growth developmental stage (Franklin et al. 2002; Larson and Franklin 2006). Measurement of these attributes in coastal BC forests will support calibration of existing models of old growth features. Re-measuring the 1992/93 plots will allow us to evaluate hypotheses regarding growth, mortality, species transitions, recruitment to canopy or coarse wood debris pool, and decay. Further, these measurements will refine our understanding of correlates with unique functional features of old growth (e.g., invertebrate complexes, lichen communities, spatial patterns of specific tree species, gap configurations) and provide a defensible, empirical basis for initiatives that seek to retain or restore old growth features in coastal BC forests.

Specifically, we will measure attributes to answer the following questions regarding old growth structure and function in coastal BC forests:

(1) What are the differences in structural and compositional complexity of stands on different sites and at different latitudes?
(a) How are species and individuals (trees) distributed among size classes (height and diameter)?
(b) How are species and individuals (trees) distributed spatially?
(c) How do species richness, diversity, dominance differ in total and among strata (canopy, subcanopy, shrub, herbaceous; bryophytes and lichens)?
(d) How useful are multivariate indices of structure for encapsulating ecological information for different variants?

(2) What are the differences in spatial patterning of trees?
(a) How do these spatial patterns vary by species and among canopy, subcanopy trees, and saplings?
(b) How do these strata relate to each other spatially?
(c) What is the density of and relative spatial relationship of legacy (emergent) canopy trees?

(3) How does stand structure change over time (in this case, over 16 years)?
(a) What are the rates of tree growth, death and fall?

(4) How is cwd recruited, and how does it decay?
(a) How do these changes vary by site and by tree species?

Previous studies do give insight into aspects of old growth structure attributes across coastal, environmental gradients. Gagnon and Bradfield (1987) evaluated composition-structure-site relationships along elevational gradients on west-central Vancouver Island; Lertzman et al. (1996) compared canopy gap characteristics and distribution among four biogeoclimatic variants (also Frazer et al. 2000). Mensuration data from biogeoclimatic ecosystem classification (BEC) plots in late seral and old-growth forests are summarized in BC Ministry of Forests (2001). Trofymow and associates measured a chronosequence of plots in the CWHxm1/2 and CWHvm1 (e, g., Trofymow and Porter 1998). However, there is currently no permanent network of old growth plots for coastal BC This study will provide a standardized characterization of old growth for development of ecological theory and scientifically-based management. The plot network will allow the Coast Forest Region to contribute to a national monitoring programme (EMAN) for evaluation of effects of climate change across ecosystems, and to participate in a biome-level study of coastal temperate forests extending from OR, along the BC coast, to AK.

Current, broad-scale management initiatives in coastal BC include developing operational approaches for ecosystem-based management (Central and North Coast), exploring the framework of ecosystem resilience for managing with climate change (within Chief Foresterís Future Forest Ecosystems Initiative), and evaluating ecosystem recovery to old growth state after disturbances. These programmes require empirical understanding of structure-function relationships from site to landscape levels, with particular attention to associations between disturbance, and other driving processes, and forest attributes and function. Our study will provide data on the variation in attributes across the current distribution of variants and potential to monitor stand structure and physical or ecological processes within unmanaged stands.

A regional, comparative study of old growth coastal forests provides an opportunity to detect and evaluate impacts of climate change on the dynamics of these systems. This may be particularly important in the coastal temperate rainforest where successional dynamics occur over long time periods and the dominant disturbance regime is characterized by relatively fine-scale, infrequent wind events. Collection of data documenting natural variability will enhance the ability to predict shifts to new states of species composition and structure. Managers can better anticipate the impacts of climate alteration for a variety of land uses. Data documenting vegetation associations among these variants may also assist in refining the provincial BEC under shifting site conditions.

In addition to describing current structure and allowing us to quantify change in structure over the past 16 years, these plots will provide an important baseline for future measurements. All of the plots established by Alaback in 1992/93 are now in protected areas of various sorts: this will ensure that they remain relatively undisturbed into the future and are thus available for remeasurements decades hence.
Related projects:  FSP_Y102053


Executive summary (20Kb)
Poster - Comparing Structure and composition of two old-growth coastal floodplain stands (0.2Mb)
Presentation - Developing a permanent plot network ... (1.4Mb)

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Updated August 16, 2010 

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