Old-Growth Forest - Case Study

Allometry, Mortality, and Spatial Patterns in an Old-Growth Douglas-Fir Forest

Acknowledgements

Introduction

There are few trees in the world like those in coastal British Columbia that are able to achieve so ultimate an expression of life in size, stature and life span. They leave nature lovers wondering how the trees and the forests in this region develop into such prominent features.

In ecology, the development and dynamics of a forest is called succession, a replacement process of trees and species driven by competition and environmental conditions. It is somewhat like a death-birth process: small/thin trees of shade-intolerant species are constantly phased out, leaving space for big/tall trees and shade-tolerant species to colonize and establish. Accompanying the succession are changes in various aspects, including structure, function and productivity, of ecosystems. If time is permitted and succession keeps going on in the absence of major disturbances (e.g., fire or harvesting), a forest ecosystem is expected to come to a climax or old-growth stage at which the system reaches a relatively steady state and achieves its ultimate function.

To understand the successional changes of the forests in coastal BC is the major goal of a research project, the Chronosequences Study, led by the Canadian Forest Service, from which the following data are derived.

Data

The study site is in an old-growth forest (~ 300 years old) located in the Greater Victoria Watershed District on southern Vancouver Island. The forest is dominated by pioneer Douglas fir with significant components of the late-successional species western hemlock and western red cedar. In the summer of 1997, a 102 by 87 m (0.8874 ha) plot was established in the forest. The plot was located at average elevation of 382 m above sea level on a south facing hillside with a slope of about 20º and an elevational range of 33 m from the lowest to the highest point. Three tree species, Douglas fir (DF), western hemlock (HL), western red cedar (CD) occurred in the plot. Trees were classified into three categories:

1. Live trees: Trees with height > 1.3 m tall.
2. Saplings: Trees with height <= 1.3 m tall.
3. Dead trees: Including standing dead, fallen logs and stumps.

There are a total of 2050 trees (observations) belonging to the 3 species (CD, DF, HL). Nine measurements were made at each observation:

TAG	Permanent tag number attached to trees.
SPECIES	Species identification: CD - Western Red cedar, DF - Douglas-fir, and HL - Western hemlock.
X	x-coordinate in meters, referring to the southwestern corner of the plot.
Y	y-coordinate in meters, referring to the southwestern corner of the plot.
Z	z-coordinate (elevation) in meters, referring to the southwestern corner of the plot.
DBH	Tree diameter (in centimeters) at breast height (i.e., diameter at 1.3 m above ground). No DBH measured for saplings (height <= 1.3 m) and dead trees.
HTT	Tree height in meters. No HTT measured for dead trees.
HTB	Height to the first live branch, in meters. Thus, HTC = HTT - HTB represents the depth of the tree crown where photosynthesis takes place. No HTB measured for dead trees.
STATUS	Three classes: live, sapling and dead.

Data Files

The data are available here as a text file with fixed-width fields and as an Excel file.

Some Questions

Here are some of the research questions we hope to answer with these data.

• What is the relationship of HTB to HTT and how does this differ by species?
• How is the presence of a dead tree affected by DBH, HTT, HTC of the first, second, ... , ith neighbouring trees and does this relationship depend on Z?
• Are the tree species randomly distributed, or are there spatial patterns?

If you require any clarification of the data or more specific suggestions for analysis, you may contact either Fangliang He (fhe@pfc.forestry.ca) or Charmaine Dean (dean@stat.sfu.ca).

Reference

He, F. and Duncan, R. (2000). Density-dependent effects on tree survival in an old-growth Douglas fir forest. Journal of Ecology 88:676-688.

Updates

1. 2001-02-27 22:45 Both of the data files (Excel and text) were modified so that the number of decimal places shown would be consistent between the two files.
2. 2001-03-30 17:30 The HTT and HTB values were switched in the original records for the trees with tag numbers 121 and 1364. This has now been corrected in the text file and in the Excel file.
3. 2001-04-07 15:40 The DBH values for the trees with tag numbers 492, 521, 619, 620, 643, 1473, 1808, 1816, 1818, 346, 781, 792, and 1167 were originally given as 0. These trees should be considered saplings, even though their HTT exceeds 1.3 m, and their DBH values shown as "missing". This correction has been made in the text file and in the Excel file.
4. 2001-04-10 18:50 There were two trees with Tag #1061. The tag numbers have been corrected as follows: Tag #1060 becomes Tag #1059, Tag #1061 that is a HL becomes Tag #1060, Tag #1061 that is a DF remains Tag #1061. This correction has been made in the text file and in the Excel file.