Canopy gaps in Douglas-fir forests of the Cascade Mountains

1990 ◽  
Vol 20 (5) ◽  
pp. 649-658 ◽  
Author(s):  
Thomas A. Spies ◽  
Jerry F. Franklin ◽  
Mark Klopsch
Keyword(s):  
Canopy Structure ◽  
Douglas Fir ◽  
Western Hemlock ◽  
Permanent Plots ◽  
Gap Size ◽  
Gap Formation ◽  
Seedling Density ◽  
Old Growth ◽  
Mature Stand ◽  
Mature Stands

Types and rates of mortality were measured and canopy gap formation rates were estimated from 5- to 15-year records of mortality in 34 permanent plots in mature (100- to 150-year-old) and old-growth (>200-year-old) Douglas-fir (Pseudotsugamenziesii (Mirb.) Franco)/western hemlock (Tsugacanadensis (Raf.) Sarg.) forests in western Oregon and Washington. Gap surveys were conducted in a mature and an old-growth stand, and characteristics of 40 gaps and regeneration were measured. Most canopy trees died without disrupting the forest in both mature (87.6%) and old-growth stands (73.3%). The amount of forest area per year representing new gaps was 0.7% in mature stands and 0.2% in old-growth stands. The gap survey found a higher proportion of gaps in the mature stand than in the old-growth stand. Most regeneration (> 1 m tall) in gaps was western hemlock; Douglas-fir regeneration did not occur. The ratio of seedling density in gaps to density under canopies was about 3 for the mature stand and about 9 for the old-growth stand. Seedling density was correlated with measures of gap age but not gap size. The study suggests that gap disturbances and vegetative responses are important processes in the dynamics of these forests. However, gap formation rates and vegetative responses appear to be slow relative to other forest types. In addition to gap size, canopy structure and disturbance severity are important determinants of gap response.

Variation in canopy gap formation among developmental stages of northern hardwood stands

1996 ◽  
Vol 26 (10) ◽  
pp. 1875-1892 ◽  
Author(s):  
Sally E. Dahir ◽  
Craig G. Lorimer
Keyword(s):  
Sugar Maple ◽  
Tree Mortality ◽  
Developmental Stages ◽  
Turnover Time ◽  
Gap Formation ◽  
Old Growth ◽  
Northern Hardwood ◽  
Hardwood Species ◽  
Shade Tolerant Species ◽  
Mature Stands

Trends in gap dynamics among pole, mature, and old-growth northern hardwood stands were investigated on eight sites in the Porcupine Mountains of western upper Michigan. Recent gaps (created between 1981 and 1992) were identified using permanent plot records of tree mortality, while older gaps (1940–1981) were identified using stand reconstruction techniques. Although canopy gaps were somewhat more numerous in pole and mature stands, gaps were <25% as large as those in old-growth stands because of smaller gap-maker size, and the proportion of stand area turned over in gaps was only about half as large. Gap makers in younger stands generally had mean relative diameters (ratio of gap-maker DBH to mean DBH of canopy trees) <1.0 and were disproportionately from minor species such as eastern hophornbeam (Ostryavirginiana (Mill.) K. Koch). Gap makers in old-growth stands had mean relative diameters >1.5 and were predominantly from the dominant canopy species. Even in old-growth forests, most gaps were small (mean 44 m2) and created by single trees. Based on the identity of the tallest gap tree in each gap, nearly all shade-tolerant and midtolerant species have been successful in capturing gaps, but gap capture rates for some species were significantly different from their relative density in the upper canopy. The tallest gap trees of shade-tolerant species were often formerly overtopped trees, averaging more than 60% of the mean canopy height and having mean ages of 65–149 years. Canopy turnover times, based on gap formation rates over a 50-year period, were estimated to average 128 years for old-growth stands dominated by sugar maple (Acersaccharum Marsh.) and 192 years for old-growth stands dominated by hemlock (Tsugacanadensis (L.) Carrière). While these estimates of turnover time are substantially shorter than maximum tree ages observed on these sites, they agree closely with independent data on mean canopy residence time for trees that die at the average gap-maker size of 51 cm DBH. The data support previous hypothetical explanations of the apparent discrepancy between canopy turnover times of <130 years for hardwood species and the frequent occurrence of trees exceeding 250 years of age.

Canopy disturbances over the five-century lifetime of an old-growth Douglas-fir stand in the Pacific Northwest

2002 ◽  
Vol 32 (6) ◽  
pp. 1057-1070 ◽  
Author(s):  
Linda E Winter ◽  
Linda B Brubaker ◽  
Jerry F Franklin ◽  
Eric A Miller ◽  
Donald Q DeWitt
Keyword(s):  
Pacific Northwest ◽  
Variable Density ◽  
Tsuga Heterophylla ◽  
Douglas Fir ◽  
Western Hemlock ◽  
Old Growth ◽  
The Pacific ◽  
History Of ◽  
Horizontal Heterogeneity ◽  
Restoration Strategies

The history of canopy disturbances over the lifetime of an old-growth Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) stand in the western Cascade Range of southern Washington was reconstructed using tree-ring records of cross-dated samples from a 3.3-ha mapped plot. The reconstruction detected pulses in which many western hemlock (Tsuga heterophylla (Raf.) Sarg.) synchronously experienced abrupt and sustained increases in ringwidth, i.e., "growth-increases", and focused on medium-sized or larger ([Formula: see text]0.8 ha) events. The results show that the stand experienced at least three canopy disturbances that each thinned, but did not clear, the canopy over areas [Formula: see text]0.8 ha, occurring approximately in the late 1500s, the 1760s, and the 1930s. None of these promoted regeneration of the shade-intolerant Douglas-fir, all of which established 1500–1521. The disturbances may have promoted regeneration of western hemlock, but their strongest effect on tree dynamics was to elicit western hemlock growth-increases. Canopy disturbances are known to create patchiness, or horizontal heterogeneity, an important characteristic of old-growth forests. This reconstructed history provides one model for restoration strategies to create horizontal heterogeneity in young Douglas-fir stands, for example, by suggesting sizes of areas to thin in variable-density thinnings.

scholarly journals Vertical gradients in photosynthetic light response within an old-growth Douglas-fir and western hemlock canopy

2000 ◽  
Vol 20 (7) ◽  
pp. 447-456 ◽  
Author(s):  
J. D. Lewis ◽  
R. B. McKane ◽  
D. T. Tingey ◽  
P. A. Beedlow
Keyword(s):  
Light Response ◽  
Douglas Fir ◽  
Western Hemlock ◽  
Old Growth ◽  
Vertical Gradients

Native forest pathogens facilitate persistence of Douglas-fir in old-growth forests of northwestern California

2011 ◽  
Vol 41 (6) ◽  
pp. 1256-1266 ◽  
Author(s):  
Ashley E. Hawkins ◽  
Terry W. Henkel
Keyword(s):  
Bark Beetles ◽  
Tree Mortality ◽  
Douglas Fir ◽  
Native Forest ◽  
Gap Formation ◽  
Old Growth ◽  
Forest Pathogens ◽  
Canopy Trees ◽  
White Fir ◽  
Closed Canopy

Forest pathogens and insects can accelerate tree mortality, increase stand structural heterogeneity, and alter tree community composition. In northern California, the canopy trees Abies concolor var. lowiana (Gord. & Glend.) Lemmon (white fir) and Pseudotsuga menziesii var. menziesii (Mirbel) Franco (Douglas-fir) co-occur but vary in shade tolerance and regenerative abilities following disturbance. Field observations suggested that mortality and turnover of white fir exceeded that of Douglas-fir and that native pathogens may be important drivers in the absence of fire. Pathogens and bark beetles were sampled in old-growth white fir – Douglas-fir stands in northwestern California to assess their contribution to tree mortality, gap formation, and regeneration. We determined abundances and size class distributions of canopy trees, presence of pathogens and bark beetles, and causes of tree mortality. We sampled canopy gaps and closed-canopy forests for overstory species composition, cause of mortality of gap-maker trees, and regeneration of white fir and Douglas-fir. Root-rot fungi accounted for significantly higher mortality and gap formation in white fir than in Douglas-fir. Relative seedling–sapling density of Douglas-fir was higher in pathogen-induced canopy gaps than in closed-canopy forest. In the absence of fire, native forest pathogens enable regeneration and persistence of Douglas-fir by enhancing mortality of white fir, resulting in canopy gap formation.

Patterns of log decay in old-growth Douglas-fir forests

1987 ◽  
Vol 17 (12) ◽  
pp. 1585-1595 ◽  
Author(s):  
Phillip Sollins ◽  
Steven P. Cline ◽  
Thomas Verhoeven ◽  
Donald Sachs ◽  
Gody Spycher
Keyword(s):  
C:N Ratio ◽  
Dry Weight ◽  
Douglas Fir ◽  
Time Span ◽  
Western Hemlock ◽  
Tissue Type ◽  
Old Growth ◽  
Total N ◽  
Red Cedar ◽  
Western Red Cedar

Fallen boles (logs) of Douglas-fir (Pseudotsugamenziesii (Mirb.) Franco), western hemlock (Tsugaheterophylla (Raf.) Sarg.), and western red cedar (Thujaplicata Donn) in old-growth stands of the Cascade Range of western Oregon and Washington were compared with regard to their physical structure, chemistry, and levels of microbial activity. Western hemlock and western red cedar logs disappeared faster than Douglas-fir logs, although decay rate constants based on density change alone were 0.010/year for Douglas-fir, 0.016/year for western hemlock, and 0.009/year for western red cedar. We were unable to locate hemlock or red cedar logs older than 100 years on the ground, but found Douglas-fir logs that had persisted up to nearly 200 years. Wood density decreased to about 0.15 g/cm3 after 60–80 years on the ground, depending on species, then remained nearly constant. Moisture content of logs increased during the first 80 years on the ground, then remained roughly constant at about 250% (dry-weight basis) in summer and at 350% in winter. After logs had lain on the ground for about 80 years, amounts of N, P, and Mg per unit volume exceeded the amount present initially. Amounts of Ca, K, and Na remained fairly constant throughout the 200-year time span that was studied (100-year time span for Na). N:P ratios converged toward 20, irrespective of tree species or wood tissue type. C:N ratios dropped to about 100 in the most decayed logs; net N was mineralized during anaerobic incubation of most samples with a C:N ratio below 250. The ratio of mineralized N to total N increased with advancing decay. Asymbiotic bacteria in fallen logs fixed about 1 kg N ha−1 year−1, a substantial amount relative to system N input from precipitation and dry deposition (2–3 kg ha−1 year−1).

Growth and yield of all-aged Douglas-fir – western hemlock forest stands: a matrix model with stand diversity effects

2005 ◽  
Vol 35 (10) ◽  
pp. 2368-2381 ◽  
Author(s):  
Jingjing Liang ◽  
Joseph Buongiorno ◽  
Robert A Monserud
Keyword(s):  
Species Diversity ◽  
Matrix Model ◽  
The United States ◽  
Douglas Fir ◽  
Growth And Yield ◽  
Western Hemlock ◽  
Permanent Plots ◽  
Forest Stands ◽  
Individual Tree ◽  
Size Diversity

A density-dependent matrix model was developed for Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) – western hemlock (Tsuga heterophylla (Raf.) Sarg.) forest stands in the Pacific Northwest of the United States. The model predicted the number and volume of trees for 4 species groups and 19 diameter classes. The parameters were based on species-dependent equations linking individual tree growth, mortality, and stand recruitment to tree and stand characteristics, including stand diversity in terms of tree species and size. The equations were estimated with individual tree and stand data from 2706 permanent plots in western Washington and Oregon, largely from private and state lands, measured twice at an average interval of 10 years. Other things being equal, diameter growth increased slightly with species diversity and decreased with size diversity. Recruitment increased with species diversity and decreased with size diversity. Mortality was independent of species diversity and tended to increase with size diversity. There was practically no relationship between individual tree volume and species or size diversity. The number of trees predicted by the model over the interval between successive inventories was generally unbiased. Long-term predictions with different initial conditions were consistent with standard yield tables and compared favorably with those of the Forest Vegetation Simulator. The model also implied that, independently of its initial condition, an undisturbed stand would eventually reach a steady state dominated by western hemlock more than 1 m in diameter, with few trees of other species and size.

The importance of canopy structure in controlling the interception loss of rainfall: Examples from a young and an old-growth Douglas-fir forest

2005 ◽  
Vol 130 (1-2) ◽  
pp. 113-129 ◽  
Author(s):  
Thomas G. Pypker ◽  
Barbara J. Bond ◽  
Timothy E. Link ◽  
Danny Marks ◽  
Michael H. Unsworth
Keyword(s):  
Canopy Structure ◽  
Douglas Fir ◽  
Old Growth ◽  
Interception Loss

Leaf area index of an old-growth Douglas-fir forest estimated from direct structural measurements in the canopy

2000 ◽  
Vol 30 (12) ◽  
pp. 1922-1930 ◽  
Author(s):  
Sean C Thomas ◽  
William E Winner
Keyword(s):  
Leaf Area Index ◽  
Leaf Area ◽  
Tsuga Heterophylla ◽  
Douglas Fir ◽  
Understory Vegetation ◽  
Western Hemlock ◽  
Old Growth ◽  
Area Index ◽  
Contact Frequency ◽  
Canopy Access

Leaf area index (LAI) in old-growth Douglas-fir (Pseudotsuga menziesii var menziesii (Mirb.) Franco) forests exceeds that of any other forest ecosystem by some estimates; however, LAI determinations in coniferous forests have generally been indirect, involving extrapolations of patterns observed in younger stands. Aided by a 75-m construction crane for canopy access, we used a vertical line-intercept method to estimate LAI for a [Formula: see text]450-year-old Douglas-fir - western hemlock (Tsuga heterophylla (Raf.) Sarg.) forest in southwestern Washington state. LAI was calculated as the product of foliage contact frequency and an "extinction coefficient" accounting for foliage angular distribution, geometry, and the ratio of "interceptable" to total leaf area. LAI estimates were 9.3 ± 2.1 (estimate ± 95% confidence interval), 8.5 ± 2.2, and 8.2 ± 1.8 in 1997, 1998, and 1999, respectively, or 8.6 ± 1.1 pooled across years. Understory vegetation, including foliage of woody stems <5 cm diameter, represented 20% of this total. Sample points in which Douglas-fir was dominant had a higher total LAI than points dominated by western hemlock, including a higher LAI of understory vegetation. Our results do not support the contention that old-growth Douglas-fir - western hemlock forests maintain an appreciably higher LAI than do other forest ecosystems. Moreover, LAI in very old stands may decline as western hemlock replaces Douglas-fir through the course of succession.

Sign in / Sign up

Export Citation Format

Share Document