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

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 15001521. 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.

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

Canadian Journal of Forest Research ◽

10.1139/x87-243 ◽

1987 ◽

Vol 17 (12) ◽

pp. 1585-1595 ◽

Cited By ~ 138

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).

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Estimating the weight of crown segments for old-growth Douglas-fir and western hemlock.

10.2737/pnw-rp-329 ◽

1985 ◽

Cited By ~ 1

Author(s):

J.A. Kendall Snell ◽

Timothy A. Max

Keyword(s):

Douglas Fir ◽

Western Hemlock ◽

Old Growth

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

Canadian Journal of Forest Research ◽

10.1139/x00-121 ◽

2000 ◽

Vol 30 (12) ◽

pp. 1922-1930 ◽

Cited By ~ 58

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.

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Coarse woody debris and soil respiration in a clearcut on the Olympic Peninsula, Washington, U.S.A.

Canadian Journal of Forest Research ◽

10.1139/x26-149 ◽

1996 ◽

Vol 26 (8) ◽

pp. 1337-1345 ◽

Cited By ~ 48

Author(s):

James L. Marra ◽

Robert L. Edmonds

Keyword(s):

Soil Respiration ◽

Respiration Rate ◽

Coarse Woody Debris ◽

Woody Debris ◽

Douglas Fir ◽

Western Hemlock ◽

Olympic Peninsula ◽

Old Growth ◽

Growth Site ◽

Respiration Rates

Coarse woody debris (CWD) and soil respiration rates were measured using soda lime traps on a clearcut site in the Hoh River Valley on the west side of the Olympic Peninsula, Washington. The influence of species of CWD (western hemlock (Tsugaheterophylla (Raf.) Sarg.) and Douglas-fir (Pseudotsugamenziesii (Mirb.) Franco)), decay class, and log diameter on respiration rates was determined. CWD and soil respiration were measured every 4 weeks from October 1991 to November 1992 along with CWD and soil temperature and moisture contents. Western hemlock logs respired at a significantly higher rate (4.05 g CO2•m−2•day−1) than Douglas-fir logs (2.94 g CO2•m−2•day−1). There were no significant differences between respiration rates for decay classes 1–2, 3, and 5 logs (4.47, 3.69, and 4.28 g CO2•m−2•day−1, respectively), and there was no strong relationship between CWD respiration rate and log diameter. The highest average respiration rate was from the soil in the clearcut (5.22 g CO2•m−2•day−1). Averaged for the year, log and soil respiration rates in the clearcut site were similar to those in an adjacent old-growth forested site. However, seasonal fluctuations were greater on the clearcut site. Higher summer respiration rates and lower winter rates observed on the clearcut relative to the old-growth site appeared to be driven more by temperature than by moisture. Clear-cutting also resulted in higher summer CWD and soil temperatures and lower winter temperatures compared with the old-growth site.

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Tree species and soil nutrient profiles in old-growth forests of the Oregon Coast Range

Canadian Journal of Forest Research ◽

10.1139/x10-199 ◽

2011 ◽

Vol 41 (1) ◽

pp. 195-210 ◽

Cited By ~ 13

Author(s):

Alison Cross ◽

Steven S. Perakis

Keyword(s):

Tree Species ◽

Forest Floor ◽

Mineral Soil ◽

Soil Nutrient ◽

Douglas Fir ◽

Western Hemlock ◽

Coast Range ◽

Old Growth ◽

Oregon Coast Range ◽

Old Growth Forests

Old-growth forests of the Pacific Northwest provide a unique opportunity to examine tree species – soil relationships in ecosystems that have developed without significant human disturbance. We characterized foliage, forest floor, and mineral soil nutrients associated with four canopy tree species (Douglas-fir (Pseudotsuga menziesii (Mirbel) Franco), western hemlock (Tsuga heterophylla (Raf.) Sarg.), western redcedar (Thuja plicata Donn ex D. Don), and bigleaf maple (Acer macrophyllum Pursh)) in eight old-growth forests of the Oregon Coast Range. The greatest forest floor accumulations of C, N, P, Ca, Mg, and K occurred under Douglas-fir, primarily due to greater forest floor mass. In mineral soil, western hemlock exhibited significantly lower Ca concentration and sum of cations (Ca + Mg + K) than bigleaf maple, with intermediate values for Douglas-fir and western redcedar. Bigleaf maple explained most species-based differences in foliar nutrients, displaying high concentrations of N, P, Ca, Mg, and K. Foliar P and N:P variations largely reflected soil P variation across sites. The four tree species that we examined exhibited a number of individualistic effects on soil nutrient levels that contribute to biogeochemical heterogeneity in these ecosystems. Where fire suppression and long-term succession favor dominance by highly shade-tolerant western hemlock, our results suggest a potential for declines in both soil Ca availability and soil biogeochemical heterogeneity in old-growth forests.

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