Fire catalyzed rapid ecological change in lowland coniferous forests of the Pacific Northwest over the past 14,000 years.

Disturbance can catalyze rapid ecological change by causing widespread mortality and initiating successional pathways, and during times of climate change, disturbance may contribute to ecosystem state changes by initiating a new successional pathway. In the Pacific Northwest of North America (PNW), disturbance by wildfires strongly shapes the composition and structure of lowland forests, but understanding the role of fire over periods of climate change is challenging, because fire-return intervals are long (e.g.

Spatial aspects of tree mortality strongly differ between young and old-growth forests.

Rates and spatial patterns of tree mortality are predicted to change during forest structural development. In young forests, mortality should be primarily density dependent due to competition for light, leading to an increasingly spatially uniform pattern of surviving trees. In contrast, mortality in old-growth forests should be primarily caused by contagious and spatially autocorrelated agents (e.

Morphological acclimation to understory environments in Abies amabilis, a shade- and snow-tolerant conifer species of the Cascade Mountains, Washington, USA.

Light-related plasticity in a variety of crown morphology and within-tree characteristics was examined in sun and shade saplings of Abies amabilis Dougl. ex J. Forbes growing in two late-successional forests with different snow regimes in the Cascade Mountains of Washington, USA.

Boundary layer conductance, leaf temperature and transpiration of Abies amabilis branches.

We used three methods to measure boundary layer conductance to heat transfer (g(bH)) and water vapor transfer (g(bV)) in foliated branches of Abies amabilis Dougl. ex J. Forbes, a subalpine forest tree that produces clumped shoot morphology on sun-formed branches.

Shoot structure, light interception, and distribution of nitrogen in an Abies amabilis canopy.

We studied the effects of variation in shoot structure and needle morphology on the distributions of light and nitrogen within a Pacific silver fir (Abies amabilis (Dougl.) Forbes) canopy. Specifically, we investigated the role of morphological shade acclimation in the determination of resource use efficiency, which is claimed to be optimal when the distribution of nitrogen within the canopy is directly proportional to the distribution of intercepted photosynthetically active radiation (PAR).

When branch autonomy fails: Milton's Law of resource availability and allocation.

The branch autonomy principle states that the critical characteristics of a branch's carbohydrate economy (photosynthesis, respiration, growth, etc.) are largely independent of the tree to which the branch is attached, as long as light is the primary factor limiting photosynthesis and growth. However, this may not be generally true because in the spring, photosynthates are translocated from a tree stem into branches, and the amount of photosynthate available for translocation should be a function of the tree's canopy status.

The effects of light acclimation during and after foliage expansion on photosynthesis ofAbies amabilis foliage within the canopy.

Variation in the photosynthetic function ofAbies amabilis foliage within a canopy was examined and related to three different processes that affect foliage function: foliage aging, sun-shade acclimation that occurred while foliage was expanding, and reacclimation after expansion was complete. Foliage produced in the sun had higher photosynthesis at light saturation (A , μmol·m·s), dark respiration (μmol·m·s), nitrogen content (g·m), chlorophyll content (g·m), and chlorophylla:b ratio, and a lower chlorophyll to nitrogen ratio (chl:N), than foliage produced in the shade. As sun foliage becomes shaded, it becomes physiologically similar to shade foliage, even though it still retains a sun morphology.