More info for the term: mesic
Pacific rhododendron is found in coastal to low montane conifer forests
on soils that are moist but well drained and frequently shallow
[3,21,52,62]. Many western Oregon sites with Pacific rhododendron as a
dominant have soils with low levels of available nitrogen [22,27,26].
Pacific rhododendron grows in several Pacific Northwest forest zones
[15].
The Sitka spruce (Picea sitchensis) zone forms a narrow band along the
coast. In this uniformly wet and frequently foggy area, Pacific
rhododendron is often found on less favorable sites [15]. On old sand
dunes and steep slopes facing the ocean Pacific rhododendron forms
thickets with salal (Gaultheria shallon) and evergreen huckleberry
(Vaccinium ovatum) [15,43]. At the southern end of this zone and
extending into northern California, Pacific rhododendron is a dominant
under coastal redwood (Sequoia sempervirens) and tanoak (Lithocarpus
densiflorus) on soils formed from sandy coastal plain deposits
[1,15,16]. It is part of the understory of northern California's pygmy
conifer forests on severely podzolized soils formed from similar
deposits [55].
While the western hemlock zone is wet and mild, summer drought and
temperature extremes are more common than in the Sitka spruce zone.
Pacific rhododendron is found on intermediate mesic sites in this zone
along the coast [15]. In this zone in the northern Cascades Pacific
rhododendron is most dominant on cooler, dry to mesic sites [22]. In
the central Cascades it can be found on most types of sites within the
western hemlock zone, although it dominates on warmer and drier sites
[12,59]. In this zone in the southern Siuslaw National Forest of the
Coast ranges, Pacific rhododendron is often a dominant on south-facing
slopes and lower elevation ridges with thin soils [27]. In the western
hemlock subzone where Port-Orford-cedar (Chamaecyparis lawsoniana) is a
dominant, communities containing Pacific rhododendron are typically on
better drained soils [24]. It is often found under mesic
Port-Orford-cedar - Douglas-fir (Pseudotsuga menziesii) forests on the
west slope of the Siskiyou Mountains at low to middle elevations on
diorite parent materials [56].
In the higher, wetter and cooler mountain hemlock (Tsuga mertensiana)
and silver fir (Abies amabilis) zones, Pacific rhododendron is an
understory dominant on relatively warm, dry soils at lower elevations
within the type [12,15,28].
In the mixed-conifer zone Pacific rhododendron is found on the moistest
sites at mid-elevations in the southern Cascade and eastern Siskiyou
Mountains. Average temperatures in this zone are similar to those in
the western hemlock zone but the summers are warmer and drier [15]. In
the South Umpqua Basin of the southern Cascades in Oregon, Pacific
rhododendron is a good indicator of high soil moisture [37]. It occurs
on cool, moist sites with soils averaging 40 inches (101.6 cm) deep in
the Siskiyou Mountains [1]. On the east side of the Siskiyous, it grows
with Douglas-fir where site conditions are most similar to coastal
conditions. It is at its environmental limit on these sites and does
not extend to drier sites [1].
Elevational ranges in some western regions are [15,28,41,56]:
Minimum Maximum
feet meters feet meters
California sea level 4,000 1,219
c Siskiyou Mts 2,500 670 5,500 1,680
Oregon sea level 5,300 1,615