Name:
Pinus ponderosa var. ponderosa - Pseudotsuga menziesii - Pinus flexilis Central Rocky Mountain Dry Forest Macrogroup
Reference:
NatureServe Biotics 2019
Description:
This macrogroup comprises conifer forests, woodlands and savannas found on dry settings of the lower montane to foothill zones of the interior Pacific Northwest, and extending east into the northwestern Great Plains regions. It is generally dominated by <i>Pinus ponderosa var. ponderosa</i> or <i>Pinus ponderosa var. scopulorum, Pseudotsuga menziesii, Pinus flexilis</i>, or <i>Juniperus osteosperma</i> or <i>Juniperus scopulorum</i>. Other occasional trees may include <i>Pinus contorta, Picea engelmannii, Picea glauca</i> (or their hybrid), and in the Great Plains, deciduous trees such as <i>Acer negundo, Betula papyrifera, Fraxinus pennsylvanica, Populus tremuloides, Quercus macrocarpa</i>, and <i>Ulmus americana</i>. Shrub and herbaceous components are widely variable, ranging from taxa found in the Great Plains mixedgrass region (such as <i>Andropogon gerardii, Juniperus horizontalis, Prunus</i> spp., <i>Schizachyrium scoparium</i>, or <i>Yucca glauca</i>) to those found across the Northern Rockies region into the eastern Cascades (e.g., <i>Amelanchier alnifolia, Arctostaphylos uva-ursi, Artemisia</i> spp., <i>Cercocarpus</i> spp., <i>Juniperus communis, Physocarpus malvaceus, Spiraea betulifolia, Symphoricarpos</i> spp., and graminoids such as <i>Achnatherum</i> spp., <i>Bouteloua gracilis, Calamagrostis rubescens, Carex geyeri, Carex inops, Festuca idahoensis, Hesperostipa comata, Koeleria macrantha, Piptatheropsis micrantha, Poa secunda</i>, or <i>Pseudoroegneria spicata</i>). This is a very wide-ranging macrogroup; it has common substrate and soil characteristics across its range, but from west to east shifts from a climate regime moderately influenced by maritime air masses, to one that is entirely continental. Generally these communities occur in lower montane to foothill settings, or on rock outcrops in the mixedgrass region of the Great Plains. Occurrences are found on all slopes and aspects; however, moderately steep to very steep slopes or ridgetops and plateaus are most common. Substrates tend to be composed of limestone, sandstone, dolomite, granite, colluvium, unweathered lava flows, pumice, cinders, or eolian sands. In most cases soil features include good aeration and drainage, coarse textures, circumneutral to slightly acidic pH, an abundance of mineral material, and periods of drought during the growing season.<br /><br />Most of the communities in this macrogroup are fire-dependent types. Presettlement fire regimes may have been characterized by frequent, low-intensity surface fires that maintained relatively open stands of a mix of fire-resistant species. <i>Pseudotsuga menziesii</i> forests were probably subject to a moderate-severity fire regime in presettlement times, with fire-return intervals of 30-100 years. Many of the important tree species in these forests and woodlands are fire-adapted (<i>Populus tremuloides, Pinus ponderosa, Pinus contorta</i>), and fire-induced reproduction of <i>Pinus ponderosa</i> can result in its continued codominance in <i>Pseudotsuga menziesii</i> forests. A subset of the macrogroup includes woodlands and scrub patches that are edaphically controlled rather than fire-dependent. In the limber pine - juniper woodlands, fire is infrequent and spotty because the rocky substrates prevent development of a continuous vegetation canopy needed to spread fire. In other locations, where ponderosa pine is the predominant tree, periodic drought or areas of sand dunes, scablands, and pumice limit tree establishment. This climate-edaphic interaction results in widely scattered trees over "shrub-steppe" of sagebrush, bitterbrush, or sparsely distributed grasses. Tree growth is likely episodic, with regeneration episodes in years with available moisture. The expansion of <i>Pinus ponderosa</i> woodlands from the Black Hills montane zone into the central Great Plains may be due to fire suppression.
Accession Code:
urn:lsid:vegbank.org:commConcept:40801-{456B3B8E-9A88-4EB2-B8F4-0AB50E2628E6}
Plot-observations of this Community Concept:
0
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