Treesearch

Extended rotations have been suggested as a strategy for balancing timber production and ecological objectives. By lengthening the period of stand development, extended rotations may increase tree size inequality and other elements of structural complexity, thus reducing the disparity between managed and old-growth stands. A potential limitation of extended rotations is the tradeoff between reduced stand-level productivity and greater large-tree growth that typically occurs with stand age. The mechanisms driving this tradeoff have not been fully explored. To fill this knowledge gap, we...

Wetlands self-organize through reciprocal controls between vegetation and hydrology, but external disturbance may disrupt these feedbacks with consequent changes to ecosystem state. Imminent and widespread emerald ash borer (EAB) infestation throughout North American forested wetlands has raised concern over possible ecosystem state shifts (i.e., wetter, more herbaceous systems) and loss of forest function, calling for informed landscape-scale management strategies. In response, we employed a large-scale manipulative study to assess the ecohydrologic response of black ash wetlands to three...

Gradient studies of wetland forests have inferred that competition from upland tree species confines waterloggingtolerant tree species to hydric environments. Little is known, however, about competition effects on individual-tree growth along stress gradients in wetland forests. We investigated tree growth and competition in mixed-species stands representing a waterlogging stress gradient in Fraxinus nigra Marsh. (black ash) forests in Minnesota, USA. Using competition indices, we examined how F. nigra basal area increment (BAI) responded to competition along the gradient and whether...

Scientists, land managers, government, and private institutions in the United States have given much attention to invasive control and restoration projects along western rivers; in the West, removal of Tamarix spp. (tamarisk, saltcedar) has been a primary focus of these projects (Dennison et al. 2009; González et al. 2017a; Harms and Hiebert 2006; Shafroth et al. 2008). These trees were first introduced to North America during the 1800s from Eurasia mainly to decrease erosion, to be wind breaks, and to slow down water flow in riparian and agriculture areas (DiTomaso 1998). Since that time,...

It is well known that nonnative tamarisk (Tamarix parviflora, T. ramosissima, T. chinensis, and their hybrids; a.k.a. saltcedar) has replaced native riparian woodland vegetation along many streams in the arid Southwest over the last 100 years. Tamarisk can form extensive, dense monocultures and may alter not only the physical structure of the riparian woodland but also soil salinity and fire frequency (Sher 2013). There is significant debate, however, over whether tamarisk is the driver or a passenger of ecological change (Johnson 2013). The decline in the numbers and range of native...

Riparian ecosystems provide the anchor for their associated aquatic habitats and the structure for a unique assemblage of life found in these exceptionally productive ecosystems. Much of upland life also is tied to this zone, particularly in arid regions. For instance, on National Forest lands in the Southwest Region, 57 percent of all vertebrates occur in riparian ecosystems, but these systems make up < 2 percent of these lands (Rickel 2005a). However, it has been estimated that 90 percent of riparian ecosystems have been lost or degraded in parts of the western United States through...

Euro-American (EA) beaver trapping was a regional and watershed-scale disturbance that occurred across the North American continent. This concentrated removal of beavers altered drainages by creating thousands of localized base-level drops as beaver dams failed and were not repaired. These base-level drops led to the development of channels as ponds drained and water eroded the fine sediment trapped behind the dams (Dobyns 1981; Fouty 1996, 2003; Parker et al. 1985). The speed at which drainages transformed from beaver-dominated to channel-dominated varied as a function of climate, upland...

Prior to human development in the West, rivers flowed freely. Flows in the Colorado River varied greatly with season, with snowmelt runoff from the Rocky Mountains resulting in annual high flows (Topping et al. 2003). The large sediment loads historically found in the Colorado River, estimated to average 160,000,000 tons passing Yuma annually (LaRue 1916), have since caused Laguna Dam (fig. 23) near Yuma, Arizona, completed in 1905, to silt in almost immediately. Even in a managed system, unpredictable unmeasured tributary inflow into the Colorado River below Hoover Dam accounts for...

Much of what we know about the functional ecology of aquatic and riparian ecosystems comes from work on regulated rivers (Johnson et al. 2012). What little we know about unregulated conditions on many of our larger rivers is often inferred from recollections of individuals, personal diaries, notes, maps, and collections from early scientific surveys (Webb et al. 2007) and from repeat photography (Turner and Karpiscak 1980; Webb 1996). Later surveys often included photographs typically taken at specific and relatively few locations. Because rivers and their related riparian ecosystems vary...

Once a mighty and wild river with abundant wetlands, the section of the Colorado River flowing through Mexico has become a trickle ... whenever it flows. Most of the time since the 1960s, until recently, it did not and was completely dry. This brought tremendous changes in the "original" constitution and biological processes of the region, although they have not been fully investigated.