Understorey plant community structure in lower montane and subalpine forests, Grand Canyon National Park, USA

Abstract

Aim Our objectives were to compare understorey plant community structure among forest types, and to test hypotheses relating understorey community structure within lower montane and subalpine forests to fire history, forest structure, fuel loads and topography.Location Forests on the North Rim of Grand Canyon National Park, Arizona, USA.Methods We measured understorey (< 1.4 m) plant community structure in 0.1-ha plots. We examined differences in univariate response variables among forest types, used permutational manova to assess compositional differences between forest types, and used indicator species analysis to identify species driving the differences between forest types. We then compiled sets of proposed models for predicting plant community structure, and used Akaike's information criterion (AIC C ) to determine the support for each model. Model averaging was used to make multi-model inferences if no single model was supported.Results Within the lower montane zone, pine-oak forests had greater understorey plant cover, richness and diversity than pure stands of ponderosa pine (Pinus ponderosa P. & C. Lawson var. scopulorum Engelm.). Plant cover was negatively related to time since fire and to ponderosa pine basal area, and was highest on northern slopes and where Gambel oak (Quercus gambelii Nutt.) was present. Species richness was negatively related to time since fire and to ponderosa pine basal area, and was highest on southern slopes and where Gambel oak was present. Annual forb species richness was negatively related to time since fire. Community composition was related to time since fire, pine and oak basal area, and topography. Within subalpine forests, plant cover was negatively related to subalpine fir basal area and amounts of coarse woody debris (CWD), and positively related to Engelmann spruce basal area. Species richness was negatively related to subalpine fir basal area and amounts of CWD, was positively related to Engelmann spruce basal area, and was highest on southern slopes. Community composition was related to spruce, fir and aspen basal areas, amounts of CWD, and topography.Main conclusions In montane forests, low-intensity surface fire is an important ecological process that maintains understorey communities within the range of natural variability and appears to promote landscape heterogeneity. The presence of Gambel oak was positively associated with high floristic diversity. Therefore management that encourages lightning-initiated wildfires and Gambel oak production may promote floristic diversity. In subalpine forests, warm southern slopes and areas with low amounts of subalpine fir and CWD were positively associated with high floristic diversity. Therefore the reduction of CWD and forest densities through managed wildfire may promote floristic diversity, although fire use in subalpine forests is inherently more difficult due to intense fire behaviour in dense spruce-fir forests.

Implication of forest zonation on tree species composition, diversity and structure in Mabira Forest, Uganda

“…Such a condition also could have been resulted from little canopy opening that affecting undergrowth and regeneration. According to Laughlin et al (2005) and Giliba et al ( 2011),one of the factors associated with this difference in population structure could be anthropogenic activities. Similarly, frequent human interference could lead in disturbing the ecosystem, community, or population structure and changes resources availability (Chapman et al 1997;Pickett and White 1999).…”

“…The low woody species diversity obtained from the production zone could be due to the excessive wood harvesting practice exhibited by the local community; as evidenced we visualized charcoal burning activities carried out in this zone (personal observation). Laughlin et al (2005)studied the effect of various types of disturbance on species diversity and had investigated their negative implication on species diversity. The higher evenness index value obtained from the strict nature zone and buffer zone indicated an even distribution of species in this management zone.…”

Restoring plant species diversity and community composition in a ponderosa pine-bunchgrass ecosystem

“…Bakker). A separate ISA was conducted for each year, and results were combined using meta-analytical techniques (Bakker 2005). For a given species in a given group, the IVs from every year, that it occurred, were averaged to yield a mean IV, and the associated P-values were combined using a weighted Z-transform (Whitlock 2005).…”

The Role of Old-growth Forests in Frequent-fire Landscapes

“…A very few sites, such as the Powell Plateau in the Grand Canyon and some regions of northern Mexico, may have experienced so little change in land use and fire regimes that contemporary measurements are possible (Fulé et al 2005). Some of the most detailed insights about the structure and function of old-growth forests come from intensive experiments that have reestablished historic forest structure.…”

“…This relationship between the density of trees and understory diversity is further influenced by the number of years between fires (the fire return interval). For example, a ponderosa pine forest on the Kaibab Plateau that burned in the past 10 years might have 35 species in the understory, compared with 28 species after 70 years without a fire, and 22 species after 120 years without a fire (Laughlin et al 2005).…”