In many forested ecosystems, the architecture and functional ecology of certain tree species define forest structure and their species‐specific traits control ecosystem dynamics. Such foundation tree species are declining throughout the world due to introductions and outbreaks of pests and pathogens, selective removal of individual taxa, and over‐harvesting. Through a series of case studies, we show that the loss of foundation tree species changes the local environment on which a variety of other species depend; how this disrupts fundamental ecosystem processes, including rates of decomposition, nutrient fluxes, carbon sequestration, and energy flow; and dramatically alters the dynamics of associated aquatic ecosystems. Forests in which dynamics are controlled by one or a few foundation species appear to be dominated by a small number of strong interactions and may be highly susceptible to alternating between stable states following even small perturbations. The ongoing decline of many foundation species provides a set of important, albeit unfortunate, opportunities to develop the research tools, models, and metrics needed to identify foundation species, anticipate the cascade of immediate, short‐ and long‐term changes in ecosystem structure and function that will follow from their loss, and provide options for remedial conservation and management.
Accurately quantifying evapotranspiration (ET) is essential for modelling regional-scale ecosystem water balances. This study assembled an ET data set estimated from eddy flux and sapflow measurements for 13 ecosystems across a large climatic and management gradient from the United States, China, and Australia. Our objectives were to determine the relationships among monthly measured actual ET (ET), calculated FAO-56 grass reference ET (ET o ), measured precipitation (P), and leaf area index (LAI)-one associated key parameter of ecosystem structure. Results showed that the growing season ET from wet forests was generally higher than ET o while those from grasslands or woodlands in the arid and semi-arid regions were lower than ET o . Second, growing season ET was found to be converged to within š10% of P for most of the ecosystems examined. Therefore, our study suggested that soil water storage in the nongrowing season was important in influencing ET and water yield during the growing season. Lastly, monthly LAI, P, and ET o together explained about 85% of the variability of monthly ET. We concluded that the three variables LAI, P, and ET o , which were increasingly available from remote sensing products and weather station networks, could be used for estimating monthly regional ET dynamics with a reasonable accuracy. Such an empirical model has the potential to project the effects of climate and land management on water resources and carbon sequestration when integrated with ecosystem models.
[1] Shallow landslides are a significant hazard in steep, soil-mantled landscapes. During intense rainfall events, the distribution of shallow landslides is controlled by variations in landscape gradient, the frictional and cohesive properties of soil and roots, and the subsurface hydrologic response. While gradients can be estimated from digital elevation models, information on soil and root properties remains sparse. We investigated whether geomorphically controlled variations in ecology affect the spatial distribution of root cohesion by measuring the distribution and tensile strength of roots from soil pits dug downslope of 15 native trees in the southern Appalachian Mountains, North Carolina, United States. Root tensile strengths from different hardwood tree species were similar and consistently higher than the only native shrub species measured (Rhododendron maximum). Roots were stronger in trees found on noses (areas of divergent topography) relative to those in hollows (unchanneled, convergent topography) coincident with the variability in cellulose content. This cellulose variability is likely related to topographic differences in soil water potential. For all species, roots were concentrated close to the soil surface, with roots in hollows being more evenly distributed in the soil column than those on noses. Trees located on noses had higher mean root cohesion than those in hollows because of a higher root tensile force. R. maximum had the shallowest, weakest roots suggesting that recent expansion of this species due to fire suppression has likely lowered the root cohesion of some hollows. Quantification of this feedback between physiologic controls on root growth and slope hydrology has allowed us to create a curvature-based model of root cohesion that is a significant improvement on current models that assume a spatially averaged value.
Analyses of long-term records at 35 headwater basins in the United States and Canada indicate that climate change effects on streamflow are not as clear as might be expected, perhaps because of ecosystem processes and human influences. Evapotranspiration was higher than was predicted by temperature in water-surplus ecosystems and lower than was predicted in water-deficit ecosystems. Streamflow was correlated with climate variability indices (e.g., the El Nino-Southern Oscillation, the Pacific Decadal Oscillation, the North Atlantic Oscillation), especially in seasons when vegetation influences are limited. Air temperature increased significantly at 17 of the 19 sites with 20-to 60-year records, but streamflow trends were directly related to climate trends (through changes in ice and snow) at only 7 sites. Past and present human and natural disturbance, vegetation succession, and human water use can mimic, exacerbate, counteract, or mask the effects of climate change on streamflow, even in reference basins. Long-term ecological research sites are ideal places to disentangle these processes.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
customersupport@researchsolutions.com
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
This site is protected by reCAPTCHA and the Google Privacy Policy and Terms of Service apply.
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.