J. Alan Yeakley

Hillslope nutrient dynamics following upland riparian vegetation disturbance

AbstractWe investigated the effects of removing near-stream Rhododendron and of the natural blowdown of canopy trees on nutrient export to streams in the southern Appalachians. Transects were instrumented on adjacent hillslopes in a first-order watershed at the Coweeta Hydrologic Laboratory (35°03′N, 83°25′W). Dissolved organic carbon (DOC), K+, Na+, Ca2+, Mg2+, NO3−-N, NH4+-N, PO43−-P, and SO42− were measured for 2 years prior to disturbance. In August 1995, riparian Rhododendron on one hillslope was cut, removing 30% of total woody biomass. In October 1995, Hurricane Opal uprooted nine canopy trees on the other hillslope, downing 81% of the total woody biomass. Over the 3 years following the disturbance, soilwater concentrations of NO3−-N tripled on the cut hillslope. There were also small changes in soilwater DOC, SO42−, Ca2+, and Mg2+. However, no significant changes occurred in groundwater nutrient concentrations following Rhododendron removal. In contrast, soilwater NO3−-N on the storm-affected hillslope showed persistent 500-fold increases, groundwater NO3−-N increased four fold, and streamwater NO3−-N doubled. Significant changes also occurred in soilwater pH, DOC, SO42−, Ca2+, and Mg2+. There were no significant changes in microbial immobilization of soil nutrients or water outflow on the storm-affected hillslope. Our results suggest that Rhododendron thickets play a relatively minor role in controlling nutrient export to headwater streams. They further suggest that nutrient uptake by canopy trees is a key control on NO3−-N export in upland riparian zones, and that disruption of the root–soil connection in canopy trees via uprooting promotes significant nutrient loss to streams.

A Review of Urban Water Body Challenges and Approaches: (1) Rehabilitation and Remediation

AbstractWe review how urbanization alters aquatic ecosystems, as well as actions that managers can take to remediate urban waters. Urbanization affects streams by fundamentally altering longitudinal and lateral processes that in turn alter hydrology, habitat, and water chemistry; these effects create physical and chemical stressors that in turn affect the biota. Urban streams often suffer from multiple stressor effects that have collectively been termed an “urban stream syndrome,” in which no single factor dominates degraded conditions. Resource managers have multiple ways of combating the urban stream syndrome. These approaches range from whole-watershed protection to reach-scale habitat rehabilitation, but the prescription must be matched to the scale of the factors that are causing the problem, and results will likely not be immediate because of lengthy recovery times. Although pristine or reference conditions are far from attainable, urban stream rehabilitation is a worthy goal because appropriate act...

Functional morphology underlies performance differences among invasive and non-invasive ruderal Rubus species

The ability of some introduced plant species to outperform native species under altered resource conditions makes them highly productive in ecosystems with surplus resources. However, ruderal native species are also productive when resources are available. The differences in abundance among invasive and non-invasive ruderal plants may be related to differences in ability to maintain access to or store resources for continual use. For a group of ruderal species in the Pacific Northwest of North America (invasive Rubus armeniacus; non-invasive R. ursinus, R. parviflorus, R. spectabilis, and Rosa nutkana), we sought to determine whether differences in functional morphological traits, especially metrics of water access and storage, were consistent with differences in water conductance and growth rate. We also investigated the changes in these traits in response to abundant vs. limited water availability. Rubus armeniacus had among the largest root systems and cane cross-sectional areas, the lowest cane tissue densities, and the most plastic ratios of leaf area to plant mass and of xylem area to leaf area, often sharing its rank with R. ursinus or Rosa nutkana. These three species had the highest water conductance and relative growth rates, though Rubus armeniacus grew the most rapidly when water was not limited. Our results suggest that water access and storage abilities vary with morphology among the ruderal species investigated, and that these abilities, in combination, are greatest in the invasive. In turn, functional morphological traits allow R. armeniacus to maintain rapid gas exchange rates during the dry summers in its invaded range, conferring on it high productivity.

Performance of management strategies in the protection of riparian vegetation in three oregon cities

Abstract The destruction of riparian vegetation in urban areas signals the loss of valuable ecosystem services. This paper documents the extent of riparian vegetation loss during a period of rapid development (1990 – 2002) in three Oregon cities with distinctive, local management strategies. Findings show that loss has occurred in all three cities, but this loss has been curtailed by implementation of protective policies. Moreover, more than half the losses in each city were due to a few large development projects, rather than a large number of smaller ones. The paper concludes that management strategies do limit destructive actions by small projects and that large losses are potentially avoidable with targeted attention to large-scale projects.

MULTIPLE SOURCE POOLS AND DISPERSAL BARRIERS FOR GALAPAGOS PLANT SPECIES DISTRIBUTION

We reexamined geographic factors explaining the number of plant species on islands in the Galapagos Archipelago. We hypothesized that plant species richness (S) was related to the number of source pools and that plant species dispersal preferentially followed direct, oceanic pathways. To test different dispersal pathways from multiple source pools, the total number of islands within a given dispersal radius (i) was posed as the sum of the number of line-of-sight islands (C) and of the number of islands without line-of- sight connection (Bi). In partial regression analyses, controlling for nearest island area (A2) and for recipient island elevation (E) and area (lnA), Ci and Ci X E were found to be positively correlated with S in the Galapagos for nearly all dispersal ranges from 10 km to 419 km (maximum inter-island separation). In contrast, Bi X E was negatively correlated with S at the longest dispersal ranges. The connectivity index, Ci, multiplied by elevation, E, explained more variation in S in the Galapagos than prior regression models using additive forms of E, lnA, A2, and isolation from the central island. Using the variables Ci X E and lnA, multiple-regression models explained >90% of the variance in both endemic and total plant species richness in the Galapagos Archipelago.

Differential effects of understory and overstory gaps on tree regeneration

Abstract Gaps in the forest canopy can increase the diversity of tree regeneration. Understory shrubs also compete with tree seedlings for limited resources and may depress tree recruitment. We compared effects of shrub removal and canopy windthrow gaps on seedling recruitment and understory resource levels. Shrub removal, with the canopy left intact, was associated with increased levels of understory light and soil moisture and coincided with increased species richness and diversity of tree regeneration compared to both control plots and canopy gaps. Canopy windthrow gaps, however, resulted in a more than 500 fold increase in soil nitrate concentrations, and seedling growth rates that were twice as high as that observed with shrub removal. Our results suggest that gaps in the understory shrub layer and the overstory canopy may have complementary effects on resource availability with corresponding benefits to seedling establishment and growth.

FIRST-YEAR RESPONSES TO MANAGED FLOODING OF LOWER COLUMBIA RIVER BOTTOMLAND VEGETATION DOMINATED BY PHALARIS ARUNDINACEA

Managers at Smith and Bybee Wetlands Natural Area (SBW), an 800-ha preserve in Portland, Oregon, recently installed a water control structure to suppress invasive reed canarygrass (Phalaris arundinacea L.) with spring and summer flooding. We hypothesized that greater depth of flooding would decrease Phalaris growth and percent cover. We randomly established 27 transects throughout SBW before completion of the water control structure and measured percent cover of vegetation prior to flooding in autumn 2003 and then after one growing season in autumn 2004. We also monitored phenological characteristics of individual stands of reed canarygrass growing in different depths during 2004. Overall reed canarygrass cover decreased from 43.7% in 2003 to 41.2% in 2004 (McNemar’s test; p < 0.001). Where inundation was > 0.85 m, reed canarygrass cover declined 6.1%. Where this deeper inundation coincided with regenerating willow forest, reed canarygrass cover declined 10.7%. Both before and after higher inundation, reed canarygrass cover was negatively correlated with plant species diversity (before: Spearman’s rho = −0.67, p < 0.001; after: Spearman’s rho = −0.41, p = 0.036). Cover of several native taxa (e.g., Polygonum spp., Bidens spp., Salix lucida) increased in 2004. After flooding, reed canarygrass stands grew more slowly and changed their structural growth pattern. These findings suggest that managed flooding might be operationally useful in suppressing reed canarygrass.

A Review of Urban Water Body Challenges and Approaches: (2) Mitigating Effects of Future Urbanization

AbstractPreviously we examined how degraded urban streams can be rehabilitated, with emphasis on identifying solutions that match the scale of the problems (Hughes et al. 2014). Our findings showed that rehabilitation techniques are challenging but that some environmental benefits can nearly always be obtained regardless of existing conditions. Although rehabilitation is useful in many present-day situations, biologists need to consider the future and think about ways of preventing or reducing future environmental damage. We need to reduce future damage because urban areas are likely to expand greatly over the next century; if historical patterns continue, the number and length of streams experiencing urban stream syndrome will increase, with resulting high repair costs. However, there are several ways of avoiding or mitigating damage that are not only cost effective but provide benefits to humans and urban ecosystems.

Combining and aggregating environmental data for status and trend assessments: challenges and approaches

Increasingly, natural resource management agencies and nongovernmental organizations are sharing monitoring data across geographic and jurisdictional boundaries. Doing so improves their abilities to assess local-, regional-, and landscape-level environmental conditions, particularly status and trends, and to improve their ability to make short- and long-term management decisions. Status monitoring assesses the current condition of a population or environmental condition across an area. Monitoring for trends aims at monitoring changes in populations or environmental condition through time. We wrote this paper to inform agency and nongovernmental organization managers, analysts, and consultants regarding the kinds of environmental data that can be combined with suitable techniques and statistically aggregated for new assessments. By doing so, they can increase the (1) use of available data and (2) the validity and reliability of the assessments. Increased awareness of the difficulties inherent in combining and aggregating data for local- and regional-level analyses can increase the likelihood that future monitoring efforts will be modified and/or planned to accommodate data from multiple sources.

Seedling Regeneration in the Alpine Treeline Ecotone: Comparison of Wood Microsites and Adjacent Soil Substrates

Although climate warming is generally expected to facilitate upward advance of forests, conifer seedling regeneration and survival may be hindered by low substrate moisture, high radiation, and both low and high snow accumulation. To better understand substrate-related factors promoting regeneration in the alpine treeline ecotone, this study compared 2 substrates supporting conifer seedlings: rotten downed wood and adjacent soil. Study locations, each with 3 levels of incoming radiation, were randomly selected at forest line–alpine meadow borders in Pacific Northwest wilderness areas extending along an east–west precipitation gradient. Associations among substrate type, seedling density, radiation, site moisture, site temperature, plant water potential, and plant stomatal conductance were assessed. Wood microsites, flush with the ground and supporting Abies spp conifer seedlings, extended up to 20 m into alpine meadows from the forest line. Although wood microsites thawed later in the spring and froze earlier in the fall, they had warmer summer temperatures, greater volumetric water content, and more growing degree hours, and seedlings growing on wood had higher water potentials than seedlings growing on adjacent soil. At drier eastern sites, there was a positive relationship between seedling density and volumetric water content. Further, there was a positive relationship between seedling stomatal conductance and volumetric water content. Our study indicates that in the Pacific Northwest. and likely elsewhere, seedlings benefit from wood microsites, which provide greater water content. Given predictions of increased summer drought in some locations globally, wood microsites at forest line–alpine meadows and forest line–grasslands borders may become increasingly important for successful conifer regeneration.