Fine roots and rhizomorphs have important implications for the global carbon balance, but the processes underlying these carbon sinks are not well understood. In this study, we coupled continuous minirhizotron observations with an array of solid-state CO2 sensors. We calculated soil respiration using a gradient flux method. Using a Kaplan-Maier survival analysis, we determined a median longevity of 347 d for fine roots and of 400 d for rhizomorphs. Radiocarbon (14C) analysis suggested an age of 7 yr for fine roots <1 mm and 17 yr for roots of 1 mm in diameter. We found rapid changes in root length (maximum of 38.1 cm m–2 d–1) and rhizomorph length (maximum of 105.4 cm m–2 d–1) during sampling of four consecutive days. Changes in rhizomorph length were more variable than root length, and rhizomorphs were negatively correlated with daily changes in soil moisture. The variation in root length may be associated to prior environmental conditions. Fine root length was correlated with daily CO2 production, and variation in daily fine root length could contribute up to 4680 g C ha–1 d–1. We observed a clockwise diurnal hysteresis effect in soil respiration with soil temperature that changed in amplitude and shape along the year. Our results show the importance of shorter intervals of minirhizotron measurements to understand rapid fine roots and rhizomorphs variation. Furthermore, continuous minirhizotron measurements should be couple with continuous measurements of multiple sensor arrays to explain biophysical factors that regulate belowground carbon dynamics.

Hurricanes are infrequent disturbances that affect tropical ecosystems and cause obvious damage on aboveground variables, but their impact on soil respiration is unclear. This study is the first attempt to continuously measure soil CO2 concentrations in a seasonally dry tropical forest to describe diel patterns of soil CO2 and respiration. Here we used solid-state CO2 sensors and the gradient flux method to calculate soil respiration following the unexpected pass of hurricaneWilma at the Yucata´n Peninsula, Mexico. Mean annual soil respiration for the year following the hurricane was 10.4 mmol CO2m-2 s-1 with a cumulative soil respiration of 3821 g CO2 m-2 a-1. Soil CO2 concentrations returned to prehurricane levels after 6 months at 16 cm depth, however, soil CO2 remained higher at 2 and 16 cm depth 1 year after the event. Contrary to previous studies, our results showed that soil respiration was 18% higher 1 year after the hurricane than during the same dates before the event. Diel patterns of soil respiration were decoupled from soil temperature with higher values at night between 2400 and 0600 h. Between 67 and 70% of total soil respiration was produced in the 2–8 cm layer, and this contribution was relatively constant across the sampled year and before the hurricane.We found seasonal shifts in the amplitude and shape and of diel hysteresis effects of soil respiration suggesting that other biophysical mechanisms regulate daily patterns of soil respiration other than soil temperature alone in this tropical forest.

California deserts are faced with unprecedented anthropogenic change. Impact factors range from expanding urban centers and military bases, to potential significant habitat loss from solar and thermal power expansions (including ground water exploitation and depletion beyond recovery, land stripping for power generation units, and fragmentation from power and associated transportation corridors), and climate change. Together these factors threaten remaining suitable habitat for endangered and for other endemic desert species. Our goal here is to outline the scope of environmental changes that are underway, and to outline research needs necessary to provide long-term sustainability of federally- and state-listed species and their habitats, ensuring that energy developments are also fully compliant with the letter and intent of state and federal resource protection statutes. We identified several topic areas that are of concern to land managers and project developers in the California deserts. These represent topic areas badly in need of research using state-of-the-art techniques coupled with known expertise, tailored to the desert areas to be impacted by the proposed developments.

The recovery plan for the California red-legged frog was reviewed. There are two main elements for our region in southern California. The first is the designation of critical habitat for recovery of this species. We suggest that the criteria for designation of critical habitat should be explicitly defined and listed. The map boundaries should then result from those criteria. This would reduce the maps to those specific areas with habitat in which recovery efforts could be made. Requiring large regions to await evaluation on an individual project basis undermines the support for the ESA and creates controversy where likely none should exist. The second element is restoration of the populations. While we support this effort, we are concerned with the use of extensive substrate disturbance in the survey for exotic pest species and the restrictive use of a single “genotype” used in recovery. Instead of seining to remove pests, we recommend careful evaluation of the literature with targeted research toward the different pests. We further suggest that having both Baja and LA populations is probably more appropriate and provides a better chance for having a survivable population.

• Characterization of spatial and temporal variation of soil respiration coupled with fine root and rhizomorph dynamics is necessary to understand the mechanisms that regulate soil respiration.

• A dense wireless network array of soil CO2 sensors in combination with minirhizotron tubes was used to continuously measure soil respiration over 1 yr in a mixed conifer forest in California, USA, in two adjacent areas with different vegetation types: an area with woody vegetation (Wv) and an area with scattered herbaceous vegetation (Hv).

• Annual soil respiration rates and the lengths of fine roots and rhizomorphs were greater at Wv than at Hv. Soil respiration was positively correlated with fine roots and rhizomorphs at Wv but only with fine roots at Hv. Diel and seasonal soil respiration patterns were decoupled with soil temperature at Wv but not at Hv. When decoupled, higher soil respiration rates were observed at increasing temperatures, demonstrating a hysteresis effect. The diel hysteresis at Wv was explained by including the temperature-dependent component of soil respiration and the variation dependent on photosynthetically active radiation.

• The results show that vegetation type and fine root and rhizomorph dynamics influence soil respiration in addition to changes in light, temperature and moisture

The County of Riverside and the City of Murrieta requested that the Regional Conservation Authority (RCA) consider a Criteria Refinement for Core 2 in Western Riverside County’s Multiple Species Habitat Conservation Plan (WRC MSHCP). The purpose of this action is to determine if Core 2 can be sustained as a reserve and if WRC MSHCP funds could be more efficiently used in other core areas. The RCA requested a review of the biological research from the Center for Conservation Biology (CCB) that could be brought into their decision-making process. The CCB convened a distinguished group of scientists to review the implications of a Core 2 Criteria Refinement to biological resources. The group evaluated three general topics at a two-day workshop in order to provide this assessment.

Habitat connectivity is a key component for the persistence of populations, for maintaining genetic diversity, and for weathering environmental extremes and climate shifts. Desert environments are stressful largely because of extreme swings in precipitation and temperature, and thus maintaining connectivity becomes a critical conservation strategy to ensure mobile species can track temporal and spatial shifts in habitat suitability. These linkages are especially critical in light of expected distributional shifts due to climate change. Expansion of urbanization and energy resource development, as well as the transportation and energy infrastructure required to support those changes, are fragmenting desert environments at an increasing rate. Highway underpasses and culverts are often identified in conservation planning as wildlife corridors, providing connections between previously contiguous suitable habitats, but do they facilitate or impede wildlife movement? I assessed wildlife use of seven pre-existing interstate freeway and state highway underpass structures to determine whether they are utilized as corridors for wildlife movement. The underpasses occur between southern California's Peninsular and Transverse Mountain Ranges, a key linkage between Baja California's biotic province and that of the Sierra Nevada. I utilized non-invasive monitoring methods, including camera traps, track-plates, and track beds, over 13 months to capture wildlife presence, determine rates of underpass usage, identify spatial and temporal wildlife use patterns, and to assess some factors that may constrain wildlife use. My results indicated a negative association between native carnivore presence and human activity within and near the underpass structures. Bobcats exhibited a strong negative relationship with motorized vehicles while coyotes displayed a weak negative relationship with humans on foot. Underpass dimensions influenced the rate of wildlife use, with small- and medium-bodied species preferring long, narrow structures whereas bobcats preferred structures that were wide, short, and open. Future strategies for maintaining or enhancing landscape connectivity in desert systems should provide a range of underpass structures to support use by many animals, and develop underpasses that discourage human use.