The effects of management on soil carbon efflux in different ecosystems are still largely unknown yet crucial to both our understanding and management of global carbon flux. To compare the effects of common forest management practices on soil carbon cycling, we measured soil respiration rate (SRR) in a mixed-conifer and hardwood forest that had undergone various treatments from June to August 2003. The mixed-conifer forest, located in the Sierra Nevada Mountains of California, had been treated with thinning and burning manipulations in 2001, and the hardwood forest, located in the southeastern Missouri Ozarks, had been treated with harvesting manipulations in 1996 and 1997. Litter depth, soil temperature, and soil moisture were also measured. We found that selective thinning produced a similar effect on both forests by elevating SRR, soil moisture, and soil temperature, although the magnitude of response was greater in the mixed-conifer forest. Selective harvest increased SRR by 43% (from 3.38 to 4.82 µmol·m -2 ·s -1 ) in the mixed-conifer forest and by 14% (from 4.25 to 4.84 µmol·m -2 ·s -1 ) in the hardwood forest. Burning at the conifer site and even-aged harvesting at the mixed-hardwood site did not produce significantly different SRR from controls. Mean SRR were 3.24, 3.42, and 4.52 µmol·m -2 ·s -1 , respectively. At both sites, manipulations did significantly alter SRR by changing litter depth, soil structure, and forest microclimate. SRR response varied by vegetation patch type, the scale at which treatments altered these biotic factors. Our findings provide forest managers first-hand information on the response of soil carbon efflux to various management strategies in different forests.Résumé : Bien que cruciaux pour comprendre et gérer le flux global de carbone, les effets de l'aménagement sur les émissions de carbone du sol dans différents écosystèmes sont encore largement inconnus. Afin de comparer les effets des pratiques courantes d'aménagement forestier sur le recyclage du carbone du sol, les auteurs ont mesuré le taux de respiration du sol (TRS) dans une forêt mélangée de conifères et une forêt feuillue qui avaient subi différents traitements de juin à août 2003. La forêt mélangée de conifères, située dans la Sierra Nevada en Californie, avait subi des traitements d'éclaircie et de brûlage en 2001. La forêt feuillue, située dans les monts Ozarks au sud-est du Missouri, avait subi différents traitements de récolte en 1996 et 1997. L'épaisseur de la litière, la température du sol et la teneur en eau du sol ont aussi été mesurées. Ils ont observé que l'éclaircie jardinatoire a produit un effet semblable dans les deux forêts en élevant le TRS, la teneur en eau du sol et la température du sol quoique l'ampleur de la réaction ait été plus forte dans la forêt mélangée de conifères. La coupe de jardinage a augmenté le TRS de 43 % (de 3,38 à 4,82 µmol·m -2 ·s -1 ) dans la forêt mélangée de conifères et de 14 % (de 4,25 à 4,84 µmol·m -2 ·s -1 ) dans la forêt feuillue. Le brûlage dans le cas des conifères et ...
Global change is likely to affect invasive species distribution, especially at range margins. In the eastern Sierra Nevada, California, USA, the invasive annual grass, Bromus tectorum, is patchily distributed and its impacts have been minimal compared with other areas of the Intermountain West. We used a series of in situ field manipulations to determine how B. tectorum might respond to changing climatic conditions and increased nitrogen deposition at the high-elevation edge of its invaded range. Over 3 years, we used snow fences to simulate changes in snowpack, irrigation to simulate increased frequency and magnitude of springtime precipitation, and added nitrogen (N) at three levels (0, 5, and 10 g m(-2) ) to natural patches of B. tectorum growing under the two dominant shrubs, Artemisia tridentata and Purshia tridentata, and in intershrub spaces (INTR). We found that B. tectorum seedling density in April was lower following deeper snowpack possibly due to delayed emergence, yet there was no change in spikelet production or biomass accumulation at the time of harvest. Additional spring rain events increased B. tectorum biomass and spikelet production in INTR plots only. Plants were primarily limited by water in 2009, but colimited by N and water in 2011, possibly due to differences in antecedent moisture conditions at the time of treatments. The threshold at which N had an effect varied with magnitude of water additions. Frequency of rain events was more influential than magnitude in driving B. tectorum growth and fecundity responses. Our results suggest that predicted shifts from snow to rain could facilitate expansion of B. tectorum at high elevation depending on timing of rain events and level of N deposition. We found evidence for P-limitation at this site and an increase in P-availability with N additions, suggesting that stoichiometric relationships may also influence B. tectorum spread.
Time is a fundamental component of ecological processes. How animal behavior changes over time has been explored through well-known ecological theories like niche partitioning and predator-prey dynamics. Yet, changes in animal behavior within the shorter 24-hour light-dark cycle have largely gone unstudied. Understanding if an animal can adjust their temporal activity to mitigate or adapt to environmental change has become a recent topic of discussion and is important for effective wildlife management and conservation. While spatial habitat is a fundamental consideration in wildlife management and conservation, temporal habitat is often ignored. We formulated a temporal resource selection model to quantify the diel behavior of eight mammal species across ten U.S. cities. We found high variability in diel activity patterns within and among species and species-specific correlations between diel activity and human population density, impervious land cover, available greenspace, vegetation cover, and mean daily temperature. We also found that some species may modulate temporal behaviors to manage both natural and anthropogenic risks. Our results highlight the complexity with which temporal activity patterns interact with local environmental characteristics, and suggest that urban mammals may use time along the 24-hour cycle to reduce risk, adapt, and therefore persist, and in some cases thrive, in human-dominated ecosystems.
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