Fire Severity in Conifer Forests of the Sierra Nevada, California

Natural disturbances are an important source of environmental heterogeneity that have been linked to species diversity in ecosystems. However, spatial and temporal patterns of disturbances are often evaluated separately. Consequently, rates and scales of existing disturbance processes and their effects on biodiversity are often uncertain. We have studied both spatial and temporal patterns of contemporary fires in the Sierra Nevada Mountains, California, USA. Patterns of fire severity were analyzed for conifer forests in the three largest fires since 1999. These fires account for most cumulative area that has burned in recent years. They burned relatively remote areas where there was little timber management. To better characterize high-severity fire, we analyzed its effect on the survival of pines. We evaluated temporal patterns of fire since 1950 in the larger landscapes in which the three fires occurred. Finally, we evaluated the utility of a metric for the effects of fire suppression. Known as Condition Class it is now being used throughout the United States to predict where fire will be uncharacteristically severe. Contrary to the assumptions of fire management, we found that high-severity fire was uncommon. Moreover, pines were remarkably tolerant of it. The wildfires helped to restore landscape structure and heterogeneity, as well as producing fire effects associated with natural diversity. However, even with large recent fires, rates of burning are relatively low due to modern fire management. Condition Class was not able to predict patterns of high-severity fire. Our findings underscore the need to conduct more comprehensive assessments of existing disturbance regimes and to determine whether natural disturbances are occurring at rates and scales compatible with the maintenance of biodiversity.     

Cache site selection by chipmunks (Tamias spp.) and its influence on the effectiveness of seed dispersal in Jeffrey pine (Pinus jeffreyi)

The effectiveness of Jeffrey pine (Pinus jeffreyi) seed dispersal performed by seed-caching yellow pine chipmunks (Tamias amoenus) and lodgepole chipmunks (Tamias speciosus) was compared to that of wind dispersal in the Sierra Nevada of western Nevada. Wind-dispersed seeds typically fall under or near the parent tree. Chipmunks removed 90 and 97% of 1064 radioactive seeds from each of two simulated wind-dispersed seed shadows in less than 24 h. Wind-dispersed seeds were deployed within 12 m of the two source trees, but chipmunk caches were found from 2–69 m from the trees. Chipmunks carried nearly all seeds away from source trees, greatly reducing the density of seeds under and near source trees. Caches contained from 1–35 seeds and most were buried 7–21 mm deep. Chipmunks cached in open bitterbrush shrubland with mineral soils much more than expected and cached in closed-canopy Jeffrey pine and lodgepole pine forests with thick needle litter much less than expected. Many Jeffrey pine seedlings and saplings grow in the bitterbrush habitat and few grow in the pine forests. Ten and 20% of the original caches survived until April, the time of seed germination, at the two sites. The movement of wind-dispersed seeds is random relative to environmental variables important in seedling survival, and the wind in coniferous forests cannot quickly bury seeds. The quality of seed dispersal rendered by chipmunks was superior to that provided by the wind because the chipmunks quickly harvested seeds on the ground, moved them away from source trees, and buried them in the ground in habitats and microhabitats where they were more likely to establish new seedlings. The increased quality of seed dispersal provided by animals relative to the wind may help explain why over twenty species of pines have evolved seeds and cones that are adapted for dispersal by seed-caching animals.     

Substrate type affects caching and pilferage of pine seeds by chipmunks

The abiotic environment often influences the ways in which animalsinteract. By affecting the cues associated with buried seeds,the type of substrate used by seed-caching rodents may alterthe relative probabilities of cache pilferage and cache retrieval.We predicted that, after a wildfire, the presence of ash wouldimpair rodents' ability to smell pine seeds on the forest floor.In a laboratory experiment, we compared the foraging success,caching frequency, and cache recovery of chipmunks (six Tamiasamoenus and six T. quadrimaculatus) in ash versus sand substrates.Initial results supported our hypothesis: chipmunks found only2.3% of 108 caches of Jeffrey pine (Pinus jeffreyi) seeds thatwe buried in ash but found 98% of caches in sand. However, chipmunksmade as many or more of their own caches in ash compared withsand (48% for T. amoenus, 73% for T. quadrimaculatus.) Whenforaging for seeds cached in ash by themselves and by otherindividuals, they found significantly higher proportions oftheir own caches (62%) than of caches made by others (25%).However, when foraging in sand, they found high proportionsboth of their own caches and those of others (86 versus 81%).These results suggest that olfaction is less effective in ashthan in sand, that spatial memory enables chipmunks to recovertheir own caches in ash, and that caching in ash may allow animalsto avoid pilferage of stored food. As chipmunks are importantdispersers of seeds, changes in their foraging patterns or competitiveinteractions after fire could significantly affect pine regeneration.     

罗汉果化学成分的研究

用硅胶柱层析、制备薄层层析和Sephadex LH-20柱层析等方法对罗汉果[Siraitia grosvenorii(Swingle)C.Jeffrey]75%乙醇提取物化学成分进行分析,共分离得到8个化合物,通过质谱法和核磁共振波谱法及理化性质鉴定为:罗汉果醇苯甲酸酯(1)、厚朴酚(2)、双[5-甲酰基糠基]醚(3)、5-羟甲基糠酸(4)、山柰酚-7-O-α-L-鼠李糖苷(5)、山柰酚-3,7-O-α-L-二鼠李糖苷(6)、山柰酚(7)、琥珀酸(8).除化合物1、6和7外,其余均为首次从该植物中分离得到.     

Does It Make Sense to Restore Wildland Fire in Changing Climate?

Forest restoration guided by historical reference conditions of fire regime, forest structure, and composition has been increasingly and successfully applied in fire‐adapted forests of western North America. But because climate change is expected to alter vegetation distributions and foster severe disturbances, does it make sense to restore the ecological role of wildland fire through management burning and related activities such as tree thinning? I suggest that some site‐ and date‐specific historical conditions may be less relevant, but reference conditions in the broad sense are still useful. Reference conditions encompass not only the recent past but also evolutionary history, reflecting the role of fire as a selective force over millennia. Taking a long‐term functional view of historical reference conditions as the result of evolutionary processes can provide insights into past forest adaptations and migrations under various climates. As future climates change, historical reference data from lower, southerly, and drier sites may be useful in places that are higher, northerly, and currently wetter. Almost all models suggest that the future will have substantial increases in wildfire occurrence, but prior to recent human‐caused fire exclusion, fire‐adapted pine forests of western North America were among the most frequently burned in the world. Restoration of patterns of burning and fuels/forest structure that reasonably emulate historical conditions prior to fire exclusion is consistent with reducing the susceptibility of these ecosystems to catastrophic loss. Priorities may include fire and thinning treatments of upper elevation ecotones to facilitate forest migration, whereas vulnerable low‐elevation forests may merit less management investment.     

AFLP用于构建罗汉果DNA指纹图谱及其幼苗雌雄鉴别

对罗汉果(Siraita grosvenorii(Swingle)C．Jeffrey ex Lu et Z．Y．Zhang)的几个品种进行AFLP标记分析,从中筛选出2个引物组合,其中一个能够用于构建不同品种的指纹图谱,另一个可以结合数量性状分析成功地鉴别罗汉果幼苗的雌雄。建立了一种可用于罗汉果幼苗雌雄鉴别的方法,并可为品种的鉴别提供依据。     

Climatic influences on fire regimes in the northern Sierra Nevada mountains, Lake Tahoe Basin, Nevada, USA

Aim The goal of this study was to understand better the role of interannual and interdecadal climatic variation on local pre‐EuroAmerican settlement fire regimes in fire‐prone Jeffrey pine (Pinus jeffreyi Grev. & Balf.) dominated forests in the northern Sierra Nevada Mountains. Location Our study was conducted in a 6000‐ha area of contiguous mixed Jeffrey pine‐white fir (Abies concolor Gordon & Glend.) forest on the western slope of the Carson Range on the eastern shore of Lake Tahoe, Nevada. Methods Pre‐EuroAmerican settlement fire regimes (i.e. frequency, return interval, extent, season) were reconstructed in eight contiguous watersheds for a 200‐year period (1650–1850) from fire scars preserved in the annual growth rings of nineteenth century cut stumps and recently dead pre‐settlement Jeffrey pine trees. Superposed epoch analysis (SEA) and correlation analysis were used to examine relationships between tree ring‐based reconstructions of the Palmer Drought Severity Index (PDSI), Southern Oscillation Index (SOI), Pacific Decadal Oscillation (PDO) and pre‐EuroAmerican fire regimes in order to assess the influence of drought and equatorial and north Pacific teleconnections on fire occurrence and fire extent. Results For the entire period of record (1650–1850), wet conditions were characteristic of years without fires. In contrast, fire years were associated with drought. Drought intensity also influenced fire extent and the most widespread fires occurred in the driest years. Years with widespread fires were also preceded by wet conditions 3 years before the fire. Widespread fires were also associated with phase changes of the PDO, with the most widespread burns occurring when the phase changed from warm (positive) to cold (negative) conditions. Annual SOI and fire frequency or extent were not associated in our study. At decadal time scales, burning was more widespread during decades that were dryer and characterized by La Niña and negative PDO conditions. Interannual and interdecadal fire–climate relationships were not stable over time. From 1700 to 1775 there was no interannual relationship between drought, PDO, and fire frequency or extent. However, from 1775 to 1850, widespread fires were associated with dry years preceded by wet years. This period also had the strongest association between fire extent and the PDO. In contrast, fire–climate associations at interdecadal time scales were stronger in the earlier period than in the later period. The change from strong interdecadal to strong interannual climate influence was associated with a breakdown in decadal scale constructive relationships between PDO and SOI. Main conclusions Climate strongly influenced pre‐settlement pine forest fire regimes in northern Sierra Nevada. Both interannual and interdecadal climatic variation regulated conditions conducive to fire activity, and longer term changes in fire frequency and extent correspond with climate‐mediated changes observed in both the northern and southern hemispheres. The sensitivity of fire regimes to shifts in modes of climatic variability suggests that climate was a key regulator of pine forest ecosystem structure and dynamics before EuroAmerican settlement. An understanding of pre‐EuroAmerican fire–climate relationships may provide useful insights into how fire activity in contemporary forests may respond to future climatic variation.     

Rely and Toxic Shock Syndrome: a technological health crisis

This essay examines factors leading to the identification of Toxic Shock Syndrome with the bacteria Staphylococcus aureus in 1978 and the specific role of Rely tampons in generating a technologically rooted health crisis. The concept biologically incompatible technology is offered to explain the relationship between constituent bacteria, women's menstrual cycles, and a reactive technology that converged to create the ideal environment for the S. aureus bacteria to live and flourish in some women. The complicated and reactive relationship of the Rely tampon to emergent disease, corporate interests, public health, and injury law reveals the dangers of naturalizing technologies.     

Influences of climate on fire regimes in montane forests of north-western Mexico

Aim To identify the influence of interannual and interdecadal climate variation on the occurrence and extent of fires in montane conifer forests of north‐western Mexico. Location This study was conducted in Jeffrey pine (Pinus jeffreyi Grev. & Balf.)‐dominated mixed‐conifer forests in the central and northern plateau of the Sierra San Pedro Mártir, Baja California, Mexico. Methods Fire occurrence was reconstructed for 12 dispersed sites for a 290‐year period (1700–1990) from cross‐dated fire‐scarred samples extracted from live trees, snags and logs. Superposed epoch analysis was used to examine the relationships of tree‐ring reconstructions of drought, the El Niño/Southern Oscillation (ENSO) and the Pacific Decadal Oscillation (PDO) with fire occurrence and extent. Results Years with no recorded fire scars were wetter than average. In contrast, years of widespread fires were dry and associated with phase changes of the PDO, usually from positive (warm) to negative (cold). The influence of the PDO was most evident during the La Niña phase of the ENSO. Widespread fires were also associated with warm/wet conditions 5 years before the fire. We hypothesize that the 5‐year lag between warm/wet conditions and widespread fires may be associated with the time necessary to build up sufficient quantity and continuity of needle litter to support widespread fires. Two periods of unusually high fire activity (1770–1800 and 1920–1950) were each followed by several decades of unusually low fire activity. The switch in each case was associated with strong phase changes in both PDO and ENSO. Main conclusions Climate strongly influences fire regimes in the mountains of north‐western Mexico. Wet/warm years are associated with little fire activity. However, these years may contribute to subsequent fire years by encouraging the production of sufficient needle litter to support more widespread fires that occur in dry/cool years.