M. Lisa Floyd

Bio: M. Lisa Floyd is an academic researcher from Prescott College. The author has contributed to research in topics: Woodland & Fire regime. The author has an hindex of 14, co-authored 23 publications receiving 3012 citations.

Regional vegetation die-off in response to global-change-type drought

Abstract: Future drought is projected to occur under warmer temperature conditions as climate change progresses, referred to here as global-change-type drought, yet quantitative assessments of the triggers and potential extent of drought-induced vegetation die-off remain pivotal uncertainties in assessing climate-change impacts. Of particular concern is regional-scale mortality of overstory trees, which rapidly alters ecosystem type, associated ecosystem properties, and land surface conditions for decades. Here, we quantify regional-scale vegetation die-off across southwestern North American woodlands in 2002-2003 in response to drought and associated bark beetle infestations. At an intensively studied site within the region, we quantified that after 15 months of depleted soil water content, >90% of the dominant, overstory tree species (Pinus edulis, a pinon) died. The die-off was reflected in changes in a remotely sensed index of vegetation greenness (Normalized Difference Vegetation Index), not only at the intensively studied site but also across the region, extending over 12,000 km2 or more; aerial and field surveys confirmed the general extent of the die-off. Notably, the recent drought was warmer than the previous subcontinental drought of the 1950s. The limited, available observations suggest that die-off from the recent drought was more extensive than that from the previous drought, extending into wetter sites within the tree species' distribution. Our results quantify a trigger leading to rapid, drought-induced die-off of overstory woody plants at subcontinental scale and highlight the potential for such die-off to be more severe and extensive for future global-change-type drought under warmer conditions.

Relationship of stand characteristics to drought-induced mortality in three Southwestern piñon–juniper woodlands

Abstract: Extreme drought conditions accompanied by rising temperatures have characterized the American Southwest during the past decade, causing widespread tree mortality in pinon-juniper woodlands. Pinon pine (Pinus edulis Engelm.) mortality is linked primarily to outbreaks of the pinyon ips (Ips confusus (Leconte)) precipitated by drought conditions. Although we searched extensively, no biotic agent was identified as responsible for death in Juniperus L. spp. in this study; hence this mortality was due to direct drought stress. Here we examine the relationship between tree abundance and patterns of mortality in three size classes (seedling/sapling, pre-reproductive, reproductive) during the recent extended drought in three regions: southwest Colorado, northern New Mexico, and northern Arizona. Pinon mortality varied from 32% to 65%, and juniper mortality from 3% to 10% across the three sites. In all sites, the greatest pinon mortality was in the larger, presumably older, trees. Using logistic regression models, we examined the influence of tree density and basal area on bark beetle infestations (pinon) and direct drought impacts ( juniper). In contrast to research carried out early in the drought cycle by other researchers in Arizona, we did not find evidence for greater mortality of pinon and juniper trees in increasingly high density or basal area conditions. We conclude that the severity of this regional drought has masked density- dependent patterns visible in less severe drought conditions. With climate projections for the American Southwest suggesting increases in aridity and rising temperatures, it is critical that we expand our understanding of stress responses expected in widespread pinon-juniper woodlands.

Climatic and human influences on fire regimes of the southern san juan mountains, colorado, usa

Abstract: Fire severity, frequency, and extent are expected to change dramatically in coming decades in response to changing climatic conditions, superimposed on the adverse cumulative effects of various human-related disturbances on ecosystems during the past 100 years or more. To better gauge these expected changes, knowledge of climatic and human influences on past fire regimes is essential. We characterized the temporal and spatial properties of fire regimes in ponderosa pine forests of the southern San Juan Mountains of southwestern Colorado by collecting 175 fire-scarred tree samples from nine sites across a wide range of topographic settings. All tree rings and fire scars were dated using standard dendrochronological techniques. Fire-free intervals were statistically modeled using the Weibull distribution to provide quantitative measures that characterized the historical range of variation in pre-EuroAmerican fire regimes. Fires during our reference period were more frequent in the low elevation ponderosa pine forests (6-10 yr) than in the high elevation, mixed conifer forests (18-28 yr). Fires at lower elevations were predominantly low-severity, isolated fires. Fires during some years (e.g., 1748) were spatially extensive throughout the entire mountain range. Intervals that delimited significantly long fire-free periods ranged from 10-19 yr (low elevation) to 27- 50 yr (high elevation). Fire histories were similar between the eastern and western portions of the mountain range, although we found significant evidence of topographic isolation on fire regimes at one site. Pre-1880 fires primarily occurred in the dormant season, and we found no temporal changes in past fire seasonality. We found no compelling evidence that Native Americans influenced fire regimes in our study sites. We found a hiatus in fire occurrence between 1750 and 1770 that we believe was likely related to weakened El Nino-Southern Oscillation activity, an extended series of cool-phase Pacific Decadal Oscillation events, and weakened monsoonal moisture, all possibly en- trained in an invasive air mass typical of locations that are more northerly. In addition, pre-1880 fires occurred during years of severe drought, conditioned by above average moisture conditions in preceding years. The 20th century is characterized by a near complete absence of fires (fire-free interval of .100 yr), suggesting future wildfires may be more widespread and ecologically severe compared to pre-1880 fires.

Fire history and vegetation pattern in mesa verde national park, colorado, usa

Abstract: Pifion-juniper woodlands (Pinus edulis, Juniperus osteosperma, and J sco- pulorum) and petran chaparral communities (Quercus gambelii, Amelanchier utahensis, Cercocarpus montanus, and other tall shrub species) cover much of the Colorado Plateau in the southwestern United States Long-term fire history and successional dynamics are poorly understood in these vegetation types Therefore, we lack a suitable historical context for interpreting the ecological significance of large fires and dramatic vegetative changes that have occurred recently in these ecosystems For example, in Mesa Verde National Park, located in southwestern Colorado, four large intense fires in the last 50 years have threatened significant cultural and natural resources and have caused debate over whether Mesa Verde's fire regime has been significantly altered by human activities in the last century In this study, we dated prehistoric fires in shrublands dominated by Gambel oak (Quercus gambelii) by aging stems that resprouted after fire We mapped the spatial extent of all fires >10 ha that occurred during the last 150 years within a 6600-ha, shrub-dominated portion of Mesa Verde National Park The turnover time (years required to burn an area equal to the entire shrubland zone) was -100 years under the "natural" fire regime of the mid- to late 19th century Fire occurrence was reduced substantially during the first half of the 20th century, but the current fire regime (since about 1950) appears to be similar to that of the 19th century-despite a continuing policy of total fire suppression The "natural" fire turnover time in pifion-juniper woodlands of Mesa Verde is about 400 years A sharp boundary exists between pinon-juniper woodlands at slightly lower elevations in the southern portion of the park and petran chaparral at slightly higher ele- vations in the north This pattern is explained, in part, by more extensive fires in the northern area, which favor resprouting shrubs and eliminate the fire-sensitive pifion and juniper The less frequent occurrence of large fires, and resulting persistence of woodland in the southern portion of the park, may be due in part to natural barriers to fire spread (cliffs and sparsely vegetated slopes) to the south and west of the pifnon-juniper woodlands Our findings demonstrate that fire frequency and extent in Mesa Verde during the last 50 years have not been greatly different from the "natural" fire regime of the late 1800s Therefore, the recent large fires in the park, and the vegetative responses to those fires, appear to be within the historic range of variation for this ecosystem

A Large and Persistent Carbon Sink in the World’s Forests

Abstract: The terrestrial carbon sink has been large in recent decades, but its size and location remain uncertain. Using forest inventory data and long-term ecosystem carbon studies, we estimate a total forest sink of 2.4 ± 0.4 petagrams of carbon per year (Pg C year–1) globally for 1990 to 2007. We also estimate a source of 1.3 ± 0.7 Pg C year–1 from tropical land-use change, consisting of a gross tropical deforestation emission of 2.9 ± 0.5 Pg C year–1 partially compensated by a carbon sink in tropical forest regrowth of 1.6 ± 0.5 Pg C year–1. Together, the fluxes comprise a net global forest sink of 1.1 ± 0.8 Pg C year–1, with tropical estimates having the largest uncertainties. Our total forest sink estimate is equivalent in magnitude to the terrestrial sink deduced from fossil fuel emissions and land-use change sources minus ocean and atmospheric sinks.

Climate Change 2007: The Physical Science Basis.

Abstract: Cause, conseguenze e strategie di mitigazione Proponiamo il primo di una serie di articoli in cui affronteremo l’attuale problema dei mutamenti climatici. Presentiamo il documento redatto, votato e pubblicato dall’Ipcc - Comitato intergovernativo sui cambiamenti climatici - che illustra la sintesi delle ricerche svolte su questo tema rilevante.

Mechanisms of plant survival and mortality during drought: why do some plants survive while others succumb to drought?

Abstract: Summary Severe droughts have been associated with regional-scale forest mortality worldwide. Climate change is expected to exacerbate regional mortality events; however, pre- diction remains difficult because the physiological mechanisms underlying drought survival and mortality are poorly understood. We developed a hydraulically based theory considering carbon balance and insect resistance that allowed development and examination of hypotheses regarding survival and mortality. Multiple mechanisms may cause mortality during drought. A common mechanism for plants with isohydric