Oak Savanna

This study was designed to examine the relationship between land management practices of Indian communities prior to contact with Europeans and the nature or character of subsequent catastrophic forest fires in the Oregon Coast Range. The research focused on spatial and temporal patterns of Indian burning across the landscape from 1491 until 1848, and corresponding patterns of catastrophic fire events from 1849 until 1951. Archival and anthropological research methods were used to obtain early surveys, maps, drawings, photographs, interviews, Geographic Information Systems (GIS) inventories, eyewitness accounts and other sources of evidence that document fire history. Data were tabulated, mapped, and digitized as new GIS layers for purposes of comparative analysis. An abundance of useful historical evidence was found for reconstructing precontact vegetation patterns and human burning practices in western Oregon. The data also proved useful for documenting local and regional forest fire histories. Precontact Indians used fire to produce landscape patterns of trails, patches, fields, woodlands, forests and grasslands that varied from time to time and place to place, partly due to demographic, cultural, topographic, and climatic differences that existed throughout the Coast Range. Native plants were systematically managed by local Indian families in even-aged stands, usually dominated by a single species, throughout all river basins of the study area. Oak, filberts, camas, wapato, tarweed, yampah, strawberries, huckleberries, brackenfern, nettles, and other plants were raised in select areas by all known tribes, over long periods of time. However, current scientific and policy assumptions regarding the abundance and extent of precontact western Oregon old-growth forests may have been erroneous. This study demonstrates a high rate of coincidence between the land management practices of precontact Indian communities, and the causes, timing, boundaries, severity, and extent of subsequent catastrophic forest fires in the same areas. Information developed from this study will be of value to researchers, wildlife managers, forest landowners, and others with an interest in the history and resources of the Oregon Coast Range.

Mediterranean oak savannas cover about 4 million ha in California (northwest America) and 3 million ha in Spain and Portugal (southwest Europe), and are ecologically and socio-economically important systems. Here we review literature on the interactions between the two dominant elements of savannas – the oak overstorey, the herbaceous understorey, and the surrounding grassland matrix. We focus on the main ecological factors affecting the oak understorey environment: shade, soil moisture, soil nutrients, and animal-mediated effects. We then review the main features of the herbaceous community in the oak understorey, as compared to the adjacent open grassland, in terms of species composition, biomass, diversity, and soil seed bank. We examine processes associated with oak regeneration and growth, and their relationships with the herbaceous layer and other woody plants cover. Finally, we discuss the complex facilitative and interference interactions that occur in oak-grassland systems and review models proposed to explain the dynamics and coexistence of oak trees and herbaceous plants in savannas.

... They provide “enemy-free space” (Jeffries and Lawton 1984, Gentry and Dyer 2002). ... Jim O'Hara, Monty Wood, and Norm Woodley helped with tachinid identifications and through valuable discussions of tachinid natural history. ...

The complexity of savanna ecosystems with the shared dominance between woody and herbaceous primary producers poses challenges to measuring such fundamental ecosystem characteristics as net primary productivity (NPP). We address these challenges in the blue oak savanna in California by constructing comprehensive estimates of NPP for three adjacent watersheds. We directly assessed annual biomass increment of all plant components in

The relative importance of environmental filtering, biotic interactions and neutral processes in community assembly remains an openly debated question and one that is increasingly addressed using phylogenetic approaches. Closely related species may occur together more frequently than expected (phylogenetic clustering) if environmental filtering operates on traits with significant phylogenetic signal. Recent studies show that phylogenetic clustering tends to increase with spatial scale, presumably because greater environmental variation is encompassed at larger spatial scales, providing opportunities for species to sort across environmental gradients. However, if environmental filtering is the cause of species sorting along environmental gradients, then environmental variation rather than spatial scale per se should drive the processes governing community assembly. Using species abundance and light availability data from a long-term experiment in Minnesota oak savanna understory comm...

This paper suggests that one can learn to read ecological indicators of past human practices where fire was used to promote and maintain culturally im- portant plant resources. Such indicators include the ecological stage and con- dition of the plant community, the composition and presence of ethnobotanically significant plants, soil characteristics, and other indicators of burning. Confirmation of such indicators is often possible through ethnographic literature, early accounts and Indian place name records (Waterman 1920, 1922), Government Land Office (GLO) survey records and maps (Galatowitsch 1990; Radeloff et al. 1999), as well as present day remnant indicators of fire. These indicators can be used to identify and recover important cultural resource places as well as inform what management practices may be necessary to maintain and restore these plant communities and ecosystems (Anderson 1996). To illustrate these points, the role and function of indigenous burning prac- tices ...

Landscape characteristics and social behavior can affect the foraging patterns of seed-dependent animals. We examine the movement of acorns from valley oak (Quercus lobata) trees to granaries maintained by acorn woodpeckers (Melanerpes formicivorus) in two California oak savanna-woodlands differing in the distribution of Q. lobata within each site. In 2004, we sampled Q. lobata acorns from 16 granaries at Sedgwick Reserve in Santa Barbara County and 18 granaries at Hastings Reserve in Monterey County. Sedgwick has lower site-wide density of Q. lobata than Hastings as well as different frequencies of other Quercus species common to both sites. We found acorn woodpeckers foraged from fewer Q. lobata seed source trees (K g = 4.1 ± 0.5) at Sedgwick than at Hastings (K g = 7.6 ± 0.6) and from fewer effective seed sources (N em* = 2.00 and 5.78, respectively). The differences between sites are due to a greater number of incidental seed sources used per granary at Hastings than at Sedgwick. We also found very low levels of seed source sharing between adjacent granaries, indicating that territoriality is strong at both sites and that each social group forages on its own subset of trees. We discovered an interesting spatial pattern in the location of granaries. At Sedgwick, acorn woodpeckers situated their granaries within areas of higher-than-average tree density, while at Hastings, they placed them within areas of lower-than-average tree density, with the outcome that granaries at the two sites were located in areas of similar valley oak density. Our results illustrate that landscape characteristics might influence the number of trees visited by acorn woodpeckers and the locations of territories, while woodpecker social behavior, such as territoriality, shapes which trees are visited and whether they are shared with other social groups.

Landscape characteristics and social behavior can affect the foraging patterns of seed-dependent animals. We examine the movement of acorns from valley oak (Quercus lobata) trees to granaries maintained by acorn woodpeckers (Melanerpes formicivorus) in two California oak savanna-woodlands differing in the distribution of Q. lobata within each site. In 2004, we sampled Q. lobata acorns from 16 granaries at Sedgwick Reserve in Santa Barbara County and 18 granaries at Hastings Reserve in Monterey County. Sedgwick has lower site-wide density of Q. lobata than Hastings as well as different frequencies of other Quercus species common to both sites. We found acorn woodpeckers foraged from fewer Q. lobata seed source trees (K g = 4.1 ± 0.5) at Sedgwick than at Hastings (K g = 7.6 ± 0.6) and from fewer effective seed sources (N em* = 2.00 and 5.78, respectively). The differences between sites are due to a greater number of incidental seed sources used per granary at Hastings than at Sedgwick. We also found very low levels of seed source sharing between adjacent granaries, indicating that territoriality is strong at both sites and that each social group forages on its own subset of trees. We discovered an interesting spatial pattern in the location of granaries. At Sedgwick, acorn woodpeckers situated their granaries within areas of higher-than-average tree density, while at Hastings, they placed them within areas of lower-than-average tree density, with the outcome that granaries at the two sites were located in areas of similar valley oak density. Our results illustrate that landscape characteristics might influence the number of trees visited by acorn woodpeckers and the locations of territories, while woodpecker social behavior, such as territoriality, shapes which trees are visited and whether they are shared with other social groups.

Natural disturbance patterns can provide useful information for ecosystem management. Our objective was to provide a detailed spatial picture of the pre-European settlement vegetation cover for the northwestern Wisconsin Pine Barrens and to compare it with the present vegetation cover. We analyzed the presettlement conditions using an extensive data set comprised of U.S. General Land Office surveyor records from the mid-19th century and related it to the vegetation cover in 1987 as depicted in a Landsat satellite forest classification. Changes were quantified by calculating differences in abundance and relative importance of tree species at presettlement time and today. Our results revealed a strong decline of jack, red, and white pine (Pinus banksiana Lamb., Pinus resinosa Ait., and Pinus strobus L., respectively), accompanied by an increase of oak (Quercus spp.), trembling aspen (Populus tremuloides Michx.), and other hardwood species. Certain vegetation types, e.g., red pine and ...

Lack of tree regeneration and persistency of species-poor shrublands represent a growing problem across Mediterranean evergreen oak forests. What constrains forest regeneration is poorly understood, and restoration attempts have been largely unsuccessful. We assessed the contribution of four different mechanisms of tree recruitment limitation (that is, source, dispersal, germination, and establishment) in a cork oak (Quercus suber) system in southern

Wisconsin (USA) oak savannas are endangered plant communities that have remarkably high plant species diversity. To investigate factors underlying this richness, we experimentally investigated the potentially interacting effects of light gradients and arbuscular mycorrhizal fungi (AMF) on plant competition in the greenhouse, using a fully randomized block design. We used four plant species, soil, and AMF from a remnant sand savanna, under two light and five AMF treatments. Plants were grown four per pot under two competition treatments (either one or four species per pot) for 20 weeks. Using ANOVA, we found that all species showed significant treatment effects on total and shoot biomass, primarily due to differences in competition and light, less to AMF. However, effects were the opposite of predictions. Putatively mycorrhizal plants showed neutral to negative responses to AMF, and a nonmycorrhizal species outcompeted AMF species in infected pots. We concluded that our experimental ...