Monitoring a Half-Century of Change in a Hardwood Rangeland
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J. Range Manage. 55: 412-419 July 2002 Monitoring a half-century of change in a hardwood rangeland KERRY L. HEISE AND ADINA M. MERENLENDER Authors are Botanist and Staff Research Associate, Integrated Hardwood Range Management Program, Hopland Research and Extension Center, Hopland, Calif. 95449; and Cooperative Extension Specialist, Environmental Science, Policy, and Management, University of California, Berkeley, Calif. 94720-3110. Abstract Resumen Changes in rangeland species composition can effect forage Cambios en la composición de especies del pastizal pueden quality, ecosystem function, and biological diversity. afectar la calidad de forraje, la función del ecosistema y la diver- Unfortunately, documenting species compositional change is dif- sidad biológica. Desafortunadamente, el documentar los cam- ficult due to a lack of accurate historic records. We took advan- bios de la composición de especies es difícil debido a la falta de tage of herbarium records dating from the early 1950’s to recon- registros históricos certeros. Tomamos ventaja de los registros struct the past flora of a 2,168 ha hardwood rangeland in del herbario, que datan de inicio de la década de 1950, para Mendocino County, California , and then compared this to the reconstruir la flora pasada de 2,168 ha de un pastizal con árboles current flora of the site. An inventory of vascular plants conduct- de madera dura en el condado de Mendocino, California, y la ed from 1996 to 2001 added 44 native and 15 non-native species comparamos con la flora actual del sitio. Un inventario de las bringing the total number of species and infraspecific taxa at the plantas vasculares conducido de 1996 al 2001 agregó 44 especies study site to 671. Of the original 612 species recorded prior to nativas y 25 especies no nativas totalizando 671el número de this study, 34 native and 1 non-native species could not be relo- especies y taxas intraespecificas en el sitio de estudio. De las 612 cated. The percentage of non-native species increased from 19% especies originales registradas antes de este estudio, 34 nativas y in 1952 to 23% in 2001. Based on estimates from the early 1950’s, una no nativa no pudieron ser relocalizadas. El porcentaje de mid 1980’s, and 1996 to 2001, at least 13 non-native species have especies no nativas se incrementó de 19% en 1952 a 23 % en increased in abundance, while some native species have 2001. Basados en las estimaciones de inicios de la década de los decreased. Livestock grazing, competition with invasive species, 50's, mediados de la década de los 80's y de 1996 a 2001, al conversions to different vegetation types, and transportation of menos 13 especies no nativas han incrementado en abundancia, propagules into the site by vehicles and livestock, combined with mientras algunas especies nativas han decrecido. El apacen- the difficulty of relocating rare species, are posed as the most tamiento de ganado, la competencia con especie invasoras, la likely causes for the documented changes. conversión a diferentes tipos vegetativos y el transporte de propágulos al sitio por vehículos y ganado, combinado con la dificultad de relocalizar especies raras son propuestas como las Key Words: Northwest California, herbarium, oak woodlands, causas más probables de los cambios documentados. livestock, flora, invasive species Hardwood rangelands in California cover an estimated 4.5 mil- lion ha and are characterized by an overstory canopy of hard- ty, change in ecosystem function, and reduction in rangeland pro- wood trees, primarily in the genus Quercus. The overstory pro- ductivity (D’Antonio and Vitousek 1992, Campbell and Smith vides at least 10% cover; the understory is generally dominated 2000). In particular, exotic annual grasses interfere significantly by exotic annual grasses and forbs. Replacement of the native with native perennial grasses during all stages of growth understory flora with a primarily non-native one occurred rapidly (Hamilton et al. 1999), resulting in an increase in exotic annuals and on a very large scale over the past 200 years (Heady 1977, over time. Invading species can also differ functionally from the Mack 1989). The primary causes of this change are human native species that they are replacing, resulting in a great overar- induced such as livestock grazing, fire suppression, and facilitat- ching effect on ecosystems (Vitousek 1986). ed dispersal (Rejmánek et al. 1991) resulting in an increased Monitoring species compositional changes in California hard- dominance by exotics and a subsequent loss of native species wood rangelands is essential for determining the sustainability of (Mooney and Drake 1987). livestock grazing and necessary to address the lack of oak Change in understory species composition of oak woodlands, seedling survival. Because the understory of California’s hard- savanna, and grasslands represents a significant component of wood rangelands are dominated by exotic grasses and forbs, global environmental change including loss of biological diversi- many lower in nutritional quality and palatability than native perennial species, the capacity of rangelands has been seriously decreased (Major 1955, Pettit et al. 1995). Annual grasses are Authors wish to thank Chuck Vaughn, Bob Keiffer, and 2 anonymous reviewers for helpful comments on the manuscript. adapted to heavy grazing and low nutrient availability (Jackson Manuscript accepted 5 Oct. 01. 1985), which has consequences for the way livestock grazing is practiced on site as well as the economic vitality of open range 412 JOURNAL OF RANGE MANAGEMENT 55(4) July 2002 grazing operations. As range conditions (Arbutus menziesii Pursh), and California areas”, research pastures, and steep, wood- deteriorate, livestock seek out less palat- buckeye (Aesculus californicus (Spach) ed terrain outside of fenced pasture bound- able plant species, increasing the use on Nutt.). Grasslands and the understory of aries. Rangeland improvement practices these species, oak seedlings included. open oak woodland and savanna are domi- during the 1960’s and 1970’s, aimed at Additionally, the establishment of exotic nated by non-native annual grasses such as increasing agricultural production, result- annual grasses has been proposed as a lim- slender wild oat (Avena barbata Link), big ed in the conversion of approximately 300 iting factor in the regeneration of some quaking grass (Briza maxima L.), hedge- ha of oak woodland and chamise chaparral native oak species (Muick and Bartolome hog dogtail (Cynosurus echinatus L.), and to exotic grassland (Murphy 1976, 1978). 1988, Gordon and Rice 1993). barbed goatgrass (Aegilops triuncialis L.). In addition, university staff and Due to the scarcity of historic baseline Chaparral scrub consisting of chamise researchers intentionally introduced at information, few studies have examined (Adenostoma fasciculatum Hook. & Arn.), least 19 exotic plant species. These were long-term change on California range- Arctostaphylos spp., Ceanothus spp., and seeded into pastures following fire or lands. Using cover data from the 1930’s, Quercus spp., along with patches of closed other forms of clearing to improve range Holzman and Allen-Diaz (1991) docu- cone pine (Pinus attenuata Lemmon) are forage, and since have expanded their mented 58 years of change in 21 blue oak common above 675 m. Douglas fir ranges well beyond the initial introduction (Quercus douglasii Hook. & Arn.) wood- (Pseudotsuga menziesii (Mirbel) Franco), sites. Some of the common species include land plots in California. Our study docu- California nutmeg (Torreya californica smilo grass (Piptatherum miliaceum (L.) ments change over nearly a half-century Torrey), and canyon live oak (Quercus Cosson), harding grass (Phalaris aquatica by reconstructing the past flora of a hard- chrysolepis Liebm.) form dense shaded L.), orchard grass (Dactylis glomerata L.), wood rangeland in northwest California, canopies on steep north and east facing rose clover (Trifolium hirtum All.) and comparing herbarium data to the modern slopes. Numerous seasonal creeks, sag subterranean clover (T. subterraneum L.). flora. This was feasible due to the estab- ponds, vernal pools and springs provide a lishment of an extensive reference collec- diversity of wetland habitats and plant tion of vascular plants for the site in the communities (Heise and Merenlender Methods early 1950’s. A flora was later published 1999). (Murphy and Heady 1983) which included Between 1996 and 2001 we conducted data on species abundance across the site Historic Data an extensive inventory of vascular plants from the early 1980’s. This comprehen- The Center was established as a range across the entire Center. First, the infor- sive set of scientific records, in combina- experiment station in 1951. The following mation from over 1,275 specimen labels tion with extensive documentation of land- year, a botanical survey was initiated to from the Center’s herbarium was updated use at the site, provided us with a means to document all species of vascular plants on to reflect mis-identifications, recent scien- identify newly established species and the property. By 1954 nearly 450 species tific name changes, and reductions due to document changes in the relative abun- were recorded. During the next 30 years of synonymy (Hickman 1993), and then dance of some taxa. sporadic collecting only 137 species were incorporated into a database. From this, added to the flora, bringing the total to species lists with location, habitat, and almost 600. At this time a list of the vas- collection date were produced to facilitate Study Site cular plants for the Center was published the relocation of previously recorded taxa. (Murphy and Heady 1983). Only a few Most of the herbarium specimens (75%) Vegetation more species were added to the flora contained general location descriptions The study area encompasses the entire through the 1980’s and mid 1990’s, bring- such as pasture name only, while the University of California Hopland ing the total number of vascular species remaining 25% had more specific site Research and Extension Center, located in and infraspecific taxa to 612. Alfred H.