Herbaceous Vegetation Responses (1992-2004) to Restoration Treatments in a Ponderosa Pine Forest

Abstract

Ecological restoration treatments are widely applied in southwestern ponderosa pine forests to convert them to an open canopy structure similar to that found at the time of Euro-American settlement. An experiment was initiated in northern Arizona in 1994 to evaluate long-term ecosystem responses to 3 restoration treatments: 1) thinning from below (thinning), 2) thinning from below plus forest floor manipulation with periodic prescribed burning (composite), and 3) an untreated control. Results focus on total herbaceous and functional-group standing crop response to these restoration treatments. Pretreatment data were collected in 1992 and posttreatment responses were measured from 1994 through 2004. Total herbaceous standing crop was significantly higher on the 2 treated areas than on the control over the entire posttreatment period, but did not differ between the thinning and composite treatments. Plant functional groups responded differently to treatments and to drought. In general, the graminoid standing crop responded within several years after the initial treatments and continued to increase through time, until a series of severe droughts reduced standing crop to pretreatment levels. C 3 graminoids dominated the standing-crop response, of which bottlebrush squirreltail (Elymus elymoides (Raf.) Swezey ssp. elymoides) was the primary contributor. C 4 graminoids had a minimal response to restoration treatments, possibly because they were less abundant before the experiment began or because they were adversely affected by autumn burning. Legumes and forbs exhibited a 4-5 year lag before responding to the thinning and composite treatments. Annual and biennial plants showed a large biomass increase approximately 5 years after implementation of the composite treatment. The restoration goal of optimizing herbaceous standing crop must be weighed against the competing goals of increasing the abundance of specific functional groups, increasing biodiversity or rare plants, and managing invasive plant species. ResumenLos tratamientos de restauració n ecoló gica son ampliamente aplicados en los bosques de ''Ponderosa pine'' del sudoeste para convertirlos en una estructura de cobertura abierta similar a la que se encontró en el tiempo de la colonizació n Euroamericana. En 1994, en el norte de Arizona, se inicio un experimento para evaluar las respuestas a largo lazo del ecosistema a tres tratamientos de restauració n: 1) aclareo desde abajo (aclareo); 2) Aclareo desde abajo mas manipulació n del piso del bosque con fuego prescrito perió dico (compuesto) y 3) control sin tratar. Los resultados se enfocaron en la respuesta de la biomasa total herbá cea y de grupos funcionales a estos tratamientos de restauració n. Los datos pre-tratamiento fueron colectados en 1992 y las respuestas post-tratamientos fueron medidas de 1994 a 2004. Durante todo el periodo post-tratamiento la biomasa total herbá cea de las dos á reas tratadas fue significativamente mayor que la del á rea control, pero no difirió entre los tratamientos d...

Short- and long-term effects of ponderosa pine fuel treatments intersected by the Egley Fire Complex, Oregon, USA

“…The only functional group that was affected by severity in 2008 was shrub cover, which was higher in sites that burned with low severity than high severity. It is not uncommon for forb, graminoid, and shrub cover to decrease one to three years post fire (Metlen et al 2004;Collins et al 2007;Knapp et al 2007;Dodson et al 2008); however, some studies have shown increases in understory vegetation cover (Armour et al 1984;Moore et al 2006;Ellsworth and Kauffman 2010). Metlen and Fiedler (2006) found that native plant cover was significantly lower initially post fire (same year as the prescribed burn) than unburned sites, however no differences were found in cover one to three years between burned sites and unburned sites in a ponderosa pine-Douglas-fir forest.…”