Restoring aspen under grazed landscapes

There is concern over the decline of aspen and the lack of successful regeneration due to overgrazing by both cattle and wildlife. Any increase of aspen or its long-term persistence in the landscape is dependent on the continuous recruitment of aspen suckers. I conducted two studies on Lassen National Forest, California, USA, to aid development of livestock grazing strategies to restore aspen stands with excessive livestock browsing. The aim of the first study was to evaluate how individual aspen suckers respond to intensity and season of browsing. Thirty-three combinations of intensity and season of brows on aspen were implemented. Greatest growth was on suckers with no terminal leader browse and < 25% biomass removed from branches. Lowest growth occurred when 90% of terminal leader length and 50% of branch biomass was removed. Growth was most negatively affected by browse on terminal leaders and when browsing occurred mid-season only or both early and mid-season. Occurrence of conifers in the overstory significantly reduced sucker growth. The second study was designed to examine cattle preference for aspen habitat. I evaluated seasonal dynamics of forage biomass, quality, and utilization of vegetation types found within aspen-meadow complexes. Utilization varied among vegetation types and season, with aspen regeneration receiving up to 100% use in late season. Aspen regeneration had higher forage quality compared to aspen understory and meadow vegetation regardless of season or year. Principal utilization during early season occurred in the meadow and aspen understory. Mid-season decreases in meadow and aspen understory forage quantity and quality coincided with a marked increase in aspen regeneration utilization. Forage quality and biomass were at the lowest levels by late season in all three vegetation types. Seasonal utilization of vegetation by cattle is a function of forage quantity, biomass, and cow nutrient demand. Browse on aspen regeneration terminal leaders during mid-season over consecutive years, and repeated browse during a single growing season should be avoided. Managers can use early season grazing to reduce aspen browsing, set stocking rates so that herbaceous forage quantity is not limiting, and provide supplements to insure that limiting nutrients are available to cattle

Aquatic Ecosystem Response to Timber Harvesting for the Purpose of Restoring Aspen

<div><p>The removal of conifers through commercial timber harvesting has been successful in restoring aspen, however many aspen stands are located near streams, and there are concerns about potential aquatic ecosystem impairment. We examined the effects of management-scale conifer removal from aspen stands located adjacent to streams on water quality, solar radiation, canopy cover, temperature, aquatic macroinvertebrates, and soil moisture. This 8-year study (2003–2010) involved two projects located in Lassen National Forest. The Pine-Bogard Project consisted of three treatments adjacent to Pine and Bogard Creeks: (i) Phase 1 in January 2004, (ii) Phase 2 in August 2005, and (iii) Phase 3 in January 2008. The Bailey Project consisted of one treatment adjacent to Bailey Creek in September 2006. Treatments involved whole tree removal using track-laying harvesters and rubber tire skidders. More than 80% of all samples analyzed for NO₃-N, NH₄-N, and PO₄-P at Pine, Bogard, and Bailey Creeks were below the detection limit, with the exception of naturally elevated PO₄-P in Bogard Creek. All nutrient concentrations (NO₃-N, NH₄-N, PO₄-P, K, and SO₄-S) showed little variation within streams and across years. Turbidity and TSS exhibited annual variation, but there was no significant increase in the difference between upstream and downstream turbidity and TSS levels. There was a significant decrease in stream canopy cover and increase in the potential fraction of solar radiation reaching the streams in response to the Pine-Bogard Phase 3 and Bailey treatments; however, there was no corresponding increase in stream temperatures. Macroinvertebrate metrics indicated healthy aquatic ecosystem conditions throughout the course of the study. Lastly, the removal of vegetation significantly increased soil moisture in treated stands relative to untreated stands. These results indicate that, with careful planning and implementation of site-specific best management practices, conifer removal to restore aspen stands can be conducted without degrading aquatic ecosystems.</p> </div

Aquatic ecosystem response to timber harvesting for the purpose of restoring aspen.

The removal of conifers through commercial timber harvesting has been successful in restoring aspen, however many aspen stands are located near streams, and there are concerns about potential aquatic ecosystem impairment. We examined the effects of management-scale conifer removal from aspen stands located adjacent to streams on water quality, solar radiation, canopy cover, temperature, aquatic macroinvertebrates, and soil moisture. This 8-year study (2003-2010) involved two projects located in Lassen National Forest. The Pine-Bogard Project consisted of three treatments adjacent to Pine and Bogard Creeks: (i) Phase 1 in January 2004, (ii) Phase 2 in August 2005, and (iii) Phase 3 in January 2008. The Bailey Project consisted of one treatment adjacent to Bailey Creek in September 2006. Treatments involved whole tree removal using track-laying harvesters and rubber tire skidders. More than 80% of all samples analyzed for NO₃-N, NH₄-N, and PO₄-P at Pine, Bogard, and Bailey Creeks were below the detection limit, with the exception of naturally elevated PO₄-P in Bogard Creek. All nutrient concentrations (NO₃-N, NH₄-N, PO₄-P, K, and SO₄-S) showed little variation within streams and across years. Turbidity and TSS exhibited annual variation, but there was no significant increase in the difference between upstream and downstream turbidity and TSS levels. There was a significant decrease in stream canopy cover and increase in the potential fraction of solar radiation reaching the streams in response to the Pine-Bogard Phase 3 and Bailey treatments; however, there was no corresponding increase in stream temperatures. Macroinvertebrate metrics indicated healthy aquatic ecosystem conditions throughout the course of the study. Lastly, the removal of vegetation significantly increased soil moisture in treated stands relative to untreated stands. These results indicate that, with careful planning and implementation of site-specific best management practices, conifer removal to restore aspen stands can be conducted without degrading aquatic ecosystems

Effect of Simulated Browsing on Aspen Regeneration: Implications for Restoration

Aspen (Populus tremuloides Michx.) is a disturbance-dependent, fire-resilient, shade-intolerant, clonal species that is in decline throughout western North America. The objective of this study was to examine the effects of intensity and season of browsing on annual height growth of aspen suckers. The goal was to aid development of livestock grazing strategies to restore stands in decline due to excessive livestock browsing. We implemented 33 combinations of intensity and season of browse on aspen suckers in three aspen stands on Eagle Lake Range District, Lassen National Forest, California, USA, during 2003 and 2004. Greatest growth was on suckers with no terminal leader browse and ≤ 25% of biomass removed from branches. Lowest growth occurred when 90% of terminal leader length and 50% of branch biomass was removed. Growth was most negatively affected by browse on terminal leader. Growth was lowest for suckers browsed midseason only and suckers browsed both early and midseason. Occurrence of conifer in the stand overstory significantly reduced sucker growth. Managers should minimize browse on terminal leaders, midseason browse over consecutive years, and repeated browse during a growing season

Cattle Selection for Aspen and Meadow Vegetation: Implications for Restoration

There is concern over the decline of aspen and the lack of successful regeneration due to excessive browsing of aspen suckers by cattle and other wild and domestic ungulates. We conducted a 2-yr study on Lassen National Forest, California, to aid development of cattle grazing strategies to enhance aspen regeneration. We evaluated seasonal biomass, nutritional quality, and utilization by cattle of aspen suckers, aspen herbaceous understory vegetation, and meadow herbaceous vegetation within six aspen–meadow complexes. Aspen suckers had greater nutritional quality compared to aspen understory and meadow vegetation regardless of season or year. Nutritional quality declined with season in all three vegetation types. Early-growing season foraging by cattle focused on meadow and aspen understory vegetation. Mid-growing season decreases in meadow and aspen understory nutritional quality coincided with a marked increase in utilization of aspen suckers. By late-growing season, utilization on aspen suckers was significantly greater than aspen understory or meadow vegetation. Managers can use early-growing season grazing to reduce aspen consumption by cattle, set stocking rates so that adequate herbaceous vegetation is available throughout the growing season, provide nutritional supplements to reduce demand for nutritious aspen suckers, construct protective fencing, and implement grazing systems that insure years with mid- and late-growing season rest from heavy browsing

Mean and standard error of soil moisture within the Pine-Bogard Phase 2 August 2005 treatment area.

<p>Measurements were made at the 15 and 45 cm depths at Stations C and D of the reference and treatment transects. % P = percent of mean annual precipitation. Lower values of soil moisture tension correspond to wetter soils.</p

Illustration of Bailey Project treatment areas and stream and soil monitoring station locations.

<p>Illustration of Bailey Project treatment areas and stream and soil monitoring station locations.</p