Final Report for GNC14-185
Ponderosa pine forest management in the Black Hills, SD currently focuses on reducing tree stocking and fuels to minimize wildfire and mountain pine beetle risks. While many of these lands are grazed by livestock, management practices which optimize both timber and cattle production simultaneously have not been identified. Better understanding of relationships among livestock grazing, timber and forage production, wildlife, aesthetics, and plant community composition is critical to reduce uncertainty and optimize management. Proposed research will investigate relationships among duration and intensity of livestock use, forage production, plant species diversity, and ponderosa pine regeneration. Research was conducted in the Black Hills for the following reasons: 1) the Black Hills National Forest is the most intensively managed National Forest in the U.S. with well documented timber harvest methods and livestock grazing practices, and 2) the forest provides many economically important ecosystem goods and services such as cattle and timber production, big game hunting, tourism, and recreation. Short-term outcomes include the collection of data and development of relationships among management practices and ecosystem goods and services. Intermediate and long-term outcomes include increases in knowledge and understanding, and guidance in management practices for ranchers and public land stewards. Progress in short-term outcomes will be monitored and reported at the end of the data collection season. A presentation of research results will be given to the Rangeland Management Specialists at the Black Hills National Forest to increasing knowledge and understanding of relationships between management practices and resource condition. Long-term outcomes of changing management practices may take several years to decades, and will not be measured as part of this project. Relationships among management practices and ecosystem goods and services can be integrated into future management plans to sustainably produce livestock and timber while maintaining a diverse and productive native plant community. Optimizing livestock and timber production and maintaining native plant communities has the potential to improve rancher profitability, and environmental quality. Enhancements to the Black Hills forest resource base may also benefit wildlife, hunting, ascetics, tourism, and recreation.
Natural resource management of ponderosa pine forests in the Black Hills, SD has generally focused on reducing tree stocking and hazardous fuels to reduce risks associated with wildfire and mountain pine beetle. While many of these lands are grazed by livestock, the relationship between management practices, tree growing stock levels, timber production, forage production, livestock grazing, wildlife, aesthetics, and ecological integrity is not well understood. Science-based management guidelines are necessary to broaden the scope of current forest management and optimize various ecosystem goods and services. The goal of this project is to develop management guidelines, which sustainably and efficiently provision multiple ecosystem goods and services for grazed forested lands, by integrating relationships among forest density, cattle and timber production, plant community structure, forage productivity, and previous management practices. These guidelines can then be incorporated into future resource management plans, and have the potential to improve rancher profitability, environmental quality, and enhance quality of life for ranchers, communities, and society as a whole.
Multiple use and ecological sustainability are increasingly important management considerations in the Black Hills, SD, which provide many economically important ecosystem goods and services including cattle and timber production, big game hunting, tourism, and recreation. Public and private forested lands of the Black Hills provide forage for cattle grazing. Ponderosa pine from the Black Hills supply mills and forest products businesses in several Black Hills communities. The Black Hills provide valuable wildlife habitat for many game animals including deer, elk, bighorn sheep, and mountain lion. Mount Rushmore National Memorial, which draws two million visitors annually, is one of many area attractions which support a large tourism industry in many Black Hills communities.
Cattle graze on both public and private lands in the coniferous forests of the Black Hills, SD. There are 1.04 million acres of suitable grazing land in the Black Hills National Forest representing 83 percent of Forest Service land (USDA 2006). This land is expected to produce 233 million pounds of forage on a sustainable annual basis with 127 million pounds or 128,000 animal unit months (AUM) allocated to livestock (USDA 2006). In 2009, 260 permittees leased the suitable grazing lands in the Black Hills National Forest (Hocking et al. 2010), and depend on public land grazing access to achieve the operational scale necessary to sustain their livelihood. Grazing also occurs on many of the 308,000 acres of private coniferous forest land in the Black Hills. Lawrence County, where conifer forests cover more than 90 percent of its area, generated nearly 12 million dollars in cattle receipts in 2007 (USDA 2009). Cattle use of forested areas will likely increase with projected temperature increases from climate change (Allred et al. 2013). There are questions relating to ecological integrity, and relationships among: cattle grazing, plant community composition, herbaceous production, and ponderosa pine regeneration.
Understanding relationships between grazing practices and plant community structure is important to economically and environmentally sustainable multiple-use of forested grazing lands. Science-based ecologically sustainable management of forested grazing lands may improve economic profitability of livestock grazing on private lands, and help ensure economically viable livestock grazing access to public lands, while also improving environmental quality of both private and public lands. Management guidelines for the Black Hills National Forest highlight sustainable use (USDA 2006), and maintaining a diverse array of native species (Mystic Ranger District 2010). While short-term livestock exclosures increase native plant cover and stature in conifer forests (Kerns et al. 2011), relationships among livestock grazing, herbaceous production and plant community composition in forested landscapes have not been identified. Identifying and incorporating these relationships into management plans has the potential to improve rancher profitability, environmental quality, and the natural resource base on which livestock production, wildlife, hunting, aesthetics, tourism, and recreation depend.
The first federal timber sale was in the Black Hills, and today virtually all of the federal forested lands in the Black Hills have had timber harvests. Approximately 865,890 acres or 70 percent of Forest Service land in the Black Hills is suitable and available for timber harvest (USDA 2006). In 2007, the allowable sale quantity from suitable lands in the Black Hills National Forest was 838 million board feet (USDA 2008). For the decade ending in 2007, 163 thousand acres were harvested yielding 656 million board feet of sawtimber (USDA 2008). Abundant ponderosa pine regeneration every two to five years in the Black Hills (Boldt and Van Deusen 1974) contributes to an ever increasing backlog of pre-commercial and commercial thinning projects which are necessary to maintain desired tree densities and cost effectiveness of timber harvest (Shepperd and Battaglia 2002).
Identifying relationships between livestock grazing and ponderosa pine regeneration has implications for rancher profitability and maintenance of the natural resource base. The effect of cattle grazing on ponderosa pine regeneration remains an open question, and may improve the long term profitability of timber harvest. Most research hypothesizes that cattle grazing increases tree density by reducing the understory vegetation which in turn leads to more resource availability for increased tree recruitment (Rummell 1951, Zimmerman and Neuenschwander 1984, Belsky and Blumenthal 1997, Shepperd and Battaglia 2002). On the other hand, cessation of grazing is associated with increased canopy cover, tree density, and basal area and decreased diameter at breast height (Bakker and Moore 2007); these changes to forest structure tend to decrease profitability of timber harvest and increase wildfire hazard. Grazing practices may reduce pine regeneration and intermediate thinning treatments required to produce merchantable timber, thereby increasing the profitability of timber harvest and improving rancher profitability. Because catastrophic wildfires cross public and private land boundaries, a reduction in wildfire risk irrespective of land ownership, helps ensure rancher profitability by protecting the natural resource base.
Better understanding of relationships among past resource use, present forage production, plant community composition, and pine seedling recruitment, may lead to management practices which maximize economic, aesthetic, and environmental ecosystem goods and services. Ranchers, communities, and society as a whole benefit from improved economics, environmental quality, wildlife, hunting, aesthetics, tourism and recreation.
Objectives for this project include: 1)field data collection and analysis, 2) a presentation for the Rangeland Management Specialists at the Black Hills National Forest, 3) extension publications and online resources, 4) one chapter of my Ph.D. dissertation, and refereed papers. Project funds were used for data collection and analysis. We collected data in 44 pastures during the summer of 2015. All data has been entered, and data analysis is well under way. Data from this project will be presented on February 1, 2016 at the 2016 Society for Range Management meeting in Corpus Cristi, TX., and discussions with some of the local public land stewards are planned for January. Data from this project is forming the basis for one of my dissertation chapters. Presentations, extension publications and online resources, my dissertation, and refereed papers will all contribute to increasing knowledge and understanding of how livestock grazing practices in forested landscapes influence the natural resource condition and its ability to sustainably provide goods and services, and may lead to improved management practices which increase profitability, environmental quality, and quality of life.
Study Area. We worked in the Mystic Range District of the Black Hills National Forest. The Black Hills of South Dakota and associated Bear Lodge Mountains of eastern Wyoming encompass about 3.5 million acres, with roughly half the area supporting forest or woodland cover. Essentially pure stands of climax Rocky Mountain ponderosa pine (Pinus ponderosa var. scopulorum Engelm) predominate on about 1.5 million acres of the Black Hills (Larson and Johnson 2007). Fire exclusion, timber harvest, and livestock grazing have altered the structure of the Black Hills, SD pine forest.
Structure of the Black Hills forest has changed since pre-settlement times (McAdams 1995, Brown and Cook 2006). Historically, the Black Hills included a mosaic of meadows, open savannah like stands, and dense closed canopy stands. While some of this heterogeneity remains, the present forest has about 5 times more trees with about twice the basal area in the 0-20 cm diameter size (McAdams 1995). Present basal area is similar to the past; however a shift in the number and size of trees has occurred (Brown and Cook 2006). Similar trends in tree density and DBH have been found in other forests of the interior west (Moore et al. 2004), and have been attributed to timber harvest and fire suppression (Cooper 1960, Fulé et al. 1997, Brown and Cook 2006).
Forest fires have played an important role in maintaining forest structure in the Black Hills. There is evidence of large stand replacing fires prior to 1900, however their frequency of occurrence remains unknown (Graves 1899, Parrish et al. 1996, Shinneman and Baker 1997). The longest fire free period for this area occurred from 1890 to 1994 and is likely the result of land use change (Brown and Sieg 1996). Black Hills regional fire years are synchronous with cool La Nina phases of the Pacific Decadal Oscillation and warm phases of the Atlantic Multi-decadal Oscillation (Brown 2006).
The Black Hills National forest is the most intensively managed in the nation (Hunter et al. 2007). Current and past management strategies in the Black Hills include commercial timber harvest, intermediate thinning, fuel reduction thinning, livestock grazing, and prescribed fire. Prescribed fire has traditionally been limited in area due to timber and grazing value.
The Black Hills were the site of the first federal timber sale in U.S. history, and today virtually all of the federal forested lands in the Black Hills have had timber harvests. Approximately 865,890 acres or 70 percent of Forest Service land in the Black Hills is suitable and available for timber harvest (USDA 2006). In 2007, the allowable sale quantity from suitable lands in the Black Hills National Forest was 838 million board feet (USDA 2008). For the decade ending in 2007, 163 thousand acres were harvested yielding 656 million board feet of sawtimber (USDA 2008). Four harvest methods have been used in the Black Hills: 1) two cut shelterwood, 2) three-cut shelterwood, 3) seed tree, and 4) clearcut (Shepperd and Battaglia 2002). In the Black Hills, there is an ever increasing backlog of pre-commercial and commercial thinning projects which are necessary to maintain desired tree densities and cost effectiveness of timber harvest (Shepperd and Battaglia 2002).
Livestock are grazed on most of the land in the Black Hills. There are 1.04 million acres of suitable grazing land in the Black Hills National Forest representing 83 percent of Forest Service land (USDA 2006). This land is expected to produce 233 million pounds of forage on a sustainable annual basis with 127 million pounds or 128,000 AUMs allocated to livestock, and the rest allocated to wildlife (USDA 2006). In 2009, 260 permittees leased the suitable grazing lands in the Black Hills National forest (Hocking et al. 2010). Grazing also occurs on many of the 308,000 acres of private forest land in the Black Hills.
We developed a suite of 16 models of herbaceous production based on soil type and tree canopy cover for each pasture in the mystic range district. We developed 4 base models from publicly available data. Soil data provided an estimate of herbaceous production based on soil type, growing conditions (favorable, normal, and unfavorable), and three tree canopy cover classes (0-25%, 25-50%, and 50-100%). A 2008 VegMap, available for the Black Hills National Forest, provided tree canopy cover and habitat structural stage. Hansen 2013 provided a second estimate of tree canopy cover based on Landsat imagery. Slope and aspect were derived from 10 meter digital elevation model. ArcGIS was used to create 2 polygon feature classes: 1) soil type and VegMap08 tree canopy cover, and 2) soil type and Hansen13_2000 tree canopy cover. This was then exported for model development using R.
Base model production is based on: 1) soil type production by tree canopy cover class and VegMap08 tree canopy cover, 2) soil type and VegMap08 tree canopy cover using nonlinear equation for production by canopy cover, 3) soil type production by tree canopy cover class and Hansen13_2000 tree canopy cover, and 4) soil type and Hansen13_2000 tree canopy cover using nonlinear equation for production by canopy cover. From the base models, we created subsequent models by removing production from: 1) areas with slope greater than 35 % or 19.29 degrees, 2) areas with more than 30% tree canopy cover, and 3) areas that do not have favorable habitat structual stage.
We identified 4 cattle grazing management practices based on the modeled herbaceous production and USFS distribution and grazing instructions and actual use data reported by each permittee for each allotment and pasture between 1999 and 2014. The management practices we identified are: 1) duration of occupancy, 2) relative use, 3) timing of use, and 4) ratio of non-forested area contribution to herbaceous production. We considered the ratio of non-forested area contribution to herbaceous production as a management practice because the land manager at some point decided how to partition the landscape in to the various pastures. The reported use data provide timing of use, days of occupancy, number and type of animals (cow calf pair, bulls, yearlings). From that we derived animals per ha, animal unit months (AUM) per ha, and estimated cattle consumption, which is the mass of forage the planned number of cattle consume during the planned grazing period (days of occupancy) based on a 450 kg cow consuming 11.8 kg / day modified by 1.25 for cow calf pairs, 0.75 for yearlings, and 1.8 for bulls to account for modern cattle weights (Uresk 2010). Relative use (herbage allowance), was calculated by dividing each herbaceous production model by dividing the estimated cattle consumption.
To investigate the influence of the 4 management practices on forage production, plant species diversity and ponderosa pine regeneration, we collected biomass and plant community composition and ponderosa pine seedling data in pastures under different grazing management strategies. We sampled pastures in the Mystic Range district of the Black Hills National Forest following a replicated regression approach (Cottingham et al. 2005) to provide the power of both regression and ANOVA that spanned the ranges of both days of occupancy and modeled production to use ratio. We visited 44 pastures that span the range of days of occupancy and relative use, and are broadly distributed throughout the Mystic Range District of the Black Hills National Forest. We included six pastures that have not been grazed by livestock for periods ranging from 10 to relative use 25 years, four pastures consistently grazed in the early summer, four pastures consistently grazed in midsummer, and five pastures consistently grazed in late summer.
Within each pasture we will collect plant community composition, biomass production, vegetation stature, and ponderosa pine regeneration data. Plant community compositioin data was collected between June and August, biomass production and vegetation stature data was collected between August and early September, and Ponderosa Pine regeneration data was collected in May and June. Within each pasture, we randomly selected 3 non-forested locations that were within either rangeland soils or grassland plant communities and were at least 250 m from water sources. We then randomly selected 12 forested locations that were at least at least 250 m from water sources and less than 500 m from the non-forested locations. Plant community composition, bare ground and litter were measured in square 1 m2 plots at the 3 non-forested locations and at 3 forested locations. Percent cover of each plant species present, bare ground and litter were grouped into seven classes based on Daubenmire (1959): 1 is < 1%, 2 is 1-5%, 3 is 5-25%, 4 is 25-50%, 5 is 50-75%, 6 is 75-95%, and 7 is 95-100%. Three circular ¼ m2 plots, collocated with the plant community composition plots, were clipped, dried and weighed to estimate biomass production. Visual obstructive readings were made along 200 m transects collocated with the 3 non-forested plant community composition and biomass clipping plots. Along each transect, visual obstructive readings (VOR) were measured at 20 points with 4 readings at each point using a modified Robel Pole with half inch bands (Benkobi et al. 2000, Uresk and Benzon 2007, Uresk et al. 2009a, Uresk et al. 2009b) at 10 m intervals. Ponderosa pine seedlings were counted in quarter sections of a circle with a 10 m radius at each of the 12 randomly selected forested locations. Stems of all ponderosa pine more than one year old (i.e., no cotyledons present and stem woody) but with DBH < 2.54 cm will be tallied by height class (≤ 50cm, > 50cm and ≤ 137 cm, and > 137 cm). Seedlings will be counted in quarters of the circle, with values being recorded separately for each quarter. In 2014, counts stopped after the sum of seedlings for one or more quarters is greater than 100; however, the count was completed for the entire quarter in which this sum was reached, and the area (number of quarters) counted for each species recorded. While this flexibility in the number of quarters in which seedlings are counted seemed necessary to prevent extraordinary amounts of time spent counting seedlings in very dense stands, in 2015 we counted all quarter sections regardless of the number of seedlings encountered.
Plant community composition changes with respect to relative use of each pasture. Native plant species richness increases up to an intermediate level of intensity of use, and then proceeds to decline. This is in agreement with the intermediate disturbance hypothesis. The pastures that have not been grazed for 10 to 25 years had the lowest native species richness.
Biomass production increased with respect to relative use. The pastures that have not been grazed for 10 to 25 years had the lowest herbaceous production.
Vegetation stature increased with respect to biomass production, however was not related to any of the grazing management practices identified..
Ponderosa pine regeneration does not seem to be related to any of the grazing management practices identified.
Educational & Outreach Activities
This work will be presented at the 2016 Society for Range Management meeting in Corpus Cristi, TX.
These preliminary results suggest that an intermediate level of grazing use may be beneficial for maintaining species richness and herbaceous production in forested ecosystems. In the Black Hills National Forest, a few grazing allotment pastures were recently taken out of grazing use because of their location within a wildlife preserve. This work suggests that grazing in these particular pastures may have been more beneficial than previously achnowledged.
Areas needing additional study
Additional data at higher ranges of intensity of use would strengthen these finding.