Effects of mastication treatments on ponderosa pine understory communities

Background/Question/Methods

Thinning by mastication has become a common and cost-effective means for fuel reduction and restoration of open ponderosa pine (Pinus ponderosa) forest, but mastication effects on the understory are still unknown. This study examined the spatial structure of fuels, soil and vegetation at Heil Valley Ranch CO in areas masticated compared to a control area and thinning. The objectives were to determine to what extent mastication alters forest floor fuels, soil structure, and vegetation composition and diversity. Further, the spatial structure of these understory components were examined to help understand the impacts of mastication and influences on understory heterogeneity. Data were collected from a stratified random placement of 100 1m² plots in each treatment type where vegetation cover was collected using a modified Daubenmire scale. Soil cores were extracted within the top 20 cm of the soil surface from 15 plots in each site, and fuel data were collected from five locations within each site. We expected the thinning and mastication sites to have the highest fuels and vegetation diversity (due to a high exotic species diveristy), but the least heterogeneity. Control plots were expected to have the lowest fuels and vegetation diversity and the most heterogeneity.

Results/Conclusions

The results show an increased level of available fuels in the mastication site when compared to thinning, especially class 2 woody biomass. Mastication also increased the levels of duff present at the site (>600g m²) while not significantly changing available soil nutrients level, which could be due to the lack of time needed for proper decay and return of the nutrients to the soil. Overall cover was similar to thinning and control sites (<50% total cover). Diversity values of the mastication site were slightly higher than the control site and less than the thinning site. Indicator species of the mastication site included Elymus trachycaulus, Phacelia hastate, Silene antirhinna, and Verbascum thapsus. The spatial structure of the understories did vary among treatments; mastication and thinning sites were more homogeneous than the control site. The results suggest that mastication may be just as effective as thinning for maintaining ponderosa pine communities, but longer term research is needed to fully determine efficacy.