Factors influencing the persistence of reindeer lichens (Cladonia subgenus Cladina) within frequent-fire environments of the Mid-Atlantic Coastal Plain, USA

Background Prescribed fire is increasingly used to accomplish management goals in fire-adapted systems, yet our understanding of effects on non-target organisms remains underdeveloped. Terricolous lichens in the genus Cladonia P. Browne, particularly cushion-forming reindeer lichens belonging to Cladonia subgenus Cladina Nyl., fit into this category, being characteristic of fire-adapted ecosystems, yet highly vulnerable to damage or consumption during burns. Moreover, inherently slow dispersal and growth rates raise questions about how to conserve these taxa in the context of fire-mediated restoration management. This research was undertaken to identify factors that contribute to Cladonia persistence within areas subject to repeated burning and involved tracking the fate of 228 spatially isolated individuals distributed across seven sites previously burned zero to two times. Site selection was determined by edaphic factors associated with a rare inland dune woodland community type known to support relatively high densities of Cladonia. Results Evaluated across all sites, the post-burn condition of Cladonia subtenuis (Abbayes) Mattick samples, categorized as intact (32%), fragmented (33%), or consumed (36%) individuals, approximated a uniform distribution. However, their status was highly variable at the different sites, where from 0 to 70% were assessed as intact and 11 to 60% consumed. Machine-learning statistical techniques were used to identify the factors most strongly associated with fire damage, drawing from variables describing the proximate fuel bed, growth substrate, and fire weather. The final descriptive model was dominated by variables characterizing the understory fuel matrix. Conclusions Areas with highly contiguous fuels dominated by pyrogenic pine needles were most likely to result in consumption of individual Cladonia, whereas those growing in areas with low fuel continuity or in areas dominated by hardwood litter were more likely to persist (intact or as fragments). Further, substrates including bare soil and moss mats afforded more protection than coarse woody debris or leaf litter in settings where fuels were both contiguous and highly flammable. Our findings describe the characteristics of within-site fire refugia, the abundance of which may be enhanced over time through restoration and maintenance treatments including thinning, promotion of mixed-species overstory composition, and periodic burning. Because lichens contribute to, and are considered reliable indicators of forest health, fire-based restoration management efforts will benefit from improved understanding of how these vulnerable organisms are able to persist.

Long-term influence of disturbance-generated microsites on forest structural and compositional development

Wind disturbance generates heterogeneous microsite structures, including downed logs, windthrow mounds, and pits. While these structures can provide opportunities for regeneration of certain tree species, the long-term influence of microsites and microsite heterogeneity on forest development has not been quantified. We used long-term measurements of a formerly old-growth Tsuga canadensis – Pinus strobus forest severely damaged by a category 3 hurricane in 1938 to quantify the impact of microsite conditions on overstory composition and structure. We asked (i) “What are the patterns in live-tree size, growth, and mortality five and seven decades after disturbance?” and (ii) “What roles do microsite heterogeneity and the presence of disturbance-generated microsites play in long-term forest development following disturbance?” We compared live-tree (>2 cm DBH) development and survival to microsite heterogeneity at the 100 m2 scale. Microsite diversity was positively related to overstory species diversity and stem density and negatively related to average tree size. We propose that plots with higher microsite diversity may have experienced more severe local disturbance, which allowed more species and individuals to establish and created varied niches that allowed these individuals to coexist and generate greater stand-level diversity. These persistent relationships highlight how microsite conditions affect forest development after severe disturbances.

Influence of dam regulation on 55-year canopy shifts in riparian forests

Floodplain and swamp forests are undergoing extensive changes due to altered flow regimes, invasive species, logging, and various land use changes. These changes often go unnoticed due to the absence of adequate baseline data and monitoring. Using a data set from 55 years ago, we resampled 50 lowland forest stands in southern Wisconsin to assess changes in forest overstory composition, structure, diversity, and dominant species abundances. We also applied univariate and multivariate analyses to determine whether these changes varied between dam-regulated and unregulated rivers, tree species with different flooding tolerances, the presence of logging, and variations in edaphic and hydrologic variables. Although these forests display various types of resilience, their forest canopies are substantially different from 55 years ago, reflecting shifts in hydrology and the impacts of disease. On average, these forests have retained the same local (alpha) diversity but have converged in species composition (declined in beta diversity). They are now composed of more and smaller trees. Along the unregulated rivers, colonizing species have declined while later successional flood-tolerant species have increased. In the aftermath of Dutch elm disease, Ulmus spp. have greatly declined in abundance and size. Species with less flooding tolerance have generally increased across sites, especially along dam-regulated rivers. Because they are subject to chronic disturbances that reset succession, floodplain forests may respond more readily to shifts in disturbances regimes. Such forests may therefore serve as sentinels for forecasting the types of change that we can expect to unfold more gradually in upland forests.

Oak Forest Composition on Contrasting Soil Types at the Mohonk Preserve, Eastern New York

This research investigated overstory and understory forest composition for 10 sites derived from either shale or sandstone conglomerate parent material on the Shawangunk Ridge in eastern New York. Overstory composition in both soil types was dominated by red oak (Quercus rubra) and chestnut oak (Quercus montana), but the overstory on shale sites was more diverse (14 tree species) and had less oak than sandstone sites (with only 6 tree species). A total of 17 species were recorded as regeneration on shale sites, where seedlings averaged 21,466/ha and saplings averaged 1,833/ha. Dominant seedling on shale sites were chestnut oak (7,100/ha) and red oak (3,583/ha); chestnut oak had significantly more seedlings on shale versus sandstone sites. Saplings on shale sites were predominantly Hamamelis virginiana and Acer pensylvanicum. On sandstone sites, seedlings averaged 6,425/ha (including 2,075 oaks and 2,250 red maple per ha). Sapling numbers for all species were low (1,400/ha) and were mostly red maple. These forests are unique because of the relatively high density of oak seedlings on certain sites and low density of red maple across all sites. This variation in regeneration as well as management strategies to promote additional oak regeneration and canopy recruitment are discussed for these and similar forests.