Justin L. Hart

Gap-scale disturbance processes in secondary hardwood stands on the Cumberland Plateau, Tennessee, USA

Disturbance regimes in many temperate, old growth forests are characterized by gap-scale events. However, prior to a complex stage of development, canopy gaps may still serve as mechanisms for canopy tree replacement and stand structural changes associated with older forests. We investigated 40 canopy gaps in secondary hardwood stands on the Cumberland Plateau in Tennessee to analyze gap-scale disturbance processes in developing forests. Gap origin, age, land fraction, size, shape, orientation, and gap maker characteristics were documented to investigate gap formation mechanisms and physical gap attributes. We also quantified density and diversity within gaps, gap closure, and gap-phase replacement to examine the influence of localized disturbances on forest development. The majority of canopy gaps were single-treefall events caused by uprooted or snapped stems. The fraction of the forest in canopy gaps was within the range reported from old growth remnants throughout the region. However, gap size was smaller in the developing stands, indicating that secondary forests contain a higher density of smaller gaps. The majority of canopy gaps were projected to close by lateral crown expansion rather than height growth of subcanopy individuals. However, canopy gaps still provided a means for understory trees to recruit to larger size classes. This process may allow overtopped trees to reach intermediate positions, and eventually the canopy, after future disturbance events. Over half of the trees located in true gaps with intermediate crown classifications were Acer saccharum, A. rubrum, or Liriodendrontulipifera. Because the gaps were relatively small and close by lateral branch growth of perimeter trees, the most shade-tolerant A. saccharum has the greatest probability of becoming dominant in the canopy under the current disturbance regime. Half of the gap maker trees removed from the canopy were Quercus; however, Acer species are the most probable replacement trees. These data indicate that canopy gaps are important drivers of forest change prior to a complex stage of development. Even in relatively young forests, gaps provide the mechanisms for stands to develop a complex structure, and may be used to explain patterns of shifting species composition in secondary forests of eastern North America.

Climate remains an important driver of post‐European vegetation change in the eastern United States

Department of Geography, University of Wisconsin-Madison, 550 North ParkStreet, Madison, WI 53706, USAThe influence of climate on forest change during thepast century in the eastern United States was evalu-ated in a recent paper (Nowacki & Abrams, 2014)that centers on an increase in ‘highly competitivemesophytic hardwoods’ (Nowacki & Abrams, 2008)and a concomitant decrease in the more xerophyticQuercus species. Nowacki & Abrams (2014) con-cluded that climate change has not contributed sig-nificantly to observed changes in forest composition.However, the authors restrict their focus to a singleelement of climate: increasing temperature since theend of the Little Ice Age ca. 150 years ago. In theirstudy, species were binned into four classifications(e.g., Acer saccharum – ‘cool-adapted’, Acer rubrum –‘warm-adapted’) based on average annual tempera-ture within each species range in the United States,reducing the multifaceted character of climate into asingle, categorical measure. The broad temperatureclasses not only veil the many biologically relevantaspects of temperature (e.g., seasonal and extremetemperatures) but they may also mask other influ-ences, both climatic (e.g., moisture sensitivity) andnonclimatic (e.g., competition).Understanding the primary drivers of forest changeis critically important. However, using annual tem-perature reduces the broad spectrum of climaticinfluence on forests (e.g., Jackson & Overpeck, 2000;Jackson et al., 2009) to a single variable. Tsuga canad-ensis illustrates one example of the complex interac-tion between trees and temperature. In the southernpart of its range, Tsuga canadensis growth is weakly,but positively correlated with early growing-seasontemperature. However, this relationship becomesstronger and shifts to later in the season toward thenorthern part of its range (Cook & Cole, 1991). More-over, Tsuga canadensis growth is significantly andnegatively correlated with just May temperaturesduring the current growing season in the northeast-ern United States (Cook, 1991; Cook & Cole, 1991;Vaganov et al., 2011), while in the southeastern Uni-ted States it is strongly and negatively correlatedwith summer (June–August) temperatures (Hart et al.,2010). Trees can also be sensitive to diverse and ofteninteracting climate variables at various stages of theirlife cycles (Jackson et al., 2009). Interactions betweenprecipitation and temperature are clearly important(Harsch & Hille Ris Lambers, 2014; Martin-Benito &Pederson, accepted), and often lead to counterintui-tive responses. For example, some plant species thatwould have been expected to move north and ups-

Forest Dynamics in a Natural Area of the Southern Ridge and Valley, Tennessee

Abstract This study was initiated to document forest development in the oldest natural area in the Ridge and Valley of east Tennessee. The Ijams Nature Reserve was established in 1910 and provided the opportunity to document secondary succession of the oldest upland forest reserve in the region. We established forest inventory plots in the original land holding of the Ijams family to quantify species composition, stand structure, and successional dynamics. We also analyzed the radial growth patterns of trees to document stand age, recruitment, and the disturbance regime of the reserve. The forest was dominated by Quercus alba and Liriodendron tulipifera while Acer saccharum and Fagus grandifolia had high densities in the understory. Liriodendron tulipifera was the most important species in the stand because it colonized the site following agricultural abandonment and subsequently established in small canopy gaps. The stand had a reverse J-shaped diameter structure typical of regenerating forests. The forest experienced one stand-wide disturbance event likely attributed to the decline of Castanea dentata in the 1920s. The return interval of stand-wide disturbances was much longer than what has been reported in other eastern hardwood forests. With the exception of this one stand-wide release, the disturbance regime was characterized by localized, asynchronous events that influenced only neighboring trees. Under the current disturbance regime, composition of the stand is projected to change as shade-tolerant mesophytes in the understory (A. saccharum and F. grandifolia) are recruited to larger size classes. This phenomenon has been widely reported throughout the eastern United States and is most commonly linked to active fire suppression. However, the forest of the Ijams Nature Reserve has not burned during development and still shows a marked change in species composition even with no change in the fire disturbance regime. We propose the composition shift is related to understory facilitation by disturbance oriented canopy species that have created conditions favorable for the establishment of mesophytes and by the loss of C. dentata that resulted in canopy gaps.

Fire history from soil charcoal in a mixed hardwood forest on the Cumberland Plateau, Tennessee, USA1

Abstract In this study, we documented the presence of macroscopic (> 2 mm) charcoal, quantified charcoal mass, and radiocarbon-dated charcoal macrofossils in 10 soil cores to develop a coarse-resolution fire history for a mixed hardwood forest on the Cumberland Plateau in Tennessee. Macroscopic charcoal occurred in all 10 soil cores. Total dry mass of macroscopic charcoal varied by core and by depth layer. Charcoal fragments were most abundant in two non-adjacent cores (separated by ca. 80 m), a finding that may be evidence of a patchy fire regime in the study area. AMS radiocarbon dating of the five deepest charcoal samples indicated that the earliest recorded fire in the study site occurred around 6735 cal yr BP (calibrated years before 1950). Charcoal in surface soils was not dated but one deep sample indicated a fire during the historic period at approximately 174 cal yr BP. No overlap occurred within the 2-sigma calibrated age ranges of the dated charcoal samples, indicating a minimum of five separate fire events have occurred on the site during the last 6700 plus years. This was the first study to use soil charcoal to document past fire events in hardwood forests of the Cumberland Plateau and the first to examine the prehistoric fire regime of Quercus stands in the region at a local-scale. Our results provide a basis for reconstructing long-term fire histories at the stand-scale in Quercus-dominated forests of eastern North America.

THE HISTORICAL DENDROARCHAEOLOGY OF THE HOSKINS HOUSE, TANNENBAUM HISTORIC PARK, GREENSBORO, NORTH CAROLINA, U.S.A.

Abstract The Hoskins House is a two-story, single pen log structure located in Tannenbaum Historic Park, Greensboro, North Carolina. The house is thought to have been built by Joseph Hoskins, who lived in Guilford County from 1778 until his death in 1799. Previous archaeological testing of soil around the house yielded over 1000 artifacts, and the ceramics of these gave a Mean Ceramic Date (MCD) of 1810 as a possible initial year of construction. Our objective was to date the outermost rings on as many logs as were accessible in the Hoskins House to determine the year or range of years when the house was likely built. We compared 37 ring-width measurement series from 28 white oak group logs with a composite reference chronology created from three oak reference chronologies from Virginia. We found that the logs were cut over a 3-year period from 1811 to 1813, lending credence to the initial MCD of 1810. Joseph Hoskins had already passed away in 1799 and the property was deeded to his two sons, Joseph and Ellis. Ellis Hoskins eventually was later deeded sole possession of the property. The two-story log house located at Tannenbaum Historic Park may be more correctly called the “Ellis Hoskins House” rather than the “Joseph Hoskins House.”

Patterns of Riparian and In-stream Large Woody Debris Across a Chronosequence of Southern Appalachian Hardwood Stands

ABSTRACT: The density and volume of riparian and in-stream large woody debris (LWD) is hypothesized to be a function of forest disturbance and developmental processes. However, these relationships are poorly understood for many forest types, including hardwood forests of the southern Appalachian Highlands. We analyzed patterns of riparian and in-stream LWD in hardwood stands across three establishment classes (pre-1900s, 1930s, and 1950s) on the Cumberland Plateau to elucidate the relationships between forest development and LWD patterns. The stands were dominated by Fagus grandifolia, Quercus alba, and Lirodendron tulipifera. Density and volume of riparian LWD did not differ across the chronosequence. Density of riparian LWD ranged from 367 (1950s) to 407 (1930s) pieces ha-1 and volume ranged from 142.0 (pre-1900s) to 187.1 (1930s) m3 ha-1. Likewise, mean density and volume of in-stream LWD did not differ across the chronosequence. Density of in-stream LWD ranged from 20 pieces 100 m-1 (pre-1900s and 1950s) to 28 pieces 100 m-1 (1930s) and volume ranged from 4.8 m3 (1950s) to 8.3 m3 100 m-1 (1930s). We documented significantly greater volume of in-stream LWD in the stabilizing or armoring banks function class in the 1950s establishment class, but no other systematic differences. Based on species composition and size, we speculate that riparian LWD largely originated from trees that grew outside the riparian zone and were transported down slope. In contrast, in-stream LWD inputs were linked directly to the adjacent riparian zones.

THE FALL LINE: A PHYSIOGRAPHIC‐FOREST VEGETATION BOUNDARY*

The range boundaries for many tree species in the southeastern United States correspond to the Fall Line that separates the Coastal Plain from the Appalachian Highlands. Trees in the Coastal Plain with northern range boundaries corresponding to the Fall Line occur exclusively in alluvial valleys created by lateral channel migration. These species grow mostly on lower bottomland sites characterized by a high water table, soils that are often saturated, and low annual water fluctuation. In contrast to the Coastal Plain, the southern Appalachian Highlands are occupied mostly by bedrock streams that have few sites suitable for the regeneration of these species. The Fall Line is also an approximate southern boundary for trees common in the southern Appalachians that typically occur on either dry, rocky ridgetops or in narrow stream valleys, habitats that are uncommon on the relatively flat Coastal Plain. The ranges for many trees in eastern North America are controlled by large‐scale climatic patterns. Tree species with range boundaries corresponding to the Fall Line, however, are not approaching their physiological limits caused by progressively harsher climatic conditions or by competition. Instead, the Fall Line represents the approximate boundary of habitats suitable for regeneration.

Canopy Disturbance Patterns in Secondary Hardwood Stands on the Highland Rim of Alabama

Abstract Disturbance regimes of many hardwood forests of the eastern United States in the complex stage of development are characterized by localized canopy disturbance events that change fine-scale biophysical conditions. Recently, research has demonstrated the importance of gap-scale disturbance processes in secondary hardwood stands of the southern Appalachian Highlands. However, information on canopy disturbance patterns during early developmental stages is required from the broader geographic region for a comprehensive understanding of stand dynamics. The goal of this study was to reconstruct canopy disturbance history for mixed hardwood stands on the Highland Rim of Alabama to elucidate disturbance patterns during early development. We analyzed radial growth from 46 Quercus individuals to reconstruct canopy disturbance history. The majority (67%) of the trees analyzed exhibited release events. In total, 42 releases were detected and some trees experienced multiple events. Of these releases, 28 (67%) were classed as minor and 14 (33%) were classed as major. Mean release duration was 4.00 years ± 0.21 (SE) and the longest release was sustained for eight years. Based on mean release duration, we speculate that most of the canopy gaps were filled by lateral crown expansion rather than subcanopy height growth. We did not document any forest-wide disturbance events; a pattern that may be a regional phenomenon or may be related to forest age. Canopy disturbances became common after ca. 40 years of development. We propose that the frequency of canopy gaps will decrease and the size and magnitude of individual gaps will increase as the stands mature.

RADIAL GROWTH RESPONSES OF THREE CO-OCCURRING SPECIES TO SMALL CANOPY DISTURBANCES IN A SECONDARY HARDWOOD FOREST ON THE CUMBERLAND PLATEAU, TENNESSEE

We analyzed the radial growth patterns of Liriodendron tulipifera, Acer rubrum, and Acer saccharum growing in 39 canopy gaps in a mature secondary hardwood forest on the Cumberland Plateau in Tennessee to compare species-specific growth responses to small canopy disturbances. We tested for differences between mean radial growth increases during the year of release initiation (i.e., first year of discernible growth increase) over the year prior, mean percent growth increases during the year of release initiation over the year prior, mean release durations, and mean lag times between canopy gap formation and radial growth response. At each level of analysis (i.e., by species, canopy position, and gap position) only the radial growth increase during the year of release initiation over the year prior revealed significant differences. In each case where a systematic difference was noted, the growth increase of L. tulipifera was greater than one or both of the Acer species. However, field observation indicated accelerated growth of L. tulipifera was largely negated in the relatively small and short-lived gaps. Our findings provide information on the successional pathway of the forest, the physiological responses of these species to small canopy openings, and the applicability of these species to reconstruct canopy gap formation in secondary stands from tree-ring records.

Legacy of Charcoaling in a Western Highland Rim Forest in Tennessee

ABSTRACT Forests of the Western Highland Rim were heavily influenced by the iron industry during the 19th and 20th centuries. The production of iron required large amounts of charcoal. Timber was cut, burned in hearths to produce charcoal and then the charcoal was transported to local furnaces and forges. The goal of our study was to document the lasting effects of charcoal production on soil characteristics, species composition and stand structure for a forest on the Western Highland Rim in Tennessee. Fires used in hearths to produce charcoal were intense, spatially concentrated events that modified soil characteristics differently than typical surface fires. We hypothesized there would still be a footprint of the charcoal making process evidenced by systematic differences in forest composition and structural attributes that could be related to soil properties. Results show there were significant differences in some soil traits between charcoal hearths and surrounding sites. However, differing soil conditions have not significantly influenced forest development. Although tree density differed between hearths and adjacent areas, there were no systematic differences in tree species richness, diversity (H′), evenness (J) or basal area between charcoal hearth and non-hearth sites. Results of this study indicate the historic land use has minimal influence on modern forest communities in our Tennessee study site.