Jodi A. Forrester

Mortality and replacement patterns of an old-growth Acer-Fagus woods in the Holden Arboretum, northeastern Ohio.

Abstract The objective of this study was to establish baseline data for the structure and dynamics of an old-growth beech (Fagus grandifolia)-sugar maple (Acer saccharum) woods in northeastern Ohio before the anticipated future impacts of disturbances such as beech bark disease. Several parameters were selected for study based on their likelihood of being influenced by these disturbances including: (1) species composition; (2) mortality and growth rates of trees, overall, by species and by size class; (3) canopy replacement patterns; (4) coarse woody debris (CWD) characteristics; and (5) the understory response to existing openings and its implications for change in the forest under present conditions. This study extends our understanding of beech-sugar maple old growth because our site is, perhaps, the most northeasterly one not yet affected by beech bark disease and because it is the only studied site influenced by weather conditions generated by Lake Erie. The overall annual mortality rate (from 1992 to 1997) of 2.3% was higher than that reported for other old-growth woods (1%). Mortality was highest for the large canopy stems (≥50 cm dbh) of beech and the subcanopy stems (10–25 cm dbh) of sugar maple. Growth rates decreased with stem size for beech, but increased with stem size for sugar maple. Over the 5 y period beech decreased in relative basal area and relative density whereas sugar maple increased in both measures. CWD mass (35.9 Mg ha−1) was similar to other old-growth deciduous forests. Beech mortality has been greater than sugar maple mortality for several years. Sugar maple and beech were dominant in the understory although few stems <1 cm dbh were found near treefall gaps. Older gaps had more numerous and larger stems. Currently, the structure and dynamics of the woods are very similar to other old-growth beech-sugar maple forests of the region. Beech is present in all size classes. However, the number of large beech stems has been declining steadily even though beech bark disease has not yet reached the area.

Conversion of open lands to short‐rotation woody biomass crops: site variability affects nitrogen cycling and N2O fluxes in the US Northern Lake States

Short‐rotation woody biomass crops (SRWC) have been proposed as a major feedstock source for bioenergy generation in the Northeastern US. To quantify the environmental effects and greenhouse gas (GHG) balance of crops including SRWC, investigators need spatially explicit data which encompass entire plantation cycles. A knowledge gap exists for the establishment period which makes current GHG calculations incomplete. In this study, we investigated the effects of converting pasture and hayfields to willow (Salix spp.) and hybrid‐poplar (Populus spp.) SRWC plantations on soil nitrogen (N) cycling, nitrous oxide (N2O) emissions, and nitrate (NO3−) leaching at six sites of varying soil and climate conditions across northern Michigan and Wisconsin, following these plantations from pre conversion through their first 2 years. All six sites responded to establishment with increased N2O emissions, available inorganic N, and, where it was measured, NO3− leaching; however, the magnitude of these impacts varied dramatically among sites. Soil NO3− levels varied threefold among sites, with peak extractable NO3− concentrations ranging from 15 to 49 g N kg−1 soil. Leaching losses were significant and persisted through the second year, with 44–112 kg N ha−1 leached in SRWC plots. N2O emissions in the first growing season varied 30‐fold among sites, from 0.5 to 17.0 Mg‐CO2eq ha−1 (carbon dioxide equivalents). N2O emissions over 2 years resulted in N2O emissions due to plantation establishment that ranged from 0.60 to 22.14 Mg‐CO2eq ha−1 above baseline control levels across sites. The large N losses we document herein demonstrate the importance of including direct effects of land conversion in life‐cycle analysis (LCA) studies of SRWC GHG balance. Our results also demonstrate the need for better estimation of spatial variability of N cycling processes to quantify the full environmental impacts of SRWC plantations.

Evidence for a recent increase in forest growth is questionable

In a recent article, McMahon et al. (1) examined forest-plot biomass accumulation across a range of stands in the mid-Atlantic United States and suggest that climate change and trends in atmospheric CO2 explain an increase in forest growth. To show this increase, they fit a simple model to live above-ground forest biomass (AGB) as a function of stand age, and then propose that the derivative of this model is the expected rate of ensemble biomass change (). They conclude that biomass changes within census plots that exceed the ensemble expectation constitute recent increases in growth rates.

Isolating the Effects of White-tailed Deer on the Vegetation Dynamics of a Rare Maritime American Holly Forest

Abstract Effects of multiple herbivores were isolated in a rare, old-growth, maritime forest that has been affected by high white-tailed deer (Odocoileus virginianus) populations for several decades. Three decades of change in the plant community was described using permanent plots and nearly two decades of recovery using deer exclosures. Additional short-term exclosure experiments were used to separate the effect of rabbit and vole herbivory and the influence of canopy type on understory vegetation. We assessed whether natural enclosures formed by high densities of greenbrier (Smilax rotundifolia and S. glauca) provide spatial refugia for plant species from deer. Significant differences in fenced plots indicate that deer, rabbits and voles individually affect the understory vegetation, though rabbits and voles are secondary to deer that are the major herbivore in the American holly (Ilex opaca) forest. Plant cover decreased within permanent plots from 1967 to 1986; during the same time period deer densities increased drastically island-wide. Since plots were fenced in 1986 no additional significant changes were detected, but this is likely due to an inadequate sample size. The cover of all species depended on the interaction of fencing and canopy type with significantly higher plant cover in fenced plots beneath mixed or exclusively deciduous canopy. The proportion of woody stems surpassing 0.5 m tall was significantly higher when stems were fenced. Browsing impacts were apparent on approximately a quarter of the vegetation in June 2003. Plant cover, richness and diversity were higher within natural greenbrier enclosures. Overall the exclosure studies indicate the potential natural recovery that could occur within the forest if deer herbivory were limited. Few species have been extirpated, although several are confined to the greenbrier enclosures. Under the current level of herbivory, the maritime holly forest composition will be altered, changing the characteristic canopy of a critically imperiled plant community.

Temporal trends and sources of variation in carbon flux from coarse woody debris in experimental forest canopy openings

Pulses of respiration from coarse woody debris (CWD) have been observed immediately following canopy disturbances, but it is unclear how long these pulses are sustained. Several factors are known to influence carbon flux rates from CWD, but few studies have evaluated more than temperature and moisture. We experimentally manipulated forest structure in a second-growth northern hardwood forest and measured CO2 flux periodically for seven growing seasons following gap creation. We present an analysis of which factors, including the composition of the wood-decay fungal community influence CO2 flux. CO2 flux from CWD was strongly and positively related to wood temperature and varied significantly between substrate types (logs vs. stumps). For five growing seasons after treatment, the CO2 flux of stumps reached rates up to seven times higher than that of logs. CO2 flux of logs did not differ significantly between canopy-gap and closed-canopy conditions in the fourth through seventh post-treatment growing seasons. By the seventh season, the seasonal carbon flux of both logs and stumps had decreased significantly from prior years. Linear mixed models indicated the variation in the wood inhabiting fungal community composition explained a significant portion of variability in the CO2 flux along with measures of substrate conditions. CO2 flux rates were inversely related to fungal diversity, with logs hosting more species but emitting less CO2 than stumps. Overall, our results suggest that the current treatment of CWD in dynamic forest carbon models may be oversimplified, thereby hampering our ability to predict realistic carbon fluxes associated with wood decomposition.

Soil fungal and bacterial responses to conversion of open land to short-rotation woody biomass crops

Short‐rotation woody biomass crops (SRWCs) have been proposed as an alternative feedstock for biofuel production in the northeastern US that leads to the conversion of current open land to woody plantations, potentially altering the soil microbial community structures and hence functions. We used pyrosequencing of 16S and 28S rRNA genes in soil to assess bacterial and fungal populations when ‘marginal’ grasslands were converted into willow (Salix spp.) and hybrid poplar (Populus spp.) plantations at two sites with similar soils and climate history in northern Michigan (Escanaba; ES) and Wisconsin (Rhinelander; RH). In only three growing seasons, the conversion significantly altered both the bacterial and fungal communities, which were most influenced by site and then vegetation. The fungal community showed greater change than the bacterial community in response to land conversion at both sites with substantial enrichment of putative pathogenic, ectomycorrhizal, and endophytic fungi associated with poplar and willow. Conversely, the bacterial community structures shifted, but to a lesser degree, with the new communities dissimilar at the two sites and most correlated with soil nutrient status. The bacterial phylum Nitrospirae increased after conversion and was negatively correlated to total soil nitrogen, but positively correlated to soil nitrate, and may be responsible for nitrate accumulation and the increased N2O emissions previously reported following conversion at these sites. The legacy effect of a much longer grassland history and a second dry summer at the ES site may have influenced the grassland (control) microbial community to remain stable while it varied at the RH site.

Experimentally linking disturbance, resources and productivity to diversity in forest ground-layer plant communities

Summary 1. Disturbance can function to maintain diversity within forest communities; however, specific mechanisms and the relationship to productivity are not well understood. 2. We examined these linkages in forest ground-layer plant communities using a replicated, manipulative field experiment. Treatments included a range of gap sizes and untreated controls. We assessed spatial and temporal responses over the first three years following gap creation. 3. Light transmittance and soil water content increased with gap size, while rates of colonization and species richness increased after a critical threshold. Subsequent increases in productivity were associated with declines in species richness, increased rates of local extirpation and a unimodal relationship between species richness and productivity at the individual quadrat scale (4 m 2 ). 4. The richness and productivity of vines, shrubs and especially graminoids, increased within 200– 380 m 2 gaps treatments. However, the productivity of forbs and tree seedlings did not, showing possible drought sensitivity overriding treatments. Spatial and temporal partitioning of gaps occurred as a result of interactions between species traits and environmental conditions. Significantly, productivity and richness showed complex relationships with canopy structure. 5. Synthesis. Our results show that richness increases to an asymptote after a critical threshold in disturbance severity initially. Decreases in species richness over time associated with increases in productivity may eventually result in the unimodal relationship predicted by the intermediate disturbance hypothesis. However, species composition continues to differ with canopy gap size, suggesting a range of canopy gap sizes is required to maintain the greatest diversity of plant species over broader spatial and temporal scales.

Disturbance History and Mortality Patterns in a Rare Atlantic Barrier Island Maritime Holly Forest

Abstract We describe the long-term regeneration dynamics of the maritime holly forest, a plant community restricted to two known locations on Atlantic barrier islands: the Sunken Forest, part of Fire Island National Seashore, New York, and the Sandy Hook holly forest, part of Gateway National Recreation Area, New Jersey. In order to assess the short-term changes in vegetation apparent at one location, we examined the long-term dynamics of these two forests. Analysis of permanent plots in the Sunken Forest indicated the overstory structure and composition had changed minimally, but the understory decreased in cover and diversity over a period of 35 years (1967–2002). Patterns differed at Sandy Hook, with little change in the forest understory evident in permanent plots monitored over a period of 14 years (1989–2003). The age distributions indicate that both forests are uneven aged, but the trees at the Sunken Forest are older than those at Sandy Hook. While there has been an overall lack of establishment of any species since the 1970s at the Sunken Forest, several stems were present in the smallest age and size classes within the Sandy Hook holly forest. Release patterns in the tree cores reveal responses to frequent moderate disturbances including hurricanes, tropical storms, and northeasters. No recent changes in the frequency of canopy disturbances were evident in the tree core analysis, but herbivory has likely increased with the dramatically rising Odocoileus virginianus population at the Sunken Forest since the 1970s. The maritime holly forest relies on new individuals establishing in openings created by moderate disturbances; the current high level of herbivory at the Sunken Forest is disrupting the long-term regeneration patterns of this critically imperiled maritime holly forest.

Arboreal vegetation, coarse woody debris, and disturbance history of mature and old-growth stands in a coniferous forested wetland1

Abstract Forrester, J. A. (SUNY, College of Environmental Science and Forestry, 1 Forestry Drive, Syracuse, NY 13210-2778), T. E. Yorks (Environmental Studies Program, Cazenovia College, 22 Sullivan Street, Cazenovia, NY 13035) and D. J. Leopold (SUNY, College of Environmental Science and Forestry, 1 Forestry Drive, Syracuse, NY 13210-2778). Arboreal vegetation, coarse woody debris, and disturbance history of mature and old-growth stands in a coniferous forested wetland. J. Torrey Bot. Soc. 132: 252–261. 2005.—We quantified the forest age and tree size structure of an old-growth and mature stand in a coniferous forested wetland in central New York, USA. We also determined the volume and decay class distribution of standing and downed coarse woody debris. The old-growth stand contains eastern white pine (Pinus strobus L.) > 400 years old and other species > 200 years old. Live tree basal area in the old-growth area (36 m2·ha−1) was dominated by approximately equal amounts of balsam fir (Abies balsamea (L.) Miller.), eastern white pine, and northern white-cedar (Thuja occidentalis L.; 11, 10, and 10 m2·ha−1, respectively), but eastern white pine was less abundant in the mature stand. Snag basal area was 7 m2·ha−1 in the old-growth and mature stands and was dominated by balsam fir and northern white-cedar. Total coarse woody debris (CWD) volumes were 145 and 83 m3·ha−1 in the old-growth and mature stand, respectively. The decay class distribution in each area was skewed toward advanced decay classes. Most CWD was in the form of logs and snags in both areas, but snag volume in the old-growth area was approximately 3 times that in the mature stand (75 vs. 26 m3·ha−1). In both stands, balsam fir and northern white-cedar each accounted for 21–30% of total CWD. Eastern white pine contributed 28% of the CWD in the old-growth area but was not present as CWD in the mature stand. Both forests are uneven-aged, with the earliest species establishing in the 1600s and 1750s for the old-growth and mature stands, respectively. No species exhibited major growth releases in the old-growth or mature stands, but several exhibited moderate releases. The age and diameter distributions of the old-growth area suggest that no stand-initializing disturbances have affected the forest for at least 250 years. Instead, fine-scale treefall gaps created by single or multiple treefalls are the dominant mode of regeneration in this forest.