Ten species of anoles at Bajo Calima within the Choco of Western Colombia separate into two principal microhabitat groups: forest species, and those inhabiting openings and edges. The ten anoles further separate according to ground and vegetation dwellers. There is a relation at Bajo Calima between the number of anole species and vegetational structural diversity. Anole diversity within a given macrohabitat is by perch microsite/microclimate heterogeneity. These are the two major ecological dimensions along which similarity is limited or resources are partitioned.

Human land use legacies have significant and long lasting impacts across landscapes. However, investigating the impacts of ancient land use legacies ( > 400 years) remains problematic due to the difficulty in detecting ancient land uses, especially those beneath dense canopies. The city of Caracol, one of the most important Maya archaeological sites in Belize, was abandoned after the collapse of the Maya civilization (ca. A.D. 900), leaving behind numerous structures, causeways, and agricultural terraces that persist beneath the dense tropical forest of western Belize. LiDAR (Light Detection and Ranging) technology enables detection of below canopy Maya archaeological features, providing an ideal opportunity to study the effects of ancient land use legacies on contemporary tropical forest composition. LiDAR also provided us with a detailed record of the 3-dimensional forest structure over the 200 km2 study area. This allowed the investigation how ancient land uses continue to impact both forest composition, in terms of tree species, and forest structure. I recorded tree species over four land use categories: 1) structures, 2) causeways, 3) terraced, and 4) non-terraced land. Using non-metric multidimensional scaling (NMS) and multiresponse permutation procedures (MRPP) to test for differences between the classes, I found significantly distinct tree communities associated with the presence of terraces and the underlying topography. Terraced slopes appear to function as micro-valleys on the side of a hill, creating an environmental "bridge" between slope and valley tree communities. Tree species composition over causeways and structures was also found to be significantly different from terraced and non-terraced plots. Forest structure was assessed by extracting LiDAR points for terraced (n=150) and nonterraced (n=150) 0.25 ha plots. I calculated average canopy height, canopy closure, and vertical diversity from the height bins of the LiDAR points, using slope, elevation, and aspect as covariates. Using PerMANOVA I determined that forest structure over terraces was significantly different from non-terraced land. Terraces appear to mediate the effect of slope, resulting in less structural variation between slope and non-sloped land. These results led to the conclusion that human land uses abandoned >1000 years ago continue to impact the contemporary forests.

The ecology of subalpine fir relative to broom rust was investigated. Broom rust infections were most common in trees growing on limestone soils, and seldom occurred on trees growing on basalt soils. Even though plant moisture stress was consistently higher in the plants from limestone soils, the studies indicated that moisture stress is not the major factor causing infection. The amounts of available magnesium and phosphorus were much lower in the limestone soil. It is postulated that the higher plant moisture stress of subalpine fir growing on limestone soils may aggrevate the lack of nutrients and be a contributing factor to the susceptibility of subalpine fir to broom rust. Even though the study raises more questions than it answers, management prescriptions relative to this disease can be proposed. Pruning and burning of diseased branches should be evaluated as a possible method to control broom rust on subalpine fir. This species must be better managed because of its strategic position on watersheds and recreation sites of higher elevations.

Six forest areas destroyed by fire representing different seral stages of aspen development and conifer invasion were studied to determine successional dynamics and the related livestock and big game use. Factors measured were: (a) age, basal area, density and frequency of aspen and conifer trees; (b) density and frequency of under-story species; (c) forage production for forbs, grasses, and browse, and (d) animal-days use for deer, cattle and sheep. Aspen appeared in the community the spring following the fire and conifers appeared fifteen to twenty years later. Conifers had begun to dominate aspen on an eighty-two year old stand. The density and frequency of understory species was influenced by grazing pressure, age of the cormnunity and conifer basal area. Maximum densities were reached twenty years after the fire. Forage production was influenced by the age of the community and conifer basal area. Maximum forage production was reached on the twenty-one year old burn. Animal use was influenced by the amount of forage production, conifer basal area and competitive use by other animals.

No description available.

The processes that regulate nutrient access by forest trees exhibit substantial variability on both large and small spatial scales. Explicit study of this spatial variability promotes a better understanding of the structure and function of forests. While the importance of space in ecological processes is being increasingly appreciated, there are major gaps in our knowledge about how space influences plant nutrient supply, particularly within a forest stand. This dissertation consists of three chapters that examine the patterns, drivers, and implications of spatial variation in three main processes that make nutrients available to trees: throughfall nutrient deposition, soil nutrient mineralization, and root system development. In Chapter 1, I use data from a field experiment to examine the effect of fertilization on nutrient transfer from the canopy to the soil via throughfall and litterfall in a tropical rainforest. I demonstrate that at small spatial scales, canopy density controls the flux of nutrients in throughfall, while at large scales, soil fertility is an important control, especially for phosphorus. I also show throughfall can be as important as litterfall in the recycling of certain essential nutrients like potassium, and depending on soil fertility, phosphorus. In Chapter 2, I investigate the small scale spatial patterning in soil nitrogen, a nutrient that frequently limits tree growth, in a temperate forest. By quantifying the degree of spatial inequality and autocorrelation in two plots characterized by different dominant tree species, I show that soil extractable nitrogen pools and net nitrogen mineralization fluxes exhibit a high degree of spatial patterning at scales less than 5 meters, with a majority of nitrogen availability contained within hotspots comprising a small proportion of soil area. I also demonstrate that this spatial patterning affects seedling access to soil nitrogen, which has consequences for seedling growth and survival. Chapter 3 examines how tree species and tree size affect the spatial distributions of root systems in two temperate tree species and explores how differences in root spatial coverage could affect tree nutrient access. I find that the spatial distributions of tree root systems can exhibit dramatic differences between species, with a tradeoff between root spatial coverage and total root length. I also discover that the effect of root spatial coverage on soil nutrient access is highly dependent on the spatial patterning of the soil nutrient, such that tree access to patchy nutrients varies greatly based on tree location within the local soil environment, even for medium-size trees. Together, these chapters characterize important patterns and mechanisms of spatial variation in the processes that regulate tree nutrient access.

Forest fragmentation is a pervasive consequence of human land use that creates novel forest boundaries in place of contiguous, intact forest. Boundary forests, or edges, experience environmental conditions distinct from the forest interior driven by lateral exposure to adjacent non-forest land cover. Forest edges tend to be hotter, drier and experience increased wind turbulence and atmospheric deposition with significant consequences for ecosystem processes and biogeochemical cycling. Much of what we know about forest edge structure and function derives from tropical forest research, despite prolific fragmentation in temperate forests. Building on recent field studies of temperate forest edges in the northeastern United States (US), I combine measurements from the US national forest inventory (NFI) with remotely-sensed maps of forest area to characterize broad patterns in the extent and impacts of fragmentation on temperate forest ecology. Using the US NFI to identify forest edges across a 20-state region, I report increased biomass and growth of edge forests compared their interior counterparts. I then compare the prevalence of forest edges in the US NFI and commonly-used forest maps to very-high-resolution land-cover maps, and I demonstrate that conventional methods of forest characterization systematically undercount and exclude forest edge area. Finally, I synthesize these findings to quantify aboveground carbon (C) cycling in New England using a novel approach that partitions forest C fluxes into forest edge and interior categories. I find that forest edges are disproportionately vulnerable to land-use conversion and are a critical component of both forest C uptake and emissions. Accounting for elevated growth rates in forest edges increases estimates of the net forest C sink in New England by 8.6% (4.36 Tg C). My dissertation research demonstrates the need to better understand the extent and effects of fragmentation in temperate forests, provides support for the treatment of forest edges as a distinct system, and highlights the need to include forest edges in current and future C accounting.

Forests face an unprecedented range of disturbances from climate change, introduced pests and pathogens, and novel species, which frequently interact causing severe consequences to forest communities and ecosystem function. Understanding the mechanisms by which forests recover from disturbance and maintain stability of function is not only an issue of ecological interest, but one of pressing human need, as forest functioning is involved in maintaining a suite of ecosystem services that provide for humanity, including the global carbon and water cycles. Using an experimental manipulation of tree species diversity within an oak-dominated temperate northeastern deciduous forest, this dissertation broadly asks: how do forest community biomass and diversity influence stability and magnitude of forest community growth and water use? All three chapters are based on data from the same forest, where four treatments had previously been established by trunk girdling, which kills a tree by severing the cambium and sapwood, but leaves it standing, similar to the effect of many pathogens on trees. The treatments represent a range of species richness (2-10 species), biomass (5.5 × 104 kg/ha to 7.1 × 105 kg/ha), and level of disturbance, with experimental plots losing anywhere from zero to 94% of their living biomass. Chapter 1 focuses on competitive release after the loss of a dominant species using an annual census of trees over the last 10 years. Community level growth rates showed that diversity positively influenced biomass recovery rate. Chapter 2 addresses the role of the tree community’s biomass and diversity on soil water content using soil moisture sensors, which have recorded data hourly for two years, as well as the trees’ water stress, by using foliar stable carbon isotope ratios. Here, diverse communities have higher and more stable levels of soil water as well as trees that are less water stressed. Using the same long term data as Chapter 1, Chapter 3 assesses whether growth in the tree communities has been more stable over the past 10 years, and investigates whether this can be explained by shorter term fluctuations in tree growth measured by automated point dendrometers. While more diverse communities are more stable in their growth rates over time, this was strongly dependent on how much of the original community had been mechanically girdled. Species showed complementarity in phenology of tree growth at the seasonal scale, but our models could not directly link this intra-annual complementarity in more diverse communities to the stability seen over 10 years. Taken together, results from these three chapters suggest that diversity plays a role in mediating recovery of function from disturbance, which has implications for both the global carbon and water cycles.

Effects of forest disturbance on leaf shredding aquatic insects were investigated by comparing leaf biomass and shredder production in disturbed versus reference forest streams. Benthic samples were collected monthly in 3 streams in a mature hardwood reference forest and 3 streams in an 11-year-old clearcut. Reference forest streams had significantly greater total leaf biomass and significantly more slow-processing leaf material than disturbed forest streams. Disturbed forest streams had significantly greater fast-processing leaf biomass than did reference streams. The leaf shredding insects Tipula abdominalis, Pycnopsyche sp., and Tallaperla maria comprised over 90% of the shredder biomass in all streams. Total shredder production was Significantly greater (p<0.05) in disturbed versus reference streams. Production of Pycnopsyche and T. maria was significantly greater (p <0.10) in disturbed versus reference streams, but T. abdominalis production was not significantly different (po =0.28). Greater T. maria production was attributed mostly to better survivorship in disturbed versus reference streams. Greater total shredder production in disturbed streams was attributed mostly to greater production by Pycnopsyche, which was due mostly to better survivorship and growth of early instar larvae in disturbed streams. T. maria and T. abdominalis were studied under laboratory conditions to determine whether feeding on various types of leaf material would affect growth. Shredder growth rates were affected more by length of instream conditioning of leaves than leaf species or leaf exposure site. Each shredder species had different patterns of growth and survivorship relative to leaf species and conditioning. There was no difference in shredder growth patterns between early versus late successional leaf species. Pycnopsyche growth was not studied, but Pycnopsyche may be more capable than the other shredders of exploiting fast-processing, early successional leaf species. Pycnopsyche production was greatest in streams having the greatest quantities of early successional leaf biomass. Pycnopsyche biomass correlated significantly with fast-processing leaf biomass typical of the early successional forest, whereas other shredders did not. Shredder production was significantly greater in disturbed versus reference forest streams, even though total leaf biomass was significantly greater in reference streams. Providing that forest clearcutting is accomplished with minimal physical disturbance to streams, shredder populations may exhibit greater production in streams 11-years after forest clearcutting than in reference forest streams. / Ph. D.

Destructive sampling was undertaken to estimate the contribution of the herb stratum and shrub stratum to above-ground phytomass and nutrients (N, P, K, Mg and Ca) in four different vegetation types in an Appalachian oak forest in southwestern Virginia. The study area is located at midslope on the southeast aspect of Potts Mountain in four non-contiguous compartments which are to be clearcut and whole-tree harvested in the near future. A partial random sampling scheme was utilized to select 20 x 20m study areas, within which 48 1 x 1 m and 16 5 x 5 m herb and shrub stratum plots were nested respectively. Statistical tests indicated that significant differences in above-ground phytomass and nutrients exist between vegetation types in both strata. The trend is towards greater amounts of understory vegetation on progressively drier sites. Total amounts (kg/ha) of nutrient elements show a similar trend. In contrast, nutrient element concentrations show a reverse trend, with higher concentrations of nutrients found on the more mesic sites. Ordination techniques were utilized to investigate differences in nutrient concentrations among species. Species groupings derived from the ordinations substantiated the sorting of vegetation types along a moisture gradient. Regression equations for individual / M. S.