Biology subjects

Orwig, D. A.

Publications and source records attributed to Orwig, D. A..

5 recordsLinked to original sources

bioRxiv2023

Latitudinal scaling of aggregation with abundance and its consequences for coexistence in species rich forests

The search for simple principles underlying the complex spatial structure and dynamics of plant communities is a long-standing challenge in ecology1-6. In particular, the relationship between the spatial distribution of plants and species coexistence is challenging to resolve in species-rich communities7-9. Analysing the spatial patterns of tree species in 21 large forest plots, we find that rare species tend to be more spatially aggregated than common species, and a latitudinal gradient in the strength of this negative correlations that increases from tropical to temperate forests. Our analysis suggests that latitudinal gradients in animal seed dispersal10 and mycorrhizal associations11,12,13 may jointly generate this intriguing pattern. To assess the consequences of negative aggregation-abundance correlations for species coexistence, we present here a framework to incorporate the observed spatial patterns into population models8 along with an analytical solution for the local extinction risk14 of species invading from low abundances in dependence of spatial structure, demographic parameters, and immigration. For example, the stabilizing effect of the observed spatial patterns reduced the local extinction risk of species when rare almost by a factor of two. Our approach opens up new avenues for integrating observed spatial patterns into mathematical theory, and our findings demonstrate that spatial patterns, such as species aggregation and segregation, can contribute substantially to coexistence in species-rich communities. This underscores the need to understand the interactions between multiple ecological processes and spatial patterns in greater detail.

ecology↗

bioRxiv2021

Land-use history impacts spatial patterns and composition of woody plant species across a 35-hectare temperate forest plot

Land-use history is the template upon which contemporary plant and tree populations establish and interact with one another and exerts a legacy on the structure and dynamics of species assemblages and ecosystems. We use the first census (2010-2014) of a 35-ha forest-dynamics plot at the Harvard Forest in central Massachusetts to explore such legacies. The plot includes 108,632 live stems [≥] 1 cm in diameter (2215 individuals/ha) and 7,595 dead stems [≥] 5 cm in diameter. Fifty-one woody plant species were recorded in the plot, but two tree species-- Tsuga canadensis (eastern hemlock) and Acer rubrum (red maple)--and one shrub-- Ilex verticillata (winterberry)--comprised 56% of all stems. Live tree basal area averaged 42.25 m2/ha, of which 84% was represented by T. canadensis (14.0 m2/ ha), Quercus rubra (northern red oak; 9.6 m2/ ha), A. rubrum (7.2 m2/ ha) and Pinus strobus (eastern white pine; 4.4 m2/ ha). These same four species also comprised 78% of the live aboveground biomass, which averaged 245.2 Mg/ ha, and were significantly clumped at distances up to 50 m within the plot. Spatial distributions of A. rubrum and Q. rubra showed negative intraspecific correlations in diameters up to at least a 150-m spatial lag, likely indicative of competition for light in dense forest patches. Bivariate marked point-pattern analysis showed that T. canadensis and Q. rubra diameters were negatively associated with one another, indicating resource competition for light. Distribution and abundance of the common overstory species are predicted best by soil type, tree neighborhood effects, and two aspects of land-use history: when fields were abandoned in the late 19th century and the succeeding forest types recorded in 1908. In contrast, a history of intensive logging prior to 1950 and a damaging hurricane in 1938 appear to have had little effect on the distribution and abundance of present-day tree species.

ecology↗

bioRxiv2020

The Wood Image Analysis and Dataset (WIAD): open-access visual analysis tools to advance the ecological data revolution

O_LIEcological data is collected and shared at an increasingly rapid pace, but it is often shared in inconsistent and untraceable processed forms. Images of wood contain a wealth of information such as colours and textures but are most commonly reduced to ring-width measurements before they can be shared in various common file formats. Archiving digital images of wood samples in libraries, that have been developed for ecological analysis and are publicly available, remains the exception. C_LIO_LIWe developed the Wood Image Analysis and Dataset (WIAD) an open-source application including a web-interface to integrate basic visual analysis of wood samples, such as increment cores, thin sections or x-ray films, basic data processing, and archiving of the images and derived data to facilitate transparency and reproducibility in studies using visual characteristics of wood. C_LIO_LIWIAD provides user-friendly tools to manipulate images of wood samples, mark and measure wood characteristics such as growth increments, density fluctuations, early- and latewood widths, and fire scars, and to visualise, process, and archive images, metadata, and the derived data. C_LIO_LIWIAD constitutes a step towards the reproducible automation of tree-ring analysis, while establishing an open-source foundation to create improved community developed repositories which would enable novel ecological studies harnessing the wealth of existing visual data. C_LI

plant biology↗

bioRxiv2019

Potential impacts of insect-induced harvests in the mixed forests of New England

Forest insects and pathogens (FIPs) have significant impacts on U.S. forests, each year affecting an area nearly three times the area of wildfires and timber harvesting combined. We surveyed family forest owners (FFOs) in the northeastern U.S. and 84% of respondents indicated they would harvest in at least one of the presented FIP infestation scenarios. This harvest response represents a potentially significant shift in the timing, extent, and species selection of harvesting in the Northeast. Here we used the landowner survey, regional forest inventory data, and characteristics of the emerald ash borer (EAB, Agrilus planipennis) invasion to examine the potential for a rapidly spreading FIP to alter harvest regimes and affect regional forest conditions. Twenty-five percent of the FFO parcels in the Connecticut River Watershed in New England are likely to be harvested in response to EAB within 10 years. This prediction represents an increase in harvest frequencies, from 2.9%/yr (historically) to 3.7%/yr, on FFO woodlands. At typical harvest intensities, this would result in 13% of the total aboveground biomass removed through these harvests, with 81% of that biomass from species other than ash, creating a forest disturbance that is over twice the magnitude of the disturbance from EAB alone.

ecology↗

bioRxiv2017

When a foundation crumbles: forecasting forest community dynamics following the decline of the foundation species Tsuga canadensis

AbstractIn the forests of northeastern North America, invasive insects and pathogens are causing major declines in some tree species and a subsequent reorganization of associated forest communities. Using observations and experiments to investigate the consequences of such declines are hampered because trees are long-lived. Simulation models can provide a means to forecast possible futures based on different scenarios of tree species decline, death, and removal. Such modeling is particularly urgent for species such as eastern hemlock (Tsuga canadensis), a foundation species in many northeast forest regions that is declining due to the hemlock woolly adelgid (Adelges tsugae). Here, we used an individual-based forest simulator, SORTIE-ND, to forecast changes in forest communities in central Massachusetts over the next 200 years under a range of scenarios: a no-adelgid, status-quo scenario; partial resistance of hemlock to the adelgid; adelgid irruption and total hemlock decline over 25 years, adelgid irruption and salvage logging of hemlock trees; and two scenarios of preemptive logging of hemlock and hemlock/white pine.We applied the model to six study plots comprising a range of initial species mixtures, abundances, and levels of hemlock dominance. Simulations indicated that eastern white pine, and to a lesser extent black birch and American beech, would gain most in relative abundance and basal area following hemlock decline. The relative dominance of these species depended on initial conditions and the amount of hemlock mortality, and their combined effect on neighborhood-scale community dynamics. Simulated outcomes were little different whether hemlock died out gradually due to the adelgid or disappeared rapidly following logging. However, if eastern hemlock were to become partially resistant to the adelgid, hemlock would be able to retain its dominance despite substantial losses of basal area. Our modeling highlights the complexities associated with secondary forest succession due to ongoing hemlock decline and loss. We emphasize the need both for a precautionary approach in deciding between management intervention or simply doing nothing in these declining hemlock forests, and for clear aims and understanding regarding desired community- and ecosystem-level outcomes.

ecology↗