George R. Parker

Relationships between landcover proportion and indices of landscape spatial pattern

Recent studies have related percolation theory and critical phenomena to the spatial pattern of landscapes. We generated simulated landscapes of forest and non-forest landcover to investigate the relationship between the proportion of forest (Pi) and indices of patch spatial pattern. One set of landscapes was generated by randomly assigning each pixel independently of other pixels, and a second set was generated by randomly assigning rectilinear clumps of pixels. Indices of spatial pattern were calculated and plotted against Pi. The random-clump landscapes were also compared with real agricultural landscapes.The results support the use of percolation models as neutral models in landscape ecology, and the performance of the indices studied with these neutral models can be used to help interpret those indices calculated for real landscapes.

Tree dynamics in an old-growth, deciduous forest.

Abstract In 1926, all trees (⩾ 10.2 cm dbh) were measured, tagged and mapped in a 20.6 ha, old-growth oak forest within the extensively farmed Tipton Till Plain of Indiana. All trees (⩾ 10.0 cm dbh) within the central 8.5 ha of this forest were measured, tagged and mapped again in 1976. Stand density and basal area increased by 93.9 and 30.8%, respectively, to 320 stems ha−1 and 31.0 m2 ha−1. Density of Ulmus americana and Acer saccharum increased most; the largest density decreases were of Quercus rubra and Fraxinus americana. Basal area increases were greatest for Q. rubra, A. saccharum, and Q. alba. The most important species in 1926 were (in order of decreasing importance value, IV) [IV = (relative density + relative basal area)/2] Q. rubra, F. americana, Q. alba, Q. macrocarpa and U. americana. In 1976, Q. rubra, U. americana, A. saccharum, Q. alba and F. americana were the most important. Nearly half (46.9%) of those trees measured in 1926 had died by 1976; however, mortality varied by species, size-class and size-class within a species. Species with low mortality (⩽ 25%) included A. saccharum, Aesculus glabra, Carya spp. (except C. cordiformis), Celtis occidentalis and Quercus spp. (except Q. rubra). Species with high mortality (⩾ 75%) included Fagus grandifolia, Ulmus americana, U. rubra, and Fraxinus nigra. The majority of ingrowth trees within a 5 m radius gap of dead dominant or codominant trees were U. americana (30% of total), followed by A. saccharum (20%). No species had greater than 50% of its ingrowth within a 5 m radius of the dead trees. Diameter growth of surviving trees varied greatly among species, size-class and size-class within a species. Q. rubra and F. americana had greatest average diameter increases after 50 years (21.8 and 18.4 cm dbh, respectively). Mortality was relatively low and diameter growth high in the 50.0–69.9 cm diameter class for all species combined. The rotated-sigmoid curve, rather than the negative exponential, appears to best describe the size-class distributions of all species in 1976. An analysis of the size-class distribution of all species suggests that early and mid-seral species such as Gleditsia triacanthos, Juglans nigra, and Quercus spp. are gradually being replaced by more tolerant, late seral and climax species such as Acer saccharum, Aesculus glabra, Carya ovata and others. Despite the old-growth appearance of this forest much structural and compositional changes have been taking place.

Using an index of habitat patch proximity for landscape design

A proximity index (PX) inspired by island biogeography theory is described which quantifies the spatial context of a habitat patch in relation to its neighbors. The index distinguishes sparse distributions of small habitat patches from clusters of large patches. An evaluation of the relationship between PX and variation in the spatial characteristics of clusters of patches showed that reduction in the isolation of patches within a cluster produced exponential increases in PX, and that increase in the size of those patches produced a more modest linear increase in PX. Simulations using neutral model landscapes were used to determine the effect of the scale of analysis on PX. Increased size of the neighborhood considered around a habitat patch (proximity buffer) produced linear increases in PX, the slope being dependent on the proportion of the habitat of interest on the landscape. The proximity index was used to evaluate three alternative conservation reserve designs in an agricultural landscape, and comparisons were made among designs consisting of the same area of forest habitat added to the landscape. The `single, large` reserve design produced the greatest increase in mean PX values among forest patches on the landscape when the total area of forest added was >= 842 ha, and the `several, small` reserve design produced the greatest increase when the total area of forest added was

Composition and diversity of woody vegetation in silvicultural openings of southern Indiana forests

Abstract Between 1993 and 1995 we sampled ground-layer vegetation on 150 plots in Facus-Acer saccharum/Arisaema Mesic Slope and Quercus alba-Acer saccharum/Parthenocissus Dry-Mesic Slope forests to determine how the understory of these forests responded to forest management. Four different stand types, clear-cuts (2–12 ha), group-selection openings (0.1–1.6 ha), single-tree selection openings (0.005–0.013 ha) and uncut 80–100 y-old reference stands were sampled. There was little relationship between the percent cover of most ecological species groups and opening age or size on either mesic or dry-mesic slopes. While clear-cuts and group-selection openings had significantly greater cover of several ecological species groups (used to classify mesic and dry-mesic slopes) than reference stands, single-tree selection openings did not differ significantly from reference stands in the cover of any ecological species group. Pearson correlation analysis indicated that more ground-layer species were significantly c...

Long-term spatial dynamics in an old-growth deciduous forest

Abstract In 1926, 1976, and 1986 stems (≥ 10 cm diameter at 1.37 m (dbh)) were measured and mapped in a 4 ha interior study area on the Davis-Purdue Research Forest in east-central Indiana. Spatial pattern type was determined using the Clark and Evanss index, and Ripleys L function. The G function was used to examine spatial dispersion at intertree distances ( 25 dbh) trees was uniform between 1926 and 1986. Density-dependent mortality and ingrowth processes are maintaining uniform spatial distributions. Initial neighborhood tree distribution was higher around trees which died in the periods 1926–1976 and 1976–1986 than for contemporary survivors, i.e. trees which survived this period had fewer neighboring trees within 6 m at the beginning of the period than did trees which died. The higher initial neighborhood densities around mortality trees than survivors supports density-dependent mortality. Ingrowth was inhibited in a 6 m zone proximite to established trees for both the 1926–1976 and 1976–1986 periods.

Spatial dispersion of woody regeneration in an old-growth forest

Spatial pattern and density for woody regeneration were examined in relation to canopy structure for an old-growth forest in east-central Indiana. All woody stems -2 cm diameter at 1.37 m were recorded by species and diameter on a 4-ha area gridded into 10 x 10 m quadrats. Canopy structure was inventoried using a 5 x 5 m grid. Canopy structure was divided into three classes: canopy gaps, secondary canopy, and primary canopy. The nonparametric dispersion index was used to examine spatial patterns of woody species and the Clark-Evans nearest neighbor index was used to examine spatial pattern of canopy gaps. Canopy gaps covered 9.0% of the 4 ha area, averaged 52.4 m2 in area, and were randomly dispersed. Most species were aggregated at scales >400 m2. While overall regeneration density did not vary significantly with canopy structure, densities for some individual species were significantly different under different canopy structures. The current disturbance regime of this forest, primarily single-tree gaps, has created a canopy structure which favors the regeneration of shade-tolerant species.

COMPOSITION AND DIVERSITY OF GROUND-LAYER VEGETATION IN SILVICULTURAL OPENINGS OF SOUTHERN INDIANA FORESTS

Abstract Between 1993 and 1995 we sampled ground-layer vegetation on 150 plots in Facus-Acer saccharum/Arisaema Mesic Slope and Quercus alba-Acer saccharum/Parthenocissus Dry-Mesic Slope forests to determine how the understory of these forests responded to forest management. Four different stand types, clear-cuts (2–12 ha), group-selection openings (0.1–1.6 ha), single-tree selection openings (0.005–0.013 ha) and uncut 80–100 y-old reference stands were sampled. There was little relationship between the percent cover of most ecological species groups and opening age or size on either mesic or dry-mesic slopes. While clear-cuts and group-selection openings had significantly greater cover of several ecological species groups (used to classify mesic and dry-mesic slopes) than reference stands, single-tree selection openings did not differ significantly from reference stands in the cover of any ecological species group. Pearson correlation analysis indicated that more ground-layer species were significantly correlated with opening size than opening age, suggesting that the size of the initial opening has more influence on species composition than opening age. Overall, forest management has not constituted a severe enough disturbance to shift ground-layer species composition away from that associated with the sampled ecological landtype phases (mesic and dry-mesic slopes). Aspect was the dominant factor determining species distribution in Canonical Correspondence Analysis ordinations of ground-layer vegetation in both openings and reference stands.

Distribution of biomass in an Indiana old-growth forest from 1926 to 1992

Abstract We examined the structural and spatial distribution of woody biomass in relationship to disturbance in an Indiana old-growth deciduous forest over a 66-yr period. Analysis was done on the core 7.92 ha of a 20.6-ha forest in which every tree 10 cm dbh and over has been tagged and mapped since 1926. Five years are compared—1926, 1976, 1981, 1986 and 1992. Dry weight of living biomass for the 7.92-ha area for these 5 yr was 154 Mg/ha, 207 Mg/ha, 220 Mg/ha, 216 Mg/ha and 211 Mg/ha, respectively. Biomass of dead trees was 1 Mg ha−1 yr−1 from 1977 through 1981; 4 Mg ha−1 yr−1 from 1982 through 1986; and 3 Mg ha−1 yr−1 from 1987 through 1992. Biomass of trees that died between 1976 and 1992 was greatest for midseral species. Living biomass of dominant early to midseral species is declining while that of late seral species is increasing. In 1926 biomass of trees 10 to 25 cm diam consisted of 14% Quercus spp. and 12% Acer saccharum. By 1992 biomass in this diameter range consisted of 1% Quercus spp. and 43% A. saccharum. Equilibrium patch size was estimated for biomass at each of the five inventory dates to determine if there was a change. Equilibrium patch size for biomass was estimated to be 0.64 ha during all five inventory dates based on the coefficient of variation (CV) of biomass for 16 different grid cell sizes. Grid cell size refers to the size of adjacent cells in a grid that covered the entire study area. The grid with the smallest cells had cells of 0.01 ha. This grid of 0.01-ha cells was aggregated to 15 additional grid cell sizes, where the largest grid cell size was 1.98 ha. CV for all grid cell sizes was highest in 1926 due to effects of prior grazing. These data indicate an increase in deadwood biomass, a shift in stand composition, recovery from grazing by an increase in small diameter trees and no change in equilibrium patch size over the five inventory dates.

The response of herbaceous-layer vegetation to anthropogenic disturbance in intermittent stream bottomland forests of southern Indiana, USA

Between 1993 and 1995 we sampled herbaceous layer vegetation on 84 plots in Platanus/Asarum Wet-Mesic Bottomland forests to determine how these forests have responded to human disturbance. Four different disturbance types were sampled (abandoned agricultural are as, clearcuts, group-selection openings, and single-tree selection openings), and uncut 80–100 year-old reference stands were sampled for comparison. Detrended Correspondence Analysis (DCA), distance analyses (chord distance and normalized Euclidean distance) and similarity analysis (Bray-Curtis similarity coefficient) suggest that agricultural use has shifted herbaceous-layer vegetation composition away from that typical of the reference forests, but that clearcutting, group-selection harvest, and single-tree selection harvest have not greatly shifted herbaceous composition. This shift in vegetation on abandoned agricultural land resulted from a loss of indicator species, such as Cardamine concatenata (Michx.) Sw., Stellaria pubera Michx., and Laportea canadensis (L.) Weddell and an influx of disturbance, exotic, and nonforest species (e.g., Lycopodium complanatum L., Lonicera japonica Thunb. and Senecio aureus L.). However, only two species found in reference stands, Erigenia bulbosa (Michx.) Nutt. and Sphenopholis obtusata (Michx.) Scribn., were missing from clearcuts, group-selection openings, and single-tree selection openings. The species richness values of abandoned agriculture, clearcut, and group-selection plots were generally greater than those of single-tree selection and reference plots. Abandoned agricultural areas had much greater total species richness because of the influx of dry-site, exotic, disturbance, and non-forest species.

Evaluating spatial pattern of wildlife habitat: a case study of the wild turkey (Meleagris gallopavo)

-The evaluation of the spatial configuration of habitat is often difficult due to large geographic areas to be evaluated and the subjective nature of spatial pattern assessment. Habitat quality for wild turkey populations has a spatial component related to the arrangement of habitat elements across large geographic areas. Indices of habitat fragmentation were used to quantitatively describe the components of habitat assessment now evaluated subjectively by experienced wild turkey biologists, including a proximity index that distinguishes isolated forest patches from those that are part of a cluster of forest patches. These indices were used to mathematically classify landscapes into discrete quality categories and the classifications were compared to subjective assessments made by experienced turkey biologists. Mathematical classifications of landscapes agreed with expert judgment when the proximity index and proportion of forest were used to characterize the spatial pattern of forest habitat. None of the indices alone were adequate to correctly classify all test landscape samples. Mean values of the indices were compared between study areas of different quality as wild turkey habitat. Study areas of optimal and suboptimal quality were more different from each other than were suboptimal and poor study sites. The proximity index is a valuable quantitative measure of habitat spatial pattern that provides information related to subjective, expert assessment of landscape suitability for use by wild turkeys. These quantitative measures add objectivity to the assessment of the spatial components of wild turkey habitat, and provide additional information that can be used to help identify the best potential turkey release sites. These methods can be extended to the evaluation of the spatial distribution of habitat for other wildlife species, and can provide quantitative spatial information for hypothesis testing.