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The Population Dynamics of a Long-Lived Conifer (Pinus palustris)
Abstract
In an old-growth longleaf pine population in which all trees of at least 2 cm in dbh were mapped and tagged, the population was of uneven age and size; tree size correlated positively with tree age. Large or old trees were only loosely aggregated, forming a background matrix that filled the forest. Juvenile trees were highly aggregated, located in areas of low adult densities. Recruitment thus occurs primarily within open spaces created by the deaths of large trees. Variable time lags may occur before the colonization of open spaces, however, because of temporal variation in seed production and occurrence of summer ground fires. Recruitment within the mapped plot has occurred frequently for at least the past 250 yr. Temporal variation in adult mortality and recruitment into open spaces, coupled with strong negative interactions between cohorts of different ages, appears likely to produce alternating phases of population growth and decline that are highly variable in length and magnitude. An upper bound to population size occurs when all available space is filled with trees; but no lower bound exists, and extinction probabilities may be increased at very low densities. The population is buffered from declines to very low densities, however, by the tendency for small trees to recruit into openings created by the deaths of adults. Longleaf pine possibly maintains the environment in an open state suitable for its own regeneration by transmuting a localized disturbance (lightning) into a widespread disturbance (ground fires). Fire facilitation results in an extended, but indefinite, increase in the persistence of environmental conditions in which longleaf pine, but no other tree species, can survive and reproduce. -from Authors
... a STIPSI identifier, http://www.fva-bw.de/forschung/bui/stipsi_en.html. b Tall pines (Pinus palustris) in Wade County (Florida), seePlatt et al. (1988). ...
Fixed-count sampling (plotless) remains attractive for forest inventories in difficult terrains and for their control of the number (k) of trees to measure. Although recent fixed-count estimators of density (PDE) are less biased than older ones, the risk of a nontrivial bias remains a deterrent. A recently published PDE based on a generic algorithm for predicting distances to the k+ m nearest tree (m = 1, 2, ...) has attractive properties in terms of average bias and average root mean squared errors across a wide spectrum of spatial point patterns. However, the risk of a sizeable bias remains an issue. Sensitivity to spatial patterns is seen as its main weakness. It is hypothesized that a new PDE with robust properties will mitigate the bias issue and encourage wider use. To this end, a new PDE estimator is proposed. It builds on a mixture of observed and predicted distances to a set of k+ m nearest trees to generate counts of actual and virtual trees inside a circle with a data-driven fixed radius. The proposed new robust fixed-count density estimator achieved an average absolute bias of 1.2% when tested across a wide range of point patterns (54 actual and four simulated). The maximum absolute bias was 4.4%, a significant reduction when compared with otherwise attractive alternative PDEs. Root mean squared errors and coverage of 95% confidence intervals were also encouraging. The deterrent bias issue in PDEs has been sharply reduced with the proposed estimator.
... At present, some endangered species are dependent on this ecosystem, such as the red-cockaded woodpecker (Picoides borealis), gopher tortoise (Gopherus polyphemus), and black pine snake (Pituophis melanoleucus) [7]. In addition, longleaf pine forests have significant potential for carbon storage [8], as trees can reach a lifespan of up to 450 years [9]. Conserving and restoring longleaf pine forests has become the priority of natural resource management in the southeastern United States. ...
Longleaf pine (Pinus palustris L [...]
... Longleaf pine natural regeneration is difficult for several reasons, including poor seed production, slow seedling growth, and low seedling survival [44]. Historically, longleaf pine forests were multi-aged with even-aged cohorts regenerating in small patches formed by the mortality of canopy trees [19], a structure now existing only in the presence of frequent fires [38]. Replicating this structure in planted stands is complicated and takes time. ...
Longleaf pine (Pinus palustris Mill.) is a conifer historically associated with an open forest ecosystem that extended across much of the coastal plain of the Southeastern United States. It now exists mainly in isolated fragments following the conversion of forests and the long-term disruption of the low-intensity fire regime upon which the species depends. Recent decades have seen efforts to restore longleaf pine forests by government and private landowners. This was reflected in analyses of national forest inventory data during two time periods, ca. 2009–2015 and 2016–2021, that showed increases in the estimated number of longleaf pine trees, the area of the longleaf pine forest type, and the number and area of planted longleaf pine, along with growth in mean plot-level longleaf pine carbon and importance value. At the same time, we found a decrease in the overall forest area containing longleaf pine, manifested across a variety of other forest types. These results point to a dynamic through which forests dominated by longleaf pine are becoming more widespread via restoration, while forests in which the species is a less important component are transitioning to other forest types or land uses. We also detected a decrease over time in the estimated number of longleaf seedlings across most states and forest types and a decline in naturally regenerated longleaf pine. To further assess regeneration trends in longleaf pine, we calculated the estimated proportion of small trees (seedlings and saplings) for the entire species and for seed zone sub-populations. We found a species-wide decrease in the proportion of small trees, from 82.1 percent to 75.1 percent. This reduction was most pronounced along the edges of the species distribution and could indicate less sustainable levels of regeneration in some areas. These results underscore the challenges of facilitating natural regeneration in this important species.
... Thus, gap dynamics in these high-light environments likely depend on belowground processes, which produces distance-dependent longleaf pine recruitment patterns during non-fire intervals (Grace and Platt 1995b). Spatially heterogeneous fuel loading and fire severity (Platt et al. 1991;Thaxton and Platt 2006;Wenk et al. 2011;Loudermilk et al. 2014;Whelan et al. 2021) may further reinforce conspecific distance-dependence due to the fire-sensitivity of some longleaf pine life stages, leading to the 'patchiness' commonly observed in longleaf pine savannas (Platt et al. 1988;Robertson et al. 2019). ...
The interplay of positive and negative species interactions controls species assembly in communities. Dryland plant communities, such as savannas, are important to global biodiversity and ecosystem functioning. Sandhill oaks in xeric savannas of the southeastern United States can facilitate longleaf pine by enhancing seedling survival, but the effects of oaks on recruitment and growth of longleaf pine have not been examined. We censused, mapped, and monitored nine contiguous hectares of longleaf pine in a xeric savanna to quantify oak-pine facilitation, and to examine other factors impacting recruitment, such as vegetation cover and longleaf pine tree density. We found that newly recruited seedlings and grass stage longleaf pines were more abundant in oak-dominated areas where densities were 230% (newly recruited seedlings) and 360% (grass stage) greater from lowest to highest oak neighborhood densities. Longleaf pine also grew faster under higher oak density. Longleaf pine recruitment was lowest under longleaf pine canopies. Mortality of grass stage and bolt stage longleaf pine was low (~1.0% yr⁻¹) in the census interval without fire. Overall, our findings highlight the complex interactions between pines and oaks—two economically and ecologically important genera globally. Xeric oaks should be incorporated as a management option for conservation and restoration of longleaf pine ecosystems.
... Most forest stands along the UWF campus nature trails are typical of second-growth longleaf pine forests that have experienced chronic fire exclusion [6,20,[24][25][26][27][28]. These comprise stands of widely-space longleaf stems primarily 50-100 yrs in age [21] with an otherwise fire-maintained open matrix [2,29,30] filled with hardwood species, especially numerous southern oaks, e.g., live oak (Quercus virginiana), water oak (Q. nigra), blackjack oak (Q. ...
The dependence of longleaf pine (Pinus palustris) ecosystems on fire is well-understood, and the anthropogenic alteration of fire cycles within its natural range has contributed to its decline. This has been increasingly exacerbated in areas of urban interfaces, wherein the use of prescribed fire can be problematic. The purpose of this study—the University of West Florida Campus Ecosystem Study—was to examine the effects of fire exclusion on longleaf pine in the unique urban interface of a university campus. This was an interconnected series of investigations on the main campus and three associated natural areas that comprised remnant longleaf stands following the cessation of widespread longleaf pine harvesting—120 years ago. This period of chronic fire exclusion allowed for a distinct shift in the stand structure and composition. The open, savanna-like structure of fire-maintained longleaf stands has transitioned into closed-canopy forests with the increased prevalence of southern evergreen oaks (especially live oak—Quercus virginiana) and Magnolia spp., resulting in the complete absence of longleaf regeneration. Fire exclusion also appeared to decrease soil fertility. The significant variation in the mean age of longleaf pine stems on the main campus; natural areas suggest that these natural areas were likely under separate ownership with contrasting land-use history prior to its purchase by the State of Florida for campus construction in 1963.
Effective conservation of old-growth ecosystems, along with their unique biodiversity and climate benefits, requires coordinated actions from the scale of individual trees to broad regions. The US government is currently developing a conservation strategy for old-growth forest on federal lands, and similar efforts are occurring globally as nations implement the Kunming-Montreal Global Biodiversity Framework. An effective strategy must include elements at three spatiotemporal scales: immediate restrictions on harvest of old-growth and mature forests and old trees, standards to ensure management activities do not degrade old growth at the stand scale, and longer-term planning for old-growth restoration and recruitment across landscapes. Lessons from previous US forest policy, especially the Northwest Forest Plan, can inform efforts to strengthen each of these three components in the US old-growth conservation strategy. Ecosystem-based standards are needed to ensure protection of sufficient mature forest so that recruitment into the old-growth stage shifts ecosystems closer to historic proportions of old growth. In addition to clarifying existing goals related to ecological integrity, comprehensive old-growth policy must incorporate specific goals for recovering at-risk species based on empirical relationships across scales of biodiversity between forest habitat and species viability that are relevant across varied ecological contexts. Reversing extinction debt and ensuring long-term adaptation potential requires designation of large landscapes anchored by remaining old-growth stands, surrounded by areas managed for restoration of ecological integrity, native biodiversity, and ecosystem services including climate change mitigation.
We introduce a new fully non-parametric two-step adaptive bandwidth selection method for kernel estimators of spatial point process intensity functions based on the Campbell–Mecke formula and Abramson’s square root law. We present a simulation study to assess its performance relative to other adaptive and global bandwidth selectors, investigate the influence of the pilot estimator and apply the technique to two data sets: A pattern of trees and an earthquake catalogue.
The demography of the palm Astrocaryum mexicanum is described from a tropical rain forest in Veracruz, Mexico. Yearly estimates of transition probabilities from one stage to the next are c0.10 individual ind-1yr-1 for most stages. This palm has a survivorship pattern with high mortalities (0.69-0.95 individual ind-1yr-1) during the first stages of the life cycle and almost no mortality (0-0.03) after its first reproduction. Individual fecundity shows an initial increase followed by constant values after the palms are c70 yr old. Estimates of the finite rate of increase (lambda) vary between 0.9932 and 1.0399. The average for all plots, 1.0046, predicts a doubling time for a population of c150 yr. A sensitivity analysis of lambda to various demographic parameters shows that fecundity and survival rates for older stages are 1-4 orders of magnitude less important in changing lambda than growth and survivorship estimates for intermediate stages.-from Authors
Caughley and Birch (1971) showed that the usual method for calculating age-specific longevities from the age distribution of living animals, mammals in particular, has built into it the assumption that r = 0. Consequently a set of l"i's calculated this way could not in turn be used with a table of fecundities to predict r. We show that when both the frequencies and fecundities of the age classes are known, provided that the fecundities correspond to what Leslie (1945) termed F"i, the assumption that r = 0. is unnecessary. It is a sample matter to calculate not only the l"i but r as well, assuming only a stable age structure. Formulas for doing so are given and applied, as an example, to data on the grey fox.
A size-classified transition matrix model of the demography of Arisaema triphyllum, a perennial herb of temperate deciduous forest, was constructed from 3 yr of field data from two different sites. Arisaema is quite unusual in that individuals change sex in a pattern determined by their sizes: small individuals do not flower, larger individuals reproduce as males, and the largest as females. As plants increase or decrease in size, they also may change sex. Though demographic parameters varied with the site and with the year, some consistent patterns were seen Mortality rates ranged from 20 to 40%/yr for small, nonflowering plants, but decreased to much lower levels as plants reached reproductive size. For these large plants, mortality rates did not differ between sexes or among size-classes. Because rates of sexual reproduction were severely pollinator limited, levels of seed production were low (averaging 7 seeds@?female^-^1@?yr^-^1) and were not correlated with plant size. All plants engaged in clonal reproduction, regardless of their size. Transition matrices based on these data were compared statistically and were found to vary in time, as a result of year-to-year environmental variability. No population had achieved a stable size distribution. The classical method of calculating rate of increase, @l, was therefore rejected, and an alternative method incorporating temporal stochasticity substituted. A sensitivity analysis was performed to evaluate the effect on population growth of changing various life history parameters. Differences in rates of individual growth and of clonal reproduction were found to be largely responsible for the relative success of the two populations, one of which was increasing, the other declining. Arisaema's status as a climax-forest herb suggests that temporally varying transition matrices might be common even in environments traditionally regarded as @'stable.@' The prevalence of temporal variability has consequences both for the future direction of demographic theory and for the design and analysis of field studies.
Results generated using the 2 techniques, using data on laboratory cohorts of Daphnia pulex, were almost identical, as were results for a hypothetical D. pulex population whose sampling distribution was approximately normal. However, for another hypothetical population whose sampling distribution was negatively skewed due to high juvenile mortality, bootstrap and full-sample estimates of r were negatively biased by 3.3 and 1.8%, respectively. A bias adjustment reduced the bias in the bootstrap estimate and produced estimates of r and SE(r) almost identical to those of the jackknife technique. In general, simulations show that the jackknife will provide more cost-effective point and interval estimates of r for cladoceran populations, except when juvenile mortality is high (at least >25%). -from Authors
Previous workers reported that, despite very different age structures and elevational ranges, there were remarkably coincident diameter curves for Engelmann spruce Picea engelmannii and ponderosa pine Pinus ponderosa, both of which are climax-type species in forests of the Colorado Rockies. The generality of this observation was tested by using data collected from upland forests of Yosemite National Park in the central Sierra Nevada, California. -from Authors
1. A linear model for population dynamics in stochastic environments is introduced by linearizing the logistic equation in discrete time for small stochastic variations around a large average carrying capacity. The analysis of this model involves the relatively simple mathematics of time-series analysis and is not restricted to white noise (i.e., totally unpredictable) environments. 2. In this linear model the population size at any time is a reflection of many historical effects. The intrinsic rate of increase, r, is a measure of the responsiveness of the population to changes in k. A responsive population (r ≈ 1) does not retain historical effects for long, whereas a sluggish population (r ≈ 0) does. 3. The variance of the population size through time always increases with r. But the presence of much predictability in the environment, as measured by the serial correlation between consecutive values of K, reduces the influence of r. High serial correlation allows time for even a sluggish population to ac...
A 2-sex size-specific population projection model is developed for this long-lived dioecious plant. Differences between sex classes (male, female, juvenile) in size-specific survivorship and size transitions are taken into account, as well as particular differences between males and females in age at first reproduction, flowering schedules and reproductive output per individual. The populations studied are near a stable structure and should show only modest changes in population size from year to year. -from Author