Adjacent Intact Forest Research Articles

Three‐Partner Symbiosis among Legumes, Mycorrhizae, and N‐Fixing Bacteria Changes with Light and Soil Nitrogen Conditions

Photo 1. A canopy gap at La Selva Biological Station in Costa Rica, created from treefalls during a storm. Seedlings planted under gap conditions were located here, and seedlings planted under understory conditions were in adjacent intact forest. Photo credit: Orlando Vargas Ramirez. Photo 2. Half of the seedlings planted in the gap were kept under a shade cloth to mimic understory light conditions (depicted in panel A). This experimental design allowed us to explore the effects of light alone on the tripartite symbiosis, as it is only one of many factors that vary between gaps and intact forest. Panel B is a top-down view of one of the experimental plots. There are two seedlings of each of the three legume species used in the experiment: (from top to bottom) Stryphnodendron microstachyum, Zygia longifolia, and Pentaclethra macroloba. Photo credit: Lindsay McCulloch. Photo 3. One mm of a root colonized by arbuscular mycorrhizal fungi, stained, and observed under 200× magnification. 100 such images were observed for each seedling to estimate the percentage of each seedling’s root system that was colonized by arbuscular mycorrhizal fungi. This metric was a proxy for carbon investment in arbuscular mycorrhizal fungi by the seedling. Photo credit: Nikayla Ficano. These photographs illustrate the article “Tripartite legume–rhizobia–mycorrhizae relationship is influenced by light and soil nitrogen in Neotropical canopy gaps” by Nikayla Ficano, Stephen Porder, and Lindsay A. McCulloch published in Ecology. https://doi.org/10.1002/ecy.3489.

Gap Size in Hyrcanian Forest Affects the Lignin and N Concentrations of the Oriental Beech (Fagus orientalis Lipsky) Fine Roots but Does Not Change Their Morphological Traits in the Medium Term

Research Highlights: Fine roots play an important role in plant growth as well as in carbon (C) and nutrient cycling in terrestrial ecosystems. Gaining a wider knowledge of their dynamics under forest gap opening would improve our understanding of soil carbon input and below-ground carbon stock accumulation. Single-tree selection is increasingly recognized as an alternative regime of selection cutting sustaining biodiversity and carbon stock, along with timber production, among ecosystem functions. However, the fine root response in terms of morphological and chemical composition to the resulting harvest-created gaps remains unclear. Background and Objectives: This paper investigates the effect in the medium term (i.e., 6 years after logging) of differently sized harvest-created gaps on fine root dynamics and chemical composition. Materials and Methods: A total of 15 differently sized gaps (86.05–350.7 m2) and the adjacent 20 m distant closed canopies (control) were selected in a temperate Fagus orientalis forest (Hyrcanian region, Iran). Eight soil cores were collected at the cardinal points of the gap edge, including four facing the gap area—the same at the adjacent intact forest. Results: For the selected edge trees, the different size of gaps, the core position, and the tree orientation did not affect the investigated morphological traits, except for the slightly higher specific root length (SRL) for the larger fine root fraction (1–2 mm) in the side facing the gap area. Differently, the investigated chemical traits such as N concentration and cellulose:lignin ratio significantly increased with increasing gap size, the opposite for C:N ratio and lignin. Moreover, N concentration and C:N significantly decreased and increased with the fine root diameter, respectively. Conclusions: This work highlighted that, in the medium term and within the adopted size range, artificial gap opening derived from single-tree selection practice affected the chemistry rather than the biomass and morphology of gap-facing fine roots of edge trees. The medium term of six years after gap creation might have been long enough for the recovery of the fine root standing biomass to the pre-harvest condition, particularly near the stem of edge trees. A clear size threshold did not come out; nevertheless, 300 m2 may be considered a possible cut-off determining a marked change in the responses of fine roots.

Wildlife forage cover and composition on pipeline corridors in Alberta: Implications for wildlife conservation

The construction of pipeline rights-of-way (ROWs, hereafter ‘pipeline’) involves mechanical site clearing, which impacts soil and ground cover vegetation and has implications for forage availability and predation risk for threatened wildlife, including woodland caribou (Rangifer tarandus) and grizzly bear (Ursus arctos). However, there has been no quantitative evaluation of vegetation communities on open pipelines as compared to the adjacent intact forest. We compared the cover of ground vegetation by vegetation type, and the cover and composition for plant taxa known for their importance as woodland caribou and grizzly bear forage, between plots located on pipeline corridors, near the edge of the pipeline corridor, and in the adjacent undisturbed forest across six different boreal forest ecosite types in west-central and north-western Alberta, Canada. Pipeline corridors were characterized by higher total ground vegetation cover, and cover of low shrubs, lichens, bryophyte and of targeted forage species of low shrubs, bryophytes, and lichens. In contrast, pipelines had higher graminoid cover and cover of target forage species of tall shrubs and graminoids, as compared to adjacent forest. Despite the substantive differences in cover and composition of ground vegetation among the ecosite types, differences between pipelines and the adjacent forest were quite consistent, with a few exceptions. For instance, forb cover was higher in the adjacent forest compared with pipelines in shrubby ecosite types, but was similar across plot locations in other ecosites. Species composition also varied among ecosites and differed between the adjacent forest and on pipelines; with pipelines dominated by graminoids, particularly Carex species. Our results demonstrate that pipelines influence ground vegetation communities, and cover and composition of wildlife forage species, across the boreal forest landscapes of Alberta; we suggest this results in pipelines being a potential ecological sink for wildlife populations, including threatened caribou. To ensure pipelines can recover, restoration strategies that promote natural recovery or purposeful re-planting may be required to accelerate forest re-establishment and put inactive pipeline corridors within caribou ranges on a recovery trajectory. Our results suggest that ecosites can be used to prioritize pipelines where restoration or management actions may be the most beneficial.

Surface fuels in recent Phytophthora ramorum created gaps and adjacent intact Quercus agrifolia forests, East Bay Regional Parks, California, USA

Phytophthora ramorum, cause of “sudden oak death” or SOD, has had significant impacts on composition and structure in coastal forests of central and northern coastal California and southwestern Oregon. Despite the proximity of susceptible coast live oak (Quercus agrifolia) forests to densely populated urban areas, the impacts of SOD on their fuels have not been studied. We sampled surface fuels and vegetation structure in 16 plots in both SOD-caused gaps and intact stands (32 plots total) across two parks in the East Bay Regional Park District, east of San Francisco Bay. Plots were selected from a set of randomly placed pre-existing locations used in determining the disease distribution and intensity across the park system. Among the vegetation characteristics examined, only coast live oak basal area and live and dead tree density, canopy cover and maximum forb height differed between SOD created gap plots and adjacent intact forest plots. However, surface fuels such as vegetation cover, litter cover, wood cover, duff depth, fuels height, ladder fuels abundance, 1h, 10h, 100h, and 1000h fuels were greater in gap plots than intact forest plots. Although no fire behavior models were run, surface fuels suggest SOD created gaps may facilitate passive crown fire due to increased ladder and other fuels. This study represents a spatially explicit (gap focused) point-in-time estimate of surface fuels that will continue to change through time as disease progresses through these stands causing vegetation changes as fuels accumulate and decompose.

Forest edge effects on Quercus reproduction within naturally regenerated mixed broadleaf stands

This paper explores the influence of forest edge on the development of tree reproduction and the use of edge as a silvicultural tool for manipulating regeneration outcomes. Oak (Quercus spp.) reproduction was sampled 9 years following edge establishment along transects extending from 8 m into clearcut openings to 40 m into the adjacent intact forest. Trends showed that oak reproduction height in the intact forest was inversely related to distance from edge up to 20 m into the intact forest. Observed oak reproduction densities were greater within 20 m of edge than in distance intervals further into the intact forest. Tree-ring analysis of 106 seedlings was used to evaluate temporal responses associated with edge development. Cross-sectional analysis indicated a mean age of 13 years, 3 years prior to edge establishment. Increased growth was associated with edge establishment, and 10-year radial growth following edge creation showed a similar spatial pattern as height with oak seedlings within 20 m of the edge exhibiting significantly greater growth than those occurring furthest into the intact forest. This study suggests that forest edge can be used to provide environments useful in building reproductive capacity for species like oaks that require advance reproduction.

Simple Plantations Have the Potential to Enhance Biodiversity in Degraded Areas of Tam Dao National Park, Vietnam

It is often difficult to restore degraded lands within protected areas because of the high costs and because so little is known about the ecological requirements of the many species involved. Experience in Tam Dao National Park in northern Vietnam suggests the reforestation of degraded areas can be catalysed by simple monoculture plantations and that the cost of this may be modest. In this case, an existing Pinus massoniana Lambert plantation that was subsequently included within the national park was retained because native plant species were re-establishing in the understory. Within 20 years, a species-rich understory composed almost entirely of native species had established under the protective cover of the pines. This comprised 64 plant families, including 122 tree species, 46 shrubs, 33 vines, 2 herbs, 2 ferns, and 1 grass. Sixteen of these species were classified as threatened. Most of the colonists were most likely brought to the site from adjacent intact forest by wildlife over distances of up to 700 m. These plants were mostly small-seeded species, and many poorly-dispersed species remain absent from the site even after 70 years and will need assistance to colonize. The pines have persisted for 70 years, and some suggestions are made for managing the transition from a pine plantation with a native species understory to regrowth forest of solely native flora. This study suggests plantation monocultures may have a useful role in enhancing biodiversity in degraded areas within other protected areas - provided natural forest areas are close by.

Comparison of Physical, Chemical and Microbial Properties of Soils in a Clear-cut and Adjacent Intact Forest in North Western Himalaya, India

Comparison of Physical, Chemical and Microbial Properties of Soils in a Clear-cut and Adjacent Intact Forest in North Western Himalaya, India

Effects of Treefall Gap Disturbances on Ant Assemblages in a Tropical Montane Cloud Forest

AbstractThe study of gap dynamics and the effects of gaps on diversity has been at the center of tropical ecology for decades. While most studies have focused on the responses of plant species and communities to gap formation, in this study, we consider the effects of treefall gap disturbances on leaf litter ant assemblages in a Neotropical montane cloud forest. We sampled leaf litter ant assemblages and estimated a suite of abiotic parameters in 12 large (>80‐m2) treefall gaps across a chronosequence and in 12 paired adjacent intact forest sites in the Monteverde Cloud Forest Preserve in Costa Rica. No species were more common in gaps than in intact forests, and in fact, species that were common in gaps were also among the most common in forests. The Chao2 estimate of species richness, however, was higher in gap sites than in intact forest sites. In addition, ant assemblages in gap sites did not become more similar to those in adjacent intact sites as gaps aged. In contrast to other studies, our work demonstrates that ant assemblages in the Monteverde Cloud Forest Preserve are weakly affected by the formation of treefall gaps. Together, these results indicate that treefall gap dynamics probably play little role in promoting ant diversity at more regional scales, or coexistence among species at more local scales.

The effect of clearing on plant composition in mulga (Acacia aneura) dry forest, Australia

AbstractDespite high deforestation rates in dry forests there are few assessments of the impacts of this transformation on biodiversity. This study addresses the impact of clearing on plant species composition and diversity in mulga (Acacia aneura) forests of Queensland, Australia using data collected from either side of 58 clearing boundaries, incorporating data on site and management conditions. The physical and climatic conditions of the study sites were narrowly constrained but had greater influence on plant composition and richness than clearing per se. In general, the abundance of perennial forbs and shrubs was higher in cleared forest compared with adjacent intact forest and there was no significant difference in abundance of other plant life forms. Perennial forb richness diminished with the age of clearings, particularly where acid sub‐soils had been exposed and shrubs proliferated. Where deforestation in the mulga dry forests is not accompanied by the establishment of exotic pasture it has a relatively benign effect on plant diversity, mulga itself remains in high density as small trees and the integrity of the forest could be maintained with restoration.

Genetic variation and gene flow among Prunus cerasoides D. Don populations in northern Thailand: analysis of a rehabilitated site and adjacent intact forest

This study describes the level of genetic variation and gene flow within and among populations of Prunus cerasoides in rehabilitated sites and adjacent intact forest. The seven microsatellite loci employed detected a total of 75 alleles (n = 401). Polymorphic information content (PIC) varied from 0.34 to 0.83. Between the adult populations there was moderate genetic differentiation with an FST value of 0.0575, which suggests that the restoration plots had a similar genetic composition to that of the natural population. The gene flow assessment provides some interesting insights into the genetic diversity of P. cerasoides. In the 16 naturally occurring trees over 83% of the genotyped seed were fathered by unidentified trees whereas in restoration plot A only about 32% of the pollen came from an unidentified father. This proportion was even less in Plot C where 25% of the pollen parents were unidentified. The naturally occurring trees within Doi Suthep were surrounded by planted trees, which were contributing to the paternity of the seed crop. This result demonstrates that ‘‘fill in’’ planting should consist of locally sourced material if it is considered important to conserve the genetic integrity of the local populations.

Vegetation responses to natural and salvage logged fire edges in Douglas-fir/hardwood forests

Natural edges created by fire are a common component of forest ecosystems with moderate-severity fire regimes and will continue to be important as the frequency of extreme fire events increases due to historical fire suppression throughout North America. The effect of high-severity fires, with and without salvage logging, on adjacent intact forest patches has not been studied. Fourteen years after a wildfire, we examined the structure and composition of vegetation along the gradient from burned stands into the adjacent forest interior at three salvage logged edges and three unsalvaged edges in Douglas-fir/hardwood forests of northwestern California. Natural, unsalvaged edges were characterized by an increase of native, ruderal species, rather than a reduction of forest interior species. Only two forest interior species reacted negatively to the edge environment, both at salvaged edges. Old-growth community types, identified by two-way indicator species analysis (TWINSPAN), occurred 30 m closer to the edge at unsalvaged sites, compared to salvaged sites. Twenty commonly observed species (>10% frequency) demonstrated significant responses to the edge environment; 11 species had a larger depth of edge influence (DEI) at salvaged edges, three had a larger DEI at unsalvaged edges, and six had an equal DEI. Our results suggest that, compared to unsalvaged stands, the removal of snags and subsequent broadcast burning of salvaged logged stands significantly altered plant composition and structure of the edge environment. By increasing the patch contrast between burned and intact forest stands, salvage logging increased the depth of edge influence of fire-created edges by 15–30 m.

Resistance of Island Rainforest to Invasion by Alien Plants: Influence of Microhabitat and Herbivory on Seedling Performance

Experiments have promise in determining mechanisms by which communities resist invasion. Growth and survivorship of transplanted seedlings of introduced tree species (Leucaena leucocephala, Muntingia calabura, Adenanthera pavonia, and Clausena excavata) were used to assess abiotic (light regime) and biotic resistance (herbivory) to invasion of rainforest on Christmas Island (Indian Ocean). At four sites, seedlings were transplanted into the forest edge along roadside verges and into adjacent intact forest; half were caged to prevent access by the dominant seedling consumer, the red land crab (Gecarcoidea natalis). Red crab densities did not differ between roadside and forest plots. Red crabs initially reduced survivorship of Leucaena in both edge and interior plots but virtually all seedlings in the forest interior were dead after 41 weeks. Survivorship of Muntingia was also initially reduced by crabs in the forest edge, but again, all but one seedling died by the end of the experiment. Seedlings of Adenanthera and Clausena fared much better overall, surviving well in both locations. Red crabs had no overall effect on Adenanthera survival but significantly reduced survival of Clausena in forest plots. For both species, seedling performance was greater in the forest edge than in the forest interior. Red crabs had no effect on height increment for either species; however, for Clausena, red crabs reduced seedling mass in the forest interior. Both Adenanthera and Clausena were able to persist in the intact forest. Clausena is now actively invading intact rainforest, but Adenanthera appears dispersal-limited. Resistance factors in intact forest appear hierarchical: biotic resistance afforded by land crabs can impede establishment of some plant invaders but seedling responses to abiotic factors (e.g., the light regime) largely overwhelm its effect. Together, these two community attributes are likely to restrict the range of plant invaders to a small suite of species that can successfully establish in intact rainforest on the island. However, increased propagule pressure from a variety of shade-tolerant species and further declines in the abundance of the dominant seedling consumer may lead to increasing invasion success in this island rainforest.

Clear cutting and burning affect nitrogen supply, phosphorus fractions and seedling growth in soils from a Wyoming lodgepole pine forest

Timber harvesting, with and without prescribed slash fire, and wild fire are common disturbances in pine forests of western North America. These disturbances can alter soil nitrogen (N) pools and N supply to colonizing vegetation, but their influence remains poorly understood for many forests. We investigated the effects of clear cut harvesting and fire on KCl extractable N pools, net N mineralization rates, phosphorus (P) fractions, seedling N uptake, and seedling growth in mineral soils sampled from a lodgepole pine forest in southern Wyoming. At a site where wild fire burned through a harvested stand of lodgepole pine and the adjacent intact forest, we analyzed mineral soils from the following four treatments: unburned clear cut, burnt clear cut, unburned forest, and burnt forest. Soils from unburned and burnt clear cut treatments had higher concentrations of KCl extractable N and higher net N mineralization rates, and produced larger pine seedlings in bioassays than soils from unburned and burnt intact forest treatments. Further, while seedlings grown in soils from the unburned and burnt forest treatments responded strongly to N fertilization, seedlings grown in clear-cut soils did not respond to fertilization. Taken together, these results suggest that harvesting had increased soil N supply. In comparing clear cut treatments, soils from the unburned clear cut had smaller extractable N and P pools, and lower net N mineralization rates, but produced larger pine seedlings than soils from the burnt clear cut.

Effect of Pasture Trees on Soil Nitrogen and Organic Matter: Implications for Tropical Montane Forest Restoration

In lower‐montane ecosystems of Ecuador, Setaria sphacelata (foxtail grass), the predominant introduced pasture species, forms a tussock grassland that reduces soil nitrogen and resists recolonization of forest vegetation. We compared the influence of individual trees or small clusters of nitrogen‐fixing (Inga sp., Fabaceae) and non‐nitrogen‐fixing trees (Psidium guajava L., guava) on the soil and abiotic conditions that affect further regeneration of forest vegetation within pastures. Pasture trees ameliorated air temperature and light intensity to levels similar to those in adjacent intact forest. Beneath Inga, soil NO3−‐N was four times higher than in open pasture. Nitrification was five times higher under Inga canopies than in open pastures for both field and laboratory incubations. This suggests that the increased soil N transformations under Inga are derived mainly from improved soil rather than microenvironmental conditions. Psidium canopies slightly increased field nitrification but had no effect under laboratory conditions. We also compared the natural abundance 13C signature and the carbon and nitrogen content of subcanopy soil with adjacent open pasture soil. Inga increased the C and N content of the upper 5 cm of soil and increased by 7% the fraction of soil organic matter derived from C3 plants. The improved soil and abiotic conditions beneath the canopies of N‐fixing pasture trees favor the establishment and growth of woody montane species, suggesting that these trees could be used to accelerate forest regeneration within abandoned pastures.

Fine root biomass under light gap openings in an Amazon rain forest.

Belowground processes in light gap openings are poorly understood, particularly in tropical forests. Fine roots in three zones of light gap openings and adjacent intact forest were regularly measured in buried bags and surface litter envelopes for 2 years. Fine root biomass does not vary significantly within gaps for either buried bags or for surface litter envelopes. When entire gaps are compared without regard for within gap zones, root growth into both surface litter and buried bags is significantly different between gaps, with highest rates of fine root biomass accumulation in the smallest gap. These results suggest that the aboveground within-gap zones do not result in a congruent pattern of below-ground zonation. Gap size, decomposition of the fallen tree, and pre-gap fine root growth rates should be considered to determine fine root growth patterns following the formation of light gap openings.