Document Vegetation Changes Research Articles

Vegetation response to climate changes in the eastern Arctic during the Middle Gelasian age of the Early Pleistocene

Palynological analysis of sediments from El'gygytgyn Lake document vegetation changes in the Eastern Arctic from early marine isotope stage (MIS) 74 to late MIS 80 (c.2.1–1.9 MA) and close the last remaining gap in the El'gygytgyn pollen record. Cooler climates were characterized by a mix of Larix forest-tundra, shrub Betula tundra, and herb-dominated communities. During interglaciations, Larix forests with tree Betula and Alnus, and perhaps with a minor component of Picea and tree Pinus, characterized areas that today are tundra. These forests included a rich shrub understory of Betula, Duschekia, Salix, and Pinus pumila. Although MIS 77 has been considered a “super” interglaciation, the data do not indicate that this stage was exceptionally warm. Interstadial conditions are denoted by pollen assemblages that indicate the regional vegetation was dominated by Larix forest -tundra and an absence of Pinus pumila. The palynological results from this Early Pleistocene interval demonstrate the need to: 1) modify the El'gygytgyn age model; 2) reevaluate the relationship of sediment facies to climate change; and 3) reconsider the occurrence and/or definition of “super” interglaciations.

Satellite Image-Based Time Series Observations of Vegetation Response to Hurricane Irma in the Lower Florida Keys

High-resolution satellite imaging represents a potentially effective technique to monitor cyclone-caused environmental damage and recovery over large areas at a high spatial scale. This study utilized a 10-m resolution Sentinel satellite image series to document vegetation changes in a portion of the Florida Keys, USA, over which the core of Category 4 Hurricane Irma passed on 10 September 2017. A previously assembled field survey was used to establish land-cover patterns in the satellite data, and concurrent field measurements verified post-hurricane changes. Normalized difference vegetation index (NDVI) was utilized as a tracer for pre-storm baseline patterns and through 19 post-storm months. NDVI patterns show that the severity of vegetation damage varied appreciably across the area, with the least damage on islands in the western sector of the hurricane’s eye and around its center, and greatest damage on islands just east of the eye. The data reveal that for 2.5 months after the storm, multiple inland vegetation classes showed substantial early regrowth. However, mangrove forests were more negatively affected. The storm caused extensive mortality of black mangrove (Avicennia germinans) and red mangrove (Rhizophora mangle), corresponding to more than 40% of the total mangrove area on some islands. The full extent of mangrove die-off was not immediately evident, and increased progressively through the first few months after the storm. In addition to demonstrating the utility of high-resolution satellite image series for post-hurricane environmental assessment, this study reveals high-resolution links between vegetation types, their location within the cyclone, and the extent of post-storm recovery.

Shining a New Light on Elmer Ottis Wooton’s Legacy Herbarium and Historical Archive: an Exercise to Increase Student Participation while Promoting Public Engagement

Elmer Ottis Wooton (1865–1945) was one of the most important early botanists to work in the Southwestern United States, contributing a great deal of natural history knowledge and botanical research on the flora of New Mexico that shaped many naturalists and scientists for generations. The extensive Wooton legacy includes herbarium collections that he and his famous student Paul Carpenter Standley (1884–1963), prolific botanist and explorer, used for the first Flora of New Mexico by Wooten and Standley 1915 , along with resources covering botany and range management strategies for the northern Chihuahuan Desert, and an extensive, yet to be digitized, historical archive of correspondence, field notes, vegetation sketches, photographs, and lantern slides, all from his travels and field work in the region. Starting in 1890, the most complete set of Wooton’s herbarium collections were deposited in the NMC herbarium at New Mexico State University (NMSU), and his archives, now stored in a Campus library, have together been underutilized, offline resources. The goals of this ongoing project are to secure, preserve, and promote Wooton’s important historical resources, by fleshing out the botanical history of the region, raising appreciation of herbarium collections within the community, and emphasizing their unique role in facilitating contemporary research aimed at addressing pressing scientific questions such as vegetation responses to global climate change. Students and the general public involved in this project are engaged through hands-on activities including cataloging, databasing and digitization of nearly 10,000 herbarium specimens and Wooton’s archives. These outputs, combined with contemporary data collection and computational biology techniques from an ecological perspective, are being used to document vegetation changes in iconic, climate-sensitive, high-elevation mountainous ecosystems present in southwestern New Mexico. In a later phase of the project, a variety of public audiences will participate through interactive online story maps and citizen science programs such as iNaturalist, Notes from Nature, and BioBlitz. Images of herbarium specimens will be shared via an online database and other relevant biodiversity portals (Symbiota, iDigBio, JStor) Community members reached through this project will be better-informed citizens, who may go on to become new stewards of natural history collections, with the potential to influence policies safeguarding the future of our planet’s biodiversity. More locally, the project will support the management of Organ Mountains Desert Peaks National Monument, which was established in 2014 to protect the area's human and environmental resources, and for which knowledge and data are currently limited.

Applying time series Landsat data for vegetation change analysis in the Florida Everglades Water Conservation Area 2A during 1996–2016

Mapping plant communities and documenting their changes is critical to the on-going Florida Everglades restoration project. In this study, a framework was designed to map dominant vegetation communities and inventory their changes in the Florida Everglades Water Conservation Area 2A (WCA-2A) using time series Landsat images spanning 1996–2016. The object-based change analysis technique was combined in the framework. A hybrid pixel/object-based change detection approach was developed to effectively collect training samples for historical images with sparse reference data. An object-based quantification approach was also developed to assess the expansion/reduction of a specific class such as cattail (an invasive species in the Everglades) from the object-based classifications of two dates of imagery. The study confirmed the results in the literature that cattail was largely expanded during 1996–2007. It also revealed that cattail expansion was constrained after 2007. Application of time series Landsat data is valuable to document vegetation changes for the WCA-2A impoundment. The digital techniques developed will benefit global wetland mapping and change analysis in general, and the Florida Everglades WCA-2A in particular.

Twenty-Five Year Record of Changes in Plant Cover on Tundra of Northeastern Alaska

Northern Alaska has warmed over recent decades and satellite data indicate that vegetation productivity has increased. To document vegetation changes in the Arctic National Wildlife Refuge, we monitored plant cover at 27 plots between 1984 and 2009. These are among the oldest permanently marked and continuously monitored vegetation plots in the Arctic. We quantified percent cover of all plant species by line-point intercept sampling and assessed change over time for seven plant growth forms. Cover of bryophytes and deciduous shrubs showed slight decreasing trends. Evergreen shrubs, horsetails, and depth of thawed soil above permafrost had no trends. For lichens, graminoids, and forbs, trends varied by plant community type. Overall, vegetation in the plots changed little over the study period, in contrast to results from other studies in northern Alaska. A few plots had dramatic changes, however, which we attributed to subsidence from melting ground ice or to floodplain dynamics. Our results demonstrate that vegetation change on the Arctic Refuge coastal plain over the past quarter century has been spatially heterogeneous and facilitated by disturbance. The findings highlight the need for greater work linking plotlevel and regional remote sensing measurements of change.

Warming experiments elucidate the drivers of observed directional changes in tundra vegetation.

Few studies have clearly linked long-term monitoring with in situ experiments to clarify potential drivers of observed change at a given site. This is especially necessary when findings from a site are applied to a much broader geographic area. Here, we document vegetation change at Barrow and Atqasuk, Alaska, occurring naturally and due to experimental warming over nearly two decades. An examination of plant cover, canopy height, and community indices showed more significant differences between years than due to experimental warming. However, changes with warming were more consistent than changes between years and were cumulative in many cases. Most cases of directional change observed in the control plots over time corresponded with a directional change in response to experimental warming. These included increases in canopy height and decreases in lichen cover. Experimental warming resulted in additional increases in evergreen shrub cover and decreases in diversity and bryophyte cover. This study suggests that the directional changes occurring at the sites are primarily due to warming and indicates that further changes are likely in the next two decades if the regional warming trend continues. These findings provide an example of the utility of coupling in situ experiments with long-term monitoring to accurately document vegetation change in response to global change and to identify the underlying mechanisms driving observed changes.

Validation of a simplified point frame method to detect change in tundra vegetation

The point frame method is ideal for vegetation monitoring because exact locations may be precisely resampled over time. Many researchers, including those associated with the International Tundra Experiment (ITEX), have used a modified point frame method to document vegetation change in response to climate change and experimental warming. To save, time only the uppermost and lowermost encounter (TB method) of a plant below each grid point is recorded as opposed to all contacts (AC method). Here, we investigate the ability of this shortcut to accurately assess the community change and estimate the aboveground plant biomass at four long-term sites in northern Alaska. We found that the TB method underrepresented the species cover (by omitting intermediate contacts) between 35 and 50 % of the taxa at a site; however, the magnitude was less than 2 % cover for all but 17 of the 109 taxa and site combinations, and despite the smaller number of contacts in the TB method, it was nearly equal in its ability to detect a change in cover in response to warming as the AC method (only 1 of the 109 cases showed differences in the significance of the response). Linear regressions showed the accuracy of the TB, and AC methods were also similar in estimating aboveground plant biomass (same cases were significant, and all but 2 were within r 2 of 0.1). Thus, we conclude that TB method outlined in the ITEX manual is an efficient and accurate way of assessing vegetation changes in tundra plant communities.

Vegetation Succession After Bauxite Mining in Western Australia

Abstract Alcoa World Alumina Australia has been rehabilitating bauxite mines in the jarrah forest of Western Australia for more than 35 years. An experiment was established in 1988 using three different seed treatments (legume and small understorey mix, small understorey mix only, and no seed) and two fertilizer treatments (N and P, and P only). The objectives of this study were to (1) document vegetation changes in the first 14 years after bauxite mining; (2) assess whether the vegetation is becoming more similar to the unmined forest; and (3) gain a better understanding of successional processes. Seed treatments significantly affected 13 of the 14 measured vegetation characteristics. Native species richness was higher in seeded than in unseeded sites at 1, 2, and 5 years of age, whereas diversity and evenness were generally higher at all assessment ages. Exotic species density was higher in unseeded than in seeded sites from 5 years onward, whereas richness was higher from 8 years onward. Nitrogen fertilizer significantly increased exotic species richness, density, and cover. Ephemerals dominated plant density in all rehabilitation treatments over time, whereas seeder species dominated cover. In contrast, resprouting species dominated density and cover in the unmined forest. Orchids were the only species that were not present in the first year in rehabilitated sites but increased in abundance over time. Vegetation composition in rehabilitated areas did not become more similar to the unmined forest during the 14 years since seeding, instead strongly reflected the initial species mix. Rehabilitated bauxite mines appear to follow the initial floristic composition model of succession.

Distribution of carbon isotope composition of modern soils on the Qinghai-Tibetan Plateau

This paper presents a large data set on carbon isotope composition (δ13C) of modern soils which were collected under the main vegetation communities along an altitude of 1250–5500 m above sea level in the Qinghai-Tibetan Plateau. The δ13C values of 198 samples range from −28.6 to −15.1‰ versus PDB and exhibit a clean relation to different vegetation communities from forest (−25.9 ± 1.2‰) to shrub (−24.7 ± 1.4‰), steppe (−23.1 ± 1.3‰), alpine meadow (−23.6 ± 0.7‰), alpine desert steppe (−21.3 ± 1.6‰), and alpine desert (−18.9 ± 2.5‰). We attributed the observed variability in δ13C values to that the mean annual precipitation (MAP) and the mean annual temperature (MAT) are the main factors controlling the distribution of vegetation types in the Tibetan Plateau, which causes the change in carbon isotope composition of modern soils at any given altitude. The result of both linear and nonlinear regression analyses also confirms that MAP and MAT are the major factors affecting the δ13C values of surface soils. In the absence of favorable moisture and temperature conditions, low pCO2 alone is not sufficient to cause the distinct changes in carbon isotope composition of modern soils in the Tibetan Plateau. This study provides some fundamental information on the carbon isotope composition of terrestrial carbon pools and bears some practical significance for the use of carbon isotope data to document vegetation changes and environmental conditions of the high plateau in the past.

Vegetation change in an urban grassy woodland 1974 - 2000

Few temporal studies document vegetation change in Australian temperate grassy woodlands. Floristic and structural data were collected from 68 randomly located sites in the Queens Domain, an urban grassy woodland remnant, in 1974, 1984, 1994 and 2000 and a search made for rare species. Species of conservation significance were concentrated at highly disturbed sites, whereas vegetation types of conservation significance decreased in area as a result of increases in the numbers of Allocasuarina verticillata, which caused a change in many unmown areas from Eucalyptus viminalis grassy woodland to E. viminalis–A. verticillata woodland/forest or A. verticillata open/closed forest. Structural changes were associated with changes in species composition and an increase in native-species richness. Increases in tree cover occurred where fires were most frequent, possibly as a result of the lack of mammalian herbivores. The frequencies of herbs and annual grasses were strongly affected by precipitation in the month of sampling. Half of the species that showed a consistent rise or fall through time were woody plants, approximately twice the number expected. In the dataset as a whole, species-richness variables were largely explained by varying combinations of variables related to moisture availability, altitude and the incidence of mowing. The strongest influences on species composition were the same, although slope and time since the last fire also contributed to multiple regression and generalised linear models. Compositional stability was positively related to native-species richness, whereas high levels of exotic-species richness occurred at both low and high levels of native-species richness. The maintenance of native-plant biodiversity on the Domain requires such counterintuitive measures as the maintenance of exotic trees and the control of native trees, demonstrating the contingencies of conservation management in fragmented vegetation that consists of a mixture of native and exotic species.

Post-burn vegetation development of rehabilitated bauxite mines in western Australia

Alcoa World Alumina Australia has been rehabilitating bauxite mines in the jarrah ( Eucalyptus marginata) forest of Western Australia for more than 35 years. Mines rehabilitated in the early 1980s contain some eastern Australian eucalypts and have built up substantial fuel loads (23–35 t/ha) that may be reduced through prescribed burning. The aim of this study was to document vegetation changes in areas rehabilitated in the early 1980s for 6 years following prescribed burning and ascertain the most appropriate fire regime to apply in these areas to achieve identified rehabilitation completion criteria. Following both autumn and spring burning, rehabilitated areas rapidly re-accumulated fuel in the first year after burning, but fuel loads have remained relatively constant since then at a level of 8–9 t/ha. Burning was successful in removing dead aerated fuel that dominated the midstorey of the vegetation and stimulating plant growth in the understorey, making the burnt rehabilitated areas more like the unmined forest. Plant density, live plant cover, Acacia density and Acacia cover were generally higher following autumn than spring burning, although differences were reduced over time. Weed density did not differ significantly between autumn and spring burning, peaking 2 years after burning and then declining back to pre-burn levels. Similarly, species richness peaked in the first few years following burning and then declined, consistent with the predictions of the initial floristic composition model of succession. Tree growth was lower in burnt than unburnt areas for the first 2 years, but 4 and 6 years after burning tree growth was not significantly different between autumn, spring and no burn areas. Alcoa is required to integrate rehabilitated areas into the fire management regime of the surrounding jarrah forest to meet completion criteria. The results suggest that this can be achieved by burning rehabilitated areas containing non-native eucalypt species in spring under low to moderate intensity. This fire regime will lead to reduced fuel accumulation, a less prominent midstorey layer resulting from reduced recruitment of Acacia spp., lower densities of eastern Australian eucalypt species, and greater similarity in the composition and abundance of the understorey to the unmined forest.

Soil carbonate decomposition by acid has little effect on δ13C of organic matter

The δ 13C of soil organic C is often utilized to document vegetation changes and to estimate rates of soil organic C turnover. Soil carbonate C is isotopically distinct from organic C, and must be removed by acidification prior to isotopic analysis of soil organic matter. We determined the effects of acid concentration (0.1, 0.5, 1, or 6 m HCl) and duration of treatment (1, 2, 3, or 8 d) on soil δ 13C and the concentration of C and N in a carbonate-free entisol and a calcareous vertisol both obtained from Texas. δ 13C values of organic C in the entisol were reduced significantly by treatment with 6 m HCl for more than 1 d; however, all other combinations of acid strength and treatment duration had no effect on δ 13C of organic C in that soil. In the calcareous soil, δ 13C of organic C was largely unaffected by acid concentration or duration of treatment; however, soils treated with 0.1 m HCl required 3 d to fully remove all carbonate and achieve δ 13C values comparable to those in other treatment combinations. Treatment of calcareous soils with 0.5 m HCl for 24 h appears sufficient to remove all carbonate C prior to isotopic analysis, and this treatment has no discernible effect on the δ 13C of the soil organic matter.

δ13C values of soil organic carbon and their use in documenting vegetation change in a subtropical savanna ecosystem

Plants with C 3, C 4, and CAM photosynthesis have unique δ 13C values which are not altered significantly during decomposition and soil organic matter formation. Consequently, δ 13C values of soil organic carbon reflect the relative contribution of plant species with C 3, C 4, and CAM photosynthetic pathways to community net primary productivity, and have been utilized to document vegetation change, to quantify soil organic matter turnover, and to refine our understanding of earth–atmosphere–biosphere interactions. Here, we review the basis of this methodology, and illustrate its use as a tool for studying grass–woody plant dynamics in a savanna ecosystem. In the Rio Grande Plains of southern Texas, C 4 grasslands and savannas have been largely replaced by C 3 subtropical thorn woodlands dominated by Prosopis glandulosa. We used δ 13C values of soil organic matter, above- and belowground plant biomass, and litter in conjunction with radiocarbon dating and dendrochronology to test the hypotheses that: (1) C 3 Prosopis groves in uplands and C 3 Prosopis woodlands in low-lying drainages have been long-term components of the landscape; and (2) Prosopis woodlands of low-lying drainages have expanded up-slope since Anglo-European settlement. Current organic matter inputs were not in isotopic equilibrium with soil organic carbon in any of the patch types sampled. In upland grasslands, δ 13C values of vegetation (−20‰) were lower than those of soil organic matter (−17‰), suggesting increased C 3 forb abundance in response to long-term, heavy grazing (herbaceous retrogression). In wooded landscape elements, δ 13C values of current organic matter inputs were characteristic of C 3 plants (−28 to −25‰), while those of the associated soil organic matter were typically −20 to −15‰. These δ 13C values indicate that woodlands, groves, and shrub clusters dominated almost exclusively by C 3 plants now occupy sites once dominated by C 4 grasses. A particularly strong memory of the C 4 grasslands that once occupied these sites was recorded in the δ 13C values of organic carbon associated with fine and coarse clay fractions (−18 to −14‰), probably a consequence of the slow organic carbon turnover rates in those soil fractions. When δ 13C values of soil organic carbon were evaluated in conjunction with radiocarbon measurements of that same carbon, it appeared that herbaceous retrogression and a shift from C 4 grassland to C 3 woodland occurred recently, probably within the last 50–100 years. Demographic characteristics of the dominant tree species corroborated the δ 13C and 14C evidence, and indicated widespread establishment of P. glandulosa and associated shrubs over the past 100 years. Together, these data provide direct, spatially explicit evidence that vegetation change has occurred recently across the entire landscape at this site. Environmental conditions where C 3, C 4, and CAM plants coexist (e.g., dry, alkaline soils) generally do not favor the preservation of pollen and phytoliths, and these same areas usually lack historical records of vegetation change. Consequently, vegetation dynamics have been difficult to quantify in grasslands, savannas, and woodlands. However, our results demonstrate clearly that δ 13C values of soil organic matter afford a direct and powerful technique for reconstructing vegetation change in these areas.

Holocene Forest Development and Paleoclimates Within the Central Sierra Nevada, California

(1) The pollen and plant macrofossils in sediments from three high-altitude lakes in the Sierra Nevada, California, document vegetation changes that have occurred over the last 12500 years. (2) Trees became established around the lakes by c. 10 000 years ago. Early Holocene forests were structurally different from those of today; they were more open than at present, with more montane chaparral shrubs. Several tree species characteristic of modern subalpine forests were rare and restricted to mesic habitats. Significantly drier conditions are inferred. (3) By c. 6000 B.P., effective precipitation had increased, as shown by an increase in subalpine conifers, principally Tsuga mertensiana (mountain hemlock) and Abies magnifica (red fir). (4) The upper altitudinal limits of many subalpine conifers began to fall c. 2500 B.P., coincident with the beginning of Neoglacial cooling. (5) The climatic interpretations are consistent with those previously described for the Pacific North-west region of North America, but not consistent with those for the American South-west.

Restoration of an Impounded Salt Marsh in New England

The restoration of a 20 ha tidal marsh, impounded for 32, yr, in Stonington, Connecticut was studied to document vegetation change 10 yr after the reintroduction of tidal flushing. These data were then compared to a 1976 survey of the same marsh when it was in its freshest state and dominanted byTypha angustifolia. Currently,T. angustifolia remains vigorous only along the upland borders and in the upper reaches of the valley marsh. Live coverage ofT. angustifolia has declined from 74% to 16% and surviving stands are mostly stunted and depauperate. Other brackish species have also been adversely effected, except forPhragmites australis which has increased. In contrast, the salt marsh speciesSpartina alterniflora has dramatically expanded, from <1% to 45% cover over the last decade. Locally, high marsh species have also become established, covering another 20% of the marsh.

Computer-aided classification of forest cover types from small scale aerial photography

The US National Park Service must map forest cover types over extensive areas in order to fulfill its goal of maintaining or reconstructing presettlement vegetation within national parks and monuments. Furthermore, such cover type maps must be updated on a regular basis to document vegetation changes. Computer-aided classification of small scale aerial photography is a promising technique for generating forest cover type maps efficiently and inexpensively. In this study, seven cover types were classified with an overall accuracy of 62 percent from a reproduction of a 1∶120,000 color infrared transparency of a conifer-hardwood forest. The results were encouraging, given the degraded quality of the photograph and the fact that features were not centered, as well as the lack of information on lens vignetting characteristics to make corrections. Suggestions are made for resolving these problems in future research and applications. In addition, it is hypothesized that the overall accuracy is artificially low because the computer-aided classification more accurately portrayed the intermixing of cover types than the hand-drawn maps to which it was compared.

Plant invasion and extinction in a suburban coastal reserve

In recent years there has been increasing concern with the problems of conservation of native biotic communities. While in most parts of Australia the area of land devoted to nature conservation has been increasing rapidly, little is known about such basic questions as the minimum area needed to maintain native communities in at least part of a reserve, or even the effects of intensive land use in surrounding areas on directly unmodified native vegetation. Yet, given the small areas contained in a large number of reserves devoted to nature conservation, these questions are of some importance. There is general acceptance of the view that the least desirable reserve for nature conservation in the long term is small in area with a large boundary/area ratio (Frankenburg, 1971). While surrounded by unmodified native communities such reserves remain viable. However, with increasing intensity of land use around their boundaries, they become more and more prone to a series of edge effects. These edge effects can include fertilizer drift, pesticide and herbicide drift, an increased susceptibility to firing, and increasing probabilities of introduction of exotic plants and animals. This and a subsequent article will document vegetation changes in the Sandringham Foreshore Reserve in the Melbourne Metropolitan Area, Victoria. The changes in the flora of the reserve will be traced from 1911 to 1971, covering the period in which the areas abutting on to the reserve developed from largely uncleared heath and scrub to upper middle class suburbia. The later article will describe and analyze the plant communities present in 1971, and will attempt to follow their development to that date. The value of this study lies in the insight it will give to the types of changes that can be expected in a reserve of unsuitable shape which has been subjected to increasingly intensive landuse both within and outside its boundaries. It is hoped that an understanding of the changes that have taken place in the extreme case will elucidate and allow the control of changes taking place in better situations.