Trajectories Of Vegetation Change Research Articles

Monitoring ecosystem reclamation recovery using optical remote sensing: Comparison with field measurements and eddy covariance

Time series remote sensing vegetation indices derived from SPOT 5 data are compared with vegetation structure and eddy covariance flux data at 15 dry to wet reclamation and reference sites within the Oil Sands region of Alberta, Canada. This comprehensive analysis examines the linkages between indicators of ecosystem function and change trajectories observed both at the plot level and within pixels. Using SPOT imagery, we find that higher spatial resolution datasets (e.g. 10 m) improves the relationship between vegetation indices and structural measurements compared with interpolated (lower resolution) pixels. The simple ratio (SR) vegetation index performs best when compared with stem density-based indicators (R2 = 0.65; p < 0.00), while the normalised difference vegetation index (NDVI) and soil adjusted vegetation index (SAVI) are most comparable to foliage indicators (leaf area index (LAI) and canopy cover (R2 = 0.52–0.78; p > 0.02). Fluxes (net ecosystem production (NEP) and gross ecosystem production (GEP)) are most related to NDVI and SAVI when these are interpolated to larger 20 m × 20 m pixels (R2 = 0.44–0.50; p < 0.00). As expected, decreased sensitivity of NDVI is problematic for sites with LAI > 3 m2 m−2, making this index more appropriate for newly regenerating reclamation areas. For sites with LAI < 3 m2 m−2, trajectories of vegetation change can be mapped over time and are within 2.7% and 3.3% of annual measured LAI changes observed at most sites. This study demonstrates the utility of remote sensing in combination with field and eddy covariance data for monitoring and scaling of reclaimed and reference site productivity within and beyond the Oil Sands Region of western Canada.

Different Fire Frequency Impacts Over 27 Years on Vegetation Succession in an Infertile Old-Field Grassland

We examined the effect of fire on vegetation composition with the use of an experiment with four different fire frequencies (annual, 2-yr interval, 4-yr interval, and an intended control with no burning) over a 27-yr period in an infertile, old-field grassland at the Cedar Creek Ecosystem Science Reserve, located in Minnesota, United States. We measured the plant species' aboveground biomass in permanent plots in 1983, 1987, 1991, 2000, and 2010. None of these fire frequencies, even after 27 yr, had a large impact on the vegetation composition. The plant functional groups' responses to fire frequency were consistent with their respective dominant species. The most abundant C4 grass, little bluestem (Schizachyrium scoparium Michx.), did not change in biomass with fire frequency over time. The biomass of the introduced, invasive grass, Kentucky bluegrass (Poa pratensis L.) decreased significantly with increasing fire frequency, but this decrease did not result in change to the rate and trajectory of vegetation change. Bush clover (Lespedeza capitata Michx.), the only legume in the community, strongly increased with more frequent fire, but only after 20yr. Species richness and litter mass decreased significantly with increasing fire frequency. These small fire-induced vegetation changes contrast with large fire-induced vegetation changes in fertile grasslands. Management strategies using fire in infertile grasslands can lower Poa abundance; however, increased fire also decreased overall plant diversity.

Estimating Vegetation Reference Conditions by Combining Historical Source Analysis and Soil Phytolith Analysis at Pepperwood Preserve, Northern California Coast Ranges, U.S.A

AbstractThe vegetation on many Californian landscapes changed substantially after the late eighteenth century arrival of European settlers. Restoring vegetation to pre‐settlement status requires an understanding of reference conditions, the range of variability of vegetation and the trajectory of vegetation change through time. We used parallel, independent studies of historical evidence and soil phytoliths to increase temporal depth and estimate reference conditions at 39 sites in a mosaic of grassland–savanna–woodland–chaparral vegetation at Pepperwood Preserve, in California's northern Coast Ranges. Historical evidence consisted of mid‐1800s General Land Office survey records and repeat aerial photographs. Survey points were relocated and survey descriptions compared with modern vegetation; vegetation type had not changed on 16 of 19 sites. Aerial photographs showed increasing tree cover and decreasing grassland from 1942 to 2000. Phytolith analysis, including soil phytolith percent weight and absolute counts of grass short cells, was used to estimate long‐term vegetation. Sites containing greater than 0.30% soil phytolith weight and greater than 90,000 rondel short cells/g soil were classified as grassland/savanna; sites below the 0.30% threshold with less than 32,000 and 32,000‐90,000 rondels/g soil were classified as forest and woodland, respectively, while chaparral had low (&lt;0.70) rondel/elongate ratios. Phytolith‐based classification of long‐term vegetation indicated that vegetation type has not changed on 30 of 39 sites. Both historical and phytolith evidence indicated most of the vegetation landscape at Pepperwood has been long‐term stable. Historical source analysis and phytolith analysis are highly complementary approaches that should be routinely performed to provide accurate estimates of site reference conditions prior to commencing vegetation restoration.

Vegetation Change from the Euro-American Settlement Era to the Present in Relation to Environment and Disturbance in Southwest Oregon

Faced with landscapes degraded by fire suppression, logging, and grazing, land managers in the interior western US are attempting to restore habitat structure and function. In southwest Oregon, landscape-scale fuels treatments are being implemented with goals including recreating historic vegetation structure, despite poor understanding of the nature of the landscape prior to widespread Euro-American influence, or the patterns and processes of vegetation change over time. We compared a General Land Office-based reconstruction of Euro-American settlement era (1850s) vegetation in southwest Oregon's interior valleys and foothills with modern vegetation interpreted from aerial orthoimages to determine patterns of vegetation distribution in both eras, trajectories of vegetation change, and environmental and disturbance factors related to these themes. We found that this landscape was primarily occupied by closed plant community types in both eras, with a comparatively minor proportion in open types; vegetation was distributed along a dominant environmental gradient that ran from prairies in xeric lowlands to conifer forests in steeper, cooler uplands. Temporal shifts from open to closed vegetation were consistent with expected effects of fire suppression in many cases, but in other cases, the long-term persistence of open vegetation in the absence of recorded fire indicated that other mechanisms were also in operation. Human encroachment into wildlands, particularly in valleys, has also been a major driver of landscape-level change in the past 150 yr. Our results suggest that conservation should focus on lowlands, particularly where uncommon vegetation types such as savanna, shrubland, and prairie still exist.

Factors influencing vegetation cover change in Mediterranean Central Chile (1975–2008)

AbstractQuestions: Which are the factors that influence forest and shrubland loss and regeneration and their underlying drivers?Location: Central Chile, a world biodiversity hotspot.Methods: Using land‐cover data from the years 1975, 1985, 1999 and 2008, we fitted classification trees and multiple logistic regression models to account for the relationship between different trajectories of vegetation change and a range of biophysical and socio‐economic factors.Results: The variables that most consistently showed significant effects on vegetation change across all time‐intervals were slope and distance to primary roads. We found that forest and shrubland loss on one side and regeneration on the other often displayed opposite patterns in relation to the different explanatory variables. Deforestation was positively related to distance to primary roads and to distance within forest edges and was favoured by a low insolation and a low slope. In turn, forest regeneration was negatively related to the distance to primary roads and positively to the distance to the nearest forest patch, insolation and slope. Shrubland loss was positively influenced by slope and distance to cities and primary roads and negatively influenced by distance to rivers. Conversely, shrubland regeneration was negatively related to slope, distance to cities and distance to primary roads and positively related to distance from existing forest patches and distance to rivers.Conclusions: This article reveals how biophysical and socioeconomic factors influence vegetation cover change and the underlying social, political and economical drivers. This assessment provides a basis for management decisions, considering the crucial role of perennial vegetation cover for sustaining biodiversity and ecosystem services.

Long-term heathland restoration on former grassland: The results of a 17-year experiment

European lowland heaths have declined by up to 80% due to land use change and lack of management. There has been considerable research into the restoration of this threatened habitat. However, long-term outcomes of restoration are poorly understood, especially in situations where past agricultural land use imposes severe constraints on community re-assembly. In 1989 a large-scale experiment was established to examine the effectiveness of five treatments to restore heathland on formerly productive grassland: (i) natural regeneration; (ii) herbicide application to facilitate regeneration; (iii) cultivation and application of seed-rich heathland vegetation; (iv) soil removal and incorporation of heathland topsoil; and (v) heathland translocation. After 17 years the pH of the unamended agricultural soil remained significantly higher than that of the adjacent heathland. All treatments showed different trajectories of vegetation change in the long-term. Natural colonisation by heathland species was slow due to seed limitation, resulting in formation of an acid grassland community. Heathland community assembly was not facilitated by destruction of the initial grassland with herbicide. Incorporation of topsoil had an intermediate effect on pH reduction. This may explain the subsequent failure of the plant community to assemble in the anticipated proportions, and the dominance of leguminous scrub species ( Ulex spp.). Turf translocation was effective in reducing pH to the required range and restoring the heathland community in the long-term. However, this technique should only be considered as a means of ‘rescue’ when habitat destruction is otherwise unavoidable. The only practical and sustainable means of increasing heathland extent on former farmland is the application of seed-bearing vegetation cut as part of routine management. However, this technique needs refining in order to establish the full range of characteristic heathland species.

Potential effects of climate change on ecosystem distribution in Alberta

We propose a new and relatively simple modification to extend the utility of bioclimatic envelope models for land-use planning and adaptation under climate change. In our approach, the trajectory of vegetation change is set by a bioclimatic envelope model, but the rate of transition is determined by a disturbance model. We used this new approach to explore potential changes in the distribution of ecosystems in Alberta, Canada, under alternative climate and disturbance scenarios. The disturbance model slowed the rate of ecosystem transition, relative to the raw projections of the bioclimatic envelope model. But even with these transition lags in place, a northward shift of grasslands into much of the existing parkland occurred over the 50 years of our simulation. There was also a conversion of 12%–21% of Alberta’s boreal region to parkland. In addition to aspatial projections, our simulations provide testable predictions about where ecosystem changes as a result of climate change are most likely to be initially observed. We also conducted an investigation of model uncertainty that provides an indication of the robustness of our findings and identifies fruitful avenues for future research.

Conceptual ecological models for the Long Island pitch pine barrens: implications for managing rare plant communities

Fire dependent pitch pine ( Pinus rigida Mill.) and scrub oak ( Quercus ilicifolia Wang.) barrens are found on coarse-textured, droughty soils in the northeastern United States. These communities are globablly rare and, in many areas, dependent on active management to sustain them. We used historic and recent aerial photographs of the Central Pine Barrens in New York to develop transition matrices and trajectories of vegetation change. A vegetation map for 1990 provided pre-burn cover type information for a 1,200 ha area burned by an extremely severe wildfire in August 1995. Geographic information system analyses, a fire-history study, post-wildfire research and existing literature provided additional information for development of three conceptual models that describe our understanding of vegetation change in response to fire and land clearing. A simulation model was then used to predict the amount of each cover type in 2046. The reasonableness of the prediction was assessed based on our understanding of pine barrens vegetation dynamics. In 1938, following a period of frequent, intense wildfires of the region, 90% of vegetation in the study area was open canopy barrens (including dwarf pine plains, pitch pine–scrub oak woodland, heath, pine–heath woodland, and scrub oak shrubland). Between 1938 and 1994, wildfires decreased in size, the average area burned per year generally declined, and there were no fires in 70% of the study area. As a result, barrens decreased to ∼45% of study area vegetation. In August 1995, an unusually severe summer wildfire converted 810 ha of woodland and forest into scrub oak shrubland, and increased barrens to 60% of study area vegetation. Most areas of heath and pine–heath, which comprised 24% of barrens vegetation in 1996, are successional types that developed on formerly cleared land. In the absence of extensive burning, we expect barrens vegetation to be converted to closed-canopy forest as coppice trees and new seedlings mature. Recent changes in fire regimes are likely to result in a loss of barrens vegetation that exceeds predictions of the simulation model. Careful use of prescribed fire and/or mechanical treatments to simulate the effects of fire are recommended for future restoration and maintenance of pitch pine barrens, and for protection of human life and property.

Climate Change Effects on Vegetation Distribution and Carbon Budget in the United States

The Kyoto protocol has focused the attention of the public and policymarkers on the earth’s carbon (C) budget. Previous estimates of the impacts of vegetation change have been limited to equilibrium “snapshots” that could not capture nonlinear or threshold effects along the trajectory of change. New models have been designed to complement equilibrium models and simulate vegetation succession through time while estimating variability in the C budget and responses to episodic events such as drought and fire. In addition, a plethora of future climate scenarios has been used to produce a bewildering variety of simulated ecological responses. Our objectives were to use an equilibrium model (Mapped Atmosphere‐Plant‐ Soil system, or MAPSS) and a dynamic model (MC1) to (a) simulate changes in potential equilibrium vegetation distribution under historical conditions and across a wide gradient of future temperature changes to look for consistencies and trends among the many future scenarios, (b) simulate time-dependent changes in vegetation distribution and its associated C pools to illustrate the possible trajectories of vegetation change near the high and low ends of the temperature gradient, and (c) analyze the extent of the US area supporting a negative C balance. Both models agree that a moderate increase in temperature produces an increase in vegetation density and carbon sequestration across most of the US with small changes in vegetation types. Large increases in temperature cause losses of C with large shifts in vegetation types. In the western states, particularly southern California, precipitation and thus vegetation density increase and forests expand under all but the hottest scenarios. In the eastern US, particularly the Southeast, forests expand under the more moderate scenarios but decline under more severe climate scenarios, with catastrophic fires potentially causing rapid vegetation conversions from forest to savanna. Both models show that there is a potential for either positive or negative feedbacks to the atmosphere depending on the level of warming in the climate change scenarios.

Moorland vegetation succession after the control of bracken with asulam

A range of moorland sites in the North York Moors, North Yorkshire, UK, where bracken control with the herbicide asulam has been carried out, has been re-surveyed. The trajectory of vegetation change at each site has been analysed using a range of techniques. Vegetation change after spraying appears to depend on three things—the species present at the time of control, the initial effectiveness of treatment and the amount of subsequent disturbance (mainly by sheep). Where grazing pressure was low, there was little invasion or spread of plants, except on sites with an initial moderate cover of Vaccinium myrtillus. Where high sheep activity disturbed the litter layer, invasion by the moss Campylopus introflexus characteristically occurred, followed by an increase in dominance by grasses, especially Deschampsia flexuosa. Where grazing pressure was high enough, it appeared that bracken regeneration was slowed, otherwise the bracken canopy and the stand recovered. However, in the timescale of the study, sufficient variety and cover of other species remained after the canopy regenerated to prevent the complete progression to vegetation characteristic of untreated areas.