Vegetation‐type conversion of evergreen chaparral shrublands to exotic annual herb dominated savannahs: Causes and consequences for ecosystem function

Climate driven increases in fire frequency and severity are predicted for Mediterranean climatic zones, including the Pacific coast of California. A recent high severity wildfire that burned in the Santa Cruz Mountains affected a variety of vegetation types, including ancient coast redwood (Sequoia sempervirens (D. Don) Endl.) stands. The purpose of this study was to characterize the survival and initial recovery of vegetation approximately six months after the fire. We sampled thirty randomly selected points in an old-growth coast redwood forest to examine and compare survival, crown retention, and post fire regeneration of trees by species, and the recovery of associated understory plant species. Sequoia sempervirens exhibited the highest post-fire survival (95%), with lower survival rates for subcanopy hardwood associates including tanoak (Notholithocarpus densiflorus (Hook. & Arn.) Manos) (88%), coast live oak (Quercus agrifolia Nee.) (93%), Pacific wax myrtle (Myrica californica (Cham. & Schltdl.) Wilbur) (75%), Pacific madrone (Arbutus menziesii Pursh) (71%), and the lowest survival recorded for the canopy codominant Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) (15%). Canopy retention and post fire regeneration were also highest for S. sempervirens and lowest for P. menziesii, indicating that S. sempervirens had a competitive advantage over P. menziesii following high severity crown fire. Both canopy survival and regeneration were greater for larger height and diameter trees; and basal sprouting was positively associated with tree height and diameter for S. sempervirens and N. densiflorus. Observed recovery of understory species was modest but included the reemergence of coast redwood associated herbaceous species. The robust nature of survival and recovery of S. sempervirens following this extreme fire event suggest that the removal of scorched, and the seeding or planting of trees, following this type of fire is contraindicated. The decline of P. menziesii is of concern, however, and suggests that repeated high severity fires driven by climate change could eventually lead to vegetation type conversion.

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Recent Megafires Provide a Tipping Point for Desertification of Conifer Ecosystems

10.5772/intechopen.101595 ◽

2022 ◽

Author(s):

Daniel G. Neary

Keyword(s):

Forest Ecosystems ◽

Vegetation Type ◽

Fire Suppression ◽

Coniferous Forest ◽

Thunderstorm Activity ◽

Conifer Forests ◽

Conifer Forest ◽

Type Conversion ◽

Population Demographics ◽

Severe Erosion

Recent megafires and gigafires are contributing to the desertification of conifer forest ecosystems due to their size and severity. Megafires have been increasing in their frequency in the past two decades of the 21st century. They are classed as such because of being 40,469 to 404,694 ha in size, having high complexity, resisting suppression, and producing desertification due to erosion and vegetation type conversion. Increasingly, gigafires (>404,694 ha) are impacting coniferous forest ecosystems. These were once thought of as only pre-20th century phenomena when fire suppression was in its infancy. Climate change is an insidious inciting factor in large wildfire occurrences. Fire seasons are longer, drier, hotter, and windier due to changes in basic meteorology. Conifer forests have accumulated high fuel loads in the 20th and 21st centuries. Ignition sources in conifer forests have increased as well due to human activities, economic development, and population demographics. Natural ignitions from lightning are increasing as a result of greater severe thunderstorm activity. Drought has predisposed these forests to easy fire ignition and spread. Wildfires are more likely to produce vegetation shifts from conifers to scrublands or grasslands, especially when wildfires occur with higher frequency and severity. Severe erosion after megafires has the collateral damage of reducing conifer resilience and sustainability.

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Interactions of arbuscular mycorrhizal fungi, critical loads of nitrogen deposition, and shifts from native to invasive species in a southern California shrubland

Botany ◽

10.1139/cjb-2015-0266 ◽

2016 ◽

Vol 94 (6) ◽

pp. 425-433 ◽

Cited By ~ 17

Author(s):

Edith B. Allen ◽

Louise M. Egerton-Warburton ◽

Bridget E. Hilbig ◽

Justin M. Valliere

Keyword(s):

Invasive Species ◽

Mycorrhizal Fungi ◽

Vegetation Type ◽

Arbuscular Mycorrhizal ◽

Am Fungi ◽

N Deposition ◽

Coastal Sage Scrub ◽

Native Plant ◽

Invasive Grass ◽

Type Conversion

Anthropogenic nitrogen (N) deposition and invasive species are causing declines in global biodiversity, and both factors impact the diversity and functioning of arbuscular mycorrhizal (AM) fungi. Shifts in arbuscular mycorrhizal fungal (AMF) communities can generate feedback to native plants and affect their success, as was observed in California’s coastal sage scrub, which is a Mediterranean-type shrubland threatened by invasive grasses. As vegetation-type conversion from native shrubland to exotic annual grassland increased along a gradient of increasing N deposition, the richness of native plant species and of spore morphotypes decreased. Rapid declines in all plant and fungal values occurred at the critical load (CL) of 10–11 kg N·ha−1·year−1, indicating that AM fungi respond to the same environmental signals as the plants, and can be used to assess CL. Shrub root colonization also decreased along the N gradient, but colonization of the invasive grass was dominated by a fine AMF endophyte that was unresponsive to elevated N. A greenhouse experiment to assess AMF functioning showed that the native shrub Artemisia californica Less. had a negative growth response to an inoculum from high-N but not low-N soils, whereas the invasive grass Bromus rubens L. had a positive response to both inocula. Differential functioning of AM fungi under N deposition may in part explain vegetation-type conversion and the decline of this native shrubland.

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Forest and woodland replacement patterns following drought-related mortality

Proceedings of the National Academy of Sciences ◽

10.1073/pnas.2002314117 ◽

2020 ◽

Vol 117 (47) ◽

pp. 29720-29729

Author(s):

Enric Batllori ◽

Francisco Lloret ◽

Tuomas Aakala ◽

William R. L. Anderegg ◽

Ermias Aynekulu ◽

...

Keyword(s):

Tree Mortality ◽

Community Dynamics ◽

Plant Traits ◽

Vegetation Type ◽

Species Turnover ◽

Type Conversion ◽

Environmental Preferences ◽

Biological Legacies ◽

Distribution Ranges ◽

Species Specific

Forest vulnerability to drought is expected to increase under anthropogenic climate change, and drought-induced mortality and community dynamics following drought have major ecological and societal impacts. Here, we show that tree mortality concomitant with drought has led to short-term (mean 5 y, range 1 to 23 y after mortality) vegetation-type conversion in multiple biomes across the world (131 sites). Self-replacement of the dominant tree species was only prevalent in 21% of the examined cases and forests and woodlands shifted to nonwoody vegetation in 10% of them. The ultimate temporal persistence of such changes remains unknown but, given the key role of biological legacies in long-term ecological succession, this emerging picture of postdrought ecological trajectories highlights the potential for major ecosystem reorganization in the coming decades. Community changes were less pronounced under wetter postmortality conditions. Replacement was also influenced by management intensity, and postdrought shrub dominance was higher when pathogens acted as codrivers of tree mortality. Early change in community composition indicates that forests dominated by mesic species generally shifted toward more xeric communities, with replacing tree and shrub species exhibiting drier bioclimatic optima and distribution ranges. However, shifts toward more mesic communities also occurred and multiple pathways of forest replacement were observed for some species. Drought characteristics, species-specific environmental preferences, plant traits, and ecosystem legacies govern postdrought species turnover and subsequent ecological trajectories, with potential far-reaching implications for forest biodiversity and ecosystem services.

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Vegetation Change Detection Based on TM and SPOT Images Spectrum Fusion in the Typical Area of Xishuangbanna Area

Advanced Materials Research ◽

10.4028/www.scientific.net/amr.347-353.2393 ◽

2011 ◽

Vol 347-353 ◽

pp. 2393-2399

Author(s):

Ya Fei Li ◽

Gao Huan Liu

Keyword(s):

Tropical Forest ◽

Vegetation Change ◽

Vegetation Type ◽

Research Area ◽

Vegetation Changes ◽

Type Conversion ◽

Rubber Plantations ◽

Comprehensive Information ◽

Data Pretreatment ◽

The One

There are many tropical forest resources in Xishuangbanna area; it is a very important status in China. But because a large number of rubber plantations are expanding as far as possible and the areas of urban construction land are increasing, the areas of tropical forest are decreasing rapidly, which lead to serious fragmentation. In the paper, we choose the typical area of Xishuangbanna area as the research area to study the vegetation change trajectory using ETM and SPOT images acquired on different time. On the base of data pretreatment, two aspects researches were carried out. On the one hand, spectral information and NDVI information of each type of vegetation were analyzed to classify the ETM and SPOT images using the method of decision tree respectively. By classification post-processing, we could get the ways of the vegetation type conversion. On the other hand, ETM and SPOT PAN Images were integrated by the PCA to acquire the information of vegetation change including vegetation gain or loss. Finally, comprehensive information on two aspects of the vegetation changes was analyzed to acquire the vegetation change trajectory from 2000 to 2007 in the Xishuangbannan area. The result showed vegetation conversions that changed from one type to another type were frequent. A larger proportion of other type vegetation was transformed to rubber plantations.

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