Monitoring succession from space: A case study from the North Carolina Piedmont

Question: Is the successional transition from pine to hardwood, which has been inferred from chronosequence plots in previous studies, validated through a time line of satellite imagery? Location: Durham, North Carolina, USA. Methods: We examined successional trends in a time‐series of winter‐summer pairs of Thematic Mapper imagery from 1986 to 2000. We calculated the normalized difference of vegetation index (NDVI) for winter and summer, as well as the difference between summer and winter NDVI (i.e., summer increment NDVI). A set of approximately 50 forest stands of known age and phenology were used to interpret patterns in winter and summer increment NDVI over successional time, and a continuum was found to exist between pine‐dominance and hardwood‐dominance. We fitted a series of linear regressions that modeled the change in winter and summer increment NDVI as a function of initial winter and summer increment NDVI, and additional explanatory variables. Results: All regressions were highly significant (P < 0.0001, R²= ca. 0.3). Predicted dynamics are in accord with successional theory, with pixels moving from evergreen dominance to deciduous dominance along a line of fairly constant summer NDVI. A large disturbance event that occurred over the course of this study, Hurricane Fran, appeared to slow rates of succession in the short term (1–3 years), but increase the rate of conversion to hardwoods over longer time spans. Conclusions: We conclude that temporal sequences of remote sensing images provide an excellent opportunity for broad‐scale monitoring of successional processes, and that continuous metrics of that change are essential to accurate monitoring.     

Biomass and quality changes of forages along land use and soil type gradients in the riparian zone of Lake Naivasha,Kenya

The recession of the water level of Lake Naivasha has incrementally exposed land surfaces creating a chronosequential transect representing durations of 1–30 years of exposure to grazing. This chronosequence provides a unique model to study the effects of land use duration on resource availability and resource base quality. Particularly, pasture quality changes in the riparian land of tropical fresh water lakes have so far not been studied. We assessed the effect of the duration of exposure to grazing on the biomass production, crude protein content and energy quality of pastures in a 4 × 4 latin square design (4 chronosequence positions × 4 soil types). Species composition was recorded and biomass was sampled at monthly intervals from February to August 2011. Soil moisture was recorded using frequency domain reflectometry sensors. Vegetation samples were analyzed for dry matter, nitrogen and metabolizable energy. Increased land use duration favored a shift in species dominance from Pennisetum clandestinum to Cynodon plectostachyus, which was associated with a reduction in dry matter yield and increased plant nitrogen content. All measured variables tended to be higher in soils formed on alluvial than in those formed on lacustrine deposits. Increased soil N and gravimetric moisture content stimulated biomass accumulation. The crude protein yield and metabolizable energy changed with phenological stages of the pasture and declined significantly towards maturity (seed setting of grasses). Continuous grazing and reduced soil moisture content, both during low rainfall and increased distance from the lake shore, affected the composition of pasture grasses as well as forage yield and quality. This may thus differentially affect the suitability of the riparian land as pasture ground and feed resource area for grazing animals.     

Plant growth and ectomycorrhiza formation by transplants on deglaciated land near Exit Glacier, Alaska

 Ectomycorrhiza (EM) formation on plant roots in successional communities may vary with plant species, plant age, and age of vegetation after disturbance. To evaluate differences in mycorrhizal fungus communities on roots of same-aged seedlings across a deglaciated chronosequence, indoor-grown bioassay plants of four dominant species Epilobium latifolium L. (dwarf fireweed), Populus balsamifera ssp. trichocarpa (Torr.&Gray) Hult. (black cottonwood), Alnus sinuata (Regel) Rydb. (Sitka alder), and Picea sitchensis (Bong.) Carr. (Sitka spruce) were transplanted into five successional stages (Barren, Isolated Plant, Patchy, Alder, and Cottonwood) following deglaciation near Exit Glacier, Alaska. The species were selected for their successional status and mycorrhiza formation potential [EM or arbuscular mycorrhiza (AM) or both]. Seedlings were transplanted in June 1992, and half were harvested at the ends of the two subsequent growing seasons. The EM communities on P. balsamifera differed across the chronosequence while those of the other species did not. Morphotype B dominated the EM on P. balsamifera after the Barren stage, and the greatest EM colonization was in the Isolated Plant and Patchy stages. No AM were found. The EM observed on even-aged seedlings in this study were a subset of the EM found on naturally occurring plants (seedlings to mature trees) in a prior study, and some were common to multiple plant species. Most plant growth responses were not significant across stages or were inconsistent among plant species. Accepted: 25 December 1998     

Ants accelerate succession from mountain grassland towards spruce forest

Question: What is the role of mound‐building ants (Lasius flavus) in successional changes of a grassland ecosystem towards a spruce forest? Location: Slovenské Rudohorie Mountains, Slovakia; ca. 950 m a.s.l. near the Obrubovanec point (1020 m a.s.l.; 48°41′N, 19°39′E). Methods: Both chronosequence data along a successional gradient and temporal data from long‐term permanent plots were collected on ants, spruce establishment, and vegetation structure, together with additional data on spruce growth. Results: There are more spruce seedlings on ant mounds (4.72 m^?2) than in the surrounding vegetation (0.81 m^?2). Spruce seedlings grow faster on these mounds compared to surrounding areas. The first colonization wave of seedlings was rapid and probably occurred when grazing prevailed over mowing. Ant colony presence, mound volume, and plant species composition change along the successional gradient. Mounds become bigger when partly shaded but shrink in closed forest, when ant colonies disappear. Shade‐tolerant acidophylic species replace grassland plants both on the mounds and in surrounding areas. Conclusions: The massive occurrence of Lasius flavus anthills contributes to a runaway feedback process that accelerates succession towards forest. The effect of ants as ecosystem engineers is scale‐dependent: although they stabilize the system at the scale of an individual mound, they may destabilize the whole grassland system over a longer time scale if combined with changes in mowing regime.     

How do soil fauna and soil microbiota respond to beech forest growth?

The dynamics and performance of soil biota during forest rotation were studied in monoculture beech stands forming a chronosequence of four different age-classes(30,62,111,153 yr).Biomass was monitored in major groups of microflora,microfauna,mesofauna,and macrofauna.Resource availability(litter layer,soil organic mater),biomass of the two dominant decomposer groups(microflora,earthworms)as well as the biomass of mesofauna and microfauna were found to remain quite stable during forest succession.Nevertheles...     

Post-cultivation Secondary Succession in a Venezuelan Lower Montane Rain Forest

Since tropical rain forests are widely threatened by conversion to agriculture, even within protected areas, an understanding of recovery processes is important for restoration of forest ecosystems and thus conservation of their biodiversity. Secondary succession following land clearance and crop cultivation was studied in a lower montane rain forest in a protected area of the Venezuelan Cordillera de la Costa Central. Forest recovery was studied using a chronosequence of eight 20 × 20 m plots which represented four forest types ca.10 year-old Secondary Forest, ca. 20 year-old Secondary Forest, ca. 35 year-old (uncultivated) secondary forest and mature forest. Species richness and structural complexity increased during succession, with the oldest secondary forest having a physiognomy comparable to the mature forest. Species diversity was lower in the secondary forests than the mature forest, and their floristic composition was distinct. Four phases are hypothesized to occur in the succession process, each with a distinctive species assemblage: initial colonisation by non-woody vegetation; establishment and canopy closure by short-lived small-seeded woody pioneer species; replacement by longer-lived secondary species; and gradual replacement by mature forest large-seeded climax species. Full recovery of the forests in the protected area is likely to take many years, although it may be assisted through conservation management measures.