Figure 5 - uploaded by Sanjeev Joshi
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Scatter plot showing the relationship between water-elm tree ages and their corresponding diameter at breast heights (dbhs). “R” represents the correlation coefficient between the two variables (age and dbh) which was found to be statistically significant at α = 0.05.
Source publication
Hydrologic alterations frequently lead to vegetation changes in floodplain ecosystems. In
Louisiana, there has been an expansion of water-elm (Planera aquatica) and to a lesser extent
baldcypress (Taxodium distichum) at Catahoula Lake, a Ramsar Wetland of International
Importance. Water-elm and baldcypress both are flood tolerant species; baldcypre...
Contexts in source publication
Context 1
... tree ages showed a significant positive relationship with their corresponding dbhs (R = 0.72 at α = 0.05) which indicated that increase in age of a tree was followed by increase in its dbh ( Figure 5). Generally, pre-control trees had greater dbh than post-control trees; ...
Context 2
... there were some trees which were established during the pre-control period that had a lower dbh than most post-control trees ( Figure 5). Also, there were some old trees (≥ 60 years) that had a relatively small dbh (≤ 10 cm) (Figure5). ...
Citations
... The objective of this research is to quantify the amount, rate, and location of woody expansion into the lake and better understand patterns of expansion. To do this, we used aerial imagery in combination with tree ages obtained from tree rings by Joshi (2012). In 1940 there was a total of 35.5 km 2 of woody vegetation in the water-elm zone, which was 29.1% of the lake bed ( There was no obvious spatial distribution of the three patterns of encroachment ( Figure 2.8). ...
... Historic practices evident in aerial imagery are A.) scars consistent with extensive removal of vegetation by heavy equipment and B.) clearings created around hunting blinds by waterfowl hunters (USDA aerial imagery from 2007) re-colonized. In many places around the lake, management by waterfowl hunters is evident in small clearings that surround hunting blinds (See B in Figure 2.4).UsingJoshi's (2012) tree ring data to confirm the aerial imagery and woody expansion delineations, we observed three patterns of expansion. In the first pattern, younger trees are at the encroaching margin and older trees behind(Figure 2.5). ...
... noted that after the Louisiana Wildlife and Fisheries commission removed about 12 km 2 of water-elm and swamp-privet during 1954-1957, the species was very slow to re-invade. This launched an aggressive campaign to remove the woody vegetation that continued through the late 1970s.Joshi (2012) discovered about 73% of the water-elm sampled were established after the canal was built in 1972. However the oldest trees were 131 years old, pre-dating any hydrologic changes to the lake. Today managers use mowing, ...
The processes that control species composition and structure in wetland ecosystems are complex and controlled by many factors including seasonality, depth and duration of flooding, and nutrient dynamics. Catahoula Lake is a floodplain lake that has existed with seasonally fluctuating water levels for at least 4,000 years. The herbaceous vegetation that attracts these waterfowl is slowly being outcompeted by woody vegetation, most notably water-elm (Planera aquatica). Our general goal is to understand the processes that cause this shift, focusing on the role of sediments. Our first objective was to use historical aerial imagery to detect historical changes in plant communities at Catahoula Lake, focusing on timing and rates of expansion of woody vegetation. Aerial imagery indicated woody vegetation has been encroaching into the lake bed and the rate of this expansion has increased 249% since major hydrologic alterations in the 1960s. There are three local patterns to this expansion: continuous expansion of woody vegetation, long-term stability of the tree line, and complex patterns of tree establishment. Second, we used 137Cs in lakebed sediments to calculate rates of sedimentation. Results indicated sedimentation was 0.26 cm yr-1, which is increased 225% from the pre-settlement rate of 0.08 cm yr-1. Peaks of 137Cs were muted and deposition rates were similar around the lake, suggesting redistribution of sediments is common. Third, we investigated elemental concentrations in sediment which revealed little spatial variation in recent sediment, but a shift from mixed coastal-plain and Mississippi Alluvial Valley sediments to dominance by acidic, coastal-plain sediments in the past ~60 yr. Sediments are low in organic matter, and carbon and nitrogen concentrations decrease with depth and are being sequestered at low rates (840 t yr-1 and 120 t yr-1, respectively). Compared to its condition prior to hydrologic alterations beginning in the 1920s, Catahoula Lake is about 15 cm shallower and the chemical composition of sediments is more acidic. Although these results are not sufficient to link these differences directly to ecological changes, it is likely the altered sedimentary and hydrologic environment is contributing to the increased dominance of woody vegetation.
