Paper 40: Effects of Forest Cutting and Herbicide Treatment on Nutrient Budgets in the Hubbard Brook Watershed-Ecosystem
Gene E. Likens et al. 1969
Introduction:
The Hubbard Brook Forest is a great example of a long-term study through the Forest Service since 1955. This large-scale manipulation of an ecosystem aims to quantify
biogeochemical and implications from changes in habitat or vegetation on an
ecosystem level. Forest Service removed all vegetation from Watershed 2 in the
Hubbard Brook Experimental Forest and sprayed herbicide to inhibit regrowth.
Methods:
Precipitation and stream
flow was measured using precipitation gauges and stream-guaging stations
(V-notch weir and San Dimas flume). Weekly samples were collected plastic
containers for chemical analysis. In November and December 1965, all vegetation
was cut and left in place then the area was treated with Bromacil herbicide.
Hydorlogic Parameters:
Precipitation and stream
flow were measured. Annual runoff showed a dramatic increase following the
clear cut.
Precipitation Chemistry:
Most of the chemical input
came from precipitation. Sulfate and hydrogen were abundant in rainfall and
show, and pH was often less than 4.0. Soil and road dust are attributed for the
metal ions. Nitrate increased every year of the study, and this is presumably
because of air pollution.
Chemical Input Through Herbicide Application
Bromacil solution was
sprayed on the watershed in 1966. There was 3,650 liters and Bromacil, and then
87 liters of ester was sprayed on the watershed in 1967. It is approximated
that 0.7 kg Cl-/ha of chemical herbicide would be added into the water-shed.
Stream Parameters
Stream temperatures are relatively constant with an annual temperature of
16 degrees C. W2 stream temperatures increased post cut in the summer and
winter. A thinker snow depth was noticed in the deforested area. Streams had
discrete seasonal regimes (Figure 2). Dissolved
oxygen was normal to slight above normal. Above normal dissolved oxygen is
called supersaturation, and it is
unknown why this occurred. Following treatment, W2 resulted in greater
discharge, more turbulence, and a constant high level of dissolved oxygen. Increased
turbidity is a direct result of
erosion of the watershed, and a 4-fold increase in particulate matter that was increasingly inorganic. Hydrogen ion
content increase 5-fold during the study, which is a significant decrease from
5.1 to 4.3 pH. Conductivity was
variable in the stream water after treatment.
Ions
Undisturbed watersheds have
low concentrations of ammonium ions
with a season pattern and showed a reciprocal pattern in the treatment of W2.
There is inconclusive evidence for nitrification.
Sulfate concentration processes are
complicated and decreased by 45% in the deforested W2. Chloride concentrations had a delayed increased in stream water by
65%. Calcium, magnesium, potassium and
sodium are typically constant in undisturbed streams but were very high
after treatment. Aluminum solubility
was also increased as a result of a decrease in pH (10-fold increase in
aluminum). Silica increased by 37%,
probably as a result of wreathing of geologic substrate. Bicarbonate nearly dropped to zero after treatment.
Effect of Nitrification on Cation Loss
According to the data, nitrification
is a major controlling factor in the quantity and quality of dissolved
materials in the clear cut watershed, more so than an undisturbed watershed.
Nutrient Budgets
Net nutrient loss in the
ecosystem was significantly increased after deforestation and herbicide
treatment, and increased stream water concentrations were likely responsible.
General Discussion
Nutrient cycling is
responsible for the retention of nutrients within an ecosystem. Disturbed
systems can no longer can maintain the nutrient cycle, which results in a loss
of nutrients.
Questions:
Do you agree that turbidity
has “little value” in the assessment of water quality? (p. 887)
How could this experiment be
improved with modern technology?
Does this paper portray a
realistic or idealized scenario?
How have forestry practices
changed since this study? Have we learned from our mistakes?
Last question:
http://www.hubbardbrook.org/data/dataset_search.php
What do you think of the Hubbard Brook dataset?
Last question:
http://www.hubbardbrook.org/data/dataset_search.php
What do you think of the Hubbard Brook dataset?
Again, another classic example glossed over in Ecology 101. I was initially confused by the pitch the authors make: they advertise the 6 small watersheds of Hubbard Brook as ideal for designing a well replicated large scale manipulation experiment…then they only use one of the six to do the actual treatment and apparently use the other 5 as controls. I feel like they could have had at least one other treatment, but this is a heavily destructive and likely expensive treatment, so I can understand why they might have opted for only one treatment. I like their design, but I’d like more rationale on why they used the herbicide treatment. It seems like there is really no natural or artificial homologue, other than herbicide treatment. Even with all the insanely destructive things people do to natural systems, I have never heard on widespread herbicide use outside of agriculture. They note that the herbicide did skew chloride measurements in the first few years as well. Overall they found some really cool stuff, namely that clear cutting and accompanying herbicide treatment cause a huge amount of nutrients to be lost from the system via large disruptions to the biological side of the nutrient cycle. I like how this shows the effects of clear cutting, but I just feel that this might be a good candidate for a big-science-little-results award. The authors mention tons of similar experiments that don’t use herbicide and do less nutrient analysis. Why couldn’t they just piggyback on these treatments rather than destroying another system in the name of science? Moreover I can’t see many examples of the continuous biological suppression they impose in the real world, so while it’s nice to see, I’m not seeing the applications side of this that was so revolutionary.
ReplyDeleteI agree with you Eric. It seems like there are few if any natural systems or even altered systems where regrowth is prevented. I have never heard of a clear cut being treated with herbicide, but perhaps they were trying to prolong the increase of water input to see if the chemistry stabilized or returned to normal? The one exception of regrowth being continually removed is overgrazing.
DeleteThis was an amazing study. The first to comprehensively measure the homeostatic ability of a watershed ecosystem to retain nutrients by experimentally manipulating the vegetation component in the field on an ecosystem level. It was great to see how all the biogeochemical compounds were accounted for and how the implications of each were explained in context. The big take away here that everything is connected so “unless these ecological interrelationships are understood, naïve management practices can produce unexpected and possibly widespread deleterious results.” I especially love science that can be applied to management and that provides useful knowledge. This was a great synthesis of how management practices can greatly affect ecosystem functioning in both direct and indirect ways.
ReplyDeleteI agree Martina, this study ties in nicely with our projects in the Jemez Mountains.
DeleteI wish we had read this paper prior to Odum's paper. Although this study is mentioned by Odum, I believe the details of it are further appreciated when it has actually been read. Odum mentioned the importance of these studies as they look at how the overuse of resources through deforestation can impact the immediate environment. Furthermore, he also stressed how these experiments would be able to look at broader impacts of the reduction of vegetation may have downstream. In this, he was highlighting the importance of looking at the global rather than local impacts of "getting 'too much of a good thing'" (Odum 1969:267[601]).
ReplyDeleteThanks Melyssa, I had forgotten Odum had mentioned this study!
DeleteI think this paper show an amazing evolution from very first paper in the book by simply showing how connected the terrestrial and aquatic ecosystems are. As we recall the very first paper by Forbes, spoke of the aquatic and terrestrial biomes being so disconnected that, to paraphrase; it would take a long time for the aquatic environment to feel any effect at all if all terrestrial life was destroyed. We can clearly see this is not the case. I truly enjoy looking at that aspect as these foundational papers come full circle.
ReplyDeleteYes, another study I remember from my undergrad. I too was questioning the single treatment as mentioned above. However, doing this to more than a single site would be very destructive, I agree.
Good connection Matt! Its nice to see a treatment in a forest ecosystem. then monitor how it affects the watershed. I think this was an important realization for 1969. We will discuss this in further detail in class! Something major happened in 1972... Can anyone guess what that was?
DeleteIt is awesome to see as we have gone through that the interconnectedness of different ecosystems have come more into the consciousness of the authors of the papers. This paper showcases how connected they are very well just like everyone else has stated. Another thing that I really liked was the amount of data that they collected. This paper was getting closer to being able to use and interpret large amounts of data so it was cool to see how much analysis they were doing and how many data points they had.
DeleteI agree with Eric that it is unfortunate that a forest area had to be destroyed for this study, and also question the necessity of using herbicides; however, maybe the sacrifice was for the greater good. Runnels (1995) mentions that "deforestation and catastrophic soil erosion" has been going on in Greece for over 8,000 years. I was surprised that the annual runoff increased so much after deforestation, and that most of the ions increased so much. A useful result of the study was a documentation of the effect of pollution.
ReplyDeleteGood point Julie. At first, I cringed thinking about clear cutting, but we have to put this in perspective of the time period. Clear cutting was common practice on forest lands, usually with a little more discretion (i.e. leaving intact trees -unfortunately deformed or irregular trees unsuitable for logging- or planting new trees to promote recruitment), but there are examples within our own state where clear cutting still has a major impact on our ecosystems. For example, the Valles Caldera was clear cut because the land rights were split from the timber rights. Nearly all of the Valles Caldera National Preserve is second growth forest, which has a major impact on management practices to this day.
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ReplyDeleteReally neat study that I'm glad to have finally read. Though short on biology, there are profound implications for ecosystem functioning and the importance of vegetation in the regulation of nutrient cycling. While it was destructive, and probably not a perfect analogue for normal management practices or natural disturbances, I'd argue that the knowledge gained has made it well worth it. Following most clearcutting or disturbances, vegetation of some sort will generally quickly return (not necessarily the same type though), unless something like extreme erosion occurs (e.g. landslide, mining w/o remediation). The herbicide treatment was high magnitude, going beyond anything that had been done before, and highlights the important of the returning vegetation, which prior to this study I don't believe had been demonstrated or quantified. I don't know that this had profound impact on forestry practices, but does emphasize the importance of revegetation and a worst-case-scenario result of clearcutting.
ReplyDeleteA lot of other cool concepts and applications were addressed or touched on here including the effects of microbes on nutrient cycling, observations relating to acid and nitrate deposition, nutrient budgets and cycling regulation, and water quality issues. In some ways the systems is idealized in terms of the impermeable bedrock making it closed. A modern study might replicate this across different substrates or ecosystem types, and measure nutrients pools and fluxes, like ground water leaching and mineral weathering, in a more detailed and accurate way (stable isotopes might be interesting here). It'd be interesting to see the results over a longer period of time, as well as the effects of other treatments done on the other watersheds. That's fantastic that they have all the datasets available on the web, with excellent metadata too. Ecology seems to be moving increasingly towards an open data, and even open code, paradigm; a good thing in my book.
This study reminds of some work that was going on in my former lab where folks were looking at the effects of whole tree removal from forests on N cycling and future productivity. Most logging involves removing just the bole of a tree where the valuable wood is, while leaving the limbs and fine woody material where nutrients tend to be concentrated on site. But if trees are to be used to produce woody bioenergy then whole tree harvesting may make economic sense, though not necessarily ecological sense, particularly on sandy soils with high nutrient leaching. Cool stuff.
This was a great study that looks at something (deforestation) becoming ever more present in our world. Clearly, the evidence exists that clear-cutting and herbicides don't complement an ecosystem, and this study went about showing that in an extreme way. I agree with what's been said above that it doesn't seem necessary to have applied herbicide after already clear-cutting the area, but I can see the scientific appeal to the authors of seeing what happens with absolutely no vegetation over time. As Julie mentioned, I was also surprised at how much the ions increased in the runoff. I wonder if this study had effects on any human communities downstream, and if so, how they compare to the water quality we experience in rivers today. This is such a perpetually applicable article - I've recently read so much regarding areas that have been clear cut or burnt past a beneficial point and the effects they have on not just the immediate area, but the "trickle-down" effects on the ecosystem.
ReplyDeleteAlthough not completely the same situation, the visual effects of deforestation are powerful. Here is a short, yet intriguing, pop media article on burning in the Amazon: http://www.npr.org/2015/11/05/453239276/in-the-amazons-fire-season-you-either-burn-or-you-starve
In answer to Sami's last question, wow! From entries in 1956 up through 2012, and all conveniently accessible on the Hubbard Brook Ecosystem Study website. Truly a collaborative venture.
ReplyDeleteThe bush cutting has to be done with a proper technique like cutting out wayward branches, take out thin growth, remove stems growing up from the roots, and water sprouts (upright shoots growing from the trunk and branches). Trees of the forest can stay healthy if the diseased branches are removed, dead, pest-ridden, or rubbing together. The best professional service provider in Estonia is MetsaABC that provides all kinds of services related to forests.
ReplyDelete