How to determine carrying capacity of land?
07-07-2007, 09:18 PM
#2
Nontypical Buck
Join Date: Feb 2007
Location: Denton, Texas
Posts: 1,335
RE: How to determine carrying capacity of land?
CARRYING CAPACITY OF DEER HABITAT
For the purposes of this discussion, carrying capacity (CC) is defined as the number of animals a given unit of habitat can sustain in good physical condition without causing damage to the habitat. The term CC, as used in this section, should not be confused with the terms absolute CC or CC K. These later definitions of CC are used by population biologists to describe the maximum number of animals a unit of habitat can support (the theoretical point in a population growth model in which births equal deaths and the population stops growing).
Determining CC for deer habitat can be useful when attempting to formulate management strategies. Developing a CC estimate gives the deer manager a ceiling with respect to the maximum population
size that should be carried on a given unit of habitat. As with population estimates, the exact number of animals in a CC estimate is not precise. For example, if an estimated population of 500 animals
occupy a given unit of habitat and these animals are in excellent condition, then it may be assumed the given unit of habitat has a CC of at least 500 animals.
Deer managers often assume the maximum CC can be determined by noting the number of the total estimated population at the point when physical indices begin to deteriorate. At this point, deer
managers may infer the herd is at or slightly above the CC. The danger of this assumption is often a deer herd can exist at and periodically exceed CC for several years before physical indices show signs of severe
overpopulation. The actual CC may, in fact, be substantially lower than the point at which a decline in physical condition is first observed.
When a deer herd has been allowed to exceed CC for any period of time, habitat quality is adversely affected. The most nutritious forage species in the habitat are the first to be depleted. A deer herd can eliminate some of these species from the habitat entirely. If no seed source or rootstock is left, some of these species may never be re-established naturally. The long-term effects of such overpopulation on habitat quality, deer quality, and CC are severe. The CC may actually be reduced to a point much lower than it had originally been. Once the quality of habitat has been significantly reduced and measures are then taken to reduce the population to within the CC, the total number of animals that can be supported in good condition may be much lower than before overpopulation occurred.
Natural mortality remains too low in many of these cases to return these herds to CC. As these populations are allowed to exceed CC, habitat quality is further diminished and actual CC is lowered. Deer managers in many areas are faced with this dilemma, particularly on sites with poor to marginal habitats. Deer populations have not been kept at levels low enough to allow for habitat quality to recover. This may be due to either pressures from user groups or the sheer inability to implement an adequate harvest.
In some cases, habitat quality may never recover regardless of how low population levels are reduced. Exceeding CC can lead to a repetitive The relationship between carrying capacity and deer density is relatively simple—when deer density exceeds carrying capacity (CC) for a significant
period of time, both CC and deer density often are reduced. Exceeding CC can lead to a repetitive cycle of poor deer herd and habitat conditions. This cycle is not easily interrupted and often cannot be stopped.
FACTORS INFLUENCING CARRYING CAPACITY
Carrying capacity fluctuates throughout the year depending on habitat conditions, rainfall, and various habitat changes, such as timber and farming operations. Supplemental feeding and planting
often are employed in an attempt to increase CC for a particular unit of deer habitat. These activities are seldom of sufficient scale to affect CC significantly. Such practices may only serve to compound problems
associated with gross overpopulation. In these instances, attempts to reduce herd density are more desirable than attempts to increase carrying capacity.
Actual biological CC for deer may not coincide with a social or ecologically based carrying capacity. An area where deer/human interactions are a primary concern may have a much lower CC based on
factors such as deer/vehicle collisions or deer damage to crops and ornamental plants. This may be referred to as social carrying capacity. A case involving endangered or fragile plant communities may have an
acceptable CC for deer much lower than is biologically practical. In many cases, social CC is greater than biological CC as people often desire to have more deer than the habitat can support.
Rainfall usually is the only climatic factor affecting CC in the Deep South. Habitat quality may be improved in the form of abundant mast crops and increased amounts of native browse in years with abundant rainfall. Physical indices may show corresponding improvements resulting from increased rainfall in herds maintained below CC. In 44cases where population levels are at CC, increases in habitat quality are generally negated because coinciding reproductive increases may add additional deer to the herd, further compounding the problem of too many deer.
For the purposes of this discussion, carrying capacity (CC) is defined as the number of animals a given unit of habitat can sustain in good physical condition without causing damage to the habitat. The term CC, as used in this section, should not be confused with the terms absolute CC or CC K. These later definitions of CC are used by population biologists to describe the maximum number of animals a unit of habitat can support (the theoretical point in a population growth model in which births equal deaths and the population stops growing).
Determining CC for deer habitat can be useful when attempting to formulate management strategies. Developing a CC estimate gives the deer manager a ceiling with respect to the maximum population
size that should be carried on a given unit of habitat. As with population estimates, the exact number of animals in a CC estimate is not precise. For example, if an estimated population of 500 animals
occupy a given unit of habitat and these animals are in excellent condition, then it may be assumed the given unit of habitat has a CC of at least 500 animals.
Deer managers often assume the maximum CC can be determined by noting the number of the total estimated population at the point when physical indices begin to deteriorate. At this point, deer
managers may infer the herd is at or slightly above the CC. The danger of this assumption is often a deer herd can exist at and periodically exceed CC for several years before physical indices show signs of severe
overpopulation. The actual CC may, in fact, be substantially lower than the point at which a decline in physical condition is first observed.
When a deer herd has been allowed to exceed CC for any period of time, habitat quality is adversely affected. The most nutritious forage species in the habitat are the first to be depleted. A deer herd can eliminate some of these species from the habitat entirely. If no seed source or rootstock is left, some of these species may never be re-established naturally. The long-term effects of such overpopulation on habitat quality, deer quality, and CC are severe. The CC may actually be reduced to a point much lower than it had originally been. Once the quality of habitat has been significantly reduced and measures are then taken to reduce the population to within the CC, the total number of animals that can be supported in good condition may be much lower than before overpopulation occurred.
Natural mortality remains too low in many of these cases to return these herds to CC. As these populations are allowed to exceed CC, habitat quality is further diminished and actual CC is lowered. Deer managers in many areas are faced with this dilemma, particularly on sites with poor to marginal habitats. Deer populations have not been kept at levels low enough to allow for habitat quality to recover. This may be due to either pressures from user groups or the sheer inability to implement an adequate harvest.
In some cases, habitat quality may never recover regardless of how low population levels are reduced. Exceeding CC can lead to a repetitive The relationship between carrying capacity and deer density is relatively simple—when deer density exceeds carrying capacity (CC) for a significant
period of time, both CC and deer density often are reduced. Exceeding CC can lead to a repetitive cycle of poor deer herd and habitat conditions. This cycle is not easily interrupted and often cannot be stopped.
FACTORS INFLUENCING CARRYING CAPACITY
Carrying capacity fluctuates throughout the year depending on habitat conditions, rainfall, and various habitat changes, such as timber and farming operations. Supplemental feeding and planting
often are employed in an attempt to increase CC for a particular unit of deer habitat. These activities are seldom of sufficient scale to affect CC significantly. Such practices may only serve to compound problems
associated with gross overpopulation. In these instances, attempts to reduce herd density are more desirable than attempts to increase carrying capacity.
Actual biological CC for deer may not coincide with a social or ecologically based carrying capacity. An area where deer/human interactions are a primary concern may have a much lower CC based on
factors such as deer/vehicle collisions or deer damage to crops and ornamental plants. This may be referred to as social carrying capacity. A case involving endangered or fragile plant communities may have an
acceptable CC for deer much lower than is biologically practical. In many cases, social CC is greater than biological CC as people often desire to have more deer than the habitat can support.
Rainfall usually is the only climatic factor affecting CC in the Deep South. Habitat quality may be improved in the form of abundant mast crops and increased amounts of native browse in years with abundant rainfall. Physical indices may show corresponding improvements resulting from increased rainfall in herds maintained below CC. In 44cases where population levels are at CC, increases in habitat quality are generally negated because coinciding reproductive increases may add additional deer to the herd, further compounding the problem of too many deer.
07-07-2007, 09:31 PM
#3
Nontypical Buck
Join Date: Feb 2007
Location: Denton, Texas
Posts: 1,335
RE: How to determine carrying capacity of land?
The harvest guide (Table 1) indicates how many antlerless deer you should remove in relation to the bucks you harvest depending on whether you want to increase, decrease, or stabilize your herd. As deer may not restrict their home range to your farm, you will need to take into account what your neighbors do and adjust your harvest accordingly unless you have an extremely large farm (2,000+ acres).
07-07-2007, 09:42 PM
#5
Nontypical Buck
Join Date: Feb 2007
Location: Denton, Texas
Posts: 1,335
RE: How to determine carrying capacity of land?
[align=left]When deer populations are above carrying capacity, the number of fawns born per doe is reduced. This is dictated by available nutrition and stress. When populations are kept below carrying capacity by including does in the harvest, available nutrition is increased and more fawns are born per doe. In Area A, only three fawns per 10 does are born annually. On Area B, more than twice as many fawns are born each year from HALF as many does. The optimum sustained yield is that harvest level where the population is kept below carrying capacity and recruitment is at its highest. Note that both populations shown above have an equal number of deer. Where populations are established, this type of management requires a certain number of does to be killed each year.[/align][align=left][/align][align=left][/align][align=left]By keeping the deer population below the carrying capacity of the available habitat, more forage (nutrition) is available per deer. Thus, does are healthier, reproductive[/align][align=left]success is higher and more does are able to carry two fawns. Ironically, this can result in a greater deer harvest each year. Depending on the relationship of the population and the carrying capacity, an “optimum sustained yield” can be achieved where a relatively high reproductive rate allows an abundant harvest each fall. With highquality habitat and increased nutrition, the percentage of doe fawns that breed their fi rst fall increases (sometimes up to 25 percent). Also, a higher percentage of yearling does produce two fawns instead of one. Because fawns are born at approximately a 1:1 sex ratio, more bucks may be born each year. Therefore, in some areas, you actually can increase the number of bucks born by shooting more[/align][align=left]does.[/align][align=left][/align][align=left]Along with population management, habitat management is essential to ensure deer receive optimum nutri tion. To provide increased nutritional benefi ts to a deer herd, 2 to 5 percent of a management area may need to be planted in quality warm- and cool-season food plots (as opposed to tall fescue or orchardgrass) properly distributed across the property. This strategy helps prevent overgrazing and provides nutrition on a year-round basis, especially during late summer and late winter stress periods. Other habitat management practices that can improve the quantity and quality of forage available to deer (thus increasing carrying capacity) include: forest management (e.g., timber harvest and/or thinning), controlled burning (both old fi elds and woods — especially after thinning), using selective herbicides, and planting soft and hard mast-bearing shrubs and trees (especially in hedgerows designed to break-up fi elds larger than two acres).[/align][align=left][/align][align=left][/align]
07-07-2007, 09:48 PM
#6
Nontypical Buck
Join Date: Feb 2007
Location: Denton, Texas
Posts: 1,335
RE: How to determine carrying capacity of land?
[align=left]Carrying Capacity:[/align][align=left]balancing animal numbers to[/align][align=left]available vegetation[/align][align=left][/align][align=left]The concept of carrying capacity is complex and varies annually from ranch to ranch. Carrying capacity can be defined as balancing annual animal numbers to native vegetation. We consider there are two levels of carrying capacity for management purposes: optimum and maximum.[/align][align=left][/align][align=left]Optimum carrying capacity is reached when deer are receiving a diet that promotes good antler production, body growth, and reproduction. When 50% or more of preferred browse is utilized, optimum carrying capacity is usually exceeded. Physical parametersvof deer, including body weights and measurements of antlers can be used as a gauge of optimum carrying capacity. The addition of extra animals would degrade the physicalquality of the herd.[/align][align=left][/align][align=left]Maximum carrying capacity is defined as the point at which the range is saturated with white-tailed deer and/or other animals and additional animals would trigger a die-off. If 50% or more of the available nutritionally poor browse is utilized, maximum carrying capacity is often exceeded. The effects of animal numbers on the habitat should be[/align][align=left]monitored to insure that overuse does not occur. There are obviously many stages between optimum and maximum carrying capacity.[/align]
07-07-2007, 09:54 PM
#7
Nontypical Buck
Join Date: Feb 2007
Location: Denton, Texas
Posts: 1,335
RE: How to determine carrying capacity of land?
Just articles from different places....but when it comes down to it determing the CC... is a lot of work... doing surveys, analyzing game camera pictures (like number of deer, age structure, body appearances, etc.), keeping harvest records, looking at recruitment each spring, analyzing available food sources in spring, summer, fall and winterand seeing if over browsing is occurring.
07-07-2007, 09:56 PM
#8
Nontypical Buck
Join Date: Feb 2007
Location: Denton, Texas
Posts: 1,335
RE: How to determine carrying capacity of land?
07-07-2007, 10:00 PM
#9
Nontypical Buck
Join Date: Feb 2007
Location: Denton, Texas
Posts: 1,335
RE: How to determine carrying capacity of land?
Q: If we take the mature producing does what is left?
A: Does that will still produce fawns. Doe fawns can conceive in their first year and some studies link early pregnancy to higher production of spikes. Though the spike question is another topic entirely, shooting mature does is the most desirable situation when harvesting does. By harvesting the mature does, you allow sociological niches to open to be filled by sub-dominant does that will remain in the general area and occupy their range. There is no hard scientific evidence that I've seen to suggest that there are any "barren does" that don't produce young. By being able to properly identify older does (bigger body size, long jaw line, rounded head, etc.) you'll also avoid shooting button bucks. Shooting button bucks isn't something most people prefer to do in trying to produce quality deer.
Q: Is there such a thing as over killing the does?
A: Absolutely! It really depends on what the goals of the landowner, deer manager, or wildlife agency wants though. If crop depredation is severe, one farmer may wish to kill every single deer on their property as well as within 5 miles of it! To them, there is no such thing as overkilling the does or any other deer. For hunters who like to see a lot of deer, killing does may seem counterproductive and in some cases can be if their goal is to see as many deer as possible. Notice I say "deer" and not "bucks". Generally, there's a happy middle ground where most professional managers like to keep the total number of deer at or below the carrying capacity of the land they manage. This is healthy for the habitat as deer food and cover isn't crowded and destroyed. Also, it improves the quality of the deer because there is more to go around.
Bottom line - there are rarely any one size fits all answers. Rather, it depends on the habitat and the deer herd that lives on it.
Hope this helps answer your question.
For many of us, especially Shadow, there’s been the concern of overharvesting of does, sighting few deer, and question of what is a normal age structure for deer. Here’s a few tidbits that will help light the way. I’ve been reading a most excellent book entitled “Quality Whitetails – The Why and How of Quality Deer Management” which has become the updated bible of quality deer management in the science community. I’d like to share tidbits I’ve gleaned that may help answer these often brought up topics.
In every situation, regardless of the location of your hunting grounds, be it north or south, there are several concepts that will chart deer management decisions. First there is the concept of “carrying capacity” which most of us know is the number of deer within a given range that the habitat can support. Note that I said “support” which is very different from “produce quality deer”, including big bucks. Then there is the concept of “mortality” which includes hunter harvest. Though there are many other concepts, I’d venture to say that these two are of greatest influence.
How many does should you take? This is a subjective question really and the answer lies with the property owner, manager, leasee or hunt club. Most private properties today are managed under a QDM system, while a select few are managed under a trophy management system. Most public lands are managed under traditional systems. Both call for doe harvests. Interestingly, there was a study done by R.L. Downing and D.C. Guynn in 1985. When things are “good” for the herd, production will be at such a level that a given number of animals can be harvested year after year. This is known as a “sustained yield.” Downing and Guynn’s theoretical model showed that the highest sustained yield of deer occurred at when deer populations were maintained at 50-60% of the carrying capacity. Realistically, with wild deer populations, 40-80% is acceptable. Above 60% nutrition quality will be diminished though hunters will “see more deer and deer sign.” Below 40% the opposite can be expected. This calls for 20-35% of the female population to be harvested annually, assuming that poaching and competition with grazing livestock aren’t significant factors. Doe harvest rates in excess of 35% are difficult to achieve.
What about bucks? Well the Downing-Guynn model assumes that 30% of the bucks are harvested annually. Using this model, few bucks will live to old age (4 ½ years +). When the overall herd is managed at 90% carrying capacity (versus 40-80%), only 19% of the buck population can be harvested before the buck population starts to decrease. Harvesting more bucks, greater than 30% of the total buck population, results in a decreasing population over time. Harvesting fewer bucks results in more mature deer but of lesser quality as nutrition will be of lower quality with more deer. How do you increase mature buck numbers through harvesting? Obviously harvesting 1 ½ year old deer, including spikes, dramatically causes a shortage of that age class. The same applies to any age class which receives disproportionate harvesting. Protecting the 1 ½ year old age class causes increased harvest pressure on older age classes. In 10 years of protected 1 ½ year old bucks, there have still been no 5 ½ year old deer harvested on one study property. On another area, with the exact same protection policy for 1 ½ year old bucks, there were several 5 ½ + year old bucks harvested. The difference between the two was hunting pressure. The second area had significantly less hunting pressure than the first. So, the inferred answer as to how to bring about more mature bucks is to decrease hunting pressure and harvest of bucks while keeping the total deer population below carrying capacity. This begs the question, what is a natural age structure for deer if they’re left to the forces of nature. Answers are hard to find since modern hunters have impacted deer herds for over 200 years! But archaeological digs show three things. Dr. Elder in 1965 showed that 8% or less of the deer skulls found in Native American digs were fawns. Two, 20-26% of the deer taken was 6 ½ years or older. Three, deer lived longer, each sampling had some deer 10 ½ years or older. These are similar to the age structures found in herds where QDM is practiced, unlike modern trends where Dr. Elder reported that in 1965 midwestern deer harvest was nearly 1/3 fawns and only about 2% were 6 ½ years of age or older.
A: Does that will still produce fawns. Doe fawns can conceive in their first year and some studies link early pregnancy to higher production of spikes. Though the spike question is another topic entirely, shooting mature does is the most desirable situation when harvesting does. By harvesting the mature does, you allow sociological niches to open to be filled by sub-dominant does that will remain in the general area and occupy their range. There is no hard scientific evidence that I've seen to suggest that there are any "barren does" that don't produce young. By being able to properly identify older does (bigger body size, long jaw line, rounded head, etc.) you'll also avoid shooting button bucks. Shooting button bucks isn't something most people prefer to do in trying to produce quality deer.
Q: Is there such a thing as over killing the does?
A: Absolutely! It really depends on what the goals of the landowner, deer manager, or wildlife agency wants though. If crop depredation is severe, one farmer may wish to kill every single deer on their property as well as within 5 miles of it! To them, there is no such thing as overkilling the does or any other deer. For hunters who like to see a lot of deer, killing does may seem counterproductive and in some cases can be if their goal is to see as many deer as possible. Notice I say "deer" and not "bucks". Generally, there's a happy middle ground where most professional managers like to keep the total number of deer at or below the carrying capacity of the land they manage. This is healthy for the habitat as deer food and cover isn't crowded and destroyed. Also, it improves the quality of the deer because there is more to go around.
Bottom line - there are rarely any one size fits all answers. Rather, it depends on the habitat and the deer herd that lives on it.
Hope this helps answer your question.
For many of us, especially Shadow, there’s been the concern of overharvesting of does, sighting few deer, and question of what is a normal age structure for deer. Here’s a few tidbits that will help light the way. I’ve been reading a most excellent book entitled “Quality Whitetails – The Why and How of Quality Deer Management” which has become the updated bible of quality deer management in the science community. I’d like to share tidbits I’ve gleaned that may help answer these often brought up topics.
In every situation, regardless of the location of your hunting grounds, be it north or south, there are several concepts that will chart deer management decisions. First there is the concept of “carrying capacity” which most of us know is the number of deer within a given range that the habitat can support. Note that I said “support” which is very different from “produce quality deer”, including big bucks. Then there is the concept of “mortality” which includes hunter harvest. Though there are many other concepts, I’d venture to say that these two are of greatest influence.
How many does should you take? This is a subjective question really and the answer lies with the property owner, manager, leasee or hunt club. Most private properties today are managed under a QDM system, while a select few are managed under a trophy management system. Most public lands are managed under traditional systems. Both call for doe harvests. Interestingly, there was a study done by R.L. Downing and D.C. Guynn in 1985. When things are “good” for the herd, production will be at such a level that a given number of animals can be harvested year after year. This is known as a “sustained yield.” Downing and Guynn’s theoretical model showed that the highest sustained yield of deer occurred at when deer populations were maintained at 50-60% of the carrying capacity. Realistically, with wild deer populations, 40-80% is acceptable. Above 60% nutrition quality will be diminished though hunters will “see more deer and deer sign.” Below 40% the opposite can be expected. This calls for 20-35% of the female population to be harvested annually, assuming that poaching and competition with grazing livestock aren’t significant factors. Doe harvest rates in excess of 35% are difficult to achieve.
What about bucks? Well the Downing-Guynn model assumes that 30% of the bucks are harvested annually. Using this model, few bucks will live to old age (4 ½ years +). When the overall herd is managed at 90% carrying capacity (versus 40-80%), only 19% of the buck population can be harvested before the buck population starts to decrease. Harvesting more bucks, greater than 30% of the total buck population, results in a decreasing population over time. Harvesting fewer bucks results in more mature deer but of lesser quality as nutrition will be of lower quality with more deer. How do you increase mature buck numbers through harvesting? Obviously harvesting 1 ½ year old deer, including spikes, dramatically causes a shortage of that age class. The same applies to any age class which receives disproportionate harvesting. Protecting the 1 ½ year old age class causes increased harvest pressure on older age classes. In 10 years of protected 1 ½ year old bucks, there have still been no 5 ½ year old deer harvested on one study property. On another area, with the exact same protection policy for 1 ½ year old bucks, there were several 5 ½ + year old bucks harvested. The difference between the two was hunting pressure. The second area had significantly less hunting pressure than the first. So, the inferred answer as to how to bring about more mature bucks is to decrease hunting pressure and harvest of bucks while keeping the total deer population below carrying capacity. This begs the question, what is a natural age structure for deer if they’re left to the forces of nature. Answers are hard to find since modern hunters have impacted deer herds for over 200 years! But archaeological digs show three things. Dr. Elder in 1965 showed that 8% or less of the deer skulls found in Native American digs were fawns. Two, 20-26% of the deer taken was 6 ½ years or older. Three, deer lived longer, each sampling had some deer 10 ½ years or older. These are similar to the age structures found in herds where QDM is practiced, unlike modern trends where Dr. Elder reported that in 1965 midwestern deer harvest was nearly 1/3 fawns and only about 2% were 6 ½ years of age or older.
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