Basal Area

[jayfed]

Over the years  I have always used the 6" DBH class and therefore 5.0" DBH as the bottom diameter limit of my plot sampling.  As I written elsewhere, I am now marking down to the more machine convienent 4" DBH trees (and really close by 3").

So, if I was using decades ago a general goal of about a 75 BA basal area in a second growth northern hardwoods stand down to the aforementioned 6" DBH class, what, if anything, will change with the residual goal of 75 BA still being applied further downward to a 4" diameter.

Does the goal of 75 BA still exist down to the 4" DBH or as one forester said, "The residual BA would have to increase to perhaps 90 BA". Just a guess on his part as he did say.

(As a side note, one book mention going to 4.6" DBH since that is the break point for the 5" DBH, though really it should not(?) be so for the 6" DBH class. Another forester mentioned that the 75 BA 'goal' already does apply to the 4" DBH limit.)

So either I was taught wrong back in the days of the cable skidders where even too many 8 inchers were frowned upon.  Or something is amiss with what I have been told in this day of mechanization.

The only thing I know for sure, it seems, is that more trees will show up on the plot. Lets hear it... 'Duh!".

How should I treat those additional oversized 4" 'twigs' in my residual BA considerations?

Jay with a full moonlight over my desktop.

[WDH]

I have always thought in terms of merchantable volume.  If a 4" DBH stem yields a stem that is sub-merchantable, I would tend to ignore it.  However, that may not apply to Northern hardwood management.

[SwampDonkey]

We go down to 4" here as well Jay. Although in most all harvests up here we are talking clearcuts and selection harvest equates to high grading and not timber improvement unfortunately. I am wondering if you could find the answer your looking for by recalling the TF for a 4" diameter class at that particular prism BAF?

For me personally it would not make a difference in the residual BA because aren't you looking to remove culls and suppressed first and trying to maintain the distribution of diameters as found in the pre-harvest situation? Nice small young trees have the potential to make nice big mature trees down the road.   And you want to get paid for what you cut to. ;)

TF=BAF/(0.005454 X Diameter Class²)

As you know, gives you an idea of #'s of trees expected at that dbh, per acre, when multiplied by tally for that diameter class at that point.

For BAF = 9 , 2 tallied 4" class trees

TF = 9/(0.005454 x 4"²) x 2 trees tallied at that point
TF= 206 trees/acre

[Black_Bear]

Disclaimer: I hope to receive some feedback on my theory listed below, mainly because I am still learning the dynamics of northern hardwood silviculture and I find this to be one of the better ways to learn. I am concentrating on my land surveying career right now and thus have not been able to work for a forester. I constantly study forestry from books and papers, but I find the best way to learn is to actually do something or talk with an experienced forester.   

The scenarios are endless, but if that 4" HW tree is one of many per point (plot) and is in the dominant or co-dom class then the data is highly relevant to the stand. If however, and this may be more common in a merchantable stand, you have 1-2 4" trees per point and the remaining trees are 10"+, then the overtopped trees, which are not part of the dominant or co-dom strata, may never be merchantable or may never reach sawlog size or quality.

In scenario #1 the cumulative BA of the lower classes, which are in the dominant or co-dom strata, is more relevant to the future of the stand, mainly because they should grow in to the sawlog class at some point. If you don't tally them now, then the ingrowth of sawlogs recorded in 20-30 years cannot be explained. This would seem to be more important if you are tallying volume of a stand and that volume will be used as a baseline for the property's tax basis, and thus for future timber depletion rates.   

In scenario #2 the cumulative BA of the overtopped lower classes is probably not as relevant to the BA of the stand, mainly because they will probably never occupy relevant growing space unless the upper classes are removed. The trees above them are occupying that space and by tallying the 4" trees you may be overstating the total BA of the point, and thus the stand, unless it is broken into a merchantable/unmerchantable grouping.

Of course, overtopped trees can develop into sawlog class, but in northern hardwoods it is rarely ecologically possible that an older stand (species dependent, but >80 years) will produce quality stems from overtopped trees that have been released by a thinning from above. Mainly because of what was mentioned before: the stand usually is high graded or merchantably clearcut and the "thinning" is actually a regeneration cut with poor quality stems now in the dominant class.

So, the decision comes down to whether short term or long term management goals are being considered and whether the tallying of the lower classes is economically feasible for the forester and the landowner. I know from an operations point of view, if the 4" class is tallied then that class must be labeled unmerchantable. There aren't many operators who strive to cut a high percentage of timber under 10". But if the lower classes can be harvested simultaneously with the merchantable classes, then the prescription should be feasible in a silvicultural sense and in an operations sense.

[SwampDonkey]

Well put black bear. However in the Maritimes at least, there are thousands of cords of wood cut below 10" sizes, down to 4" for hardwood. The average woodlot with hardwood stands have an average stem size of less than 10 inches, generally around 8". That 8" hard maple up here is almost 80 years old in unmanaged stands. Most of the management has been stove wood harvesting, high grading and clear cutting. Just another perspective. Loggers tell owners to take the big ones out, foresters try to convince them to take a few trees from each diameter class. Very few listen because the $$/cord harvested does not change whether you do the right thing or butcher the place. While at the same time costs go up doing the right treatment because it's slower and piece size is small and quality isn't there.

Now you fellows to the south have an advantage because you aren't working with 'fringe wood'. The environment down there is more favorable for growth, allowing for a larger volume of trees of good quality to be grown a bit faster.

[BaldBob]

Black Bear ,
Whether or not you include the Basal area of the "submerchantable" trees depends on what you are doing with the information. If it is to be used for a current inventory for merchantability, you obviously don't need to know about those smaller trees. If you are planning a harvest and those smaller trees are of a species and quality to eventually become crop trees, then it is equally obvious that you would want to know how many (by species and quality) of these you have.

Another thing to keep in mind is that any given site has a maximum and an optimum basal area that it can support. Those smaller trees are utilizing some of the resources of that site whether or not they are ever likely to become crop trees. Their use of those resources is roughly proportional to the percentage of the basal area that they make up. If your TOTAL basal area stocking levels are anything above optimum, then those submerchantable trees are utilizing some of the resources that could be going to your crop trees. This is important information to have when pondering how to manage a specific stand.

[Dodgy Loner]

I can't really answer the question, because I was trained in the school of loblolly pine plantations, but here's some food for thought:

a 4" tree has a basal area of .0873 ft², so it would require 172 of those 4" trees per acre to increase the BA from 75 to 90, if you were only counting trees in the 5" DBH class before.  That's probably WAY too high.  Your target BA might be increased by, perhaps, 5 ft², which is a more reasonable (but perhaps still too-high) 57 trees in the 4" DBH class per acre.  I don't think that including the extra DBH class would have an appreciable effect on actual practices due to the difficulties of actually getting an exact BA on a given piece of land, but obviously it depends on just how many 4-inchers you have lurking in your woods.

[SwampDonkey]

And you can get quite few of those with suppressed shade tolerant species like balsam fir and beech. They won't usually be worth much though and usually quite common in poorly managed woods. "Oh, we'll leave those small ones."  :