One more oak adventure in the steppe!

I know I've been pretty oak-centric in my blogging, but I wanted to relate one more great experience I had in the oak forests of Vinnitska Oblast before I find another topic. After finishing my field work at Vinnitsya Forest Management Unit I joined my friend Oleksandr Schinder from the Nat'l Botanical Garden on a expedition to Pridnistrovie, the region along the Dniester River on the Ukraine-Moldova border. Our goal: to find Quercus pubescens, an oak of mediterranean climates that is quite common on the Crimean peninsula, but in the far northern extent of its range here. 

Pridnistrovia is a fascinating landscape: open rolling steppe (lots of orchards) broken by steep shallow ravines (yari) and cut by the deep valley of the Dniester, almost a canyon in places. There are little patches of productive hornbeam-oak forests on the plateaus, and xeric oak with open steppe glades in the yari and on the cliffs above the Dniester. Our first day we searched a hornbeam-oak forest on a productive site. We found Quercus robur (no surprise) and Q. petraea (an interesting find), but no Q. pubescens. The stand was pretty typical of "protective forests" in the region: well-formed mature hornbeam, oak and linden, with no understory to speak of and practically no dead wood. No clearcutting here, but obsessive "sanitary" removal of weak and dead trees. The ecological consequences of sanitation harvesting for wildlife dependent on deadwood is going to be a major theme of my work here. 

Our second day brought success. We caught a taxi from the town of Yampil' and stopped at a cornfield about 15 km out. On the horizon you could see a fringe of oak trees. What was not visible was the spectacular drop off from there to the Dniester, a steep tumble of dry oak forest, limestone cliffs and steppe glades. We instantly found Quercus pubescens, a runty looking scrub oak. We then descended a bit farther downslope into the steppe glades and Oleksandr entered botanist heaven: he found a new "Red Book" species about every ten minutes. (The Red Book is the list of rare and endangered organisms in Ukraine requiring protection. All European countries have Red Books. Do we?) The view was unbelievable: the cliffs hugging a big bend on the Dniester, with endless rolling chernozem fields on the Moldovan side of the river. 

We got back into the forest and hiked a bit farther, suddenly coming across a steep limestone canyon. The slopes were really unstable, with multiple springs flowing out of the karst. Towards the river the slopes became sheer cliffs (with caves) and isolated limestone "chimneys" between them. Really jaw-dropping scenery. The list of rarities kept growing, including velika khvosh, a huge Equisetum. The stream that ran through the canyon was forested all the way to the Dniester. The little delta forest at its end had its own diverse suite of plants, and is an extremely rare biotope. Nearly all of the intervale lands along the river are farmland. We agreed to make a return trip to this fascinating forest in March, when a whole new world of plants (spring ephemerals) will be visible.

It was a pleasure to participate in some pure science for a day, but I kept thinking about the forest management angle. This forest is part of a lishosp, so it is available for harvesting. I'm sure it is entirely zoned as protective forest, so only sanitary cutting is permitted. Productivity is extremely low; I doubt more than 10% of the oak here is sawtimber. There is a campaign right now to increase the acreage of the "Nature Preservation Fund" in Vinnitska Oblast, which includes landscape parks, and zoological, botanical and geological reserves. We discussed how this forest is nearly ideal for park designation, with its high concentration of rare species and unique landscape features. Oleksandr even plans to petition the State Forestry Committee to give it that status. But is it necessary? If park status ended forest management in this area, there would be gains and losses. The presence of snags, cavity trees and downed logs would gradually increase with the exclusion of sanitation harvesting (good for such species as Dryocopus martius, Europe's largest woodpecker). I suspect ending this practice would help Quercus pubescens too. Pubescent oak is very hard to distinguish from common oak but has worse growth and form, so it might get culled disproportionately during sanitation. 

But as Oleksandr pointed out, the small gaps created during harvest could facilitate regeneration of pubescent oak, the least shade-tolerant species in the mix. And of course, excluding forest management reduces the supply of firewood to local villages and removes an important employment source. Might it not be better to maintain the forest as lishosp territory but adapt harvesting to better protect pubescent oak and promote natural structure? I hope to address this question in my project, and to help develop adaptations to sanitation harvesting. In many cases, I think it would be possible to cut more wood and achieve better regeneration through the use of gap selection that the single-tree sanitary selection practiced most commonly. Hopefully I'll have some more to blog about on this topic as my project advances...

Natural regeneration of Quercus robur

I recently posted about the bleak situation with Quercus petraea silviculture in the south of Vinnitska Oblast. Now I'll give a bit of better news, about efforts to develop natural regeneration techniques in Quercus robur forests in the central part of the oblast. This is the work of Evgeniia Krementska at the National Agricultural University, who is leading a great effort by the forestry faculty to diversify the range of silvicultural options available to Ukrainian foresters. 

All forest harvests in Ukraine must be identifiable as one of a short list of "approved" harvest types listed in the Forest Code. For obvious reasons, this limits creativity and experimentation. But recently a new type was added: rubka pereformiruvannye, which translates like "reformation harvest". This broad category allows for a variety of treatments that aim to develop desirable structural or compositional characteristics in even-aged stands. Dr. Kremenetska has been establishing experiments in Vinnitska Oblast to demonstrate what this might mean in practice. The best examples are on Tulchinske Forest Management Unit.

In Tulchyn, it is often possible to find good cover of oak seedlings in open areas such as roads and clearings. But a dense midstory of hornbeam often shades them out in the forest. The goal of "reformation harvesting" here is to begin developing advance regeneration of oak as the first step towards creating an uneven-aged stand. This very much resembles the first stage of  an oak shelterwood: remove the midstory of shade-tolerants and thin the oak canopy. But in theory the next harvests will start trending more towards selection. Some proportion of the canopy cohort will be retained (they talk about a 200 year rotation for these trees, and hopefully some will be permanently retained), while good patches of advance regeneration will be released with gaps ("windows"). 

We saw an interesting array of stands where this treatment is taking place. A 70 year old stand where oak and hornbeam were both in the upper canopy, and the latter made up at least 40% of the stand. A really beautiful 100+ year old stand of oak sawtimber with full canopy cover, no hornbeam midstory, and a nice cover of first-year oak seedlings. A 2-age stand with a dominant cohort of 200 year old oaks and a younger oak-hornbeam cohort. In all of these stands high-quality oaks have been selected for retention, while low-grade oak and most of the hornbeam are slated for cutting. It will be very interesting in the next few years to see if advance oak regeneration was successfully released (or established in those places where it is currently shaded out). 

Would these treatments actually get used outside of the experimental context? I think they are attractive to foresters whose management units contain a high proportion of "protective forests." In this forest category clearcutting is prohibited, which eliminates the primary method of regeneration here: clearcut-plant. Usually protective forests are managed under a "sanitary selection harvest" regime, in which low-grade trees are gradually culled out in a series of light cuts. This makes for lovely forests, but is not very economical and usually makes no provision for oak regeneration. I think some foresters are beginning to think seriously about real regeneration methods when clearcutting is not available. But I doubt "reformation harvesting" would be much used in the exploitation forest category. 

However, we also saw a 3 ha clearcut that was nicely stocked with natural oak regeneration one year after harvest. It seems that this good result could perhaps be replicated if clearcuts were targeted for good acorn years. But the foresters told me that not all stands have sufficient acorn production to achieve such seedling stocking, even in a good acorn year. I suspect this might have to do with crown size, as many stands are very high-density and thus have poorly formed oak crowns. 

Quercus petraea in the forest-steppe

I have spent a couple more weeks in Vinnitska Oblast since my last post, and have learned even more about forest-steppe oak and the challenges of managing it. I took a great field trip with my colleague from the Agricultural University, Evgeniia Kremenetska. She is trying to demonstrate new silvicultural methods in the region, and has plots in Krizhopil in the south of oblast. In this region Quercus petraea naturally dominates, while Q. robur makes up a lesser component. 

Krizhopil got slammed by the same ice storm that I described in my last post. Nearly 100% of the management unit was effected, and most tree crowns sustained heavy damage. The foresters told me right off that this crown damage made natural regeneration of oak (which they already consider really hard) next to impossible. I was skeptical, especially when we saw a clearcut from last year that had abundant Q. petraea regen mixed between the planted rows of Q. robur. But then we visited a mature stand that is slated for salvage clearcutting. We found two beautiful petraea that still had good crowns, and the ground was absolutely covered in acorns. (We did a little measuring and found that 50% of them were viable). I thought, "see, you could regenerate this naturally!" But when we walked around the rest of the stand pulling back the leaf litter we could barely find another viable acorn. When you looked up the oak crowns were just a bunch of broken branches and watersprouts. We repeated this experience in several more stands and I started to believe that the regenerative potential of these stands was really compromised by the storm. Whether these crowns could recover to acorn-producing quality with more time is another question...

The solution in Krizhopil has mostly been to salvage these damaged stands (often several decades before rotation age) and to establish plantations of Q. robur (it is really hard to grow petraea in nurseries, so all artificial regen here is the other oak species). When they can get some good post-clearcut natural regeneration, that's icing on the cake. But they aren't going to rely on it. Here Evgeniia is experimenting with underplanting oak seedlings before the final harvest, in the hope that they will be more established and competitive after a few years in the understory than seedlings planted post-harvest. If they are, it might be necessary to do less intensive cleaning treatments, because the oak will be more capable of competing with the hardwood brush and ruderals. We saw nice rows of seedlings growing beneath a lightly thinned canopy. The next stage of the experiment will be to see whether it is possible to protect these seedlings during harvesting. 

My impression from Krizhopil was a bit sad - in response to the ice storm damage, a large area of natural forest (albeit highly modified natural forest) is going to be converted to intensive oak plantations. This would have happened anyway as rotation age was reached, but the storm greatly accelerated the process. The foresters do not have any realistic alternative to salvage-plant (both due to the natural challenges and a dearth of research on natural regen). What makes this sadder is that the storm basically pounded the region where Q. petraea is dominant. The area of petraea forests in Ukraine was already shrinking; now it will contract even faster. 

I think there should be some measures taken to maintain a significant acreage of natural petraea forests, since the Ukrainian forest-steppe population is isolated and genetically unique. Even damaged forests could be important for maintaining this species, but of course conserving these areas would entail a major sacrifice for the forest management units. I imagine a survey of existing petraea forests in Vinnitska and Odeska Oblasts, in which the healthiest and most viable stands are identified and excluded from conversion. Perhaps even individual trees could be conserved, like those good acorn producers we saw in Krizhopil.

Oak silviculture in the forest-steppe

For the past couple of days I have been visiting a forest management unit in Chechelnik, Vinnitsya Oblast. This is the "forest-steppe" region- a mixture of wide open chernozem fields and oak-ash forests.  I've been here getting acquainted with the management unit and planning a little botanical expedition in the spring with a colleague from the National Botanical Garden.

I've had a short but fascinating introduction to forestry in this region. It is quite far to the south (near the Moldovan border), and almost in the true steppe zone, where forests are extremely scarce. Natural forests are dominated by Quercus robur and it's less common cousin Quercus petraea, with a sizable component of Fraxinus excelsior, Carpinus betulus, Tilia cordata, Acer platanoides, Acer pseudoplatanus, and Ulmus carpinofolia. There is also a species of wild cherry and "bereka", a rare Sorbus. Moisture is limiting here so the forests are on the xeric side. Typical structure might be oak and ash as dominants, with a midstory of hornbeam, bereka and linden and advance regen of maple, ash and hornbeam. 

Silviculture in this region leans heavily towards artificial regeneration. Seed is collected locally and sown in nurseries around the management unit. Rows are heavily scarified in clearcut areas and either acorns or oak seedlings are planted at quite close spacing. I think the rows are about eight feet apart and within the rows seedlings are 2-3 feet apart. The foresters very frequently enter these young stands to do cleaning and liberation treatments. I think four or five of these pre-commercial treatments is not unusual, followed still by early-commercial thinnings for firewood. (Can these treatments pay for themselves? I'm dubious). Often these plantations are mixed - every fourth row will be maple, linden, ash, spruce, walnut or cherry. 

The management unit was hit hard by an ice storm in 2002. Damage was quite severe, and a large proportion of the trees here have damaged crowns with lots of water sprouts. As a result, many "sanitary clearcuts" have been carried out to salvage heavily damaged stands. However, a large proportion of the management unit is classified as "botanical reserve" (the mixture of northern forest and southern steppe species is quite unique), where clearcutting is prohibited. So here they have been carrying out a series of extremely light "sanitary selection" harvests. These target trees with broken crowns, otherwise unhealthy trees and snags. The volume removed seems very low to me - I would guess that less than 5% is removed in any given harvest. From a silvicultural perspective, it is great to be able to enter these stands so frequently and lightly. But again I have to wonder- can such silviculture pay for itself? Is this management regime self-sustaining, or subsidized by the State Forestry Committee? 

These sanitary selection harvests have some downsides, too. They are not effective at regenerating oak - the gaps created are extremely small and are quickly occupied by advance regeneration of ash, maple and hornbeam. In general, the goal in these forests is to maintain mature crown cover (as is mandated by law), so regeneration is of secondary concern. From an ecological perspective, the constant "cleaning" of these forests is quite severe. They are almost literally without snags and coarse woody material - this is obsessively collected for firewood. Even cavity trees are extremely scarce- I saw one nice ash cavity tree, and the forester I was working with grumbled "why didn't they cut that? Sloppy work..." A few times I broached the subject of whether leaving some snags, downed logs and wildlife trees would be appropriate in an ecological reserve. The reaction was not positive! The foresters here love order and cleanliness, and that means that deadwood is not tolerated. 

Happily, they are beginning to experiment with group selection in protective forests. I saw one really nice mature oak stand where 2-3 tree gaps were cut. (Interestingly, they call gaps "windows"). The natural oak regeneration was beautiful - see the photo above. The foresters seemed quite enthusiastic about this and told me that they plan to try this method in other protective forests in the management unit. But I need to put this in perspective: for every couple hectares where they are trying out group selection, there are probably 50 hectares of intensive clearcut-scarify-plant. The movement towards natural regeneration is very tentative, despite lots of research and support from Kyiv. Ukrainian foresters just love planting trees - it is a major part of their professional image and they regard it as "correct" silviculture.