The Benefits of Blackberries

As a kid, one of summer's highlights was blackberry (Rubus allegheniensis) season. It was a big deal! We went to the "mountains" and frequented those thorny patches. The buckets of berries and the expectation of pies, dumplings, and preserves, not to mention the frequent handfuls of freshly picked jewels more than offset the occasional (okay - frequent) pricks and jabs. It is almost blackberry season in much of Pennsylvania - August is just around the corner.

If you are a bit eager to get picking, black raspberry (Rubus occidentalis) season is even closer. These smaller and less seedy relatives of blackberries are forming up fast. Soon the now red fruit will turn black and offer handfuls of enjoyment.

If you have never enjoyed a day afield collecting berries, this is the year you should try it. Nothing like socially distancing in a berry patch.

While our native blackberries are wonderful to eat and fun to pick, they are an important part of a healthy forest. Surprisingly, many forest users and visitors believe they are a problem. Know that these are amazing plants. Studies have estimated that a good five-year old berry patch can have 4 million seeds stored in its leaf litter. Four decades later, one million seeds may remain in storage, and, one estimate is that after 120 years there could be 50,000 seeds still waiting to germinate - more than one per square foot.

That their seeds can wait so long is a real benefit to forest function. Following a disturbance - think windstorm or harvest - those seeds provide essential ecological services. First, they easily and quickly germinate in response to increased light, moisture, and nutrients. The loss of overstory trees obviously increases light, which warms the leaf litter. Without the canopy trees pulling out water, soil moisture increases, and together light and moisture increase leaf litter decomposition, which releases nutrients.

Those stored seeds respond quickly, occupying the new canopy opening. Then, after the two years necessary for a cane to mature and produce fruit the patch will begin to accumulate and store new seeds. The two-year old canes die after fruiting, and, depending on the amount of light striking the patch, will begin to self-thin as each year the maturing canes shade out the younger ones. Blackberries have shallow roots that quickly expand in the disturbed opening and spread across the area. In two to three years, blackberries may dominate the area. In the process, the growing plants capture nutrients, specifically nitrogen. This is important, because the leaf litter is decaying rapidly - as much as half can decompose in the first year. The litter created by the blackberries over time recycles these nutrients back into the site.

Ideally, when canopy disturbance from storms or harvesting occurs, young tree seedlings are either already growing, which should be the case with tree species that can grow in shaded conditions, or stump sprout and seeds from remaining trees and seeds stored in the litter will germinate and initiate regeneration creating the next forest. If in the sequence of events, blackberries begin to flourish, studies show seedlings will continue to grow in height and will quickly start to shade the canes, which will, under these conditions, begin to decline in five to seven years. Unfortunately, if tree regeneration is lacking, the blackberries can hold the disturbed area for 15 or more years. Logically storm or natural tree loss is unpredictable; however, harvesting should be a planned activity. Therefore, it is important before harvesting trees to assess seedling numbers, species, and condition before moving forward, and if blackberries show up, a natural progression of changing conditions should occur leading to a successful outcome.

In parts of Pennsylvania, selective deer browsing can shift understory plant composition to what ecologists call an alternate steady state. One common alternate steady state situation is large areas of rhizomatous ferns, which quickly spread by sending out rhizomes that are root like structures from which the fern fronds develop. The resulting fern patches may not affect overstory tree growth; however, they can remain unchanged for decades and may require specific management treatments to re-establish tree cover. Studies show that these ferns, most commonly hayscented and New York, create intense shade close to the forest floor that suppresses tree seedling germination and height growth. When deer populations are low and more in balance with their habitat, blackberries can flourish and can suppress fern development, which may allow tree seeds to germinate, establish, and grow taller and through cane cover.

Blackberry season will soon be here. Those prickly sometimes annoying plants not only yield tasty treats, they provide important ecological services when conditions allow them to germinate and grow. They shade the soil, reducing ground temperatures and increasing water for other plants, capture nutrients from decaying leaf litter, recycle those nutrients back to the site, protect plants from browsing, rebuild leaf letter, and suppress ferns. Beyond this they are important sources of soft mast or forest food for songbirds and small mammals.

Take the time this August to socially distant in your favorite blackberry patch! You will start a family tradition and enjoy the fruit of your labor.