Move the bioh of clusters without wood harvest area to the clusters that still have some. Their recalculated bioh (harvest area times harvest rate) is zero, so rates times land cannot equal target bioh and would be stranded. Per subcategory and year, the stranded bioh is added to clusters with recalculated bioh > 0 in the same region proportional to their recalculated bioh, falling back to the global pool if a region has no such clusters. Bioh that cannot be moved anywhere is reported and dropped, so the returned bioh is zero everywhere where the recalculated bioh is zero.